Scotia Sea Research Articles

Number of the Most Abundant Sea Mammal Species in the Vicinities of the Antarctic Peninsula, Scotia Sea and Powell Basin Area

Observations were conducted from the Research Vessel “Akademik Mstislav Keldysh” in the Drake Passage, vicinities of the Antarctic Peninsula, Scotia Sea and the northern part of the Weddel Sea during two voyages in January–early March 2020 (the vessel trip number 79) and during the single voyage in January–February 2022 (trip number 87). Data allow to evaluate the number of the most abundant sea mammals in the area near South Shetland Islands, Scotia Sea and Powell Basin. Observation area of 2022 in the Antarctic were located in about 150 km eastwards of the area of 2020. The area under survey of a little bit greater than 343 th. square km in January-February 2020 held approximately 1200 Humpback Whales (Megaptera novaeangliae) and 2800 Fin Whales (Balaenoptera physalus). In 2022 this area held approximately 2500 Fin Whales and again 1200 or more amount of Humpback Whales. Numbers of the Antarctic Fur Seals in each season here assessed approximately 2000-3000 animals. Type of distribution of these two whale species along the vessel track pointed on the absence of food competition either within or between these species during Antarctic summers of 2020 and 2022. It was possible to evaluate the total numbers of the Antarctic Fur Seal (Arctocephalus gazella), however this evaluation appeared to be less precise than the same ones for Humpback Whales and Fin Whales.

Cretaceous–Paleogene tectonic reconstructions of the South Scotia Ridge and implications for the initiation of subduction in the Scotia Sea

The Cenozoic development of the Scotia Sea and the opening of Drake Passage led to the dispersal of crustal blocks of the North and South Scotia ridges, which today have a strong influence on the pathway of the Antarctic circumpolar current. The pre-translation positions of the crustal fragments of the Scotia ridges are uncertain, with correlations to both the Antarctic and South American plates. We present direct geochronology results ( 40 Ar/ 39 Ar) from the Bruce and Jane banks of the South Scotia Ridge that yield Late Cretaceous–Paleogene ages, indicating a pre-translation magmatic history. The basaltic magmatism from Bruce Bank is calc-alkaline, akin to the Cenozoic magmatism of the South Orkney microcontinent and the South Shetland Islands, and agrees with pre-translation tectonic models that place the crustal blocks of the South Scotia Ridge adjacent to the northern Antarctic Peninsula arc. The intra-oceanic arc magmatism at Jane Bank is Late Cretaceous in age (97.2 ± 1.1 Ma) and is therefore inconsistent with models suggesting a Miocene origin as part of the ancestral South Sandwich arc. The development of westwards-directed subduction adjacent to Jane Bank is predicted in some tectonic models as a consequence of Late Cretaceous plate dynamics that developed prior to the Oligocene–Miocene ancestral arc. Supplementary material: Full 40 Ar/ 39 Ar datasets and GPlates reconstruction files are available at https://doi.org/10.6084/m9.figshare.c.6639909

Distribution and biomass estimation of Antarctic krill (Euphausia superba) off the South Orkney Islands during 2011–2020

Abstract Antarctic krill is a key species in the Southern Ocean and subject to the most extensive fishery in the Antarctic. The Norwegian Institute of Marine Research has conducted acoustic-trawl monitoring of krill off the South Orkneys annually since 2011 in collaboration with the krill fishing industry. Average krill biomass within the 60000 km2 survey area ranged from 1.4 to 7.8 million tonnes in the period 2011–2020, strongly supporting that this is among the regions in the Scotia Sea with consistently highest krill densities. There were no significant (p ≈ 0.18, non-parametric Mann–Kendall test) monotonic trends in estimated krill biomass over the 10 years. The highest krill densities were associated with the shelf edge and submarine canyons on the north side of the South Orkneys. Our comparison with the CCAMLR 9.3% reference exploitation rate suggests that management of the krill fishery in the South Orkneys region is precautionary. The monitoring is run on fishing vessels, so e.g. acoustic frequencies applied could not always be in compliance with the standard CCAMLR methodology. Estimated deviance in krill backscatter when comparing 38 kHz to the standard 120 kHz ranged from −1.1% to 12.8%. Our results show that industry-based surveys are cost-efficient approaches to high-quality monitoring of krill.

Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate change

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(formerlyLimacina helicina antarctica) andLimacina retroversa. An annual timeseries ofLimacinashell morphometrics was derived from individuals collected in a moored sediment trap at 400 m depth. We found thatL. rangiiandL. retroversahave contrasting life history strategies.L. rangiihas a continuous spawning and recruitment period from November to March and can overwinter as juveniles and adults.L. retroversahas 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 ofL. rangiiandL. retroversato a changing ocean. For example, since all life stages ofL. rangiico-exist, vulnerability of one cohort is not detrimental to the stability of the overall population whereas, if oneL. retroversacohort fails to recruit, the entire population is threatened. Changes in pteropod populations could have cascading ramifications to Antarctic ecosystems and carbon cycling.

Carbon budgets of Scotia Sea mesopelagic zooplankton and micronekton communities during austral spring

Zooplankton form an integral component of epi- and mesopelagic ecosystems, and there is a need to better understand their role in ocean biogeochemistry. The export and remineralisation of particulate organic matter at depth plays an important role in controlling atmospheric CO2 concentrations. Pelagic mesozooplankton and micronekton communities may influence the fate of organic matter in a number of ways, including: the consumption of primary producers and export of this material as fast-sinking faecal pellets, and the active flux of carbon by animals undertaking diel vertical migration (DVM) into the mesopelagic. We present day and night vertical biomass profiles of mesozooplankton and micronekton communities in the upper 500 m during three visits to an ocean observatory station (P3) to the NW of South Georgia (Scotia Sea, South Atlantic) in austral spring, alongside estimates of their daily rates of ingestion and respiration throughout the water column. Day and night community biomass estimates were dominated by copepods >330 μm, including the lipid-rich species, Calanoides acutus and Rhincalanus gigas. We found little evidence of synchronised DVM, with only Metridia spp. and Salpa thompsoni showing patterns consistent with migratory behaviour. At depths below 250 m, estimated community carbon ingestion rates exceeded those of metabolic costs, supporting the understanding that food quality in the mesopelagic is relatively poor, and organisms have to consume a large amount of food in order to fulfil their nutritional requirements. By contrast, estimated community rates of ingestion and metabolic costs at shallower depths were approximately balanced, but only when we assumed that the animals were predominantly catabolising lipids (i.e. respiratory quotient = 0.7) and had relatively high absorption efficiencies. Our work demonstrates that it is possible to balance the metabolic budgets of mesopelagic animals to within observational uncertainties, but highlights the need for a better understanding of the physiology of lipid-storing animals and how it influences carbon budgeting in the pelagic.

Taxonomy of Antarctic Buccinoidea (Gastropoda: Neogastropoda) revisited based on molecular data

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 cox1 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

Tracing the impacts of recent rapid sea ice changes and the A68 megaberg on the surface freshwater balance of the Weddell and Scotia Seas.

The Southern Ocean upper-layer freshwater balance exerts a global climatic influence by modulating density stratification and biological productivity, and hence the exchange of heat and carbon between the atmosphere and the ocean interior. It is thus important to understand and quantify the time-varying freshwater inputs, which is challenging from measurements of salinity alone. Here we use seawater oxygen isotopes from samples collected between 2016 and 2021 along a transect spanning the Scotia and northern Weddell Seas to separate the freshwater contributions from sea ice and meteoric sources. The unprecedented retreat of sea ice in 2016 is evidenced as a strong increase in sea ice melt across the northern Weddell Sea, with surface values increasing approximately two percentage points between 2016 and 2018 and column inventories increasing approximately 1 to 2 m. Surface meteoric water concentrations exceeded 4% in early 2021 close to South Georgia due to meltwater from the A68 megaberg; smaller icebergs may influence meteoric water at other times also. Both these inputs highlight the importance of a changing cryosphere for upper-ocean freshening; potential future sea ice retreats and increases in iceberg calving would enhance the impacts of these freshwater sources on the ocean and climate. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Oxygen and pCO2 in the Surface Waters of the Atlantic Southern Ocean in 2021–2022

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.

