The relative abundances of 18 selected taxonomic groups of Radiolaria were determined for 145 trigger-weight core-top samples collected between long 80°E and 55°W and lat 35°S and 60°S. Seventy-two samples were considered to represent nonreworked recent sediments. A factor analysis of these 72 samples resolved Antarctic, subantarctic, and subtropical assemblages, with distributions closely corresponding to the main surface water masses in the area. Using the technique of Imbrie and Kipp, paleoecologic equations have been developed to estimate surface-water temperatures for August (winter) and February (summer). Estimated temperatures range from near 20°C in the northern parts of the area to 0°C at the location of the southernmost cores. The standard error of estimate of the equations is less than 1.5°C. The CaCO 3 content of the 145 surface-sediment samples shows that variations in the calcite compensation depth (CCD) for locations north of the Antarctic Polar Front depends mainly on varying dissolution. The CCD is about 4,800 m in the western basin of the Atlantic Ocean but is deeper than 5,200 m, at least locally, in the Indian Ocean. South of the Antarctic Polar Front the CCD is shallower than 3,700 m. Radiolaria are common in most samples, with the maximum number per gram of sediment being found in samples collected near or beneath the Antarctic Polar Front.

Using relative-abundance changes of the radiolarian Cycladophora davisiana calibrated using O 18 /O 16 values and C 14 ages, we have established a high-resolution biostratigraphy for the Antarctic and subantarctic ocean covering the past 150,000 yr. Extremes of this species' relative abundance have been estimated to have occurred approximately 18,000, 35,000, 60,000, 85,000, 105,000, and 120,000 yr ago. Crosscorrelation between O 18 /O 16 values and the most recent C. davisiana maximum shows that this maximum is isochronous over a broad area of the Antarctic and subantarctic sea floor. Using diverse stratigraphic criteria, we selected 34 cores from the Atlantic and western Indian Ocean sectors of the Antarctic and subantarctic ocean containing a strong C. davisiana relative-abundance maximum near the core top, believing that this maximum occurred approximately 18,000 yr ago in the Antarctic and subantarctic. Using techniques including radiolarian-based paleoecological equations, Radiolaria per gram of sediment, and percentage of calicum carbonate, we show that 18,000 yr ago the Antarctic Polar Front was displaced north of its present position by as much as 7° of latitude. The subtropical convergence was little changed from its present position ; consequently, the width of subantarctic waters was reduced. Using C. davisiana as a stratigraphie indicator, we estimate the sedimentation rate in one Antarctic core of the upper diatom-ooze layer (11.5 cm/1,000 yr) and the immediately underlying silty clay (2.7 cm/1,000 yr). The slower sedimentation rate of the silty clay strongly suggests that diatom production was inhibited during its deposition relative to production during deposition of the younger diatom ooze. We interpret this to indicate that summer ice cover extended nearly to lat 55°S 18,000 yr ago, whereas today it melts back to the Antarctic continent.

Abstract We present biogenic opal flux records from two deep-sea sites in the Scotia Sea (MD07-3133 and MD07-3134) at decadal-scale resolution, covering the last glacial cycle. In addition to conventional and time-consuming biogenic opal measuring methods, we introduce new biogenic opal estimation methods derived from sediment colour b *, wet bulk density, Si/Ti-count ratio and Fourier transform infrared spectroscopy (FTIRS). All methods capture the biogenic opal amplitude; however, FTIRS–a novel method for marine sediment – yields the most reliable results. 230 Th normalization data show strong differences in sediment focusing with intensified sediment focusing during glacial times. At MD07-3134 230 Th normalized biogenic opal fluxes vary between 0.2 and 2.5 g cm −2 kyr −1 . Our biogenic opal flux records indicate bioproductivity changes in the Southern Ocean, strongly influenced by sea ice distribution and also summer sea surface temperature changes. South of the Antarctic Polar Front, lowest bioproductivity occurred during the Last Glacial Maximum when upwelling of mid-depth water was reduced and sea ice cover intensified. Around 17 ka, bioproductivity increased abruptly, corresponding to rising atmospheric CO 2 and decreasing seasonal sea ice coverage.

Abstract This study of landscape evolution presents both new modern and palaeo process-landform data, and analyses the behaviour of the Antarctic Peninsula Ice Sheet through the Last Glacial Maximum (LGM), the Holocene and to the present day. Six sediment-landform assemblages are described and interpreted for Ulu Peninsula, James Ross Island, NE Antarctic Peninsula: (1) the Glacier Ice and Snow Assemblage; (2) the Glacigenic Assemblage, which relates to LGM sediments and comprises both erratic-poor and erratic-rich drift, deposited by cold-based and wet-based ice and ice streams respectively; (3) the Boulder Train Assemblage, deposited during a Mid-Holocene glacier readvance; (4) the Ice-cored Moraine Assemblage, found in front of small cirque glaciers; (5) the Paraglacial Assemblage including scree, pebble-boulder lags, and littoral and fluvial processes; and (6) the Periglacial Assemblage including rock glaciers, protalus ramparts, blockfields, solifluction lobes and extensive patterned ground. The interplay between glacial, paraglacial and periglacial processes in this semi-arid polar environment is important in understanding polygenetic landforms. Crucially, cold-based ice was capable of sediment and landform genesis and modification. This landsystem model can aid the interpretation of past environments, but also provides new data to aid the reconstruction of the last ice sheet to overrun James Ross Island.