10:15 〜 10:30
[MIS06-05] Northernmost Patagonian Ice Sheet history during the last glacial period revealed by Be isotopes analysis on marine sediment
キーワード：パタゴニア氷床、ベリリウム同位体、最終氷期、海洋堆積物、地球化学
History of the Patagonian Ice Sheet has been revealed by various technique such as cosmogenic nuclide (10Be and 26Al) exposure dating of boulders on a moraine crest, radiocarbon dating on materials existed ice-free conditions and optically stimulated luminescence dating of outwash plains. However, the relatively large age uncertainty of dating results and limited distribution of datable material hinder Patagonian Ice Sheet reconstruction, especially around the northernmost Patagonian Ice Sheet during the last glacial period. Here, we performed reactive phase of beryllium isotopes (10Be and 9Be) analysis on marine sediment Core J1007A recovered from Chilean margin (36.5°S), where detritus from the northern edge of the Patagonian Ice Sheet deposit.
The stable isotope 9Be is present in silicate rocks and is released to rivers during chemical weathering. The cosmogenic radionuclide 10Be (T1/2 = 1.39Myr) is produced by the interaction of cosmic rays with oxygen and nitrogen in the atmosphere and deposited onto the Earth’s surface via precipitation or dust. Seawater is enriched in 10Be due to the accumulation of atmospheric inputs. On the other hand, fresh water is enriched in 9Be sourced from continental weathering in river catchments. This leads to the accumulation of reactive phases from distinct 10Be/9Be environments that can be used to reconstruct terrestrial vs. open ocean mixing in the past. The variation of reactive phase 10Be/9Be ratio from Site J1002 on the Chilean margin (46°S) corresponded to the Patagonian Ice Sheet activities during the last glacial period. Thus, it is expected that the fluctuation of the Patagonian Ice Sheet can be revealed by Be isotopes analysis.
10Be/9Be ratio obtained was mainly controlled by the fluctuation of the Patagonian Ice Sheet which had been controlled the mixing of ocean and terrestrial endmember values of 10Be/9Be. Our 10Be/9Be data revealed that the size of the ice sheet in the northernmost Patagonian Ice sheet is larger than modeling results. Moreover, existing 10Be/9Be ratio and our data show that the rate of the volume change of the Patagonian Ice Sheet during the last deglaciation was faster than the period of the glaciation to Marine Isotope Stage 2. Glacier and Ice sheet in the southwest part of Pacific and the Northern Hemisphere also experienced similar pattern of ice volume change to South America. Our research also highlights that potential of beryllium isotope analysis on marine sediments for reconstructing ice sheet variability on centennial or millennial time scale.
The stable isotope 9Be is present in silicate rocks and is released to rivers during chemical weathering. The cosmogenic radionuclide 10Be (T1/2 = 1.39Myr) is produced by the interaction of cosmic rays with oxygen and nitrogen in the atmosphere and deposited onto the Earth’s surface via precipitation or dust. Seawater is enriched in 10Be due to the accumulation of atmospheric inputs. On the other hand, fresh water is enriched in 9Be sourced from continental weathering in river catchments. This leads to the accumulation of reactive phases from distinct 10Be/9Be environments that can be used to reconstruct terrestrial vs. open ocean mixing in the past. The variation of reactive phase 10Be/9Be ratio from Site J1002 on the Chilean margin (46°S) corresponded to the Patagonian Ice Sheet activities during the last glacial period. Thus, it is expected that the fluctuation of the Patagonian Ice Sheet can be revealed by Be isotopes analysis.
10Be/9Be ratio obtained was mainly controlled by the fluctuation of the Patagonian Ice Sheet which had been controlled the mixing of ocean and terrestrial endmember values of 10Be/9Be. Our 10Be/9Be data revealed that the size of the ice sheet in the northernmost Patagonian Ice sheet is larger than modeling results. Moreover, existing 10Be/9Be ratio and our data show that the rate of the volume change of the Patagonian Ice Sheet during the last deglaciation was faster than the period of the glaciation to Marine Isotope Stage 2. Glacier and Ice sheet in the southwest part of Pacific and the Northern Hemisphere also experienced similar pattern of ice volume change to South America. Our research also highlights that potential of beryllium isotope analysis on marine sediments for reconstructing ice sheet variability on centennial or millennial time scale.