Bellingshausen Sea Research Articles

Sources, variability and fate of freshwater in the Bellingshausen Sea, Antarctica

During the second half of the twentieth century, the Antarctic Peninsula was subjected to a rapid increase in air temperatures. This was accompanied by a reduction in sea ice extent, increased precipitation and a dramatic retreat of glaciers associated with an increase in heat flux from deep ocean water masses. Isotopic tracers have been used previously to investigate the relative importance of the different freshwater sources to the adjacent Bellingshausen Sea (BS), but the data coverage is strongly biased toward summer. Here we use a regional model to investigate the ocean's response to the observed changes in its different freshwater inputs (sea ice melt/freeze, precipitation, evaporation, iceberg/glacier melt, and ice shelf melt). The model successfully recreates BS water masses and performs well against available freshwater data. By tracing the sources and pathways of the individual components of the freshwater budget, we find that sea ice dominates seasonal changes in the total freshwater content and flux, but all sources make a comparable contribution to the annual-mean. Interannual variability is dominated by sea ice and precipitation. Decadal trends in the salinity and stratification of the ocean are investigated, and a 20-year surface freshening from 1992 to 2011 is found to be predominantly driven by decreasing autumn sea ice growth. These findings will help to elucidate the role of freshwater in driving circulation and water column structure changes in this climatically-sensitive region.

The role of Amundsen–Bellingshausen Sea anticyclonic circulation in forcing marine air intrusions into West Antarctica

Persistent positive 500-hPa geopotential height anomalies from the ECMWF ERA-Interim reanalysis are used to quantify Amundsen–Bellingshausen Sea (ABS) anticyclonic event occurrences associated with precipitation in West Antarctica (WA). We demonstrate that multi-day (minimum 3-day duration) anticyclones play a key role in the ABS by dynamically inducing meridional transport, which is associated with heat and moisture advection into WA. This affects surface climate variability and trends, precipitation rates and thus WA ice sheet surface mass balance. We show that the snow accumulation record from the Roosevelt Island Climate Evolution (RICE) ice core reflects interannual variability of blocking and geopotential height conditions in the ABS/Ross Sea region. Furthermore, our analysis shows that larger precipitation events are related to enhanced anticyclonic circulation and meridional winds, which cause pronounced dipole patterns in air temperature anomalies and sea ice concentrations between the eastern Ross Sea and the Bellingshausen Sea/Weddell Sea, as well as between the eastern and western Ross Sea.

Foraminifera from the 58th and 59th Russian Antarctic Expeditions, 2013-2014

Foraminifera were examined in samples collected during the 58th (2013) and 59th Russian Antarctic Expeditions (2013-2014) in the Western and Eastern Antarctic areas in the Bellingshausen Sea, Bransfield Strait, Prydz Bay, Davis Sea, and Southern Ocean at depths between 107 and 995 meters, with the majority of samples situated in the shelf zone. In total 39 benthic and one planktonic species were found. All the benthic species are pan-Antarctic, only Neogloboquadrina pachyderma shows a bipolar distribution. The assemblages at several stations were fully or predominantly agglutinated, possibly as a consequence of dissolution processes, at some others - predominantly or fully calcareous. Calcareous forms prevailed at relatively shallow depths (70-220 m). Among the calcareous species miliolids prevail, their magnesium containing shells are obviously more resistant to dissolution processes. Foraminifera of all the samples were recent and living, containing cytoplasm. The new data on the distribution of the recent benthic foraminifera permits a better understanding of the paleoecological conditions of the geological past. The new data obtained are also important for the comparison of the marine biotas in the Western and Eastern parts of Antarctica.

Isotopic evidence of the effect of warming on the northern Antarctic Peninsula ecosystem

