Adjacent Shelf Areas Research Articles

Mollusca collected by Agassiz trawl from the 2016 SO-AntEco (JR15005) expedition to the South Orkney Islands, Antarctica - data.

This dataset contributes to the knowledge of macro- and megafaunal Mollusca associated with a range of benthic habitat types in the South Orkney Islands, Antarctica, an exceptionally diverse region of the Southern Ocean. The information presented is derived from Agassiz trawl samples collected on the archipelago's shelf plateau and slope, within and outside of the South Orkney Islands Southern Shelf Marine Protected Area (SOISS MPA). Sampling was conducted in the framework of the British Antarctic Survey/SCAR "South Orkneys - State of the Antarctic Ecosystem" (SO-AntEco) project aboard RRS James Clark Ross during expedition JR15005 in Austral summer 2016. This dataset is published by the British Antarctic Survey under the licence CC-BY 4.0. We would appreciate it if you could follow the guidelines from the SCAR Data Policy (SCAR 2023) when using the data. If you have any questions regarding this dataset, do not hesitate to contact us via the contact information provided in the metadata or via data-biodiversity-aq@naturalsciences.be. Issues with the dataset can be reported at https://github.com/biodiversity-aq/data-publication/. This dataset is part of the Biodiversity, Evolution and Adaptation Project of the Environmental Change and Evolution Program of the British Antarctic Survey. The cruise report of the expedition is available at https://www.bodc.ac.uk/resources/inventories/cruise_inventory/reports/jr15005.pdf. We report occurrences of Mollusca from individual samples taken with a 2 m-wide Agassiz trawl (AGT) in the framework of the February - March 2016 research expedition JR15005 of RRS James Clark Ross to the SOISS MPA and adjacent shelf and slope areas. Of 78 successful AGT deployments, 44 trawls at depths ranging from 235-2194 m yielded living Mollusca, totalling 2276 individuals, 67 morphospecies and 163 distributional records. One hundred and fifteen empty shells were also collected and recorded in the dataset. Three morphospecies (one Bivalvia and two Gastropoda) were sampled exclusively as empty shells, yielding a total of 70 morphospecies and 2391 specimens represented in the dataset. All specimens were preserved in 96% undenatured ethanol and are stored as vouchers in the collections of the British Antarctic Survey (BAS), Cambridge, United Kingdom. The publication of this dataset aims at increasing the knowledge on the biodiversity, abundance and geographical and bathymetric distribution of larger-sized epi- and shallow infaunal Mollusca of the South Orkney Islands.

Sources and dynamics of suspended particulate matter in a large-river dominated marine system: Contributions from terrestrial sediments, biological particles, and flocculation

Elucidating the sources and dynamics of suspended particulate matter (SPM) in large-river dominated estuarine and coastal areas is challenging, because these areas are characterized not only by high turbidity with complex terrestrial sediment transportation and deposition processes, but also by high primary production and plankton biomass. In addition, flocculation occurring near the river mouth can also markedly modify SPM dynamics, and its roles in affecting SPM concentrations, variations, and inherent properties remain inadequately addressed. In July 2016, an exceptional flood event occurred in the Changjiang (Yangtze) River basin, and a cruise on the Changjiang River Estuary and the adjacent shelf area was conducted. During this cruise, we deployed instrument of OBS (optical backscatter sensor) and LISST (laser in situ scattering and transmissometry) at 87 stations to study the SPM variations in 32 size classes (2.5–500 μm) and to elucidate the contributions of terrestrial sediments, biological particles, and flocculation to SPM sources and dynamics. The entire water columns at inner stations and the seawaters in the lower-depth waters at outer stations were found to be generally dominated by terrestrial SPM with smaller sizes. The waters in the upper depths at the outer stations were generally occupied by autochthonous and biological SPM with larger sizes, which mostly showed maximum values in the subsurface layers and were closely associated with fluorescence. In two stations near the river mouth and estuarine salinity front, the SPM, also with larger sizes, probably experienced flocculation. The findings from this study may greatly improve our understanding of SPM sources and dynamics under the multiple influences of physical and biogeochemical processes in large-river dominated estuarine and coastal areas.

