Abstract

The Antarctic Ocean during Cenozoic time experienced four periods of enhanced siliceous productivity. The beginning of the Miocene and the Pliocene-Quaternary are the two major periods. The Pliocene-Quaternary increase in productivity began 5 m.y. ago and has progressively increased to the present level of intense surface productivity. Two short-lived periods of slightly increased surface productivity were the middle Eocene and the middle Miocene.

The major control of Antarctic surface productivity through the Cenozoic has been climate. Climate in the Southern Ocean is ultimately controlled by tectonic changes in the Antarctic Ocean basin, which altered the patterns of surface and thermohaline circulation. Antarctic surface waters became more conducive to siliceous biological productivity with the progressive latitudinal and thermal isolation of Antarctica. Opal production during the Neogene increased particularly during globally cooler times, due to the intensification of upwelling south of the Polar Front. This intensification was caused by accelerated atmospheric circulation and an increased volume production of Antarctic Bottom Water.

Since the Oligocene, times of increasing productivity in the Antarctic correspond to periods of decreasing productivity in the central equatorial Pacific Ocean. It appears that high concentrations of limiting nutrients upwelling in the Southern Ocean have enabled the region to successfully “compete” for silica. The efficiency of the biological cycling of silica has progressed to the extent in the Antarctic that much of the silica assimilation and accumulation has transferred to the Antarctic at the expense of other productive oceanic regions such as the central equatorial Pacific.

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