Abstract

Carbonate ooze in Bahamian troughs displays cyclic variation in the content of aragonite. A 10 m core devoid of turbidites shows 3.5 cycles, each defined by a sharp increase, followed by a gradual decrease of aragonite. The aragonite curve matches closely the oxygen-isotope curve of planktic foraminifera from the same core. Aragonite highs correspond to light oxygen-isotope values and thus to interglacial stages. Content of terrigenous material is low during interglacials and higher during glacial periods. Intermittent flooding and exposure of the Bahama Banks is most probably not the cause of the cycles, because the latest increase in aragonite precedes bank flooding by 8,000 yr and because the cycles are distinctly asymmetric, with rapid increase and gradual decrease of aragonitic content. Carbonate dissolution cycles tied to the glacial rhythm of Earth's climate are a more likely explanation of the variations in aragonite content.

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