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We demonstrated in laboratory experiments that temperature control of marine bacteria action on diatoms strongly influences the coupling of biogenic silica and organic carbon preservation. Low temperature intensified the selective regeneration of organic matter by marine bacteria as the silicon:carbon preservation ratio gradually increased from -1 at 33 deg C to -6 at -1.8 deg C. Temperature control of bacteria-mediated selective preservation of silicon versus carbon should help to interpret and model the variable coupling of silicon and carbon sinking fluxes and the spatial patterns of opal accumulation in oceanic systems with different temperature regimes.
Diatom productivity is largely responsible for downward fluxes of biogenic silica (BSiO^sub 2^; opal) and organic matter in the global ocean (1, 2). An understanding of the mechanisms that couple the relative fates of diatom Si and C within the water column is critical in order to elucidate the role of diatoms in the biological carbon pump and in order to use opal effectively for paleoproductivity reconstruction.
Oceanic systems display large regional differences in the accumulation and preservation of opal in sediments, but accumulation does not necessarily correspond to C and Si production rates (3). Only 25 to 40% of global biogenic silica production occurs above high-accumulation regions (regions consisting of >5% opal by weight), such as coastal upwelling zones, the subarctic Pacific, and the Southern Ocean (3, 4). The Southern Ocean alone supplies -50% of the global opal accumulation, while accounting for only 20 to 30% of global opal production (3--5). In contrast, virtually no opal is accumulating below the Sargasso Sea and other oligotrophic midocean gyres, even though their combined annual opal production is also estimated at 20 to 30% of the global average (3, 4, 6).
Enhanced preservation of opal is one mechanism that has been proposed to explain high accumulation in open ocean areas, such as the Southern Ocean (3). However, recent revisions of the silica budget in the Southern Ocean [giving higher opal production rates (50 x 10^sup 12^ mol year-1 to 80 x 10^sup 12^ mol year^sup -1^) and lower opal accumulation rates (3.1 X 10^sup 12^ mol year ')] have placed opal preservation efficiencies (the ratio of burial to production) near the global average of 3% (4, 7, 8) for the Polar...