D. P D POISE: O -I Imuenchow.cms.udel.edu/papers/MuenchowPubs/NSF2010_POISE.pdfD. PROJECT DESCRIPTION POISE: OBSERVING OCEAN-ICE INTERACTIONS D-4 of 15 similar velocities of about

D. PROJECT DESCRIPTION POISE: OBSERVING OCEAN-ICE INTERACTIONS

D-1 of 15

D1. Introduction

We propose an intensive observational research project focused on ocean-ice shelf interactions in Petermann Fjord, site of a major outlet glacier draining northwest Greenland. This collaborative, interdisciplinary project consists of coordinated ocean and glacial ice measurements by 8 principal investigators at 5 US institutions plus international partners from Canada, the UK, and Denmark. This project is further coordinated with two other collaborative projects focusing on modeling of (PI R. Samelson, OSU) and the paleo context for (PI A. Mix, OSU) ocean/ice interactions in this region. Together these projects comprise the program we call POISE: Petermann Ocean-Ice Shelf Experiment.

Based on observations of glaciers further south in Greenland and changes in ocean and air temperature and sea-ice conditions in the area of north Greenland, we believe that the mass balance of Petermann Gletscher (PG) is poised for change; thus, the time to study it is now. The configuration of PG makes it particularly amenable to a well-constrained observational study. A detailed understanding of its mass balance will generate insight into ocean-ice interactions that will be relevant to many other sites in Greenland and Antarctica, and will provide a transformative advance in our developing knowledge of ice sheet discharge and its future effect on sea-level rise.

D2. Motivation

A major concern that emerged from the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (FAR) is the increasing rate of sea-level rise (SLR: [Solomon et al., 2007]). This could have considerable consequences for over 200 million people that live in coastal flood plains and the trillion dollars worth of assets lying less than 1 m above current sea level around the globe [Milne et al., 2009; Stern, 2007]. The rate of globally-averaged SLR appears to have nearly doubled over recent decades with both satellite altimetry and sea-level tide gauge data supporting a linear trend of 3.3 + 0.4 mm/year over the 1992–2006 time frame [Rahmstorf et al., 2007].

The FAR estimated that three factors—namely thermal expansion of seawater, melting of small ice caps and glaciers and melting of the ice sheets both on Greenland and Antarctica—contributed roughly 60:30:10% respectively to SLR over the decade of 1993–2003 [Technical Summary in Solomon et al., 2007]. Both the thermal expansion of seawater and loss of glaciers and ice caps are expected to continue to contribute to SLR as the planet warms. However future ice discharge from Greenland and Antarctica holds the greatest potential for surprises. For perspective, it is estimated that the entire remaining inventory of mountain ice caps and glaciers is equivalent to 0.15–0.37 m of SLR whereas Greenland and Antarctica hold equivalent potentials of 7.3 and 56.6 m respectively [Table 4.1 in Solomon et al., 2007].

The IPCC Working Group I struggled with quantifying future ice sheet contributions to SLR because a number of recent and paleo observations revealed far more dynamic behavior than had been previously appreciated. Moreover, such rapid responses of ice sheets to change had yet to be captured in models. Since the FAR was released, independent sources of evidence have been accumulating that Greenland and Antarctica are currently losing ice mass to the oceans at roughly equivalent rates and that the rates have risen over recent decades although the absolute magnitudes remain uncertain [Rignot et al., 2008; van den Broeke et al., 2009; Velicogna, 2009; Wu et al., 2010]. Available estimates for Greenland loss range from about 100–250 km3/yr or 0.3–0.8 mm/yr equivalent SLR [Wu et al., 2010].

There are several climate-related factors that have been proposed to be driving current ice sheet losses but one of the most important appears to be interactions with a warming ocean [Holland et al., 2008a; Jenkins and Jacobs, 2008; Rignot and Jacobs, 2002; Rignot et al., 2010; Shepherd et al., 2004; Straneo et al., 2010]. To date, evidence regarding ocean-ice sheet interactions is largely indirect and inferred from correlations of accelerated ice thinning with conditions in the adjacent ocean. Simple numerical models suggest that such ice loss rates may be a greater than linear function of the contacting ocean temperature [Holland et al., 2008b]. Hence, continued ocean warming could further accelerate land ice loss. Models also indicate that specific loss rates will vary from site to site as they are sensitive to a variety of factors

TPI 7081896


D-2 of 15

such as ice shelf cavity shape, ice thickness and relative ice and ocean temperatures [Holland et al., 2008b; Little et al., 2009] and other sources of ocean turbulence such as tides. It is also important to know where melt inputs will be occurring because sea level does not rise uniformly around the globe with freshening but is a function of ocean circulation patterns and gravimetric adjustments associated with the mass transfer [Mitrovica et al., 2009; Siddall et al., 2009; Wunsch et al., 2007].

Thus enhanced understanding of ocean-ice sheet interactions at key locations emerges as a new imperative for improving our ability to chart the future course of sea-level rise. The ocean-ice sheet interface is an extremely challenging environment in which to make direct observations, model and reconstruct past behavior but these are all sorely needed for progress. Furthermore, because such environments have been under-observed, the potential for discovery of new phenomena is high.

D3. Background: Why Petermann Gletscher?

Petermann Gletscher, located in northwest Greenland (Fig. 1), is a major outlet glacier draining ~6% (71,580 km2) of the Greenland ice sheet area [Rignot and Kanagaratnam, 2006]. PG is one of four major outlet glaciers of Greenland that have grounding lines well below sea level, and one of two such outlet glaciers that retain a substantial intact ice tongue or shelf floating seaward of its grounding line. The other one is at 79 North, in northeast Greenland. Humboldt Glacier, located just south of PG, is grounded below sea level but has a broad tidewater terminus.

Fig. 1. Polar stereographic projection of under ice sheet land surface of Greenland; contour internal 250-m. The mass of the ice sheet depresses more than half of the island at or below sea level [Bamber et al., 2001a; b].

The ice shelf of the other major outlet glacier grounded below sea level, Jakobshavn Isbrae in southwest Greenland, began to retreat rapidly starting in 1997 and by 2003 had melted back to its grounding line [Joughin et al., 2004]. As the ice shelf retreated, the rate of ice discharge from land to the ocean increased many-fold and continues to be high (about 30 km3/yr) at present. Two other major outlet glaciers in southeast Greenland, Helheim and Kangerdlugssuaq, whose grounding lines are at sea level, also experienced considerably accelerated flows upon losing their ice shelves in recent years [Rignot et al., 2008; Rignot and Kanagaratnam, 2006]. Similar speedups have been recorded for ice flows on the Antarctic Peninsula as ice shelves have collapsed there [Rignot et al., 2004; Scambos et al., 2004]. In fact, extensive dynamic thinning on the margins is observed at all latitudes in Greenland and has intensified on key Antarctic grounding lines [Joughin et al., 2010; Pritchard et al., 2009; Thomas et al., 2004]. Collectively, these findings show that fast flowing glaciers can alter ice sheet discharge on sub-decadal timescales and so argue for a potentially rapid ice sheet response to changing climate.

Over the same time frame that Jakobshavn Isbrae lost its ice shelf, rising atmospheric temperatures increased melt over the perimeter of the entire Greenland ice sheet [Hanna et al., 2005]. While surface

TPI 7081896


D-3 of 15

derived melt can penetrate to the bottom of the ice sheet and so facilitate sliding by lubricating the bed, this factor does not appear to fully account for the speedups [Joughin et al., 2008]. It has become clear that floating ice shelves play a buttressing role in holding back land ice, and their loss generates rapid thinning of the land ice behind them. Jakobshavn Isbrae now exhibits only a seasonal ice wedge that floats over the ocean and exerts a small seasonal buttressing effect, slowing the ice stream to a small extent in winter [Joughin et al., 2008].

The timing of the Jakobshavn retreat coincided with a significant increase in Atlantic Water temperature in the adjacent fjord (Disko Bay), from a typical value of ~1oC prior to 1997 to ~3oC [Holland et al., 2008b], as a consequence of regional ocean circulation changes bringing warmer water northwards over the adjacent Greenland continental shelf. These authors concluded that it was likely that the retreat was driven largely by ocean melting of the underside of the ice shelf. However, there are no direct ocean measurements under the shelf from before or during the Jakobshavn Isbrae ice shelf retreat to reveal the processes by which the warmed offshore ocean waters actually interacted with the ice shelf. The intact ice shelf of PG, however, presents an excellent opportunity to make baseline observations before any comparable major changes take place.

Fig. 2. Left MODIS image (10 Sep 03) of the Petermann Gletscher floating ice tongue. The relatively sea ice-free conditions in front of the ice tongue are unusual but seem to be growing in frequency over the satellite record. Red dot: location of thru-ice TS profile in 2002. Green squares: proposed broadband seismic station locations. Yellow: grounding line. Fjord sidewall cliffs reach 1000 m above sea level. Blue box enlarged on right: Proposed mooring array superimposed on sea floor bathymetry seaward of ice tongue. Triangles are 2009 hydrographic station locations (for data see Fig. 5) seaward of ice tongue edge at that time.

Petermann Gletscher terminates near 60W and 80N in a floating ice shelf that fills much of a long (~80 km), narrow (15–20 km), high-walled fjord (Fig. 2). The ice shelf is ~600 m thick at the grounding line (500 m below sea level) and thins along its currently 55 km length to about 30–60 m at its seaward end. Petermann Fjord connects to Nares Strait, which is situated between Greenland and Ellesmere Island and joins the Arctic Ocean to northern Baffin Bay. Our recent data combined with 2007 IBCAO bathymetry reveal a sill that separates Petermann Fjord from the adjacent Hall Basin (Fig. 2). While the sill is not yet completely mapped, available data and hydrographic measurements constrain it to lie between 350 and 450 m [Johnson et al., 2010]. The bottom deepens from the sill to more than 1100 m near the current seaward edge of the ice tongue. There are no soundings in the ocean under the ice tongue. On the Nares Strait side of the sill, the adjacent Hall Basin attains depths of 800 m. Sills at about 400 m at 83N latitude in the Lincoln Sea and at 220 m near 80N in Kane Basin restrict ocean interaction with the Arctic Ocean and Baffin Bay respectively.

