Biogenic Opal Deposition in the Surveyor Fan (IODP Site U1417) in the Gulf of Alaska (North Pacific) During the Late Miocene to Early Pleistocene

Abstract International Ocean Discovery Program (IODP) Site U1417, located in the Surveyor Fan (Gulf of Alaska), preserves hemipelagic sediments influenced by glacial and fluvial depositional processes from the Cordilleran Ice Sheet in the Chugach–St. Elias Mountains and Coastal Mountains. The biogenic opal content was measured for a total of 441 samples from the late Miocene to early Pleistocene intervals and its flux for hemipelagic sediments was calculated to trace the history of biogenic opal deposition. On the whole, the biogenic opal content confirms the division of the lithostratigraphic units and subunits: diatom‐bearing clay‐rich intervals versus clast‐rich terrigenous intervals. The high biogenic opal content results from the better preservation of diatom ooze, whereas the low biogenic opal content is due to diatom‐poor terrigenous sediments including diamict deposited from sedimentary gravity flows during the late Miocene. On the other hand, the biogenic opal deposition from the late Miocene to early Pleistocene might have been attributed to the degree of diatom production controlled by global climate change. The variation of biogenic opal flux at Site U1417, compared with other regions in the North Pacific, represents the global climate events such as Late Miocene Biogenic Bloom, mid‐Pliocene Warmth, and Northern Hemisphere Glaciation. Despite regional differences in oceanographic conditions, surface water productivity in the Gulf of Alaska has been attributed to the basin‐to‐basin redistribution of nutrients by global thermohaline circulation and the related Pacific Ocean ventilation. This study underlines that biogenic opal deposition at IODP Site U1417 has recorded global climate evolution since the late Miocene.