Southern Ocean Research Articles

Metaproteomic analysis decodes trophic interactions of microorganisms in the dark ocean

Proteins in the open ocean represent a significant source of organic matter, and their profiles reflect the metabolic activities of marine microorganisms. Here, by analyzing metaproteomic samples collected from the Pacific, Atlantic and Southern Ocean, we reveal size-fractionated patterns of the structure and function of the marine microbiota protein pool in the water column, particularly in the dark ocean (>200 m). Zooplankton proteins contributed three times more than algal proteins to the deep-sea community metaproteome. Gammaproteobacteria exhibited high metabolic activity in the deep-sea, contributing up to 30% of bacterial proteins. Close virus-host interactions of this taxon might explain the dominance of gammaproteobacterial proteins in the dissolved fraction. A high urease expression in nitrifiers suggested links between their dark carbon fixation and zooplankton urea production. In summary, our results uncover the taxonomic contribution of the microbiota to the oceanic protein pool, revealing protein fluxes from particles to the dissolved organic matter pool.

Resolving the conflictive phylogenetic relationships of Oceanites (Oceanitidae: Procellariiformes) with the description of a new species

The family Oceanitidae, formerly considered a subfamily of Hydrobatidae, includes all the small storm-petrels of the southern hemisphere. The ancestor-descendent relationships and evolutionary history of one of its genera, Oceanites, have been partially studied, yielding contrasting results. We revised the phylogenetic relationships of this group using Bayesian inference (BI) based on new sequence data of the mitochondrial gene Cytb and linear morphological measurements of all species and five subspecies-level taxa in Oceanites, including a new taxon from the Chilean Andes. Our BI results show that the Oceanites genus is monophyletic and composed of four well-supported clades (posterior probability > 0.95): (1) chilensis; (2) exasperatus; (3) gracilis, pincoyae, and barrosi sp. nov.; and (4) oceanicus and galapagoensis. The species O. chilensis is a basal clade within Oceanites. According to our time-calibrated tree, the split between Oceanites and the other genera in Family Oceanitidae is estimated to be ~35.9 Mya, and the oldest divergence within Oceanites (the split between O. chilensis and other Oceanites) was dated to the early Miocene, around c. 21.3 Mya. The most probable geographic origin of Oceanites is the Southern Ocean. The morphological data suggest continuous size variation between Oceanites taxa, ranging from smallest in gracilis to largest in exasperatus. Based on our phylogenetic hypothesis, and morphological analyses, we suggest elevating to species status the taxa galapagoensis, chilensis, and exasperatus, and we describe a new taxon barrosi sp. nov., thus recognizing a total of seven species within the genus Oceanites.

Impact of ocean heat transport on sea ice captured by a simple energy balance model

Future projections of Arctic and Antarctic sea ice suffer from uncertainties largely associated with inter-model spread. Ocean heat transport has been hypothesised as a source of this uncertainty, based on correlations with sea ice extent across climate models. However, a physical explanation of what sets the sea ice sensitivity to ocean heat transport remains to be uncovered. Here, we derive a simple equation using an idealised energy-balance model that captures the emergent relationship between ocean heat transport and sea ice in climate models. Inter-model spread of Arctic sea ice loss depends strongly on the spread in ocean heat transport, with a sensitivity set by compensation of atmospheric heat transport and radiative feedbacks. Southern Ocean heat transport exhibits a comparatively weak relationship with Antarctic sea ice and plays a passive role secondary to atmospheric heat transport. Our results suggest that addressing ocean model biases will substantially reduce uncertainty in projections of Arctic sea ice.

