Scotia Sea Research Articles

Geodynamic setting of Scotia Sea and its effects on geomorphology of South Sandwich Trench, Southern Ocean

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 free- air 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.

New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio‐Pleistocene

AbstractInternational 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.

Mercury biomagnification in a Southern Ocean food web.

Biomagnification of mercury (Hg) in the Scotia Sea food web of the Southern Ocean was examined using the stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) as proxies for trophic level and feeding habitat, respectively. Total Hg and stable isotopes were measured in samples of particulate organic matter (POM), zooplankton, squid, myctophid fish, notothenioid fish and seabird tissues collected in two years (austral summers 2007/08 and 2016/17). Overall, there was extensive overlap in δ13C values across taxonomic groups suggesting similarities in habitats, with the exception of the seabirds, which showed some differences, possibly due to the type of tissue analysed (feathers instead of muscle). δ15N showed increasing enrichment across groups in the order POM to zooplankton to squid to myctophid fish to notothenioid fish to seabirds. There were significant differences in δ15N and δ13C values among species within taxonomic groups, reflecting inter-specific variation in diet. Hg concentrations increased with trophic level, with the lowest values in POM (0.0005±0.0002μgg-1 dw) and highest values in seabirds (3.88±2.41μgg-1 in chicks of brown skuas Stercorarius antarcticus). Hg concentrations tended to be lower in 2016/17 than in 2007/08 for mid-trophic level species (squid and fish), but the opposite was found for top predators (i.e. seabirds), which had higher levels in the 2016/17 samples. This may reflect an interannual shift in the Scotia Sea marine food web, caused by the reduced availability of a key prey species, Antarctic krill Euphausia superba. In 2016/17, seabirds would have been forced to feed on higher trophic-level prey, such as myctophids, that have higher Hg burdens. These results suggest that changes in the food web are likely to affect the pathway of mercury to Southern Ocean top predators.

Otolith-derived field metabolic rates of myctophids (Family Myctophidae) from the Scotia Sea (Southern Ocean)

Myctophids (Family Myctophidae, commonly known as the lanternfishes) are critical components of open ocean food webs and an important part of the ocean biological carbon pump, as many species actively transport carbon to the deep ocean through their diel vertical migrations. Estimating the magnitude of myctophids’ contribution to the biological carbon pump requires knowledge of their metabolic rate. Unfortunately, data on myctophid metabolic rates are sparse, as they rarely survive being captured and placed in a respirometer. Because of this limitation, many studies estimate myctophid metabolic rates indirectly from body mass and temperature scaling relationships, often extrapolating regressions from global data sets to regional scales. To test the validity of these estimates, we employed a newly developed proxy for mass-specific field metabolic rate (Cresp: the proportion of metabolically derived carbon in the otolith) based on the stable carbon isotope composition (δ13C) of otolith aragonite. We recovered estimates of Cresp for individuals of 6 species of myctophids from the Scotia Sea, giving a range in Cresp values from 0.123-0.248. We found that ecological and physiological differences among species are better predictors of variation in Cresp values than body mass and temperature. We compared our results to estimates of metabolic rates derived from scaling relationships and from measurements of electron transport system activity. When considering myctophids as a whole, we found that estimates of oxygen consumption from different methods are broadly similar; however, there are considerable discrepancies at the species level. Our study highlights the usefulness of metabolic proxies where respirometry is currently unavailable, and provides valuable information on field metabolic rates of myctophids.

Dropstones in the Mar del Plata Canyon Area (SW Atlantic): Evidence for Provenance, Transport, Distribution, and Oceanographic Implications

AbstractA 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.

Pseudotanaidae Sieg, 1976 (Crustacea: Peracarida) from the Southern Ocean: diversity and bathymetric pattern

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

Comparative analysis of the diet of Arctocephalus gazella (Pinnipedia), at two localities of the South Shetland Islands, with emphasis on the fish component

ABSTRACT We studied the diet of non-breeding male Antarctic fur Seals Arctocephalus gazella (Peters, 1875) at two different localities of the South Shetland Islands: Stranger Point, King George Island/Isla 25 de Mayo and Duthoit Point, Nelson Island, by the analysis of 65 faecal samples collected in February 2012. Overall, Antarctic krill Euphausia superba (Dana, 1850) and fish were the main prey taxa followed by penguins and cephalopods. Myctophids were dominant among fish; Gymnoscopelus nicholsi (Gilbert, 1911) was the most important prey species at both sampling sites, followed by Electrona antarctica (Gunther, 1878) at Stranger Point and by the nototheniid Pleuragramma antarctica (Boulenger, 1902) at Duthoit Point. The relative similarity found in the dietary composition of fur seals from both locations suggest they might have been sharing common feeding areas. Our results were compared with those reported in the literature for different localities of the South Shetland Islands and the Scotia Sea region. The absence of formerly harvested demersal notothenioid species in the diet of fur seals may reflect the negative impact that commercial fisheries had on some fish populations and supports the importance of implementing long-term monitoring studies on the feeding habits of A. gazella in the area.

