Central Shelf Research Articles

Assessment of phytoplankton photosynthetic efficiency based on measurement of fluorescence parameters and radiocarbon uptake in the Kara Sea

Spatial distribution of relative electron transport rate (rETR) values, the maximum quantum efficiency of PSII (Fv/Fm), and biomass-specific primary production (PB, mg C (mg Chl a)−1 h−1) were described for the eastern part of the Kara Sea in the autumn (September). A characteristic feature of this period was a noticeable decrease in the length of the day and the elevation angle of the sun, leading to a significant decrease in surface photosynthetically active radiation (PAR). Despite low light in the euphotic zone, the phytoplankton maximum quantum efficiency of PSII (Fv/Fm) was high (0.5–0.7) in the upper 30-m layer of the water column, which indicates a potentially active state of phytoplankton. At the same time, the main productive activity of phytoplankton was linked to the surface 0–3 m and was closely related to the daily incident PAR and the share of diatoms in the total phytoplankton biomass. Despite a decrease in light level and following a reduction in the values for productive characteristics of the phytoplankton community, diatoms continued to play a major role in primary productivity in the eastern Kara Sea at the end of the vegetative season. Comparative analysis of data obtained by two different techniques – fluorescence measurements and experimental carbon fixation estimations – demonstrated a close relationship between rETR and PB. However, surface values of PB changed more strongly than rETR, which may, apparently, reflect different efficiency in the use of absorbed light energy in the synthesis processes. Photosynthetic efficiency, reflecting the extent of use of the light energy caught in processes of organic matter synthesis, can be expressed through the ratio between PB and rETR values. The PB/rETR ratio increased in areas characterized by drastic gradients of hydrophysical conditions: over the external coastal shelf, central shelf and lower continental slope of the St Anna Trough.

Anaerobic ammonium oxidation (anammox) and denitrification in Peru margin sediments

The upwelling system of coastal Peru supports very high primary production, contributing to an oxygen deficient zone (ODZ) in subsurface waters and high organic matter deposition rates to underlying sediments. Although anammox and denitrification have been relatively well studied in ODZ waters, few studies have investigated these processes in the underlying sediments. We sampled seven stations over a large geographic area along the Peru margin, spanning a water depth of 100–3240 m. At two of the central shelf stations (100 m and 325 m), we observed Thioploca , with a well-developed mat at the shallowest station (100 m). We measured sediment properties and conducted shipboard 15 N-incubations of homogenized sediments to determine potential rates of anammox and denitrification and potential controlling factors at each station. Diversity of anammox bacteria based on 16S rRNA and hydrazine oxidoreductase ( hzo ) sequences and hzo gene abundances were measured at each station. Overall, organic C content was high across the stations (3–12%), except for two of the deepest stations (~1.5%). Porewater ammonium fluxes and ammonium production rates in shipboard incubations, reflecting sediment organic carbon decomposition rates, were higher at the two central shelf stations compared to the other stations. The range in average potential rates was 2.1–80.4 nmol N cm −3 h −1 for denitrification and 1.8–44.2 nmol N cm −3 h −1 for anammox. The range in relative anammox ( ra ) across stations was 2.6–47.4%, with an average of 34.2%. The lowest ra was found at the shallowest shelf station with Thioploca mats and highest ammonium production rates. The ra jumped up to 45.9% at the station with the next highest ammonium production rates, corresponding to the deeper shelf station (325 m). At the other stations, ra was relatively high (39.6–47.4%), except at one station (16.3%), reflecting similar ammonium production rates due to decomposition across these stations. Anammox bacteria in the Candidatus Scalindua genus were the only anammox bacteria detected in Peru margin sediments based on 16S rRNA or hzo sequences. Copy number of hzo indicated abundant populations of anammox bacteria across the stations. However, hzo copy number did not correlate with anammox rates or ra . Overall, our results suggest that anammox contributes significantly to N 2 production in Peru margin sediments, except in shelf sediments with high decomposition rates and dense Thioploca mats. • Anammox and denitrification rates were generally high in Peru margin sediments. • Intracellular nitrate was a complicating factor in shelf sediments in the study. • Anammox rates were inhibited in the presence of a dense Thioploca mat. • Anammox rates jumped up in the presence of low density Thioploca . • Density and metabolic status of Thioploca may influence anammox rates.

