Sub sea surface temperatures in the Nordic Seas during the LGM by planktic foraminiferal Mg/Ca temperature reconstructions

In order to reconstruct the changes in (sub)surface water mass since 20.0kaBP, multiproxy investigations, including Ice Rafted Debris (IRD) abundance, AMS¹⁴C dating, foraminiferal abundance, stable oxygen and carbon isotopes of planktonic foraminifera Neogloboquadrina. pachyderma (sin.) (Nps), and (sub)surface temperature derived from Nps Mg/Ca ratios, have been carried out for two cores collected from the Nordic Seas during the Fifth Chinese National Arctic Expedition. The LGM (20.0~17.5kaBP) is characterized by low subsurface water temperature(~3℃), poor calcium productivity, and enhanced IRD input. During the deglaciation (17.5~11.7 kaBP). Nps-δ¹⁸O and-δ¹³C depletions suggested a freshwater event during Heinrich Stadial 1(HS1). Stronger water stratification and north Atlantic water gathering in the subsurface layer caused the increase in subsurface temperature. At the onset of Bølling-Allerød (B/A) event, the subsurface water temperature (4.5℃) indicated an increased advection of Atlantic water. The early Holocene (11.7~8.2kaBP) was characterized by higher subsurface temperature (6.5℃), bioproductivity, and lower IRD input. During the middle Holocene (8.2~4.2kaBP), the gradual increase in bioproductivity during 8.2~5.6kaBP indicated the enhanced ventilation, which led to an increase in nutrient supply. Lower subsurface temperature (~4℃) during the 6.6~5.6kaBP may suggest the decrease in summer solar radiation and weakening of Atlantic water advection. During 5.6~4.2kaBP, the depletion of Nps-δ¹³C and δ¹⁸O values indicated poor bioproductivity and subsurface water warming, respectively. During the late Holocene (4.2~0.8kaBP), the Neoglaciation (4.2~3.0kaBP), was characterized by low subsurface temperature and poor bioproductivity. The light values of Nps-δ¹⁸O and the increase in IRD reflected a meltwater event. Since 3kaBP, the continuous increasing of subsurface temperature and bioproductivity may be explained by the increased advection of Atlantic water.