The Antarctic Peninsula (AP) region is one of the areas under faster warming rates worldwide, and where food web changes have been observed in the last decades. Among these changes are the development of cryptophytes under warmer conditions in detriment of diatoms, and the reduced krill availability in the environment. An isotopic approach was used to investigate whether the temporal and spatial patterns of energy transfer from phytoplankton (using particulate organic matter – POM – as a proxy of primary producers) to baleen whales (humpback – Megaptera novaeanglieae, fin – Balaenoptera physalus, Antarctic minke – Balaenoptera bonaerensis), and killer whales – Orcinus orca – is similar in areas under different effects of warming around the northern Antarctic Peninsula (NAP). Samples of POM (n = 65), krill (n = 29) and skin of baleen (n = 106) and, opportunistically, killer whales (n = 5) were collected in Gerlache and Bransfield Straits (western AP) and the Powell Basin (northeastern AP) during the austral summers of 2013–2016. Mean isotope values for δ13C and δ15N values were, respectively, ‐26.3‰ (± 2.9) and 0.9‰ (± 1.7) for POM, ‐25.6‰ (± 0.9) and 5.3‰ (± 1.1) for krill, ‐24.1‰ (± 2) and 8.9‰ (± 1.5) for humpback, ‐24.6‰ (± 1.2) and 8.2‰ (± 0.7) for fin, ‐24.4‰ (± 1.6) and 8.7‰ (± 1) for Antarctic minke whales, and −23.6‰ (± 1.2) and 8.9‰ (± 1.7) for killer whales. Interannual significant differences were found for δ13C values of POM and fin whales’ samples, while spatial differences were found for δ13C values of POM samples and humpback whales and for δ15N values of POM, humpback and Antarctic minke whales. Lower δ13C and δ15N values for the base of the food web tended to be observed towards open sea regions (Powell Basin and an area under the influence of the Bellingshausen Sea waters). The isoscapes generated for the baseline of the NAP ecosystem provided unprecedented information, to the best of our knowledge, of how the δ13C and δ15N values of POM varied spatially and temporally in the region. HPLC-CHEMTAX pigment analysis indicated that two of the main phytoplankton groups in the study region were diatoms and cryptophytes. The contribution of these groups to the total phytoplankton biomass was positively and negatively correlated with the POM δ13C values, respectively. Despite the spatial and temporal limited interpretation of our results due to our reduced sampling effort to the east of the AP and to the relatively short temporal range investigated, the differences observed in the isotopic composition are considered representative of contrasting environmental conditions. The present study provides new insights on stable isotope values in the Antarctic ecosystem and may help to foresee the consequences of physico-chemical changes in water properties to the biota due to global warming.

On the temporal variability of intermediate and deep waters in the Western Basin of the Bransfield Strait

The Western Basin (WB) of the Bransfield Strait has a complex water mass structure derived from a variety of sources, and is located next to the Antarctic region most affected by climate change. The WB is one of the three Bransfield Strait deep basins and the one most directly influenced by the waters from the Bellingshausen Sea and Drake Passage. The objective of this paper is to study the variability of the inflow of water masses to the WB and to detect the possible impact of regional climate change. We focus on the modified Circumpolar Deep Water (mCDW) that enters the WB through the northwestern passages. To achieve this goal, this study uses historical hydrographic data collected between 1960 and 2014. Warming (0.0161 ± 0.0079 °C yr−1) and lightening (−0.0023 ± 0.0010 kg m−3 yr−1) of the mCDW core (γn = 27.85–28.27 kg m−3) are observed in the WB between 1960 and 2013. The waters within the 27.85–28 kg m−3 γn range presented warming and salinization. Waters deeper than 500 m showed cooling and freshening between the 1960s and 1990s; however, warming and lightening are observed if 1981–2013 is considered. These trends appear to be associated with the positive SAM trend observed since the mid-20th century. Statistically significant negative correlations between θ, S and γⁿ of the mCDW core with ENSO were found between 1980 and 2014. During La Niña phases, the mCDW core extended along the southern slope of the South Shetland Islands while during El Niño phases, it was present in patches or was totally absent. Since the 2000s, the mCDW core extends southward within the WB, possibly associated to positive SAM phases. Statistically significant negative correlations between θ and S of the WB deeper waters with ENSO and SAM were found. These waters were in general more saline and denser during negative ENSO and SAM phases. Positive SAM phases with La Niña events suggest the increase (decrease) of mCDW (Weddell Sea shelf waters) contribution to the deep WB during the 2000s. Thus, high interannual variability in the thermohaline properties within the WB seem to be linked to the effect of these modes of climate variability on the source water masses.

