Enhancement/reduction of biological pump depends on ocean circulation in the sea-ice reduction regions of the Arctic Ocean |
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| Authors: | Shigeto Nishino Takashi Kikuchi Michiyo Yamamoto-Kawai Yusuke Kawaguchi Toru Hirawake Motoyo Itoh |
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| Institution: | (1) Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka Kanagawa, 237-0061, Japan;(2) Research Center for Advanced Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan;(3) Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate Hokkaido, 041-8611, Japan |
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| Abstract: | The biological pump is a central process in the ocean carbon cycle, and is a key factor controlling atmospheric carbon dioxide
(CO2). However, whether the Arctic biological pump is enhanced or reduced by the recent loss of sea ice is still unclear. We examined
if the effect was dependent on ocean circulation. Melting of sea ice can both enhance and reduce the biological pump in the
Arctic Ocean, depending on ocean circulation. The biological pump is reduced within the Beaufort Gyre in the Canada Basin
because freshwater accumulation within the gyre limits nutrient supply from deep layers and shelves hence inhibits the growth
of large-bodied phytoplankton. Conversely, the biological pump is enhanced outside the Beaufort Gyre in the western Arctic
Ocean because of nutrient supply from shelves and greater light penetration, enhancing photosynthesis, caused by the sea ice
loss. The biological pump could also be enhanced by sea ice loss in the Eurasian Basin, where uplifted isohaline surfaces
associated with the Transpolar Drift supply nutrients upwards from deep layers. New data on nitrate uptake rates are consistent
with the pattern of enhancement and reduction of the Arctic biological pump. Our estimates indicate that the enhanced biological
pump can be as large as that in other oceans when the sea ice disappears. Contrary to a recent conclusion based on data from
the Canada Basin alone, our study suggests that the biological CO2 drawdown is important for the Arctic Ocean carbon sink under ice-free conditions. |
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