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Over the last 3.3 million years, the Antarctic Ice Sheet (AIS) has undergone phases of ice sheet growth and decay, impacting sea level and climate globally. Presently, the largely marine‐terminating AIS loses mass primarily by iceberg calving and basal melt of ice shelves. Quantifying past rates and timing of AIS melt is vital to understanding future cryosphere and sea level changes. One proxy for past ice sheet instabilities is iceberg rafted debris (IRD) fluxes. However, traditional methods of IRD quantification are labor‐intensive. Here, we present a new method of identifying IRD grains in sediment core X‐ray images using a convolutional neural network machine learning algorithm. We present a 3.3‐million‐year record of AIS IRD melt events using sediment cores from International Ocean Discovery Program Sites U1536, U1537, and U1538 in the Southern Ocean's "Iceberg Alley." We identify two increases in the IRD fluxes throughout this period, at ∼1.8 and 0.43 Ma. We propose that after 1.8 Ma, the AIS expanded and transitioned from a primarily terrestrial‐terminating to a primarily marine‐terminating ice sheet. Therefore, after 1.8 Ma, glacial terminations and AIS iceberg discharge are associated with variations in global ice volume, presumably through the mechanism of sea level and, therefore, grounding line change. The second AIS regime change occurs during the Mid‐Brunhes Event (∼0.43 Ma). After this time, there are heightened and continuous IRD fluxes at each glacial termination, indicating increased AIS size and instability after this time. Plain Language Summary: Understanding the timing and magnitude of the melt and retreat of the Antarctic Ice Sheet (AIS) in the past can help us understand its sensitivity to future global climate change. One way to understand ice sheets in the past is to identify and quantify sand to pebble‐sized rock and mineral grains incorporated into ice sheets and exported to the ocean by icebergs. These so‐called iceberg rafted debris (IRD) grains get deposited on the seafloor when icebergs melt, and they are easily identifiable in deep‐sea sediment core X‐ray images. Here, we present an artificial intelligence image detection method to identify IRD in sediment cores collected in the heart of "Iceberg Alley," a region that today receives the majority of Antarctic icebergs. We find that over the past 3.3 million years, there have been two increases in the amount of IRD deposited. We propose that the first major increase in IRD just after 1.8 Ma is evidence of an expansion of the AIS to an ice sheet with marine margins and ice shelves. We further propose that after 430,000 years ago, the AIS undergoes additional expansion and sees consistent, rapid retreat at the end of each global glaciation. Key Points: We present a machine learning method to quantify iceberg rafted debris (IRD) in deep‐sea sediment coresWe quantify IRD at three International Ocean Discovery Program sites in the heart of Iceberg Alley over 3.3 million yearsWe propose that Antarctica transitions from a primarily terrestrial‐terminating to marine‐terminating ice sheet 1.8 million years ago [ABSTRACT FROM AUTHOR]

The glacial‐interglacial cycle of elements and the linkage with biological production is very important. Nonetheless, records on incorporation of elements into diatom frustules are very poor in the Southern Ocean where diatom productivity is very high. As a result, there is a big gap in our understanding of elemental cycles in association with biological production and the controlling mechanisms. Here, we documented concentrations of major, trace, and rare earth elements of diatom frustules in two cores collected from the Southern Ocean since the Last Glacial Maximum to understand changes of incorporation of these elements into diatom frustules and to investigate mechanisms for changing incorporation. We found that there are three types of glacial‐interglacial variation patterns. Most elements showed increased (decreased) concentrations during the glacial period (interglacial) with decreased (increased) diatom production in the surface water following the variation pattern of magnetic susceptibility, whereas P, Ge, and Sb showed the opposite trend following the variation pattern of biogenic opal. Li, Ni, Ag, W, U, and I showed no clear glacial‐interglacial variation pattern. These different variation patterns imply that elemental incorporation into diatom frustules are also different according to elements. Our results revealed that biologically mediated removal of most elements from surface water to deep‐sea is comparable between glacial (low diatom production with high elements assimilation) and interglacial (high diatom production with low elements assimilation) periods in the Southern Ocean. However, more removal of P, Sb, and Ge in the surface water by diatoms occurs during interglacial periods in the Southern Ocean. Key Points: Concentrations of multi‐elements within diatom frustules were documented from the Southern Ocean since the Last Glacial Maximum (LGM)Most elements were assimilated/incorporated into diatoms synchronously: high (low) during glacial (interglacial) periodsP, Ge, and Sb showed low incorporation into diatom frustules during the LGM but increased during the Holocene [ABSTRACT FROM AUTHOR]

We document an apparent downward displacement of the Matuyama‐Brunhes magnetic reversal by ∼20 m at Scotia Sea International Ocean Discovery Program Site U1538 (Pirie Basin) by comparison with the well‐defined paleomagnetic record at nearby Site U1537 (Dove Basin). Detailed stratigraphic correlation between the two sites is possible due to similar lithologic variations. However, the two sites have distinctly different porewater geochemistry. Notably, Site U1538 indicates a greater demand for electron acceptors to oxidize organic carbon and Fe2+ enrichment below the depth of SO42− depletion. Magnetic parameters indicate enrichment of an authigenic magnetic mineral with strong remanence properties around the depth of SO42− depletion (∼46 m at Site U1538) relative to magnetic parameters at correlative depths at Site U1537. Fe2+ enrichment below the depth of SO42− depletion is not predicted based on the energetically favorable order of electron acceptors for microbial respiration but is documented here and in other depositional settings. This indicates Fe2+ production exceeds the production of H2S by SO42− reduction, providing a geochemical environment that favors the production and preservation of ferrimagnetic remanence‐bearing iron sulfides over paramagnetic pyrite and, thus, a mechanism for deep chemical remanent magnetization acquisition at depths of tens of meters. The influence of authigenic ferrimagnetic iron sulfides on paleomagnetic signals can be difficult to demonstrate with magnetic properties alone; therefore, this finding has implications for evaluating the fidelity of magnetostratigraphic records with complementary geochemical data. Such situations should be considered in other depositional environments with similar porewater Fe2+ accumulation below the SO42− reduction depth. Plain Language Summary: Sediment on the seafloor is an archive of Earth history, including past climate variations, ice sheet dynamics, and geomagnetic field variations. The lattermost include a history of when the Earth's magnetic field flipped upside down in the past so that compass needles would have pointed to the South Pole instead of the North Pole. Scientists have a good understanding of when these flips happened and, once identified in sedimentary layers, the flips can be used to identify time horizons—which are useful for dating other events recorded by the sediment. In this study, we present two magnetic reconstructions from nearby locations that initially recorded the same geomagnetic signals. After deposition, one of the magnetic records changed as a result of chemical reactions that modified the magnetic minerals in the sediment, making it difficult to correlate to the geomagnetic time scale. We have a nearby record with minimal chemical modifications so we could identify the chemical reactions were likely responsible for the changes. This observation will provide additional insights into what signals to look for when studying similar complications from other locations in the world. Key Points: The last magnetic reversal at Scotia Sea Site U1538 is offset downward by ∼20 m compared to the more reliable Site U1537 recordFerrous iron enrichment below the sulfate reduction depth is observed at Site U1538Anomalous magnetic minerals and porewater differences reveal a geochemical setting conducive to chemical remanent magnetization acquisition [ABSTRACT FROM AUTHOR]