Epimeria of the Southern Ocean with notes on their relatives (Crustacea, Amphipoda, Eusiroidea)

Epimeria of the Southern Ocean with notes on their relatives (Crustacea, Amphipoda, Eusiroidea)

Spatial variability of photophysiology and primary production rates of the phytoplankton communities across the western Antarctic Peninsula in late summer 2013

Primary production measurements in the Southern Ocean are generally carried out during phytoplankton blooms in the Antarctic summer, whereas information from late summer is scarcer, especially in the northernmost part of the western Antarctic Peninsula (wAP). Here, we present data on phytoplankton photophysiology, chlorophyll-a concentration (Chl a), phytoplankton communities and primary productivity for 3 sub-regions, as follows: Transitional Water with Bellingshausen Sea influence (TBW-dominated sub-region), Transitional Water with Weddell Sea influence (TWW-dominated sub-region), both occupying the Bransfield Strait (BS), and a mixture of both transitional waters in the Gerlache Strait (Gerlache sub-region). Comparisons between these sub-regions have shown that, on average, Chl a, (0.65mgm−3) was lower and upper mixed layer depth (ZUMLD = 52.62m) was deeper in TWW-dominated waters, whereas intermediate Chl a (1.22mgm−3) and moderate ZUMLD (36.46m) values were found in the TBW-dominated sub-region and the lowest ZUMLD (22.33m) and highest Chl a values (1.58mgm−3) were found in the Gerlache sub-region. However, similar values of Fv/Fm were found in the 3 sub-regions, which indicate a high physiological plasticity, even considering different phytoplankton communities. A canonical correspondence analysis highlighted the association between the TBW-dominated sub-region and the dominance of diatoms, coupled with higher photosynthetic carotenoids (especially fucoxanthin), contrasting with the Gerlache sub-region, mainly associated with photoprotective carotenoids (particularly alloxanthin from cryptophytes) and relative lower ZUMLD. Primary production rates estimated from the PAM (Pulse-Amplitude Modulate) fluorometric technique agreed very well with 14C measurements (r2=0.91, n=5, p=0.01). Although higher maximum chlorophyll a specific primary production rates were found in the TWW sub-region (1.91 ± 1.22 mgCmg Chl a−1h−1), the other two areas also showed relatively high assimilation numbers as compared to previous works in the region. In short, despite the large spatial variability of physical water column features, adequate photophysiological traits allowed high primary production rates by those late summer phytoplankton communities in the northern wAP region.

Conditions leading to the unprecedented low Antarctic sea ice extent during the 2016 austral spring season

AbstractThe 2016 austral spring was characterized by the lowest Southern Hemisphere (SH) sea ice extent seen in the satellite record (1979 to present) and coincided with anomalously warm surface waters surrounding most of Antarctica. We show that two distinct processes contributed to this event: First, the extreme El Niño event peaking in December–February 2015/2016 contributed to pronounced extratropical SH sea surface temperature and sea ice extent anomalies in the eastern Ross, Amundsen, and Bellingshausen Seas that persisted in part until the following 2016 austral spring. Second, internal unforced atmospheric variability of the Southern Annular Mode promoted the exceptional low sea ice extent in November–December 2016. These results suggest that a combination of tropically forced and internal SH atmospheric variability contributed to the unprecedented sea ice decline during the 2016 austral spring, on top of a background of slow changes expected from greenhouse gas and ozone forcing.

Accumulation in coastal West Antarctic ice core records and the role of cyclone activity

AbstractCyclones are an important component of Antarctic climate variability, yet quantifying their impact on the polar environment is challenging. We assess how cyclones which pass through the Bellingshausen Sea affect accumulation over Ellsworth Land, West Antarctica, where we have two ice core records. We use self‐organizing maps (SOMs), an unsupervised machine learning technique, to group cyclones into nine SOM nodes differing by their trajectories (1980–2015). The annual frequency of cyclones associated with the first SOM node (SOM1, which generally originate from lower latitudes over the South Pacific Ocean) is significantly (p < 0.001) correlated with annual accumulation, with the highest seasonal correlations (p < 0.001) found during autumn. While significant (p < 0.01) increases in vertically integrated water vapor over the South Pacific Ocean coincide with this same group of cyclones, we find no indication that this has led to an increase in moisture advection into, nor accumulation over, Ellsworth Land over this short time period.