Моделирование напряженно-деформированного состояния земной коры о. Сахалин: влияние гидроизостазии

The paper attempts to answer the question about the role of contribution of the hydroisostasy to the stress-strain state of the Earth’s crust on the Island of Sakhalin. The hydroisostasy contribution was estimated by simulation by means of finite element method. The mesh grid for the calculation was constructed using the real values of the depth of the Moho discontinuity surface and the topography of Sakhalin Island with adjacent shelf areas. The calculation took into account the Central Sakhalin fault zone. Lateral displacements as a result of strain and lateral displacements combined with vertical ones were simulated separately. Comparison of the results of the stress-strain state simulation, taking lateral displacements and their combination with vertical ones into account, clearly demonstrates the significance of the hydroisostasy contribution to the stress-strain state of the Earth’s crust in the Sakhalin region.

Use of molecular markers and compound-specific isotopic signatures to trace sources of black carbon in surface sediments of Peninsular Malaysia: Impacts of anthropogenic activities

Black carbon (BC) acts as a reservoir of carbon in sediment due to its high persistency. Southeast Asia (SEA) is a main source region for BC emissions across the globe due to extensive biomass burning and escalating fossil fuel consumption. However, our understanding of the sources and sinks of BC in SEA is limited. Here, we have analysed BC structure using benzene polycarboxylic acid (BPCA) method in combination of stable carbon isotope (δ13C) signatures for B5CA and B6CA using HPLC-IRMS in sediment samples from riverine, coastal and shelf areas in Peninsular Malaysia. BPCA molecular markers indicated higher degree of aromatic condensation and lighter isotopic composition in relatively pristine environment of the East coast compared to developed environment of the West and South coast. n-Alkane biomarkers clearly demonstrated higher anthropogenic impacts on the sediments of the West and South coast compared to the East coast. Biomass burning with the predominance of C3 plants and the large share of natural gas in the energy mix in Malaysia are possibly the main reasons for the isotopically light composition of sedimentary BC (−45.4 to −26.4‰). Atmospheric soot and petrogenic BC are the possible main sources of BC in the East coast sediments, while char residues of low temperature biomass burning likely contribute more to sedimentary BC in the West and South coast. The n-alkane indices implied that the sediments of the Kelantan adjacent shelf area receive great proportion of terrestrial organic matter and the associated BC.

Hydro-biogeochemical alterations to optical properties of particulate organic matter in the Changjiang Estuary and adjacent shelf area

Base-extracted particulate organic matter (BEPOM) collected in low (spring) and high (summer) runoff seasons in the Changjiang Estuary and adjacent nearshore/offshore shelf areas was examined using absorption and fluorescence spectroscopy. Parallel factor analysis (PARAFAC) identified two humic-like (C1p and C2p) biologically-refractory components and two protein-like (C3p and C4p) bioreactive components. Absorption coefficient a350p, C1p and C2p of BEPOM showed strong positive correlations with particulate organic carbon (POC), and were generally higher in spring than in summer. C4p correlated positively with Chl a, and was higher in summer than in spring. In the inner estuary, an anthropogenic POM signal from the highly polluted Huangpu River was effectively identified by the fluorescent component ratio (IT:IC)P. In the nearshore area during spring, resuspension within the well-developed turbidity maximum zone (TMZ) supplied large amounts of refractory POM into the water column. POM fractions from an autochthonous source (i.e., algal bloom) were dominant in the offshore area during the summer. A multivariate regression model inferred that POM export fluxes from the Changjiang River during spring had a higher percentage of labile POM fractions, which were subsequently retained by the TMZ. However, these labile fractions were discharged into the offshore shelf area contributing to hypoxia in the summer. The summer high runoff season also transported large amounts of refractory POM that was subsequently buried in the sediment. This study highlights the utilization of optical analyses to trace pollution sources and reveal POM fate and transport dynamics allowing better assessment of its ecological consequences in estuaries.

