Remote input of nutrients in a changing climate

J. SegschneiderMax-Planck-Institut für Meteorologie

KlimaCampus, Hamburg

CarboOcean final meeting, 5-9 October 2009, Os, Norway

WP 16

Main nutrients addressed

• Iron from dust input • Nitrogen from agriculture and fossil fuel burning

• Nutrients from rivers

• + nutrients from volcanic eruptions

The dust/iron cycle and climate

• Iron is supplied to the ocean from atmospheric dust, which in turn is mobilized from arid land surfaces. Solubility of iron in ocean water differs with distance from dust source - atmospheric chemistry-

• Iron is thought to be the limiting nutrient in large areas of the ocean

(the Southern Ocean, equatorial Pacific, North-West Pacific)

• A model study shows a reduction of dust supply in a 2xCO2 climate by 30% (Mahowald et al., 2006) – does this impact on the carbon cycle?

A simplified view of the marine carbon cycle

Atmosphere

Thermocline

Ocean

Sediment

3142

90

solubility pump dissolved

carbon

Fluxesin

GtC/ Year

dissolvedcarbon

11

103

92

biologicalpump

Plankton

The biological pump

• pump is driven by nutrients and solar radiance

• Redfield ratio 1 P : 16 N

DEPTH

NO3 CO2

PO4

PO4 NO3

CO2

NO3

CO2

PO4

PO4 NO3

CO2

Bacterial remineralisation

Fe

Jickells et al

The iron cycle

Model test: difference in dust deposition

(2xCO2 climate - present climate)

Mahowald et al, 2006 on GR30 grid

Difference in oceanic iron concentration (surface)

(2xCO2 dust - present dust )

ocean only experiment:

Change in photosynthesis

Change in photosynthesis 2xCO2 minus preindustrial dust

deposition as annual average [units: 10-10 kmol P /day /m3]

Effect on export production

2xCO2 minus preindustrial climate dust deposition

[annual average, units 10-6 gC/m2/day]

CO2-Flux

Difference in atmosphere to ocean net CO2 flux

2xCO2 – preindustrial dust deposition

[annual average, units: 10-7 kmol/m2/day]

Impact on Cant uptake

• Decrease in export production by ~0.4 GtC/a • Around 20% of current oceanic uptake of

anthropogenic carbon

• Not first order process but not negligible either

Ongoing Research • oceanic uptake of CO2 • biological feedbacks

Further processes

• Nitrogen from agriculture and fossil fuel burning

• Nutrients from rivers

• + nutrients from volcanic eruptions

Ongoing Research • oceanic uptake of CO2 • biological feedbacks

Volcanoes: Pinatubo Carbon Anomaly

~1.6 x 1015 g C(Sarmiento, 1993; Watson, 1997)

Future Plans • Volcanic eruptions

Do volcanic eruptions have an impact on the marine carbon cycle and a

feedback on climate?

• can the additional ash/nutrients trigger algae blooms and additional CO2 uptake of the ocean?

• does reduced radiation significantly reduce biological production and hence carbon uptake, how does this impact on atmospheric pCO2?

(potential for stabilizing temperature)

• is the physical pump affected (colder water?)

Future Plans • Volcanic eruptions •

N-cycle and climate change Gruber & Galloway, Nature, 2008

Future Plans • N-cycle and climate change