Southern Ocean mesocyclones and polar lows from manually tracked satellite mosaics

AbstractA new reference data set of mesocyclone activity over the Southern Ocean has been developed from the manual analysis of high‐resolution infrared satellite mosaics for winter 2004. Of the total 1735 mesocyclones which were identified and analyzed, about three quarters were classified as being “polar lows” (i.e., intense systems; see Rasmussen and Turner, 2003). The data set includes mesocyclone track, size, associated cloud vortex type, and background synoptic conditions. Maxima in track density were observed over the Bellingshausen Sea and around East Antarctica and are highly correlated with cyclogenesis regions. A comparison against QuikSCAT and reanalyses wind characteristics shows that the reanalyses, while capturing mesocyclone events, tend to considerably underestimate their wind speed (by up to 10 m s−1). This mesocyclone data set is available as a reference for further analysis of mesocyclones and for the evaluation and development of cyclone‐tracking algorithms.

The Transient Response of Ice Shelf Melting to Ocean Change

AbstractIdealized modeling studies have shown that the melting of ice shelves varies as a quadratic function of ocean temperature. However, this result is the equilibrium response, derived from steady ice–ocean simulations subjected to a fixed ocean forcing. This study considers instead the transient response of melting, using unsteady simulations subjected to forcing conditions that are oscillated with a range of periods. The results show that the residence time of water in the subice cavity offers a critical time scale. When the forcing varies slowly (period of oscillation ≫ residence time), the cavity is fully flushed with forcing anomalies at all stages of the cycle and melting follows the equilibrium response. When the forcing varies rapidly (period ≤ residence time), multiple cold and warm anomalies coexist in the cavity, cancelling each other in the spatial mean and thus inducing a relatively steady melt rate. This implies that all ice shelves have a maximum frequency of ocean variability that can be manifested in melting. Between these two extremes, an intermediate regime occurs in which melting follows the equilibrium response during the cooling phase of the forcing cycle, but deviates during warming. The results show that ice shelves forced by warm water have high melt rates, high equilibrium sensitivity, and short residence times and hence a short time scale over which the equilibrium sensitivity is manifest. The most rapid melting adjustment is induced by warm anomalies that are also saline. Thus, ice shelves in the Amundsen and Bellingshausen Seas, Antarctica, are highly sensitive to ocean change.

Amundsen and Bellingshausen Seas simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters

AbstractRecent studies suggest that the thickness of Winter Water (WW), that is, water with potential temperature below ∼−1°C located below Antarctic Surface Water and above Circumpolar Deep Water (CDW) is critical in determining the ice shelf melt rate, especially for the Pine Island Glacier (PIG). Existing model studies, however, misrepresent WW thickness and properties in the Amundsen Sea (AS). Here, we adjust a small number of model parameters in a regional Amundsen and Bellingshausen Seas configuration of the Massachusetts Institute of Technology general circulation model in order to reproduce properties and thickness of WW and CDW close to observations, with significant improvement for WW compared to previous studies. The cost, which is defined as weighted model‐data difference squared, is reduced by 23%. Although a previous modeling study points out that the local surface heat loss upstream from Pine Island Polynya could be the reason for the observed 2012 PIG melt decline and WW thickening, they did not show WW freshening, which was observed at the same time. Model sensitivity experiments for surface heat loss, PIG melt rate, and precipitation fail to replicate WW freshening concurrent with PIG melt decline, implying that these processes cannot fully explain the observed PIG melt decrease.

Diagnosis of Decadal Predictability of Southern Ocean Sea Surface Temperature in the GFDL CM2.1 Model

The average predictability time (APT) method is used to identify the most predictable components of decadal sea surface temperature (SST) variations over the Southern Ocean (SO) in a 4000-yr unforced control run of the GFDL CM2.1 model. The most predictable component shows significant predictive skill for periods as long as 20 years. The physical pattern of this variability has a uniform sign of SST anomalies over the SO, with maximum values over the Amundsen–Bellingshausen–Weddell Seas. Spectral analysis of the associated APT time series shows a broad peak on time scales of 70–120 years. This most predictable pattern is closely related to the mature phase of a mode of internal variability in the SO that is associated with fluctuations of deep ocean convection. The second most predictable component of SO SST is characterized by a dipole structure, with SST anomalies of one sign over the Weddell Sea and SST anomalies of the opposite sign over the Amundsen–Bellingshausen Seas. This component has significant predictive skill for periods as long as 6 years. This dipole mode is associated with a transition between phases of the dominant pattern of SO internal variability. The long time scales associated with variations in SO deep convection provide the source of the predictive skill of SO SST on decadal scales. These analyses suggest that if the SO deep convection in a numerical forecast model could be adequately initialized, the future evolution of SO SST and its associated climate impacts are potentially predictable.