Using water age to study the biogeochemistry of nutrients in a large-river estuary and the adjacent shelf area

Whether a large-river estuary and the adjacent area behave as a water sink or as a source for important terrestrial biogeochemical compounds is a challenging question. Such aquatic systems are very complex and can be overwhelmed by physical circulation and estuarine mixing. In this study, physical oceanography and marine biogeochemistry were combined to address this question. Seven cruises were conducted in the Changjiang River (Yangtze) Estuary and the adjacent East China Sea shelf in February–March and in July over a three year period (2014 to 2016). During each cruise, nutrient concentrations (NO3−, SiO32−, PO43−, NH4+, and NO2−) and salinity were measured at the surface, middle, and bottom layers of 75–106 sampling stations, and water age was derived from numerical modeling. Two-variable regression analysis among salinity, water age, and nutrients was applied to calculate the specific variation rates of nutrient concentration versus water age. A positive rate value indicated that the water was a source of nutrients, and a negative value indicated the site as a sink. In both seasons tested, calculations for the five nutrients analyzed showed that all biogeochemical processes occurring in Changjiang Diluted Water (salinity <31.5) could distinctly change terrestrial fluxes from the Changjiang River in both seasons. Thus, the proposed method has the potential to elucidate the nonconservative behaviors, net fluxes, and budgets of important biogeochemical compounds through large-river dominated estuarine, coastal, and shelf areas worldwide.

Nitrate processing traced by nitrate dual isotopic composition in the early spring in the Changjiang (Yangtze River) Estuary and adjacent shelf areas

Nitrate is the major chemical form of N-nutrient to sustain primary production in Changjiang Estuary and adjacent seawaters. We employed δ15N-NO3− and δ18O-NO3− to constrain the source, cycling, and sink of nitrate in early spring. Both δ15N-NO3− and δ18O-NO3− differentiate significantly among Changjiang Diluted Water (CDW), Yellow Sea Coastal Current (YSCC), and Taiwan Warm Current (TWC). In coastal areas, nitrate distribution and its isotopes are mainly affected by Changjiang inputs. Chemical fertilizers and sewage & manure originated nitrate jointly contribute the most nitrate in CDW. In offshore areas, nitrification contributes 44 ± 21% of the nitrate in YSCC and 17 ± 16% in TWC; assimilation is the dominant process to remove nitrate in TWC (35 ± 16%). Overall, nitrification and assimilation are the key nitrate cycling processes in early spring and co-shape the offshore distribution pattern of nitrate and its dual isotopes.

Location and characteristics of the X-discontinuity beneath SW Morocco and the adjacent shelf area usingP-wave receiver functions

SUMMARYReceiver function approaches have proven to be valuable for the investigation of crustal and upper mantle discontinuities whose sharp changes in seismic velocities cause wave conversions. While the crustal and mantle transition zone discontinuities are largely understood, the X-discontinuity at 250–350 km depth is still an object of controversial debate. The origin and global distribution of this structure with a velocity jump of 1.5–4.8 % for compressional and shear waves is still unexplained. Although the crustal and mantle transition zone discontinuities beneath SW Morocco and surroundings have been investigated, only a few studies observed the X-discontinuity and place the depth at 260–370 km beneath the region of western Morocco. In order to better locate and characterize the X-discontinuity beneath southwest Morocco, we create P-wave receiver functions using data recorded by the Morocco–Münster array and detect the X-discontinuity at apparent depths of 285–350 km. In the western part of our study region we find apparent depths of ∼ 310–340 km. The eastern part of the study area appears more complex: we locate two velocity jumps at apparent depths of around 285–295 km and 330–350 km in the northeast, and in the southeast we find a discontinuity at apparent depths of 340–350 km. Due to the large depth range and the twofold appearance of the X-discontinuity, we suggest that two different phase transitions cause the X-discontinuity beneath SW Morocco. The velocity contrasts at larger depths likely point to the coesite–stishovite phase transition occurring in deep eclogitic pools. The shallower depths can be explained by the transition from orthoenstatite to high-pressure clinoenstatite which requires the reaction between eclogite and peridotite to form orthopyroxene-rich peridotite. This reaction is likely related to previously proposed small-scale mantle upwellings beneath SW Morocco. Since both phase transitions require eclogite occurrence, the location of the X-discontinuity in this region can be used to indicate the location of recycled oceanic crust.