Marine heatwaves in a shifting Southern Ocean induce dynamical changes in primary production

Marine heatwaves are discrete, albeit prolonged, episodes of extreme ocean temperatures that are significantly impacting marine ecosystems worldwide. However, there is limited research solely focusing on marine heatwaves and their concomitant effects on ecosystem dynamics in the Southern Ocean, known to play a major role in the Earth’s climate system. Here we use daily high-resolution satellite-derived and modelled data from 1982 to 2021 to characterise general spatiotemporal patterns of marine heatwaves in the Southern Ocean, assess their physical drivers and explore their interconnections with marine biogeochemistry. We find that increasing climate change-related marine heatwave activity, primarily explained by sea-air heat fluxes and vertical diffusion anomalies, enhances net primary production through stabilization of the water column. We empirically reveal causal nonlinear relationships between ocean extremes and primary productivity, especially in the southernmost subantarctic areas where the concurrent sea ice decrease also plays a key role. Furthermore, our study shows zonally asymmetric responses of primary producers to changing physical conditions north of the Antarctic polar front. These results provide key insights into the role of marine heatwaves promoting carbon assimilation (and uptake) in the Southern Ocean through the biological carbon pump, which is crucial for constraining the oceanic carbon cycle under climate change.

Direct observational evidence of strong CO2 uptake in the Southern Ocean.

The Southern Ocean is the primary region for the uptake of anthropogenic carbon dioxide (CO2) and is, therefore, crucial for Earth's climate. However, the Southern Ocean CO2 flux estimates reveal substantial uncertainties and lack direct validation. Using seven independent and directly measured air-sea CO2 flux datasets, we identify a 25% stronger CO2 uptake in the Southern Ocean than shipboard dataset-based flux estimates. Accounting for upper ocean temperature gradients and insufficient temporal resolution of flux products can bridge this flux gap. The gas transfer velocity parameterization is not the main reason for the flux disagreement. The profiling float data-based flux products and biogeochemistry models considerably underestimate the observed CO2 uptake, which may be due to the lack of representation of small-scale high-flux events. Our study suggests that the Southern Ocean may take up more CO2 than previously recognized, and that temperature corrections should be considered, and a higher resolution is needed in data-based bulk flux estimates.

Winter entrainment drives the mixed layer supply of manganese in the Southern Ocean

AbstractDespite the subnanomolar dissolved manganese concentrations that can co‐limit Southern Ocean primary production, their physical supply mechanisms during winter, for biological consumption in spring and summer have not yet been explored. During austral winter and spring 2019, two cruises were conducted in the Atlantic sector of the Southern Ocean, to determine the distribution and surface water supply mechanisms of dissolved manganese in the upper water column. The supply mechanisms were used to calculate the total flux of dissolved manganese to productive surface waters and were compared to biological consumption estimates. Mean dissolved manganese concentrations in the upper water column (< 500 m) during winter and spring were comparably low (≤ 0.34 nmol kg−1; p > 0.05), with seasonal mixed layer reservoir sizes averaging 65.21 ± 12.93 and 21.64 ± 19.32 μmol m−2, respectively. Winter entrainment contributed 89.33–99.99% (average 97.26% ± 5.28%) of the total dissolved manganese flux, while diapycnal diffusion contributed 0.52–10.58% (average 4.92% ± 5.14%), was identified as the dominant mechanisms for transporting dissolved manganese into the mixed layer in the subantarctic zone, polar frontal zone, and antarctic zone. Here, the winter physical supply rates were higher than the estimated consumption rates during spring, meeting phytoplankton biological demands. Whereas in the subtropical zone, the supply rates were lower than the consumption rates, indicating the presence of additional supply mechanisms such as coastal upwelling, which may help to meet the biological demands in this region.

Methane Emissions From Seabed to Atmosphere in Polar Oceans Revealed by Direct Methane Flux Measurements

