The Sea-Surface Temperature Changes Based On Lipid Biomarker Proxies Of The Past 149 Ka In The Newfoundland Basin Of The Northwest Atlantic

The sea-surface temperature and salinity in the Newfoundland Basin of the northwest Atlantic Ocean are affected by the warm and salty North Atlantic current and the cold and fresh Labrador current.The interaction is as such that when the impact of Labrador current increases,it cools the temperature and lowers the salinity.In contrast,when the North Atlantic Current inflow increases,the sea-surface temperature and salinity increase.This interaction between the Labrador and North Atlantic currents must have been intensified due to imposition of the Laurentide Ice Sheet(LIS)and southward invasion of the Arctic Front during the last glacial cycle.A sediment core Hu9007-08collected from the top of the Milne Seamount in the Newfoundland Basin was used to test that hypothesis.In this study,sedimentological,geochemical,stable carbon and oxygen isotopes,radiocarbon dating,and organic biomarker proxies have been applied to the sediment core Hu9007-08pc to reconstruct the abrupt paleoclimate events and the development and changes in the sea-surface of the Newfoundland Basin.The summary of the completed work is listed below:(1)10 sediment facies were identification by integrating the bulk sediment magnetic susceptibility,digital spectrophotometric reflectance,core photography,and portable X-ray fluorescence(p XRF)data;(2)5 Heinrich iceberg-rafting layers were identified by combining the Magnetic susceptibility(Mag.Sus.),Ca/Ti,L*,a*,etc.data;(3)Various components of the glycerol dialkyl glycerol tetraether lipids(GDGTs)using a high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry(HPLC-APCI-MS)were identified and analyzed;(4)An attempt has been made to use the br GDGTs indicators,MBT'and CBT,to reconstruct the CBT-PH and MBT'/CBT-temperatures;(5)Age model construction:a.The planktonic foraminifera AMS-¹⁴C dates were used in the Undatable age modeling program in the MATLAB programming language to construct the age model of core Hu9007-08;b.Due to the limitation of the Undatable age model program,the"g2n"script which was applied to construct the age model of Greenland ice cores,was modified and develop a programing code Ra Ca2020 to construct the age model of the entire core.The latest version of the radiocarbon calibration program Calib 8.1(software to calibrate acquired ¹⁴C age to the calendar age)was used.By aligning the Neogloboquadrina pachyderma-?¹⁸O curve with the North Atlantic centric age model,15 tie points were obtained.The ¹⁴C-AMS dates and tie points are used together in the Ra Ca2020 MATLAB code to construct the age-depth of the entire core,i.e.,up to1111cm.The main findings of the study are as follows:(1)Heinrich events H1:15.8-17.1ka;H2:21.9-24.1ka;H3:27.3-30.2ka;H4:35.1-39.5ka;H5:49.9-54.7ka;and H11:130-133.7 ka are identified in core Hu9007-08.(2)The multiple indices of i GDGTs/Cren,i GDGT2/Cren,MI,%i GDGT2 suggest that the main source of i GDGTs is Thaumarchaeota;Ternary graph of fractional abundance of BIT,??a/??a,and br GDGT suggests that the core deposition in core Hu90007-08 was affected by the terrestrially-derived organic matter in stages.(3)The correlation between each component of i GDGTs and Cren,TEX^L₈₆and between GDGTs index and?¹⁸O(PDB),it proves the availability of TEX₈₆^L and RI-OH in the study area for temperature reconstruction;(4)Analysis and comparison with available temperature calibration equations suggests that calibration equation of Haring et al.(2019)is suitable for core Hu9007-08.According to the RI-OH temperature calibration formula proposed by(Lüet al.2015)applied to the Chinese marginal sea,the attempt to reconstruct the temperature using OH-GDGTs compounds was completed;(5)Based on the TEX₈₆^L-SST,OH-SST reconstruction temperature,Neogloboquadrina pachyderma-?¹⁸O,Neogloboquadrina pachyderma-?¹³C index,the Hu9007-08 core record is divided into the climate stage since 149.5 ka BP.(6)Combining the previously published sedimentary records of CH69-K09,Su90-24,and ODP Site 1603 to assess the sea-surface environment and the reconstruction of ocean current changes:During H1,H2,H4,H5,and H11,there is a significant shift in the light value of NPS-?¹⁸O,and the freshwater input signal is more significant than that of H3;During H3,the deposition rate is lower,but the BIT value still reaches a higher value,which proves that although there is insufficient input of iceberg rafting and meltwater during H3,the input of terrestrial materials is still maintained.Combining with CH69-K09,MD03-2644,ODP Site 984 records,it is found that H11 is common in the Labrador Sea in the northwestern North Atlantic Ocean.The MIS6/5-5e warm up rapidly,the reconstruction temperature was higher than the Holocene temperature,AMOC and NADW are in active mode,and the influence of NAC and Irminger Current is strengthened.In the late MIS5e-MIS5a period,the AMOC and NAC were active but slowly and steadily decreasing.The influence of fresh water input during H7,H9,and H10 weakened for a short time,and LC strengthened for a short time.During MIS4 and MIS2,the study area was mainly affected by LC.The NAC had a weaker vitality at the end of MIS4 and affected the seas south of the study area.NAC only weakened for a short time in the early and end of MIS2,and MIS2 affected the northern part of the study area in a short period of time;The early warm phase of MIS 3corresponds to the strong North Atlantic warm current.The North Atlantic warm current gradually weakens in the mid-late MIS 3,and the Labrador cold current becomes stronger.During the MIS1(Holocene)period,it was mainly affected by the North Atlantic warm current,and the Labrador cold current was weaker.During the H1 and Younger Dryas events,the Labrador cold current was strengthened for a short time.