Southern Scotia Sea Research Articles

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.

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.

One‐To‐One Coupling Between Southern Ocean Productivity and Antarctica Climate

AbstractThe Southern Ocean is supposed to play a crucial role in influencing atmospheric CO2 concentrations. However, the dynamic relationships among the rate of Southern Ocean upwelling, atmospheric CO2 concentration, and Antarctic climate at millennial timescales remain unclear. Here, we present high‐resolution color reflectance component b* and natural gamma radiation from the southern Scotia Sea sector of the Southern Ocean to reconstruct productivity over the past 160 ka. We find that these two independent productivity proxies, reflecting the signal of nutrient supply in this region, captured millennial‐scale upwelling that covaried in timing with Heinrich Stadials and Antarctic warming events, supporting the bipolar seesaw mechanism. The one‐to‐one coupling of variability between productivity and atmospheric CO2 concentrations reveals that the upwelling is closely linked to atmospheric CO2 and climate change.

Geochronology and geochemistry of the South Scotia Ridge: Miocene island arc volcanism of the Scotia Sea

The ancestral South Sandwich arc (ASSA) records evidence of Oligocene – Miocene intra-oceanic island arc volcanism in the central Scotia Sea and potentially formed an important topographic barrier to deep ocean currents during the early development of the Antarctic Circumpolar Current. New geochemistry and geochronology of dredged basaltic samples from multiple sites across Discovery Bank, in the southern part of the ASSA, provide key information about this poorly understood volcanic arc in the Scotia Sea. Two new 40 Ar/ 39 Ar ages confirm volcanism was active in the Discovery Bank segment from 14 to 10 Ma, overlapping with the initial phase of spreading along the East Scotia Ridge. These ages are younger than previously determined for the ASSA and the island arc chain would have influenced deep ocean pathways in the southern Scotia Sea during the mid-Miocene. Geochemical analysis indicates that magmatism was derived from a depleted asthenospheric source, modified by subduction, akin to the present day South Sandwich island arc. Evidence from across Discovery Bank suggests that arc volcanism developed on pre-existing basaltic crust potentially related to Weddell Sea subduction, although the submerged bank is dominated by Miocene arc volcanic rocks. Evidence for an intra-oceanic island arc setting is also provided by the identification and imaging of a linear chain of rear-arc seamounts, characteristic of several volcanic centres in the present day South sandwich island arc. Mafic volcanic rocks, including ultramafic lithologies, from the neighbouring Bruce Bank topographic high have also been investigated and are demonstrated to have been generated in a different tectonic setting to the volcanic rocks of Discovery Bank. They are interpreted to be associated with the opening of Scan Basin during the Late Eocene, or potentially distal evidence of the gabbroic Pacific Margin Anomaly. • Discovery Bank forms part of an ancestral intra-oceanic island arc. • Basaltic volcanic rocks derived from a depleted mantle source. • Volcanism has been dated in the interval 14–10 Ma. • Volcanism on the ancestral arc overlaps with initial spreading on the East Scotia Ridge. • The arc volcanoes formed a barrier to deep ocean currents into the Late Miocene.

Recent morpho-sedimentary processes in Dove Basin, southern Scotia Sea, Antarctica: A basin-scale case of interaction between bottom currents and mass movements