AbstractSea‐air methane flux was measured directly by the eddy‐covariance method across approximately 60,000 km of Arctic and Antarctic cruises during a number of summers. The Arctic Ocean (north of 60°N, between 20°W and 50°E) and Southern Ocean (south of 50°S, between 70°W and 30°E) are found to be on‐shelf sources of atmospheric methane with mean sea‐air fluxes of 9.17 ± 2.91 (SEM (standard error of the mean)) μmol m−2 d−1 and 8.98 ± 0.91 μmol m−2 d−1, respectively. Off‐shelf, this region of the Arctic Ocean is found to be a source of methane (mean flux of 2.39 ± 0.68 μmol m−2 d−1), while this region of the Southern Ocean is found to be a methane sink (mean flux of −0.77 ± 0.37 μmol m−2 d−1). The highest fluxes observed are found around west Svalbard, South Georgia, and South Shetland Islands and Bransfield Strait; areas with evidence of the presence of methane flares emanating from the seabed. Hence, this study may provide evidence of direct emission of seabed methane to the atmosphere in both the Arctic and Antarctic. Comparing with previous studies, the results of this study may indicate an increase in sea‐air flux of methane in areas with seafloor seepage over timescales of several decades. As climate change exacerbates rising water temperatures, continued monitoring of methane release from polar oceans into the future is crucial.

Biogenic opal δ18O in marine deep-sea sediments through the Cenozoic Era and implications for ocean cooling

Benthic foraminifera δ18O increased by 5.4 ‰ through the Cenozoic Era, the past 65 million years of Earth's history. This increase is attributed to growth of global ice sheets and global ocean cooling. On the other hand, δ18O measurements of planktonic foraminifera do not exhibit significant change. These measurements initially were interpreted to suggest cool tropical and subtropical temperatures and introduced the concept of the “cool tropics paradox”, in which global bottomwater temperatures were significantly warmer but tropical surface temperatures were not during the early Cenozoic. This lack of change in δ18O of planktonic foraminifera was explained by secondary postburial alteration of the primary planktonic isotope signal.We provide an alternative record of sea surface water characteristics of Cenozoic Era by measuring δ18O of siliceous microfossils. This scarce phase of marine silica, unaltered biogenic opal-A, composed of diatoms, radiolaria and sponge spicules, was separated and purified from deep-sea Cenozoic sediments. We measured δ18O of siliceous microfossils from a set of drilled cores: DSDP 278 from the South Pacific, DSDP 513 from the South Atlantic, and ODP 1050–1053 and DSDP 391 from the subtropical North Atlantic. The purity of the biogenic opal and its mineralogical phase was assessed with SEM, SEM/EDS, XPS, and XRD.The δ18O of biogenic opal-A fluctuates around an average value of 43.0 ‰ through the Cenozoic Era, comparable to the Southern Ocean average of 43.2 ‰ of diatoms and radiolaria from the last 30,000 years which represent the last glacial and interglacial period and suggesting cold surface temperatures of 2–7 °C, both in the subtropical and polar latitudes. Taking into consideration changes in δ18O associated with bottomwater interaction with the lower crust and changes in sea level associated with waxing and waning of ice sheets, we conclude lack of or minimal change in the surface water temperature through the Cenozoic Era. This revives the original idea of the “cool tropics” paradox with a carbonate independent δ18O record and without issues associated with diagenesis of benthic and planktonic foraminifera.

Asymmetries in the Southern Ocean contribution to global heat and carbon uptake

The Southern Ocean provides dominant contributions to global ocean heat and carbon uptake, which is widely interpreted as resulting from its unique upwelling and circulation. Here we show a large asymmetry in these contributions, with the Southern Ocean accounting for 83 ± 33% of global heat uptake versus 43 ± 3% of global ocean carbon uptake over the historical period in state-of-the-art climate models. Using single radiative forcing experiments, we demonstrate that this historical asymmetry is due to suppressed heat uptake by northern oceans from enhanced aerosol forcing. In future projections, such as SSP2-4.5 where greenhouse gases increasingly dominate radiative forcing, the Southern Ocean contributions to global heat and carbon uptake become more comparable, 52 ± 5% and 47 ± 4%, respectively. Hence, the past is not a reliable indicator of the future, with the northern oceans becoming important for heat uptake while the Southern Ocean remains important for both heat and carbon uptake.

