[M-IS12] 古気候・古海洋変動

[MIS12-27] The influence of the East Asian Winter Monsoon on the marine biological pump efficiency in the northwestern Philippine Sea

*Pierrick Fenies¹、Maria-Angela Bassetti²、Natalia Vazquez Riveiros³、Sze Ling Ho¹、Yuan-Pin Chang⁴、Ludvig A Lowemark⁵、Florian Bretonnière²、Nathalie Babonneau³、Gueorgui Ratzov⁶、Shu-Kun Hsu^7,8、Chih-Chieh Su¹ (1.Institute of Oceanography, National Taiwan University, Taiwan、2.CEFREM, Université de Perpignan via Domitia, France、3.Geo-Ocean, IFREMER, Université de Bretagne Occidentale, France、4.Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Taiwan、5.Department of Geosciences, National Taiwan University, Taiwan、6.Géoazur, Université Côte d'Azur, France、7.Department of Earth Sciences, National Central University, Taiwan、8.Institute of Earth Sciences, Academia Sinica, Taiwan)

キーワード：Marine biological pump, Deglaciation, Benthic foraminifera, East Asian Winter Monsoon

The marine biological pump is the ocean's ability to capture atmospheric CO₂ in the form of organic carbon through primary productivity, and to retain this organic carbon within the ocean under conditions of low oxygenation that prevent its remineralization into CO₂. The weakening of this mechanism during the Heinrich Stadial 1 is believed to have played a central role in the increase in atmospheric CO2 during the Last Deglaciation - up to 30 ppm of the 90 ppm difference between the Last Glacial Maximum and the Holocene. However, previous studies suggest that the global nature of this decline in intensity is questionable, particularly in the tropics. In the Philippine Sea, the enhanced East Asian Winter Monsoon winds during the Heinrich Stadial 1 as recorded in the Chinese Loess Plateau, might have transported iron to the Pacific Ocean through dust and deepened the mixing layer, causing nutrient-rich subsurface water to upwell into low-nutrient surface water. The Heinrich Stadial 1 is also marked by a first oxygenation pulse from the Southern Ocean. This pulse would have affected oxygenation of the North Pacific Deep Water (< 2000 m) with a delay of 2 kyr according to records in the subarctic Pacific, resulting in low oxygenation of the North Pacific Deep Water during the Heinrich Stadial 1. The combination of these two configurations – intensified primary productivity due to the stronger winds from the East Asian Winter Monsoon and reduced oxygenation from the North Pacific Deep Water - might lead to an increase in the efficiency of the Philippine Sea’s marine biological pump during Heinrich Stadial 1. To answer this hypothesis, we perform a multi-proxy study on the sediment core MD18-3523 collected from a levee of the Hoping Canyon, northwest of the Philippine Sea, at a depth of 2972 m. Applying multivariate statistics and transfer function on benthic foraminifera assemblages, and combining these results with Mn/Fe ratios of bulk sediment, we have reconstructed the evolution of the water bottom oxygenation at ~ 3000 m over the last 19 kyr. A transition from anoxic-dysoxic bottom waters during Heinrich Stadial 1 to oxic-suboxic conditions during the Holocene was observed across the Bølling–Allerød. Furthermore, enhanced primary productivity and more efficient carbon transfer to the seafloor during Heinrich Stadial 1 were highlighted through the use of Total Organic Carbon, Br/Ti ratios of bulk sediment, accumulation rates of benthic foraminifera, and multivariate statistics on benthic foraminifera assemblages. These observations imply a heightened marine biological pump during Heinrich Stadial 1, diverging notably from the evolution of this process in high-latitude oceans. They emphasize a more intricate involvement of the tropics and subtropics in the marine biological pump's efficiency changes during the last deglaciation than previously understood.