decadal changes in ocean carbon uptake c.l. sabine, r.a. feely, g.c. johnson, r. wanninkhof, f.j....

DECADAL CHANGES IN OCEAN CARBON UPTAKEDECADAL CHANGES IN OCEAN CARBON UPTAKE

C.L. Sabine, R.A. Feely, G.C. Johnson, R. Wanninkhof, F.J. Millero, A.G. Dickson, N. Gruber, R. Key and

P. Covert

OutlineOutline

1.1. Briefly review recent improvements in ocean Briefly review recent improvements in ocean carbon uptake estimates. carbon uptake estimates.

2.2. Discuss observational approaches for Discuss observational approaches for estimating changes in ocean uptake.estimating changes in ocean uptake.

3.3. Illustrate a new potential approach for Illustrate a new potential approach for extrapolating ocean carbon measurements to extrapolating ocean carbon measurements to basin and global scales.basin and global scales.

4.4. Briefly touch on future needs.Briefly touch on future needs.

Pre 1990s view of the global carbon cycle

A missing carbon sink?Source: LDEO

WOCE/JGOFS/OACES Global CO2 Survey

~72,000 sample locations collected in the 1990s

DIC ± 2 µmol kg-1

TA ± 4 µmol kg-1

Mapped Inventory = 106±17 Pg C+ marginal seas = 6± 6 Pg C+ Arctic Ocean = 6± 6 Pg C

Total Inventory = 118±19 Pg C

Sabine et al., 2004

http://cdiac.esd.ornl.gov/oceans/glodap/Glodap_home.htm

Anthropogenic CO2 Column Inventory (mol/m2)

Method Carbon Uptake Reference (Pg C yr-1)

Measurements of sea-air 2.1 ± 0.5 Takahashi et al. [2002] pCO2 Diff erence I nversion of atmospheric 1.8 ± 1.0 Gurney et al. [2002] CO2 observations I nversions of ocean transport models and observed DI C 2.0 ± 0.4 Gloor et al. [2003] Model simulations evaluated with CFC’s and pre-bomb C-14 2.2 ± 0.4 Matsumoto et al. [2004] OCMI P-2 Model simulations 2.38 ± 0.28 Orr et a.l [2004] Based on measured atm. O2 and CO2 inventories corrected f or ocean warming and strat. 2.2 ± 0.5

Keeling & Manning [submitted]

GCM Model of Ocean Carbon 1.93 Wetzel et al. (2005) CFC ages 2.0 ± 0.4 McNeil et al. (2003) Fluxes are normalized to 1990-1999 (except Keeling & Manning which is f or 1993-2004) and corrected f or pre-industrial degassing flux of ~0.6 Pg C yr–1.

Recent assessments of 1990s ocean uptake

Sabine and Feely, 2005

1

The Global Carbon Budget [Pg C]. Positive values represent atmospheric increase (or ocean/ land sources), negative numbers

represent atmospheric decrease (sinks).

1800-1979 1980-1999

Atmospheric increase 116 ± 4 65 ± 1

Emissions (f . f uel, cement) +156 ± 20 +117 ± 5

Ocean I nventory –90 ± 19 -37 ± 8

Net terrestrial +50 ± 28 -15 ± 9

Land-use change +82 to +162 +24 ± 12

*Resid. terrestrial sink –32 to -112 -39 ± 18

First 180 years the ocean absorbed 44% of emissions

Last 20 years the ocean absorbed 36% of emissions

36%

43%

29%

13-23%55-26%

+ to -

Sabine and Feely, 2005

Is Ocean Carbon Uptake Changing with Time?If so, how do we monitor and understand these

changes?

OSP

KNOT

HOT

BATS ESTOC

One way is through long time-series measurements of carbon

NZTS

U.S. JGOFS Time Series Measurements

From: N. GruberGruber et al. (2002) Keeling et al. (2004)

There are regional differences in the rate of ocean carbon increases

Another approach is CLIVAR/CO2 Repeat Hydrography Goal

: To quantify decadal changes in the inventory and transport of heat, fresh water, carbon dioxide (CO2), chlorofluorocarbon tracers and related parameters in the oceans. Approach

:Reoccupy a subset of the WOCE/JGOFS global survey cruises

approximately every decade. The US has identified 19 cruises to be run over 10 years.

Achievements:

The U.S. CLIVAR/CO2 Repeat Hydrography Program has completed 6 of 19 cruises and is on schedule. For further details see: http://ushydro.ucsd.edu/ A16N

June ‘03A20Sept. ‘03

A22Oct. ‘03

P2June. ‘04

P16SJan. ‘05

A16SJan. ‘05

U.S. CLIVAR/CO2 Repeat Hydrography

Obtaining the decadal anthropogenic CO2 signal in the ocean

1)Fit older cruise DIC as a function of non-carbon tracers

2)Use non-carbon tracers from new cruise to predict DIC

3)Examine difference between measured DIC and predicted

DIC = a + bT + cS + dAOU + DIC = a + bT + cS + dAOU + eNOeNO33

Multiple Linear Multiple Linear Regression ApproachRegression Approach

Pre

ssu

re (

db

ar)

Pre

ssu

re (

db

ar)

Pre

ssu

re (

db

ar)

DIC

(µm

ol/kg

)∆

DIC

(µm

ol/kg

)

CO2 Accumulation Rate on Isopycnal Surfaces along 30°N Based on P2 2004 - 1994 Comparison

Vertically Integrated Accumulation: 1.1±0.1 mol m-2 yr-1

Preliminary results suggest that North Atlantic accumulation rate over the last decade may have been about half of the North Pacific accumulation rate.