Multibeam bathymetric imagery and acoustic sub-bottom profiles are used to reveal distribution patterns of sub-surface sedimentation in Dove Basin (Scotia Sea). The goals of the study are to determine the imprint of the inflow of deep Antarctic water masses from the Weddell Sea into the Scotia Sea, to establish the factors driving the styles of contourite deposition and to discern the relative contribution of alongslope versus downslope processes to the construction of the uppermost late Quaternary sedimentary record in the basin.The most significant morpho-sedimentary features in Dove Basin are linked to contouritic processes and to mass movements. Plastered drifts on the flanks of the basin constitute the most common contouritic deposits. Basement-controlled drifts on top of structural elevations are common along the central ridge, the central basin plain and scattered along the basin flanks. Sheeted drifts occur on top of adjacent banks or are restricted to the deep basin. In contrast, mounded drifts are poorly represented in Dove basin. A laterally extensive contouritic channel runs along the central ridge. Contouritic channels are also identified in the upper parts of the lateral banks and slopes. Numerous slide scars along the upper parts of the slopes evolve downslope into semitransparent lens-shaped bodies, with occasional development of across-slope channels. Semitransparent lenses occur intercalated within stratified deposits in the slopes of the basin, in the central ridge and in the deepest basin plain.The spatial arrangement of contouritic morphologies points to the influence of the water column structure and the basin physiography. In the eastern sub-basin, two different fractions (lower and upper) of Weddell Sea Deep Water (WSDW) leave an imprint on contourite deposits owing to the sloping interface between the two fractions. Contouritic influence is more subdued in the western sub-basin, and limited to the imprint of the lower WSDW. The upper parts of the surrounding banks are under the influence of deep-reaching Circumpolar waters (i.e., Lower Circumpolar Deep Water), which develops both depositional and erosional morphologies. The cross-section V-shaped morphology of the basin and the common occurrence of structural highs drive the predominance of plastered and basement-controlled drifts in the sediment record. The frequent alternation between contourites and downslope gravity-flow deposits is likely due to different processes associated with over-steepening in the basin, such as basement-controlled steep slopes, deformed drifts atop basement elevations, and the development of thick contouritic piles. Dove Basin is an example of a basin without mounded, plastered or mixed hybrid drifts in the transition between the lower slope and the deep basin, because the upper boundary of the deepest water mass —the Weddell Sea Deep Water— flows shallower along the middle slope. This fact underlines the relevance of the position and depth of water masses in shaping the morphology of the feet of slopes along continental margins.

Ecological Networks in the Scotia Sea: Structural Changes Across Latitude and Depth

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.

Sinking Diatom Assemblages as a Key Driver for Deep Carbon and Silicon Export in the Scotia Sea (Southern Ocean)

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.

Miocene to present oceanographic variability in the Scotia Sea and Antarctic ice sheets dynamics: Insight from revised seismic-stratigraphy following IODP Expedition 382

Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.

Facies Structure and Quantitative Parameters of Pleistocene Sedimentation on the Deep-Sea Floor of the Southern Pacific Ocean and in the Scotia Sea

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.

Geomorphology of Ona Basin, southwestern Scotia Sea (Antarctica): Decoding the spatial variability of bottom-current pathways

Ona Basin, the westernmost oceanic basin in the southern Scotia Sea, is affected by the opposite flows of Circumpolar Deep Water (CDW) and Weddell Sea Deep Water (WSDW); thus, it represents a key location for exploring seafloor morphologies influenced by bottom currents. The present study aims to capture the spatial arrangement of recent subsurface contourite features, assuming a latitudinal influence of water masses and the interactions between along- and downslope processes, in order to contribute to the knowledge of regional deepwater flow pathways and to the sedimentary model of small sediment-starved oceanic basins. To this end, the investigation combines an interpretation of multibeam bathymetry and parametric echo sounder seismic data complemented with hydrological data. The distribution of morpho-sedimentary features in Ona Basin reveals two major domains. The southern margin of the basin can be regarded as a mixed/hybrid system containing abundant sediment drifts with channels and contourite moats and a lateral continuity interrupted by downslope morphologies. In contrast, the northern abyssal setting comprises relatively homogeneous large sheeted drifts with superimposed sediment waves, mounded drifts, and several scattered erosive features, likely reflecting the more distinct influence of deepwater contourite processes. Our work demonstrates that tectonic features in the southern basin control the interaction between deepwater along- and downslope processes, as the westward flow of the WSDW is deflected, channelized, and intensified along its westward route. In the northern region, the study indicates an overall clockwise rotation of the WSDW flow, with the spatial and vertical variability of CDW and WSDW affecting the distribution of bottom-current features around seamounts and/or structural highs. The results underscore the importance of sloping interphases in the water mass vertical structure, the degree of basin confinement, and the influence of local bathymetric elevations in sedimentation models of small sediment-starved oceanic basins.

Thirty years of marine debris in the Southern Ocean: Annual surveys of two island shores in the Scotia Sea