Тяжёлые металлы в поверхностной воде Атлантического сектора Антарктики в 79-м рейсе научно-исследовательского судна «Академик Мстислав Келдыш»

Актуальность мониторинга содержания тяжёлых металлов в водах Атлантического сектора Антарктики определяется необходимостью современной оценки качества водной среды для принятия ответственных решений по сохранению морских живых ресурсов в этом уникальном регионе Мирового океана. Цель проводимых исследований — получить новые данные об уровнях и пространственном распределении концентрации микроэлементов, преимущественно тяжёлых металлов, в поверхностной воде. Отбор проб поверхностной морской воды производили в антарктической экспедиции 79-го рейса НИС «Академик Мстислав Келдыш» на 21 станции в районе проливов Дрейка, Брансфилда, Антарктика, а также в морях Уэдделла и Скотия. Экстракцию и концентрирование растворённой формы 13 микроэлементов (Be, Se, Sb, Tl, V, Pb, Cd, Cu, Zn, Ni, Mo, Co и Fe) осуществляли с помощью диэтилдитиокарбамата натрия и четырёххлористого углерода (CCl4). Измерение элементов проводили масс-спектрометрическим методом. Только для Mo на девяти станциях, расположенных в проливах Дрейка и Брансфилда, в северном районе моря Уэдделла, а также возле южного побережья острова Огненная Земля, отмечали превышение его концентрации в морской воде в 1,2–2,8 раза по отношению к ПДК микроэлементов в воде рыбохозяйственных объектов РФ (ПДКРХ). Согласно международным нормативно-правовым актам, таким как «Голландские листы», зарегистрированы единичные случаи превышения MPC (maximum permissible concentration — ПДК при краткосрочном воздействии) для Cd и Zn, а также превышение TV (target value — контрольные уровни при хроническом воздействии) для Cu, Pb, Cd, Zn, Se и Co на нескольких станциях. Исследования показали, что, несмотря на ограниченный режим антропогенной нагрузки в этом регионе Южного океана, в морской воде отдельных районов Атлантического сектора Антарктики в современный период зафиксированы повышенные концентрации некоторых микроэлементов, включая тяжёлые металлы. Необходимо дальнейшее изучение источников поступления и особенностей распределения микроэлементов в морских водах Атлантической части Антарктики для объяснения происходящих процессов, а также для принятия мер по рациональному управлению и экологически приемлемому природопользованию в Антарктическом регионе.

Geomorphology and sedimentary processes on the Sloggett Canyon, Northwestern Scotia Sea, Argentina

The southern Argentine Continental Margin hosts the Tierra del Fuego Submarine Canyon System, located in the northwestern Scotia Sea, and formed by 4 main canyons: Valentín, Sloggett, Nueva Canyon, and Wollaston. This region is especially interesting due to its complex tectonic setting and its proximity to the polar regions where intense bottom currents associated with the Argentine Contourite Depositional System take place. Here, we present for the first time the complete high-resolution swath bathymetry, 28 m grid size, of the Sloggett Canyon obtained during the YTEC-GTGM 0 cruise on board the Argentine R/V Austral. This new information allowed us to make a detailed morphosedimentary description of the architectural elements of the canyon and to identify the main sedimentary processes that controlled its formation and evolution together with other oceanographic, climatic, and tectonic ruling factors. The Sloggett Canyon, with a total length of 147 km, starts in the continental shelf with the head area located at 90 m water depth, only 8.5 km away from the coast, and ends at 3690 m water depth joining the abyssal Yahgán Basin. It is deeply carved into the continental slope, with 1600 m as the maximum incision observed in its middle sector. The canyon head area is characterized by two different tributary systems that act as routing conduits for sediment supply from the shelf to the canyon domain. On the western flank, the tributary system is densely spaced with deeply incised V-shaped valleys that suggest the occurrence of active sediment flows that probably evolve into erosive turbidity currents. On the eastern flank, on the contrary, the tributary channels are sparse less incised, and U-shaped, suggesting that they are no longer active. Here, mass wasting processes seem to dominate as evidenced by the presence of slumping and sliding scars. The canyon valley shows two predominant orientations, NW-SE and NE-SW, with sharp bends of approximately 90°. These orientations would have been controlled by the lineaments of the West Scotia Ridge and the Beagle Channel Fault System, respectively. The completely surveyed Sloggett Canyon highlights the complexity of the Tierra del Fuego continental margin, and brings new insight for future multidisciplinary research in this region.

