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[MIS16-14] Reconstruction of organic matter inflow fluctuations from the Bolling-Allerod interstadial to Late Holocene using Lake Baikal sediments
Keywords:Lake Baikal, TMAH method, Holocene
Stable oxygen isotope (d18O) records in ice cores obtained by the North Greenland Ice Core Project show climate change due to periodic temperature changes from 130,000 to 20,000 years ago. Whereas, the records show a more stable warm period during Holocene (present to 11,700 years ago) when comparing to the previous temperature changes. However, Bond et al. (1997) have reported that rapid climate change (RCC; Mayewski et al., 2004) has occurred in the Holocene. Most of such reports are discovered from marine area including the North Atlantic Ocean and the Indian Ocean regions, but the elucidation of the actual situation on continental regions has been delayed because it is difficult to secure samples for restoration of the paleoenvironment.
Lake Baikal is located in the area that receives the most significant solar radiation fluctuations on the earth (Short et al., 1991). Therefore, it is recognized that the lake records continental climate changes relating the solar radiation fluctuations in detail, and therefore many studies have been conducted using various paleo-environmental proxies. However, most of such papers were focused on glacial to interglacial cycles due to the limitation on sedimental time resolution (> 1 kyr sample–1). Thus, in previous studies, elucidating short-term and rapid climate changes such as the Bolling-Allerod, the Younger Dryas, and Holocene was difficult to (Horiuchi et al., 2000). Therefore, using high time resolution sediment samples obtained from Lake Baikal, the purpose of this study is to reconstruction climate changes from the last glacial termination to Holocene and the accompanying changes in the inflow of organic matter into the lake.
A 1.9 m-long gravity core (VER98-1 St.5GC) was collected from the Academician Ridge, Lake Baikal central basin in 1998. We selected on the upper 0.8 m sediment to study focused on the Pleistocene–Holocene interval including the Bolling-Allerod warming period and the Younger Dryas period. At two intervals of 70–63 cm (the Bolling-Allerod) and 60–20 cm (pre-boreal to sub-boreal in Holocene), TOC ranged from 1–2%, slightly higher than before and after of the depths, the C/N ratios (terrestrial input proxy) ranged from 8.4–11.3 and the ratios of Va to Vh ((Ad/Al)v) were showed maximum 5.6, and these records suggesting high degraded terrestrial material inputs to the lake during these intervals (the Bolling-Allerod and the pre-boreal to sub-boreal period). At the same intervals, δ13C values showed lighter values of −26 to −29 ‰, which is within the values of C3 plants (C3 plants: −20 to −37 ‰; Kohn, 2010), and ratios of syringyl to vanillyl phenols (S/V) and cinnamyl to vanillyl phenols (C/V) was shown that sediments OM was derived from the non-woody angiosperms (grasses and leaves). The vegetation around Lake Baikal from the last glacial period to about 6,000 years ago was composed of tundra (herbs) characteristic of the permafrost zone (Demske et al., 2005). Additionally, at the present, δ13C values in DOM of Siberian permafrost melting water showing −25 to −27.6 ‰ (Tesi et al., 2016) and Canadian high arctic permafrost spring flush (Ad/Al)v in DOM implying maximum at 3.6 (Woods et al., 2011) were reported. From these results and investigations, it is considered that the inflow of high decomposition products from the pre-boreal period to the late Holocene is caused by the inflow of permafrost melting water containing herbaceous plants into the lake. Such a Siberian permafrost melting during the Bolling-Allerod and pre-boreal periods has also been reported in lake Baikal southern basin and lake Hovsgol (Katsuta et al., 2019). In addition, in this study, Siberian permafrost melting during the sub-boreal period was inferred because similar organic records were observed during this interval as well as the previous one. However, the organic records probably also be influenced by increasing amount of vegetation by warmer climates.
Lake Baikal is located in the area that receives the most significant solar radiation fluctuations on the earth (Short et al., 1991). Therefore, it is recognized that the lake records continental climate changes relating the solar radiation fluctuations in detail, and therefore many studies have been conducted using various paleo-environmental proxies. However, most of such papers were focused on glacial to interglacial cycles due to the limitation on sedimental time resolution (> 1 kyr sample–1). Thus, in previous studies, elucidating short-term and rapid climate changes such as the Bolling-Allerod, the Younger Dryas, and Holocene was difficult to (Horiuchi et al., 2000). Therefore, using high time resolution sediment samples obtained from Lake Baikal, the purpose of this study is to reconstruction climate changes from the last glacial termination to Holocene and the accompanying changes in the inflow of organic matter into the lake.
A 1.9 m-long gravity core (VER98-1 St.5GC) was collected from the Academician Ridge, Lake Baikal central basin in 1998. We selected on the upper 0.8 m sediment to study focused on the Pleistocene–Holocene interval including the Bolling-Allerod warming period and the Younger Dryas period. At two intervals of 70–63 cm (the Bolling-Allerod) and 60–20 cm (pre-boreal to sub-boreal in Holocene), TOC ranged from 1–2%, slightly higher than before and after of the depths, the C/N ratios (terrestrial input proxy) ranged from 8.4–11.3 and the ratios of Va to Vh ((Ad/Al)v) were showed maximum 5.6, and these records suggesting high degraded terrestrial material inputs to the lake during these intervals (the Bolling-Allerod and the pre-boreal to sub-boreal period). At the same intervals, δ13C values showed lighter values of −26 to −29 ‰, which is within the values of C3 plants (C3 plants: −20 to −37 ‰; Kohn, 2010), and ratios of syringyl to vanillyl phenols (S/V) and cinnamyl to vanillyl phenols (C/V) was shown that sediments OM was derived from the non-woody angiosperms (grasses and leaves). The vegetation around Lake Baikal from the last glacial period to about 6,000 years ago was composed of tundra (herbs) characteristic of the permafrost zone (Demske et al., 2005). Additionally, at the present, δ13C values in DOM of Siberian permafrost melting water showing −25 to −27.6 ‰ (Tesi et al., 2016) and Canadian high arctic permafrost spring flush (Ad/Al)v in DOM implying maximum at 3.6 (Woods et al., 2011) were reported. From these results and investigations, it is considered that the inflow of high decomposition products from the pre-boreal period to the late Holocene is caused by the inflow of permafrost melting water containing herbaceous plants into the lake. Such a Siberian permafrost melting during the Bolling-Allerod and pre-boreal periods has also been reported in lake Baikal southern basin and lake Hovsgol (Katsuta et al., 2019). In addition, in this study, Siberian permafrost melting during the sub-boreal period was inferred because similar organic records were observed during this interval as well as the previous one. However, the organic records probably also be influenced by increasing amount of vegetation by warmer climates.