Impact of the climate regime shift around 2000 on recruitment of Antarctic krill at the Antarctic Peninsula and South Georgia

We examined how the climate regime shift around 2000 affected Antarctic krill recruitment variability at the North Antarctic Peninsula (NAP) and South Georgia (SG) during the period of 1990s through to 2000s. We used sea surface temperature (SST) as a proxy of the monthly sea ice extent and related it to the recruitment index (proportion of 1-year-old krill) of each succeeding year for NAP and SG by examining the correlation of the time series before and after 2000. For NAP, recruitment index was negatively correlated with winter SST at NAP in the 1990s but with autumn SST in the 2000s, suggesting that good recruitment was supported by extensive winter sea-ice in the 1990s but by extensive autumn sea-ice in the 2000s. This was attributed to the regime shift featured by winter warming and autumn cooling after 2000. For SG, recruitment was negatively correlated with winter SST at NAP in the 1990s but positively correlated with autumn SST in the southern Scotia Sea (SSS) in the 2000s. According to particle tracking experiment from NAP to SG in relation to the sea-ice extent and position of SACCF (Southern Antarctic Circumpolar Current Front), less sea-ice extent in 2000s meant less larvae distributing as north as SACCF, resulting in much fewer larval being transported to SG. Hence, we hypothesized that the regime shift weakened the connection between NAP and SG, but instead SSS became the main driver of recruitment at SG. We presume the krill population demonstrated adaptability to the regime shift by offsetting the unfavorable winter condition with the favorable autumn condition at NAP and for SG, replacing the source of recruits with those closer to it.

A note on the movement of a humpback whale from Abrolhos Bank, Brazil to South Georgia

Most models of population structure for Southern Hemisphere humpback whales (Megaptera novaeangliae) assume that individuals feeding in the Scotia Sea migrate primarily to breeding and calving areas off Brazil. However data to support this are few and mostly indirect. Abrolhos Bank, Brazil, is the largest breeding and calving ground for humpback whales in the western South Atlantic Ocean. Historically, the waters near South Georgia held the largest concentrations of humpback whales in Antarctic Area II and were among the largest in the Southern Ocean. Photographs of individually distinctive natural markings on humpback whale flukes collected from the Scotia Sea (n=9) were compared with two collections of photographs from Brazilian waters (n=829 and n=735) to identify re-sightings. A humpback whale photographed in August 2000 at Abrolhos Bank was subsequently photographed in December 2004 near Shag Rocks off South Georgia. The migratory distance between these sightings is 3,945km. This finding constitutes the first long-distance individual resighting to be documented from either of these areas.

Baleen whales in the Scotia Sea during January and February 2003

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.

A simple method for taxon-specific purification of diatom frustules from ocean sediments using a cell sorter

It is necessary to purify diatom frustules by taxon to perform accurate geochemical analyses of diatom fossils preserved in sediments. However, the small size of diatoms has hitherto prevented taxon-specific purification; therefore, previous geochemical analyses of diatom frustules have been performed with mixtures of various taxa. In this study, we developed a taxon-selective collection method of diatom fossils that uses a cell sorter. The experimental material comprised six samples from a sediment core of Hole U1538A in the Scotia Sea, Atlantic sector of the Southern Ocean drilled during the International Ocean Discovery Program Expedition 382. Following conventional pretreatments (removal of organic matter and carbonates as well as clay minerals), we conducted cell sorter experiments focusing on the optical and fluorescence characteristics of the diatom fossils. We succeeded in selectively isolating with high purity five diatom taxa representing the Southern Ocean diatom flora: (1) discoid diatoms (mainly Thalassiosira) with a moderate degree of fluorescence; (2) Fragilariopsis (mainly Fragilariopsis kerguelensis), which exhibits the highest fluorescence values; (3) Rhizosolenia; (4) Eucampia antarctica; and (5) needle-shaped diatoms (Thalassiothrix). This taxon-specific diatom purification method will enable more accurate geochemical analyses, such as the oxygen isotope ratio (δ18O) of diatom frustules, which is likely to lead to significant advances in paleoceanography, especially at high latitudes or in upwelling zones where diatoms are abundant. This method will also be useful in paleolimnology, ocean biology, and phycology.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Decreasing Trends of Chinstrap Penguin Breeding Colonies in a Region of Major and Ongoing Rapid Environmental Changes Suggest Population Level Vulnerability

