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Coring the Line Islands Ridge for Paleoceanographic Research

PIs: Lynch-Stieglitz, Polissar, Lyle, Pockalny

In this proposal we show that: 1. The Central Tropical Pacific is an ideal place to monitor changes in the Pacific

Marine ITCZ and ENSO variability. 2. Previous work in Pleistocene and Holocene sediment has been equatorward of ~4-

6°N, with low time resolution in the northern cores. This is a consequence of the lack of carbonate and the low sedimentation rates in deep waters north of the equator.

3. The Line Islands Ridge is a broad, relatively shallow feature topped in many areas with carbonate sediments that span an ideal latitude range (0- 10°N) to monitor past changes in the ITCZ.

Then we propose to: 1. Survey selected areas of the Line Islands Ridge that appear promising for collecting

cores suitable for paleoceanographic work. 2. Collect multi-cores, gravity cores, and piston cores from a meridional transect. 3. Perform on-board and shore based analyses in order to determine the sedimentation

rates and time scales covered by the collected cores, and perform first-order geochemical characterization to guide future, more focused studies a group of investigators who have expressed interest in this critical region of the tropical ocean.

Intellectual Merit: 1. This project will likely provide new material for geochemical and

micropaleontological studies of changes in the Pacific Marine ITCZ and ENSO over glacial and orbital cycles (time scales of 10-100 kyr), and which can be used to constrain ocean-atmosphere models of climatic change.

2. It may provide new material from the last 10,000 years, which can be used to provide perspective to ongoing work from corals and lake sediments on the Line Islands.

3. It may provide information which can lead to future long coring or drilling efforts to understand changes in the ITCZ over longer time scales (millions to tens of millions of years).

Broader Impacts: 1. It will provide sample material for numerous investigators interested in the history of

climate and productivity in the Tropical Pacific, and provide much new information about the geology and sedimentology of previously unexplored parts of the seafloor.

2. It will enhance scholarly exchange between the participating institutions, interface with a multi-agency federal program, and contribute to centralized and federally-supported oceanographic databases.

3. It will introduce graduate students to seagoing paleoceanography, and enhance public dissemination of scientific research.

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A. Rationale for Coring: Understanding the Central Pacific ITCZ and ENSO

The atmospheric circulation in the tropics and subtropics, including the state of the El-Nino Southern Oscillation (ENSO) and the position of the Intertropical Convergence Zone (ITCZ), determines the patterns of rainfall and drought that influence a vast number of people on the planet today. Unfortunately, our current understanding of these circulation patterns is not complete. The most sophisticated coupled ocean atmosphere climate models still often vary from observations, for example persistently exhibiting a double ITCZ (Lin, 2007) or failing to produce the proper magnitude and periodicity of modern ENSO variability.

The Central Tropical Pacific is an ideal place to monitor the marine ITCZ, as it is far from the influence of the monsoons and other land-ocean linkages. Here, the ITCZ is well organized, largely confined to the Northern Hemisphere, and has less seasonal variation than in the Eastern and Western Pacific. This area is also ideally situated to monitor past ENSO activity, given that variability is dominated by inter-annual rather than seasonal variability. We seek funding to undertake a reconnaissance coring program to recover material from the Line Islands Ridge that will help document the paleoclimatic history of the Central Tropical Pacific, and the behavior of ENSO and the Pacific marine ITCZ over past climatic changes.

Previous work (Woodroffe et al., 2003, Cobb et al. 2001, 2003, Sachs et al., 2009, Nurhati et al., 2009) demonstrates the utility of chemical and isotopic measurements in the Line Islands for the paleo-reconstruction of ENSO and the ITCZ, but extending this work for continuous Holocene reconstructions or for reconstructions during glacial times has not been possible due to the difficulty in obtaining fossil corals covering these time intervals. Continuous records from marine sediments are needed in order to extend this work and place the short fossil corals in context. Unfortunately, such cores do not currently exist and this proposal aims to rectify this deficiency.