Like Jakobshavn Isbrae, PG is a fast moving glacier with speeds, based on feature identification in aerial photography, averaged over a 17–19 year period ending in 1978, ranging from 855–950 m yr-1 [Higgins, 1991]. More recent interferometric synthetic aperture radar satellite (InSAR) observations gave

TPI 7081896


D-4 of 15

similar velocities of about 1000–1200 m yr-1 that increased ~8% in summer but did not vary detectably on an interannual basis between 2000 and 2006 [Rignot and Steffen, 2008].

D4. Current knowledge regarding ocean-ice shelf interactions at Petermann

Rignot and Steffen [2008] recently described the PG ice tongue mass balance terms based on available data. Combining measured surface velocity and thickness at the grounding line during 2000–06, they estimated that the ice sheet supplies about 12 km3 yr-1 to the ice tongue. Petermann is supplied from one of the driest regions of the Greenland Ice Sheet; two automatic weather stations (AWS) deployed on and adjacent to the ice tongue in 2002–04 showed only 10–15 cm annual snow accumulation and 1.2 m yr-1 net surface ablation. This equates to a 1.7 km3 yr-1 surface loss term for the ice tongue. As discussed in more detail below, time averaged calving losses are of similar magnitude or about 1 km3 yr-1. Taking the system to be at steady state, these losses account for about 20% of the supply and so it can be deduced that the remaining 80% is driven by ocean driven melting.

Ice divergence determined from gridded velocity vectors indicate basal melt rates that vary along the length of the Petermann ice shelf but are maximal (up to 30 m yr-1) about 10 km downstream of the grounding line where the ice is 400 m thick [see Fig. 3, from Rignot and Steffen, 2008]. Intensified melting near the grounding line is observed in other ice shelf locations and is consistent with general findings from numerical models with idealized ice shelf configurations [Little et al., 2009 and references therein]. However, even these idealized models with smooth ice surfaces suggest that melting is not laterally uniform across an ice shelf and the configuration of both the sea floor and ice shelf as well as the nature and rate of the waters feeding the ocean cavity beneath it are important. Moreover, evidence is accumulating to suggest that the undersides of ice shelves generally tend to be far from smooth [Jenkins et al., 2010; Nicholls et al., 2006; Rignot and Steffen, 2008].

Fig. 3. Petermann Glacier steady-state bottom melt rate in m yr-1 calculated on a 600-m grid from the divergence in ice flux. Negative values imply mass loss (melt). Values upstream of the grounding line (thick black line) are affected by large errors due to sparse ice thickness data. On the ice shelf, ice thickness is better constrained by surface elevation data (Rignot and Steffen, 2008). The graph on the right depicts a three-dimensional view of the sub-ice-shelf melt channel (location given with red arrow) obtained from ground penetrating radar (GPR) on the floating ice tongue. The melt channel deepens in the flow direction from -160 m to -80 m below the ice surface over a distance of 4.5 km.

Airborne and on the ground radar observations at Petermann revealed the presence of channel

structures incising the underside of the ice shelf that begin at the grounding line and are aligned along the

TPI 7081896


D-5 of 15

direction of ice flow (Fig. 3). The features are about 1–2 km wide and 200–400 m deep and are separated by about 5 km. Estimates of bottom melting exhibit a complex pattern with high melting in the upper channel and deposition along the sides. The channels have no surface expression on the surface of the grounded ice, but do show approximately 20–25 m of relief over the floating shelf, suggesting that they are created by interactions with the underlying ocean.

Our current knowledge of the nature of ocean-ice shelf interactions at PG has been recently summarized [Johnson et al., 2010, Fig. 4]. A temperature and salinity profile was obtained under the ice shelf directly through the center or thinnest part (about 60 m ice thickness) of one of these channels in May, 2004 (red dot in Fig. 2 left panel). Summer profiles from north of the ice tongue were obtained during one-day hydrographic surveys from the US Coast Guard Cutter Healy (2003) and the Canadian Coast Guard Ship Henry Larsen (2007, 2009) during the Canadian Arctic Throughflow Study (CATS). The principle aim of CATS was to measure and understand the oceanic volume and fresh water flux from the Arctic Ocean to Baffin Bay (and hence the North Atlantic Ocean) via Nares Strait. As such, the oceanography of the wider region has been relatively well characterized [Melling et al., 2008; Muenchow et al., 2007; Muenchow et al., 2006; Muenchow and Melling, 2008; Rabe et al., 2010].

Fig. 4. Schematic illustrating the distributions of water masses in Petermann Fjord in the vertical versus along-fjord plane. However, the circulation is known to be three dimensional, at least on the scale of the fjord and possibly also on the scale of the under-ice channels.

In brief, we surmise that modified Atlantic water with a temperature close to 0.2C and a salinity of 34.77 psu flows over the sill and episodically renews the deep waters of the fjord. The frequency of such renewal events is unclear; tracer data (dissolved oxygen and nutrients) suggest that the deeper parts of the fjord are relatively isolated, while the difference in water mass properties between surveys in the upper 500 m of the water column implies a much shorter renewal timescale.

Extraction of the latent heat of melting from seawater in contact with glacial ice generates a characteristic slope on a TS plot referred to as a Gade line [Gade, 1979]. Melting glacial ice also injects relatively high gas concentrations (in atmospheric ratios) from its trapped bubbles into seawater. Such characteristics were observed below 135 m in the through-shelf profile taken in 2002, at 300–500 m depth in the single profile in the fjord 2003 and on the northeast side of the fjord in the 200–500 m depth range in 2007. However, dissolved O2-salinity trends governed by mixing and biological processes in regional waters outside of the fjord can be quite similar. While dissolved oxygen is not an unambiguous tracer of ice shelf melt, noble gas concentration ratios should be.

Interestingly, “Gade” behavior does not extend from the water column to the depths of the underside of the ice in profiles collected to date. Properties directly under the ice surface at the one through-shelf site are characteristic of polar surface waters conditioned by sea ice formation in winter. In the open waters seaward of the PG ice tongue, summer insolation plus both sea ice and glacial melt can stratify the upper part (less than 40 m) of the former winter mixed layer (about 130 m in depth). Limited observations to date have not directly captured processes of basal ice melt or formation in the ice shelf cavity. The

TPI 7081896


D-6 of 15

small thermal conductivity of thick floating glacial ice limits its in-situ basal ice formation. Marine ice deposition has been inferred beneath other ice shelves (e.g., Filchner Ronne), but the conditions require colder source waters that are already close to the surface freezing point (~-1.8 °C) upon first contacting the ice [Bombosch and Jenkins, 1995; Schlosser et al., 1990]. The PG ice shelf has relatively warm source water and there is no evidence in the temperature record to suggest conditions are cold enough for marine ice deposition. Instead, it appears that the buoyant meltwater plume finds its neutral density at or below 135 m, and therefore it must detach and drift out into the interior.

Fig. 5. Hydrographic data from along the ice-shelf front in Petermann Fjord in 2009 (see Fig. 2) [Johnson et al., 2010]. Dashed line in inset is seawater freezing line. Not evident on this scale is a break in slope at about 600 m depth that corresponds to an O2 minimum with associated nutrient increases in Redfield-like proportions characteristic of marine respiration.

During the surveys in August 2007 and August 2009, subsurface geostrophic flow out of the fjord over the northeastern half of the section was compensated by inflow on the southwestern side of the fjord. Semidiurnal tidal currents in the fjord have similar magnitude as the geostrophic flow and are smaller than those in Nares Strait [Münchow and Melling, 2008]. Remote sensing suggests a cyclonic circulation at the surface in the mouth of the fjord. The flow structure is fundamentally three dimensional on both the scale of the fjord and the under-ice channels [Rignot and Steffen, 2008]. The !18O tracer data indicate the presence of glacial melt water in the upper portion of the water column. However !18O-salinity trends can be complicated by the inheritance of a net sea-ice formation signal in the Arctic Ocean. Dissolved oxygen suggests that the water below sill depth but above the depth of the glacier’s grounding line is the least well ventilated in the fjord, supporting the idea of intermittent renewal of deep water via spillover at the sill with subsequent lifting of mid-depth waters.

The net heat flux into the fjord based on the 2009 section is at least three times as large as the melt rate of glacial ice deduced from the ice shelf mass balance. Although the geostrophic flux is based on a summer snapshot, the 3-year long temperature time series in Nares Strait from the CATS program [Rabe et al., 2010] suggest that water mass properties at sill depth do not exhibit large seasonal variability. Nares Strait thus appears to supply ample heat to the fjord throughout the year to accommodate the implied melt rates. Any temporal variations in net heat flux across the sill, however, remain unknown. The available summer snapshot surveys indicate to us that, apart from the temperature and volume flux of the modified Atlantic water entering the fjord, ocean winter mixed layer depth, mobile versus landfast sea-ice cover, and fjord geometry may also be important factors determining melt.

