Paleoceanography Changes And Implications Of Site 1312 In The North Atlantic During The Last 4.1Myr

The global climate change since the latePliocene is characterized by the waxing and waning of the continental ice sheets in the northern hemisphere.The North Atlantic Ocean has become a key target area for studying paleoclimate changesduetoitsposition which is closed to the ice sheet formation area and easily affected by the ocean-atmosphere-cryosphere interaction.In this study,we analysed the major paleoceanography events indicated by multi-proxies,such as planktic?¹⁸O and?¹³C,sea surface temperature?SST?,foraminifera census,ice-rafted debris?IRD?,grain size at Integrated Ocean Drilling Project?IODP?Site U1312 in the south margin of Ruddiman's IRD belt during the last 4.1 Myr,on the basis of an age model by tuning the G.ruber?¹⁸O curve to the LR04 and U1308 benthic?¹⁸O stack with the aid of the high-resolution lightness parameter L*,which mirrors the marine oxygen isotope stages?MIS?.Moreover,the regional paleoenvironmental evolution of the North Atlantic was discussed.The main conclusions are as follows:The record of Site U1312 can play a clear role as a monitor of regional environmental changes since the late Pliocene.The first IRD pulseof Site U1312 occurred at 2.52 Ma,which may imply the maturation of the Northern Hemisphere ice sheet and the drifting icebergs bearing lithic grainscould have affected mid-latitude regions during this climate-sensitive period.During¹.3 Ma to 0.62 Ma,the paleoceanography recordsof Site U1312 responded to the Mid-Pleistocene Transition?MPT?.At⁰.9 Ma,Site U1312 displayed a strong cooling with an increase IRDinput,which was the result of regional ice sheets expansion.Since⁰.65Ma,the largeglacial-interglacial amplitudes andlong duration,the high content and frequency of IRD input,and the occurrence of Heinrich?-like?events indicated that a new ice sheet dynamics model was established and began to dominate the regional environments,which was related to the extremely large ice sheets and long-term glacials.The long-term SST evolution of U1312 was mainly controlled by the obliquity and eccentricity forcing,and the reorganization of the surface currents and the migration of the ocean fronts'position also influenced the SST records during the last¹.28 Ma.In general,SiteU1312 was mainly affected by the North Atlantic Current?NAC?water masses since the Middle Pleistocene.However,during Marine Isotope Stage?MIS?24–22,MIS 12,MIS 8,SST decreased significantly,IRD input increased,accompanied by the invasion of polar/subpolar water mass,indicating the Arctic front?AF?may move southward to the Site U1312 or more southern position during the peak period of these glacials,reflecting by thethe almost zero temperature gradients between high and middle latitudes and between east and west of middle latitudesin the North Atlantic,whichimplied the surface ocean circulation experienced a significant reorganization.During the interglacial peaks of MIS 17,MIS 13,MIS 11 and MIS 5,a warmer SST suggesting the AF moved northward,and the influence of subtropical water mass on Site U1312 increased.It should pay more attention to the important paleoceanography events and their control factors reflected by U1312 records.For example,during MIS 16,the first occurrence of detrital carbonate originating from the Hudson Strait,which marked the Heinrich-like events,and the decoupling between SST and IRD inputs,indicated that the increased iceberg dischargesresulted by the expansion of the Laurentide ice sheet may play an instrumental role in triggering the first Heinrich-like event.During MIS 12,Site U1312 experienced the maximum cooling since¹.28 Ma with detrital carbonates in the IRD during the deglacial period,and it was extremely warm during MIS 11,which maybe a response to the Mid-Brunhes event.Besides orbital forcing and ocean currents,additional climate mechanisms were needed to match the changes during MIS 12 to MIS 11.