Isotopic tracing of mercury sources in estuarine-inner shelf sediments of the East China Sea

Large river estuarine-inner shelf systems play an important role in the coastal biogeochemical cycling of heavy metals; however, the source-to-sink of mercury (Hg) in these environments remain poorly understood. In this study, the Hg isotopic composition of surface sediments in the Yangtze River Estuary (YRE) and inner shelf of the East China Sea (ECS) were examined to quantitatively track Hg sources in this region. We detected large spatial variation in δ202Hg (−1.88 to −0.29‰) and Δ199Hg (−0.22 to 0.13‰) in sediments of the YRE-ECS inner shelf. The impact of sediment resuspension and transport from the YRE to the inner shelf of the ECS could have little effect on Hg isotopic composition, and the two regions shared similar Hg isotopic composition. An isotope-based triple mixing model further revealed major contributors to sediment Hg from industrial Hg discharge into water (51.8 ± 24.5%), soil Hg from surface runoff (29.2 ± 17.0%), and precipitation-derived atmospheric deposition Hg (19.1 ± 17.5%). The Hg isotopic compositions of the YRE sediments and other local river estuaries were similar to those of direct industrial Hg discharge, indicating that contaminated riverine discharge was the dominant Hg source for estuarine and adjacent shelf areas. Soil Hg delivered through surface runoff was the primary source of Hg to the coastal areas not near large river estuaries, whereas precipitation-derived atmospheric deposition had a greater influence on offshore sediment Hg content. Industrial Hg discharged to rivers had the highest mean depositional flux (35.0 ± 27.3 ng cm−2 yr−1) and mass inventory (25.6 t yr−1), accounting for 77.4% of the total Hg variance. The findings of this study demonstrate that large rivers such as the Yangtze River can supply substantial amounts of industrial Hg to the estuary and adjacent shelf.

Accurate measurements of atmospheric carbon dioxide and methane mole fractions at the Siberian coastal site Ambarchik

Abstract. Sparse data coverage in the Arctic hampers our understanding of its carbon cycle dynamics and our predictions of the fate of its vast carbon reservoirs in a changing climate. In this paper, we present accurate measurements of atmospheric carbon dioxide (CO2) and methane (CH4) dry air mole fractions at the new atmospheric carbon observation station Ambarchik, which closes a large gap in the atmospheric trace gas monitoring network in northeastern Siberia. The site, which has been operational since August 2014, is located near the delta of the Kolyma River at the coast of the Arctic Ocean. Data quality control of CO2 and CH4 measurements includes frequent calibrations traced to World Meteorological Organization (WMO) scales, employment of a novel water vapor correction, an algorithm to detect the influence of local polluters, and meteorological measurements that enable data selection. The available CO2 and CH4 record was characterized in comparison with in situ data from Barrow, Alaska. A footprint analysis reveals that the station is sensitive to signals from the East Siberian Sea, as well as the northeast Siberian tundra and taiga regions. This makes data from Ambarchik highly valuable for inverse modeling studies aimed at constraining carbon budgets within the pan-Arctic domain, as well as for regional studies focusing on Siberia and the adjacent shelf areas of the Arctic Ocean.