TPI 7081896


D-7 of 15

Fig. 6. (a) NASA satellite Modis Aqua true color image, 08:40 UTC, 5 August 2010, showing calving of Petermann Gletscher. (b) Depiction of 31 known frontal positions with red and yellow from 1876 and 1922, respectively; green dots indicate grounding line and black star locates Automatic Weather Station [Rignot and Steffen, 2008]; black arrow: total movement 1922–2010; white: glacial ice. (c) Times series of ice shelf length measured along the central axis from the grounding line. Lines connecting 1876 and 1922 are hypothetical trajectories. Blue arrows indicate steady ice advance velocities between calvings (brown arrows).

Calving events visible from satellite imagery in 2001, 2008 and particularly 2010 focused considerable attention on PG. However, there is no evidence that either the frequency of episodic calving or the rate of glacial advance has markedly changed since observations were first recorded in the late 1800s [Falkner et al., 2010]. The sizeable ice island (253+17 km2) that calved in August 2010 brought the ice front as close as it has ever been observed toward the grounding line (Fig. 6); but large gaps in the record of ice extent preclude final judgment on whether this is unprecedented as illustrated by the hypothetical trajectories in Fig. 6c. Because the recently calved ice is relatively thin, its loss is not expected to have a large immediate impact on PG ice dynamics.

At the moment, the PG drainage and shelf configuration appears to be almost curiously stable given that thinning is occurring at neighboring drainages and elsewhere around Greenland [Joughin et al., 2010; Luthcke et al., 2006; Pritchard et al., 2009]. We suspect that the PG Ice Shelf may be poised to undergo change in the coming decades. Changing patterns of atmospheric pressure and temperature are affecting sea ice and ocean circulation in the Arctic. Ever warmer pulses of Atlantic water have been observed to circulate in the Arctic Ocean over recent decades [Dmitrenko et al., 2008; Polyakov et al., 2005]. This may change the temperature of Arctic Atlantic seawater delivered to the sill. Whether this will have an effect depends upon the processes controlling import of warm water into the fjord and sub-ice-shelf cavity, and basal ice melt. Seasonally fast sea ice has been presumed to inhibit calving along the coasts of northern Ellesmere Island and Greenland. It has been proposed that fast ice buffers ice shelves from wave energy originating from storm activity [i.e., Bromirski et al., 2010; Macayeal et al., 2006]. Stationary sea ice that typically forms and prevents free movement of sea ice in Nares Strait for several months each year was virtually absent in 2006–07, 2008–09 and 2009–10: such a sequence is unusual in the satellite record [Kwok et al., 2010; Muenchow et al., 2007]. Surface atmospheric temperatures in the region are currently trending upward and are leading to increased glacial surface melt [Box and Cohen, 2006; Hall et al., 2008; Hanna et al., 2005]. Increasing amounts of surface water has been observed to promote fracturing of ice shelves and render them vulnerable to break up on the Antarctic Peninsula [Scambos et al., 2004].

Will a combination of regional climate change enhance basal melting, increase calving rates and potentially lead to a retreat of the shelf and accelerated ice losses? The answer requires understanding of the interplay of several processes that govern the ocean/ice-shelf interactions and the ice mass balance in this setting. We thus propose an interdisciplinary experiment to observe and understand those processes.

TPI 7081896


D-8 of 15

D5. Questions & Hypotheses Hypotheses guiding our experiment are aimed at the following questions.

1) Why is there a quasi-stable floating ice shelf in Petermann Fjord? Hypotheses linked to (1) include: a) Ice-shelf thinning is dominated by basal melting, but this slows dramatically when shelf thickness decreases to ~ 100 m or less because cold, low salinity water from the wintertime polar mixed layer isolates the underside of the ice shelf from warmer ocean waters beneath. b) The fraction of heat delivered into the fjord that is used for basal melting is limited by stable density stratification within the sub-ice-shelf cavity. Turbulent kinetic energy is insufficient to entirely break down this stratification. c) The main sources of turbulent kinetic energy under the ice shelf are vertical shear instability due to the rising of buoyant melt waters on sloping under-ice topography, and tidal currents. d) A progressive narrowing of the fjord between the grounding line and the shelf front impedes the escape of shelf fragments that may separate from the main body of the shelf. e) Landfast sea ice and congested mobile sea ice in Nares Strait impede the escape of ice shelf fragments that may separate from the main body of the ice shelf. f) Tides and storm-generated wave energy augment the rate of basal melting and calving, while land-fast sea ice impedes ice shelf advance and calving. g) Downstream glacier motion is balanced by basal drag at the rock/till bed, and ice/rock interactions along the glacier and ice tongue sidewalls. 2) What change in climatic conditions might cause the shelf front to retreat back towards the grounding line? Hypotheses linked to (2) include: a) Arctic Intermediate Water is the primary source of heat linked to basal melting of the PG Ice Shelf. This layer within the Arctic Ocean has been warming and freshening in recent decades. Penetration of warmer, less dense AIW into Petermann Fjord will enhance basal melting and thinning, and so also increase susceptibility to mass loss via calving. b) Enhanced top surface melting of the ice tongue will increase susceptibility to mass loss by calving caused by hydrofracture. c) Reduced presence of sea ice in Nares Strait, in consequence of declining Arctic multi-year sea ice, will facilitate the escape of shelf fragments from the fjord. d) Reduced presence of sea ice in the fjord will facilitate seasonal solar warming of fjord surface waters; advection of these warmer waters under the ice-shelf front will increase near-front basal melting and precondition the shelf to more rapid calving.

To test these hypotheses, we will obtain comprehensive observations of both the ice and ocean over a two-year period. We will require aircraft and ship support as described in the following section.

D6. Experimental approach (mapped to hypotheses: indicated as 'H.n.m')

Muenchow, Padman, Torres, Loose & Jenkins: We propose to use ship surveys and moorings (see Fig. 2 for array design) to provide the first comprehensive description of Petermann Fjord regarding: (a) its bottom topography seaward of the terminus of the glacier (b) water masses entering and leaving the fjord; and (c) the circulation within the fjord, over its sill, and in adjacent Hall Basin of Nares Strait (H.1.b-f, H.2.a, H.2.c, H.2.d). More specifically, the moored array will (1) quantify temperature, velocity and thus heat fluxes in and out of Petermann Fjord from tidal to interannual times scales and thus constrain heat losses due to melting; (2) determine the circulation at the entrance to the fjord; (3) investigate how variable ocean temperatures contribute to melting and calving in response to changing ambient forcing such as ice cover, pressure gradients, and volume, heat, and energy fluxes into the fjord. An auxiliary objective requires the vessel-mounted ADCP of the USCGC Healy to determine the

TPI 7081896


D-9 of 15

orientation and spatial variability of the principal axes of tidal currents at the mooring locations in order to reference the torsionally-rigid ADCP moorings near the magnetic North Pole [Münchow and Melling, 2008], where magnetic compasses are unreliable. Remotely sensed optical (MODIS) and radar (ASAR) signatures of the glacier, sea ice, and ocean water are routinely acquired and processed by us and Danish collaborators.

We propose to deploy an array of 11 moorings across the entrance of Petermann Fjord to measure full water column salinity, temperature, and pressure at 6 locations and velocity profiles from acoustic Doppler current profilers at 5 locations (Fig. 2). Muenchow & Melling (2008) and Rabe et al. (2010) provide mooring design details. The array resolves the ~5 km scale of motion of a baroclinic circulation subject to the Earth’s rotation. Moorings with ice-profiling sonars at 100-m depth will be placed inside the fjord and in adjacent Nares Strait along with temperature sensors below to identify temporal and spatial variations of ice thickness as well as heat content below 100-m depth. Two shallow pressure sensors across Nares Strait and one at Alexandra Fjord, to complement a permanent Canadian tide gauge at Alert, will permit estimates of along and across channel pressure gradients.

A 17-hour snapshot of direct velocity observations in 2003 indicates tidal and subtidal currents "0.2 m/s over the sill [Johnson et al., 2010]. Froude numbers that measure flow velocities relative to (internal) wave speeds are «1 and thus indicate that wave-like perturbations are free to propagate energies both into and out of the fjord. Therefore, the 350–450 m deep sill is unlikely to impose dynamical control. This helps to assure that the moored array across the sill will provide accurate flux estimates of volume, heat, and energy at tidal to interannual timescales. While the flux of heat provides an upper bound on the available potential energy to melt the ice shelf, the flux of kinetic energy as a source of turbulence to facilitate mixing inside the fjord under the ice shelf is also germane. Our dynamical and statistical analyses will be guided by ideas presented elsewhere [Edwards et al., 2004; Inall et al., 2004; Stigebrandt, 1999].

Using the USCGC Healy’s unique capabilities, we propose spatial surveys of bottom topography (multibeam), velocity (ADCP), and water masses (24 bottle CTD rosette). Full water column sampling at 35 stations will map the distribution of water masses and their sources using both traditional tracers [nutrients, dissolved oxygen, !18O, tritium, and “ignoble” gases SF6, CFC-11, 12, 113] as well as noble gases (Helium, Neon, Argon, Krypton, and Xenon). We distinguish between modified Atlantic Water (T=0.2 °C, S = 34.77), polar surface water (T = -1.6 °C, S = 33.8), and glacial meltwater whose end-member contribution to the mixture is T ~ -72 °C and S=0, due to latent heat loss. The fate of the meltwater reflects dynamical processes related to basal melting and thus constitutes a focus of the hydrographic program. Fig. 5 suggests that most glacial meltwater is contained in diluted form at 135 to 600 m depth between winter mixed polar surface above and modified Atlantic waters below [Johnson et al., 2010].