The Southern Ocean carbon sink has been overestimated in the past three decades

Employing machine learning methods for mapping surface ocean pCO2 has reduced the uncertainty in estimating sea-air CO2 flux. However, a general discrepancy exists between the Southern Ocean carbon sinks derived from pCO2 products and those from biogeochemistry models. Here, by performing a boosting ensemble learning feed-forward neural networks method, we have identified an underestimation of the surface Southern Ocean pCO2 due to notably uneven density of pCO2 measurements between summer and winter, which resulted in about 16% overestimating of Southern Ocean carbon sink over the past three decades. In particular, the Southern Ocean carbon sink since 2010 was notably overestimated by approximately 29%. This overestimation can be mitigated by a winter correction in algorithms, with the average Southern Ocean carbon sink during 1992-2021 corrected to −0.87 PgC yr−1 from the original −1.01 PgC yr−1. Furthermore, the most notable underestimation of surface ocean pCO2 mainly occurred in regions south of 60°S and was hiding under ice cover. As the surface ocean pCO2 under sea ice coverage in the winter is much higher than the atmosphere, if sea ice melts completely, there could be a further reduction of about 0.14 PgC yr−1 in the Southern Ocean carbon sink.

Patagonian dust, Agulhas Current, and Antarctic ice-rafted debris contributions to the South Atlantic Ocean over the past 150,000 years

Disentangling inputs of aeolian dust, ice-rafted debris (IRD), and eroded continental detritus delivered by ocean currents to marine sediments provide important insights into Earth System processes and climate. This study uses Sr-Nd-Pb isotope ratios of the continent-derived (lithogenic) fraction in deep-sea core TN057-6 from the subantarctic Southern Ocean southwest of Africa over the past 150,000 y to identify source regions and quantify their relative contributions and fluxes utilizing a mixing model set in a Bayesian framework. The data are compared with proxies from parallel core Ocean Drilling Program Site 1090 and newly presented data from potential South America aeolian dust source areas (PSAs), allowing for an integrated investigation into atmospheric, oceanic, and cryospheric dynamics. PSA inputs varied on glacial/interglacial timescales, with southern South American sources dominating up to 88% of the lithogenic fraction (mainly Patagonia, which provided up to 68%) during cold periods, while southern African sources were more important during interglacials. During the warmer Marine Isotope Stage (MIS) 3 of the last glacial period, lithogenic fluxes were twice that of colder MIS2 and MIS4 at times, and showed unique isotope ratios best explained by Antarctic-derived IRD, likely from the Weddell Sea. The IRD intrusions contributed up to 41% at times and followed Antarctic millennial warming events that raised temperatures, causing instability of icesheet margins. High IRD was synchronous with increased bioavailable iron, nutrient utilization, high biological productivity, and decreased atmospheric CO2. Overall, TN057-6 sediments record systematic Southern Hemisphere climate shifts and cryospheric changes that impacted biogeochemical cycling on both glacial/interglacial and subglacial timescales.

Controls on Early Cretaceous South Atlantic Ocean circulation and carbon burial – a climate model–proxy synthesis

Abstract. Black shale sediments from the Barremian to Aptian South Atlantic document the intense and widespread burial of marine organic carbon during the initial stages of seafloor spreading between Africa and South America. The enhanced sequestration of atmospheric CO2 makes these young ocean basins potential drivers of the Early Cretaceous carbon cycle and climate perturbations. The opening of marine gateways between initially restricted basins and related circulation and ventilation changes are a commonly invoked explanation for the transient formation and disappearance of these regional carbon sinks. However, large uncertainties in palaeogeographic reconstructions limit the interpretation of available palaeoceanographic data and prevent any robust model-based quantifications of the proposed circulation and carbon burial changes. Here, we present a new approach to assess the principal controls on the Early Cretaceous South Atlantic and Southern Ocean circulation changes under full consideration of the uncertainties in available boundary conditions. Specifically, we use a large ensemble of 36 climate model experiments to simulate the Barremian to Albian progressive opening of the Falkland Plateau and Georgia Basin gateways with different configurations of the proto-Drake Passage, the Walvis Ridge, and atmospheric CO2 concentrations. The experiments are designed to complement available geochemical data across the regions and to test circulation scenarios derived from them. All simulations show increased evaporation and intermediate water formation at subtropical latitudes that drive a meridional overturning circulation whose vertical extent is determined by the sill depth of the Falkland Plateau. The densest water masses formed in the southern Angola Basin and potentially reached the deep Cape Basin as Walvis Ridge Overflow Water. Palaeogeographic uncertainties are as important as the lack of precise knowledge of atmospheric CO2 levels for the simulated temperature and salinity spread in large parts of the South Atlantic. Overall temperature uncertainties reach up to 15 °C and increase significantly with water depth. The ensemble approach reveals temporal changes in the relative importance of geographic and radiative forcings for the simulated oceanographic conditions and, importantly, nonlinear interactions between them. The progressive northward opening of the highly restricted Angola Basin increased the sensitivity of local overturning and upper-ocean stratification to atmospheric CO2 concentrations due to large-scale changes in the hydrological cycle, while the chosen proto-Drake Passage depth is critical for the ocean dynamics and CO2 response in the southern South Atlantic. Finally, the simulated processes are integrated into a recent carbon burial framework to document the principal control of the regional gateway evolution on the progressive shift from the prevailing saline and oxygen-depleted subtropical water masses to the dominance of ventilated high-latitude deep waters.

