m.racault@uea.ac.uk

Changes in the Southern Ocean biological export production

over the period 1968-2004

Marie-F. Racault, Corinne Le Quéré & Erik Buitenhuis

CARBOOCEAN Annual MeetingGran Canaria, December 2006

Strengthening and poleward shifting of the winds in the Southern Ocean

2004 mean

2004 minus 1967

NCEP winds (m/s)

Decrease in the Southern Ocean sink of CO2

modelled

expected

observations

Changes in Export and Primary Production?

Carbon content (PgC/y) of the Southern Ocean

Total ΔFCO2 = 0.15

ΔFHeat = 0.01

ΔPP = ?

ΔExp = ?

ΔDIC = 0.4PgC/yΔDIC = ?

Atmosphere

Euphotic

zone

Deep

ocean

• OPA General Circulation model • 0.5-1.5ox2o resolution• 31 vertical levels • Calculated vertical mixing• NCEP daily forcing

OPA model

• PISCES-T ecosystem model • 2 phyto, 2 zoo., 2 sinking particles• Limitation by Fe, P, and Si• Initialise with observations in 1948

(Buitenhuis et al., GBC 2006)

PISCES-T model

Chla (mg/m3) and biological export production (molC/m2/y) from the model and based on observations

SeaWiFS Chla

PISCES-T Chla PISCES-T bio. export

Obs. bio. export *

* Schlitzer, 2002

eratio in the Southern Ocean over the period 1968-2004

mean

Export Production (PgC/y) 1.4

Primary Production (PgC/y) 4.7

Southern Ocean eratio

mean eratio

ExpPP

= 0.3

eratio in the Southern Ocean (SO) vs. Global Ocean

SO mean

Export Production (PgC/y) 1.4 8.9

Primary Production (PgC/y) 4.7 61

Global eratio

SO mean eratio

ExpPP

= 0.3

SO

global mean

global mean

eratioExpPP

= 0.15

• OPA General Circulation model • 0.5-1.5ox2o resolution• 31 vertical levels • Calculated vertical mixing• NCEP daily forcing

Have the changes in circulation induced a trend in the biological export production?

Simulation of PISCES-T with observed atmospheric forcing

• OPA General Circulation model • 0.5-1.5ox2o resolution• 31 vertical levels • Calculated vertical mixing• NCEP daily forcing from year 1967 repeated onward

Have the changes in circulation induced a trend in the biological export production?

Simulation of PISCES-T with constant atmospheric forcing

Trend in the Southern Ocean Chla (mg/m3)

Time series of the Chla induced by changes in circulation

PISCES-T with obs. atmo. forcing minus PISCES-T with constant forcing

Increase of 0.07 mgChl/m3

over 38 years

Increase in the eratio in the Southern Ocean caused by changes in circulation

mean changes

Δ Export Production (PgC/y) 0.3

Δ Primary Production (Pgc/y) 0.6

mean eratio

PISCES-T eratio with obs. atmo. forcing minus PISCES-T eratio with constant forcing

= 0.3ΔExpΔPP

= 0.57

eratio due to changes in circulation

Increase in Export and Primary Production

Carbon content (PgC/y) of the Southern Ocean

Total ΔFCO2 = 0.15

ΔFHeat = 0.01

ΔPP = 0.6

ΔExp = 0.3

ΔDIC = 0.4PgC/yΔDIC = 0.4

Atmosphere

Euphotic

zone

Deep

ocean

Conclusions

Further work

High eratio in the Southern Ocean

Export production compensates 3/4 of the DIC

Model results supported by observations

Investigate the structure of the ecosystem and estimate its role in this context of circulation changes

Further modelling studies

Prototype version of PLANKTON 10 currently working

Diatoms N2 fixers Phaeocystis Nanophyto plankton

Fe

CaCO3

DMS

DOMMesozoo-plankton

Microzoo-planktonZoopl. filter

feeders

Bacteria

Picophytoplankton

Light

Si

Coccolitho-phorids

NO3PO4 NH4