Core Theme 4 : Biogeochemical Feedbacks on the Oceanic Carbon Sink. M. Gehlen (CEA/DSM/LSCE) CarboOcean Amsterdam 22-24/11/2005

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

Bellerby, et al, Predicted Nordic Seas wintertime mixed layer pH reduction between 1997 and 2070 Core Theme 4: Feedbacks on the Oceanic C Sink Estimation of centennial changes to the CO 2 system in the Nordic Seas and the near Arctic Ocean Bellerby and co-workers

Core Theme 4: Feedbacks on the Oceanic C Sink Atlantic Meridional Transect (AMT17) October/November 2005 Experimental work in the South Atlantic Gyre : Response of phytoplankton to nutrient addition Strength of CO 2 sink associated with the rate of N fixation depending on iron and phosphorus input by dust. PIs R. Geider, C.M. Moore & J. LaRocha

Core Theme 4: Feedbacks on the Oceanic C Sink AMT17 Key findings South Atlantic sub-tropical gyre nutrient addition experiment: 1) N-limitation of phytoplankton; 2) No evidence for Fe limitation; 3) Evidence that atmospheric dry or wet deposition (dust or rain) would have the potential to relieve N limitation. R. Geider, C.M. Moore (Essex University) & J. LaRoche (IFM Kiel)

Core Theme 4: Feedbacks on the Oceanic C Sink Enhanced biological carbon consumption in a high CO 2 ocean U. Riebesell1, K.G. Schulz1, R.G.J. Bellerby2,3, P. Fritsche1, M. Meyerhöfer1, C. Neill2, G. Nondal2,3, A. Oschlies2, J. Wohlers1, E. Zöllner1 1Leibniz Institute of Marine Sciences, IFM-GEOMAR, Kiel, Germany 2Bjerknes Centre for Climate Research, University of Bergen, Allégaten 55, 5007, Bergen, Norway 3Geophysical Institute, University of Bergen, Allégaten 70, 5007, Bergen, Norway Manuscript under review (Nature)

Core Theme 4: Feedbacks on the Oceanic C Sink no difference was obsered in nutrient uptake increase of stoichiometry of C:N drawdown from 6.6 (= today’s Redfield ratio) 8.9 at high CO 2 increase of 35 % of inorganic carbon consumption at elevated pCO 2 Enhanced C consumption in a high CO 2 world = strong negative feedback to rising atmospheric CO 2 Tentative quantification for a business-as-usual CO 2 emission scenario : biological carbon sink of ~117 Pg C until 2100 or - 58 µatm in terms of atmospheric pCO 2. Initial pCO  atm

Core Theme 4: Feedbacks on the Oceanic C Sink Temperature sensitivity of organic matter degradation J. Bendtsen, T. G. Nielsen, J. Hansen, K. M. Hilligsøe National Environmental Research Institute, Denmark 5ºC 15ºC Ongoing incubation experiments: Atlantic, Indian and Pacific Ocean: duration 2 weeks for POC and 2 months for DOC. Mesocosm experiment in Bergen day incubation of TOC North Sea & the Baltic Sea transition zone 4 incubation experiments, duration 4 weeks  temperature sensitivity quantified for POC and DOC  feedback of T sensitivity of OC degradation to atmospheric CO 2 increase: global simulations, with MPI-OM1, of temperature changes

Quantification of the change in ocean sink associated with a decrease in pelagic calcification in response to rising pCO 2. M. Gehlen, R. Gangsto, B. Schneider, L. Bopp, C. Ethé (LSCE) Core Theme 4: Feedbacks on the Oceanic C Sink 1. Calcification2. CaCO 3 dissolution 3. Forcing 1xCO 2 – 4xCO 2, no climate change off-line simulation (PISCES/NEMO) 4. Simulations CAL01: calcification dependent on Ω CAL02: calcification independent of Ω CAL03: calcification & dissolution independent of Ω with (PIC/POC) max = 0.8, K max = 0.4 for 0<Ω<1, dissolution rate constant: k = 10.9 day -1, derived from sediment trap data + CaCO 3 = calcite  (calcite) PIC/POC

Saturation with respect to calcite  < 1 = undersaturation Core Theme 4: Feedbacks on the Oceanic C Sink M. Gehlen, R. Gangsto, B. Schneider, L. Bopp, C. Ethé (LSCE)

CAL % CAL % CAL % CAL % Core Theme 4: Feedbacks on the Oceanic C Sink M. Gehlen, R. Gangsto, B. Schneider, L. Bopp, C. Ethé (LSCE)

Core Theme 4: Feedbacks on the Oceanic C Sink M. Gehlen, R. Gangsto, B. Schneider, L. Bopp, C. Ethé (LSCE) cumulative air – sea flux difference between cumulative CO2 uptake: CAL01 - CAL04: 5.9 GtC = increase in CO2 uptake due to combined calcification/dissolution response

Core Theme 4: Feedbacks on the Oceanic C Sink 1) S. Hohn et al., A process oriented parameterisation for variable silica to nitrogen uptake ratios under different iron concentrations for marine diatoms. 2) J. Bendtsen, Temperature sensitivity of organic matter degradation 3) S. Martin and J.P. Gattuso, Response of the temperate coralline alga, Lithophyllum cabiochae, to elevated pCO2 and temperature 4) M. Racault and C. LeQuéré, CO2 and ecosystems (DGOM) 5) R. Bellerby et al., Centennial high latitude ocean acidification, some ecological and climate feedbacks 6) C. De Bodt et al., Calcification and transparent exopolymer particles (TEP) production in batch cultures of Emiliania huxleyi exposed to different pCO2 7) J. Segschneider et al., Describing POC fluxes in a global ocean biogeochemical model: impact of fixed settling velocities vs. aggregation scheme on surface pCO2 Tuesday 5/12 at 10h15