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Temperature dependent remineralisation of organic matter and its influence on the oceanic CO2-uptake Jørgen Bendtsen Centre for Ice and Climate, University of Copenhagen Change in surface temperature LGM-present day (WOA98) Margo et al., Nature Geoscience, 2009 Average change in 0cean temperature between m IPCC model simulation ( ) A2-scenario:ECHAM5/MPIOM1 CO2 - blev transporteret til have ved LGM Usikkerhed om processerne - en del årsag - fysi/kemisk (tranposrt) k versus biologi feedback fra land q10 This study is based on experimental data which has been measured and analysed in colaboration with Karen Marie Hilligsøe(AAU), Jørgen L. S. Hansen(AAU,NERI), Katherine Richardson(Univ. Cop.) The model simulations has been made with contributions from Jochen Segschneider (MPI-Hamburg)
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Hypothesis of feedback loop: Feedback proces on CO2 uptake
from a warming of the upper ocean due to increased remineralisation air-sea CO2 exchange z Light OM production sinking/advection Mixing Mixed layer remineralisation increase increased DIC and nutrients reduced OM sinking/advection ~1000 – 100 m
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Incubations during the 2006-7 Galathea3 expedition
POC-experiments of deep large volume filtered samples (triangles) DOC-experiments of mixed layer water samples (dots)
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Example of DOC incubation at 30m and
POC Incubations at 100 and 200 m at a station south of the Azores (st. 5.1) Temperature (°C) Incubation of 0.25 l water sample from 30 m. (O2 consumption during 140 days at 15 °C (blue) , 20 °C (green) and 25 °C (red)) Incubations of concentrate of 60 l 0.2 μm filtered water from 100 m (O2 consumption during 400 hours at 15 °C (blue) , 20 °C (green) and 25 °C (red)). Depth (m) Filter volume 75 l Incubations of concentrate of 75 l 0.2 μm filtered water from 200 m.
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Remineralisation of Total organic carbon (TOC)
Oxygen were assumed to be related through a constant remineralisation ratio (O2/TOC=138/106) The remineralisation ratio (α) and the initial TOC(t0) were determined by a Levenberg-Marquardt non-linear least mean-square method
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Results-POC Remineralisation rates increases when temperature increases Global mean: POC: Q10 = 2.4
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Results-DOC Remineralisation rates increases when temperature increases Global mean: DOC: Q10 = 3.8
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Sensitivity study of the temperature effect
for example: a 3 °C increase would cause an increase of remineralisation of POC(Q10=2.4) by a factor of 1.30 DOC(Q10=3.8) by a factor of 1.50
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Model studies Model simulations was started during a spin-up of the biogeochemical model. Therefore the fields of DIC and other tracers had not equilibrated yet. Only the relative diffe- rence due to increased remineralisation is therefore analysed below. Two 100-year simulations are started: CTRL: A control run EXP: A simulation where the remineralisation rates are increased by 30% and 50% for POC and DOC, respectively. .
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Dic Inventory 28 PgC/100 yr Difference in the global DIC inventory during a 100 year simulation compared to the initial conditions. The models initial conditions are obtained from a 630 year spinup. The control simulation (blue) is based on the “reference” parametrisation of the remineralisation rates of organic carbon, and the increase in the global DIC inventory reflects that the model has not reached a “quasi stationary” equilibrium for DIC. In a corresponding model simulation the POC and the DOC remineralisation rates have been increased by 30% and 50%, respectively (red curve). The difference between the control simulation and the “increased remineralisation” experiment is 28 Pg C after 100 year.
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O2 difference at 150 m Difference of the 150m oxygen concentration (μM) averaged between the control run and the increased remineralisation experiment at year 730. Red areas reflects higher concentrations in the control run.
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Summary Remineralisation rates in the upper mesopelagic zone increases
when temperature increases Global mean: POC: Q10 = 2.4 DOC: Q10 = 3.8 Preliminary model studies show a relative large change in DIC, O2 and nutrients fields after 100 years of simulation. The DIC inventory changes by 28 PgC/100yr for a 3 °C temperature increase, and assuming that the warming occurs gradually during the next 100 year this would correspond to about the half of this; 14 Pg C This will transfer to a significant change on millenial time scales.
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