The bulk of the chinstrap penguin (Pygoscelis antarcticus) global population inhabits the Antarctic Peninsula and Scotia Sea, which is a region undergoing rapid environmental changes. Consequently, regional level decreases for this species are widespread. This study aimed to evaluate the level of breeding colony changes in the Antarctic Peninsula and South Orkney Islands, which, roughly, hold 60% of the global chinstrap penguin population. The results indicated that within a period of 40 to 50 years, 62% of colonies underwent decreases, and the majority of colonies experienced decreases over 50%, which is represented by numbers in the range of 2000 to 40,000 pairs. Within three generations’ time, the whole population for the area had experienced decreases of around 30%. These levels of decrease add to the fact that the suspected causes are not likely reversible in the short- to mid-term, calling for increased concern about the conservation of this species.

A seasonal transition in biological carbon pump efficiency in the northern Scotia Sea, Southern Ocean

The biological carbon pump (BCP) contributes to the oceanic CO2 sink by transferring particulate organic carbon (POC) into the deep ocean. The magnitude and efficiency of the BCP is likely to vary on timescales of days to seasons, however characterising this variability from shipboard observations is challenging. High resolution, sustained observations of primary production and particle fluxes by autonomous vehicles offer the potential to fill this knowledge gap. Here we present a 4 month, daily, 1 m vertical resolution glider dataset, collected in the high productivity bloom, downstream of South Georgia, Southern Ocean. The dataset reveals substantial temporal variability in primary production, POC flux and attenuation. During the pre-bloom peak phase we find high export efficiency, implying minimal heterotrophic POC consumption, i.e. productivity is decoupled from upper ocean remineralisation processes. As the bloom progresses from its peak through its declining phase, export flux decreases, but transfer efficiency within the upper 100 m of the mesopelagic increases. Conversely, transfer efficiency in the lower mesopelagic decreases in the post-bloom phase, implying that the flux attenuation processes operating in the upper and lower mesopelagic are effectively decoupled. This finding underscores an important limitation of using a single parameter, such as Martin's ‘b’, to characterise POC flux attenuation in a given location or season. Frequent pulses of export flux are observed throughout the deployment, indicating decoupling between primary production and the processes driving export of material from the upper ocean. The mechanisms underlying the observed seasonal changes in BCP magnitude and efficiency are unclear, as temperature and oxygen concentration changed minimally, although the nature of the sinking particles changed substantially as the bloom progressed. Our results highlight the difficulty of capturing temporal variability and episodic flux events with traditional shipboard observations, which affects our conceptual understanding of the BCP. The increasing use of autonomous vehicles to observe particle fluxes will be essential to characterising the temporal variability in magnitude and functioning of the BCP.

Plate Rotation of the Northern Antarctic Peninsula Since the Late Cretaceous: Implications for the Tectonic Evolution of the Scotia Sea Region

AbstractPlate 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.

A database of marine macronutrient, temperature and salinity measurements made around the highly productive island of South Georgia, the Scotia Sea and the Antarctic Peninsula between 1980 and 2009

