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Sea-ice diatom taxa (Fragilariopsis cylindrus and Fragilariopsis oceanica) and their relative abundance in the Okhotsk Sea were used to reconstruct the history of sea-ice distribution and atmospheric pressure patterns since the Last Glacial Maximum (LGM). The temporal state of sea-ice distribution and atmospheric pressure patterns since the LGM can be divided into three modes: northern Aleutian Low mode, southern Aleutian Low mode, and strong Siberian High mode. The Southern Aleutian Low mode was dominant before 15 ka and after 6.5 ka, respectively, showing expanded sea-ice distribution into the central and southern Okhotsk Sea. During the deglaciation period (15 ka to 10 ka), sea-ice retreated from the southern Okhotsk Sea because of the pronounced westerly winds under the strong Siberian High mode. However, sea-ice distribution expanded in the northern Okhotsk Sea, which favors the development of extensive polynyas on the northern continental shelf. Occurrences of northern Aleutian Low mode were frequent between 10 and 6.5 ka, while sea-ice distribution expanded into the eastern Okhotsk Sea. Formation of the Okhotsk Sea Intermediate Water, inferred from radiolarian species Cycladophora davisiana, intensified under both northern Aleutian Low mode and strong Siberian High mode.

A sediment core drilled from Lake Langer on King George Island was analyzed for a variety of textural and geochemical properties along with 14 C age dates. These data were combined with published records of other cores to provide a detailed history of Holocene variation of total organic carbon (TOC) con- tents with respect to terrestrial paleoclimate change. The lithologic contrast of the lower diamicton and upper fine-grained sediments shows the glacier activity and subsequent lake formation. Low TOC contents fluc- tuated during the diamicton deposition whereas the increase of TOC began with the lake formation during the postglacial period that started about 5,000 yr B.P. More notable are the distinct TOC peaks that may imply enhanced primary productivity during the warm period. The uniform and low TOC contents may reflect the limited productivity during the evolution of the lake. However, the recent TOC readvance clearly indicates gradual warming on King George Island. However, the paleoclimatic signature in the terrestrial lake envi- ronment during the Holocene seems to be subtle and less distinct, compared to the marine environment.

Marine sediment cores were obtained from in front of the tidewater glaciers in Marian and Potter coves in the South Shetland Islands in the austral summer of 1998–1999. Sedimentological and geochemical data from these cores document an advance of ice tongue for the deposition of clast-supported, massive diamicton, interpreted as having been produced by ice rafting in front of glacier margin and/or releasing of clasts from basal debris zones in the sub-ice tongue setting. A C-14 chronology for a core indicates that glacial advance took place ca. 1450–1700 yrs B.P., coincident with warm, humid phase in the study area. During this period, the glacier margin was likely to advance and release diamicton clasts, inferred from a reduction in the total organic carbon content, and an increase in sand and clasts within the diamicton facies. The glacial advance probably caused enhanced ice-edge blooms near the core sites, resulting in increased abundance of sea-ice related diatoms i.e.,Fragilariopsis curta andFragilariopsis cylindrus in the diamicton. The warm and humid conditions between 1450–1700 yrs B.P. might allow the intrusion of warm circumpolar deep water within the fjords, bringing about increased abundance of warm water form, i.e.,Fragilariposis kerguelensis. On the other hands, this warming condition probably prohibited the intrusion of Weddell Ice shelf water from the fjord, as evidenced by lack of cold water form,Thalassiosira antarctica, in the diamicton. Clearly, the response of the outlet glacier system along the periphery of the South Shetland Islands Ice Sheet during the late Holocene warm, humid period (1450–1700 yrs B.P.) was expansion. Thus the process of clast-supported massive diamicton formation is likely to be applicable to a number of areas of the modern and Quaternary Antarctic Peninsula.

