Recent 210 Pb, 137 Cs and 241 Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)

Over the past 50 years, 210Pb, 137Cs and 241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of 222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for 210Pb, 137Cs and 241Am radionuclides using an underground ultra-low background gamma spectrometer. The 210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and 241Am) that are related to nuclear weapon tests. We compared the AMS 210Pb data with an updated 210Pb deposition database. The 210Pb flux of 98 ± 6 Bq·m−2·y−1 derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced 222Rn activity and frequent rainfall in AMS. This enhanced 222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The 210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low 222Rn activities. We report a 137Cs inventory at AMS of 144 ± 13 Bq·m−2 (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere

Unequal Anthropogenic Enrichment of Mercury in Earth's Northern and Southern Hemispheres

Remote Northern Hemisphere (NH) and Southern Hemisphere (SH) lake sediment and peat records of mercury (Hg) deposition have shown a ×3 to ×5 Hg enrichment since pre-industrial times (<1880 AD), leading to the perception that global atmospheric Hg enrichment is moderate and uniform across the hemispheres. Anthropogenic Hg emissions in the NH are, however, approximately 4 times higher than those in the SH. Here, we reconstruct atmospheric Hg deposition in four remote SH peatlands and review sediment and peat Hg records from both hemispheres. We observe a ×4 all-time enrichment in SH Hg deposition from pre-anthropogenic (<1450 AD) to the late 20th-century periods, which is lower than the large ×16 all-time enrichment in NH Hg deposition. We attribute this difference to lower anthropogenic Hg emissions in the SH, and higher natural atmospheric SH Hg concentrations, supported by ×2 higher natural background Hg accumulation in SH peat records. We suggest that the higher SH natural atmospheric Hg deposition reflects the SH land-ocean distribution, and is driven by important SH marine Hg emissions. Our findings indicate that atmospheric Hg background levels and anthropogenic enrichment in both hemispheres are different and should be taken into account in international Hg assessments and environmental policy

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors

De rol van terrestrisch Sub-Antarctica binnen het klimaats­onderzoek op wereldvlak

Past climate change is studied in terrestrial, deep ocean and ice cores. For the last ten years, climatological research has been focused on climatic connections between data from different sources and environments on earth and on the driving mechanism behind these climatic connections. The North Atlantic region is the best known region only because of the many palaeoclimatological data present in this area. Past climate change in the Southern Hemisphere has been attained especially by research of Antarctic ice cores. The number of studies of terrestrial and oceanic cores in the Southern Hemisphere is lower than in the north. The significance of the sub-Antarctic region for the palaeoclimatological discussion has been rather ‘neglected’ in the past. However, the restricted published data and our own research show that sub-Antarctic islands have a great potential for high resolution terrestrial palaeoclimatological research. Moreover, these islands represent the only terrestrial archives in the circum-Antarctic ocean

Nathalie Van der Putten, Paléoécologie et paléoclimatologie des îles sub-antarctiques pour la période post-pléniglaciaire, Thèse d’université soutenue le 16 juin 2008 à l’université de Gand (Belgique), Département de géographie, faculté des sciences. Thèse en cotutelle, université Paul Cézanne (Aix-Marseille III), faculté des sciences de Saint-Jérôme

Van der Putten Nathalie. Nathalie Van der Putten, Paléoécologie et paléoclimatologie des îles sub-antarctiques pour la période post-pléniglaciaire, Thèse d’université soutenue le 16 juin 2008 à l’université de Gand (Belgique), Département de géographie, faculté des sciences. Thèse en cotutelle, université Paul Cézanne (Aix-Marseille III), faculté des sciences de Saint-Jérôme. In: Ecologia mediterranea, tome 34,2008. pp. 92-93

Nathalie Van der Putten, Paléoécologie et paléoclimatologie des îles sub-antarctiques pour la période post-pléniglaciaire, Thèse d’université soutenue le 16 juin 2008 à l’université de Gand (Belgique), Département de géographie, faculté des sciences. Thèse en cotutelle, université Paul Cézanne (Aix-Marseille III), faculté des sciences de Saint-Jérôme

Van der Putten Nathalie. Nathalie Van der Putten, Paléoécologie et paléoclimatologie des îles sub-antarctiques pour la période post-pléniglaciaire, Thèse d’université soutenue le 16 juin 2008 à l’université de Gand (Belgique), Département de géographie, faculté des sciences. Thèse en cotutelle, université Paul Cézanne (Aix-Marseille III), faculté des sciences de Saint-Jérôme. In: Ecologia mediterranea, tome 34,2008. pp. 92-93