Core Theme 4 :

Biogeochemical Feedbacks on

the Oceanic Carbon Sink.

M. Gehlen (CEA/DSM/LSCE)

CarboOceanAmsterdam 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 CO2 uptake.

Core Theme 4: Feedbacks on the Oceanic C Sink

Bellerby, et al, 2005.

Predicted Predicted Nordic Seas Nordic Seas wintertime wintertime

mixed mixed layer pH layer pH reduction reduction between between 1997 and 1997 and

20702070

Core Theme 4: Feedbacks on the Oceanic C Sink

Estimation of centennial changes to the CO2 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 CO2 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 CO2 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. Zöllner11Leibniz 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 innutrient uptake

increase of stoichiometry of C:N drawdown from 6.6 (= today’s Redfield ratio) 8.9 at high CO2

increase of 35 % of inorganic carbon consumption at elevated pCO2

Enhanced C consumption in a high CO2 world = strong negative feedback to rising atmospheric

CO2

Tentative quantification for a business-as-usual CO2 emission scenario : biological carbon sink of ~117 Pg C until 2100

or - 58 µatm in terms of atmospheric pCO2

.

Initial pCO2

350 atm

700

1050

Core Theme 4: Feedbacks on the Oceanic C Sink

Temperature sensitivity of organic matter degradation

J. Bendtsen, T. G. Nielsen, J. Hansen, K. M. HilligsøeNational Environmental Research Institute, Denmark

1007

Dage

0 10 20 30 40

Mu

M

0

5

10

15

20

25

30

35

10 C 15 C20 C

5ºC

15ºC

Ongoing incubation experiments: Atlantic, Indian and Pacific Ocean: duration 2 weeks for POC and 2 months for DOC.

Mesocosm experiment in Bergen 2005 100 day incubation of TOC

North Sea & the Baltic Sea transition zone4 incubation experiments, duration 4 weeks

temperature sensitivity quantified for POC and

DOC

feedback of T sensitivity of OC degradation to

atmospheric CO2 increase: global simulations, with

MPI-OM1, of temperature changes 1860-2100

Quantification of the change in ocean sink associated with

a decrease in pelagic calcification in response to rising pCO2.

M. Gehlen, R. Gangsto, B. Schneider, L. Bopp, C. Ethé (LSCE)

Core Theme 4: Feedbacks on the Oceanic C Sink

1. Calcification 2. CaCO3 dissolution

3. Forcing

1xCO2 – 4xCO2, 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 Ωwith (PIC/POC)max = 0.8, Kmax = 0.4

for 0<Ω<1,dissolution rate constant: k = 10.9 day -1, derived from sediment trap data

+

CaCO3 = calcite

(calcite)

PIC

/PO

C

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)

CAL01 - 26 %

CAL02 + 19 %

CAL01 - 16 %

CAL01 - 29 %

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