Well-known cores in the Central Pacific such as RC11-210 (Rea et al., 1986; Chuey et al., 1987) and TT013-PC72 (Murray et al., 1995, 2000; Anderson et al., 2006, 2008, Winckler et al., 2008) that have been studied by multiple teams of researchers are at or near the equator. Directly north of the equatorial region’s carbonate-bearing Quaternary sediments is the Pelagic Clay Province (Leinen, 1989). This region itself has been extensively studied for eolian records (e.g., Leinen & Pisias, 1984; Olivarez et al., 1991; Kyte et al., 1993; Jones et al., 2000; Rea, 1994; Pettke et al., 2002, plus others), but due to the ultra-low sedimentation rate of clay (and the significant authigenic component, Ziegler et al., 2007), it is unsuitable for Pleistocene and Holocene study. In short, the northern hemisphere Pleistocene record in the central and eastern equatorial Pacific is surprisingly limited--quite simply because there is no modern pelagic carbonate sediment north of ~ 4°-6°N on the abyssal plain.

Studies of paleoproductivity in the region have been hampered by the effects of dissolution in these deeper sediments (e.g., Murray et al., 2000, and references therein). The Line Islands Ridge stands above CCD fluctuations, and even in the south there are coring targets more than 1 km shallower than the typical sea floor. The Line Islands Ridge will provide the best location to minimize the effects of carbonate dissolution. The carbonate preservation is achieved at a price, however, as ridges typically have much more horizontal sediment transport than the abyssal sea floor. This transport may (or may not) result in fine-sediment loss from bathymetric highs and variable accumulation in basins. Turbidites from higher topography can fill otherwise attractive sediment basins. Areas of high hemipelagic sediment accumulation provide the opportunity of much better temporal resolution than deep cores and will also minimize problems with proxies that are dissolution sensitive (e.g., Mg/Ca in foraminifera). Provided that we understand sediment movement via adequate geophysical site surveys and the use of calibrated geochemical tracers, we can get much better records of paleoproductivity. Also, by comparing deposition in shallow cores to deeper ones, we can better understand deep Pacific carbonate dissolution and its relationship to the carbon cycle.

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B. Geology and Sediments on the Line Islands Ridge

The Line Islands are a complex NW-SE trending chain of atolls, seamounts and volcanic ridges in the central Pacific extending from the Mid-Pacific Mountains to the Tuamotu Plateau (Figure 1). The island chain is typically divided into northern, central and southern provinces based on the volcanic morphology (Winterer, 1976). The region of interest for this proposal is the central section from 0° - 10°N, which is dominated by a continuous, relatively broad (100-300 km-wide), volcanic ridge (Figure 1). The top of the volcanic ridge, as outlined by the 3000-m isobath, resembles a plateau with a series of en echelon and overlapping ridges defining the edge of the plateau. Larger isolated seamounts are also present on top of the ridge and coincide with the location of Kingman Reef, Palmyra Atoll, Washington Island, Fanning Island, and Christmas Island.

Jim Gardner of UNH did some very detailed mapping of the Northern Line Islands Ridge for NOAA’s Law of the Sea Mapping Program. The bathymetry and backscatter data show smooth sediments on the local highs, with erosional gullies on the flanks. The Chirp sub-bottom data confirms that sediment thickness exceeds 50-m deep in most places on top of the ridge. Nice parallel reflectors indicate long sequences of undisturbed sedimentation along the broad, flat regions near 3000 m depth (see line B-B' in Figure 2), an example of a promising coring site. Sub-parallel and truncated reflectors observed atop shallow highs (~2000m, see line A-A') likely indicate sediment redistribution, which will not be targeted for coring. More limited data indicate a similar character further south along the ridge.