When glacial ice is melted at depth, air that was trapped in the ice matrix dissolves in the water, under pressure. The resulting trace gas composition and relative concentration is unique from seawater [Hohmann et al., 2002]. The proposed noble gas measurements thus provide an unambiguous metric for distinguishing meltwater from other water masses (Fig. 7). Additionally, sediment pore water from behind the grounding line, surface-melt or “moulin” water from the ice tongue, and hydrothermal water from beneath the grounding line may also be present. Combined analyses of noble gases, helium isotopes, and ignoble gases will identify the relative distribution of these water types [Aeschbach-Hertig et al., 1999; Aeschbach-Hertig et al., 1998; Mensch et al., 1998] The analytical precision for the noble gases is 0.5% (0.3% for Kr) [Stanley et al., 2009b] and glacial meltwater concentration are determined within 5% uncertainty if we use the same set of tracers[Loose et al., 2009]. The "ignoble" gases (e.g., SF6, CFC-11, 12 and 113) and tritium have unique atmospheric time histories beginning ~70 years ago. They are typically absent in glacial meltwater, and can vary over their entire range in water that has had contact with the atmosphere in the past century. We will use the ignoble gases to quantify arctic surface waters inside the PG ice shelf cavity and beneath the winter mixed layer (H.1.a, H.1.b, H.2.a,b). The tracer

TPI 7081896


D-10 of 15

distributions will also suggest timescales for circulation by comparing the age of subsurface water masses in Hall Basin, Petermann Fjord, and under the ice shelf near the grounding line, thus complementing flow estimates from both the mooring array and surveys.

Fig. 7. The saturation anomaly (!C = [C/Cref-1]x100) for Kr and Ne and SF6 inferred from T and S, for water masses that may be present beneath the PG ice shelf. Hall Basin surface water is the reference water mass.

Tracer measurements near the grounding line will be collected in conjunction with the UK hot water drilling program. More specifically, we propose to collect pumped water samples using a Grundfos 904 L alloy submersible pump and Franklin Electric motor to provide 12 L/min of water. Consultations with the UK drill team (see support letter by Mackinson and Nicholls) improved the design of this pump system that allows us to profile to a maximum depth of 650 m below the oxygen minimum at 500 m. Measurements of tracer concentrations in the water column beneath the ice shelf will permit direct comparison of the water mass modifications that take place during transit from the grounding line to the cavity front (H.1.a, H.1.b, H.2.a). We anticipate to document mixing of meltwater with Atlantic source waters as the ignoble gases in this mixture will become diluted while the noble gas saturation anomaly increases. The vertical extent of the trace gases in these water layers can be compared with the layers at the ice shelf front. Extrapolation of these layers back to the point of contact with the ice shelf will be compared with the region of greatest melting from surface divergence (H.1.a, H.2.a).

Steffen and Abdalati: We will examine bottom and surface melting near the grounding zone (H.1.a–b, H.2.a-b). The Greenland Climate Network AWS placements as of summer 2010 are primarily south of 75°N. We propose to install one new AWS on the floating tongue of PG at the same location, ~10 km from the grounding line, where we monitored the surface climate during the 2002–05 project. The proposed PG AWS will provide data to calculate the hourly surface energy balance (radiative, turbulent and conductive heat flux) to assess the surface melt component of the floating ice tongue. The AWS data will be transmitted via the ARGOS satellite link and made available on our Greenland climate network homepage, together with the other Greenland AWS data. This information will be complemented by the AWS stations emplaced within Nares Strait though a Danish and Canadian collaboration.

Surface ablation can vary considerably within several kilometers due to wind speed (turbulent exchange), aspect, albedo and ice type variability on the glacier surface. Therefore, we propose two additional micrometeorological stations (so-called "smart stakes") at locations 5 km up- and down-glacier of the PG AWS to assess the spatial variability of melt parameters (H.1.a, H.2.b). These stations will record climate parameters at one level, in addition to the surface height change.

We will use a high-resolution three-dimensional mass and energy flux model that will resolve the surface energy balance at grid points (1-km x 1-km) on the PG floating tongue. It will include a detailed elevation model derived from existing NASA P3 laser altimeter data and ongoing IceBridge airborne data, and differential GPS traverses made on snowmobile. The various components of the energy balance measured at the AWS and smart stakes in combination with the high-resolution albedo parameterization

TPI 7081896


D-11 of 15

from satellite will be used to run a surface energy balance model to calculate the energy available for melt at each grid point. These results will be constrained by the hourly surface-height changes measured by sonic-depth sounders at the AWS and smart stakes. The ablation values on a 1 km x 1 km grid will then be used in the assessment of temporal ice thickness change on the Petermann floating tongue for the 2–3 year period of field observations.

We plan to characterize tides and ice velocities at the grounding line using a GPS receiver (Trimble 4000 SSE) located at the PG AWS. Along with a subsurface pressure sensor deployed at the entrance of the fjord (Fig.2), the vertical tidal motion near the grounding line allows estimation of tidal dissipation within the fjord (H.1.b-c). We will also place one GPS unit above the grounding line to characterize the differences between the sliding and floating ice tongue. The GPS data will be referenced to the baseline stations in Thule, Kangerlussuaq and Kulusuuk, and will be used as a relative reference station for the differential GPS measurements (height and location) along the surface profiles to support ground penetrating radar measurements. The receiver will be provided by CU/CIRES on loan at no cost.

We propose to re-measure, using 50 and 100 MHz GPR, the melt channel mapped in 2002–04 that, we hypothesize, will have moved ~10 km downstream. We will re-track our GPR profiles from the earlier field campaign to assess decadal variability at a site (H.1.a). The bottom melt channels in the western side of the ice tongue have not yet been measured with GPR, but their existence is known from both Ice Sounding Radar (ISR) and ice flux divergence (Fig. 3). The high-resolution bottom topography map of the floating ice tongue will provide insights into the bottom melt features that have previously been observed close to the grounding line (2nd field season). With the improved resolution of our GPR equipment, we will be able to measure annual bottom melt rates along these channels using repeat surveys. We propose to map a major melt channel 30–40 km in length at the beginning and the end of the project to infer temporal and spatial melt rates in the floating ice tongue (3rd field season).

Trehu: Broadband seismic observations of glaciers show a rich diversity of waveforms associated with a variety of dynamic processes, including: tidally-modulated microearthquake activity generated as a grounded glacier flows over its rough bed [Anandakrishnan and Bentley, 1993; Weins et al., 2008]; large “slow earthquakes” generated by calving and overturning of the icebergs thus created [Ekstrom et al., 2003; Ekstrom et al., 2006; Nettles and others, 2008; Qamar, 1988]; tremor-like signals possibly related to water flow through the glacier [West et al., 2010]; changes in activity related to migration of the grounding line [Walter et al., 2010]; and modulation of glacier behavior in response to tides and seasons [de Juan and others, 2010; Walter et al., 2010; Weins et al., 2008]. (H.1.f-g).

In May 2012, we propose to install 4 broadband seismic stations near the grounding line (Fig.2). Three stations will be sited on rock along the sides of the glacier and one will be on the ice adjacent to a GPS (AWS) site to be installed by K. Steffen. Stations will be left in place for 2 years, with a visit to retrieve data in May 2013. Instrumentation will be provided by IRIS/PASSCAL. Each station for installation on rock includes a broadband seismometer protected beneath a thermally insulated dome, a 1000 amp-hr battery pack, solar panels, and an insulated enclosure for recording equipment. This station configuration has been developed by PASSCAL (www.passcal.nmt.edu/content/polar). The station installed on the glacier will be a new design that is currently being developed by PASSCAL for on-ice installations.

We will analyze the data for signals representing earthquakes, tremor and slow earthquakes using techniques we have developed for our studies of such signals in the Cascadia subduction zone [Trehu and Williams, 2009; Williams et al., 2010]. Earthquakes will be located using the Antelope software package for event detection and correlation across the network. Tremor and very low frequency earthquakes will be identified and located using band-pass filters and wavefield envelop cross-correlation techniques used to identify such signals in subduction zones [Brudzinski and Allen, 2007; Gomberg and Group, 2010; Obara, 2002; Shelly et al., 2007]. We anticipate seeing a variety of signal types in addition to the three mentioned above (e.g., the mixed events of West et al., 2010) and will use adaptive filters we are

TPI 7081896


D-12 of 15

currently developing for automated classification of the wide variety of signal we see in data from a recent ocean bottom seismology experiment (see Trehu prior results).

While the location accuracy (especially depth precision) and ability to resolve source mechanism of a 4station seismic array is limited, we will determine how ice deformation is distributed between the calving front, the grounding line, and the rock-ice interfaces along the side of the floating ice shelf as well as beneath the grounded part of the glacier. We will compare seismic activity with the GPS data to detect tidal modulation of stick-slip behavior at ice-rock contacts, as has been documented for ice streams in Antarctica [Bindschadler et al., 2003; Weins et al., 2008]. Modeling broadband waveforms, we will provide constraints on the mechanism and source time function of events to distinguish between shear slip on a plane or extensional cracking (H.1.f-g). This will also reveal whether hydrofracturing is a significant mechanism for calving at the seaward edge of the ice shelf (H.1.f, H.2.b) and for the transfer of meltwater from the surface to the base of the ice shelf, as has been observed elsewhere [Das et al., 2008]. Continuous recording through two full years will enable us to determine seasonal [Nettles and Ekstrom, 2010] as well as tidal changes in glacier dynamics and their relationship to ocean and fjord sea ice properties (H.1.f-g, H.2.b).

