Argo: Tracking the Pulse of the Global Oceans Dean Roemmich 2 and Susan Wijffels 1 1 Scripps Institution of Oceanography, UCSD, USA 2 CSIRO/Centre for

Argo: Tracking the Pulse of the Global Oceans

Dean Roemmich2 and Susan Wijffels1

1Scripps Institution of Oceanography, UCSD, USA2CSIRO/Centre for Australian Weather and Climate Research, Australia

15th Argo Steering Team MeetingHalifax, March 2014

Argo is a large endeavor that would not be possible without important contributions by hundreds of individuals around the world:• Argo Directors - W.J. Gould and H. Freeland - and M. Scanderbeg• Argo Tech. Coordinator M. Belbeoch and JCOMMOPS• Argo Steering Team members.• Argo Data Management Team members including A. Thresher, S.

Pouliquen and the IFREMER team, and M. Ignaszewski.• Float and sensor engineers and manufacturers.• Logistics experts.• Float deployers.• Data quality control experts.• National agency representatives.• And many others!

Outline:

The Earth’s energy budget

• Ocean temperature and climate.• The Challenger Expedition, 1872-1876: the beginning of global-scale ocean

observations.• The technologies of ocean sampling: 1870s-present. • The Argo Program: toward global ocean observations.• Global change observed by Argo - tracking the pulse of the global oceans. • The future of Argo.

Outline:

HMS Challenger

• Ocean temperature and climate.• The Challenger Expedition, 1872-1876: the beginning of global-scale

ocean observations.• The technologies of ocean sampling: 1870s-present. • The Argo Program: toward global ocean observations.• Global change observed by Argo - tracking the pulse of the global oceans. • The future of Argo.

Outline: Clamping a Nansen bottle on the wire



Outline:

The Argo array of profiling floats.



Outline:

Ocean temperature from Challenger to Argo



Outline: A prototype Deep Argo float capable of 0 – 6000 m sampling



55-year heat gain by the oceans is 24 x 1022 Joules ± 1.9 (0-2000 m) = 0.39 Watts per meter-squared (Levitus et al., 2012).

This is the longest period with continuous global-scale temperature data.

Ocean temperature is a fundamental index for the state of the climate.

• The oceans dominate (> 90%) heat gain in the climate system (air/sea/land/ice). In other words, as the Earth receives more heat than is re-radiated into space, nearly all of the excess heat is stored in the ocean.

• Temperature of the sea surface (i) sets the temperature at the base of the atmosphere, and (ii) determines evaporation and hence the Earth’s water cycle.

• Warming and expansion of sea water accounts for ~1/3 of global sea global rise.

Blue bars: % of 1° squares with 4 T-profiles in 5 years.

Radiation balance of the Earth (Trenberth and Fasullo, 2007)

Outgoing sum: 340.4

HMS Challenger was a square-rigged wooden ship, 2300 tons displacement, 60 m overall. (R/V Revelle is ~80 m, 3200 tons, 59 berths). All but 2 guns were removed to make way for laboratories and workrooms.

The commanding officer was Captain George Nares, with about 20 naval officers and 200 crew. The six civilian staff/scientists were under the direction of Charles Wyville Thomson.

Between her departure in December 1872 and her return to Spithead on 24 May 1876, H.M.S. Challenger traversed 68,890 nautical miles.

Global-scale oceanography (including ocean temperature measurements) began with the Challenger Expedition (1872 – 1876)

Capt. George Nares Charles Wyville Thomson Track of the Challenger Expedition, 1872-1876

Miller-Casella Min/Max thermometer from Challenger

Challenger made deep temperature measurements at over 300 stations.

(Steam-driven winch, 8-mm hemp line, 75 kg bottom-weight)

``One of the objects of the Expedition was to collect information as to the distribution of temperature in the waters of the ocean . . . not only at the surface, but at the bottom, and at intermediate depths'‘ (Wyville Thomson and Murray, 1885)

Worthington, 1976, using Challenger data. New York-Bermuda-St Thomas

The Challenger voyage was multi-disciplinary, and was responsible for many discoveries in biology, marine chemistry, and geology.

Map of stations containing temperature observations > 2500 mFrom Wust, The Stratosphere of the Atlantic Ocean, 1935

Following Challenger, there were few ocean-scale expeditions until the 1920’s, when R/V Atlantis, Meteor, and Discovery were all commissioned and made ocean-scale surveys.

As of 1935, nearly all deep temperature data in the Atlantic came from a few expeditions by Challenger, Meteor, Discovery and Atlantis.

Coverage in the Pacific and Indian Oceans was even sparser.

Technologies of ocean temperature (and salinity) measurement:

Progress in oceanography is synonymous with technology advances.

Challenger used pressure-protected minimum thermometers, assuming incorrectly that T decreased with depth everywhere.

Pressure effects on the thermometers were carefully measured by P.G. Tait (1881).

Thermometers could be read to 0.25°F (0.14°C) accuracy (Wyville Thomson).