To the question of the existence of a strike-slip fault in the Arctic Ocean between the underwater Lomonosov ridge and the adjacent shelf

The research object is the junction zone between the underwater Lomonosov ridge and East Siberian shelf. We intend to prove the absence of the strike-slip fault within this junction zone. The existence of the fault zone within this junction zone is still debatable. Formerly used geological and geophysical datawere unsufficient. To remove this ambiguity, seismological data obtained in neighboring areas was applied. Analysis of the earthquakes epicenters in the region showed that in cases of existence of such a fault zone, modern intraplate seismic activity should be certainly registered within its limits. The aseismicity of the junction zone between the underwater Lomonosov ridge and adjacent shelf areas clearly indicates the genetic unity exhisting between these tectonic structures.

New Information on the Structure, Geological Development and Oil and Gas Potential of the Northwestern Territories of Yakutia and the Adjacent Shelf of the Laptev Sea

In the XX-th century, scientific ideas prevailed on the genetic connection of the marginal Arctic territory, stretching far into the Laptev Sea shelf, with the mesozoids of the Verkhoyansk-Kolyma’s mountain-fold system. At the same time, this coastal strip of elevation was considered as the northwestern branch of this system. At the end of the last century, there have been significant changes in these views. The opinions of the geological development of the northern continental and adjacent shelf areas during the pre-Cenozoic geological epochs get very broad support under the conditions of a typical platform regime. The latest results of the seismic survey of the CDP-2D carried out in the Laptev Sea area was played an important role. The geological model of the structure and oil and gas content of the large area of the articulation of the continental land and the adjacent East Arctic shelf is justified and for the first time a preliminary characteristic of the new large Olenek-Laptevskaya oil and gas bearing region was given. The marginal structural-tectonic elements of sub latitudinal strike are constituent parts of the southern side of a large sedimentary basin, mainly located on the shelf Laptev Sea (Olenek-Laptevskaya syneclise). The tectonic regime of the concordative deflection, carried out earlier under the conditions of the passive continental margins of the Siberian Platform, was replaced with the conditions typical for the areas of interplate activation at the end of the Cretaceous and further in the Paleogene-Neogene. At the same time, the predominant stretching established earlier in the spreading zone on the continuation of the Gakkel ridge in the south-west direction was replaced by the conditions of regional subhorizontal compression. The obtained results indicate a regional continuation on the shelf of a large Riphean focus of oil and gas formation, established earlier by seismic prospecting in the northeast of the Siberian platform. As a result, it assumes the presence of a very significant hydrocarbon potential, much exceeding the high predictive estimates of past years.

Structural and Functional Characteristics of Zooplankton in the Ob Estuary and Adjacent Shelf Areas of the Kara Sea in Summer

The study was carried out in the Ob estuary and the adjacent shelf of the Kara Sea in July 2016. For the first time data on the species composition, abundance and distribution as well as on feeding of zooplankton were obtained during the period of intensive river runoff. The biomass of zooplankton in terms of wet weight (without jelly animals and chaetognaths) varied over a wide range from 40 to 1880 mg/m3. The biomass was dominaned by the Limnocalanus macrurus population, represented by all age stages, and Pseudocalanus spp. (an average 60% and 17% of biomass, respectively). Maxima of zooplankton biomass were associated with the boundary of the distribution of freshwater and with the southern periphery of the estuary frontal zone (EFZ). The short-term temporal variation of the abundance of zooplankton was observed when the transect was repeated after 2 days: the biomass at the southern periphery of the EFZ decreased from 1900 to 250 mg/m3. The observed changes is supposed to be caused by the shift of the southern boundary of the EFZ under changing in the wind regime. At high phytoplankton biomass in the estuary (>7 μg Chl-a/L), the daily ingestion of Limnocalanus macrurus was 5.77, 4.46, 2.59 and 1.4 μg C/day in CVI, CV, CIV and CIII, respectively. Energy intake by younger copepodite stages not only covered the metabolic requirements, but also enabled the copepods to growth. At lower Chl-a concentration on the shelf (<2 μg/L), the mean values were lower (1.56 μg C/day and 1.17 μg C/day in CVI and CV, respectively) and hardly met the metabolic demands. The zooplankton grazing impact estimated with the gut fluorescence method varied from 0.2 to 7.3% of phytoplankton standing stock and from 2.2 to 30% of primary production. The results are discussed in relation to the specific hydrophysical conditions in the summer period and in comparison with the data obtained for the autumn season.