The interplay between regional tectonics and the development of a major ocean gateway between the Pacific and the Atlantic Ocean has resulted in numerous paleogeographic reconstruction studies that describe the Cenozoic tectonic history of the Scotia Sea region. Despite the multitude of published tectonic reconstructions and the variety of geological and geophysical data available from the Scotia Sea, the geological history remains ambiguous. We present a comparative paleogeographic analysis of previously published tectonic reconstructions to identify agreements and conflicts between these reconstructions. We propose an alternative model to explain the Cenozoic evolution of the Scotia Sea region. The paleogeographic comparison shows that most reconstructions agree on the tectonic evolution of the South Scotia Ridge and the East Scotia Ridge. Major differences between the reconstructions are the role of the westward subducting plate below the South Sandwich plate, and the age and origin of the Central Scotia Sea. Tectonic reconstructions assume that the Central Scotia Sea is either part of a Cenozoic back‐arc basin, or a captured piece of Cretaceous oceanic crust. We propose a new alternative tectonic reconstruction that brings these two prevailing hypotheses elegantly together. Here, we identified new geographical blocks consisting of thinned continental or Cretaceous oceanic fragments that originate from the Paleo‐Pacific Weddell Sea gateway from high‐resolution bathymetry. These fragments are now part of the Central Scotia Sea and have been affected by early back‐arc tectonic activity of the South Sandwich subduction zone, leading locally to the formation of Cenozoic‐aged crust in the Central Scotia Sea. Key Points: New tectonic reconstruction based on qualitative comparison endmember reconstructionsThe Central Scotia Sea consists of fragments of Cretaceous and Cenozoic oceanic crustA shallow gateway at Drake Passage potentially existed already during the Eocene [ABSTRACT FROM AUTHOR]

Abstract We document an apparent downward displacement of the Matuyama‐Brunhes magnetic reversal by ∼20 m at Scotia Sea International Ocean Discovery Program Site U1538 (Pirie Basin) by comparison with the well‐defined paleomagnetic record at nearby Site U1537 (Dove Basin). Detailed stratigraphic correlation between the two sites is possible due to similar lithologic variations. However, the two sites have distinctly different porewater geochemistry. Notably, Site U1538 indicates a greater demand for electron acceptors to oxidize organic carbon and Fe2+ enrichment below the depth of SO42− depletion. Magnetic parameters indicate enrichment of an authigenic magnetic mineral with strong remanence properties around the depth of SO42− depletion (∼46 m at Site U1538) relative to magnetic parameters at correlative depths at Site U1537. Fe2+ enrichment below the depth of SO42− depletion is not predicted based on the energetically favorable order of electron acceptors for microbial respiration but is documented here and in other depositional settings. This indicates Fe2+ production exceeds the production of H2S by SO42− reduction, providing a geochemical environment that favors the production and preservation of ferrimagnetic remanence‐bearing iron sulfides over paramagnetic pyrite and, thus, a mechanism for deep chemical remanent magnetization acquisition at depths of tens of meters. The influence of authigenic ferrimagnetic iron sulfides on paleomagnetic signals can be difficult to demonstrate with magnetic properties alone; therefore, this finding has implications for evaluating the fidelity of magnetostratigraphic records with complementary geochemical data. Such situations should be considered in other depositional environments with similar porewater Fe2+ accumulation below the SO42− reduction depth.

Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to "dirty" icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world.

The fish community of the Scotia Sea is diverse and plays key roles in Antarctic food webs and biogeochemical cycling. However, knowledge of the spatial and community structure of their early life stages is limited, particularly in the region surrounding the South Orkney Islands. Here we examine the structure of the early life stage fish community in the epipelagic using data from a basin-scale survey conducted in early 2019, which sampled the top 200 m of the water column. 347 early life stage fish from 19 genera were caught in 58 hauls. A third of all specimens belonged to the genus Notolepis and the nine most common genera comprised over 90% of specimens. Cluster analysis revealed five distinct groupings, the most common were a group dominated by pelagic and shelf slope genera (Notolepis, Muraenolepis and Electrona) found mainly in oceanic waters (depth ≥ 1000 m), and a group dominated by species with demersal or benthopelagic adults (Chionodraco, Chaenocephalus and Nototheniops) found mainly in shelf waters. Bottom depth was the main environmental determinant of community structure, separating the diverse on-shelf assemblage at the South Orkneys from the less species-rich community of widespread oceanic taxa. Our results indicate the highest diversities of early life stages of endemic fish occur on the shelf and near-shelf areas. Dedicated monitoring is recommended to understand the seasonal differences in larval community assemblages and the implications of early life stages fish bycatch within the krill fishery. [ABSTRACT FROM AUTHOR]

Increased knowledge about marine mammal seasonal distribution and species assemblage from the South Orkney Islands waters is needed for the development of management regulations of the commercial fishery for Antarctic krill (Euphausia superba) in this region. Passive acoustic monitoring (PAM) data were collected during the autumn and winter seasons in two consecutive years (2016, 2017), which represented highly contrasting environmental conditions due to the 2016 El Niño event. We explored differences in seasonal patterns in marine mammal acoustic presence between the two years in context of environmental cues and climate variability. Acoustic signals from five baleen whale species, two pinniped species and odontocete species were detected and separated into guilds. Although species diversity remained stable over time, the ice-avoiding and ice-affiliated species dominated before and after the onset of winter, respectively, and thus demonstrating a shift in guild composition related to season. Herein, we provide novel information about local marine mammal species diversity, community structure and residency times in a krill hotspot. Our study also demonstrates the utility of PAM data and its usefulness in providing new insights into the marine mammal habitat use and responses to environmental conditions, which are essential knowledge for the future development of a sustainable fishery management in a changing ecosystem.

The Black-browed Albatross (BBA), Thalassarche melanophris, is one of the most abundant and widespread pelagic seabirds in the southern hemisphere, considered an indicator species of climate change in Antarctica. In addition to the known negative interactions with fisheries, other threats may act indirectly on this species whose effects have not yet been evaluated, such as increased sea surface temperature due to climate change. Under the assumption that carbon emissions modify the distribution of BBA, we modeled the environmental suitability and inferred BBA distribution under future climate scenarios for 2050 and 2100. We used 23 years of observation data (1991–2020) from research vessels in the Southwest Atlantic Ocean and Antarctica to estimate habitat suitability and predict change in suitability for the two future time ranges (2040–2050 and 2090–2100) under four representative concentration pathway scenarios: optimistic, intermediate pessimistic. Our projections predict a reduction in the total habitat suitability for BBA by 8% and 31.4% by 2050 and 2100, respectively, in the worst-case scenario compared to the present. Our study enhances understanding of the factors driving distribution dynamics for the species and aid in the development of conservation areas under future global change scenarios. [ABSTRACT FROM AUTHOR]