Based on sedimentation rates above the lysocline in similar productivity regimes in the open ocean today, we would expect actual sedimentation rates (at least 1 cm kyr-1), to fully resolve glacial cycles. It is possible that we will also be able to find some areas of sediment focusing by bottom currents, which can be used for higher resolution studies of the coarse fraction (foraminifera) and could, indeed, serve as interesting locations to test effects of sediment focusing on the geochemical and isotopic signals recorded

Figure 1: The Line Islands Ridge in the Central Tropical Pacific. Survey and potential coring locations are indicated by the boxes.

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in sediments (e.g., Marcantonio et al., 2001; Lyle et al., 2005; Broecker, 2008). Past coring experience and available data indicate that we are most likely to find undisturbed Quaternary sediments along local bathymetric highs, saddles or shoulders at depths between 3000 and 2000 m on or near the top of the volcanic plateau. The 3000 m depth limit is imposed to stay well above the regional CCD. A minimum depth of 2000 m is well below the oceanic mixed layer and avoids the regional 50 cm/s surface currents (http://www.oscar.noaa.gov/) that may cause sediment transport.

C. Cruise Plan and Activities

To meet our principal objectives, we propose a 26-day (16 days science, 10 days transit) campaign of geophysical surveying, gravity coring, piston coring, multi-coring, CTD/rosette operations, and scientific analysis. We have identified 6 potential sites between 0° and 10°N (Figure 1): 3 sites along the broad volcanic ridge and 3 sites on promising seamounts/ridges at the northern and southern limits of our proposed study area. Our general approach will include an initial geophysical survey followed by an extensive and flexible coring program.

The geophysical surveys will involve the real-time analysis of underway data to locate optimal coring locations. The site survey will begin with a 4-hour line (~50 km @ 7 knots) oriented along a regional bathymetric high followed by two orthogonal crossing lines for a total survey time of 12 hours. Multi-beam swath bathymetry and backscatter data will be used to identify smooth, sedimented seafloor devoid of potential basement outcrops or evidence of mass-wasted sediments. The sub-bottom 3.5kHz seismic data will characterize the sediment thickness and internal structure of the overlying sediments. Multi-channel seismic reflection gives the opportunity to study the variability of sediment deposition. These data will provide a detailed and informative view of the long-term depositional environment that is critical for recognizing issues such as episodic non-deposition due to bottom currents, or areas where turbidites or slumps interrupt normal accumulation. Coring sites will be selected by looking for undisturbed sedimentation (in particular avoiding the steep gulleys and debris flows on the flanks of many of the topographic highs) and the potential for higher-than-normal sedimentation rates. The two crossing points of the seismic lines will be chosen to coincide with the best potential coring sites along our initial

Figure 2. Two Chirp seismic sections from the Northern Line Islands (Jim Gardner, UNH) indicating laminated sediments potentially useful for paleoceanographic studies.

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survey line. This survey approach will provide a more complete 3D view of the seismic stratigraphy and yield two options for coring sites.

Once a site has been chosen, a representative station protocol will include an initial gravity core, a CTD/Niskin rosette cast, a piston core, and a multi-core, to be followed by supplemental coring or site survey operations. The initial gravity core will be used to verify surface-sediment lithology and to determine if the site is suitable for the full suite of coring operations. The multi-core is essential to

recover the sediment-water interface and maximize the possibility of reliable Holocene climate reconstructions. We anticipate that our piston cores will recover sediments spanning back to 0.5 and 1.8 my BP depending on core length and sedimentation rates. Supplemental coring or additional geophysical survey operations will be added at the end of the site in order to target areas where sediments might be accumulating more rapidly.

Cores will be refrigerated immediately after arrival on deck. Our on-board sampling and analytical program will focus on evaluating each site for extended coring. When a core arrives on the ship, samples from the core breaks will be immediately surveyed by the micropaleontologists and sedimentologists for the general lithology, sedimentary preservation, and foraminifera assemblage. The depth at which G. ruber pink appears in the core will provide a quick assessment of late Quaternary sedimentation rates since this variant last appears in the Pacific at 120 kyr BP (Thompson et al., 1979). After suitable thermal equilibrium, the whole round will be run through the shipboard multi-sensor track (MST) to assess the degree of sedimentary variability (e.g., orbital and/or sub-orbital cycles) and other, potentially climate-related signals. Finally, most of the gravity and piston core sections will be split for first-order observation. Multi-cores will be sectioned on deck into 0.5 mm sections and refrigerated or frozen. At least one multi-core from each site will be kept intact for any subsequent studies that require this (e.g., split and core scanning on lower portion).

