ORCID Profile
0000-0002-4028-6723
Current Organisations
The Graduate University for Advanced Studies (SOKENDAI)
,
National Institute of Polar Research
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Publisher: Wiley
Date: 22-12-2021
Publisher: Wiley
Date: 28-01-2022
Publisher: American Geophysical Union (AGU)
Date: 09-2023
DOI: 10.1029/2022GB007510
Abstract: To clarify the impacts of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a , and stable oxygen isotopic ratios (δ 18 O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf off the TIS and flowed along bathymetric troughs into the TIS cavity, where it formed a buoyant mixture with glacial meltwater from the ice shelf base. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, photosynthesis and dilution by meltwater from sea ice and the ice shelf base decreased DIC, TA, and nutrient concentrations in surface water near the ice front. These causes also reduced the CO 2 partial pressure in surface water by more than 100 μatm with respect to mCDW in austral summer of 2018 and 2020, and the surface water became a strong CO 2 sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, CO 2 partial pressure decreased mostly as a result of photosynthesis while dilution by glacial and sea ice meltwater had a small effect. The nutrient consumption ratio suggested that photosynthesis was stimulated by iron in the water column, supplied to the surface layer via buoyancy‐driven upwelling and basal ice shelf meltwater in addition to sea ice meltwater.
Publisher: American Geophysical Union (AGU)
Date: 07-2022
DOI: 10.1029/2021JC018371
Abstract: We elucidated the effects of snow and remineralization processes on nutrient distributions in multi‐year landfast sea ice (fast ice) in Lützow‐Holm Bay, East Antarctica. Based on sea‐ice salinity, oxygen isotopic ratios, and thin section analyses, we found that the multi‐year fast ice grew upward due to the year‐by‐year accumulation of snow. Compared to ice of seawater origin, nutrient concentrations in shallow fast ice were low due to replacement by clean and fresh snow. In deeper ice of seawater origin (the lower half of the multi‐year fast ice column), remineralization was dominated by the degradation of organic matter. By comparison between first‐ and muti‐year ice, the biological uptake and the remineralization were dominated in relatively young ice and older ice, respectively, under the physical process of brine drainage.
Publisher: Springer Science and Business Media LLC
Date: 24-08-2020
DOI: 10.1038/S41467-020-17527-4
Abstract: Mass loss from the Antarctic ice sheet, Earth’s largest freshwater reservoir, results directly in global sea-level rise and Southern Ocean freshening. Observational and modeling studies have demonstrated that ice shelf basal melting, resulting from the inflow of warm water onto the Antarctic continental shelf, plays a key role in the ice sheet’s mass balance. In recent decades, warm ocean-cryosphere interaction in the Amundsen and Bellingshausen seas has received a great deal of attention. However, except for Totten Ice Shelf, East Antarctic ice shelves typically have cold ice cavities with low basal melt rates. Here we present direct observational evidence of high basal melt rates (7–16 m yr −1 ) beneath an East Antarctic ice shelf, Shirase Glacier Tongue, driven by southward-flowing warm water guided by a deep continuous trough extending to the continental slope. The strength of the alongshore wind controls the thickness of the inflowing warm water layer and the rate of basal melting.
Location: Japan
No related grants have been discovered for Shuki Ushio.