The carbon dioxide concentration in the atmosphere has progressively risen since pre-industrial times. About one-third of the anthropogenically generated CO2 is absorbed by the waters of the World Ocean, whereas the waters of the Southern Ocean take up about 40% of this CO2. The concentrations of oxygen and carbon dioxide dissolved in seawater are sensitive to climate changes, transferring anthropogenic pressures with consequences for the biogeochemical cycles in the World Ocean. The Southern Ocean is a key region for the exchange of oxygen and carbon between the surface water and the atmosphere and for their transfer with cold water masses to the deep layers of the Ocean. In this paper, we discuss the dynamics of the carbon dioxide partial pressure (pCO2) and dissolved oxygen (O2) in the surface waters of the Atlantic Southern Ocean based on data collected during the 87th cruise of the R/V "Academik Mstislav Keldysh". The study area includes the Bransfield Strait, Antarctic Sound, the Powell Basin, the Weddell, and Scotia Seas. We have analyzed the spatial distribution of pCO2 and oxygen for the areas of transformation of water masses and changes in biogeochemical processes. In the zone of Scotia and Weddell Seas, we have observed an increase in pCO2 and a decrease in oxygen concentrations at the transect from the Weddell Sea at 56° W to the Powell Basin. From the Antarctic Sound to the Bransfield Strait, a decrease in oxygen saturation and an increase in pCO2 has been traced. The surface waters of the Bransfield Strait have revealed the greatest variability of hydrochemical characteristics due to a complex structure of currents and intrusions of different water masses. In general, this area has been characterized by the maximum pCO2, while the surface waters are undersaturated with oxygen. The variability of the AOU/ΔpCO2 (w-a) ratio has revealed a pCO2 oversaturation and an O2 undersaturation in the waters of the Bransfield Strait. It is evidence of active organic carbon decomposition as the major controlling process. Yet, photosynthesis is the major biogeochemical process in the studied areas of the Weddell and Scotia seas, and their waters have been undersaturated with pCO2 and oversaturated with O2. As it comes from the analysis of the distribution and correlation coefficients of AOU and the sea-air gradient of pCO2 with other physical and biogeochemical properties, the predominance of the biotic processes to the dynamics of O2 and pCO2 in the surface water layer has been demonstrated for the studied areas. Yet, there is evidence of additional sources of CO2 not associated with the production and destruction processes of organic matter. [ABSTRACT FROM AUTHOR]

Bycatch of nontarget species can contribute to overfishing and slow efforts to rebuild fish stocks. Controlling bycatch is fundamental to sustainable fishing and maintaining healthy populations of target species. The Antarctic krill (Euphausia superba) fishery is the largest volume fishery in the Southern Ocean. Understanding the significance of bycatch and its diversity is critical to managing this keystone species. Registered bycatch data from the Antarctic krill fishery in the southwest Atlantic sector of the Southern Ocean were analysed. Observers collected data following an internationally agreed method during the 2010–2020 fishing seasons, with a 20 (± 9) % coverage of fishing activity of Total catch of Antarctic krill which increased from 200,000 tonnes to 450,000 tonnes, with the greatest increase over the last 3 years. Except in 2010 (2.2%), the bycatch ratio was stable and ranged 0.1–0.3%. Fish dominated the bycatch, followed by tunicates and other crustaceans. Observer coverage was high, and bycatch levels were generally low across gear types. Given that accurate information on bycatch is important for sustaining developing fisheries, maintaining high observer coverage of this fishery will be important for detecting impacts from a warming climate and for moving back into historical fishing grounds. [ABSTRACT FROM AUTHOR]

The superfamily Buccinoidea is the most speciose group of Neogastropoda within the Antarctic Convergence, with ~70 species classified in 21 genera, but is still poorly represented in molecular phylogenies. The first molecular data on the group presented in the recent phylogeny of the Buccinoidea (Kantor et al. 2022) lacked many important lineages, thereby limiting inference of the relationships of Antarctic Buccinoidea. We revisited relationships of the Antarctic Buccinoidea, involving recently collected molecular-grade samples from the bathyal and abyssal depths of the Scotia Sea, the Weddel Sea and adjacent regions. Our data set includes 25 species (including six genera studied on a molecular basis for the first time), sequenced for five phylogenetic markers: the barcode fragment of cox 1 gene, fragments of ribosomal 12S , 16S rRNA and 28S and nuclear H3 genes. Based on phylogenetic reconstructions, we synonymise the genus Lussitromina with Falsitromina and reassign the latter from Cominellidae to Prosiphonidae. We confirm the placement of four further genera, Drepanodontus , Germonea , Parabuccinum and Spikebuccinum in Prosiphonidae. We detect a previously unrecognised deep lineage of the family Prosiphonidae and describe this as the new genus Scotiabuccinum. The genus Parabuccinum , previously recorded in the Magellanic province and off the eastern coast of Argentina was reported for the first time within the Antarctic Convergence. We discover four previously unrecognised species of Antarctic Prosiphonidae and these are the first Buccinoidea from Antarctic waters described based on molecular data. According to our data, all but two species of Antarctic Buccinoidea belong to the family Prosiphonidae. Seven of the nineteen Recent Antarctic Prosiphonidae genera (36%) cross the boundaries of the Convergence and eight Antarctic genera are monotypic (42%). Currently no Buccinoidea species are known to occur both within and outside the Antarctic Convergence. ZooBank: urn:lsid:zoobank.org:pub:DEEA1599-C951-414E-9098-563EAD10BD57 The superfamily Buccinoidea is the most speciose group of Neogastropoda within the Antarctic Convergence with ~70 species classified in 21 genera. We revisited the relationships of the Antarctic Buccinoidea based on published molecular phylogeny and recently collected samples. In total, 25 species attributed to 17 (out of 21) genera were sequenced for five phylogenetic markers. We synonymised the genus Lussitromina with Falsitromina and reassigned the latter to Prosiphonidae. The new genus Scotiabuccinum and four new species are described. Parabuccinum is reported within the Antarctic Convergence for the first time. All but two species of Antarctic Buccinoidea belong to Prosiphonidae. No Buccinoidea species are known to occur both within and outside the Convergence. [ABSTRACT FROM AUTHOR]

Pteropods are a key part of biogeochemical cycling and epipelagic food webs in the Southern Ocean. However, shelled pteropods are vulnerable to climate change, due to their aragonite shells being particularly sensitive to ocean acidification. Currently our understanding of pteropod responses to environmental change is hindered by uncertainties surrounding their life cycles and population dynamics. In this study, we describe polar shelled pteropod diversity in the north-eastern Scotia Sea, inferring life history and population structures of the dominant pteropod species, Limacina rangii (formerly Limacina helicina antarctica) and Limacina retroversa. An annual timeseries of Limacina shell morphometrics was derived from individuals collected in a moored sediment trap at 400 m depth. We found that L. rangii and L. retroversa have contrasting life history strategies. L. rangii has a continuous spawning and recruitment period from November to March and can overwinter as juveniles and adults. L. retroversa has discrete spawning events from November to May, producing non–overlapping cohorts of juveniles and adults. Their development to the adult stage takes between two and five months, upon which they overwinter as adults. Our findings suggest different vulnerabilities of L. rangii and L. retroversa to a changing ocean. For example, since all life stages of L. rangii co-exist, vulnerability of one cohort is not detrimental to the stability of the overall population whereas, if one L. retroversa cohort fails to recruit, the entire population is threatened. Changes in pteropod populations could have cascading ramifications to Antarctic ecosystems and carbon cycling.

Microplastics (MP) have been reported in Southern Ocean (SO), where they are likely to encounter Antarctic zooplankton and enter pelagic food webs. Here we assess the presence of MP within Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) and quantify their abundance and type by micro-Fourier transform infrared microscopy. MP were found in both species, with fibres being more abundant than fragments (krill: 56.25% and salps: 22.32% of the total MP). Polymer identification indicated MP originated from both local and distant sources. Our findings prove how in situ MP ingestion from these organisms is a real and ongoing process in the SO. MP amount was higher in krill (2.13 ± 0.26 MP ind−1) than salps (1.38 ± 0.42 MP ind−1), while MP size extracted from krill (130 ± 30 µm) was significantly lower than MP size from salps (330 ± 50 µm). We suggest that differences between abundance and size of MP ingested by these two species may be related to their food strategies, their ability to fragment MP as well as different human pressures within the collection areas of the study region. First comparative field-based evidence of MP in both krill and salps, two emblematic zooplankton species of the SO marine ecosystems, underlines that Antarctic marine ecosystems may be particularly sensitive to plastic pollution.

