[M-IS06] Evolution and variability of the Tropical Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS06-05] Northernmost Patagonian Ice Sheet history during the last glacial period revealed by Be isotopes analysis on marine sediment

*Karin Nemoto^1,2, Yusuke Yokoyama^1,2, Adam David Sproson³, Yosuke Miyairi², Takahiro AZE², Yair Rosenthal⁴, Samantha Bova⁵, Hailey Riechelson⁴ (1.Department of Earth and Planetary Science, The University of Tokyo, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.National Oceanography Centre, 4.Department of Marine Science, Rutgers University, 5.San Diego State University)

Keywords:Patagonian Ice Sheet, Be isotopes, The last glacial period, marine sediment, geochemistry

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 (T_1/2 = 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.