The impacts of El Niño on the observed sea ice budget of West Antarctica

AbstractWe assess the impact of El Niño‐induced wind changes on seasonal West Antarctic sea ice concentrations using reanalysis data and sea ice observations. A novel ice budget analysis reveals that in autumn a previously identified east‐west dipole of sea ice concentration anomalies is formed by dynamic and thermodynamic processes in response to El Niño‐generated circulation changes. The dipole features decreased (increased) concentration in the Ross Sea (Amundsen and Bellingshausen Seas). Thermodynamic processes and feedback make a substantial contribution to ice anomalies in all seasons. The eastward propagation of this anomaly is partly driven by mean sea ice drift rather than anomalous winds. Our results demonstrate that linkages between sea ice anomalies and atmospheric variability are highly nonlocal in space and time. Therefore, we assert that caution should be applied when interpreting the results of studies that attribute sea ice changes without accounting for such temporally and spatially remote linkages.

The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate

Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet.

Wind‐driven ocean dynamics impact on the contrasting sea‐ice trends around West Antarctica

AbstractSince late 1978, Antarctic sea‐ice extent in the East Pacific has retreated persistently over the Amundsen and Bellingshausen Seas in warm seasons, but expanded over the Ross and Amundsen Seas in cold seasons, while almost opposite seasonal trends have occurred in the Atlantic over the Weddell Sea. By using a surface‐forced ocean and sea‐ice coupled model, we show that regional wind‐driven ocean dynamics played a key role in driving these trends. In the East Pacific, the strengthening Southern Hemisphere (SH) westerlies in the region enhanced the Ekman upwelling of warm upper Circumpolar Deep Water and increased the northward Ekman transport of cold Antarctic surface water. The associated surface ocean warming south of 68°S and the cooling north of 68°S directly contributed to the retreat of sea‐ice in warm seasons and the expansion in cold seasons, respectively. In the Atlantic, the poleward shifting SH westerlies in the region strengthened the northern branch of the Weddell Gyre, which in turn increased the meridional thermal gradient across it as constrained by the thermal wind balance. Ocean heat budget analysis further suggests that the strengthened northern branch of the Weddell Gyre acted as a barrier against the poleward ocean heat transport, and thus produced anomalous heat divergence within the Weddell Gyre and anomalous heat convergence north of the gyre. The associated cooling within the Weddell Gyre and the warming north of the gyre contributed to the expansion of sea‐ice in warm seasons and the retreat in cold seasons, respectively.

Viruses and Protists Induced-mortality of Prokaryotes around the Antarctic Peninsula during the Austral Summer.

During the Austral summer 2009 we studied three areas surrounding the Antarctic Peninsula: the Bellingshausen Sea, the Bransfield Strait and the Weddell Sea. We aimed to investigate, whether viruses or protists were the main agents inducing prokaryotic mortality rates, and the sensitivity to temperature of prokaryotic heterotrophic production and mortality based on the activation energy (Ea) for each process. Seawater samples were taken at seven depths (0.1–100 m) to quantify viruses, prokaryotes and protists abundances, and heterotrophic prokaryotic production (PHP). Viral lytic production, lysogeny, and mortality rates of prokaryotes due to viruses and protists were estimated at surface (0.1–1 m) and at the Deep Fluorescence Maximum (DFM, 12–55 m) at eight representative stations of the three areas. The average viral lytic production ranged from 1.0 ± 0.3 × 107 viruses ml−1 d−1 in the Bellingshausen Sea to1.3 ± 0.7 × 107 viruses ml−1 d−1 in the Bransfield Strait, while lysogeny, when detectable, recorded the lowest value in the Bellingshausen Sea (0.05 ± 0.05 × 107 viruses ml−1 d−1) and the highest in the Weddell Sea (4.3 ± 3.5 × 107 viruses ml−1 d−1). Average mortality rates due to viruses ranged from 9.7 ± 6.1 × 104 cells ml−1 d−1 in the Weddell Sea to 14.3 ± 4.0 × 104 cells ml−1 d−1 in the Bellingshausen Sea, and were higher than averaged grazing rates in the Weddell Sea (5.9 ± 1.1 × 104 cells ml−1 d−1) and in the Bellingshausen Sea (6.8 ± 0.9 × 104 cells ml−1 d−1). The highest impact on prokaryotes by viruses and main differences between viral and protists activities were observed in surface samples: 17.8 ± 6.8 × 104 cells ml−1 d−1 and 6.5 ± 3.9 × 104 cells ml−1 d−1 in the Weddell Sea; 22.1 ± 9.6 × 104 cells ml−1 d−1 and 11.6 ± 1.4 × 104 cells ml−1 d−1 in the Bransfield Strait; and 16.1 ± 5.7 × 104 cells ml−1 d−1 and 7.9 ± 2.6 × 104 cells ml−1 d−1 in the Bellingshausen Sea, respectively. Furthermore, the rate of lysed cells and PHP showed higher sensitivity to temperature than grazing rates by protists. We conclude that viruses were more important mortality agents than protists mainly in surface waters and that viral activity has a higher sensitivity to temperature than grazing rates. This suggests a reduction of the carbon transferred through the microbial food-web that could have implications in the biogeochemical cycles in a future warmer ocean scenario.

