1. CarboOcean Annual Meeting Bremen 4-7/12/2007 Core Theme 4 : Biogeochemical Feedbacks on the Oceanic Carbon Sink. M. Gehlen (CEA/DSM/LSCE)

2. Core Theme 4: Feedbacks on the Oceanic C Sink 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.

3. Core Theme 4: Feedbacks on the Oceanic C Sink Identification of key regions: Changes in the Arctic Ocean A comparison of anthropogenic carbon during the LOMROG 07 and IAOE 91 cruises in the Arctic OceanS. 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.

4. Core Theme 4: Feedbacks on the Oceanic C Sink  Changes in DCant (mmol/kg) and CFC-11 (pmol/kg) 1991 DCant 2007-1991 MLR approach after Wallace (1995) MLR, DC* (Gruber et al., 1996), TrOCA (Touratier & Goyet, 2004 a,b; Touratier et al. 2007) all yield similar results 2007

5. Core Theme 4: Feedbacks on the Oceanic C Sink Evidence for rapid changes in C chemistry Saturation depth () for aragonite and calcite over the section. Warag 1991 2007 1.4 1.2 1.0 0.8 Wcalcite 2.25 2.0 1.75 1.50 1.25

6. Core Theme 4: Feedbacks on the Oceanic C Sink Quantitative evaluation of the pelagic calcification/dissolution feedback on atmospheric pCO2 including climate change. Pelagic calcification = calcite + aragonite D16.12 report - Schneider et al.

7. PI+CO2: -13.1 % PI-CO2: 0 % CC+CO2: -21.44 % CC-CO2: -9.20 % PI+CO2: -28.5 % PI-CO2: 0 % CC+CO2: -44.6 % CC-CO2: -24.5 % 80 GtC Core Theme 4: Feedbacks on the Oceanic C Sink relative to PI-CO2

8. 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

9. Core Theme 4: Feedbacks on the Oceanic C Sink Identifying and quantifying of new feed-backs: C/N = f(pCO2) Photosynthetic C drawdown Pelagic Ecosystem CO2Enrichment Study (PeECE) (Bergen May 10 – June 12, 2005) present CO2 2xCO2 3xCO2 C/N=6.7 C/N=7.9 C/N=8.9 Riebesell et al. (subm.)

10. Core Theme 4: Feedbacks on the Oceanic C Sink C:N = f(pCO2) projected (SRES A2) • 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 levels NPZD + diazotrophs ecosystem, (N,P,C,O2) • Simulations from 1765 to 2100 forced by CO2 emissions (historical+SRES A2) observed C:N=const. C:N=f(pCO2) Oschlies et al. (subm.)

11. Cumulative signal Int(del EP) Int(del C storage) Core Theme 4: Feedbacks on the Oceanic C Sink Export production and C-storage Export production C:N=const. C:N=f(pCO2) Oceanic carbon storage Direct impact on marine carbon uptake: minor Oschlies et al. (subm.)

12. National Environmental Research Institute, Aarhus University Denmark Core Theme 4: Feedbacks on the Oceanic C Sink Temperature dependent remineralisation of organic matter 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. Bendtsen et al.)

13. Core Theme 4: Feedbacks on the Oceanic C Sink Temperature sensitivity of DOM in the Global ocean Incubation experiments with upper ocean waters from the Atlantic, Southern Ocean and Pacific 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 days of incubation in 0.5 l bottles. National Environmental Research Institute, Aarhus University Denmark

14. Core Theme 4: Feedbacks on the Oceanic C Sink  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. Hilligsøe 2. 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. National Environmental Research Institute, Aarhus University Denmark