Continuous moulting by Antarctic krill drives major pulses of carbon export in the north Scotia Sea, Southern Ocean

Antarctic krill play an important role in biogeochemical cycles and can potentially generate high-particulate organic carbon (POC) fluxes to the deep ocean. They also have an unusual trait of moulting continuously throughout their life-cycle. We determine the krill seasonal contribution to POC flux in terms of faecal pellets (FP), exuviae and carcasses from sediment trap samples collected in the Southern Ocean. We found that krill moulting generated an exuviae flux of similar order to that of FP, together accounting for 87% of an annual POC flux (22.8 g m−2 y−1). Using an inverse modelling approach, we determined the krill population size necessary to generate this flux peaked at 261 g m−2. This study shows the important role of krill exuviae as a vector for POC flux. Since krill moulting cycle depends on temperature, our results highlight the sensitivity of POC flux to rapid regional environmental change.

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.

The Skytrain plate and tectonic evolution of southwest Gondwana since Jurassic times

Uncertainty about the structure of the Falkland Plateau Basin has long hindered understanding of tectonic evolution in southwest Gondwana. New aeromagnetic data from the basin reveal Jurassic-onset seafloor spreading by motion of a single newly-recognized plate, Skytrain, which also governed continental extension in the Weddell Sea Embayment and possibly further afield in Antarctica. The Skytrain plate resolves a nearly century-old controversy by requiring a South American setting for the Falkland Islands in Gondwana. The Skytrain plate’s later motion provides a unifying context for post-Cambrian wide-angle paleomagnetic rotation, Cretaceous uplift, and post-Permian oblique collision in the Ellsworth Mountains of Antarctica. Further north, the Skytrain plate’s margins built a continuous conjugate ocean to the Weddell Sea in the Falkland Plateau Basin and central Scotia Sea. This ocean rules out venerable correlation-based interpretations for a Pacific margin location and subsequent long-distance translation of the South Georgia microcontinent as the Drake Passage gateway opened.

Unveiling Powell Basin’s Tectonic Domains and Understanding Its Abnormal Magnetic Anomaly Signature. Is Heat the Key?

Rifting of continental lithosphere leading to oceanic basins is a complex process conditioned by different factors such as the rheology and thermal structure of the underlying lithosphere, as well as underlying asthenospheric dynamics. All these processes, which finally lead to oceanic domains, can better be recognized in small oceanic basins. Powell Basin is a small oceanic basin bounded to the north by the South Scotia Ridge, to the east by the South Orkney Microcontinent, and to the west by the Antarctic Peninsula. It was formed between the Oligocene and Miocene, however, its age is not well defined, among other reasons due to the small amplitude of its spreading magnetic anomalies. This basin is an ideal framework to analyze the different rifting and spreading phases, which leads from continental crust to the formation of an oceanic domain through different extensional regimes. To identify the different boundaries during the formation of Powell Basin from the beginning of the rifting until the end of the spreading, we use different data sources: magnetic, gravity, multichannel seismic profiles and bathymetry data. We use seismic and bathymetry data to estimate the Total Tectonic Subsidence (TTS). TTS has proven to be useful to delineate the different tectonic regimes present from early rifting to the formation of oceanic seafloor. This result together with magnetic data has been used to delimit the oceanic domain and compare with previous authors’ proposals. This method could be applied in any other basin or margin to help delimiting its boundaries. Finally, we analyze the role that an asthenospheric branch intruding from the Scotia Sea played in the evolution of the magnetic anomaly signature on an oceanic basin.

