High Biomass Low Export Regimes in the Southern Ocean Page: 4 of 75
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4
2 Introduction
The biological carbon pump transfers carbon from the atmosphere to the deep ocean via
the settling of particulate organic carbon (POC) from the surface ocean, where it is produced
from photosynthesis, to the deep ocean. Because the biological carbon pump partly determines
the equilibrium CO2 concentration in the atmosphere (Volk and Hoffert 1985), understanding the
controls on its efficiency is important for understanding global carbon cycling.
There exist several models that predict the magnitude of POC export out of the euphotic
zone as a function of various surface properties, including primary production (Eppley and
Peterson 1979), ecosystem structure (Michaels and Silver 1988), sea surface temperature (Laws
et al. 2000), and combinations of the above (Dunne et al. 2005). In the deep sea, the decay of
POC export with depth is most commonly modeled as an empirically fit function of shallow
export (Martin et al. 1987). The search for a more mechanistic understanding of controls on
deep POC flux (> 1000 m) has most recently focused on the importance of mineral ballast
(Armstrong et al. 2002; Frangois et al. 2002; Klaas and Archer 2002). The idea of ballast
minerals being important for the settling of POC to depth arises from the observation that the
density of organic matter (~1.05 g/cm3) is roughly the same as that of seawater (~1.03 g/ cm3),
and that particles require a source of weight ("ballast") in order to sink. The most obvious
sources of ballast for marine particulates in the open ocean are the biogenic minerals such as
calcite (CaCO3) and opal (biogenic silica) that form the shells of coccolithophores and diatoms,
respectively. Calcite has a density of 2.71 g/ cm3, and diatom Si frustules have a density of 2.0
g/ cm3(Hurd and Theyer 1977). Particles with a higher fraction of ballast minerals have a greater
excess density over seawater, and thus sink faster.
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Lam, Phoebe J. & Bishop, James K.B. High Biomass Low Export Regimes in the Southern Ocean, article, January 27, 2006; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc880389/m1/4/?rotate=90: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.