Water mass analysis and contribution estimation using heavy rare earth elements: Significance of Kuroshio intermediate water to Central East China Sea shelf water

Abstract The East China Sea (ECS) has complicated water masses, in which it is difficult to clarify the various sources solely by estimating the potential temperature (PT) and salinity. High-nutrient bottom water was identified on the central ECS shelf. The pattern of heavy rare earth elements (HREEs) suggested the important contribution of Kuroshio intermediate water (KIW) in this bottom water. HREEs combined with hydrographic and chemical parameters indicated that the bottom water is a mixture of KIW, Kuroshio tropical water (KTW), and mixed shelf water (MSW). The mixing ratios of these three water sources estimated by four HREEs are comparable with the results calculated by PT and salinity. Then, PT and salinity are combined with HREEs to quantify the mixing of four water masses (KTW, MSW, KIW, and Kuroshio surface water) in the entire water column on the central shelf of the ECS. Our results indicate that the high amounts of nutrients at 130 m (bottom) on the ECS middle shelf mainly originate from the 400–600-m depth of KIW and the 150–300-m depth of KTW. The fractional nutrient concentration from the KIW in the bottom water yielded NO 3 + NO2: 63 ± 23% and P: 62 ± 22%, suggesting the significance of the KIW's material transport to the central ECS shelf. This study demonstrates that HREEs, in combination with conventional temperature and salinity, effectively increase the number of available tracers so that water mass analysis can be done with more robust results achieved.

Organic matter degradation in surface sediments of the Changjiang estuary: Evidence from amino acids

Organic matter degradation is a key component of the processes of carbon preservation and burial in seafloor sediments. The aim of this study was to explore organic matter degradation state within the open-shelf Changjiang Estuary of the East China Sea, using an amino acids–based degradation index (DI) in conjunction with information about organic matter source (marine versus terrestrial), bottom water oxygenation state, and sediment grain size. The relative molar percentages of 17 individual amino acids (characterized using principal component analysis) in surface sediments indicate that organic matter is degraded to varying extents across the estuary seabed. Sediments with DI >0 (relatively labile) were found mostly within a coastal hypoxic area. Sediments of DI less than −1 (relatively refractory) were found near the Changjiang River mouth and the northern and southern parts of the central shelf. We consider DI to be a more reliable indicator of degradation than simple ratios of AAs. DI was inversely correlated with the proportion of terrestrial organic material (Ft) in the sediments, indicating that relatively fresh/labile organic matter was generally associated with marine sources. DI was significantly correlated with Ft and bottom water apparent oxygen utilization (AOUbot) together. The parameter DI and the (labile) amino acid tyrosine were highest in hypoxic areas, suggesting the presence of relatively fresh organic matter, probably due to a combination of marine-source inputs and better preservation of organic matter in the silt and clay sediments of these areas (as compared to sandy sediments). Less degraded organic matter with high amino acids was also favorable to benthic animals. Overall, sedimentary estuarine organic matter was least degraded in areas characterized by marine sources of organic matter, low-oxygen conditions, and fine-grained sediments.

Seasonal variation of zooplankton community structure and trophic position in the Celtic Sea: A stable isotope and biovolume spectrum approach

Zooplankton on continental shelves represent an important intermediary in the transfer of energy and matter from phytoplankton to the wider ecosystem. Their taxonomic composition and trophic interactions with phytoplankton vary in space and time, and interpreting the implications of this constantly evolving landscape remains a major challenge. Here we combine plankton taxonomic data with the analysis of biovolume spectra and stable isotopes to provide insights into the trophic interactions that occur in a shelf sea ecosystem (Celtic Sea) across the spring-summer-autumn transition. Biovolume spectra captured the seasonal development of the zooplankton community well, both in terms of total biomass and trophic positioning, and matched trophic positions estimated by stable isotope analysis. In early April, large microplankton (63–200 µm) occupied higher trophic positions than mesozooplankton (>200 µm), likely reflecting the predominance of nanoplankton (2–20 µm) that were not readily available to mesozooplankton grazers. Biomass and number of trophic levels increased during the spring bloom as elevated primary production allowed for a higher abundance of predatory species. During July, the plankton assemblage occupied relatively high trophic positions, indicating important links to the microbial loop and the recycling of organic matter. The strong correlation between biomass and community trophic level across the study suggests that the Celtic Sea is a relatively enclosed and predominantly energy-limited ecosystem. The progression of the zooplankton biomass and community structure within the central shelf region was different to that at the shelf-break, potentially reflecting increased predatory control of copepods by macrozooplankton and pelagic fishes at the shelf break. We suggest that the combination of size spectra and stable isotope techniques are highly complementary and useful for interpreting the seasonal progression of trophic interactions in the plankton.