Paleoceanographic changes in the Southern Ocean off Elephant Island since the last glacial period: Links between surface water productivity, nutrient utilization, bottom water currents, and ice-rafted debris

To understand past changes in ocean–cryosphere interactions in the Southern Ocean off the Antarctic Peninsula, multi-proxy analyses of three sediment cores located off Elephant Island were used to reconstruct changes in paleoproductivity, nutrient utilization, bottom current intensity, and iceberg calving since the last glacial period. The glacial period was characterized by low surface water productivity with high nutrient utilization, indicating surface water stratification. During the deglaciation, surface water productivity increased with decreasing nutrient utilization, implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing Antarctic Circumpolar Current (ACC) influence as fronts migrate southward with warming. Abundant occurrence of grains >1 mm during the deglacial period indicates rapid ice sheet retreat with large-scale melting and calving. During the glacial period, however, coarse silt–fine sand-sized fraction represented ice-rafted debris (IRD). The different IRD grain size characteristics are thought to be related to the IRD source material characteristics. Regardless of IRD input, the running downcore correlation (5 to 9-point) between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current. However, the cross plot of them showed different temporal relationships. Sediments were sorted by the ACC and southwestward flowing bottom current. Along with southward migration of fronts and the ACC, southwestward flowing bottom current influence diminished, whereas the ACC influence increased particularly from 7 ka. Our results indicate that the sedimentary processes in the Scotia Sea largely depend on the regional interactions between the ocean and the cryosphere.

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.

Antarctic Bottom Water Flow through the Eastern Part of the Philip Passage in the Weddell Sea

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.

Modeling the Impact of Ocean Circulation on Chlorophyll Blooms Around South Georgia, Southern Ocean

AbstractThe 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.

What's the catch? Profiling the benefits and costs associated with marine protected areas and displaced fishing in the Scotia Sea.

Both costs and benefits must be considered when implementing marine protected areas (MPAs), particularly those associated with fishing effort displaced by potential closures. The Southern Ocean offers a case study in understanding such tradeoffs, where MPAs are actively being discussed to achieve a range of protection and sustainable use objectives. Here, we evaluated the possible impacts of two MPA scenarios on the Antarctic krill (Euphausia superba) fishery and krill-dependent predators in the Scotia Sea, explicitly addressing the displacement of fishing from closed areas. For both scenarios, we employed a minimally realistic, spatially explicit ecosystem model and considered three alternative redistributions of displaced fishing. We projected both MPAs to provide positive outcomes for many krill-dependent predators, especially when closed areas included at least 50–75% of their foraging distributions. Further, differences between the scenarios suggest ways to improve seal and penguin protection in the Scotia Sea. MPA scenarios also projected increases in total fishery yields, but alongside risks of fishing in areas where relatively low krill densities could cause the fishery to suspend operations. The three alternatives for redistributing displaced fishing had little effect on benefits to predators, but did matter for the fishery, with greater differences in overall catch and risk of fishing in areas of low krill density when displaced fishing was redistributed evenly among the open areas. Collectively, results suggest a well-designed MPA in the Scotia Sea may protect krill-dependent predators, even with displaced fishing, and preclude further spatial management of the krill fishery outside the MPA. More broadly, outcomes denote the importance of delineating fishing and predator habitat, spatial scales, and the critical trade-offs inherent in MPA development.

Microcontinents and Continental Fragments Associated With Subduction Systems

AbstractMicrocontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions, and a “proto‐microcontinent,” in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back‐arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and their formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for their formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in‐situ subduction‐related microcontinents is meager (an area of 0.56% and 0.28% of global, non‐cratonic, continental crustal area and crustal volume, respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.

Observed Eddy–Internal Wave Interactions in the Southern Ocean

AbstractThe physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct energy transfer to the internal wave field in the ocean interior, via eddy-induced straining and shearing of preexisting internal waves. The magnitude, vertical structure, and temporal variability of the rate of energy transfer between eddies and internal waves is quantified from a 14-month deployment of a mooring cluster in the Scotia Sea. Velocity and buoyancy observations are decomposed into wave and eddy components, and the energy transfer is estimated using the Reynolds-averaged energy equation. We find that eddies gain energy from the internal wave field at a rate of −2.2 ± 0.6 mW m−2, integrated from the bottom to 566 m below the surface. This result can be decomposed into a positive (eddy to wave) component, equal to 0.2 ± 0.1 mW m−2, driven by horizontal straining of internal waves, and a negative (wave to eddy) component, equal to −2.5 ± 0.6 mW m−2, driven by vertical shearing of the wave spectrum. Temporal variability of the transfer rate is much greater than the mean value. Close to topography, large energy transfers are associated with low-frequency buoyancy fluxes, the underpinning physics of which do not conform to linear wave dynamics and are thereby in need of further research. Our work suggests that eddy–internal wave interactions may play a significant role in the energy balance of the Southern Ocean mesoscale eddy and internal wave fields.