Neogloboquadrina pachyderma is the most abundant planktonic foraminifera species found in the modern polar oceans.The δ18O and δ13C of N.pachyderma from the Western Arctic Ocean sediments were analyzed to reveal the implications of the proxies to environmental changes.The δ18O from N.pachyderma in the Chukchi Sea reflect the water mass distribution in this area.Heavier δ18O values were found along the Anadyr Current(AC) and lighter values in the central and eastern Chukchi Sea.These may reflect the freshwater signal from the Alaska Coastal Current(ACC) and Bering Sea Shelf Water(BSSW) .The light δ18O signature in the high Arctic basin comes from the freshwater stored in the Arctic surface layer.The δ13C distribution pattern in the Chukchi Sea is also influenced by the current system.High primary productivity along the AC results in heavy δ13C.The relatively low primary productivity and the freshwater component from the BSSW and ACC may be the reason for this light δ13C signal in the central and eastern Chukchi Sea.Our data reveal the importance of well ventilated Pacific Water through the Chukchi Sea into the Arctic Ocean.
Terrigenous components in sediment core B84A from the Alpha Ridge,Western Arctic Ocean,have been investigated to reconstruct Mid to Late Quaternary variations in sedimentation,provenance,and related climate changes. The core stratigraphy,evaluated by a combination of variations in Mn content,color cycles,foraminiferal abundance,and lithological correlation,extends back to estimated Marine Isotope Stage 12. Twelve Ice Rafted Detritus(IRD,>250 μm) events were identified and interpreted to mostly occur during deglaciation.The Canadian Arctic,which was covered by ice sheets during glacial periods,is suggested to be the major source region. The IRD events likely indicate the collapses of ice sheets,possibly in response to abrupt climate changes.Grain size analysis of B84A indicates sedimentologically sensitive components in core B84A in the 4-9 μm and 19-53 μm silt subfractions,which are inferred to be mainly transported by currents and sea ice,respectively. Down core variability of these two fractions may indicate changes in ice drift and current strength. In accordance with previous studies in the central Arctic Ocean,the average sedimentation rate in core B84A is about 0.4 cm·ka-1.Compared with the relatively high sedimentation rates on the margins,sedimentation in the central Arctic Ocean is limited by sea ice cover and the correspondingly low bioproductivity,as well as the long distance from source regions of terrigenous sediment.
LIU WeinanWANG RujianCHEN JianfangCHENG ZhenboCHEN ZhihuSUN Yechen
Primary productivity has played an important role in the global carbon cycle during the Quaternary. The average Corg/N ratio was 7.0 from the core MD97-2140 in the West Pacific Warm Pool (WPWP) over the last 1 755 ka, which indicates a main contribution of marine organic carbon to the organic matter in the sediments. Large fluctuations in mass accumulation rates (MARs) of biogenics and lithogenics from this core since the marine isotope stage (MIS) 6 reflected the moderate variability in oceanographic condition, while little fluctuations in MAR-biogenics and -lithogenics from the MIS 59 to MIS 7 implied the relatively stable and uniform oceanographic condition, although the sea surface temperatures (SSTs) probably fluctuated by ca. 5 ℃. MAR-organic since the MIS 6 increased evidently during the glacial periods, which ascribed to terrestrial inputs, including lithogenic matter and dissolved nutrient, which also contribute to stimulating primary productivity. The results compared among the four cores in the WPWP since the MIS 9 indicate that in the western sector with the shallow thermocline, high primary productivity during the glacial periods was controlled by wind-induced surface water mixing, upwelling, and terrestrial inputs, while in the central and eastern sectors, the little different medium to low productivity might have been made by more intense upwelling driven by strong winds because the thicker warm surface water pool and the deeper thermocline prevented nutrient-bearing water from upwelling to upper water column even during the glacial times.