Collaborators: Our experimental approach includes partnerships with foreign partners and agencies as described in letters provided in the supplementary section of this proposal. In brief, our British colleagues propose to augment our observations with under-ice surveys of ocean properties, basal surface topography and bathymetry via deployment of the UK Autosub. The UK hot water drilling capability will enable us to sample waters underlying the ice tongue for hydrographic properties including noble gases; our UK partners will deploy CTDs through the ice for profiling, and set up stations where CTD instrumentation is left in place with data transmitted to the surface. This will allow examination of processes directly at the ocean-ice interface and provide a temporal context for the Autosub “snap shot.” Dr. Melling’s Canadian mooring group will be aboard the USCGC Healy in 2012 to recover a Canadian/UDel moored array in Nares Strait and to assist in the deployment of the UDel array in Petermann Fjord (see attached support letter). A Canadian program led by Dr. Melling may be in place by 2014 should NSF lease a Canadian icebreaker, as we here propose, to recover instrumentation.

Our science will be further enhanced through coordination with modeling and paleo-context projects. The coordination maximizes returns on what are necessarily expensive mobilization costs of aircraft and vessels. We will provide data to aid in model development and testing and so expand the value of our spatially and temporally limited observations for developing insights for processes controlling the PG mass balance. Critical bathymetric mapping data will be shared among all proposals in its current form and as it develops. We will use Icebridge gravimetry (see Danish collaborator Forsberg’s letter) data in conjunction with Autosub (See BAS letter) and ship-based swath mapping (POISE-Paleo Context of Ocean Ice Interactions project) to better constrain fjord bathymetry.

D7. Work plan including timeline of activities

The following work plan assumes a fully coordinated POISE program. The elements specific to this proposal are underlined; those of our most closely allied foreign collaborators are starred. International commitments are detailed in letters from collaborators (see supplemental materials). Laurie Padman will serve as chief scientist on the Healy and will coordinate all science activities of POISE-OOII. Marta Torres will oversee integration of education and outreach activities for the project. She will also oversee chemical hydrographic sampling in 2012. Andreas Muenchow and Humfrey Melling (Canada) will lead survey and mooring activities. In the spirit of the legacy of the IPY, the POISE program depends upon the funding situations of multiple national and international partners that cannot all be known at this time. Hence an iterative planning process will be the most cost effective approach to meet science objectives. We expect face-to-face meeting of all partners with logistic providers and program managers at the outset.

POISE PI & Logistics personnel planning meeting Winter 2012, Arlington, VA McAuliffe begins process to engage native participants; see McAuliffe letter in supplementary materials

TPI 7081896


D-13 of 15

Aircraft Based: Year 1, May 2012 AWS and GPS installation & initial radar survey (Team lead Steffen) Seismic station installations (Team lead Trehu) Through-lake ice, sediment-coring reconnaissance (Team lead Stoner: PI Mix).

Ship based: Year 1, August 2012 44-day Cruise on the USCGC Healy Hydrography (Team lead Padman w/Torres and Loose) ADCP surveys (Team lead Muenchow w/Padman) Mooring deployment (Team lead Muenchow w/Melling Canada) Marine geology and geophysics (Team lead Mix)

Seismic survey w/ towed Huntec and GI-Gun & Streamer (CGC & Trehu); Bathymetric survey (Mayer & postdoc); Coring OSU piston and multi-cores (Mix w/ 2 coring techs and 2 students); Core logging and archival (Stoner w/2 students)

*Autosub (Team lead Jenkins/Makinson/Nicholls UK) Host helos (possibly via Melling & Polar Continental Shelf Project (PCSP), Canada) *Hot water drilling (Makinson/Nicholls UK, w/Loose, Padman) Exposure age dating (Team lead Brook)

Aircraft Based: Year 2, May 2013 Radar surveys (Team lead Steffen w/Nicholls UK); GPR profiles on western part of floating ice tongue 10–20 km from grounding line, and high-resolution gridding around British Antarctica Survey (BAS) multi-phase radar measurements; *Install 4-phase sensitive array radar stations (Team lead Nicholls UK); service AWS, GPS & seismic stations as appropriate (Steffen & Trehu). Through lake-ice long coring (Team lead Stoner w/2 others, PI Mix)

POISE PI Science Meeting, Corvallis OR: Year 2 Fall 2013 Aircraft Based: Year 3, May 2014

Radar surveys, GPS (Team lead Steffen); GPR repeat profiles of major melt channels, retrieval of GPS and AWS and possibly seismic stations, retrieval of 4-phase radar stations (Nicholls UK team lead).

Ship based: Year 3, August 2014 Cruise on ice breaker (Canadian assets via Melling) Retrieve moorings (Team Lead Melling Canada w/Muenchow and Johnson UK); Hydrography (Melling and/or Padman); *Retrieve shore based instrumentation (Trehu, Makinson) need helo support

POISE PI Results, Integration & Comprehensive Synthesis Meeting, Oxford UK: Year 3 D8. Data plan

Data for the POISE-OOII project will be posted immediately in preliminary form and as soon as possible in quality controlled form at the University of Delaware website similar to 2003–06 CATS program at http://www.cats.udel.edu. It will be linked to the project web sites at OSU. The quality-controlled versions archived to the distributed sites appropriate and directly publically accessible for the various data types. PASSCAL data will be made available to the community through the IRIS Data Management Center. Ocean hydrographic data will go to the CLIVAR Hydrographic Data Office. Mooring data will go to the UK International mooring holdings office. Atmospheric and radar data will similarly be accessible through already established channels. D9. Broader impacts • Integrate research & education: Torres will incorporate elements of this research in a public outreach

effort through an ongoing and highly successful program to train instructors in Adult Education [Cowles et al., 2004; Torres et al., 2004]. This program at reaches adult learners by integrating ocean sciences into the science, math, and critical thinking curriculum through formal institutes and teacher at sea opportunities and includes efficacy assessment (http://literacyworks.org/ocean/). We anticipate a teacher to participate in the cruise and to generate curriculum to be incorporated into the GED training program. We plan to partner this teacher with another and/or a media contact through

TPI 7081896


D-14 of 15

existing programs. Imagery and video footage engages learners in formal and informal settings; thus we will bring an imaging/media specialist onboard. Scott McAuliffe (see supplementary materials) will spearhead native participation and outreach that interfaces with Canadian and Greenlandic communities as part of permitting process. Established connections exist in Qanaaq, Greenland and Grise Fjord, Canada. Four PhD students and 1 post doc will be sponsored in this research.

• Broaden participation: 2 PIs are members of underrepresented groups (female, Hispanic); native participants are included in the cruise; we will seek diversity in recruiting students.

• Enhance infrastructure (networks and partnerships): In moving forward, we acknowledge that it will be important to integrate inherently limited and hard won site-based ocean/ice-sheet interactions insights into a larger regional and eventually continental scale. We intend to actively share our observational findings with the concerted efforts underway to improve ice sheet models that are eventually to be fully coupled into global climate models [Lipscomb et al., 2009]. Our project complements analogous projects underway or proposed at other sites circum-Greenland. We plan to contribute to a network of researchers to develop a whole Greenland ice-ocean interactions synthesis.

• Broad dissemination: a teacher will participate in the cruise and populate an accessible web blog, enhanced by McAuliffe photography/videography; we will continue outreach efforts to the global media begun by Muenchow in 2010 regarding calving events and the implication of global climate change for policy makers (http://muenchow.cms.udel.edu/html/PetermannClimate/).

• Potential benefits to society: significantly improve basis for projecting sea-level rise (section D-2).

D9. Results of Prior NSF Support

Torres: OPP-0230354 Collaborative research: Variability and forcing of fluxes through Nares Strait and Jones Sound. (co-PI Torres component $19,680; 2003–07). Torres supervised a Master’s student (D. Zima) to reconstruct salinity conditions in Nares Strait (Canadian Arctic Archipelago) from stable isotope profiles in bivalve shells [Zima, 2007]. Oxygen isotopic profiles along the growth axis of shells collected live over the 5–30 m depth range from the Greenland and Ellesmere Island sides of the strait were used to reconstruct changes in the hydrography of the region over the past century [Torres et al., 2010]. Variability in oxygen isotope ratios is mainly attributed to variations in salinity, and suggests that the northern end of Nares Strait began experiencing an increase in freshwater runoff since the mid 1980s. In addition to this intellectual contribution, this project supported an additional Masters student (S. McAuliffe) who developed a suitcase lesson in oceanography (icebergs and sea-ice) to complement the ongoing science curriculum of third grade in the Corvallis school district. Trehu: OCE050402 Monitoring seismicity associated with a possible asperity on the Cascadia megathrust (07/01/06 to 12/31/10, $308,906). Primary results to date include: 1) confirmation that seismicity in a persistently active cluster on the continental margin is located on the plate boundary near the downdip edge of the nominally locked zone; 2) better localization seismic tremor in this segment of Cascadia; 3) tomographic inversion of fan shots from legacy active source data to generate a “2.5D” velocity model of the continental shelf and Coast Range that shows lateral velocity variations within and beneath the Siletz terrane; 4) identification of tremor-like signals from the outer accretionary complex that may be related to dewatering of accreted sediments; 5) documentation of considerable microearthquake activity across the entire margin; 6) characterization of the many different types of signals observed on the continental margin; 7) initial testing of an automated technique to identify local earthquakes in this very noisy environment. To date, this project has resulted in 4 publications [Gomberg and Group, 2010; Torres et al., 2009; Trehu et al., 2008; Williams et al., 2010], 2 papers in preparation (Kannberg et al., to be submitted to G3; Trehu et al., to be submitted to Geology) and many presentations at national meetings by the PI and graduate students Williams and Kannberg. Muenchow: Collaborative Research: Variability and Forcing of Fluxes through Nares Strait and Jones Sound" OPP-0230236 (Münchow and Wong); 1/1/2003 to 12/31/2007, $2,052,911. This 5-year effort with Oregon State University (Dr. Falkner) and the Institute of Ocean Sciences, Canada (Dr. Melling) provided moored and survey data from Nares Strait to estimate fluxes via the Canadian

