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[1] Regional formation of deep and bottom water masses around the Antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell. Southern Ocean hydrographic data collected during the years 1958-2010 indicate that dense shelf waters cooled and freshened during that period. In the surrounding open ocean, Antarctic Bottom Water (AABW) warmed, with no evidence of salinity change. As a result of source-water property changes, AABW exported from the Southern Ocean to the deep world ocean became lighter over the period analyzed. The average rate of density change within the areas that experienced statistically significant change was À0.0019 kg m À3 yr À1 . For the last 20 years of the analysis, a negative AABW volume anomaly (relative to the half-century average, 1958-2010) was indicated, possibly due to production of a lighter AABW variety or to changes in formation rates. Over the entire five decades, the upper isopycnal of the AABW layer deepened at a rate of À8.1 m yr À1 . Changes in fundamental hydrographic properties such as these can have important implications for long-term global ocean circulation and climate.

Changes in phytoplankton composition from large diatoms to small cryptophytes and their implications to the food web have been previously associated with rapid warming of surface waters in the western Antarctic Peninsula (WAP).However, ecological and physiological attributes that favor dominance of these flagellates in the region have not been fully explored. The overall aim of this work was to characterize the phytoplankton pigments and assemblages in relation to environmental conditions during three successive summer cruises (2013, 2014 and 2015) in the Gerlache Strait − a coastal area in the northern WAP. Data on phytoplankton (through HPLC/CHEMTAX pigment analysis) and associated physical (water column structure) and chemical (macronutrients) parameters were determined. Cryptophytes were conspicuously found in shallow mixed layers, under stratified conditions, as the main contributors to total phytoplankton biomass. Their greatest contributions were associated with warmer surface waters at the northwestern sector of the strait. Other phytoplankton groups (Phaeocystis antarctica in 2013 and small diatoms in both 2014 and 2015) were also important components. Photoprotective carotenoids (mainly alloxanthin), with an important role in preventing photodamage caused by excess light, were closely linked with the dominance of cryptophytes at surface layers. The results of this study suggest that the prevalence of cryptophytes in WAP coastal waters can be, to a great extent, due to a particular ability of those small flagellates to successfully grow in highly illuminated conditions in shallow upper mixed layers and strong water column stratification.

Diatoms are considered the main base of the Southern Ocean food web as they are responsible for more than 85% of its annual primary production and play a crucial role in the Antarctic trophic structure and in the biogeochemical cycles. Within this context, an intense diatom bloom reaching > 45 mg m−3 of chlorophyll a was registered in the Northern Antarctic Peninsula (NAP) during a late summer study in February 2016. Given that nutrient concentrations and grazing activities were not identified here as limiting factors on the bloom development, the aim of this study was to evaluate the effect of water column structure (stability and upper mixed layer depth) on the phytoplankton biomass and composition in the NAP. The diatom bloom, mainly composed by the large centric Odontella weissflogii (mostly > 70 μm in length), was associated with a local ocean carbon dioxide uptake that reached values greater than −60 mmol m−2 d−1. We hypothesize that the presence of a vertically large water column stability barrier, just below the pycnocline, was the main driver allowing for the development of the intense diatom bloom, particularly in the Gerlache Strait. Contrarily, a shift from diatoms to dinoflagellates (mainly Gymnodiniales < 20 μm) was observed associated with conditions of a highly stable thin layer. The results suggest that a large fraction of this intense diatom bloom is in fast sinking process, associated with low grazing pressure, showing a crucial role of diatoms for the efficiency of the biological carbon pump in this region.

The deep waters of the Bransfield Strait receive considerable amounts of water from the Weddell Sea continental shelf. The restricted connections to the surrounding ocean and relatively easier access makes the Bransfield Strait an important proxy region for monitoring changes in the dense Weddell Sea shelf water masses, which are an important precursor of Antarctic Bottom Water (AABW). Long‐term hydrographic data from the period 1960s–2010s showed freshening and lightening of the deep water masses of the Bransfield Strait, which was likely caused by large freshwater inputs originating from the western shelf of the Weddell Sea. The rates of freshening and lightening were −0.0010 ± 0.0005 yr−1 and −0.0016 ± 0.0014 kg m−3 yr−1 for the central basin, respectively, and −0.0010 ± 0.0006 yr−1 and −0.0029 ± 0.0013 kg m−3 yr−1 for the eastern basin, respectively. The deep waters showed a high degree of interannual thermohaline variability, which appeared to be caused by changes in the proportions of source water mass mixing between the years. Statistically significant negative correlations between salinity/neutral density fields and the Southern Annular Mode (SAM) were observed (−0.56 and −0.62 for the central basin, respectively, and −0.58 and −0.68 for the eastern basin, respectively) between 1980 and 2014. During SAM positive phases, communication between the Weddell Sea and the Bransfield Strait is reduced, which leads to less saline and lighter water masses in the Bransfield Strait; however, the opposite trends are observed during SAM negative phases.