The relationship between Antarctic sea-ice extent change and the main modes of sea-ice variability in austral winter

Accompanying global warming, Antarctic sea-ice extent shows a somewhat increasing trend from 1979 to 2014, followed by an abrupt decrease after 2016. Our previous study examined the change of Antarctic sea-ice extent in austral summer, autumn and spring. In this study, we turn our attention to the austral winter, relating the main modes of sea-ice variability to sea-ice extent in the Pacific, Atlantic and Indian sectors of the Southern Ocean. We find that the modes with the strongest correlation with the sea-ice extent are the third, first and first modes in the Pacific, Atlantic and Indian sectors, respectively. Atmospheric circulation anomalies of zonal wavenumber three over the Southern Ocean, related to planetary wave trains induced by the SST anomalies over the south-western Pacific and the southern Indian oceans, can explain sea-ice concentration anomalies of the third mode in the Pacific sector through thermodynamic and dynamic processes. Sea-ice anomalies of the first modes in the Atlantic and Indian sectors result from atmospheric circulation anomalies of a positive and negative phases of the Southern Annular Mode, respectively. The anomalous Southern Annular Mode is also associated with wave trains over the Southern Ocean excited by SST anomalies over the southern Indian Ocean and the south-western Pacific Ocean. The relationship between SST anomalies and Antarctic sea-ice anomalies can provide a reference for the prediction of Antarctic sea-ice anomalies in austral winter on interannual and decadal timescales.

Author Correction: The role of biota in the Southern Ocean carbon cycle

Author Correction: The role of biota in the Southern Ocean carbon cycle

Biodiversity and functioning of mesozooplankton in a changing Ross Sea

Literature on Ross Sea zooplankton is limited, although it is the most productive system and has the highest biomass of phytoplankton in the Southern Ocean. Energy transfer within the food web and response of continental shelf food web to climate change depend on the knowledge of the density and distribution of zooplankton. We evaluated its density, composition, spatial distribution and their potential relations with environmental factors and specific water mass presence. Particular attention was given to copepods. Mesozooplankton samples were collected between 14 January and February 11, 2017 from 14 stations in the western Ross Sea and Terra Nova Bay, while other micronekton samplings were completed at 6 stations. Results highlighted three pools of stations: one inside Terra Nova Bay with the highest densities, one on the platform with lower mean density, and the third represented by a N–S transept at 175°E with the lowest mean density. This partitioning of the region fit with the grouping of stations according to a ternary plot based on the different percentages of water masses in each station and reflected the similarity of zooplankton. The presence of specific water masses and their contribution in the upper 200 m influences zooplankton biodiversity and density. A phylogenetic tree of the zooplankton was constructed to analyse the distance among the observed taxa. The area located near the coast exhibited the highest degree of phylogenetic overdispersion. In coastal waters, typical copepod species constituted the main part of the neritic zooplankton of Terra Nova Bay and Ross Sea. Oithona similis was the most abundant species both in coastal and offshore sectors, followed by pteropods, polychaetes and euphausiids.