In addition to the coring, we will collect a modest number of water column samples by CTD/Niskin casts at the primary coring sites in order to help calibrate the core top sediment properties to modern water column properties. CTD casts will be taken at 5 sites, with water samples taken in the top 500 meters and near the seafloor at close intervals and at lower resolution through the complete water column. These water samples will be collected and analyzed by several participating investigators (likely including nutrients, salinity, oxygen and hydrogen isotopes of the water, and radionuclides). Characterizing the water column in terms of these parameters is important to help provide at least broad constraints on the oceanographic and geochemical environment of the Line Islands Ridge in the areas we are coring.

We request use of the Oregon State University Coring Group funded through the Ship Facilities Program of NSF. From the OSU group, we will need the large (4" diameter) piston corers, gravity corers, a multi-corer, MST, a refrigerated core container, standard core supplies (core liners, storage tubes, etc.), standard sediment description instruments (microscope, etc.), a core cutter, and shipboard coring support. Our shipboard science party will be responsible for all analysis and processing of cores (including core splitting, labeling, and curation).

Estimated Schedule 1) Transit from Honolulu, HI @ 10 kts 5 days 2) Coring activities at 6 sites (2 days per site) 12 days a. Initial geophysical survey (12 hours) b. Gravity core (5 hours) c. CTD/rosette lowering (5 hours) d. Piston core #1 (5 hours) e. Multi-core (5 hours) f. Supplemental coring and survey (16 hours) 3) Transit between coring sites 2 days 4) Weather or Equipment days 2 days 5) Transit to Honolulu, HI @ 10 kts 5 days Total 26 days

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We request 26 days of total ship time on a global class vessel for a cruise beginning and ending in Honolulu, Hawaii to minimize transit time to our area of operation. Cores will be stored at the LDEO core repository. The ship will require standard UNOLS underway oceanographic instrumentation including deepwater swath bathymetry (with backscatter), Chirp sonar, a CTD Rosette, and enough deck space and service connections for a refrigerated core container (to be provided by the UNOLS operator). Additional space will be required for the Oregon State University Coring Group facilities.

D. Personnel and Potential Future Collaborators

This project evolved from combining two separately proposed cruises and involves six investigators. Jean Lynch-Stieglitz (Georgia Tech) and Pratigya Polissar (LDEO) will bear the responsibility for overall oversight and project coordination and serve as co-chief scientists of the cruise, ensuring that the primary objective (collection of cores suitable for paleoceanographic research) is met. Rob Pockalny (GSO-URI) will be primarily responsible for the swath-mapping data (bathymetry and backscatter), providing real-time interpretation of raw data for regional morphology and understanding the depositional and erosional setting. Mitch Lyle (TAMU) will be primarily responsible for the sub-bottom (MCS and Chirp) data. He will provide real-time interpretation of depositional/erosional environments, information on sediment thickness and likely sedimentation rates, and likely composition (based on reflection character). Both Pockalny and Lyle will provide near-time (within 2-hours of collection) interpretation of preliminary data with initial processing in order that this information can contribute to decisions on core siting, especially important in this unknown and complex sedimentary environment. Such extensive on-board analysis and processing could not be accomplished without at least two highly trained specialists and will maximize the benefit to the coring program (will result in better choice of sites, and minimize delays in site selection). This cooperative model (one person responsible primarily for swath mapping, the other for sub-bottom) has worked very well with recent successful coring cruises. Rick Murray (Boston University) and Christina Ravelo (UC Santa Cruz) will participate in all aspects of the project, including pre-cruise planning. There will be a pre-cruise meeting several months before the cruise in Atlanta where the six investigators will meet along with a member of the OSU coring team to discuss specific strategies and plans for the cruise. We feel this is necessary given the large number of personnel and objectives involved in this joint effort.