Plate reconstructions provide basic constraints on the tectonic evolution of the Antarctic Peninsula but they are limited by a scarcity of paleomagnetic data. Here, using a combination of new and published paleomagnetic data and geological evidence, we present an updated reconstruction of the plate rotation and spatio‐temporal history of magmatism of the northern Antarctic Peninsula since ∼90 Ma. The Phoenix Plate‐Antarctic Peninsula convergence variation and back‐arc extension of the Scotia Plate are correlated to five distinct plate rotation periods. The initiation of the ancestral South Sandwich subduction zone and the late Paleocene separation between the Antarctic Peninsula and South America may be explained by the small‐ and large‐scale clockwise rotation of the Antarctic Peninsula starting at ∼80 and 62 Ma, respectively. Furthermore, we have identified five pulses of magmatism, which are correlated to the Phoenix Plate‐Antarctic Peninsula convergence rates. The Antarctic Peninsula plate rotation fits well with the process observed in the Phoenix Plate subduction, long‐term variation of the magmatism and tectonic evolution in the Scotia Sea, clarifying the relationship between these geological events. Plain Language Summary: In this study, we update the northern Antarctic Peninsula‐South Shetland Islands plate rotation process since ∼90 Ma. Five new enhanced magmatic events are identified in the northern Antarctic Peninsula‐South Shetland Islands, and we also reconstruct the migration of magmatism. Then, we compare plate rotation and magmatic migration to the Phoenix Plate‐Antarctic Peninsula convergence, and find a strong correlation between these events. The abrupt change in the convergence rate is attributed to the enhanced magmatic events. The clockwise rotation of the northern Antarctic Peninsula also corresponds to the Late Cretaceous initiation of the ancestral South Sandwich subduction zone and the late Paleocene separation of the northern Antarctic Peninsula from South America, indicating a causal relationship. The counterclockwise rotation of the northern Antarctic Peninsula after ∼47 Ma facilitated lithospheric extension and basin opening in the South Scotia Ridge region, contributing to the opening of the Scotia Sea. Therefore, this study provides a comprehensive interpretation of the geological process in Scotia Sea regions, from slab subduction and overlaying plate rotation to magmatic evolution and continental separation. Key Points: We provide an updated reconstruction of the plate rotation and magmatic process of the northern Antarctic Peninsula since ∼90 MaThe relationship between Phoenix Plate subduction, northern Antarctic Peninsula plate rotation, and magmatic migration is reconstructedThe northern Antarctic Peninsula's plate rotation is linked to Weddell Sea crust subduction and the late Paleocene opening of the Scotia Sea [ABSTRACT FROM AUTHOR]

From the BIOPEARL 1 and 2 Programs to the Amundsen and Scotia Seas a large series of Tanaidacea was collected using an epibenthic sled. We carried out a thorough morphological analysis of 169 individuals and provide a description of 14 pseudotanaid species distributed in three genera. Twelve species of the genus Pseudotanais are represented by three morphogroups: “affinis+longisetosus”, “denticulatus+abathagastor”, and “forcipatus”. We provide a redescription of Akanthinotanais gaussi, supplement the definitions of the genera Akanthinotanais and Beksitanais, and transfer Pseudotanais abyssi to the genus Beksitanais. Based on the literature and new data, we summarize knowledge of the Antarctic Pseudotanaidae and discuss this family’s spatial and bathymetric distribution. http://www.zoobank.org/urn:lsid:zoobank.org:pub:1A8F69F7-454D-4CB1-B745-3660AFD3BB82

The Scotia Sea is a productive pelagic ecosystem in the Southern Ocean, which is rapidly changing as a consequence of global warming. Species range shifts are particularly evident, as sub-Antarctic species expand their range from North to South, potentially rearranging the structure of this ecosystem. Thus, studies are needed to determine the current extent of variation in food web structure between these two biogeographic regions of the Scotia Sea and to investigate whether the observed patterns are consistent among depth zones. We compiled a database of 10,888 feeding interactions among 228 pelagic taxa, underpinned by surveys and dietary studies conducted in the Scotia Sea. Network analysis indicated that the Northern Scotia Sea (NSS), relative to the Southern Scotia Sea (SSS), is more complex: with higher species richness (more nodes) and trophic interactions (more links) is more connected overall (greater connectance and linkage density). Moreover, the NSS is characterised by more groups of strongly interacting organisms (greater node clustering) than the SSS, suggesting a higher trophic specialisation of Antarctic compared to sub-Antarctic species. Depth also played a key role in structuring these networks, with higher mean trophic position and more dietary generalism in the mesopelagic and bathypelagic zones relative to the epipelagic zones. This suggests that direct access to primary producers is a key factor influencing the trophic structure of these communities. Our results suggest that under current levels of warming the SSS ecosystem will likely become more connected and less modular, resembling the current structure of the NSS. [ABSTRACT FROM AUTHOR]

The Southern Ocean (SO) is the least understood environment on earth, but anthropogenic impacts related to climate change, fishing activities and tourism are already well-established in the region. Herein, we investigate biodiversity patterns in the Atlantic Sector of the SO by investigating a considerable number of samples collected from a wide depth range (89–6224 m). Three topics are addressed: (1) which taxa occur in the SO; (2) if there are distinct shelf, slope and abyssal faunas; and (3) which abiotic parameters explain the ostracod assemblages. We also tested putative ecological preferences of ostracod genera, widely used in palaeoceanographical reconstruction. For this, almost 5000 living ostracods from 51 epibenthic sledge samples were identified to 140 species. Statistically significant differences were observed among the faunas from the shelf, slope and abyssal faunas, indicating that the shelf fauna survived in refugia during the glacial periods of the Quaternary. Our analyses showed that the main variables influencing ostracod distribution is depth, followed by nitrate and phosphate. Temperature, salinity and oxygen content do not seem to be as important as previously proposed. Putative ecological preferences of ostracod genera, for example, low oxygen for Cytherella , could not be confirmed, suggesting that this topic requires further investigation. [ABSTRACT FROM AUTHOR]

From the BIOPEARL 1 and 2 Programs to the Amundsen and Scotia Seas a large series of Tanaidacea was collected using an epibenthic sled. We carried out a thorough morphological analysis of 169 individuals and provide a description of 14 pseudotanaid species distributed in three genera. Twelve species of the genus Pseudotanais are represented by three morphogroups: "affinis+longisetosus", "denticulatus+abathagastor", and "forcipatus". We provide a redescription of Akanthinotanais gaussi, supplement the definitions of the genera Akanthinotanais and Beksitanais, and transfer Pseudotanais abyssi to the genus Beksitanais. Based on the literature and new data, we summarize knowledge of the Antarctic Pseudotanaidae and discuss this family's spatial and bathymetric distribution. [ABSTRACT FROM AUTHOR]