Depth was from line out, with the ship maneuvering on station for a vertical line. The sounding line “was kept quite perpendicular for 5 minutes”.

Challenger carried prototypes for more advanced technologies (reversing thermometer, water bottles, piezometers) but these were not widely deployed.

Miller-Casella Min/Max thermometer from Challenger

Nansen bottles and Deep-Sea Reversing Thermometers

Clamping Nansen bottle on the wire.

A pressure-protected Deep-Sea Reversing thermometer

Nansen bottles came into use around 1910.DSRT’s were accurate to a few thousandths of a °CDepth, from protected/unprotected pairs of thermometers, to ~5 m.

1956 Schleicher Bradshaw salinometerModern Guildline Autosal

Slight digression: Salinity – a key index of the Earth’s water cycle

Until the 1950s, salinity was measured by chemical titration.

Much more accurate salinity, based on measurement of conductivity ratios (water sample compared to standard sea water) began in the late 1950s.

Changes in sea surface salinity over 50 years are strong evidence of an increase in the Earth’s hydrological cycle (Durack and Wijffels, 2010).

Electronic Conductivity-Temperature-Depth recordersCTDs were developed in the late1960s and gradually refined over time.

High accuracy electronic measurements of temperature, salinity, and depth (.002°C, .003 psu, 5 m) became possible in the 1980s.

The only drawback: a research vessel had to be present.

A modern 24-bottle Niskin rosette and CTD (U Hawaii).

Early Neil Brown CTD

The culmination of the CTD era. A global survey of the oceans – the World Ocean Circulation Experiment – was carried out in 1991-1997, obtaining about 8000 CTD profiles to the sea bottom.

The shift to autonomous instruments (floats and gliders)

John Swallow preparing an early neutrally buoyant “Swallow float” in 1955

An acoustically-tracked SOFAR float, ~1973 (URI)

The purpose of these instruments was to measure ocean current (drift), not temperature.

Floats go global, then combine with a CTD

By the early 1990s, floats could be deployed anywhere. Instead of acoustic tracking, these (Davis/Webb) floats returned from 900 m to the sea surface about once a month, where they could be tracked by satellite.

Five years later, a CTD was added, and the Argo Program was begun: A global array of 3000 floats, each returning a CTD profile 0-2000 m every 10 days.

A related technology, the glider, is a profiling float with positioning control.

How do Argo floats work?Argo floats collect a temperature and salinity profile and a trajectory every 10 days, with data returned by satellite and made available within 24 hours via the GTS and internet (http://www.argo.net) .

Temperature Salinity

Map of float trajectory Temperature/Salinity relation

Cost of an Argo T,S profile is ~ $150 (all-inclusive).Cost of a WOCE T,S profile was ~$15,000

20 min on sea surface

1000 m

2000 m

9 days drifting

Collect T/S profile on ascent

The Argo array in 2014: 3500 floats, 30 nations

Concept diagram: Argo was planned in 1998

2013 deployments

Yearly deployments – 863 in 2013

Left: from the 1998 Argo Design document: See http://www.argo.ucsd.edu/argo-design.pdf

Argo transformed global-scale oceanography into global oceanography.

20th Century: 500,000 T/S profiles > 1000 m

Argo: 1,000,000 T/S profiles milestone achieved in 2012.

5 years of August Argo T,S profiles (2008-2012).

All August T/S profiles (> 1000 m, 1951 - 2000).

The World Ocean Circulation Experiment was a global survey of 8,000 T/S profiles in 7 years (1991-1997).

Argo is a global survey of 10,000 T/S profiles every month.

Argo

Mean dynamic height of the sea surface.Winter mixed layer salinity and depth

Research applications of Argo • Heat and freshwater storage• Water mass formation and characteristics• Ocean circulation and transport• Large-scale ocean dynamics• Global change assessments

Global mean temperature, °C, 0 – 2000 m.

Pap

ers

per

yea

r

Research papers using Argo data

Global mean temperature anomaly 0 – 2000 m Northern Hemisphere

Southern Hemisphere

http://www.argo.ucsd.edu/Bibliography.html

Operational applications of Argo

About 15 operational centers around the world use Argo data for:

• Ocean state estimation.• Short-term forecasting.• Seasonal-to-interannual prediction.• Decadal climate prediction.

See: http://www.argo.ucsd.edu/FrUse_by_Operational.html

NOAA CPC Global Ocean Data Assimilation System: Present equatorial temperature anomaly. Argo is the dominant global data source.

http://www.cpc.noaa.gov/products/GODAS/

An El Niño this year?

Education and outreach applications of Argo

• Education programs (secondary and primary) using Argo data are being developed in many nations.

• Education/outreach tools: The Global Marine Atlas was created for easy interactive display of data: http://www.argo.ucsd.edu/Marine_Atlas.html .

• Argo in Google Earth. ftp://ftp.jcommops.org/Argo/TMP/Google/kmz_ocean_data.kmz

• Over 100 PhD theses have used Argo data so far.

