“…The core top age obtained at WRS_CH agrees with those reported by ref. 50 and confirms the decreasing trend of DC contamination towards the northern WRS 48 . The corrected AMS 14 C dates were then converted into calibrated ages using the CALIB REV 7.1.0 calibration program 51 and the MARINE13 calibration curve.…”
The causes of the recent increase in Antarctic sea ice extent, characterised by large regional contrasts and decadal variations, remain unclear. In the Ross Sea, where such a sea ice increase is reported, 50% of the sea ice is produced within wind-sustained latent-heat polynyas. Combining information from marine diatom records and sea salt sodium and water isotope ice core records, we here document contrasting patterns in sea ice variations between coastal and open sea areas in Western Ross Sea over the current interglacial period. Since about 3600 years before present, an increase in the efficiency of regional latent-heat polynyas resulted in more coastal sea ice, while sea ice extent decreased overall. These past changes coincide with remarkable optima or minima in the abundances of penguins, silverfish and seal remains, confirming the high sensitivity of marine ecosystems to environmental and especially coastal sea ice conditions.
“…The core top age obtained at WRS_CH agrees with those reported by ref. 50 and confirms the decreasing trend of DC contamination towards the northern WRS 48 . The corrected AMS 14 C dates were then converted into calibrated ages using the CALIB REV 7.1.0 calibration program 51 and the MARINE13 calibration curve.…”
The causes of the recent increase in Antarctic sea ice extent, characterised by large regional contrasts and decadal variations, remain unclear. In the Ross Sea, where such a sea ice increase is reported, 50% of the sea ice is produced within wind-sustained latent-heat polynyas. Combining information from marine diatom records and sea salt sodium and water isotope ice core records, we here document contrasting patterns in sea ice variations between coastal and open sea areas in Western Ross Sea over the current interglacial period. Since about 3600 years before present, an increase in the efficiency of regional latent-heat polynyas resulted in more coastal sea ice, while sea ice extent decreased overall. These past changes coincide with remarkable optima or minima in the abundances of penguins, silverfish and seal remains, confirming the high sensitivity of marine ecosystems to environmental and especially coastal sea ice conditions.
“…resting spores, Corethron pennatum, Rhizosolenia spp. or mixed diatom species assemblages were reported from sediments deposited from 13 267 to 9809 14 C a BP (uncorrected ages interpolated between AIO ages) in the Mertz-Ninnis Trough , while diatomaceous ooze laminae dominated by Corethron pennatum, Hyalochaete Chaetoceros resting spores and Fragilariopsis curta were deposited between 10 920 AE 50 and 9130 AE 40 (both AIO ages) 14 C a BP in Cape Hallett Bay in the western Ross Sea (Finocchiaro et al, 2005).…”
Section: Chronology Of Postglacial Sedimentation On the Inner Shelf Omentioning
Reliable dating of glaciomarine sediments deposited on the Antarctic shelf since the Last Glacial Maximum (LGM) is challenging because of the rarity of calcareous (micro-) fossils and the recycling of fossil organic matter. Consequently, radiocarbon ( 14 C) ages of the acid-insoluble organic fraction (AIO) of the sediments bear uncertainties that are difficult to quantify. Here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the western Amundsen Sea (West Antarctica). In three cores conventional 14 C dating of the AIO in bulk samples yielded age reversals down-core, but at all sites the AIO 14 C ages obtained from diatomaceous ooze within the diatom-rich unit yielded similar uncorrected 14 C ages between 13 517 AE 56 and 11 543 AE 47 years before present (a BP). Correction of these ages by subtracting the core-top ages, which probably reflect present-day deposition (as indicated by 210 Pb dating of the sediment surface at one core site), yielded ages between ca. 10 500 and 8400 cal. a BP. Correction of the AIO ages of the diatomaceous ooze by only subtracting the marine reservoir effect (MRE) of 1300 a indicated deposition of the diatom-rich sediments between 14 100 and 11 900 cal. a BP. Most of these ages are consistent with age constraints between 13.0 and 8.0 ka for the diatom-rich unit, which we obtained by correlating the relative palaeomagnetic intensity (RPI) records of three of the sediment cores with global and regional reference curves. As a third dating technique we applied conventional radiocarbon dating of the AIO included in acid-cleaned diatom hard parts extracted from the diatomaceous ooze. This method yielded uncorrected 14 C ages of only 5111 AE 38 and 5106 AE 38 a BP, respectively. We reject these young ages, because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for 14 C dating. The deposition of the diatom-rich unit in the western Amundsen Sea suggests deglaciation of the inner shelf before ca. 13 ka BP. The deposition of diatomaceous oozes elsewhere on the Antarctic shelf around the same time, however, seems to be coincidental rather than directly related.
“…Sediment cores from the basin recovered a very expanded Holocene sequence characterized by soft biogenic laminated sediments. The lamination corresponds to several bloom cycles of diatoms species 22,23 . The thick Holocene sequence contains a very detailed Holocene paleoenvironmental and paleoclimatic record for the last 4.5 ka that is undergoing investigation.Figure 1( A ) Map of Antarctica showing the locations of BAY05-c20 core (red dot), Antarctic deep and shallow ice cores and blue ice field (yellow dots) where the 1254 C.E.…”
We report the discovery of an important new cryptotephra within marine sediments close to Cape Hallett (northern Victoria Land), in the western Ross Sea, Antarctica. The cryptotephra is fully characterized for its texture, mineralogy and major- and trace-element data obtained on single glass shards. On the basis of geochemical composition, the cryptotephra is unequivocally correlated with the proximal deposits of an explosive eruption of the poorly known Mount Rittmann volcano, situated in northern Victoria Land. The cryptotephra is also correlated with a widespread tephra layer, which was erupted in 1254 C.E. and is present in numerous ice-cores and blue ice fields across East and West Antarctica. The characteristics of the tephra indicate that it was produced by a prolonged, moderate energy, mostly hydromagmatic eruption. This is the first time that a cryptotephra has been identified in marine sediments of the Ross Sea and in ice cores. It provides an important new and widespread stratigraphical datum with which the continental cryosphere and marine sedimentological records in Antarctica can be correlated. Moreover, from a purely volcanological point of view, the discovery further confirms the occurrence of a long-lasting, significant explosive eruption from Mount Rittmann in historical times that produced abundant widely dispersed fine ash. The study also highlights the inadequacy of current hazard assessments for poorly known volcanoes such as Mount Rittmann, located at high southern latitudes.
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