Selected intervals of laminated diatom ooze (Holocene) from the eastern Bransfield Strait, Antarctic Peninsula were analyzed using high-resolution section images of impregnated samples to reveal potential annual-to-seasonal scale signatures of the lamination. The results show a probable seasonality within individual diatom ooze laminae which mainly reflects spring blooms ofChaetoceros followed by summer production ofCorethron orRhizosolenia. Alternating monospecific diatom ooze and terrigenous laminae are suggestive of annual cyclicities, representing alternation of diatom mass flux during the spring or autumn with terrigenous flux during the rest of year.

Core A9-EB2 from the eastern Bransfield Basin, Antarctic Peninsula, consists of pelagic (diatom ooze-clay couplets and bioturbated diatom ooze) and hemipelagic (bioturbated mud) sediments interbedded with turbidites (homogeneous mud and silt–clay couplets). The cyclic and laminated nature of these pelagic sediments represents alternation between the deposition of diatom-rich biogenic sediments and of terrigenous sediments. Sediment properties and geochemical data explain the contrasting lamination, with light layers being finer-grained and relatively rich in total organic carbon and biogenic silica content. Also, the high-resolution magnetic susceptibility (MS) variations highlight distinct features: high MS values coincide with clastic-rich sections and low MS values correspond to biogenic sections. The chronology developed for core A9-EB2 accounts for anomalous ages associated with turbidites and shows a linear sedimentation rate of approximately 87 cm/103 yr, which is supported by an accumulation rate of 80 cm/103 yr calculated from 210Pb activity. The late Holocene records clearly identify Neoglacial events of the Little Ice Age (LIA) and Medieval Warm Period (MWP). Other unexplained climatic events comparable in duration and amplitude to the LIA and MWP events also appear in the MS record, suggesting intrinsically unstable climatic conditions during the late Holocene in the Bransfield Basin of Antarctic Peninsula.

We used diatom and porewater data of two piston cores from the central subbasin and one from the western subbasin in the Bransfield Strait in the northern Antarctic Peninsula to elucidate the depositional mechanism of the layered diatom ooze. The layered diatom ooze is characterized by an abundance of organic carbon, biogenic silica, sulfde sulfur, and lower porewater sulfate concentration. This lack of pore-water sulfate concentration in the diatom ooze interval may reflect development of reducing micro-environment in which bacterially mediated sulfate reduction occurred. The negative relationship between the total organic carbon and sulfate contents, however, indicates that sulfate reduction was partly taking place but does not control organic carbon preservation in this unit. Rather, well-preserved Chaetoceros resting spores in the layered diatom ooze indicate a rapid sedimentation of the diatom as a result of repetitive iceedge blooms on the Bransfield shelf during the cold period (around 2500 yrs BP) when the permanent seaice existed on the shelf, During this period, it is expected that the downslope-flowing cold and dense water was also formed on the Bransfield shelf as a result of sea ice formation, playing an important role for the formation of layered diatom ooze in the Bransfield subbasins.

Analyses of sedimentological, geochemical and micropaleontological parameters from radiocarbon-dated sediment cores retrieved from the Antarctic Peninsula’s western continental shelf reveal a detailed paleoclimatic and/or paleoceanographic history over the last 15 000 radiocarbon years. Deglaciation of the outer shelf off Anvers Island commenced prior to at least 15 000 yr BP, marked by the deposition of distal glaciomarine diamicton (facies 2) beneath a floating ice shelf, and lasted for 3800 years with increasing diatom abundance and total organic carbon (TOC) over time. A return to colder conditions occurred between 12 800 and 11 600 yr BP with a drop in TOC content and diatom abundance, which is coincident with the Younger Dryas event in the North Atlantic region. At this time, an abrupt increase in percentage sea-ice taxa as well as in the ratio of ( Fragilariopsis curta+Fragilariopsis cylindrus )/ Thalassiosira antarctica suggests renewed ice-shelf advance. In contrast, the inner shelf was deglaciated somewhat later about 11 000 yr BP, that is, 3000 years after the outer shelf. Prior to 11 000 yr BP, deposition of proximal glaciomarine diamicton (facies 1) close to the grounding line under a floating ice shelf and/or persistent sea ice may have occurred on the inner shelf. After this date, deposition of distal glaciomarine diamicton (facies 2) followed. A climatic optimum is recognized between 6000 and 2500 yr BP, coinciding with a ‘mid-Holocene climatic optimum’ from several other Antarctic sites, e.g. the Palmer Deep. During this time, as the glacial system receded from the shelf, greatly enhanced primary productivity occurred in open marine conditions, resulting in the deposition of diatomaceous mud (facies 3) and causing post-depositional dissolution of calcareous benthic and planktonic foraminifers in sediment. Around 2500 yr BP (the onset of the Neoglacial), diatomaceous sandy mud (facies 4), characterized by a decrease in TOC and diatom abundance, reflects the formation of more extensive and seasonally persistent sea ice, as evidenced by an increase in percentage of sea-ice taxa and in the ratio of ( F. curta+F. cylindrus ) /T. antarctica . Our results provide evidence of climatic change on the Antarctic Peninsula’s western shelf that helps to refine the existence and timing of late Pleistocene and Holocene millennial-scale climatic events in the Southern Hemisphere.