In addition to our team there are a number of other researchers whose work in the tropical Pacific on a number of fronts (ITCZ, understanding past ENSO variability, paleoproductivity) could be extended if a suitable collection of cores above the lysocline in the Central Tropical Pacific were available. The following researchers have expressed interest in participating in the cruise and working on the material we collect: Bob Anderson (LDEO), Julian Sachs (Univ. Wash.), Tim Herbert (Brown Univ.), Matthew Schmidt (TAMU), Franco Marcantonio (TAMU), Steve Hovan (IUP) and Kim Cobb (Georgia Tech).

The scientific party will consist of the six principal proponents of the cruise and one member from each of their research groups (12). Up to one member of the research group of each of the investigators that have expressed interest in post-cruise work (7) and five undergraduates will have the option of participating in the cruise providing that they are able to support their own travel expenses.

E. Post Cruise Analyses

We propose a limited number of post-cruise analyses, focused on determining the sedimentation rates and composition of the cores and their suitability for further paleoceanographic and geochemical studies. We will characterize two of the most promising cores spanning a range of latitudes by scanning XRF, using the facilities at WHOI. Scanning XRF is a very useful technique to provide high-resolution geochemical data to document climatically-mediated records in marine sediment. Because the cores will be curated at LDEO, it is relatively easy to transport them to WHOI for analysis. While the XRF will provide data on sediment composition that will be critical for many of the anticipated post-cruise geochemical studies, it

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is not certain that the XRF data will provide stratigraphy (elemental cycles well correlated to glacial cycles) in this region. Because an accurate stratigraphic framework is essential for all anticipated post-cruise activities, oxygen isotope stratigraphies using planktonic foraminifera will be generated as well. Within the constraints of this limited plan for post-cruise analysis, we will develop a full oxygen isotope stratigraphy for only 1 piston core at 6 cm resolution. For the remaining 5 sites we will develop an isotope stratigraphy on the top 440 cm of the piston core. Assuming sedimentation rates of about 2 cm kyr-1, this will cover approximately 2 glacial cycles and establish the sedimentation rate for the recent sediments at the site. If the isotope data can be correlated to cycles in the XRF and/or MST data, we will also be able to establish a provisional stratigraphy for these piston cores. We will also generate isotope stratigraphies at 6 cm resolution on the top 220 cm 5 supplemental gravity cores that will be taken in an environment with potentially higher sedimentation rates. This post-cruise analysis strategy may be modified after the cruise to adjust for the nature of the sediments collected, and the presence or absence of regionally coherent, climatically related cycles in the XRF and/or MST data. All of this stratigraphic information will be completed within 1 year of the cruise and made available to all investigators who have interests in post-cruise analyses.

F. Potential Paleoceanographic Investigations

Because we currently know so little about the sediments of the Line Islands Ridge, this proposal only funds the collection and some preliminary stratigraphic, geologic, and geochemical analyses. If we are successful in collecting material that is useful for paleoceanographic reconstruction, the PIs involved in this cruise will submit additional proposals for that work. Here, however, we briefly—and only representatively—outline the science that could be done if we are able to collect an array of cores spanning 0°-10°N with sedimentation rates > 2 cm kyr-1. If sedimentation rates do not exceed this rate at all five sites, the post-cruise science plan will be adjusted to ensure equitable participation by the principal proponents. This adjustment will be overseen by the Sample Request Committee, described later in this proposal.

