Diatomaceous ooze in a sedimentary core from Mariana Trench: implications for paleoceanography

Abstract

Diatomaceous ooze sampled from near the Mariana Trench sediment surface by gravity corer (Core JL7KGC05) revealed a high sedimentary abundance of Ethmodiscus rex (Rattray, 1890) Wiseman and Hendey, 1953 fragments and tropical open ocean planktonic diatom taxa including Azpeitia nodulifera (Schmidt, 1878) Fryxell and Watkins in Fryxell, Sims and Watkins, 1986 and Alveus marinus (Grunow, 1880) Kaczmarska and Fryxell, 1996. Subsurficial sediments from the ooze are assigned a Marine Isotope Stage 2 age, approximately at the Last Glacial Maximum. The occurrence of Ethmodiscus ooze suggests massive late Pleistocene blooms in the Northwestern Pacific Ocean and provides a plausible link to paleoceanographic and paleoclimatic changes related to Antarctic Intermediate Water mass, which carried a high dissolved silica content as silicon leakage that reduced dissolution rate of diatom frustules. Northward flow of Antarctic Intermediate Water was probably related to surface current migration and southward shift of the Northwest Pacific Gyre to form oligotrophic conditions that triggered Ethmodiscus rex blooms under unusual nutrient recycling conditions within the ocean system. This bloom hypothesis may help explain differential silica dissolution during the last glacial stage.