A high-resolution study including oxygen and carbon stable isotopes as well as planktonic foraminifera, carbonate, ice-rafted debris (IRD) contents, were performed on one core sediment (DP00-02) taken from the seamount top near Antarctic Polar Front (APF) in the Drake Passage, Western Antarctica. Based on the oxygen stable isotope records measured onNeoglo-boquadrina pachyderma (sin.), this sediment core is interpreted to represent a stratigraphic record back to the lower isotope stage 5 (−129 kyr). Isotope stages 5, 4 and 1 show a high abundance of carbonate and planktonic foraminifer with relatively low IRD content. In contrast, isotope stages 3 and 2 are characterized by low abundance of carbonate with remarkably high IRD content. This is probably attributed by a local/regional influence due to front structural changes, related to the fluctuation of APF, i.e., the south and northward migration of polar water mass. The glacial-interglacial shifts in δ18O values ofN. pachyderma (sin.) may reach up to 1 to 1.2‰ indicating that, global ice volume changes have affected the isotope records. However, the isotope stage 3, generally interpreted as the less warmer period in the global record than Holocene and stage 5, corresponds to much lighter values compared to the global climate curve. This may be resulted from change in the salinity rather than change in the global ice volume or the temperature.

Total organic carbon (TOC), biogenic silica (Bsi), and total sulfur (TS) contents in core sediments of Maxwell Bay are examined in order to investigate paleoclimatic changes during the Holocene. Both TOC and Bsi contents generally show a downcore decrease, which reflects that primary productivity in surface waters has increased during the Holocene. In contrast, TS contents show a downcore increase, which is probably due to a decrease in terrigenous input of hydrothermal-origin pyrite. In Maxwell Bay, primary productivity was low prior to 4700 yr BP because sea ice permanently covered the surface. As the climate became relatively warm after 4700 yr BP, sea ice in surface waters sporadically melted, causing an increase in productivity. The climate probably became warm between about 4700 and 3000 yr BP, evidenced by the rapid increase in TOC and Bsi. Grounding glaciers were located near the core sites of Maxwell Bay prior to about 4700 yr BP. As the climate became warm, grounding glaciers have retreated and been located at the present site since about 3000 yr BP.

The subvolcanic granitic pluton in the Barton and Weaver Peninsulas, King George Island, is mainly composed of granodiorite with small volumes of gabbro, diorite and aplitic dikes. The pluton shows a vertically compositional zonation; the lower part consists of gabbro and diorite, whereas the upper part is mainly granodiorite. Various geochemical signatures of the pluton confirm that all subunits of the pluton were formed by accumulation and fractionation in a calc-alkaline magma at a shallow level of the crust. The positive Sr and Eu anomalies as well as textural features of gabbro strongly support that gabbro was the cumulate derived from accumulation of calcic plagioclase and in situ crystallization of ferromagnesian minerals. Taking into account the geochemical features of gabbro as a cumulate, the primary magma of the pluton is considered to have been intermediate (dioritic or quartz dioritic) in composition.