Paleoclimate Changes Of The Canterbury Basin In The Southwest Pacific During The Last 900 Kyr

The Canterbury basin is adjunct to the Southern Alps.The Southern Alps now host>3000 glaciers,which are sensitive to climate perturbations because of their high accumulation and ablation rates.At the same time,the water properties in the Canterbury basin are influenced by the Subtropical Front?STF?.The STF is controlled by the westerlies,which is relevant to the ventilation of the Southern Ocean.Thus,the oceanographic characteristics of the study region are sensitive to the global climate change.Moreover,the waters in this region are well stratified.The study of water properties at different depth allows us to discuss the circulation of the deep waters and its mechanism.During the Integrated Ocean Drilling Program?IODP?Expedition 317,sediments were cored in four sites in the Canterbury Basin.In this study,we analyzed the carbon isotope of planktonic and benthic foraminiferal,planktonic foraminiferal assemblages,total organic carbon content,and grain size of the sediment in Sites IODP U1351,U1352,and U1354.Planktonic foraminiferal assemblages from IODP Site U1352 were used to derive SST estimates by using the MAT.Our results combined with the study results of the former researchers allow us to discuss the paleoceanographic changes in the study region over the last 900 kyr.We have constructed a 900 kyr oxygen isotope stratigraphy for three IODP 317sites in the Canterbury Bight of the southwest Pacific Ocean?two shelf sites U1354and U1351 and one slope site U1352?.Planktonic foraminiferal assemblages from IODP Site U1352 were used to derive SST estimates over the last 450 kyr.Comparisons of the planktonic foraminiferal assemblage and SST record of IODP Site U1352 with those of ODP Site 1119,DSDP Site 594 and core MD06?2986,combined with the carbon isotope of planktonic foraminiferal in IODP Site U1352,ODP Site 1119 and DSDP Site 594 over the last 900 kyr,allow us to reconstruct the spatial change of the STF by locating the positions of its SF section,which runs nearly parallel to the South Island's shoreline.The carbon isotope of Gg.bulloides from sites IODP U1352 and DSDP 594showed that the two sites were influenced by STW?SAW during most time of the MPT?MIS 21?MIS 13?.The SAW migrated north after the MPT?since MIS 12?.The planktonic foraminiferal assemblage,SST record,and the?¹³C of Gg.bulloides in IODP Site U1352,ODP Site 1119 and DSDP Site 594 showed that Sites IODP U1352,ODP 1119,DSDP 594 were covered by a Subtropical Water–Subantarctic Water?STW–SAW?mixture in the inshore band of the Southland Current during MIS 11c,MIS 7a–c and MIS 5e.IODP Site U1352 recorded a similar scenario during MIS 7e.In comparison with previous studies,the higher resolution record of IODP Site U1352showed the influence of an STW–SAW mixture was limited to MIS 11c,MIS 7e,MIS7a–c and MIS 5e at this site.The offshore band of the Southland Current which is dominated by the SAW influenced Sites IODP U1352 and ODP 1119 during MIS11a–b and MIS 9a–d.However,in this period,DSDP Site 594 was influenced by the SAW.The SF is situated between DSDP Site 594 and Sites IODP U1352,ODP 1119during MIS 7d and glacial periods of MIS 12,MIS 10,MIS 8,and MIS 6.DSDP Site594 was covered by the offshore band of the Southland Current during MIS 12,and was covered by the SAW during MIS 7d,MIS 10 and MIS 6.Hence,unlike previous studies in the region,MIS 7d is identified as a glacial period.Comparison of the carbon isotope of Gg.bulloides from IODP Site U1352 with the grain size of the sediment from IODP Site U1352 found that the migration of the surface water masses over IODP Site U1352 was always accompanied by the sudden change of the grain size at this site.Based on the analysis of sedimentation rate and composition?e.g.<2?m clay,2⁶3?m silt and>63?m coarse fraction?from the IODP U1351 Hole and U1352 Hole,with the migration of the surface water masses taken into account,we analyzed the sedimentary characteristics of the study area.During the transition from glacial to interglacial stages/periods,the melting of the Southern Alps and the migration of the surface water masses influenced IODP Site U1352,ultimately leading to an increase in coarse fraction and sedimentation rate.The study of the water properties in the Southwest Pacific during the last 900kyr found that changes in the volume of polar ice sheets which is relevant to the MPT,the ventilation of the deep water in the Southern Ocean,and the flux of North Atlantic Deep Water to the Southern Ocean drive the changes of carbon isotope in the benthic foraminiferal from sites ODP 1123 and DSDP 594.Furthermore,the influences of the volume of polar ice sheets which is relevant to the MPT,the ventilation of the deep water in the Southern Ocean,and the flux of North Atlantic Deep Water to the Southern Ocean were also reflected in the surface water masses,as shown in the carbon isotope of benthic foraminiferal from IODP Site U1352 during MIS 21?MIS13.The variable carbon isotope of benthic foraminiferal from IODP Site U1352 since MIS 12 was response to the migration of the surface water masses.