We report on three decades of repeat surveys of beached marine debris at two locations in the Scotia Sea, in the Southwest Atlantic sector of the Southern Ocean. Between October 1989 and March 2019 10,112 items of beached debris were recovered from Main Bay, Bird Island, South Georgia in the northern Scotia Sea. The total mass of items (data from 1996 onwards) was 101 kg. Plastic was the most commonly recovered item (97.5% by number; 89% by mass) with the remainder made up of fabric, glass, metal, paper and rubber. Mean mass per item was 0.01 kg and the rate of accumulation was 100 items km−1 month−1. Analyses showed an increase in the number of debris items recovered (5.7 per year) but a decline in mean mass per item, suggesting a trend towards more, smaller items of debris at Bird Island. At Signy Island, South Orkney Islands, located in the southern Scotia Sea and within the Antarctic Treaty area, debris items were collected from three beaches, during the austral summer only, between 1991 and 2019. In total 1304 items with a mass of 268 kg were recovered. Plastic items contributed 84% by number and 80% by mass, with the remainder made up of metal (6% by number; 14% by mass), rubber (4% by number; 3% by mass), fabric, glass and paper (<1% by number; 3% by mass). Mean mass per item was 0.2 kg and rate of accumulation was 3 items km−1 month−1. Accumulation rates were an order of magnitude higher on the western (windward) side of the island (13–17 items km−1 month−1) than the eastern side (1.5 items km−1 month−1). Analyses showed a slight decline in number and slight increase in mean mass of debris items over time at Signy Island. This study highlights the prevalence of anthropogenic marine debris (particularly plastic) in the Southern Ocean. It shows the importance of long-term monitoring efforts in attempting to catalogue marine debris and identify trends, and serves warning of the urgent need for a wider understanding of the extent of marine debris across the whole of the Southern Ocean.

Habitat partitioning in Antarctic krill: Spawning hotspots and nursery areas.

Antarctic krill, Euphausia superba, have a circumpolar distribution but are concentrated within the south-west Atlantic sector, where they support a unique food web and a commercial fishery. Within this sector, our first goal was to produce quantitative distribution maps of all six ontogenetic life stages of krill (eggs, nauplii plus metanauplii, calyptopes, furcilia, juveniles, and adults), based on a compilation of all available post 1970s data. Using these maps, we then examined firstly whether “hotspots” of egg production and early stage nursery occurred, and secondly whether the available habitat was partitioned between the successive life stages during the austral summer and autumn, when krill densities can be high. To address these questions, we compiled larval krill density records and extracted data spanning 41 years (1976–2016) from the existing KRILLBASE-abundance and KRILLBASE-length-frequency databases. Although adult males and females of spawning age were widely distributed, the distribution of eggs, nauplii and metanauplii indicates that spawning is most intense over the shelf and shelf slope. This contrasts with the distributions of calyptope and furcilia larvae, which were concentrated further offshore, mainly in the Southern Scotia Sea. Juveniles, however, were strongly concentrated over shelves along the Scotia Arc. Simple environmental analyses based on water depth and mean water temperature suggest that krill associate with different habitats over the course of their life cycle. From the early to late part of the austral season, juvenile distribution moves from ocean to shelf, opposite in direction to that for adults. Such habitat partitioning may reduce intraspecific competition for food, which has been suggested to occur when densities are exceptionally high during years of strong recruitment. It also prevents any potential cannibalism by adults on younger stages. Understanding the location of krill spawning and juvenile development in relation to potentially overlapping fishing activities is needed to protect the health of the south-west Atlantic sector ecosystem.

Fe sources and transport from the Antarctic Peninsula shelf to the southern Scotia Sea

The Antarctic Peninsula (AP) shelf is an important source of dissolved iron (Fe) to the upper ocean in the southern Scotia Sea, one of the most productive regions of the Southern Ocean. Here we present results from a four-year (2003-2006) numerical simulation using a regional coupled physical-biogeochemical model to assess the Fe sources and transport on the AP shelf and toward the southern Scotia Sea. The model was validated with a suite of data derived from in situ surveys and remote sensing. Model results indicate that sediments in the AP shelf and the South Orkney Plateau (SOP) provide the dominant source of Fe to the upper 500 m in the southern Scotia Sea. Additional Fe inputs to the region are associated with the Antarctic Circumpolar Current (ACC) and the northern limb of the Weddell Gyre, deep-ocean sediment sources, dust deposition, and icebergs. Fe on the AP shelf originates primarily from sediments on the relatively shallow inner shelf and is directly injected into the water column and subsequently transported toward Elephant Island by the confluent shelf currents. Off-shelf Fe export is primarily through entrainment of shelf waters by the ACC’s Southern Boundary frontal jet along the northern edge of the AP shelf, the Hesperides Trough, and the SOP shelf. About 70% of the off-shelf export takes place below the surface mixed layer, and is subsequently re-supplied to the euphotic zone through vertical mixing, mainly during austral fall and winter. The exported shelf-derived Fe is then advected downstream by the ACC and Weddell Gyre and spread over the southern and eastern Scotia Seas. Taken together, shelf Fe export witin top 500 m meets nearly all of the Fe demand of phytoplankton photosynthesis in the southern Scotia Sea. Waters with elevated Fe concentrations in the Scotia Sea are largely restricted to south of the Southern ACC Front.

Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 610:149-162 (2019) - DOI: https://doi.org/10.3354/meps12861 Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean Anna Belcher*, Ryan A. Saunders, Geraint A. Tarling British Antarctic Survey, Natural Environment Research Council, Cambridge, CB3 0ET, UK *Corresponding author: annbel@bas.ac.uk ABSTRACT: Mesopelagic fish have recently been highlighted as an important, but poorly studied component of marine ecosystems, particularly regarding their role in the marine pelagic food webs and biogeochemical cycles. Myctophids (Family Myctophidae) are one of the most biomass-dominant groups of mesopelagic fishes, and their large vertical migrations provide means of rapid transfer of carbon to the deep ocean where it can be sequestered for centuries or more. In this study, we develop a simple regression for the respiration rate of myctophid fish using literature-based wet mass and habitat temperature data. We apply this regression to net haul data collected across the Scotia-Weddell sector of the Southern Ocean to estimate respiration rates of the biomass-dominant myctophid species. Electrona carlsbergi, Electrona antarctica, and Gymnoscopelus braueri made a high contribution (up to 85%) to total myctophid respiration. Despite the lower temperatures of the southern Scotia Sea (-1.46 to 0.95°C), total respiration here was as high (reaching 1.1 mg C m-2 d-1) as in the warmer waters of the mid and northern Scotia Sea. The maximum respiratory carbon flux of the vertically migrating community was 0.05 to 0.28 mg C m-2 d-1, equivalent to up to 47% of the gravitational particulate organic carbon flux in some parts of the Scotia-Weddell region. Our study provides the first baseline estimates of respiration rates and carbon flux of myctophids in the Southern Ocean. However, direct measurements of myctophid respiration, and of mesopelagic fish generally, are needed to constrain these estimates further and incorporate these fluxes into carbon budgets. KEY WORDS: Myctophid · Respiration · Lantern fish · Carbon · Active flux · Southern Ocean Full text in pdf format Supplementary materialCorrigendum PreviousNextCite this article as: Belcher A, Saunders RA, Tarling GA (2019) Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean. Mar Ecol Prog Ser 610:149-162. https://doi.org/10.3354/meps12861 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 610. Online publication date: February 01, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Vertical Structure of Near-Surface Sediments in the Central Parts of the Yaghan and Scan Basins (Scotia Sea)

The structure of the sediment sequence of the Scotia Sea is the basis for reconstructing the geological history of the development of its floor in the late Quaternary. One of the most important elements of the floor of the southern Scotia Sea is the Scan Basin, the formation of which played a substantial role in the breakup of the American–Antarctic continental bridge that connected the Bruce and Discovery banks. By now, the main parameters of the sediment sequence in the Scan Basin have been reconstructed, but the literature reflects the lack of data on the upper part of the section. On an observation profile, the Spanish R/V Hesperides, using a TOPAS PS 18/40 high-resolution seismic profiler, distinguished three beds in the central part of the basin. The total mean thickness of the first reflector is 3.7 ms; the second, 2.3 ms; and the third, 1.8 ms. The beds have a relatively consistent thickness and are distinctly traced along the profile. The literature data on the sedimentation parameters make it possible to estimate the total mean deposition time for the first bed of 133 ka; the second, 84 ka; and the third, 64 ka; the total mean sediment accumulation time for all three beds is 281 ka.

Giant mass-transport deposits in the southern Scotia Sea (Antarctica)

Abstract On the basis of 2D multichannel and very-high-resolution seismic data and swath bathymetry, we report a sequence of giant mass-transport deposits (MTDs) in the Scan Basin (southern Scotia Sea, Antarctica). MTDs with a maximum thickness of c. 300 m extend up to 50 km from the Discovery and Bruce banks towards the Scan Basin. The headwall area consists of multiple U-shaped scars intercalated between volcanic edifices, up to 250 m high and 7 km wide, extending c. 14 km downslope from 1750 to 2900 m water depth. Seismic sections show that these giant MTDs are triggered by the intersection between diagenetic fronts related to silica transformation and vertical fluid-flow pipes linked to magmatic sills emplaced within the sedimentary sequence of the Scan Basin. This work supports that the diagenetic alteration of siliceous sediments is a possible cause of slope instability along world continental margins where bottom-simulating reflectors related to silica diagenesis are present at a regional scale.