Comparative phylogeography, a tool to increase assessment efficiency of polar assemblage resilience and vulnerability

The Southern Ocean benthos is remarkably rich and diverse, and managed under a complexity of treaties and conventions, further complicated by geopolitical boundaries. Traditionally, conservation management is largely informed by species lists augmented, when data are available, by known vulnerability of the taxa. Species presence absence database resources are valuable tools with proven and positive management outcomes, however, in a vast, difficult to access and thus understudied region such as the Southern Ocean, there are large gaps in knowledge regarding the ecology, ecophysiology, life history and even species identity. Conservation biogeography identifies regions of conservation concern, rather than a species-by-species approach, but also relies on the availability of high-quality presence data from species lists and thus both approaches are undermined when species lists are inaccurate or species in general are poorly described. In addition, the data provide a snapshot of the current species diversity and have inadequate power to identify the processes underlying the patterns uncovered. Identifying historical processes common to shaping diversity (species or genetic) can be generalized across assemblages and regions, providing a more robust basis for conservation policy and decisions. In this study, largely based on consideration of Southern Ocean ophiuroids, we discuss the challenges inherent in using species lists, the power and limitations of genetic analyses, and revisit previous suggestions of building a spatial model of diversity that includes underlying evolutionary relationships transcending the simple species diversity approach, and that is applicable to assemblages, rather than just to individual taxa.

New distributional records of Southern Ocean Isopoda based on vouchers from the Italian National Antarctic Museum (MNA, Section of Genoa).

The order Isopoda Latreille, 1816 consists of species occurring in terrestrial, marine and freshwater environments. In the Southern Ocean (SO), this group is amongst the most speciose and occur at all depths. Isopoda biogeography, despite being studied since the first Antarctic expeditions, is still poorly known from a geographical point of view and shows large occurrence gaps for some groups in specific sectors of the SO. In this paper, we update the isopod checklists of the Ross Sea (RS) and of some peri-Antarctic areas, such as the South Orkney Islands (SOI) and the South Sandwich Islands (SSI), based on the study of museum vouchers curated by the Italian National Antarctic Museum (MNA, Section of Genoa). A total of 279 MNA samples from 15 different expeditions were studied. From this material, consisting of 419 specimens, 41 accepted species distributed in 24 families and 51 genera were identified. Comparing this newly-obtained information with the GBIF (Global Biodiversity Information Facility) and OBIS (Ocean Biodiversity Information System) portal, 15 species are here reported for the first time in the Ross Sea, with five new records in the Ross Sea Marine Protected Area. All records are new for the Terra Nova Bay area, for which a checklist of this group has never been produced before.

Decadal Trends in the Southern Ocean Meridional Eddy Heat Transport

Abstract Meridional heat transport induced by oceanic mesoscale eddies (EHT) plays a significant role in the heat budget of the Southern Ocean (SO) but the decadal trends in EHT and its associated mechanisms are still obscure. Here, this scientific issue is investigated by combining concurrent satellite observations and Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) reanalysis data over the 24 years between 1993 and 2016. The results reveal that the surface EHTs from both satellite and ECCO2 data consistently show decadal poleward increasing trends in the SO, particularly in the latitude band of the Antarctic Circumpolar Current (ACC). In terms of average in the ACC band, the ECCO2-derived EHT over the upper 1000 m has a linear trend of 1.1 × 10−2 PW decade−1 or 16% per decade compared with its time-mean value of 0.07 PW. Diagnostic analysis based on “mixing length” theory suggests that the decadal strengthening of eddy kinetic energy (EKE) is the dominant mechanism for the increase in EHT in the SO. By performing an energy budget analysis, we further find that the decadal increase in EKE is mainly caused by the strengthened baroclinic instability of large-scale circulation that converts more available potential energy to EKE. For the strengthened baroclinic instability in the SO, it is attributed to the increasing large-scale wind stress work on the large-scale circulation corresponding to the positive phase of the Southern Annular Mode between 1993 and 2016. The decadal trends in EHT identified here may help understand decadal variations of heat storage and sea ice extent in the SO. Significance Statement Oceanic mesoscale-eddy-induced meridional heat transport (EHT) is a key process of heat redistribution in the Southern Ocean (SO), but the decadal variations of EHT and the associated mechanisms remain obscure. Here, by analyzing satellite and reanalysis data between 1993 and 2016, we find that the poleward EHT has significant decadal increasing trends in the SO, particularly in the Antarctic Circumpolar Current latitude band. Further analysis suggests that the increasing EHT is mainly caused by enhanced eddy kinetic energy converted by the strengthened baroclinic instability of large-scale circulation, which is attributed to the strengthening winds modulated by the Southern Annular Mode. The above findings may improve our understanding of the decadal variations of heat storage and sea ice extent in the SO.