• In situ measurements were made close to giant iceberg A-68A during its break-up phase. • Surface meltwater deepened underlying water masses by around 50 m. • Particulates and phytoplankton were rapidly displaced downwards close to A-68 icebergs. • Nutrients concentrations typical of deeper layers were found closer to the surface. • Ice-associated phytoplankton were present both upstream and downstream of the icebergs. • The dynamic oceanographic environment dominated over larger scale iceberg impacts. Large icebergs (>20 km long) are responsible for most of the freshwater discharged into the Southern Ocean. We report on in situ and satellite observations made during the break-up phase around South Georgia of the giant tabular iceberg A-68A. The in situ measurements were obtained during a 4-day visit by a research vessel in February 2021, where physical, chemical and biological measurements were made at a range of distances away from the main and subsidiary icebergs. These results were compared to a far-field station 133 km away. Upstream of the iceberg field, water column structure was similar to ambient water although there was evidence of iceberg-associated phytoplankton as a likely remnant of the passage of the icebergs. Nevertheless, enhancement of primary productivity along the path of the icebergs was not resolved in either in situ or monthly mean satellite observations. There was a considerable brash-ice field moving ahead of the icebergs which limited the number of downstream sampling stations. One downstream station within 2 km of iceberg A-68P showed several ice-melt influenced features that distinguished it from most other stations. Firstly, there was a strong stratified meltwater influenced layer that reached to around 120 m. This had the effect of deepening underlying water masses, with the core of the temperature minimum layer around 50 m deeper than elsewhere. Secondly, there was evidence of rapid downward displacement of both particulate material and certain phytoplankton taxa that may be a further result of this water mass deepening. Thirdly, macronutrient profiles were altered, with concentrations of nitrate, silicic acid and phosphate characteristic of deeper layers being found closer to the surface and a dilution of the ambient nutrient pool just above the iceberg draft that we ascribe to meltwater released from basal melting. Meanwhile, nutrient recycling processes associated with organic matter remineralisation were also modified by the physical restructuring of the water column and biotic components. Finally, the ice-associated phytoplankton taxa Pseudo-nitszchia/Nitszchia , found in both upstream and downstream locations, were abundant at this < 2 km-distant station through melting out from the iceberg and subsequent rapid growth. Overall, we resolved alterations to water column structure, nutrient profiles and phytoplankton community composition at fine to medium scales around the iceberg field. Nevertheless, although there may have been longer term and larger scale impacts, the dynamic oceanographic environment, including the presence of a strong oceanographic front and shelf-edge processes, dominated during the collapse of A-68A. [ABSTRACT FROM AUTHOR]

In aquatic environments, plastic pollution occurs concomitantly with anthropogenic climate stressors such as ocean acidification. Within the Southern Ocean, Antarctic krill (Euphausia Superba) support many marine predators and play a key role in the biogeochemical cycle. Ocean acidification and plastic pollution have been acknowledged to hinder Antarctic krill development and physiology in singularity, however potential multi-stressor effects of plastic particulates coupled with ocean acidification are unexplored. Furthermore, Antarctic krill may be especially vulnerable to plastic pollution due to their close association with sea-ice, a known plastic sink. Here, we investigate the behaviour of nanoplastic [spherical, aminated (NH2), and yellow-green fluorescent polystyrene nanoparticles] in Antarctic seawater and explore the single and combined effects of nanoplastic (160 nm radius, at a concentration of 2.5 μg ml–1) and ocean acidification (pCO2 ∼900, pHT 7.7) on the embryonic development of Antarctic krill. Gravid female krill were collected in the Atlantic sector of the Southern Ocean (North Scotia Sea). Produced eggs were incubated at 0.5 °C in four treatments (control, nanoplastic, ocean acidification and the multi-stressor scenario of nanoplastic presence, and ocean acidification) and their embryonic development after 6 days, at the incubation endpoint, was determined. We observed that negatively charged nanoplastic particles suspended in seawater from the Scotia Sea aggregated to sizes exceeding the nanoscale after 24 h (1054.13 ± 53.49 nm). Further, we found that the proportion of embryos developing through the early stages to reach at least the limb bud stage was highest in the control treatment (21.84%) and lowest in the multi-stressor treatment (13.17%). Since the biological thresholds to any stressors can be altered by the presence of additional stressors, we propose that future nanoplastic ecotoxicology studies should consider the changing global ocean under future climate scenarios for assessments of their impact and highlight that determining the behaviour of nanoplastic particles used in incubation studies is critical to determining their toxicity.

Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global-ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.

Southern Ocean waters enter the South Atlantic Ocean through the Scotia Sea along pathways constrained by the bathymetry of the northern Scotia Sea passages. We use the Argo profiling‐float data set to calculate the water transports in and out of the region, focusing on the water balances down to the deepest isoneutral sampled in all passages (γn = 28.0 kg m−3, located between about 500 and 2,000 m in the Drake Passage and even shallower in the Northern Passages). Down to this reference level, the water inflow through the Drake Passage is 140.8 ± 7.4 Sv and the water outflow through the deeper portions of the Northern Passages is 115.9 ± 8.3 Sv, implying a leakage of about 25 ± 11.1 Sv over topography shallower than 1,000 m. Below the reference isoneutral and down to 2,000 m, an additional 23.4 Sv enter through the Drake Passage; when added to reported inputs of about 20 Sv through the South Scotia Ridge, this accounts well for the observed 43.4 Sv outflow–from 28.0 kg m−3 to 2,000 m–through the Northern Passages. Relative to the 2,000 m reference level, the mean barotropic contribution always represents over half the total transports. We also observe substantial seasonal and moderate interannual variations in the water transports and composition (peak differences occur seasonally in the Drake Passage, with a range of 111–174 Sv), associated with changes in water exchange across the frontal systems. Two independent measures set the water mean‐residence time in the Scotia Sea at about 6–8 months. Plain Language Summary: The Scotia Sea is the entryway for Southern Ocean waters into the western South Atlantic Ocean, with waters entering through the Drake Passage (the Southern Ocean narrowest conduit) and exiting through several deep northern passages. Most of this transit water follows convoluted bands characterized by sharp horizontal gradients in water properties (frontal systems). We use the large set of profiles of temperature and salinity from the Argo network of drifting ocean profilers to measure the amount, characteristics, and pathways of those waters entering and leaving the Scotia Sea down to 2,000 m, as well as to assess their seasonal and interannual variability. This data set allows us to explore the water transports and transformations down to a certain ocean density level that is well sampled within all passages. Down to this level, about 141 million cubic meters per second (Sverdrups) enter through the Drake Passage, and 116 Sverdrups eventually exit through the deeper portions of the Northern Passages. Our calculations also reveal variations in water transport at interannual scales, although these are fairly small compared with variability within a year. We also show that most water parcels take about 6–8 months to travel the Scotia Sea along pathways that often cross the frontal systems. Key Points: We use Argo float data to calculate mean water transports into and out of the Scotia Sea and assess volume balances for fully sampled layersOur study reveals high seasonal and moderate interannual water‐transport variability, with substantial interannual changes in compositionThe water transports and float trajectories expose the influence of frontal systems and bottom topography, with high cross‐frontal exchange [ABSTRACT FROM AUTHOR]

This study investigates the relevance of the Elephant Island (EI) region for Southern Hemisphere fin whales (Balaenoptera physalus) in their annual life cycle. We collected 3 years of passive acoustic recordings (January 2013 to February 2016) northwest of EI to calculate time series of fin whale acoustic indices, daily acoustic occurrence, spectrograms, as well as the abundance of their 20 Hz pulses. Acoustic backscatter strength, sea ice concentration and chlorophyll-a composites provided concurrent environmental information for graphic comparisons. Acoustic interannual, seasonal and diel patterns together with visual information and literature resources were used to define the period of occupancy and to infer potential drivers for their behaviour. Spectral results suggest that these fin whales migrate annually to and from offshore central Chile. Acoustic data and visual information reveal their arrival at EI in December to feed without producing their typical 20 Hz pulse. For all 3 years, acoustic activity commences in February, peaks in May and decreases in August, in phase with the onset of their breeding season. Our results emphasize the importance of EI for fin whales throughout most of the year. Our recommendation is to consider EI for establishing a marine protected area to expedite the recovery of this vulnerable species.