Abstract. We present a database from substantial collections of macronutrient data made on 20 oceanographic cruises, primarily from around the island of South Georgia and the Scotia Sea. This sector of the Southern Ocean was studied comprehensively during the Discovery Investigations between ∼1920 and 1950 and resulted in the hugely influential Discovery Reports. Following this pioneering research period, there was a lull of several decades prior to the British Antarctic Survey (BAS) initiation of an offshore biological programme to study the ecology of the South Atlantic sector of the Southern Ocean. These studies began in the late 1970s and have continued until the present day. Between 1980 and 2009, the programme included macronutrient measurements as part of an integrated ecosystem analysis. In addition to South Georgia and the Scotia Sea, measurements were also made in the Bellingshausen Sea and the waters to the west of the Antarctic Peninsula. Data were collected during all months of the year with the exceptions of May and June and compiled into a database. Vertical profile samples were taken from water bottles, while data along transects were collected by monitoring the ship's non-toxic seawater supply. Nutrients measured were silicate (Si(OH)4–Si), phosphate (PO4–P), nitrate (NO3–N), ammonium (NH4–N), and nitrite (NO2–N). Our database includes nutrient data along with contemporaneous temperature and salinity data where available. Further background and supporting information is included for context. The profile and underway sample data have been deposited at the UK Polar Data Centre and are publicly available in NetCDF and CSV formats from https://doi.org/10.5285/4014370F-8EB2-492B-A5F3-6DC68BF12C1E (Whitehouse et al., 2022).

The South Shetland Islands, Antarctica: Lithostratigraphy and geological map

Over the last few decades, numerous geological studies have been carried out in the South Shetland Islands, which have greatly contributed to a better understanding of its geological evolution. However, few attempts have been conducted to correlate the geological units throughout this archipelago. We present herein a review of the literature available in the South Shetland Islands, which we use to propose a lithostratigraphical correlation that constitutes a coherent stratigraphy for the main Mesozoic and Cenozoic rocks of the South Shetland Islands along with a new geological map. The lithostratigraphical correlation shows that the geological and environmental evolution comprises three main stages: 1) deep marine sedimentation from ∼164 to 140 Ma, 2) subaerial volcanism and sedimentation with a proliferation of plants and fauna from ∼140 to 35 Ma and 3) glacial and interglacial deposits from ∼35 Ma. The lithostratigraphical correlation also shows a broad geographical trend of decreasing age of volcanism from southwest to northeast, which has been previously suggested. However, this spatial age trend is disrupted by the presence of Eocene magmatism in Livingston Island, located in the centre of the archipelago. We suggest that the migration of volcanism occurred from the Late Cretaceous until the early Eocene. Subsequently, enhanced magmatic activity took place from the mid-Eocene until the Miocene, which we associate with processes related with the waning of subduction. Constraining the protolith age of the metamorphic complex of Smith Island remains challenging, yet holds key implications for the tectonic and accretionary evolution of the Antarctic Peninsula. The rocks recording the glaciation of this sector of Antarctica are well exposed in the northern South Shetland Islands and hold critical information for understanding the timings and processes that lead to the greenhouse to icehouse transition at the end of the Eocene. Finally, contemporaneous rocks to the breakup of Antarctic Peninsula from Patagonia that led to the opening of the Drake Passage and the development of the Scotia Sea are exposed in the centre and north of the South Shetland archipelago. Better constraints on the age and tectonic settings on these units may lead to further understanding the paleobiogeographical evolution of the region, which may have played an important role for speciation as a land bridge between South America and Antarctica. The dataset containing the geological map and associated information is shared as a shapefile or KML file.

Antarctica, South Georgia Island, Scotia Sea Coast

Antarctica, South Georgia Island, Scotia Sea Coast

Identifying seasonal distribution patterns of fin whales across the Scotia Sea and the Antarctic Peninsula region using a novel approach combining habitat suitability models and ensemble learning methods

Following their near extirpation by industrial whaling of the 20thcentury, the population status of Southern Hemisphere fin whales (SHFW) remains unknown. Systematic surveys estimating fin whale abundance in the Southern Ocean are not yet available. Records of fin whale sightings have been collected by a variety of organisations over the past few decades, incorporating both opportunistic data and dedicated survey data. Together, these isolated data sets represent a potentially valuable source of information on the seasonality, distribution and abundance of SHFW. We compiled records across 40 years from the Antarctic Peninsula and Scotia Sea from multiple sources and used a novel approach combining ensemble learning and a maximum entropy model to estimate abundance and distribution of SHFW in this region. Our results show a seasonal distribution pattern with pronounced centres of distribution from January-March along the West Antarctic Peninsula. Our new approach allowed us to estimate abundance of SHFW for discrete areas from a mixed data set of mainly opportunistic presence only data.