Factors influencing haulout behaviour of non-breeding weddell seals (Leptonychotes weddellii) at Cape Royds, Antarctica

The Weddell seal (Leptonychotes weddellii) is a fast-ice obligate species that plays an important role as both predator and prey within the high-latitude, coastal Southern Ocean. Weddell seals are affected by pressures of marine resource extraction and variation in sea-ice extent and characteristics that are affected by climate. Thus, monitoring their population dynamics provides an indicator of the effectiveness of fisheries management, and impacts of changing climate in the high latitude Southern Ocean ecosystem. Satellite imagery is increasingly being used to monitor the populations of this species, but assessment techniques require a better understanding of the environmental factors influencing the likelihood that individuals will be on the sea-ice and therefore visible in a satellite image. Addressing that goal, we captured 5054 trail camera photos during spring 2017 in the 24-h light at Cape Royds, Antarctica, and then counted seals on the fast ice every 30 min over 59 days. Using a generalised additive model (63% deviance explained) we described the haulout behaviour of non-breeding Weddell seals according to time of day, date, air temperature, pressure, solar radiation, and wind speed. We found that the seals’ haulout cycle is driven to a significant degree by weather variables, primarily temperature and wind speed. Quantifying these haulout patterns can be used to determine the time of day, and under what conditions, that most seals are hauled out. Integrating environmental parameters to correct time-of-day patterns would allow better cross-site abundance comparisons, leading to better Weddell seal population estimates for the Ross Sea region and the wider coastal Antarctica.

Existence of rare actinobacterial forms in the Indian sector of Southern Ocean: 16S rRNA based metabarcoding study.

The significance of the Southern Ocean (SO) as a sink of atmospheric CO2 and other greenhouse gases is well established. Earlier studies have highlighted the role of microbes in various SO ecosystem processes. However, the diversity and role of actinobacteria in the Indian sector of SO (ISO) water and sediments are unknown. This study aimed to analyze the diversity of actinobacteria in water and sediment samples of SO based on amplicon microbiome analyses. The taxonomic analysis identified a total number of 27 phyla of which Proteobacteria (40.2%), Actinobacteria (13.6%), and Firmicutes (8.7%) were found to be dominant. The comparative study of water and sediment samples revealed the dominance of different actinobacteria in water and sediments. While the order Streptomycetales was dominant in the water samples, Micrococcales was found to be dominant in the sediment samples. The genus level analysis found the presence of eight and seventeen genera in the sediment and water samples, respectively. The genus Streptomyces, Saccharopolyspora, Nocardioides, Sva0996 marine group, and Mycobacterium were seen both in sediment and water samples. Marmoricola, Ilumatobacter, and Glaciihabitans were observed only in sediment samples whereas Rhodococcus, Corynebacterium, Micrococcus, Turicella, Pseudonocardia, Bifidobacterium, Nesterenkonia, Collinsella, Knoellia, Cadidatus, Actinomarina, Libanicoccus and Cutibacterium were noticed exclusively in water samples. Our study also emphasizes the need for further detailed study to understand the links between actinobacterial diversity and their ecological functions in the ISO. The available metabarcoding data paves the way for future research in cultivable forms of novel and rare Actinobacteria for their bioprospecting applications.