TPI 7081896


D-15 of 15

Archipelago into the North Atlantic to the west of northern Greenland as part of the Arctic-Subarctic-Ocean-Flux (ASOF) experiment. Our web-site http://www.udel.edu/CATS contains processed data, reports, peer-reviewed papers, and outreach materials. In 2003 we deployed 17 moorings to measure ocean current, salinity, and temperature profiles as well as subsurface pressure and ice thickness from the USCGC Healy. In 2006, 15 moorings were recovered with complete and gap-free 3-year data records [Münchow and Melling, 2008]. The Healy vessel-mounted acoustic Doppler current profiler (ADCP) revealed unexpectedly rich ocean currents after we processed the data with a newly designed algorithm. Results indicated that both barotropic (1/3) and baroclinic (2/3) processes contribute to volume, and freshwater flux [Muenchow et al., 2006]. Combining tracer with velocity observations, we demonstrated that Pacific water contributes to the throughflow at Nares Strait contrary to previous assertions [Muenchow et al., 2007]. We reported on the interaction of strong ageostrophic atmospheric motion in Nares Strait and the formation of ice-arches anchored to the coasts of both Greenland and Canada whose formation is impacted by strong tidal currents [Samelson et al., 2006]. The project supported 3 undergraduate summer interns and 3 graduate students. Ms. Zweng completed an MS degree reporting on significant warming and freshening trends in Baffin Bay and along Baffin Island, respectively, for the 1916–2003 period [Zweng and Muenchow, 2005]. Ms. Brown was an undergraduate intern in 2003 who is in the final stages of completion of an MS thesis on Nares Strait hydrography. Dr. Rabe defended her dissertation in the summer of 2010 and has one paper published (Rabe et al., 2010) and another pending. Steffen: Assessment of basal melt of Petermann Glacier in northwestern Greenland: (OPP-ARC-0135450, 3/1/2002 to 28/2/2006, NSF & NASA combined budget: $487,000). The results of our project on the floating ice tongue of PG are reviewed in this proposal and described in 6 publications [Nghiem et al., 2005; Painter et al., 2007; Rignot and Steffen, 2008; Steffen and Box, 2001; Steffen et al., 2004; Steffen and Ohmura, 1985; Stewart et al., 2004]. L. Padman (w/ R. D. Muench): Collaborative Research: AnSlope, Cross-slope Exchanges at the Antarctic Slope Front, OPP-01256023, 6/1/2002 to 5/31/2005, $513,475. Collaborative Research: AnSlope Analysis, ANT-0440656, 7/1/2005 to 6/30/2008, $196,815. These grants supported the collection and analysis of turbulence data as a component of the Antarctic Slope (“AnSlope”) experiment in the northwest Ross Sea in 2003–04, and 2-D and 3-D ocean modeling including tides. Peer-reviewed results from this work include: an improved barotropic tide model using novel assimilation of currents from vessel-mounted ADCP [Erofeeva et al., 2005]; a detailed description of the gravity current [Gordon et al., 2009]; a high resolution 3-D model of tidal influence on outflow path and mixing [Padman et al., 2009]; a study of mixing rates affecting the evolution of the outflow [Muench et al., 2009a]; and an assessment of the role of bottom corrugations on downslope flow of dense water [Muench et al., 2009b]. W. Jenkins, OCE-0221247: “Is there an ocean primary production paradox?” April 1, 2002 to August 31, 2007, $1,647,417. (B. Loose is a Beginning Investigator and has not had prior NSF funding.) This program addressed an apparent primary production paradox in the subtropical North Atlantic by measuring a times series of noble gases, helium isotopes and tritium at the BATS site and using the results to make tracer-based determinations of primary production at that location. New methodologies for high precision quantitative noble gas measurements on seawater were developed using programmed cryogenic vacuum system technology and quadrupole mass spectrometric ion beam manometry [Stanley et al., 2009]. The time series was used to compare three independent tracer-based measures of primary production [Stanley, 2007]. We also developed an improved formulation of gas-exchange processes that allowed a unique determination of the air-sea gas exchange rate on seasonal timescales to an unprecedented accuracy of approximately 10% [Stanley et al., 2006; Stanley, 2007; Stanley et al., 2009]. A deeper understanding of the linkage between water mass formation, circulation and large-scale new primary production has been achieved [Jenkins and Doney, 2003], as well as the impact of climate change on basin scale biogeochemical cycling and new production [Jenkins, 2008] A substantial part of this work formed the basis of a PhD project for Rachel Stanley [Stanley, 2007] who graduated and interned as a postdoctoral scholar working at Princeton University with Michael Bender. She is now an Assistant Scientist at WHOI.

TPI 7081896

E. REFERENCES POISE: OBSERVING OCEAN ICE INTERACTIONS

E-1 of 7

Aeschbach-Hertig, W., P. Schlosser, M. Stute, H. J. Simpson, A. Ludin and J. F. Clark (1998) A 3H/3He study of groundwater flow in a fractured bedrock aquifer, Groundwater, 36, 661–670.

Aeschbach-Hertig, W., F. Peeters, U. Beyerle and R. Kipfer (1999) Interpretation of dissolved atmospheric noble gases in natural waters, Water Resources Research, 35, 2779–2792.

Anandakrishnan, S. and C. R. Bentley (1993) C.R., Microearthquakes beneath Ice Streams B and C, West Antarctica: observations and implications, Journal of Glaciology, 39, 455-462.

Bamber, J. L., R. L. Layberry and S. P. Gogenini (2001a) A new ice thickness and bed data set for the Greenland ice sheet 1: Measurement, data reduction, and errors, Journal of Geophysical Research, 106, 33,773–733,780.

Bamber, J. L., R. L. Layberry and S. P. Gogenini (2001b) A new ice thickness and bed data set for the Greenland ice sheet 2: Relationship between dynamics and basal topography, Journal of Geophysical Research, 106, 33,781–733,788.

Bindschadler, R. A., M. A. King, R. B. Alley, S. Anandakrishnan and L. Padman (2003) Tidally controlled stick-slip discharge of a West Antarctic ice stream, Science, 301, 1087–1089.

Bombosch, A. and A. Jenkins (1995) Modeling the formation and deposition of frazil ice beneath the Filchner-Ronne Ice Shelf, Journal of Geophysical Research, 100, 6983–6992.

Box, J. E. and A. E. Cohen (2006) Upper-air temperatures around Greenland: 1964-2005, Geophysical Research Letters, 33, doi:10.1029/2006GL025723.

Bromirski, P. D., O. V. Sergienko and D. R. Macayeal (2010) Transoceanic infragravity waves impacting Antarctic ice-shelves, Geophysical Research Letters, 37, doi:10.1029/2009GL041488.

Brudzinski, M. R. and R. M. Allen (2007) Segmentation in episodic tremor and slip all along Cascadia, Geology, 35, 907–910.

Cowles, S., R. W. Collier and M. E. Torres (2004) Adult rated oceanography Part 1: Project integrating ocean sciences into adult basic education programs, Am. Geophys. Union, Fall Meeting, OS23A-1287

Das, S. B., I. Joughin, M. D. Behn, I. M. Howat, M. A. King, D. Lizarralde and M. P. Bhatia (2008) Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage, Science, doi 10.1126/science.1153360.

de Juan, J. and others (2010) Sudden increase in tidal response linked to calving and acceleration at a large Greenland outlet glacier, Geophysical Research Letters, 37, doi:10.1029/2010GL043289.

Dmitrenko, I. A., I. V. Polyakov, S. A. Kirillov, L. A. Timokhov, I. E. Frolov, V. T. Sokolov, H. L. Simmons, V. V. Ivanov and D. Walsh (2008) Toward a warmer Arctic Ocean: Spreading of the early 21st century Atlantic warm anomaly along the Eurasian Basin margins, Journal of Geophysical Research, 113, doi:10.1029/2007JC004157.

Edwards, K. A., P. MacCready, J. Moum, G. Pawlak, J. M. LKlymak and A. Perlin (2004) Form drag and mixing due to tidal flow past a sharp point, Journal of Physical Oceanography , 34, 1297–1312.

Ekstrom, G., M. Nettles and G. A. Abers (2003) Glacial earthquakes, Science, 302, 622–624. Ekstrom, G., M. Nettles and V. C. Tsai (2006) Seasonality and increasing frequency of

Greenland glacial earthquakes, Science, 311, 1756–1758. Erofeeva, S. Y., G. D. Egbert and L. Padman (2005) Assimilation of ship-mounted ADCP data

for barotropic tides: Application to the Ross Sea, Journal of Atmospheric and Oceanic Technology, 22, 721–734.

TPI 7081896


E-2 of 7

Falkner, K. K., H. Melling, A. M. Münchow, J. E. Box, Wohlleben, H. L. Johnson, P. Gudmandsen, R. Samelson, L. Copland, K. Steffen, E. Rignot and A. K. Higgins (2010) Context for the Recent Ice Island Calving of Petermann Gletscher, northwest Greenland, EOS Transactions of the American Geophysical Union, submitted.

Gade, H. G. (1979) Melting of ice in sea water: A primitive model with applications to the Antarctic Ice Shelf and icebergs, Journal of Physical Oceanography, 9, 189–198.

Gomberg, J. and C. B. W. Group (2010) Slow-slip phenomena in Cascadia from 2007 and beyond, Geological Society of Amreica Bulletin, July/August.

Gordon, A. L., A. H. Orsi, R. D. Muench, B. A. Huber, E. Zambianchi and M. Visbeck (2009) Western Ross Sea continental slope gravity currents, Deep-Sea Research II, 56, 796–817. doi:10.1016/j.dsr2.2008.10.037.