Principal Proponents:

Lynch-Stieglitz: Investigate the relationship between the intensity and latitude of the Northern Hemisphere ITCZ and changes in both local insolation and the more global changes associated with the glacial cycles (atmospheric CO2, Northern Hemisphere cooling). This will be approached with paired analyses of δ18O and Mg/Ca on surface dwelling planktonic foraminifera on a north-south transect of cores. The reconstruction of the position of the ICTZ will also be approached through examining the thermocline structure of the upper ocean as reconstructed from oxygen isotopic measurements on subsurface calcifying planktonic foraminifera. If sediments capable of resolving the Holocene are recovered, isotopic and Mg/Ca measurements will be made on cores nearest the islands where Kim Cobb (GT) has developed coral records in order to provide a continuous context in which to interpret her fossil coral records.

Polissar/Ravelo: Develop new records of equatorial Pacific surface ocean temperature (SST) trends and variability during the Holocene and late Pleistocene that test hypotheses for the mechanisms responsible for changes in tropical climate. An equator and off-equator site will be sampled in parallel to develop records of SST evolution and variability. The intra-sample distribution of individual foraminifera paired δ18O-Mg/Ca values will be used as a measure hydrographic variability related to ENSO. New planktonic Mg/Ca and alkenone temperatures based on these cores will be combined with existing records to better understand the evolution of zonal temperature gradients over the late Pleistocene.

Ravelo: Develop records to better understand the relative roles of nitrogen fixation to denitrification in the Pacific. First, a bulk δ15N record will be generated if possible, but afterwards, a record of organics bound in diatoms or foraminifera may be needed to eliminate the effects of diagenesis that probably occurs in oxic, low-productivity regions. These records will be compared to records from the eastern equatorial

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Pacific which provide a history of changes in denitrification and/or upwelling of water with a denitrification signature

Murray: Geochemical studies of the terrigenous component in carbonate sediment to identify source (provenance) and discern the subtle geochemical differences between eolian, volcanic, and authigenic minerals. The changes in the source of the terrigenous material will be interpreted in the context of atmospheric-oceanic processes, including eolian dust inputs and other sources, based on bulk chemistry as well as the sequentially extracted aluminosilicate component. Use a variety of mineralogical, chemical and isotopic, micropaleontological and other approaches to constrain changes in paleoproductivity vs preservation in the equatorial Pacific.

Lyle/Pockalny: Interpret geophysical data collected on the cruise to better understand the history of sedimentation on the Line Islands Ridge.

Other Investigators:

R. Anderson: Generate high-resolution records of 230Th-normalized CaCO3 accumulation rates to detect carbonate preservation events. Measure 230Th-normalized accumulation rates of opal, excess barium, C37 alkenones (coccolithophorid origin), brassicasterol (diatom origin) and other biomarkers to be determined in order to investigate changes in bottom water oxygen in collaboration with investigators measuring biomarkers in the cores (Herbert, Polissar, Ravelo, Sachs).

F. Marcantonio: Investigate 230Th water-sediment dynamics via work on excess 230Th in the water column along the transect to complement his current work in eastern equatorial Pacific.

T. Herbert: Paleotemperature (Uk'37 and TEX86) and paleoproductivity biomarker analyses to the study millenial to glacial-interglacial gradients in sea surface temperatures and productivity in the equatorial Pacific. Cores from the Line Islands would complement ongoing studies of the Equatorial Pacific cold tongue over the last glacial cycle from high deposition rate cores at the Peru-Ecuador border and in the Galapagos Islands. Analyze and compile data from multi-cores to verify the calibration of the organic proxies to modern climatology, and then produce biomarker time series on selected cores.

M. Schmidt: Mg/Ca on planktonic foraminifera for temperature reconstruction and for combined isotope/trace metal reconstructions of seawater δ18O over the range of latitudes covered by the coring sites

K. Cobb: Seawater and rainwater δ18O measurements to complement ongoing work on Line Island corals. Possible drop off of weather station at Christmas Island (air cargo limited to 40 kg)

J. Sachs: Reconstruct surface ocean hydrology over the range of latitude covered by the coring sites using hydrogen isotopic composition of lipid biomarkers produced by phytoplankton over MIS 2-1, MIS 6-5e and MIS 12-11.

