How will biogeochemical processesin the ocean respond to

surface warming?

Anja EngelAlfred Wegener Institute

for Polar and Marine Research (AWI)

The Naked EarthThe Discovery of Global Warming

Joseph Fourier

1768-1830

Svante Arrhenius

1859-1927

John Tyndall

1820-1893

Air traps the

heat from

the sun

Its the water

vapour and the

CO2..

CO2 and

temperature.

Thats

the feedback!

Pictures:wikipedia

Future projections of GHG Emissions andGlobal Mean temperature

IPCC, synthesis report (2007)

Surface temperature-projected Changes until 2100-

IPCC-A1F1 Scenario business as usual

Largest temperature changes are expected for the northern hemisphereExceptional strong warming may occur in the Arctic Ocean

Biogeochemistry and surface warming outline:

Surface Ocean Physics:

Mixed layer depth

Stratification strengthNutrients

Light

Ice coverage

Direct Temperature Effects:Plankton MetabolismPrimary & Secondary Production

POM-DOM Partitioning

Organic Matter Remineralisation

Biogenic Silica Dissolution

Sea Surface Warming

Marine Biogeochemistry

feedba

ck

feedba

ck

Increase in surface ocean stratification

Present Future

Low Low LatitudeLatitude and and

TemperateTemperate OceanOcean

PresentPresent FutureFuture

High High LatitudeLatitude OceanOcean

Sea ice

Thermocline

Pycnocline/Thermocline

nutrientreservoir

nutrientreservoir nutrient

reservoirnutrientreservoir

Temperature Nutrients

Temperature Light

Thermocline

stratification reduces primary production(in warm regions)

Behrenfeld et al. (Nature, 2006)

Net primary production (NPP)

anomaly follows changes instratification patterns

Behrenfeld et al. (Nature, 2006)

For 74% of the permanently

stratified ocean, NPP and SST changes are inversely related

Changes in annual averageSST between 1994 and 2004

Changes in annual averageNPP between 1994 and 2004

What to expect for the polar Oceans?

2006

2007

Arrigo et al. 2008

25% more open water

What to expect for the polar Oceans?

Arrigo et al. 2008

20072006

Difference in NPP Extended season

Bacterioplankton Phytoplankton Zooplankton

Direct effects of Temperature on biology-metabolic processes-

Temperature

Enzym

atic

Rea

ction

Rate

Arrhenius-typeincrease

Proteindenaturation

Q10

Q10:1-2Q10:2-3 Q10:1.8-2.5

Kirchman et al. (Nature, 2009)

temperature sensitivityof Bacterial Production in the ocean

Kirchman et al. 2009

Polar Seas Temperate & Low Latitude Seas

temperature sensitivityof Bacterial Production in the ocean

Temperature

Kirchman et al. 2009

Polar Seas

Temperate & Low Latitude Seas

Kirchman et al. 2009

temperature sensitivityof Bacterial Production in the ocean ?

Polar Seas Temperate & Low Latitude Seas

Hypothesis: The balance between Primary and Secondary(Bacterial) Production is primarily determined

by the availability of nutritious DOM

Project: Temperature effects on DOM-POM-partitioning

Riebesell & Engel

Source of DOM: - Phytoplankton

Sink of DOM: - Bacterial Production

- DOM aggregation

DOM sinks and sources display

different temperature-sensitivities

DIC/DIN/DIP

Phytoplankton

DOM Bacteria

Zooplankton

TEP Aggregation

Sinking

Hypothesis:

DOM-POM partitioning istemperature-sensitive

(2005-2010)

temperature increase above

baseline (mean 92-02)

actual temperatures

1400 l mesocosms

Aquashift:

experimental design of mesocosm studies

Sommer et al (2007)

Aquashift: Temperature effect on phytoplankton blooms

Wohlers et al. (2009)

8C

4C

6C

2C

Chlorophyll a

Bloom peak: -1.3 d/ 1C

Aquashift: Temperature effect on phytoplankton blooms

Temperature accelerates nutrient draw-down

Wohlers et al. (2009)

22M NO30.9M PO4

+6C

+2C

+4C

+0C

Phosphate: -0.7d/CNitrate: -1d/C

Aquashift: Temperature effect on phytoplankton blooms

Wohlers et al. (2009)

22M NO3

0.9M PO4

No temperature effect on total yield of PN and POP

PN: -1d/C POP: -0.7d/C

DIC

TOC

POC

DICmax

loss

Settling

loss

2C

8C

Wohlers et al. (2009)

Temperature control Of heterotrophy

Bacterial Secondary Production increases with temperature

Community Respiration >3mincreases with temperature

20 m

organic matter degradation in aggregates

Piontek et al (AME, 2009)

Remineralisation of Biogenic silica

Bidle & Azam (Nature 1999)

with bacteria

without bacteria

Faster dissolution of silica from diatom frustules

after bacterial degradation of organic surface coating

Remineralisation of Biogenic silica

Bidle & Azam (Nature 1999)

with bacteria

without bacteria

Faster dissolution of silica from diatom frustules

after bacterial degradation of organic surface coating

Dissolution of diatom frustules

8C

2C

Piontek et al (AME, 2009)

What we learned from Aquashift:

Higher partitioning of carbon into DOM that satisfies increased bacterial carbon demand and supports microbial metabolic activity (growth & remineralisation).

Earlier onset and higher activity of microbial heterotrophic community that enhances organic matter remineralisation and reduces net DIC draw down.

Stimulation of microbial loop that results in reduced carbon export (particularly for cold system).

Warming leads to:

Summary:warming effects on biogeochemical cycling

CO2CO2 CO2CO2

Phytoplankton BacteriaDOM

Deeper, coldermixed layer

nu

trie

nts

Export

Phytoplankton BacteriaDOM

Shallower, warmer mixed

layer

nu

trie

nts

H+

Present day Future scenario

remineralisation remineralisation

ZoomicroZoomicro

Zoomeso/AggregatesExport

Zoomeso/Aggregates

Temperature effects on a Global scale

Laws et al. 2000

Exp

ort

Pro

duction :

Tota

l P

roduction

Temperature

Inreased

Organic Matter Recycling

Reduced

Organic Matter Export

What do we need to know better?

Will warming alter the balance between primary and bacterial production in the polar ocean?

How will the increased amount of respiratory CO2 affect ocean acidification projections?

Will the ocean ecosystems change from a CO2 sink to a CO2 source?

How large is the feedback to atmospheric CO2 concentration?

How will biogeochemical processesin the ocean respond to

surface warming?

Acknowledgements:

Ulf Riebesell, Julia Wohlers, Judith Piontek, Nicole Hndel, Ullrich Sommer,

Peter Fritsche, Petra Breithaupt, Mascha Wurst