High Salinity Shelf Water production rates in Terra Nova Bay, Ross Sea from high-resolution salinity observations

High Salinity Shelf Water (HSSW) formed in the Ross Sea of Antarctica is a precursor to Antarctic Bottom Water (AABW), a water mass that constitutes the bottom limb of the global overturning circulation. HSSW production rates are poorly constrained, as in-situ observations are scarce. Here, we present high-vertical-and-temporal-resolution salinity time series collected in austral winter 2017 from a mooring in Terra Nova Bay (TNB), one of two major sites of HSSW production in the Ross Sea. We calculate an annual-average HSSW production rate of ~0.4 Sv (106 m3 s-1), which we use to ground truth additional estimates across 2012-2021 made from parametrized net surface heat fluxes. We find sub-seasonal and interannual variability on the order of [Formula: see text] [Formula: see text], with a strong dependence on variability in open-water area that suggests a sensitivity of TNB HSSW production rates to changes in the local wind regime and offshore sea ice pack.

Endocrine disrupting effects of copper and cadmium in the oocytes of the Antarctic Emerald rockcod Trematomus bernacchii

Antarctica has long been considered a continent free from anthropic interference. Unfortunately, recent evidence indicate that metal contamination has gone so far and that its effects are still unknown. For this reason, in the present work, the potential endocrine disrupting effect of two highly polluting metals, copper and cadmium, were examined in the Antarctic teleost Trematomus bernacchii. After a 10 days waterborne exposure, ovarian metal uptake was determined by atomic absorption; in parallel, classical histological approaches were adopted to determine the effects on oocyte morphology, carbohydrate composition and presence and localization of progesterone and estrogen receptors. Results show that both metals induce oocyte degeneration in about one third of the previtellogenic oocytes, no matter the stage of development. In apparently healthy oocytes, changes in cytoplasm, cortical alveoli and/or chorion carbohydrates composition are observed. Cadmium but not copper also induces significant changes in the localization of progesterone and beta-estrogen receptors, a result that well correlates with the observed increase in ovarian metals concentrations. In conclusion, the acute modifications detected are suggestive of a significantly impaired fecundity and of a marked endocrine disrupting effects of copper and cadmium in this teleost species.

Rebound of shelf water salinity in the Ross Sea

Antarctic Bottom Water (AABW) supplies the lower limb of the global overturning circulation and ventilates the abyssal ocean. In recent decades, AABW has warmed, freshened and reduced in volume. Ross Sea Bottom Water (RSBW), the second largest source of AABW, has experienced the largest freshening. Here we use 23 years of summer measurements to document temporal variability in the salinity of the Ross Sea High Salinity Shelf Water (HSSW), a precursor to RSBW. HSSW salinity decreased between 1995 and 2014, consistent with freshening observed between 1958 and 2008. However, HSSW salinity rebounded sharply after 2014, with values in 2018 similar to those observed in the mid-late 1990s. Near-synchronous interannual fluctuations in salinity observed at five locations on the continental shelf suggest that upstream preconditioning and large-scale forcing influence HSSW salinity. The rate, magnitude and duration of the recent salinity increase are unusual in the context of the (sparse) observational record.

Ross Sea Bottom Water, a major source of Antarctic Bottom Water, has experienced significant freshening in recent decades. Here the authors use 23 years of summer measurements to document temporal variability in the salinity of the Ross Sea High Salinity Shelf Water (HSSW) and found that HSSW salinity decreased between 1995 and 2014 and rebounded sharply after 2014.

Identification of five partial ABC genes in the liver of the Antarctic fish Trematomus bernacchii and sensitivity of ABCB1 and ABCC2 to Cd exposure

Several ABC transporters have been characterized from many aquatic organisms, but no information is yet available for Antarctic fish. The aim of this work was to identify the expression of genes for ABC proteins in Trematomus bernacchii, a bioindicator species of the Southern Ocean. Partial cDNA sequences of ABCB1, ABCC1, ABCC2, ABCC4 and ABCC9 were cloned from liver. Using RACE technology, 3.5 and 2.2 kb contigs were obtained for ABCB1 and ABCC2. Considering the elevated natural bioavailability of cadmium at Terra Nova Bay, responsiveness of ABCB1 and ABCC2 to this element was investigated under laboratory conditions. ABCB1 and ABCC2 mRNA levels were approximately four-fold higher in Cd-exposed fish compared to the controls. Induction of ABCB1 protein was also found by western blot. This study provides the first identification of five ABC genes in the liver of an Antarctic key species, some of which may be involved in cellular detoxification.

Vitellogenin gene expression in males of the Antarctic fish Trematomus bernacchii from Terra Nova Bay (Ross Sea): a role for environmental cadmium?

Synthesis of vitellogenin (VTG) in male fish is a widely recognized effect for estrogenic pollutants in temperate environments, while similar investigations are still lacking for Antarctic organisms. In this study, a preliminary characterization of vitellogenin gene expression was performed by RT-PCR in the key species Trematomus bernacchii sampled in different phases of reproductive cycle and food availability. Females exhibited the highest gene expression during the spawning period, but VTG mRNA was always detected also in males; a significant increase of gene expression was observed both in males and females at the end of the feeding season. These results were not fully supported by a differential exposure to phyto- or anthropogenic estrogens during the planctonic cycle; on the other side, the endocrine properties of cadmium, naturally elevated in Terra Nova Bay and increasing during algal bloom, would explain both the presence of VTG mRNA in males and the seasonal changes of gene induction. Laboratory exposures did not reveal short-term estrogenic effects of cadmium while an elevated responsiveness of T. bernacchii was observed toward a classical estrogenic receptor agonist (17beta-estradiol). Different hypotheses were considered to suggest delayed endocrine effects of cadmium, including the early interaction with other cellular detoxification systems or alterations at multiple levels of the hypothalamus-pituitary-gonad-liver axis. Although molecular mechanisms of VTG gene expression in males of T. bernacchii remain unclear, obtained results provide interesting insights on this species which should stimulate future research activities.