Conceptual Basis for Research Infrastructure Restoration to Ensure Marine Studies in Ukraine

Purpose. Substantiation and formulation of conceptual basis to establish an effective National marine research system as a basic constituent of information support of Ukrainian economic and military interests in the Black and Azov Seas. Results. Current state of marine research infrastructures in Ukraine has been analysed, as well as the current legal framework. The issues of finding the ways to resolve the problem has been considered, first of all principles and mechanisms of an integrated system of marine studies restoration and functioning. Measures and steps have been substantiated to establish the National system of sustainable marine studies in Ukraine. The National system will be aimed at provision of the Government and the interested ministries and departments with up-to-date information for protection of National interests, enhancement of security, protection of sovereignty of the state. The list of concrete measures of the future programme has been presented and divided into three blocks: a) institutional, b) establishing of the up-to-date research infrastructure, c) performing of studies in the exclusive (marine) economic zone of Ukraine. Conclusions. Research potential of Ukraine has decreased during the past decade down to minimal critical level out of all the years since independence, first of all as the result of annexation of the Crimea and the adjacent Black Sea shelf area by Russian Federation. The departmental system of research financing and performing currently used in Ukrainian for goal-orientated marine studies in the interests of specific ministries and departments is unable to solve the existing problems. The only way out is to develop and implement a State target scientific and technical programme; its key priorities shall be solving of a number of similar international problems existing in all the Black Sea countries and the National interests of Ukraine. Establishing of a newest national research system is impossible without creation of a respective infrastructure, restoration of research fleet and an up-to-date system of marine specialists training taking into account the experience of European and world science.

Bathymetry and Canyons of the Eastern Bering Sea Slope

We created a new, 100 m horizontal resolution bathymetry raster and used it to define 29 canyons of the eastern Bering Sea (EBS) slope area off of Alaska, USA. To create this bathymetry surface we proofed, edited, and digitized 18 million soundings from over 200 individual sources. Despite the vast size (~1250 km long by ~3000 m high) and ecological significance of the EBS slope, there have been few hydrographic-quality charting cruises conducted in this area, so we relied mostly on uncalibrated underway files from cruises of convenience. The lack of hydrographic quality surveys, anecdotal reports of features such as pinnacles, and reliance on satellite altimetry data has created confusion in previous bathymetric compilations about the details along the slope, such as the shape and location of canyons along the edge of the slope, and hills and valleys on the adjacent shelf area. A better model of the EBS slope will be useful for geologists, oceanographers, and biologists studying the seafloor geomorphology and the unusually high productivity along this poorly understood seafloor feature.

Assessment of heavy metal pollution in surficial sediments from a tropical river-estuary-shelf system: A case study of Kelantan River, Malaysia

To understand the source-to-sink of pollutants in the Kelantan River estuary and the adjacent shelf area in Malaysia, a total of 42 surface sediment samples were collected in the Kelantan River-estuary-shelf system to analyze for grain size, total organic carbon (TOC) content, Al and heavy metals (Cr, Ni, Cu, Zn, Cd and Pb). The surficial sediments were mainly composed of clayey silt and the TOC content in sediments decreased from the river to the shelf. The surficial sediments experienced Pb pollution; Cr only showed a certain level of pollution in the coastal area of the estuary but not in other areas, and Ni, Cu, Zn, and Cd showed no pollution. The heavy metals mainly originated from natural weathering and erosion of rocks and soils in the catchment and enriched near the river mouth. Total organic carbon can promote the enrichment of heavy metals in sediments.