S. Hovan: Physical and mineralogical studies on sediments over the range of latitude to track eolian inputs and ITCZ migration (in collaboration with Murray)

G. Sample Management and Community Access

Information about the samples collected on the cruise (core locations, descriptions, shipboard MST data) will be posted on a publically accessible website immediately post-cruise. The post-cruise XRF and isotope data generated under this proposal in order to establish the stratigraphy and stratigraphic integrity of the cores will be posted as soon as it has been completed.

Initial sampling shipboard and immediately post-cruise will focus on development of stratigraphy and age models for the cores as described above. In addition, a limited number of exploratory samples may also be requested by the cruise participants in order to establish the suitability of the sediments for further work. Cruise participants will have the opportunity to submit exploratory sample requests prior to the pre-

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cruise meeting where they will be assembled and approved if they are scientifically justified and do not conflict with the current or immediate plans of other PIs.

As soon as sufficient stratigraphic information is available post-cruise, a call for sampling requests, with a deadline allowing the simultaneous evaluation of these requests, will be issued to interested investigators. For the first two years, all post-cruise sample requests will be approved by a Sample Request Committee which will consist of Lynch-Stieglitz, Polissar, Ravelo, Murray and an independent committee chair who is not involved in the planning of the cruise or post-cruise analyses. Requests will be approved if they are scientifically justified and do not conflict with the current or immediate plans of other PIs. After sample requests are approved, the core sampling itself will be coordinated by the LDEO core repository staff according to their standard procedures. After two years, sample requests will be processed through the LDEO core repository according to LDEO’s existing approval structure.

H. Broader Impacts

Benefits to Society. Paleoclimate data sets provide additional opportunities to validate climate models. Portions of our proposed expedition area are located in regions designated by the U.S. State Department as an area of interest for the Law of the Sea-Extended Continental Shelf (ECS) Project. Data from our proposed cruise will likely be utilized by the ECS program, since one of the proponents (Pockalny) is a member of the Central Pacific Integrated Regional Team.

Enhancing infrastructure for research and education. The project will enhance infrastructure for research and education by establishing collaborations between the PIs and institutions represented in the cruise team. The material we collect will be made available to other researchers for the investigation of the physical and biological conditions in the Central Tropical Pacific and is suitable for a wide variety of geochemical and micropaleontological approaches on the timescales of glacial cycles. The geophysical data and cores may also be used to justify future long coring and drilling efforts aimed at understanding the history of the tropics over longer time scales.

Broaden dissemination to enhance scientific and technological understanding. All appropriate isotopic and chemical data will be deposited into the appropriate databases (SedDB, NCDC). Samples will also be catalogued through SESAR (System for Earth Sample Registration, http://www.geosamples.org).

Advance discovery and understanding while promoting teaching, training, and learning. Graduate students will participate in the cruise, and will be able to use the information and materials collected as part of their dissertation work. Collectively, the members of the scientific party have long records of incorporating research results into learning and education at the undergraduate and graduate level, and this project is well suited to continuing such activities. We will also encourage student participation at meetings and activities of professional societies.

I. Suitability for EAGER Funding

Most coring proposals for paleoceanographic research include detailed justification for the proposed coring sites based on existing geophysical data and sediment cores from the region. This is not possible for the Line Islands Ridge given both the heterogeneity of the environment and the lack of previous work related to sedimentation on the Ridge. This makes this coring cruise quite a bit more risky than most and therefore not suitable for submission to NSF MGG core programs. However, there is good reason to believe that sediments useful for paleoceanography exist on the ridge. If we are able to collect good sediment cores, there is tremendous community interest, and many potentially rewarding studies could result. This makes it a good fit for the EAGER program.

J. Results from prior support

Here we list results from prior support to each PI on the most closely related grants to this proposal.