Hall, D. K., R. S. J. Williams, S. B. Luthcke and N. E. Digirolamo (2008) Greenland ice sheet surface temperature, melt and mass loss: 2000-2006, Journal of Glaciology, 54, 81-93.

Hanna, H., P. Huybrechts, I. Janssens, J. Cappelen, K. Steffen and A. Stephens (2005) Runoff and mass balance of the Greenland ice sheet: 1958–2003, Journal of Geophysical Research, 110, doi:10.1029/2004JD005641.

Higgins, A. K. (1991) North Greenland glacier velocities and calf ice production, Polarforschung, 60, 1–23.

Hohmann, R., P. Schlosser, S. Jacobs, A. Ludin and R. Weppernig (2002), Excess helium and neon in the southeast Pacific: Tracers for glacial meltwater, Journal of Geophysical Research, doi:10.1029/2000JC000378.

Holland, D. H., R. H. Thomas, B. De Young, M. H. Ribergaard and B. Lyberth (2008a) Acceleration of Jakobshavn Isbrae triggered by warn subsurface ocean waters, Nature Geoscience, 1, doi:10.1038/ngeo1316.

Holland, P. R., A. Jenkins and D. M. Holland (2008b) The response of ice shelf basal melting to variations in ocean temperature, Journal of Climate, 21, 2558–2572.

Inall, M. E., F. Cottier, C. Griffiths and T. Rippeth (2004) Sill dynamics and energy transformation in a jet fjord, Ocean Dynamics, 54, 307–314.

Jenkins, A., P. Dutrieux, S. S. Jacobs, S. D. McPhail, J. R. Perrett, A. T. Webb and D. White (2010) Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat, Nature Geoscience, 3, 468–472.

Jenkins, A. and S. Jacobs (2008) Circulation and melting beneath George VI Ice Shelf, Antarctica, Journal of Geophysical Research, 113, doi:10.1029/2007JC004449.

Jenkins, W. J. (2008) The biogeochemical consequences of changing ventilation in the Japan/East Sea, Marine Chemistry, 108, 137–147.

Jenkins, W. J. and S. Doney (2003) The bubtropical nutrient spiral, Global Biogeochemical Cycles, 17, doi:10.1029/2003GB002085.

Johnson, H. L., A. Münchow, K. K. Falkner and H. Melling (2010) Ocean circulation and properties in Petermann Fjord, Greenland, Journal of Geophysical Research, in press.

Joughin, I., W. Abdalati and M. Fahnestock (2004) Large fluctuations in speed on Greenland's Jakobshavn Isbrae glacier, Nature, 432, 608–610.

Joughin, I., S. B. Das, M. A. King, B. E. Smith, I. M. Howat and T. Moon (2008) Seasonal speedup along the western flank of the Greenland Ice Sheet, Science, 320, doi:10.1126/science.1153288.

Joughin, I., B. E. Smith, I. M. Howat, T. Scamblos and T. Moon (2010) Greenland flow variability from ice-sheet-wide velocity mapping, Journal of Glaciology, 56, 415–430.

TPI 7081896


E-3 of 7

Kwok, R., L. Toudal Petersen, P. Gudmandsen and S. Pang (2010) Large sea ice outflow into the Nares Strait in 2007, Geophysical Research Letters, 37, doi:10.1029/2009GL041872.

Lipscomb, W., R. Bindschadler, E. Bueler, D. H. Holland, J. Johnson and S. Price (2009) A Community Ice Sheet Model for Sea Level Prediction, EOS Transactions, AGU, 90, doi:10.1029/2009EO030004.

Little, C. M., A. Gnanadesikan and M. Oppenheimer (2009) How ice shelf morphology controls basal melting, Journal of Geophysical Research, 114, doi:10.1029/2008JC005197.

Loose, B., P. Schlosser, W. M. Smethie and S. Jacobs (2009), An optimized estimate of glacial melt from the Ross Ice Shelf using noble gases, stable isotopes, and CFC transient tracers, Journal of Geophysical Research, doi:10.1029/2008JC005048.

Luthcke, S. B., H. J. Zwally, W. Abdalati, D. D. Rowlands, R. D. Ray, R. S. Nerem, F. G. Lemoine, J. J. McCarthy and D. S. Chinn (2006) Recent Greenland ice mass loss by drainage system from satellite gravity observations, Science, 314, 1286–1289; doi:1210.1126/science.1130776.

Macayeal, D. R., E. A. Okal, A. R. C., J. N. Bassis, K. M. Brunt, L. M. Cathles, R. Drucker, H. A. Fricker, K. Y.-J., S. Martin, M. H. Okal, O. V. Sergienko, M. P. Sponsler and J. E. Thom (2006) Transoceanic wave propagation links iceberg calving margins in Antarctica with storms in tropics and northern hemisphere, Geophysical Research Letters, 33, doi:10.1029/2006GL027235.

Melling, H., T. A. Agnew, K. K. Falkner, D. A. Greenberg, C. M. Lee, A. Muenchow, B. Petrie, S. J. Prinsenberg, R. Samelson and R. Woodgate (2008), Fresh-water Fluxes via Pacific and Arctic Outflows across the Canadian Polar Shelf, in Arctic-Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate, edited by R. R. Dickson, J. Meincke and P. B. Rhines, pp. 193–248, Springer, Dordrecht, The Netherlands.

Mensch, M., A. Simon and R. Bayer (1998) Tritium and CFC input functions for the Weddell Sea, Journal of Geophysical Research, 103, 15923–15937.

Milne, G. A., W. R. Gehrels, C. W. Hughes and M. E. Tamisiea (2009) Identifying the causes of sea-level change, Nature Geoscience, 2, doi:10.1038/ngeo1544.

Mitrovica, J. X., N. Gomez and P. U. Clark (2009) The sea-level fingerprint of West Antarctic collapse, Science, 323, doi:10.1126/science.1166510.

Muench, R., L. Padman, A. Gordon and A. Orsi (2009a) A dense water outflow from the Ross Sea, Antarctica: Mixing and the contribution of tides, Journal of Marine Systems, 77, 369–387, doi:310.1016/j.jmarsys.2008.1011.1003.

Muench, R. D., A. K. Wåhlin, T. M. Özgökmen, R. Hallberg and L. Padman (2009b) Impacts of bottom corrugations on a dense outflow: Ross Sea, Antarctica, Geophysical Research Letters, 36, 23, doi:10.1029/2009GL041347.

Muenchow, A. and H. Melling (2008) Ocean current observations from Nares Strait to the west of Greenland: Interannual to tidal variability and forcing, Journal of Marine Research, 66, 801–833.

Muenchow, A., K. K. Falkner and M. H. (2007) Spatial continuity of measured seawater and tracer fluxes through Nares Strait, a dynamically wide channel bordering the Canadian Archipelago, Journal of Marine Research, 65, 759–788.

Muenchow, A., H. Melling and K. K. Falkner (2006) Volume and freshwater fluxes in Nares Strait from observed salinity and velocity fields, Journal of Physical Oceanography, 36, 2025–2041.

TPI 7081896


E-4 of 7

Nettles, M. and G. Ekstrom (2010) Glacial earthquakes in Greenland and Antarctica, Annual Review of Earth and Planetary Sciences, 38, 467–491.

Nettles, M. and others (2008) Step-wise changes in glacier flow speed coincide with calving and glacial earthquakes at Helheim Glacier, Greenland, Geophysical Research Letters, 35, doi:10.1029/2008GL036127.

Nghiem, S. V., K. Steffen, G. Neumann and R. Huff (2005) Mapping of ice layer extent and snow accumulation in the percolation zone of the Greenland ice sheet, Journal of Geophysical Research, 110, F02017, doi:02010.01029/02004JF000234.

Nicholls, K. W., E. P. Abrahamsen, J. J. H. Buck, P. A. Dodd, C. Goldblatt, G. Griffiths, K. J. Heywood, N. E. Hughes, A. Kaltezky, G. F. Lane-Serff, S. D. McPhail, N. W. Millard, K. I. C. Oliver, J. Perrett, M. R. Price, C. J. Pudsey, K. Saw, K. Stansfiled, M. J. Stott, P. Wadhams, A. T. Webb and J. P. Wilkinson (2006) Measurements beneath an Anarctic ice shelf using an autonomous underwater vehicle, Geophysical Research Letters, 33, doi:10.1029/2006GL025998.

Obara, K. (2002) Nonvolcanic deep tremor associated with subduction in SW Japan, Science, 296, 1679–1681.

Padman, L., S. L. Howard, A. Orsi and R. D. Muench (2009) Tides of the northwestern Ross Sea and their impact on dense outflows of Antarctic Bottom Water, Deep-Sea Research II, 56, 818–834.

Painter, T. H., N. P. Molotch, M. Cassidy, M. Flanner and K. Steffen (2007) Contact spectroscopy for determination of stratigraphy of snow grain size, Journal of Glaciology, 53, 121–127.

Polyakov, I. V., A. Beszczynska, E. C. Carmack, I. A. Dmitrenko, E. Farbach, I. E. Frolov, R. Gerdes, E. Hansen, J. Holfort, V. V. Ivaniv, M. A. Johnson, M. Karcher, F. Kauker, J. Morison, K. A. Orvik, U. Schauer, H. L. Simmons, Ø. Skagseth, V. T. Sokolov, M. Steele, L. A. Timokhov, D. Walsh and J. E. Walsh (2005) One more step towards a warmer Arctic, Journal of Geophysical Research, 32, doi:10.1029/2005GL023740.

Pritchard, H. D., R. J. Athern, D. G. Vaughan and L. A. Edwards (2009) Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets, Nature, doi:10.1038/nature08471.

Qamar, T. (1988) Calving icebergs: a source of low-frequency seismic signals from Columbia Glacie, Journal of Geophysical Research, 93, 6615–6623.

