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Temperature sensitivity of organic matter degradationJørgen BendtsenNational Environmental Research Institute

In colaboration with:

Torkel Gissel NielsenJørgen HansenKaren Marie Hilligsøe

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Temperature dependence ofOrganic matter remineralisation

A simple modelof the water column

surface

main thermocline

A simple model oftemperature dependence: Q

10 (T-T0)/T0

National Environmental Research InstituteDenmark

An example of potential temperature regulation of POC remineralisation

Using a Q10-factor of 3 and a temperature increase of 2 °C => 25% fasterremineralisation.

Assuming a POC-flux of: F(z) = F(z=-100m) (z/z0)^(-b) , b = -0.858

and assuming a global export of 7.2 Pg C/yr (cf. Martin et al., VERTEX, 1987)

This imply that 75% of the POC is remineralised between 100 – 500 m, corresponding to a remineralisation of 5.4 Pg C/yr

Increasing this by 25% => a reduced export below 500 m of 1.4 Pg C/yr!

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Potential importance of temperature controlled feedback

Feedback

Currentvalue

(Pg C/yr)

Newvalue

(Pg C/yr)

Change

(Pg C/yr)

1.1 1.4 -0.3

5.4 6.8 -1.4

Semilabile DOC-remineralisationz > -100 m

POC-remineralisation-100 > z > - 500 m

Estimates of current remineralisation rates and future values, assuming 25% faster remineralisation rates

Change ofexport out of surface layer

Change ofexport below500 m

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Key questions

What is the future temperature change?

What is the sensitivity of the remineralisation rate to temperature?

How is the C/N/P ratio in the organic matter influenced?

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Temperature change in 2100

SST change 2100-1860

Reference: Roeckner et al., Transient climate change simulations with a coupled atmosphere-ocean GCM including the tropospheric sulfur cycle, J. Clim., 12, 3004-3032, 1999.

Ocean only climate scenario with MPI-OM1

Forcingfields from previous coupled ocean/atmosphere/sea-ice model (Roeckner et al., 1999)

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Temperature changes2100 - 1860

Atlantic vertical section

Pacific vertical section

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Incubation experimentsMethod description

Water is collected in bottles and stored in incubators in 5 °C intervals

Measurements of oxygen by titration or optodes

Measurements of nutrients, DIC, ALK, POC/PON, TOC, TN/TP Bacteria, Chl-a

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Location of incubation experimentsBergen, mesocosmTOC-experiment100 days (bottomwater, titration)

Kattegat and Belt SEATOC and POC-experiments4 weeks (30 m, titration, optodes)

Atlantic experiments:

TOC-experiments2 months (30m, optodes)

POC-experiments2 weeks (100-350 m,optodes)

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Mesocosm experiment, Bergen 2005Oxygen

Incubation experiment during 100 daysOxygen (blue: 5 °C; red 15 °C)

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Mesocosm experiment, Bergen 2005Ammonification and nitrification

Incubation experiment during 100 daysDissolved inorganic N (blue: 5 °C; red 15 °C)

NitriteAmmonium

Nitrate

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Mesocosm experiment, Bergen 2005Bacteria, Chl-a

Incubation experiment during 100 daysChl-a and bacteria (blue: 5 °C; red 15 °C)

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Temperature control of pelagic respiration in the Kattegat

Oxygen consumption during 4 – 5 weeks on 3 stations inKattegat and the Belt Sea at 30 m depth

1007

Dage

0 10 20 30 40

Mu

M

0

5

10

15

20

25

30

35

10 C 15 C20 C

905

0 10 20 30 40

MuM

0

5

10

15

20

25

30

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Incubation experiments on theGalathea expedition

The Galathea expedition goes “round the globe” in total 39.000 nm

Started august 2006 from Copenhagen and returns april 2007

Incubation experiments are done during the whole trip

Funded by the Danish Expedition fund and the Danish natural sciencefoundation (FNU)

2

24

POC

5

(2)

(4)POC (3)

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Incubation experiments of POC

z=-100 m

z = -200 m

z = -300 m

z = -400 m

POC-incubation

POC-incubation

POC-incubation

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Incubation experiment on POC

POC-incubation from 100 mStation P5-1, september 2006 located south of the Azores

Blue: 15 °CGreen: 20 °CRed: 25 °C

Duration: 16 days

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Preliminary conclusions and ongoing work

Incubation experiments show a significant influence from temperature onremineralisation of POC and DOC

Analysis of the mesocosm measurements show that data can be explainedwith two pools of organic matter with different remineralisation rates

Overall Q10-factor for the mesocosm experiment is 1.8

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Ongoing and future work

Coming TOC and POC-incubation experiments in the Southern Ocean, Pacific and the north Atlantic will be analysed

New parameterisations for temperature controlled remineralisation is nowmade, based on results from the experiments

Analysis of temperature changes in a climate change scenario will be combined with the new paramerisations to quantify the impact on the global export of organic matter

Derived implications will be analysed – in particular the influence on O2 and

on feedbacks in the surface layer due to reduced export