Distribution of water masses and meltwater on the continental shelf near the Totten and Moscow University ice shelves

AbstractWarm waters flood the continental shelf of the Amundsen and Bellingshausen seas in West Antarctica, driving rapid basal melt of ice shelves. In contrast, waters on the continental shelf in East Antarctica are cooler and ice shelves experience relatively low rates of basal melt. An exception is provided by the Totten and Moscow University ice shelves on the Sabrina Coast, where satellite‐derived basal melt rates are comparable to West Antarctica. Recent oceanographic observations have revealed that relatively warm (∼−0.4°C) modified Circumpolar Deep Water (mCDW) enters the cavity beneath the Totten Ice Shelf through a 1100 m deep trough, delivering sufficient heat to drive rapid basal melt. Here we use observations from a recent summer survey to show that mCDW is widespread on the continental shelf of the Sabrina Coast, forming a warm (up to 0.3°C) and saline (34.5–34.6) bottom layer overlaid by cold (∼freezing point) and fresh (salinity ∼34.3) Winter Water. Dense Shelf Water is not observed. A 1000 deep m trough allows water at −1.3°C to reach the Moscow University ice‐shelf cavity to drive basal melt. Freshening by addition of glacial meltwater is widespread on the southern shelf at depths above 300–400 m, with maximum meltwater concentrations up to 4–5 ml L−1 observed in outflows from the ice‐shelf cavities. Our observations indicate that the ocean properties on the Sabrina Coast more resemble those found on the continental shelf of the Amundsen and Bellingshausen seas than those typical of East Antarctica.

Links between atmosphere, ocean, and cryosphere from two decades of microseism observations on the Antarctic Peninsula

The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between the latitudes of 50°S to 65°S produce exceptional storm‐driven wave conditions in the Southern Ocean. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high‐amplitude wave activity and thus, ocean‐swell‐driven microseism noise in both the primary (direct wave‐coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined across 23 years (1993–2015) from Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from East Falkland Island (EFI). These records provide a spatially integrative measure of both Southern Ocean wave amplitudes and the interactions between ocean waves and the solid Earth in the presence of sea ice, which can reduce wave coupling with the continental shelf. We utilize a spatiotemporal correlation‐based approach to illuminate how the distribution of sea ice influences seasonal microseism power. We characterize primary and secondary microseism power due to variations in sea ice and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the Southern Annular Mode, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, thus strongly increasing microseism power levels.

Some remarks on selected diastylid genera. Part II: Leptostylis (Crustacea, Cumacea) from the deep southern Atlantic and Pacific, with the description of six new species

Six new species of the genus Leptostylis are described: L. dentantipus n. sp. from the Southern Ocean, L. peruensis n. sp. from the Peru Trench, L. extendus n. sp. from the Weddell and Amundsen seas, L. levicarinatus n. sp. from the Weddell Sea, L. lacunatus n. sp. from the Brazil and Argentine basins and the north-western Weddell and Bellingshausen seas, and L. rasmi n. sp. from the western Weddell Sea. A determination key is provided for genera of the family Diastylidae with a short, globose and posteriorly swollen carapace, a long pereiopod 1 and a three-articulated uropod endopod.