Deep Sea Benthic Foraminifera from Marine Gas Hydrate Environment and Paleoceanographic Changes in the Northern Cascadia Margin

Abstract

Deep-sea benthic foraminifera are found in different marine settings including gas seepages, gas hydrates, having great potential to reconstruct past climate and oceanic changes owing to their wide distribution, strong sensitivity to different oceanographic variables, high morphological diversity, and well documented fossil record. The benthic foraminifera can be used as proxy to identify methane and bacteria-rich environments. Several studies suggest that certain species of benthic foraminifera prefer to feed on rich bacterial mats in methane rich environments. The ecological preferences of benthic foraminiferal records constituting 52 individual species belonging to 31 genera in methane rich sediments of Cascadia Margin, NE Pacific Ocean during Pleistocene. The quantitative analyses of deep-sea benthic foraminifera, particularly Bulimina exilis, Cibicides kullenbergi, Elphidium batialis, Epistominella exigua and Uvigerina proboscidea generally show higher abundances in the studied interval. The Alaska Current, North Pacific Current and California Current also known as Eastern Boundary Currents (EBC) plays a major role in the transportation of suspended sediments and coastal upwelling throughout the coast. Benthic foraminiferal accumulation rate (BFAR), Benthic foraminiferal oxygen index (BFOI), Total Organic Carbon (TOC), and calcium carbonate (CaCO3) deposition provides the information on paleo-productivity, scarcity of fauna, in the Early Middle Pleistocene Transition (EMPT) which caused the increased cyclic seasonality and served as the major responsible factor for low biological productivity. The TOC in addition estimates the amount of pore space methane hydrate as 0.88% and the amount of methane generated at 146.48 mM in the IODP Hole U1325B. Stable isotope values in benthic foraminifera arrived at the conclusion that in methane rich settings benthic foraminiferal and#948; 13C are typically depleted and have a high negative correlation with and#948; 18O signatures