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Genetic structure and natal origins of green turtle mixed stocks in southern Brazil were assessed based on analyses of mtDNA control region sequences from the Arvoredo Island (n = 115) and Cassino Beach (n = 101) feeding areas. These were compared to other mixed aggregations to examine structuring, and to Atlantic Ocean nesting colonies to evaluate natal origins through Bayesian mixed stock analysis (MSA). In order to develop novel priors, surface drifter trajectories in the Atlantic were analyzed and combined with rookery data, and we used KulbackLeibler information measures in order to compare the difference of information among the 4 proposed priors. Each study area presented 12 haplotypes, 10 of which were shared at similar frequencies. Haplotypes CM-A8 and CM-A5 represented ~60 and 20%, respectively, and remaining haplotypes accounted for < 5% of samples. The 2 study areas were genetically similar to all feeding grounds in the western South Atlantic except Almofala, in northeast Brazil, and genetically different from Caribbean and North American mixed stocks. Drifter trajectory analysis revealed that drifters from Ascension and Trindade Islands have a larger chance of reaching Brazil. The priors drifter data and rookery size/drifter data combined contained the most information, but stock estimates were not greatly changed. MSA indicated that Ascension, Aves/Surinam and Trindade were the main stock contributors to the study areas. Since impacts on mixed stocks may affect populations thousands of km away, the results presented here have important implications for the conservation of this endangered species.KEY WORDS: Green turtle · Feeding grounds · South Brazil · Genetic structure · Natal origins · Dispersal patternsResale or republication not permitted without written consent of the publisher

The seasonal advance and retreat of sea ice around the northern Antarctic Peninsula can have a significant impact on phytoplankton, mainly due to alterations in the availability of ice-free areas, micro-nutrient inputs by meltwater and variations in water column structure. The aim of this work was to evaluate the effect of sea ice conditions on phytoplankton biomass and community composition in an area off the northern Antarctic Peninsula, a region undergoing important warming processes. In two consecutive summer cruises (2013 and 2014), seawater samples were analysed for nutrients and phytoplankton (through HPLC-CHEMTAX approach), and measurements were made for water column physical structure evaluation. Two contrasting conditions were studied: a strong environmental gradient around the sea ice edge, with a marked meltwater signal (summer 2013) and the same area with little indication of meltwater and no detectable sea ice conditions (summer 2014). In the first year, the phytoplankton communities were massively dominated by nanoflagellates such as cryptophytes, small dinoflagellates and Phaeocystis antarctica, but with differences between stations with less influence of meltwater (dominance of dinoflagellates type B, mainly Gymnodinium spp., mean chlorophyll a = 1.37 mg m −3 ) and stations closer to the sea ice edge (dominance of cryptophytes, mean chlorophyll a = 0.98 mg m −3 ). In the second year, cryptophytes were apparently replaced by diatoms type B (mainly Pseudonitzschia spp., 24% contribution, mean chlorophyll a = 0.93 mg m −3 ), although dinoflagellates were also important. Therefore, there was a clear distinction between the phytoplankton communities under sea ice influence, where mainly cryptophytes were associated with shallow mixed layers and high water column stability in 2013 and an important presence of diatoms in 2014, associated with deeper mixed layers, lower silicic acid concentrations and higher magnitudes of both salinity and temperature, under very little sea ice influence. Gymnodinioid dinoflagellates were an important component in both years, apparently occupying sites/conditions less favourable to cryptophytes. These results support previous suggestions that climate factors leading to shortening of the sea ice season in the region do have an important impact particularly in shaping the dominance of the main phytoplankton functional groups in the region.