Below: Exploring the 2009/2010 El Niño with the Global Marine Atlas

Niño 3.4 temperature anomaly

Above: Argo SEREAD teacher training workshops in Tonga and Samoa

Data from a typical Argo float

Temperature is shown in the white contours.Salinity is shown in the colours.This is only the upper 500m of a surface - 2000m depth record.

The subsurface ocean is full of interesting variability!

Time

Dep

th (m

)

How does the ‘Argo Ocean’ compare to historical measurements?

Argo atlases differ consistently with pre-Argo atlases:• warmer - mostly near the surface but also at depth in some

places• There are distinct salinity changes

[Gilson and Roemmich, 2010]

We can detect a 135 years of warmingArgo(2004-2010)-HMS Challenger (1872-76)

Roemmich, Gould and Gilson, NCC, 2012

A warming hiatus?

Ocean heat content continues to rise

Surface and deep oceans are ‘decoupled ‘ – vertical heat movements

Surface global temperatures rise rates have ‘stalled’ several times

Total Ocean Heat Content

Sea level shows no decadal pauses – consistent ocean expansion plus more melting ice

The ocean salinity field has changed– both at the surface and at depth

• 50 years of salinity change

~80% of total Earth surface fluxes occur at the ocean surface

97% of the Earth’s free water is contained in the ocean

Evaporation makes water saltier, rainfall makes the water fresher

Why look at Ocean Salinity?

Global oceans are the engine room of the water cycle

The Earth’s hydrological cycle leaves a clear fingerprint in the ocean salinity field

Mean Surface SalinitySurface Freshwater Flux (m/year)

Can we detect a changing water cycle in ocean salinity?

50-Year Trends in Ocean Surface Salinity • Surface salinity trends show remarkable similarity to the mean

spatial pattern• Inter-basin contrasts increase (saltier Atlantic, fresher Pacific)

Durack and Wijffels, 2010

Warming-driven amplification of the Earth’s hydrological cycle Due to simple physics - warm air carries more water vapour

Argo and Seasonal climate forecasting

• Pastoralists in NE Australia are already in dire straits this season

Recent Sub-Surface Temperature Departures (oC) in the Equatorial Pacific

Longitude

Time

NOAA Climate Prediction Centre

•A subsurface deep warm patch appears to be strengthening and starting to move to the east

•this is sometimes how an El Nino event can be triggered - warming upwelling from the western Pacific.

Argo’s Future Evolution?

Canada’s Bedford Institution of Oceanography uses Argo to track conditions in the Labrador Sea

Can Argo be truly Global?

New Missions ?Deep Argo

Why?• Sparse repeat ship data show us that the ocean below Argo is warming

consistently, particularly in the Southern Hemisphere• This matters for sea level rise and the Earth’s energy budget• Ocean and climate forecasters also want data below 2000 m

Bottom Water warming from 1990’s to 2000’s Purkey and Johnson (2010)

Deep ArgoReadiness?Deep floats are being developed and tested by several

groupsA new CTD sensor is under parallel development with

improved stability is needed for the smaller deep signalsField tests of handfuls of floats are underwayA regional pilot is being discussed

New Missions?Bio-Argo

Why?• Understand the fundamental bio-geo-chemical cycling in the

oceans, and thus the foundation of biological productivity patterns

• To track any long term trends – there is already evidence of significant ocean oxygen changes

Subsurfacepartner of ocean colour satellite data

Bio-ArgoReadiness?• > 200 floats already carry oxygen – QC and sensor stability is still a work in

progress• nitrate, pH (acidity), and bio-optical sensors are being developed and

proposed on a subset of Argo floats (regional pilot)

Challenges • ongoing improvement in sensor stability • resourcing and development of data management protocols, especially for quality control.• Territorial sensitivities are high with many nations

Summary

• Argo has revolutionised our ability to measure the pulse of the ocean

• Argo now provides a key dataset for global change studies, delivering >120,000 temperature/salinity profiles every year.

• The coming decade will see Argo extended into the deep ocean, marginal and coastal seas, and seasonal ice zones, and including new biogeochemical sensors

For more information or to access Argo Data go to:

www.argo.net

Thanks to Argo Canada for hosting this talk

The international Argo partnership:Argo is a key component of the Global Ocean Observing System.All Argo data are freely available: http://www.argo.net

The 90-foot N.Z. RV Kaharoa has deployed over 1200 floats in the remotest regions of the globe!

Deployment locations: RV Kaharoa

CSIRO

JAMSTEC

AWI

NIWA

NIWA

NOAA IFREMER

NOAA

Other New Missions ?• Near surface profiles – via additional dual sensors or sampling

T-only – calibration of satellite data• Frequent shallow profiles for coupled near term forecasting• Shallow frequent profiles on the shelves

These are possible but are likely to delivery lower accuracy data

Should different Argo missions have different data quality targets?

Understanding the global sea level budget

Church et al, GRL, 2011

Documents

Argo: Tracking the Pulse of the Global Oceans Dean Roemmich 2 and Susan Wijffels 1 1 Scripps Institution of Oceanography, UCSD, USA 2 CSIRO/Centre for