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 CO 2 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  Cant

Saturation depth (  ) for aragonite and calcite over the section.  arag  calcite Core Theme 4: Feedbacks on the Oceanic C Sink Evidence for rapid changes in C chemistry

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: % CC-CO2: % CC+CO2: % CC-CO2: % CC+CO2: % PI-CO2: 0 % PI+CO2: % relative to PI-CO2 80 GtC

Core Theme 4: Feedbacks on the Oceanic C Sink D16.12Quantitative evaluation of the pelagic calcification dissolution feedback on atmospheric pCO2 including climate change.  contrasting effects of warming and atmospheric pCO 2 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

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

C:N = f(pCO 2 ) 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 levels NPZD + diazotrophs ecosystem, (N,P,C,O 2 ) Simulations from 1765 to 2100 forced by CO 2 emissions (historical+SRES A2) C:N=const. C:N=f(pCO 2 ) Core Theme 4: Feedbacks on the Oceanic C Sink

C:N=const. C:N=f(pCO 2 ) 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

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 University Denmark

Core Theme 4: Feedbacks on the Oceanic C Sink Temperature sensitivity of DOM in the Global ocean National Environmental Research Institute, Aarhus University Denmark 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.

Core Theme 4: Feedbacks on the Oceanic C Sink National Environmental Research Institute, Aarhus University Denmark  Significant temperature dependence for DOM and POM remineralisation rates.  A first calculation of the “overall” temperature dependence from mesocosm experiments gave a Q 10 of 1.7.  A simple Q 10 -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.