WATER COLUMN STRUCTURE CHANGES ON THE NORTHWIND RIDGE, WESTERN ARCTIC OCEAN SINCE THE MARINE ISOTOPE STAGE 5: EVIDENCES FROM FORAMINIFERAL ASSEMBLAGES AND THEIR OXYGEN AND CARBON ISOTOPES

Foraminifera assemblages and planktonic foraminiferal stable oxygen and carbon isotopes have been investigated for the core ARC3-P37, retrieved from the Northwind Ridge, Western Arctic Ocean, in order to decipher the water column structure and circulation changes in response to climate variations. The abrupt increase in foraminiferal abundance may indicate warm intervals with warm Pacific inflow to the Western Arctic Ocean. Planktonic species Neogloboquadrina pachyderma (sin.) (Nps) dominate the foraminiferal assemblage by over 90%. Benthic assemblage mainly comprises of deep water dwellers Cibicidoides wuellerstorfi and Oridorsalis umbonatus. The occurrence of Atlantic species Cassidulina neoteretis indicates the deepening of Arctic intermediate water. Nps-δ¹³C is generally heavy during warm intervals, reflecting good ventilation and high productivity. Nps-δ¹⁸O variation is complicated and affected by the habitat of the species, water temperature, halocline depth, and meltwater etc., generally showing heavy values during cold periods, while light values corresponding to meltwater input. Above the brown layer B2b in MIS 3, light Nps-δ¹⁸O is affected by warm sea water and meltwater discharge; while below B2b, the heavy Nps-δ¹⁸O during warm intervals may suggest shallowing of the halocline and the migration of Nps habitat to deeper layers.