Monitoring of early euphausiid larvae provides valuable information on the mechanisms involved in recruitment to the adult populations. As the Antarctic is undergoing rapid environmental change, these mechanisms are key to ecosystem-based management of the krill fishery. We analyzed the distribution and abundance of early euphausiid larvae (calyptopes I to late furciliae) from 76 plankton samples from surface to 300 m depth in the Atlantic sector in January 2011 in relation with a previous survey and published information. Thysanoessa macrura (mean density: 209 ind m−2) dominated the sampling while Euphausia superba (mean density: 13.63 ind m−2) and Euphausia frigida (mean density: 10.05 ind m−2) were also present. T. macrura density increased while E. superba experienced a high decrease respect to historical data. Clustering of stations and correspondence analysis showed that the associations of larvae and water masses are in agreement with literature reports, so the differences on the abundance of early larvae are within the observed variability and cannot be attributed to any single factor, suggesting that it is due to more subtle changes such as the stability of the water column and/or vorticity in the fronts. [ABSTRACT FROM AUTHOR]

International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea's Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world. Key Points: Extended composite and correlated equivalent depth scales are presented for Antarctic proximal International Ocean Discovery Program Sites U1536 and U1537U1536 and U1537 have excellent magnetostratigraphy and clear imprint of orbital variations in their lithologyChanges in terrigenous versus diatomaceous Dove Basin facies are out of phase with benthic δ18O during intervals between 3.3 and 1 Ma [ABSTRACT FROM AUTHOR]

The South Sandwich Trench located eastward of the Drake Passage in the Scotia Sea between Antarctica and South America is one of the least studied deep-sea trenches. Its geomorphological formation and present shape formed under the strong influence of the tectonic plate movements and various aspects of the geological setting, i.e., sediment thickness, faults, fracture zones and geologic lineaments. The aim of this paper is to link the geological and geophysical setting of the Scotia Sea with individual geomorphological features of the South Sandwich Trench in the context of the phenomena of its formation and evolution. Linking several datasets (GEBCO, ETOPO1, EGM96, GlobSed and marine freeair gravity raster grids, geological vector layers) highlights correlations between various factors affecting deep-sea trench formation and development, using the Generic Mapping Tools (GMT) for cartographic mapping. The paper contributes to the regional studies of the submarine geomorphology in the Antarctic region with a technical application of the GMT cartographic scripting toolset. [ABSTRACT FROM AUTHOR]

A variety of gravel‐ to cobble‐sized rocks, recovered from the Mar del Plata (MdP) Canyon area (Western South Atlantic at 38°S) and interpreted as ice‐rafted debris, represent the first evidence that large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. The drift process could have started as early as at the beginning of the last deglaciation, according to an age obtained from a cold‐water coral fragment associated with one of the dropstones. At the end of the Last Glacial Maximum, large icebergs have been supplied to the Antarctic Circumpolar Current, captured by those ocean current branches that circumvent the Falkland (Malvinas) Islands and entered the Argentine Margin. When the iceberg fleets approached the Brazil‐Falkland (Malvinas) Confluence Zone with its steep latitudinal temperature gradient, the icebergs got oceanographically trapped and melted off rapidly. The sediment load sinking down to the seafloor formed a dropstone blanket particularly where the MdP Canyon had incised into the continental slope. Here, mass‐flow processes, induced by local slope instability, and along‐slope sediment resorting, due to the erosional effects of strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit. Plain Language Summary: Icebergs can transport sand‐ to cobble‐sized sediment while drifting with the ocean currents over large distances away from the high latitudes. When seawater temperature forces the ice to melt, this "ice‐rafted debris" will sink down as "dropstones" to the seabed. Offshore dropstone deposits are common in polar regions but rarely found in lower latitudes because icebergs barely survive if the ocean water is not extremely cold. We found evidence of dropstone deposits along the Argentine Margin at the relatively low latitude of 38°S. They rest inside morphological seafloor depressions at the continental slope in association with the Mar del Plata Canyon. Here, also the oceanic Brazil‐Falkland (Malvinas) Confluence Zone is located, which acts as a barrier for northward drifting icebergs. The presence of icebergs in the Argentine Sea was already known; we, however, describe the first finding of rocks that clearly had originated from the Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea, and Tierra del Fuego, the southern tip of the South American continent. These dropstones are often found together with fragments of cold‐water corals, suggesting that the imported rocks have locally served as hard substrate for coral colonies to establish. Key Points: Rocks recovered from the Mar del Plata Canyon area, 38°S in the Western South Atlantic, are interpreted as ice‐rafted debrisAntarctic Peninsula, sub‐Antarctic islands in the Scotia Sea and Tierra del Fuego are identified as plausible source areasDropstones lie as a coarse sediment drape inside morphological depressions [ABSTRACT FROM AUTHOR]

The West Antarctic Ice Sheet (WAIS) is one of the largest potential sources of future sea-level rise, with glaciers draining the WAIS thinning at an accelerating rate over the past 40 years. Due to difficulties in calibrating palaeoceanographic proxies for the Southern Ocean, it remains difficult to assess whether similar changes have occurred earlier during the Holocene or whether there is underlying centennial to millennial scale forcing in oceanic variability. Archaeal lipid – based proxies, specifically Glycerol Dialkyl Glycerol Tetraether (GDGT) (e.g. TEX86 and TEX86) are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL) - GDGTs, representing (recently) living archaeal population in suspended particulate matter from the Amundsen Sea and the Scotia Sea. Shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean revealed a correlation between the physicochemical parameters of these water masses and IPL-GDGT distributions. Further analysis is required to elucidate the additional role of productivity and nutrient availability on Southern Ocean IPL-GDGT distributions. Of particular note for proxy development in the Amundsen Sea is that IPL GDGTs are likely actively synthesised at Circumpolar Deep Water depths and may be a significant source of GDGTs exported to the sedimentary record in this region. [ABSTRACT FROM AUTHOR]86) are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL) - GDGTs, representing (recently) living archaeal population in suspended particulate matter from the Amundsen Sea and the Scotia Sea. Shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean revealed a correlation between the physicochemical parameters of these water masses and IPL-GDGT distributions. Further analysis is required to elucidate the additional role of productivity and nutrient availability on Southern Ocean IPL-GDGT distributions. Of particular note for proxy development in the Amundsen Sea is that IPL GDGTs are likely actively synthesised at Circumpolar Deep Water depths and may be a significant source of GDGTs exported to the sedimentary record in this region. [ABSTRACT FROM AUTHOR]

Based on the data from long sediment cores retrieved by R/V Eltanin (United States) during the 1950s–1960s, Neo- and Eopleistocene lithofacies maps of the southern Pacific Ocean (scale 1 : 20 000 000) and Scotia Sea (scale 1 : 10 000 000) were compiled for the first time. For the Scotia Sea, schemes of isopachites are shown on the respective lithofacies maps. All maps are processed with the volumetric method proposed by A.B. Ronov. The results revealed that accumulation rates of the terrigenous and siliceous sediments increased during the Pleistocene in both sedimentation basins due to neotectonic activity in the Antarctic Peninsula, which enhanced fluxes of not only terrigenous matter but also nutrients delivered by melted waters to the photosynthesis zone via vertical circulation. [ABSTRACT FROM AUTHOR]

Measurements of currents and Antarctic Bottom Water properties overflowing the sill from the Weddell to the Scotia Sea are described. The bottom water overflows the sill of one of the passages through the South Scotia Ridge (eastern part of the Philip Passage approximately at 48° W). A weak flow of Weddell Sea Deep Water to the north was found. The northward flow was recorded only in the western part of the passage, which is 14 km wide. The velocity of the flow is 4 cm/s; the bottom water transport is 0.1–0.2 Sv. [ABSTRACT FROM AUTHOR]

