1. 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)

2. 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

3. Incubations during the 2006-7 Galathea3 expedition
POC-experiments of deep large volume filtered samples (triangles)‏
DOC-experiments of mixed layer water samples (dots)‏

4. 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.

5. 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

6. Results-POC
Remineralisation rates increases when temperature increases
Global mean: POC: Q10 = 2.4

7. Results-DOC
Remineralisation rates increases when temperature increases
Global mean: DOC: Q10 = 3.8

8. 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

9. 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. .

10. 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.

11. 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.

12. 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.