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Dissolved zinc and cadmium isotope systematics in the Amundsen and Weddell coastal Antarctic marginal seas

2025-06-01T00:00:00Z

Title: Dissolved zinc and cadmium isotope systematics in the Amundsen and Weddell coastal Antarctic marginal seas Authors: Tian Hung-An; van Manen Mathijs; Eich Charlotte; Jung, Jinyoung; Poll Willem H. V. D.; Reichart Gert-Jan; Conway Tim M.; Middag Rob Abstract: Coastal Antarctica is experiencing rapid environmental change with potential effects on regional marine trace element biogeochemistry. Here, we investigate the biogeochemistry of two dissolved bioactive trace elements, zinc (Zn) and cadmium (Cd), and their isotope ratios (delta 66Zn and delta 114Cd) in two coastal marginal seas with distinct oceanographic features-the Amundsen Sea with the intrusion of Circumpolar Deep Water (CDW) onto the Antarctic continental shelf, and the Weddell Sea where formation of Antarctic Bottom Water occurs. In the Amundsen Sea, our isotope data show CDW predominantly controls delta 66Zn and delta 114Cd on the continental shelf. This result is consistent with previous concentration-focused studies that suggested only a negligible addition of Zn and Cd from continental sediments and ice shelf meltwater, and other processes (e.g., scavenging) play a limited role in their cycling on the shelf region. In the Weddell Sea, homogeneous delta 66Zn and delta 114Cd within different water masses across the Antarctic Peninsula shelf, while Zn and Cd concentrations increase via physical mixing with deep water masses, suggest a preformed isotope signature on the continental shelf. In surface waters of both regions, delta 114Cd exhibited isotope fractionation linked to biological uptake, with different Rayleigh closed system fractionation factors (alpha = Rbiomass/Rseawater) for regions dominated by haptophytes (0.99930-0.99960) and diatoms (0.99970-0.99995) and we speculate that such differences may be associated with variability between species. In contrast, estimated fractionation factors for Zn in haptophytes (0.99995) and diatoms (0.99980-0.99995) dominated blooms are similar and comparable to reported values in the Southern Ocean (0.99995 +/- 0.00001). At the intermediate depth (250-1500 m) in the Weddell Sea, significantly lower delta 114Cd in the inner gyre compared to the outer gyre implies Cd regeneration and reduced ventilation. This pattern was not observed for delta 66Zn, likely due to its smaller biological fractionation in the surface. These findings confirm the role of CDW as the main source of Zn and Cd to the Amundsen Sea and the importance of physical mixing in setting global dissolved Zn and Cd distributions during the formation of deep waters in the Weddell Sea, providing insights into the impacts of regional coastal systems on the biogeochemistry of Zn and Cd.

The Responses of Antarctic Sea Ice and Overturning Cells to Meridional Wind Forcing

2025-02-01T00:00:00Z

Title: The Responses of Antarctic Sea Ice and Overturning Cells to Meridional Wind Forcing Authors: SONG, HAJOON; CHOI, YEONJU; EDWARD W. DODDRIDGE; JOHN MARSHALL Abstract: Meridional wind changes over the Antarctic seasonal ice zone have influenced recent sea ice extent variability. Using observations and an eddy-resolving channel model, this study examines how meridional wind anomalies alter sea ice distribution and the underlying ocean. Southerly wind anomalies in winter increase sea ice extent by driving equatorward ice drift, leading to more leads/polynyas, enhanced ice production, and coastal buoyancy loss, while freshening occurs farther offshore. In summer, the same southerly anomalies reduce sea ice extent by warming the sea ice edge through a strengthened meridional overturning circulation (MOC) driven by increased surface heat loss and brine rejection. Water-mass transformation analysis shows increased bottom water formation associated with brine rejection and coastal cooling. Northerly wind anomalies produce opposite responses. Overall, meridional wind anomalies regulate sea ice extent, polynya activity, buoyancy fluxes, MOC strength, and deep water properties.

Characterization of Phytoplankton-Derived Amino Acids and Tracing the Source of Organic Carbon Using Stable Isotopes in the Amundsen Sea

2024-10-01T00:00:00Z

Title: Characterization of Phytoplankton-Derived Amino Acids and Tracing the Source of Organic Carbon Using Stable Isotopes in the Amundsen Sea Authors: Min, Jun-Oh; Kim M.-S.; Lee. BoYeon; Gal J.-K.; Jung, Jinyoung; Kim, Tae-Wan; Park, Jisoo; Ha, Sun-Yong Abstract: We utilized amino acid (AA) and carbon stable isotope analyses to characterize phytoplankton-derived organic matter (OM) and trace the sources of organic carbon in the Amundsen Sea. Carbon isotope ratios of particulate organic carbon (δ13C-POC) range from ？28.7‰ to ？23.1‰, indicating that particulate organic matter originated primarily from phytoplankton. The dissolved organic carbon isotope (δ13C-DOC) signature (？27.1 to ？21.0‰) observed in the sea-ice melting system suggests that meltwater contributes to the DOC supply of the Amundsen Sea together with OM produced by phytoplankton. A negative correlation between the degradation index and δ13C-POC indicates that the quality of OM significantly influences isotopic fractionation (r2 = 0.59, p < 0.001). The AA distribution in the Amundsen Sea (5.43 ± 3.19 μM) was significantly larger than previously reported in the Southern Ocean and was associated with phytoplankton biomass (r2 = 0.49, p < 0.01). Under conditions dominated by P. antarctica (DI = 2.29 ± 2.30), OM exhibited greater lability compared to conditions co-dominated by diatoms and D. speculum (DI = 0.04 ± 3.64). These results highlight the important role of P. antarctica in influencing the properties of OM, suggesting potential impacts on carbon cycling and microbial metabolic activity in the Amundsen Sea. ⓒ 2024 by the authors.

Substrate Preferences and Interspecific Affinities of Antarctic Macroalgae: Insights from Maxwell Bay, King George Island

2024-10-01T00:00:00Z

Title: Substrate Preferences and Interspecific Affinities of Antarctic Macroalgae: Insights from Maxwell Bay, King George Island Authors: Ko, Young Wook; Yang K.M.; Choi, Han-Gu Abstract: This study investigates the diversity and ecological dynamics of macroalgae in Maxwell Bay, King George Island, Antarctica, focusing on species distribution, substrate composition, and interspecific interactions. Across nine survey sites, 31 macroalgal species were recorded, with 12 species identified as significant due to their considerable relative frequency, coverage, and biomass. Palmaria decipiens was the most dominant species in terms of frequency and coverage, while Desmarestia anceps had the highest biomass. The study revealed distinct substrate preferences, with P. decipiens favoring cobble and mud substrates, and Himantothallus grandifolius associating predominantly with pebble substrates. A core group of species, including Plocamium sp., H. grandifolius, Picconiella plumosa, Iridaea sp., and Trematocarpus antarcticus, exhibited strong ecological interactions characterized by high substrate similarity and mutual affinity. In contrast, pioneer species like P. decipiens and Monostroma hariotii showed lower affinity with other species, reflecting their early successional roles. These findings enhance our understanding of the complex interspecific relationships within Antarctic macroalgal assemblage and provide valuable baseline data for future ecological studies in the region. ⓒ 2024 by the authors.