The northeast periphery of the Scotia Sea hosts one of the largest chlorophyll‐a blooms of the Southern Ocean. This bloom peaks to the northwest of the island of South Georgia, extending eastward for hundreds of kilometers. Although the Southern Ocean has many islands of similar size, South Georgia is ecologically one of the most significant: It not only sustains one of the Southern Ocean's largest and most diverse ecosystems but also constitutes its single most important region for biological carbon sequestration. While the exceptional nature of South Georgia's blooms has been recognized widely, both the physical processes that contribute to their fertilization and the reasons why these blooms are larger than those of other similar regions (e.g., Kerguelen or Crozet Islands) are poorly understood. We use the results of a high‐resolution ocean model to investigate the physical processes that mediate the entrainment of deep, iron‐rich waters into the surface layers of the South Georgia region. We show that the Southern Antarctic Circumpolar Current Front, the southernmost jet of the Antarctic Circumpolar Current (ACC), pumps iron‐enriched waters from the deep ocean onto the bottom layers of South Georgia's shelf. These waters are upwelled along the northern coast of the island and are then exported into the Georgia Basin, where topographically steered circulation shields them from the dispersive effects of local currents and eddies, thus allowing the bloom development. Plain Language Summary: The growth of phytoplankton in the ocean is the base of the marine food web and is fueled by the supply of nutrients. In the Southern Ocean, this growth is anomalously strong downstream of islands and seamounts and very markedly so downstream of the island of South Georgia. We use a high‐resolution ocean model to explain how the ocean circulation supplies nutrients to the South Georgia bloom and find that the pumping of iron‐rich waters from depth onto the South Georgia shelf is key, as is upwelling of water on the northern side of the island and subsequent flow into the open ocean beyond. This marine growth supports a rich and diverse ecosystem, including some species which are commercially valuable. Key Points: The northwestern coast of South Georgia is an important upwelling regionThe SACCF generates strong obduction of deep waters around the South Georgia shelfLocal wind stress forcing is the primary driver of cross‐shelf mass exchanges [ABSTRACT FROM AUTHOR]

Reconstructing sedimentary redox history provides valuable insights into for understanding of paleoceanographic/paleoclimatic changes in the climatically sensitive Southern Ocean. However, our comprehension of the spatial variations in historical redox changes and the driving forces in the Southern Ocean, especially the Antarctic Zone, remains incomplete. Here, we present detailed sedimentary records of the redox state (i.e., sulfur isotopes), bottom-water oxygenation conditions (i.e., redox-sensitive metals), export production (i.e., 230Th-normalized biogenic opal and barium), and carbon burial flux over the last ∼35 kyr in the Protector Basin, the deepest basin of the southern Scotia Sea. The studied sediment record in this basin reveals significant variations in geochemical redox proxies throughout the glacial (MIS 2)–interglacial (MIS 1) period, featuring a significant 34S depletion of up to ∼40‰ relative to seawater sulfate and a noticeable increase in ER Mo /ER U ratio in interglacial sediments. These findings highlight a significant shift in bottom-water and/or sediment oxygenation from glacial oxic to interglacial anoxic/euxinic conditions, primarily driven by climate-induced changes in biogenic productivity, rather than the deep circulation and ventilation dynamics previously emphasized in the Antarctic Zone. Signs of the climate-driven redox change are also evident in two millennial-scale cold events (∼9–8 ka and ∼3–2 ka), marked by sudden shifts toward oxic conditions. Importantly, our results reveal a contrasting scenario to previous observations in the glacial–interglacial redox history within the Antarctic Zone, signifying spatial disparity in bottom-water and sediment redox chemistry. • Sedimentary δ34S and metals records reveal dramatic redox changes in the Antarctic Zone. • Results highlight a glacial (oxic)-to-interglacial (anoxic/sulfidic) change, with millennial-scale variations. • Redox variability in the Antarctic Zone is closely linked to climate-driven productivity changes. • A regional disparity in the glacial–interglacial redox change within the AZ region was observed. [ABSTRACT FROM AUTHOR]

Understanding the biodiversity of an ecosystem is crucial to determine its structure and resistance to climate change. The South Sandwich Islands (SSI) are located in the Scotia Sea (Southern Ocean), within the South Georgia and the South Sandwich Islands Marine Protected Area. However, the biodiversity of the archipelago remains poorly studied, whilst climate change has the potential for wide-ranging impacts in the Antarctic and Subantarctic regions. Here we used predators as biological samplers to study the bathyal communities of SSI. A total of 61 species including fish, cephalopods and crustaceans, were identified from the diet of 13 predatory taxa (11 fish and two cephalopod). Common Subantarctic and Antarctic species were found, with Moroteuthopsis longimana being the species with the highest density (1.74 individuals per stomach at Montagu Island). Eleven fish and one cephalopod species were recorded for the first time at the archipelago. Furthermore, 16 fish species had their bathymetric range increased. Fifteen fish and one crustacean appear to have SSI as the northern or southern limit of their distribution. Community analysis found two major groups at SSI, one in the north and one in the south, with the southern group subdivided into two groups. This separation is related to the environmental conditions at the archipelago that abruptly change at Saunders Islands. Latitude (correlated with sea surface temperature) and sea surface height (proxy for upwelling) both correlated with the dissimilarity between communities. These results suggest that climate change may affect the biodiversity at SSI in the future as warming waters of the Scotia Sea and changes in the upwelling system may favour range extensions of more northerly species into the archipelago. Furthermore, it could lead to local extinctions of some species exclusively found in the southernmost areas of the archipelago. • Biological samplers allow the study of the deep-sea biodiversity of remote locations. • Twelve species were identified for the first time at South Sandwich Islands. • Subantarctic and Antarctic species were identified at the archipelago. • Two communities exist at South Sandwich Islands, one at north and one at south. • Sixteen species have South Sandwich Islands as the limit of their distribution. [ABSTRACT FROM AUTHOR]

Different species of baleen whales display distinct spatial distribution patterns in the Scotia Sea during the austral summer. Passive acoustic and visual surveys for baleen whales were conducted aboard the RRS James Clark Ross in the Scotia Sea and around South Georgia in January and February 2003. Identified calls from four species were recorded during the acoustic survey including southern right (Eubalaena australis), blue (Balaenoptera musculus), fin (B. physalus) and humpback whales (Megaptera novaeangliae). These acoustic data included up calls made by southern right whales, downswept D and tonal calls by blue whales, two possible types of fin whale downswept calls and humpback whale moans and grunts. Visual detections included southern right, fin, humpback and Antarctic minke whales (B. bonaerensis sp.). Most acoustic and visual detections occurred either around South Georgia (southern right and humpback whales) or south of the southern boundary of the Antarctic Circumpolar Current (ACC) and along the outer edge of the ice pack (southern right, blue, humpback and Antarctic minke whales). Fin whales were the exception, being the only species acoustically and visually detected primarily in the central Scotia Sea, along the southern ACC front. In addition to identifiable calls from these species, two types of probable baleen whale calls were detected: 50Hz upswept and pulsing calls. It is proposed that minke whales may produce the pulsing calls, based on their similarities with minke whale calls recorded in the North Atlantic Ocean. There was an overlap between locations of fin whale sightings and recordings and locations of 50Hz upswept calls in the central Scotia Sea, but these calls were most similar to calls attributed to blue whales in other parts of Antarctica. More study is required to determine if baleen whales produce these two call types, and if so, which species. The efficiency of acoustics and visual surveys varied by species, with blue whales being easier to detect using acoustics, Antarctic minke whales being best detected during visual surveys and other species falling in between these two extremes.

