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Chlorofluorocarbon (CFC) and sulfur hexafluoride (SF6) were used to investigate the timescale of Antarctic Bottom Water (AABW) that spreads off Cape Darnley (CD) in East Antarctica. The age of the AABW was estimated based on the observed SF6/CFC-12 ratio while taking into account tracer dilution by Lower Circumpolar Deep Water. Along the western canyons off CD and the ~ 3000 to 3500 m isobaths, the bottom water age was < 5 years, reflecting the spread of newly formed CD Bottom Water. Higher ages of ~ 8 years obtained for areas east of CD and > 20 years in the northwestern offshore region indicate inflows of AABW through the Princess Elizabeth Trough and Weddell Sea Deep Water, respectively. This study determined the age distribution in the region off CD, where three different types of AABW spread. [ABSTRACT FROM AUTHOR]

• Circumpolar distribution of age of Antarctic Bottom Water (AABW) was revealed. • Young age of AABW reflected the spread of newly formed AABW. • Anthropogenic CO 2 (C ant) content of AABW in the Southern Ocean (SO) was estimated. • C ant amount in AABW was estimated to be 15% of total C ant in the whole SO. • Atlantic Ocean sector of the SO is the largest reservoir of the C ant in AABW. Antarctic Bottom Water (AABW) sequesters anthropogenic CO 2 (C ant) over the long-term and impacts the global carbon cycle. In this study, data of chlorofluorocarbon and sulfur hexafluoride observed from 2005 to 2020 in the Southern Ocean (SO) were used to investigate the age and C ant content of AABW. In the coastal regions of the Cosmonaut, Cooperation, D'Urville, and Somov Seas and near the Pacific-Antarctic Ridge, the age of AABW was < 5 years, reflecting the spread of newly formed AABW. Higher C ant inventory in AABW was detected in the Atlantic Ocean sector of the SO such as the Weddell and Lazarev Seas (29–55 ± 19–39 mol m−2) and the Cosmonaut and Cooperation Seas (35 ± 14 mol m−2) than those in the other regions. The amount of C ant in AABW in this region (7 ± 1–2 PgC) was estimated to be 78 % of the total C ant in AABW of the SO, suggesting the Atlantic Ocean sector as a major player to C ant sequestration in the abyssal ocean. The high C ant inventory in the Cosmonaut and Cooperation Seas is attributed to the presence of new AABW. The high C ant inventory also corresponded to the thick layer and high formation rate of AABW. Similar to the Cosmonaut and Cooperation Seas, the high C ant inventory in the Weddell and Lazarev Seas reflects the thick layer and high formation rate of AABW. The total amount of C ant in AABW in the SO (9 ± 1–2 PgC that would be the upper limit) was roughly estimated to be 15 % of the total C ant in the whole water column in the SO. This study highlights that AABW formation, transport, and storage processes play important roles in the total C ant sequestration in the SO. [ABSTRACT FROM AUTHOR]

Phytoplankton community structures and primary productivity were assessed in relation to the oceanographic conditions in the coastal waters of Funka bay and the eastern end of the Tsugaru Strait, adjacent to southwestern Hokkaido, Japan, from April 2010 to January 2012. Phytoplankton community compositions, as estimated from chemotaxonomic analysis based on high-performance liquid chromatography of pigments, showed diatom blooms during spring in both 2010 and 2011. However, spatial heterogeneity of chlorophyll a (Chl a ) concentration and primary productivity were found between regions investigated within and outside of Funka Bay during the spring diatom blooms in April 2010. The low Chl a concentrations within Funka Bay in April 2010 were related to the depletion of dissolved inorganic macronutrients, which implies that this difference was related to both the small inflow of the cold Coastal Oyashio Current (COW) into the bay and the development of clockwise circulation caused by discharge of fresh water into the bay. After the spring diatom blooms, the major phytoplankton groups in the study area were Chl b -containing phytoplanktons (chlorophytes and prasinophytes) because of changes in salinity associated with river discharge during the melting season. The results indicate that these phytoplanktons play an important role in the carbon cycle after the spring bloom in Funka Bay and the eastern end of the Tsugaru Strait. The thermohaline fronts created by the COW and the Tsugaru Warm Water in late February produced north–south differences in phytoplankton community structures in the eastern end of the Tsugaru Strait. Diatoms with high Chl a concentrations dominated in the northern section of the front. In the southern section, the proportions of chlorophytes and cryptophytes were high. Increases in cyanobacterial abundance and temperature were detected in both regions. Additionally, the contribution of pico- plus nano-sized phytoplankton productivity to the total primary productivity at the surface was concomitant with increases in temperature. Our results suggest that small-sized phytoplankton become more important part of the food web during summer, even in the coastal waters. [ABSTRACT FROM AUTHOR]