This appears to be a change from the historical operation of these basins.

Water columnWater columnAccumulationAccumulation~ 1.1 mol/m~ 1.1 mol/m22/yr/yr

Water columnWater columnAccumulationAccumulation~ .6 mol/m~ .6 mol/m22/yr/yr

SurfaceSurfaceAccumulationAccumulation1.3 µmol/kg/yr1.3 µmol/kg/yr


∆CT = DIC m - DICMLR

North PacificZonal section2004-1994

North AtlanticMeridional section2003-1997

For more information see Feely et

al. and Wanninkhof et

al. posters ∆DIC (µmol/kg)

How do we take observations from a few regions and evaluate basin-scale or global changes in uptake rate?

Water columnWater columnAccumulationAccumulation~ 1.1 mol/m~ 1.1 mol/m22/yr/yr

Water columnWater columnAccumulationAccumulation~ .6 mol/m~ .6 mol/m22/yr/yr

As we continue to expand our observational data base we need to focus on how to extrapolate results to basin and global scales



Is it possible to use ARGO to estimate carbon changes?

Approach: Use MLR fits of shipboard data (A16N, A22, A20) to derive functions to estimate carbon from ARGO profiles.

Measured Parameters: T, S, P, Lat., Lon.

2003 N. A. ARGO Profileshttp://www.argo.ucsd.edu/

Physical Parameters used in MLR Fits: Potential Temperature (θ), Salinity (S), Potential Density (σθ), Spiciness (π), Brunt-Vaisala frequency (N2)

Examined Fits for a Variety of Carbon Parameters

Rmse = 5.6 µmol/kgRmse = 5.6 µmol/kgRmse = 4.4 µmol/kgRmse = 4.4 µmol/kgRmse = 11.4 µmol/kgRmse = 11.4 µmol/kg

Dissolved Inorganic CarbonDissolved Inorganic Carbon Total AlkalinityTotal Alkalinity C* = DIC+0.688oxy- C* = DIC+0.688oxy- 0.5(Talk-0.094oxy)0.5(Talk-0.094oxy)

Measured Parameters: Temperature, Salinity, Pressure, Latitude, Longitude

Rmse = Rmse = 11.4 µmol/kg11.4 µmol/kgRmse = Rmse = 4.4 µmol/kg4.4 µmol/kgRmse = Rmse = 5.6 µmol/kg5.6 µmol/kg

C* = DIC+0.688oxy-

0.5(Talk-0.094oxy)

Maps of North Atlantic C* Distributions

ARGO based C* distributions agree well with data along sections and maps are consistent with expected patterns.

WOCE C* maps appear to have significant mapping errors due to extrapolation between cruises.

Approach: •Use fits of modern hydrographic sections with ARGO profiles from same year to map C* values across basin.

•Map C* values from WOCE cruises

•Subtract WOCE maps from modern maps to determine anthropogenic accumulation.

Another complication with C* approach is the assumption of constant Redfield ratios.

There appear to be large AOU changes on A16N that are of comparable magnitude to DIC changes.

∆AOU * 0.688 (µmol/kg)

Rmse = 11.4 µmol/kg without oxygen Rmse =3.7 µmol/kg with oxygen

Adding Oxygen Greatly Improves The Fit

Adding oxygen to the global ARGO data base will make these data much more relevant for biogeochemical studies.

The technology is ready and being implemented by a handful of investigators, but needs large-scale implementation to be most

effective

Phase 2: Add pH to ARGO and use MLR fits of alk. to calculate full carbon system

Conclusions

1. Comparison of inventory changes over the first 180 years of the anthropocene with uptake rates for the last 20 years suggest that the ocean uptake is not able to keep up with atmospheric growth rate.

2. Time series and repeat hydrography data suggest that the North Atlantic uptake rate has been about half of the North Pacific rate for the last decade.

3. We are continuing to examine additional regions, but need to develop improved techniques for extrapolating results to basin and global scales.

4. Correlations between carbon and ARGO data are promising, but addition of oxygen sensors would greatly improve usefulness for biogeochemical studies.

On to our Next Cruise - P16N in On to our Next Cruise - P16N in 2006!2006!

Thank You!

NAO-

NAO+

PDO+

decadal changes in ocean carbon uptake c.l. sabine, r.a. feely, g.c. johnson, r. wanninkhof, f.j....

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