An oceanographic survey around the South Shetland Islands (SSI) and the South Orkney Islands (SOI) was conducted during January 2007 and February 2008, respectively, as part of the United States Antarctic Marine Living Resources (AMLR) program ecosystems surveys. At 27 stations, concentrations of dissolved labile Fe (DFe) and total acid leachable (unfiltered, TaLFe) iron (Fe) were measured in the upper 200 m (including coastal and oceanic waters) to better resolve the factors limiting primary production in these regions. Northwest of the SSI, a region influenced by Drake Passage (DP) waters, mean DFe (∼0.26 nM) and TaLFe (∼1.02 nM) concentrations were the lowest, whereas intermediate concentrations for both DFe and TaLFe were measured in the Bransfield Strait (BS). Around Elephant Island (EI), over and off the continental shelf, Fe concentrations differed between the west and the east margins. DFe and TaLFe concentrations further support the argument that the effect of the Shackleton Transverse Ridge (STR) is a crucial structure affecting both the Fe and the chlorophyll distributions in this region. The waters around the SOI had DFe concentrations higher than those in the SSI, with the area north of the South Scotia Ridge (SSR) (60°S), having the highest DFe (0.54 nM) concentrations and the waters in Powell Basin (PB) having the lowest DFe (1.17 nM) and TaLFe (4.51 nM) and concentrations. These spatial patterns of Fe suggest that there are different Fe inputs from shelf waters near the Antarctic Slope Front (ASF). The overall TaLFe:DFe ratios, used as indicator for understanding the relative distance of Fe sources, were lower around the SOI compared to those in the SSI, suggesting that the Fe source for SOI waters was more distant. The spatial patterns between Fe and chlorophyll-a (Chl-a) concentrations in relation to the hydrography highlight the complexity and variability of the oceanographic processes in the region. These results improve the knowledge on the Fe sources and inputs in the less known SOI waters during the austral summer, and they further support the importance of advective processes from the Fe-rich waters that flow from the eastern margin of the Antarctic Peninsula (AP) into the Weddell-Scotia Confluence (WSC).

Myctophids are the most abundant and diverse mesopelagic fishes in the Southern Ocean. They are a conduit of energy between primary consumers and higher marine predators, and between the surface layers and the mesopelagic depths. However, there remain major uncertainties about their ecology, particularly regarding their role in Southern Ocean food webs in waters south of the Antarctic Polar Front, which are often regarded as dominated by Antarctic krill. Limited data on the feeding ecology of myctophids has made it difficult to assess the importance of myctophids as consumers of krill and how they fit in the traditional view of a krill-dominated system (diatom-krill-higher predator). We provide a new assessment of the role of myctophids in Southern Ocean food webs using information from recent trophodynamic studies of myctophids conducted in the Scotia Sea, one of the most productive regions of the Southern Ocean and a region that sustains both major populations of higher predators (sea birds, seals, whales) and important commercial fisheries (krill, toothfish, and mackerel icefish). Collectively, these data show that myctophids have a central role in Southern Ocean food webs as both predators and prey. Large myctophid species are prevalent consumers of krill throughout their distributional range and in different seasons in the Scotia Sea. Moreover, best estimates of both myctophid and higher predator consumption of krill to date indicate that large myctophids are the greatest predators of krill in this region, consuming almost as much krill as do all other vertebrates. Nevertheless, there are several smaller myctophid species that do not eat krill, instead consuming copepods and other small euphausiids. Myctophids therefore link primary producers to higher predators through both krill-dependent and krill-independent trophic pathways, emphasizing their importance in regional food webs. Consequently, trophic pathways involving large myctophids are unlikely to be exempt from the direct consequences of projected redistribution and/or reduction in krill population biomass under scenarios of ocean-warming, whilst trophic pathways involving small myctophids may be more resilient to such effects and become increasingly important to higher trophic levels. Further studies are required to determine the extent to which myctophids can maintain food web stability and sustain higher predator populations during periods of prolonged reductions in krill abundance. Including knowledge of the role of myctophids in Southern Ocean food webs will be important for developing robust projections of the impacts of future change to inform decision making for conservation and management.

Zooplankton fecal pellets (FPs) are important conduits of carbon from the surface to the deep ocean, as shown by their presence in deep-sea sediment traps. Zooplankton themselves are thought to play an important role in the breakdown and reworking of FPs as they sink, whilst processes such as diel vertical migration (DVM) may enhance the supply of carbon to the mesopelagic. However, comparatively little is known about the processes or variability of FP sinking/transport within the upper mesopelagic and how this relates to deeper ocean export. Profiles of FP type and size, and the contribution made by FPs to mesopelagic carbon flux to a depth of 400 m, were considered. Three contrasting locations in the Scotia Sea were compared, which together reflect the variability in physical regime and productivity encountered across the Southern Ocean. Comparing observed FPs with predictions from the mesozooplankton community, we show that, even at shallow depths, the smallest fraction of FP is under-represented, suggesting rapid remineralization, incorporation into larger aggregates or reworking into larger FPs, and that the flux is dominated by FPs from larger zooplankton. In contrast to models where POC attenuation rates are set to increase with temperature, we find that FP carbon flux attenuates rapidly in low productivity, colder regions dominated by krill, while remineralization is deeper in warmer areas where productivity is high and copepods dominate. This emphasizes the strong modulation of the zooplankton community on the supply and transfer of FP carbon between the epi- and mesopelagic. Evidence was found to suggest that DVM enhances FP flux across the upper mesopelagic, producing a pulse of fresh, dense material that may support secondary production and heterotrophic respiration in the mesopelagic. This illustrates that variability in flux at short (daily) as well as longer (seasonal) timescales may have important implications for the supply of FP carbon to deeper waters.

The sinking of the ocean sea bottom is produced by thermal cooling of the lithosphere. This evolution is determined by the underlying asthenospheric mantle. Estimation of the Curie Depth variations in the Scotia Sea by using a spectral approach and applied on magnetic anomaly data led us to determine a thermal model and derive a heat flux map. Using multichannel seismic and bathymetry data, we show that the West Scotia Sea reaches thermal equilibrium more quickly than other oceans do and thermally behaves like old oceanic crust in large oceans, following a different empirical age (t, in Ma)‐depth (d, in m) relationship, d(t) = 4,480 − 19,380 exp(−t/4). For oceanic crusts of the same age, underlain by different shallow mantle controlling the heat supply, low heat flux values imply older ages than those predicted for large oceans based on the empirical relationships of the standard plate model. These circumstances, together with the new heat flux map, shed light on the anomalous evolution of the Scotia Sea, a consequence of the present Pacific mantle outflow through the Drake Passage. Two branches of elevated heat flux surround the Shackleton Fracture Zone and extend to the northern and southern boundaries of the Scotia Plate. Most of the heat sources are located in the flanks, whereas the colder parts are centrally located. This signature supports the Drake Passage's role as a main mantle gateway for Pacific outflow toward the Atlantic reservoir favoring the oceanic spreading activity of this ocean. Key Points: The thermal evolution of the Scotia Sea is anomalous compared with other oceansThe heat flux pattern reveals asthenospheric branches close to the Scotia Sea boundariesScotia Sea and Drake Passage represent a main gateway for Pacific mantle outflow [ABSTRACT FROM AUTHOR]