Silica burp hypothesis

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The Eocene (55.8 ± 0.2 to 33.9 ± 0.1 Mya) was a period of Earth history with enhanced crustal activity and a markedly warmer climate. Additionally, the Eocene saw prolonged periods of silica accumulation on the ocean floor. The peak of this accumulation occurred at approximately 50 Mya, creating Horizon AC, a layer of silica-rich sediments spanning approximately 4 My. Significantly, Horizon AC is comparatively isolated in time from known silicic acid addition processes, and this led McGowran (1989) to propose a novel mechanism, the "silica burp" hypothesis, that centres on the temporal decoupling of silicic acid supply and burial by climatic variation.

The "silica burp" hypothesis

The "silica burp" hypothesis suggests that following a period of vulcanism (Thulean; 56.7 to 53.8 Mya), the warm climate of the Early Eocene Climatic Optimum (EECO) decreased ocean circulation and increased stratification with the result that silica added by this vulcanism was isolated from the productive surface waters and was able to accumulate within the ocean interior. According to the hypothesis, this was then compounded by the addition of silicic acid by increased, climate-induced weathering at high latitudes. This warming period persisted until approximately 49 to 48 Ma (Boharty & Zachos, 2003), after which major climate cooling occurred, reinvigorating ocean circulation, and, so the hypothesis goes, releasing the accumulated silicic acid to the surface ocean (the "silica burp") where it fuelled increased biogenic silica production which led to the creation of Horizon AC. Essentially, the hypothesis proposed that changes to the Earth’s climate during this period temporally decoupled the (geophysical) supply of silicic acid to the ocean from its (biological) removal.

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