Composition of decapod larvae in a northeastern Brazilian estuarine inlet over a full tidal cycle

ABSTRACT. Composition changes of decapod larvae in a neotropical estuarine inlet (Catuama inlet, northeast Brazilian coast) were studied in a complete tidal cycle in August 2001. Sampling was performed at three stations at two or three depth levels that were located along a transect across the inlet. The collections were performed in 3 h intervals under a neap tide regime. Samples were taken with a pump and the water was filtered through 300 μm plankton net. 27 planktonic decapod taxa were identified, which included the first larval stages of the coastal and oceanic shrimps Lucifer faxoni and Acetes americanus, besides larvae of the estuarine and coastal decapods Pinnixa spp., Uca spp., Petrolisthes armatus , Upogebia spp. and Alpheidae, which were the most frequent taxa. All of the planktonic larval stages were observed for most of the decapods, suggesting that the probable exportation from the estuary is to the inner adjacent shelf area, instead of the outer oceanic area. Keywords: decapod larvae, meroplankton, tidal changes, neotropical estuary, northeastern Brazil.

Feeding of dominant zooplankton species and their grazing impact on autotrophic phytoplankton in the Yenisei Estuary in autumn

Feeding of dominant mesozooplankton species was investigated in freshwater zone, estuarine frontal zone of Yenisei Estuary and adjacent inner shelf area during autumn season. Ingestion rate was estimated based on gut fluorescence measurements. It was shown that in spite on the end of productive season daily ingestion of phytoplankton for the most of the investigated freshwater, brackish and marine zooplankton species was higher than their metabolic requirements. Total phytoplankton consumption by zooplankton differed in different zones. In freshwater zone under high level of autotrophic phytoplankton biomass and primary production zooplankton grazing impact was low: 1.5% of standing stock and 20% of primary production. In the estuarine frontal zone 3.2–14.3% of standing stock and 150–290% of primary production was grazed by zooplankton per day, in adjacent inner shelf: 1.4–7.0% and 130%, accordingly. Based on comparatively analysis of obtained data and results of investigation of zooplankton feeding in Ob Estuary during the same season some general patterns of the zooplankton role in organic matter biotransformation in the large arctic rivers estuarine areas were revealed.

Effect of continental shelf canyons on phytoplankton biomass and community composition along the western Antarctic Peninsula

The western Antarctic Peninsula is experiencing dramatic climate change as warm, wet conditions expand poleward and interact with local physics and topography, causing differen- tial regional effects on the marine ecosystem. At local scales, deep troughs (or canyons) bisect the continental shelf and act as conduits for warm Upper Circumpolar Deep Water, with reduced sea- sonal sea ice coverage, and provide a reservoir of macro- and micronutrients. Shoreward of many canyon heads are Adelie penguin breeding colonies; it is hypothesized that these locations reflect improved or more predictable access to higher biological productivity overlying the canyons. To synoptically assess the potential impacts of regional bathymetry on the marine ecosystem, 4 major canyons were identified along a latitudinal gradient west of the Antarctic Peninsula using a high- resolution bathymetric database. Biologicalphysical dynamics above and adjacent to canyons were compared using in situ pigments and satellite-derived sea surface temperature, sea ice and ocean color variables, including chlorophyll a (chl a) and fucoxanthin derived semi-empirically from remote sensing reflectance. Canyons exhibited higher sea surface temperature and reduced sea ice coverage relative to adjacent shelf areas. In situ and satellite-derived pigment patterns indicated increased total phytoplankton and diatom biomass over the canyons (by up to 22 and 35%, respectively), as well as increases in diatom relative abundance (fucoxanthin:chl a). While regional heterogeneity is apparent, canyons appear to support a phytoplankton community that is conducive to both grazing by krill and enhanced vertical export, although it cannot compensate for decreased biomass and diatom relative abundance during low sea ice conditions.

Asymmetry in brachiopods

Bilateral symmetry is generally typical for brachiopods, although it is sometimes disturbed in living and fossil brachiopods of different orders by some topical and trophic reasons. Asymmetry is observed in both outer and inner structures of these invertebrates, mostly in the shell shape and organs connected with filtration. Asymmetry is observed primarily in brachiopods inhabiting reef facies and adjacent shelf areas.