Structure of Subsurface Sediments in the Scan Basin (Scotia Sea)

The structure of sediments in the Scotia Sea is used as a basis for reconstructing the geological history of its bottom in the Late Quaternary. The Scan Basin is one of the main elements of the topography of the southern Scotia Sea. Its formation played a considerable role in the fragmentation of the continent, which included the Bruce and Discovery banks. The main parameters of the sediment layer in the Scan Basin have been reconstructed by the present time, but its top part has not been studied. In this work, we analyze the first data obtained on the R/V Gesperidas with the use of a TOPAS PS 18/40 high-resolution seismic profilograph in 2012. Three layers in the subsurface sediments on the bottom of the Scan Basin were specified for the first time. The mean periods of their deposition in the Late Quaternary were determined as 115000 years for the first, 76000 years for the second, and 59 000 years for the third layer from the surface of the bottom. The duration of the total accumulation period of the three layers is about 250000 years.

Tectonic activity evolution of the Scotia‐Antarctic Plate boundary from mass transport deposit analysis

AbstractThe spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia‐Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia‐Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic‐Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.

High-resolution seismic stratigraphy and morphology of the Scan Basin contourite fan, southern Scotia Sea, Antarctica

The Scan Basin is the easternmost of the southern Scotia Sea basins. It is located in a complex tectonic setting, north of the boundary between the Scotia and Antarctic plates. In addition, Scan Basin is directly to the north of Bruce Passage, which connects the Scotia and Weddell seas through the northward overflow of the Weddell Sea Deep Water (WSDW). Scan Basin has been described as an isolated small oceanic basin, where the fan-shaped abyssal plain is bounded by Bruce and Discovery banks. Sedimentary processes involved in the development of the Scan Basin sediment record during the late Pliocene-Quaternary are discussed here, through the examination of the distribution and morphological and acoustic characteristics of erosional, depositional, gravitational, fluid-escape, and volcanic features in correlation to the geological and oceanographic setting. The abyssal plain reflects the action of high-energy bottom-current circulation along its western side and lower-energy bottom currents along the eastern side. In contrast, Discovery Bank reflects a highly dynamic interplay between bottom-current activity, mass-wasting processes, and processes linked to the water mass interfaces. Variations in the abyssal plain stratigraphy are associated with events that may be related to climate changes since the late Miocene, involving increased bottom-current circulation and variations in the interaction between the WSDW and the Antarctic Circumpolar Current. The Scan Basin sector is one example of a contourite depositional system developed downstream of a deep gateway exit, and its major depositional characteristics allow its classification as a contourite fan. These new findings contribute to clarifying the development of contourite fans in regions of significant bottom-water interchange.

Constraining the dating of late Quaternary marine sediment records from the Scotia Sea (Southern Ocean)

In Southern Ocean sediments south of the Antarctic Polar Front, the scarcity of calcareous microfossils hampers the development of sediment chronologies based on radiocarbon dating and oxygen isotope stratigraphy established from carbonate. In this study, radiometric dating, magnetic susceptibility (MS), biogenic opal content, diatom abundance fluctuation, and paleomagnetic information were investigated on a north–south transect of central Scotia Sea sediment cores to verify their reliability as stratigraphic tools in the study area. Radiocarbon dating on organic carbon humic acid fraction can be used to establish the stratigraphy of upper core sections, but regional comparison and correlation are needed to verify a possible bias by fossil carbon contamination. For the long-term stratigraphy, MS, which can be correlated to the Antarctic ice core dust/climate signal, represents the most valuable parameter. Fine-grained single domain magnetite, probably of biogenic origin, makes a significant contribution to the interglacial MS signal, while major contributions from detrital material affect the glacial MS record. The core from the southern Scotia Sea contains significant proportions of biogenic magnetite also in glacial sediments, suggesting depositional environments different from those of the northern Scotia Sea. Our data suggest low contributions of high-coercive minerals to the overall magnetic intensity of glacial and interglacial Scotia Sea sediments, which excludes dust as a main source of the magnetic signal. Opal content can be used to distinguish between cold and warm intervals for the past 300 thousand years. Abundance fluctuation patterns of diatom species Fragilariopsis kerguelensis and Eucampia antarctica are useful stratigraphic tools for periods back to Marine Isotope Stage (MIS) 6. The Mono Lake geomagnetic excursion is identified in Scotia Sea sediments for the first time. Possible correlations of ash layers are suggested between Scotia Sea sediments and East Antarctic ice cores. They have potential to serve as additional age markers for further studies in this area.