Wenshen Xiao

Ice rafting history and paleoceanographic reconstructions of Core 08P23 from southern Chukchi Plateau, western Arctic Ocean since Marine Isotope Stage 3

Multiproxy investigations have been performed on Core 08P23 collected from the Chukchi Plateau, the western Arctic Ocean, during the Third Chinese National Arctic Expedition. The core was dated back to Marine Isotope Stage (MIS) 3 by a combination of Accelerator Mass Spectrometric (AMS) carbon-14 dating and regional core correlation. A total of five prominent ice-rafted detritus (IRD) events were recognized in MIS 2 and MIS 3. The IRD sources in MIS 3 are originated from vast carbonate rock outcrops of the Canadian Arctic Archipelago and clastic quartz in MIS 2 may have a Eurasian origin. Most 18O and 13C values of Neogloboquadrina pachyderma (sinistral) (Nps) in Core 08P23 are lighter than the average values of surface sediments. The lighter 18O and 13C values of Nps in the two brown layers in MIS 1 and MIS 3 were resulted from meltwater events; and those in the gray layers in MIS 3 were caused by the enhanced sea ice formation. The 18O values varied inversely with 13C in MIS 2 indicate that the study area was covered by thick sea ice or ice sheet with low temperature and little meltwater, which prevented the biological productivity and sea-atmosphere exchange, as well as water mass ventilation. The covaried light values of 18O and 13C in MIS 1 and MIS 3 were resulted from meltwater and/or brine injection.

Paleoenvironmental implications of Holocene long-chain n -alkanes on the northern Bering Sea Slope

The records of high-resolution terrestrial biological markers (biomarkers) from Core B2-9 from the northern Bering Sea Slope over the last 9.6 ka BP were presented in the study. Variations in input of terrestrial long-chain nalkanes (referred to as n-alkanes) and vegetation structure in their source regions were investigated. The results show that the nC27 is the main carbon peak and has the greatest contribution rate of the total n-alkane content; this might be related to the abundance of woody plants and their spatial distribution in the source region. nC23 is another n-alkane having a relatively high content; this was mainly derived from submerged plants widespread along the coastal areas in the northern hemisphere. Total n-alkane content dropped quickly at ca. 7.8 ka BP, ca. 6.7 ka BP and ca. 5.4 ka BP, and was followed by four relatively stable stages mostly controlled by sea-level rise, climate change and vegetation distribution in the source region. Variation in carbon preference index (CPI) indicates that the n-alkanes primarily originated from higher land plants, and the average chain length (ACL) and nC31/nC27 ratio reveal the relatively stable presence of woody/herbaceous plants during the Holocene, and dominate woody plants in most of the time. Simultaneous variation in total n-alkane content, nC27 content and its contribution, CPI, ACL and nC31/nC27 ratio over several short periods suggest that the growth rate of the woody plant n-alkane contribution was lower than that of herbaceous plants and fossil n-alkanes under the particular climatic conditions of the source region.

Late Quaternary Deep Stratification‐Climate Coupling in the Southern Ocean: Implications for Changes in Abyssal Carbon Storage

The Southern Ocean plays an important role in modulating Pleistocene atmospheric CO2 concentrations, but the underlying mechanisms are not yet fully understood. Here, we report the laser grain-size distribution and Mn geochemical data of a 523 kyr-long sediment record (core ANT30/P1-02 off Prydz Bay; East Antarctica) to trace past physical changes in the deep Southern Ocean. The core sediments are predominantly composed of clay and silt-sized material. Three grain size end-members (EM) as well as three sensitive grain size classes (SC) were discerned, interpreted as Ice Rafted Debris (EM1 and SC1), and coarse (EM2 and SC2) and fine (EM3, SC3) materials deposited from bottom nepheloid layers, respectively. Ratios of EM2/(EM2+EM3) and SC2/SC3 reveal changes in the local bottom current strength, which is related to the deep ocean diapycnal mixing rate, showing higher values during interglacial periods and lower values during glacial periods. MnO was enriched at each glacial termination, probably caused by abrupt elevations in Antarctic bottom water (AABW) formation rate. Lower AABW formation rate and reduced deep diapycnal mixing during glacial periods enhanced deep Southern Ocean stratification, contributing to glacial atmospheric CO2 drawdown. The elevated AABW formation and enhanced deep diapycnal mixing during glacial terminations alleviated such deep stratification, promoting deeply sequestered CO2 to outgas.

Paleoceanographic records in the Chukchi Basin, western Arctic Ocean during the late Quaternary

The late Quaternary paleoceanographic changes in the western Arctic Ocean are revealed by quantitative studies of foraminiferal abundance, ice-rafted detritus (IRD) and its mineralogical and petrological compositions, planktonic Neogloboquadrina pachyderma (sin.) (Nps)-δ18O and -δ13C, biogenic and non-biogenic components in Core M03 token from the Chukchi Basin during the Second Chinese National Arctic Expedition cruise. Seven IRD events appeared at MIS 7, 5, 3 and 1. These IRD were carried in massive icebergs, which were exported to the Beaufort Sea through the M’Clure Strait Ice Stream, Canadian Arctic Archipelago, and then transported into the Chukchi Basin by the Beaufort Gyre. Low IRD deposition occurred during the glacial times when more extended ice cover and weakened Beaufort Gyre, while the open water condition and the intensified Beaufort Gyre during interglacial periods favored the IRD deposition. Therefore, the IRD events not only indicate the provenance of coarser detritus and ice export events, but also reflect the evolutionary histories of the Beaufort Gyre and North American ice sheet. Seven light Nps-δ18O and -δ13C excursions could respond to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines, but was irrelevant to the warm Atlantic water and freshwater inputs. Whereas, the heavy Nps-δ18O and -δ13C values separately reflect the lessened Arctic freshwater and Pacific water, and well-ventilated surface water from the continental shelf and halocline water. Variations of CaCO3 content and planktonic foraminiferal abundance during the interglacial and glacial periods can demonstrate the incremental or diminishing input of the Atlantic water, while the total organic carbon (TOC) and opal contents increased and decreased during the glacial and interglacial periods, respectively, which could be related to the TOC degradation, opal dissolution and redox conditions of interface between the bottom water and sediments.