Multiproxy analyses including hydrographical, geochemical, foraminferal, lithological and geophysical data reveal variable influences of the glaciers Tunabreen and von Postbreen as well as the river Sassenelva on the sedimentary environment in two Spitsbergen fjords during the Late Weichselian and the Holocene. Grounded ice covered the study area during the last glacial. The glacier fronts retreated stepwise during the latest Weichselian/earliest Holocene, and the glaciers were probably small during the early Holocene. A growth of Tunabreen occurred between 6 and 4 cal ka BP. Reduced input from Tunabreen from c. 3.7 cal ka BP was probably a result of suppressed iceberg rafting related to the enhanced formation of sea ice and/or reduced meltwater runoff. During the past two millennia, the glacier fronts advanced and retreated several times. The maximum Holocene glacier extent was reached at the end of a surge of von Postbreen in AD 1870. Characteristics of the modern glaciomarine environment include: (1) different colours and bulk-mineral assemblages of the turbid waters emanating from the main sediment sources; (2) variable locations of the turbid-water plumes as a consequence of wind forcing and the Coriolis effect; (3) stratified water masses during summers with interannual variations; (4) increasing productivity with increasing distance from the glacier fronts; (5) foraminifera-faunal assemblages typical for glacierproximal settings; and (6) periodical mass-transport activity.
Three marine sediment cores were collected along the length of the fjord axis of Barilari Bay, Graham Land, west Antarctic Peninsula (65°55′S, 64°43′W). Multi-proxy analytical results constrained by high-resolution geochronological methods (210Pb, radiocarbon, 137Cs) in concert with historical observations capture a record of Holocene paleoenvironmental variability. Our results suggest early and middle Holocene (>7022–2815 cal. [calibrated] yr B.P.) retreated glacial positions and seasonally open marine conditions with increased primary productivity. Climatic cooling increased sea ice coverage and decreased primary productivity during the Neoglacial (2815 to cal. 730 cal. yr B.P.). This climatic cooling culminated with glacial advance to maximum Holocene positions and expansion of a fjord-wide ice shelf during the Little Ice Age (LIA) (ca. 730–82 cal. yr B.P.). Seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming (82 cal. yr B.P. to present). Our findings agree with previously observed late Holocene cooling and glacial advance across the Antarctic Peninsula, suggesting that the LIA was a regionally significant event with few disparities in timing and magnitude. Comparison of the LIA Antarctic Peninsula record to the rest of the Southern Hemisphere demonstrates close synchronicity in the southeast Pacific and southern most Atlantic region but less coherence for the southwest Pacific and Indian Oceans. Comparisons with the Northern Hemisphere demonstrate that the LIA Antarctic Peninsula record was contemporaneous with pre-LIA cooling and sea ice expansion in the North Atlantic–Arctic, suggesting a global reach for these events.
As the western North Pacific Ocean is located downwind of the source regions for spring Asian dust, it is an ideal location for determining the response of open waters to these events. Spatial analysis of spring Asian dust events from source regions to the western North Pacific, using long‐term daily aerosol index data, revealed three different transport pathways supported by the westerly wind system: one passing across the northern East/Japan Sea (40°N–50°N), a second moving over the entire East/Japan Sea (35°N–55°N), and a third flowing predominantly over the Siberian continent (>50°N). Our results indicate that strong spring Asian dust events can increase ocean primary productivity by more than 70% (>2‐fold increase in chlorophyll‐a concentrations) compared to weak/nondust conditions. Therefore, attention should be paid to the recent downturn in the number of spring Asian dust events and to the response of primary production in the western North Pacific to this change.
During the summer, from 1996–2000, vertical profiles of conductivity, temperature and transmissivity were obtained near the tidewater glacier of Marian Cove, King George Island, Antarctic Peninsula. The aims for the study were to determine the short-term variations of water structure due to hydrographic forcings and to understand sedimentation of suspended particulate matter in Antarctic fjord environments. Four distinct water layers were identified in the ice-proximal zone of the cove: i) a surface layer composed of cold and turbid meltwater, ii) a relatively warm Maxwell Bay inflow layer with characteristics of outer fjord water, iii) a turbid/cold mid-depth layer (40–70 m) originating from subglacial discharge, and iv) a deep layer comprised of the remnant winter water. The main factor influencing the characteristics of glacial meltwater layers and driving deposition of suspended particles in the cove is tidal forcing coupled with wind stress. The relatively small amount of meltwater discharge in Marian Cove yields low accumulation rates of non-biogenic sedimentary particles in the cove. The response to north-western and western winds, coupled with flood tide, may promote settling and sedimentation of suspended particles from turbid layers in the ice-proximal zone of the cove.
15 April 2022 in Paleoceanography and Paleoclimatology
Quantification of ice rafted debris (IRD) abundances in deep‐sea records is often used as a key proxy for identifying links between ice sheet instability and the oceanic overturning circulation. There currently exist multiple methods to determine IRD content in deep‐sea sediment cores. The preference for a given method is often determined by the accessibility to core material and destructive nature of some methods. While many studies have discussed the caveats between linking IRD to ice sheet dynamics, the uncertainties relating to the methodological approaches are often not considered in the interpretation or comparisons between different IRD datasets, particularly in the Antarctic. To address this, we compare three independent methodologies of obtaining IRD abundances and also discuss how different approaches will affect determinations of mass accumulation rates (MARs). The three methodologies we examine include: counting clasts >2 mm in x‐radiographs; the sieved weight percentage of the medium‐to‐coarse sand fraction (250 μm–2 mm); and volumetric estimates of the >125 μm sand fraction using laser diffraction particle size analysis. The x‐radiograph and sieve methods produced comparable results, while the laser particle size analysis, although showing comparable long‐term signals at most locations, in general has lower correlation to the other two methods and therefore a higher potential to obtain a noisy signal. We discuss the caveats associated with all methods, and emphasize that a combination of multiple methods should ideally be employed when assessing if a core is suitable for IRD study, and if sand or gravel fractions are accurately reflecting contents of IRD.