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Polissar. EAR-074140 (7/07-7/08) “A Novel Paleoaltimetry Proxy: Calibration of Plant Biomarker δD Values” This proposal evaluated the hydrogen isotope ratios of plant biomarkers as a new paleoaltimeter using the hydrogen isotopic composition of plant-wax n-alkanes in modern lake sediments from North, Central and South America. This grant supported the post-doctoral training of Polissar and an undergraduate (Nevin Whitman) who assisted with sample preparation and analysis. Our results provide a new proxy approach and framework for interpreting δD measurements on plant-waxes that includes the effects of regional aridity and is applicable to biomarker-based paleoaltimetry. This research resulted in two publications (Polissar et al., 2009; Polissar and Freeman, 2010) one manuscript in preparation(Polissar and Freeman, in prep.) and six presentations at international meetings (2006 Gordon Research Conference on Organic Geochemistry; 2006 AGU Fall meeting; 2007 American Chemical Society National Meeting; 2007 International Meeting on Organic Geochemistry; 2007 AGU Fall Meeting; 2008 AGU Fall Meeting).

Lynch-Stieglitz: OCE-0096469 (3/01-2/04) Collaborative Research: Changes in the strength of the Florida Current since the LGM (co-PI: Curry). This grant funded the collection of sediment cores in the Florida Straits to be used to investigate the history of the Florida Current since the LGM. The materials collected were used in a number of publications addressing the paleoceanographic history in this region on various time scales: Lund & Curry (2006), Lund et al. (2006), LeGrande & Lynch-Stieglitz (2007), Came et al. (2007, 2008), Lynch-Stieglitz et al. (2009), Cleroux et al. (2009, 2010), Lynch-Stieglitz et al. (2011). We anticipate several more publications as a result of recently (PI Lynch-Stieglitz) and currently funded work on these cores (PI M. Schmidt, TAMU). Results from these studies are archived at NCDC. The core material is archived at WHOI and has been provided to other interested investigators.

Pockalny: OCE-0527167 (11/05-10/08) Collaborative Research: Drilling Site Survey-Life in Subseafloor Sediments of the South Pacific Gyre (PIs. D'Hondt, Pockalny and Spivack). The KNOX02RR expedition (Dec 2006-Jan 2007) surveyed the subseafloor sedimentary habitats and shallow subseafloor microbial communities of the South Pacific Gyre (SPG). The project had three basic objectives: (1) to survey broad characteristics of subseafloor SPG communities and habitats, to refine the planning and objectives of IODP drilling proposal 662-Full; (2) to document microbial activities, community composition and cell abundance in subseafloor sediments with very low total activity, and (3) to quantify the extent to which those communities may be supplied with electron donors by water radiolysis. All three objectives were met. These survey sites have been drilled by IODP Expedition 329. Scientific results are now being published (D'Hondt et al., 2009; Fischer et al., 2009; Halm et al., in prep.; Kallmeyer et al., in rev.).

Lyle: Mitchell Lyle, with Annette Olivarez Lyle, John Bradford: OCE0451291, transferred to Texas A&M as OCE0725301 9/1/2005 to 8/31/2009, $424,996 A Site survey in support of IODP Drilling proposal 626-Full “Cenozoic Pacific Equatorial Age Transect: Following the Palaeo-Equator” These grants funded a joint US-UK site survey for the Pacific Equatorial Age Transect, a 2-leg IODP Expedition (Exp 320/321, March-June 2009). In the subsequent study of the seismic data and drilling, we defined the number and significance of sediment pits through the sediment column (Moore et al., 2007, G3 8(3) doi:10.1029/2006GC001501), showed that the 17 Ma equatorial Pacific carbonate anomaly was caused by acidification of bottom waters, not changes in productivity (Christine Piela, MSc thesis 2010), and used seismic reflection data from AMAT-03 to define large-scale sedimentation regimes in the equatorial Pacific and define horizontal sediment transport from abyssal hills to valleys (Tominaga et al, 2011), . Abyssal hill topography is still apparent even when the sediment cover is thicker than the height of the abyssal hills.