AMOC Effects on the Carbon Cycle and Atmospheric CO2

Andreas SchmittnerOregon State University

Paleo AMOC Workshop, Boulder, May 24, 2016

Ahn and Brook (2014) Nature Communications

The Ice Core RecordMulti-Millennial Scale Changes

Marcott et al. (2014) Nature Ahn et al. (2012) GRL

The Ice Core RecordMulti-Millennial Scale Changes

Circulatio

n

CO2

Soil

CO2

Land Carbon Cycle

Circulation

CO2

Plankton

DICPO4

DICPO4

Ocean Carbon Cycle

The Carbon CycleΔCA+ΔCO+ΔCL=0

CA=600 Gt CL=2,000 Gt

CO=40,000 Gt

DIC

Marchal et al. (1998) Paleoceanography

AMOC

(Sv)

Scholze et al. (2003) Holocene

ΔT

ΔP

ΔNPP

Early modeling studies showed that changes in AMOC affect• Ocean Carbon Storage

• Land Carbon Storage

• Atmospheric CO2

SummaryIce core data suggest CO2 increases if AMOC is shutdown.

Ocean Carbon Cycle

• Solubility Pump

• Biological Pump

• Soft Tissue (organic carbon)

• Hard Tissue (CaCO3)

It contributes ~1/3 to the total globalsurface-to-deep DIC gradient

It contributes ~2/3 to the total globalsurface-to-deep DIC gradient

The Ocean’s Carbon Pumps

Solubility SoftTissue

Preformed

HardTissue

Circulati

o

n

Circulation

Plankton

DICPO4

DICPO4

DICPO4

CO2

Schmittner et al. (2013) Biogeosc.

Plankton

DICPO4

DICPO4

remineralized

PO4

PO4preforme

d

Soft-Tissue Pump and Preformed (Unused) Nutrient Inventory

PtotPpref

Ptot=Ppre+Prem

Prem

Marinov et al. 2008 GBCIto & Follows

2005 J. Mar. Res

NADW injects relatively low preformed nutrients

into deep ocean.

This makes biologicalpump efficient.

AABW & AAIW inject highpreformed nutrients

into deep ocean.

This makes biological pump

inefficient.

Preformed Nutrients Change model year 2500

Pacific Atlantic

Schmittner & Galbraith 2008 Nature

Dept

h (m

)

Schmittner & Galbraith 2008 Nature

HypothesisAMOC shutdown decreases

input of low pre-formed nutrientsthus increases the pre-formed nutrient inventory of the ocean

Schmittner & Galbraith 2008 Nature

Simulated changesin CO2 are similarto observations.

Schmittner and Lund (2015) Climate of the Past

Simulated changes

are highly correlated

with sedimentreconstructions

(r=0.85)

(2014) Paleoceanogr.

FW fluxes in SO and EEqP

required to simulate observed CO2 increase

Köhler et al. (2005)

Land carbon responseis sensitive to initial

conditions

Bauska et al. (2015) Nat. Geo.

Observedcentennial CO2 variability

remains unexplained.

Is there an AMOC connection?

Nye et al. (2014) JMS

AMO Impacts on Ecosystems Correlation SST-AMO

dryer

wetter

dryer

wetter

Conclusions• Multi-millennial CO2 changes due to AMOC

effects on biological pump efficiency

• Rapid CO2 changes remain unexplained (Land ?)

• Multi-centennial CO2 changes in Holocene remain unexplained