09:15 〜 09:30
[BCG06-02] Holocene Antarctic subglacial weathering and ice-sheet history reconstructed using the 10Be/9Be ratios of lake Maruwan Oike sediments
キーワード：Beryllium, Holocene, Antarctica, Weathering, Glacier
Glaciers play an important role in the climate system via freshwater storage and the transportation of various materials from the continents to the oceans. Enhanced discharge of the former during melting events can influence global sea-level, while enhanced silicate weathering resulting from the latter can drive a reduction in atmospheric CO2. Although these processes are known to be important through geological time, temporal changes in chemical weathering intensity and meltwater flux for the East Antarctic Ice Sheet (EAIS) are not well understood. During the last deglaciation, the EAIS retreated significantly (1, 2), forming isolated basins via glacio-hydro-isostatic adjustment (GIA) related crustal uplift. Sediment accumulated in these lakes provide a unique record of subglacial weathering and ice-sheet history throughout deglaciations when global temperatures and pCO2most notably rose.
Meteoric 10Be is produced in the atmosphere by cosmic rays and delivered to the Earth and ocean surface via dust and precipitation. In Antarctica, these sources of 10Be become locked up in ice sheets and are subsequently released to the continental shelf during periods of melting and freshwater discharge (3), where they adhere to suspended particles in the water column and subsequently accumulate on the basin floor (4, 5). Stable 9Be is present in silicate rocks and is released during subglacial weathering (5), with little simultaneous release of 10Be (4), and transported to the oceans via meltwater outflow. When Be is incorporated into the authigenic phase of marine sediments, the 10Be/9Be reflects that of the overlying water column (6), which in turn reflects the relative dominance of freshwater flux and/or subglacial weathering.
Here, we present authigenic 10Be/9Be ratios for a sedimentary core from Lake Maruwan Oike situated at the head of the Rundvåg glacier in the Lützow-Holm Bay area of East Antarctica. Sedimentary material from L. Maruwan Oike provides an ~6,000 year record of subglacial weathering and nutrient input from the nearby glacier (7). Authigenic 10Be/9Be records reflect variations in freshwater flux and subglacial weathering and indicate several periods of enhanced melting of the Rundvåg glacier. This study provides further constraints on EAIS fluctuations during the Holocene and offers an insight into the behaviour of beryllium in high-latitude subglacial-marine systems.
Reference
1. M. Yamaneet al., The last deglacial history of Lützow-Holm Bay, East Antarctica. Journal of Quaternary Science 26, 3-6 (2011).
2. A. N. Mackintoshet al., Retreat history of the East Antarctic Ice Sheet since the Last Glacial Maximum. Quaternary Science Reviews 100, 10-30 (2014).
3. Q. Simonet al., Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications. Quaternary Science Reviews 140, 142-162 (2016).
4. R. P. Schereret al., Pleistocene Collapse of the West Antarctic Ice Sheet. Science 281, 82 (1998).
5. C. Sjunneskog, R. Scherer, A. Aldahan, G. Possnert, 10Be in glacial marine sediment of the Ross Sea, Antarctica, a potential tracer of depositional environment and sediment chronology. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259, 576-583 (2007).
6. F. von Blanckenburg, J. Bouchez, River fluxes to the sea from the oceanʼs 10Be/9Be ratio. Earth and Planetary Science Letters 387, 34-43 (2014).
7. Y. Takano, H. Kojima, E. Takeda, Y. Yokoyama, M. Fukui, Biogeochemistry and limnology in Antarctic subglacial weathering: molecular evidence of the linkage between subglacial silica input and primary producers in a perennially ice-covered lake. Progress in Earth and Planetary Science 2, 8 (2015).
Meteoric 10Be is produced in the atmosphere by cosmic rays and delivered to the Earth and ocean surface via dust and precipitation. In Antarctica, these sources of 10Be become locked up in ice sheets and are subsequently released to the continental shelf during periods of melting and freshwater discharge (3), where they adhere to suspended particles in the water column and subsequently accumulate on the basin floor (4, 5). Stable 9Be is present in silicate rocks and is released during subglacial weathering (5), with little simultaneous release of 10Be (4), and transported to the oceans via meltwater outflow. When Be is incorporated into the authigenic phase of marine sediments, the 10Be/9Be reflects that of the overlying water column (6), which in turn reflects the relative dominance of freshwater flux and/or subglacial weathering.
Here, we present authigenic 10Be/9Be ratios for a sedimentary core from Lake Maruwan Oike situated at the head of the Rundvåg glacier in the Lützow-Holm Bay area of East Antarctica. Sedimentary material from L. Maruwan Oike provides an ~6,000 year record of subglacial weathering and nutrient input from the nearby glacier (7). Authigenic 10Be/9Be records reflect variations in freshwater flux and subglacial weathering and indicate several periods of enhanced melting of the Rundvåg glacier. This study provides further constraints on EAIS fluctuations during the Holocene and offers an insight into the behaviour of beryllium in high-latitude subglacial-marine systems.
Reference
1. M. Yamaneet al., The last deglacial history of Lützow-Holm Bay, East Antarctica. Journal of Quaternary Science 26, 3-6 (2011).
2. A. N. Mackintoshet al., Retreat history of the East Antarctic Ice Sheet since the Last Glacial Maximum. Quaternary Science Reviews 100, 10-30 (2014).
3. Q. Simonet al., Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications. Quaternary Science Reviews 140, 142-162 (2016).
4. R. P. Schereret al., Pleistocene Collapse of the West Antarctic Ice Sheet. Science 281, 82 (1998).
5. C. Sjunneskog, R. Scherer, A. Aldahan, G. Possnert, 10Be in glacial marine sediment of the Ross Sea, Antarctica, a potential tracer of depositional environment and sediment chronology. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259, 576-583 (2007).
6. F. von Blanckenburg, J. Bouchez, River fluxes to the sea from the oceanʼs 10Be/9Be ratio. Earth and Planetary Science Letters 387, 34-43 (2014).
7. Y. Takano, H. Kojima, E. Takeda, Y. Yokoyama, M. Fukui, Biogeochemistry and limnology in Antarctic subglacial weathering: molecular evidence of the linkage between subglacial silica input and primary producers in a perennially ice-covered lake. Progress in Earth and Planetary Science 2, 8 (2015).