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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 (δ18O) 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 partial pressure of CO2 (pCO2) 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 CO2 sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, pCO2 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. Plain Language Summary: Oceanographic observations were made from the offshore continental slope to the Totten Ice Shelf (TIS) front in Sabrina Coast, East Antarctica, during spring/summer 2018, 2019, and 2020. Results revealed that surface water was strongly influenced by phytoplankton activity and the dilution effect of meltwater from sea ice and the base of the ice shelf. The nutrient consumption ratio between the winter water near the ice shelf front and surface water suggested that enough iron was present in the water column to stimulate photosynthesis. The iron was likely introduced into the surface water by buoyancy‐driven upwelling and meltwater from the base of the TIS in addition to sea ice meltwater. Key Points: The inflow of modified Circumpolar Deep Water supplied biogeochemical components under the Totten Ice ShelfSurface water was influenced by dilution from ice shelf basal meltwater and sea ice meltwater and was changed by biological productivityIron delivered by buoyancy‐driven upwelling, basal ice shelf meltwater, and sea ice meltwater stimulated photosynthesis in surface water [ABSTRACT FROM AUTHOR]

To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80–150°E, south of 60°S), we measured ocean surface temperature, salinity, total alkalinity (TA), the partial pressure of carbon dioxide (pCO2), and concentrations of chlorophyll‐a (chl a), dissolved inorganic carbon (DIC), and nutrients during the KY18 survey (December 2018–January 2019). The sea–air CO2 flux in this region was −8.3 ± 12.7 mmol m−2 day−1 (−92.1 to +10.6 mmol m−2 day−1). The ocean was therefore a weak CO2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO2 from winter to summer (δpCO2) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO2 in the western part (80–110°E) of the study area was mainly driven by biological activity, which decreased pCO2 from December to early January, and in the eastern part (110–150°E) by temperature, which increased pCO2 from January to February. We also examined the changes in the CO2 concentrations (xCO2) over time by comparing data from 1996 with our data (2018–2019). The oceanic and atmospheric xCO2 increased by 23 and 45 ppm in 23 years, respectively. These changes of ocean xCO2 were mainly driven by an increase in CO2 uptake from the atmosphere as a result of the rise in atmospheric xCO2 and increase in biological activity associated with the change in the water‐mass distribution. Plain Language Summary: Determining the drivers of seasonal changes in ocean CO2 is important for estimating the global carbon cycle. Seawater samples were collected in the eastern Indian sector of the Southern Ocean to investigate the carbonate chemistry of the ocean surface water. During winter and summer, the partial pressure of carbon dioxide (pCO2) at the ocean surface decreased and increased due to photosynthesis and temperature changes, respectively. Surface water pCO2 was lower than the pCO2 of the atmosphere in summer: the result was CO2 uptake by the ocean. A comparison of data from 1996 with our data (2018–2019) indicated that the CO2 concentration (xCO2) of the seawater had increased by 23 ppm. This increase was due primarily to an increase in uptake of CO2 from the atmosphere as a result of the rise of atmospheric xCO2. Key Points: The eastern Indian sector of the Southern Ocean absorbs atmospheric CO2 weakly in summerBiological activity and increases in water temperature change the pCO2 from winter to summerChanges in atmospheric pCO2 and water masses explained the interannual variations of dissolved CO2 in the ocean [ABSTRACT FROM AUTHOR]

To clarify the effect of basal melting of ice tongues/ice shelf on the CO2 system in the Antarctic continental margin, seawater samples were collected for analysis of dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients, chlorophyll a (chl.a), and oxygen isotopic ratios at the ice front of the Shirase Glacier Tongue (SGT) in Lützow‐Holm Bay (LHB), East Antarctica during the summers of 2017 and 2018. At depths greater than ∼20 dbar in LHB, CO2 system parameters were strongly influenced by the dilution effect of SGT basal melting and the inflow of modified Circumpolar Deep Water (mCDW). The distributions of DIC and TA agreed well with an offshore origin of mCDW that flowed beneath the SGT and mixing of basal meltwater and mCDW beneath the SGT. The fraction of SGT meltwater was highest at the station near the ice front. Dilution by SGT basal meltwater reduced the partial pressure of CO2 in the mCDW from 431 to 387 μatm. The water then became a sink rather than source of atmospheric CO2. In the sea surface, DIC and TA were strongly influenced by biological processes. Salinity‐normalized DIC decreased with the increase of salinity‐normalized TA in accord with 106:16 C:N molar stoichiometry; the chl.a concentration at the sea surface was as high as 31 μg L−1. Plain Language Summary: Oceanographic observations were made during the summers of 2017 and 2018 near the ice shelf in an ice‐covered bay in East Antarctica. Results revealed that the parameters such as dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrients at subsurface layer (>20 m) was strongly influenced by the dilution effect of the melting of ice sheet and the inflow of warm and high salinity water from outside of the bay. In contrast, within the surface layer, DIC, TA, and nutrients were strongly influenced by phytoplankton activity. Key Points: The CO2 system is strongly influenced by the dilution effect of the basal melting of the Shirase Glacier Tongue (SGT)The decrease of pCO2 by basal melting caused the water to shift from a CO2 source to a sink of atmospheric CO2 in Lützow‐Holm BaySurface water was strongly influenced by biological processes near the SGT [ABSTRACT FROM AUTHOR]