Hydrography, nutrients, and carbon pools in the Pacific sector of the Southern Ocean: Implications for carbon flux

Authors

Kendra L. Daly
Walker O. Smith Jr., Virginia Institute of Marine ScienceFollow
Gregory C. Johnson
et al

Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

4-14-2001

Journal

Journal of Geophysical Research: Oceans

Volume

106

Issue

C4

First Page

7107

Last Page

7124

Abstract

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Abstract

We investigated the hydrography, nutrients, and dissolved and particulate carbon pools in the western Pacific sector of the Antarctic Circumpolar Current (ACC) during austral summer 1996 to assess the region's role in the carbon cycle. Low f CO₂ values along two transects indicated that much of the study area was a sink for atmospheric CO₂. The f CO₂ values were lowest near the Polar Front (PF) and the Subtropical Front (STF), concomitant with maxima of chlorophyll a and particulate and dissolved organic carbon. The largest biomass accumulations did not occur at fronts, which had high surface geostrophic velocities (20–51 cm s⁻¹), but in relatively low velocity regions near fronts or in an eddy. Thus vertical motion and horizontal advection associated with fronts may have replenished nutrients in surface waters but also dispersed phytoplankton. Although surface waters north of the PF have been characterized as a “high nutrient‐low chlorophyll” region, low silicic acid (Si) concentrations (2–4 μM ) may limit production of large diatoms and therefore the potential carbon flux. Low concentrations (4–10 μM Si) at depths of winter mixing constrain the level of Si replenishment to surface waters. It has been suggested that an increase in aeolian iron north of the PF may increase primary productivity and carbon export. Our results, however, indicate that while diatom growth and carbon export may be enhanced, the extent ultimately would be limited by the vertical supply of Si. South of the PF, the primary mechanism by which carbon is exported to deep water appears to be through diatom flux. We suggest that north of the PF, particulate and dissolved carbon may be exported primarily to intermediate depths through subduction and diapycnal mixing associated with Subantarctic Mode Water and Antarctic Intermediate Water formation. These physical‐biological interactions and Si dynamics should be included in future biogeochemical models to provide a more accurate prediction of carbon flux.

DOI

doi: 10.1029/1999JC000090

Recommended Citation

Daly, Kendra L.; Smith, Walker O. Jr.; Johnson, Gregory C.; and et al, Hydrography, nutrients, and carbon pools in the Pacific sector of the Southern Ocean: Implications for carbon flux (2001). Journal of Geophysical Research: Oceans, 106(C4), 7107-7124.

doi: 10.1029/1999JC000090