Core Theme 4 :

Biogeochemical Feedbacks on the Oceanic Carbon Sink.

M. Gehlen (CEA/DSM/LSCE)

CarboOcean Annual Meeting Bremen 4-7/12/2007

4. Identification and understanding of biogeochemical feedback mechanisms which control marine carbon uptake and release:Operational goal: The quantitatively important feedbacks between CO2 partial pressure and other carbon cycle variables will be identified and analysed. Quantitative descriptions that can be used in models will be derived. Key regions for feedback processes will be identified and strategies to monitor the evolution of feedbacks will be developed

Delivery: Assessment of the role of biogeochemical feedbacks for oceanic CO2 uptake.

Core Theme 4: Feedbacks on the Oceanic C Sink

A comparison of anthropogenic carbon during the LOMROG 07 and IAOE 91 cruises in the Arctic Ocean

S. Jutterström, S. Hjalmarsson, L. G. Anderson, K. G. Olsson

Cruise tracks for the cruises in 1991 (IAOE-91) and 2007 (LOMROG-07). Marked in black is the section used in the study.

Core Theme 4: Feedbacks on the Oceanic C Sink

Identification of key regions: Changes in the Arctic Ocean

Core Theme 4: Feedbacks on the Oceanic C Sink

Changes in Cant (mol/kg) and CFC-11 (pmol/kg)

MLR approach after Wallace (1995)

MLR, C* (Gruber et al., 1996), TrOCA (Touratier & Goyet, 2004 a,b; Touratier et al. 2007) all yield similar results

2007

1991

Cant 2007-1991

Saturation depth () for aragonite and calcite over the section.

arag

calcite

1991 2007

Core Theme 4: Feedbacks on the Oceanic C Sink

Evidence for rapid changes in C chemistry

1.4

1.2

1.0

0.8

2.252.01.751.501.25

Core Theme 4: Feedbacks on the Oceanic C Sink

Quantitative evaluation of the pelagic calcification/dissolution feedback on atmospheric pCO2 including climate change.

D16.12 report - Schneider et al.

Pelagic calcification = calcite + aragonite

Core Theme 4: Feedbacks on the Oceanic C Sink

PI-CO2: 0 %PI+CO2: -13.1 %

CC-CO2: -9.20 %CC+CO2: -21.44 %

CC-CO2: -24.5 %CC+CO2: -44.6 %

PI-CO2: 0 %PI+CO2: -28.5 %

relative to PI-CO2

80 GtC

Core Theme 4: Feedbacks on the Oceanic C Sink

D16.12 Quantitative evaluation of the pelagic calcification dissolution

feedback on atmospheric pCO2 including climate change.

contrasting effects of warming and atmospheric pCO2 increase on future saturation state of ocean surface waters warming induced circulation changes aggravate the impact of ocean acidification on calcite and aragonite production positive feed-back of warming on air-sea exchange is likely to overcompensate the negative FB from decreasing calcification the overall magnitude of feed-back controlled by circulation changes and solubility pump

3xCO2

2xCO2

present CO2

C/N=7.9C/N=8.9

C/N=6.7

Riebesell et al. (subm.)

Core Theme 4: Feedbacks on the Oceanic C Sink

Pelagic Ecosystem CO2 Enrichment Study (PeECE)(Bergen May 10 – June 12, 2005)

Identifying and quantifying of new feed-backs: C/N = f(pCO2)

Photosynthetic C drawdown

C:N = f(pCO2)

Oschlies et al. (subm.)

projected (SRES A2)

observed• Assumption: Mesocosm results can be

extrapolated to global ocean …

• UVic Earth system model (Schmittner et al., subm.)1.8 x 3.6 degree resolution, 19 levelsNPZD + diazotrophs ecosystem,

(N,P,C,O2)

• Simulations from 1765 to 2100forced by CO2 emissions (historical+SRES

A2)

C:N=const.C:N=f(pCO2)

Core Theme 4: Feedbacks on the Oceanic C Sink

C:N=const.C:N=f(pCO2)

Export production

Oceanic carbon storage

Int(del EP)Int(del C storage)

Cumulative signal

Direct impact on marine carbon uptake: minor

Oschlies et al. (subm.)

Core Theme 4: Feedbacks on the Oceanic C Sink

Export production and C-storage

Experiment location Period no. of experiments Incubation period Depth range

OM-remineralisation Bergen, Mesocosm LSF 2005 1 100 days (12 m), in bags

POM-remineralisation Kattegat, Danish waters 2006-2007 5 x 5 stations 30 days 30 m

POM-remineralisation Atlantic, Pacific Ocean 2006-2007 9 stations 30 days 50 - 450 m

DOM-remineralisation Global Ocean 2006-2007 19 stations 100 days 30 m

Project status:Experimental studies have been completed for quantifying the effect from changes in temperature on the remineralisation rate of organic matter.Experimental results:A significant temperature effect is seen from oxygen consumption during organic matter degradation. Nitrification rates and the relative rate of C- and N-release during remineralisation is influenced by temperature.

Core Theme 4: Feedbacks on the Oceanic C Sink

Temperature dependent remineralisation of organic matter

Bendtsen et al.)

National Environmental Research Institute, Aarhus UniversityDenmark

Core Theme 4: Feedbacks on the Oceanic C Sink

Temperature sensitivity of DOM in the Global ocean

National Environmental Research Institute, Aarhus UniversityDenmark

Incubation experiments with upper ocean waters from the Atlantic, Southern Ocean andPacific ocean at 30 m depth. Oxygen consumption is measured by optodes during 100 days at three different temperatures in triplicates.

Example from north of the Azores.Oxygen consumption during 100 daysof incubation in 0.5 l bottles.

Core Theme 4: Feedbacks on the Oceanic C Sink

National Environmental Research Institute, Aarhus UniversityDenmark

Significant temperature dependence for DOM and POM remineralisation rates. A first calculation of the “overall” temperature dependence from mesocosm experiments gave a Q10 of 1.7.

A simple Q10-parameterisation is not sufficient for explaining the transient behaviour of Oxygen and DIN in the experiments.

This and more results are presented on two posters:1. Temperature dependence of remineralisation of organic matter; J. Bendtsen, T. G. Nielsen,

J. L. S. Hansen and K.M. Hilligsøe2. Influence of temperature change on remineralization rates in the world oceans. Results from

the circumnavigating Galathea 3 expedition; K. M. Hilligsøe, T. G. Nielsen, K. S. Jensen, K. Richardson, J. Bendtsen.