17:15 〜 19:15
[U02-P05] Dust deposition and hydroclimate history revealed by Be isotope analysis on lake sediments from Lake Motosu during the Holocene
キーワード：ダスト、偏西風、ベリリウム同位体、富士山、モンスーン
We performed geochemical analysis on lake sediments recovered from Lake Motosu to reconstruct dust deposition and hydroclimate history during the Holocene. Aeolian quartz flux was determined by X-ray diffraction analysis to reveal dust deposition history (Nemoto et al., 2024). Be isotopes (10Be and 9Be) analysis was performed to reconstruct hydroclimate change.
Work on reconstructing past changes in dust transport in East Asia is complicated by difficulties in distinguishing local sedimentation from aerial material and lack of suitable material for age determination. We address these issues and present a new dust proxy record from Lake Motosu. The record is anchored by a high-quality tephra and radiocarbon chronology. Because Lake Motosu is situated in a quartz-free basaltic volcanic province, all quartz deposited in the lake is likely to be aerially sourced, and variations in quartz content should reflect past changes in dust transport. Nemoto et al. (2024) detects a low dust deposition event from 3.0 ka to 2.0 ka. This event corresponds to elevated sea surface temperature in the Sea of Japan and climate conditions similar to a negative phase of the Arctic Oscillation, indicating an association with weakened Westerlies and with less frequent dust storms in the source region. The increase in spatial resolution of past dust transport reconstructions will further improve our understanding of the mechanism related to dust emission from East Asia.
Using the same sediment core which analyzed by Nemoto et al. (2024), we newly reconstructed changes in hydroclimate using Be isotopes analysis as precipitation controls the processes of both isotopes’ deposition. The cosmogenic radionuclide 10Be (T1/2 = 1.39Myr) is produced by the interaction of cosmic rays with oxygen and nitrogen in the atmosphere (meteoric production), and deposited onto the Earth’s surface via precipitation or dust (Lal 1991). The stable isotope 9Be is present in silicate rocks and is released to rivers during chemical weathering. An advantage of using the ratio of 10Be to 9Be (10Be/9Be) is the removal of secondary effects such as grain size and dilution effects. We present Be isotope variations and compare them with the dust deposition history and proxy records from East Asia to reconstruct hydroclimate change associated with the East Asian Monsoon.
Reference
Karin Nemoto, Yusuke Yokoyama, Stephen P Obrochta, Yosuke Miyairi, Osamu Fujiwara, Shinya Yamamoto, Atsunori Nakamura, Aurelia Hubert Ferrari, Vanessa Heyvaert, Marc De Batist, 2024, A lake at the Mt. Fuji (Lake Motosu) recording prolonged negative Arctic Oscillation as reduction of aeolian dust due to westerly pathways during the Holocene, Paleoceanography and Paleoclimatology, 39(9), e2023PA004805, https://doi.org/10.1029/2023PA004805.
Work on reconstructing past changes in dust transport in East Asia is complicated by difficulties in distinguishing local sedimentation from aerial material and lack of suitable material for age determination. We address these issues and present a new dust proxy record from Lake Motosu. The record is anchored by a high-quality tephra and radiocarbon chronology. Because Lake Motosu is situated in a quartz-free basaltic volcanic province, all quartz deposited in the lake is likely to be aerially sourced, and variations in quartz content should reflect past changes in dust transport. Nemoto et al. (2024) detects a low dust deposition event from 3.0 ka to 2.0 ka. This event corresponds to elevated sea surface temperature in the Sea of Japan and climate conditions similar to a negative phase of the Arctic Oscillation, indicating an association with weakened Westerlies and with less frequent dust storms in the source region. The increase in spatial resolution of past dust transport reconstructions will further improve our understanding of the mechanism related to dust emission from East Asia.
Using the same sediment core which analyzed by Nemoto et al. (2024), we newly reconstructed changes in hydroclimate using Be isotopes analysis as precipitation controls the processes of both isotopes’ deposition. The cosmogenic radionuclide 10Be (T1/2 = 1.39Myr) is produced by the interaction of cosmic rays with oxygen and nitrogen in the atmosphere (meteoric production), and deposited onto the Earth’s surface via precipitation or dust (Lal 1991). The stable isotope 9Be is present in silicate rocks and is released to rivers during chemical weathering. An advantage of using the ratio of 10Be to 9Be (10Be/9Be) is the removal of secondary effects such as grain size and dilution effects. We present Be isotope variations and compare them with the dust deposition history and proxy records from East Asia to reconstruct hydroclimate change associated with the East Asian Monsoon.
Reference
Karin Nemoto, Yusuke Yokoyama, Stephen P Obrochta, Yosuke Miyairi, Osamu Fujiwara, Shinya Yamamoto, Atsunori Nakamura, Aurelia Hubert Ferrari, Vanessa Heyvaert, Marc De Batist, 2024, A lake at the Mt. Fuji (Lake Motosu) recording prolonged negative Arctic Oscillation as reduction of aeolian dust due to westerly pathways during the Holocene, Paleoceanography and Paleoclimatology, 39(9), e2023PA004805, https://doi.org/10.1029/2023PA004805.