Biogenic opal deposition in the Surveyor Fan (IODP Site U1417) of the North Pacific during the late Miocene to early Pleistocene

International Ocean Discovery Program (IODP) Site U1417, located in the Surveyor Fan (Gulf of Alaska), preserves hemi-pelagic sediments influenced by glacial and fluvi­al depositional processes from the Cordilleran Ice Sheet in the Chugach–St. Elias Mountains and Coastal Mountains. A total of 441 samples from the late Miocene to early Pleistocene were used to measure the biogenic opal content and calculate its flux to trace the degree of diatom productivity in surface water and depositional history. In general, the biogenic opal content confirms the division of the lithostratigraphic units and subunits: diatom-bearing clay-rich intervals versus clast-rich terrigenous intervals. Despite large fluctuations from the late Miocene to early Pleistocene, the variation of biogenic opal content and deposition of biogenic opal flux might have been controlled by global climate change, such as the high levels during the Late Miocene Biogenic Bloom (LMBB) and mid-Pliocene Warmth (MPW) and its abrupt decline at the Northern Hemisphere Glaciation (NHG). These variations of surface water productivity may be attributed to the basin-to-basin redistribution of nutrients by global thermohaline circulation and the related Pacific Ocean ventilation in response to global climate change.