The role of the Weddell Sea in the global CO2 sink

1
The role of the Weddell Seain the global CO2 sink
A. A. Bianchi, H. G. Isbert, D. Ruiz Pino
Servicio de Hidrografía Naval, FCEyN UBA, UPMC
2
ARGAU(Projet de Coopération avec lARGentine
pour létude de lOcéan Atlantique sud-Austral)

• Role of the dynamics and byological process on
  the CO2 in the Southern Atlantic Ocean and the
  Weddell Sea.
• ARGAU Partners
• Université Pierre et Marie Curie, Paris,
  Francia - CNRS
• DNA-Instituto Antártico Argentino
• Servicio de Hidrografía Naval
• RHAI
• UBA, UNLP, CENPAT

3
Vertical stratification and air-sea CO2 fluxes in
the Patagonian shelf (Bianchi et al, 2005)

• Air-sea ? pCO2 (µat). Areal mean -29µatm
• Air-sea CO2 flux (mmolm-2día-1) Areal mean
  -5 mmolm-2dia-1

Surface distribution of Chl_a (mgm-3)
4
Measurements

• Air and sea pCO2
• SSS and SST
• Fluorescence
• Meteorological data
• Phytoplankton composition
• Chlorophyll
• Dissolved oxygen and nutrients
• pH, alkalinity

5
In the Slope Front, the Antarctic Divergence,
characterized by its salinity minimum, seems to
be a boundary between the regions of maximum CO2
sink and higher chlorophyll (gt 4 mg.m-3).
A5T6 (Feb. 17 to 21-2005)
From Foster Carmack, 1976
6
A1T5 (Feb. 23 to 26-2001)

• In the Weddell southern shelf, note peaks of
  chlorophyll as high as 8 mg.m-3 related with the
  very low values of ?pCO2, that reach
• -200 µatm at both sides of the Slope front.

Promedio mensual de clorofila_a satelital
(SeaWIFS) para febrero de 2001
7
XBTs CANOPO project
8
(No Transcript)
9
Chlorophyll Horizontal Distribution Areal
mean 1.45 mg/m3

• DpCO2 Horizontal Distribution Areal
  mean -60 mAtm

10
Sea-Air CO2 Fluxes

11
CONCLUSIONS

• The summer areal CO2 uptake in the Weddell Sea is
  9.5 mmol.m-2.day-1.
• Peaks in the sea-air ?pCO2 of -200µatm, among
  the highest in the global ocean, are observed
• The Weddell cyclonic gyre drives an Ekman
  divergent flux producing a dome in the central
  region. The upwelling of deeper CO2-rich waters
  changes the sign of the sea-air CO2 flux,
  generating a region of light emission.
• In the Slope Front, the Antarctic Divergence,
  characterized by its salinity minimum, advects
  waters westward. The Front seems to be a
  boundary between the regions of maximum CO2 sink
  and high chlorophyll concentration (gt 4 mg.m-3).

12
Which is the cause of the strong CO2 uptake in
the Weddell Sea?

• The horizontal distribution of Chlorophyll shows
  that the Weddell is not oligotrophic (the areal
  mean chlorophyll concentration is 1.45 mg/m3).
  The high chlorophyll values are observed not only
  in the Weddell southern shelf, but in other
  regions too .The highest chlorophyll data,
  observed near the Slope Front, exceed 5mg/m3, a
  value remarkably high compared with precedent
  observations. It suggests that the biological
  activity in summer in the Weddell Sea is much
  higher than previously thought.
• The lipid tracers measured in the SW Atlantic,
  Drake Passage and Scotia Sea show that the
  diatom blooms enhance the CO2 sink, twice to 3
  times more than coccolithophores. Diatoms are the
  main phytoplankton group south of the Polar
  Front.
• The penetration of the anthropogenic CO2 in the
  global ocean is larger in the regions of high
  biological activity, like the Weddell Sea, and
  calcareous and silicate phytoplankton play a
  major role in the drawdown of CO2 to the deep
  ocean. These results suggest that annual CO2
  budget models may underestimate the importance of
  the biological pump, compared with the physical
  pump.