Rabe, B., A. Münchow, H. L. Johnson and H. Melling (2010) Nares Strait hydrography and salinity from a 3-year moored array, Journal of Geophysical Research, 115, doi:10.1029/2009JC005966.

Rahmstorf, S., A. Cazenave, J. A. Church, J. E. Hansen, R. F. Keeling, D. E. Parker and R. C. Somerville (2007) Recent climate observations compared to projections, Science, 316, 709.

Rignot, E. and S. S. Jacobs (2002) Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines, Science, 296, 2020–2023.

Rignot, E. and P. Kanagaratnam (2006) Changes in the velocity structure of the Greenland ice sheet, Science, 311, doi:10.1126/Science.11213181.

Rignot, E. and K. Steffen (2008) Channelized bottom melting and stability of floating ice shelves, Geophysical Research Letters, 35, doi:10.1029/2007GL031765.

TPI 7081896


E-5 of 7

Rignot, E., G. Cassassa, P. Gogineni, W. Krabill, A. Rivera and R. Thomas (2004) Accelerated ice discharge from the Antarctic Peninsual following the collapse of Larsen B ice shelf, Geophysical Research Letters, 31, doi:10.1029/2004GL020697.

Rignot, E., J. E. Box, E. Burgess and E. Hanna (2008) Mass balance of the Greenland ice sheet from 1958 to 2007, Geophysical Research Letters, 35, L20502, doi:20510.21029/22008GL035417.

Rignot, E., M. Koppes and I. Velicogna (2010) Rapid submarine melting of the calving faces of the West Greenland glaciers, Nature Geoscience, doi:10.1038/NGEO1765.

Samelson, R. M., T. Agnew, H. Melling and A. Muenchow (2006) Evidence for atmospheric control of sea-ice motion through Nares Strait, Geophysical Research Letters, 33, doi:10.1029/2005GL025016.

Scambos, T. A., J. A. Bohlander, C. A. Shuman and P. Skvarca (2004) Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica, Geophysical Research Letters, 31, doi:10.1029/2004GL020670.

Schlosser, P., R. Bayer, A. Foldvik, T. Gammelsröd, G. Rohardt and O. K. Münnich (1990) Oxygen 18 and Helium as tracers of ice shelf water and water/ice interaction in the Weddell Sea, Journal of Geophysical Research, 95, 3253–3263.

Shelly, D. R., G. C. Beroza and S. Ide (2007) Non-volcanic tremor and low frequency swarms, Nature, 446, 305-307; doi:310.1038/nature05666.

Shepherd, A., D. Wingham and E. Rignot (2004) Warm ocean is eroding the West Antarctic Ice Sheet, Geophysical Research Letters, 31, L23402, doi:23410.21029/22004GL021106.

Siddall, M., T. S. Stocker and P. U. Clark (2009) Constraints on future sea-lvel rise from past sea-level change, Nature Geoscience, doi:10.1038/NGE0587.

Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller (Eds.) (2007), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK.

Stanley, R. H. R., W. J. Jenkins and S. C. Doney (2006) Quantifying seasonal air-sea gas exchange processes using noble gas time-series: A design experiment, Journal of Marine Research, 64.

Stanley, R. H. R. (2007) A determination of the air-sea gas exchange and upper ocean biological production from five noble gases and tritiugenic helium-3, PhD thesis, 225 pp, Massachusetts Institute of Technology, Boston.

Stanley, R. H. R., G. Baschek, D. E. I. Lott and W. J. Jenkins (2009) A method for measuring noble gases and their isotopic ratios using programmed multistage cryogenic trapping and a combination of quadrupole and magnetic sector mass spectrometers, Geochemistry Geophysics Geosystems, 10, doi:10.1029/2009GC002429.

Stanley, R. H. R., W. J. Jenkins, D. E. I. Lott and S. C. Doney (2009c), Noble gas constraints on air-sea gas exchange and bubble fluxes, Journal of Geophysical Research, doi:10.1029/2009JC005396.

Steffen, K. and J. E. Box (2001) Surface climatology of the Grennland Ice Sheet: Greenland climate network 1995-1999, Journal of Geophysical Research, 106, 33,951–933,964.

Steffen, K. and A. Ohmura (1985) Heat exchange and surface conditions in the North Water, northern Baffin Bay, Ann. Glaciol., 6, 178–181.

TPI 7081896


E-6 of 7

Steffen, K., S. V. Nghiem, R. Huff and G. Neumann (2004) The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations, Geophysical Research Letters, 31, L20402, doi:20410.21029/22004GL020444.

Stern, N. (2007) The Economics of Climate Change, The Stern Review, 692 pp. pp., Cambridge University Press, Cambridge, UK.

Stewart, C., E. Rignot, K. Steffen, N. Cullen and R. Ruff (2004), Basal topography and thinning rates of Petermann Gletscher, northern Greenland, measured by ground-based phase-sensitive radar, in Filchner-Ronne Ice Shelf Project Report 15, edited, Bjerknes Center for Climate Research, Bergen, Norway.

Stigebrandt, A. (1999) Resistance to barotropic tidal flow in straits by baroclinic wave drag, Journal of Physical Oceanography, 29, 191–197.

Straneo, F., G. S. Hamilton, D. A. Sutherland, L. A. Stearns, F. Davidson, M. O'Hammill, G. B. Stenson and A. Rosing-Asvid (2010) Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland, Nature Geoscience, doi:10/1038/NGEO1764.

Thomas, R., E. Rignot, G. Casassa, P. Kanagaratnam, C. Acuña, T. Akins, H. Brecher, E. Frederick, P. Gogineni, W. Krabill, S. Manizade, H. Ramamoorthy, A. Rivera, R. Russell, J. Sonntag, R. Swift, J. Yungel and J. Zwalley (2004) Accelerated sea-level rise from West Antarctica, Science, 306, doi:10.1126/science.1099650.

Torres, M. E., R. W. Collier and S. Cowles (2004) Adult-rated Oceanography Part 2: Examples from the trenches, American Geophysical Union, Fall Meeting, OS23A-1288.

Torres, M. E., R. W. Embley, S. G. Mergle, A. M. Trehu, R. W. Collier, E. Suess and K. U. Heeschen (2009) Methane sources feeding cold seeps on the shelf and upper continental slope off central Oregon, USA, Geochemistry, Geophysics, Geosystems, 10, doi:10.1029/2009GC002518.

Torres, M. E., D. Zima, K. K. Falkner, R. W. Macdonald, M. C. O'Brien, B. R. Schöne and T. Siferd (2010) Hydrographic changes in Nares Strait (Canadian Arctic Archipelago) in recent decades based on !18O profiles of bivalve shells, The Arctic Journal, in press.

Trehu, A. M., J. Braunmiller and J. L. Nabelek (2008) Probable low-angle thrust earthquakes on the Juan de Fuca-North America plate boundary, Geology, 36, 127–130.

Trehu, A. M. and M. C. Williams (2009) Seismic activity in the outer Cascadia accretionary prism from a 2-year onshore/offshore seismic array, American Geophysical Union, Fall Meeting, abstract #T23B-1895.

van den Broeke, M., J. Bamber, J. Ettema, E. Rignot, E. Schrama, J. W. van de Berg, E. van Meijgaard, I. Velicogna and B. Wouters (2009) Partitioning recent Greenland mass loss, Science, 326, doi:10.1126/science.1178176.

Velicogna, I. (2009) Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE, Geophy. Res. Lett., 36, doi:10.1029/2009GL040222.

Walter, F., S. O'Neel, D. McNamara, W. T. Pfeffer, J. N. Bassis and H. A. Fricker (2010) Iceberg calving during transition from grounded to floating ice: Columbia Glacier, Alaska, Geophys. Res., Lett., 37, doi:10.1029/2010GL043201.

Weins, D. A., S. Anandakrishnan, J. P. Winberry and M. A. King (2008) Simultaneous teleseismic and geodetic observations of the stick-slip motion of an Antarctic ice stream, Nature, 453, 770–774.

West, M. E., C. F. Larsen, M. Truffer, S. O'Neel and L. LeBlanc (2010) Glacier microseismicity, Geology, 38, 319–322.

TPI 7081896


E-7 of 7

Williams, M. C., A. M. trehu and J. Braunmiller (2010) Seismicity at the Cascadia plate boundary beneath the Oregon continental shelf, Bulletin of the Seismology Society of America, in press.

Wu, X., M. B. Heflin, H. Schotman, B. L. A. Vermeersen, D. Dong, R. S. Gross, E. R. Ivins, A. W. Moore and S. E. Owen (2010) Simultaneous estimation of global present-day water transport and glacial istostaic adjustment, Nature Geoscience, 3, 642–646, doi:610.1038/NGEO1938.

Wunsch, C., R. M. Ponte and P. Heimbach (2007) Decadal trends in sea level patterns: 1993-2004, Journal of Climate, 20, 5889–5911.

Zima, D. (2007) Reconstructing salinity conditions in Nares Strait (Canadian Archipelago) from stable isotope profiles in bivalve shells, Masters thesis, 117 pp. http://ir.library.oregonstate.edu/jspui/handle/1957/3864 pp, Oregon State University, Corvallis, OR.

Zweng, M. and A. Muenchow (2005) Warming and Freshening of Baffin Bay, 1916–2003, Journal of Geophysical Research, 111, doi:10.1029/2005JC003093.

TPI 7081896

Documents

D. P D POISE: O -I Imuenchow.cms.udel.edu/papers/MuenchowPubs/NSF2010_POISE.pdfD. PROJECT DESCRIPTION POISE: OBSERVING OCEAN-ICE INTERACTIONS D-4 of 15 similar velocities of about