Decadal stability in top predator habitat preferences in the Bay of Biscay

Most oceanographic systems, especially shelf ecosystems, are characterised by interannual variability in the timing, extent and intensity of their seasonal patterns. Such interannual variations have important consequences on top predator habitat preferences. Capitalising on oceanographic surveys performed every spring since 2004 in the Bay of Biscay (BoB), this study explored interannual variations in habitat preferences exhibited by five mobile top predator species: bottlenose and common dolphins, auks, fulmars and northern gannets. We expected to find species with similar habitat preferences every year or species exhibiting important variability in their habitat preferences. First, we identified with a Principal Component Analysis (PCA) three different habitats of varying extent depending on year: river plumes, central shelf waters and shelf edge. Second, the Principal Components were used to explore the habitat preferences of predators through Generalized Additive Models. We fitted two kinds of models, using and not using the year as an interaction term, to test whether habitat preferences changed across years. Our results showed a range of habitat strategies based on the specificity and stability of species preferences. Species exhibiting narrower habitat preferences also exhibited stronger stability in their preferences among years while the species with wider habitat preferences exhibited higher variability among years. The target habitats differed across studied species, with bottlenose dolphins targeting the shelf edge exclusively, auks preferring river plumes, fulmars exhibiting a gradual preference from the shelf edge to river plumes and gannets being present in any of the three habitats. In contrast, the habitat preferences of common dolphins, the most sighted cetacean species in the BoB, could not be reliably inferred.

Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea

The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 – August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.

Tsunamis in the East Sea and damages to the coastline of Vietnam

According to field surveys as well as data recorded in text documents, it can be said that Vietnam has historically been hit by a tsunami. However, we still do not have enough information to accurately determine the destructive power of these tsunamis against the coastal line of Vietnam. On the other hand, in the South China Sea, there are four potential earthquakes that could lead to tsunamis affecting coastal line of Vietnam. Using models, tsunami simulations as well as computing algorithms, experts say that tsunamis will appear and attack coastal line of Vietnam when there are submarine earthquakes with magnitude of larger than 7 at the fault along Central Asia shelf with an earthquake with magnitude of greater than 8 at the Manila Trench. If an earthquake of magnitude 8 occurs in the south of Hainan, the tsunami impacting coastal line of Vietnam will be greater than 2 m. If an earthquake of magnitude 8 occurs in Manila, the tsunami from Da Nang city to Quang Ngai will reach 4 m. From there we can see that the risk of tsunami occurring and attacking the coastal cities of Vietnam is there, although the probability is not high.

Temporal and spatial variability of zooplankton on the Faroe shelf in spring 1997–2016

Abstract Zooplankton availability during spring and summer determines the growth and survival of first-feeding fish larvae, and thus impacts the recruitment to both fish prey species and commercial fish stocks. On the Faroe shelf, however, the relative importance of oceanic versus neritic zooplankton species has hitherto not been well understood. In this study, spatio-temporal variability in zooplankton community structure and size spectra on the Faroe shelf is investigated using observations from late April during the period 1997–2016. The main objective was to explore which environmental variables influence the zooplankton community structure in early spring. The zooplankton community in the permanently well mixed central shelf inside the tidal front consists of a mixture of neritic, cosmopolitan and oceanic species. In this region, redundancy analyses showed that chlorophyll concentration had a positive effect on abundance of neritic copepods and meroplankton as well as all zooplankton Calanus finmarchicus , is however observed off-shore from the tidal front, especially on the western side of the Faroe Plateau. A shift in C. finmarchicus phenology occurred around 2007, resulting in earlier reproduction of this species, and this variability could not be explained by the employed regional environmental parameters. Our results indicate that the Faroe shelf biological production is more dependent on the local primary production and neritic zooplankton species than on the large oceanic C. finmarchicus stock.

Faroe shelf bloom phenology – The importance of ocean-to-shelf silicate fluxes

The highly variable primary production on the spatially confined Faroe shelf has been comprehensively monitored since the early 1990s. Utilizing these data together with output from a realistic high-resolution numerical model, we here give a unique description of an interplay between bloom phenology in a productive temperate well mixed Central Shelf and the mixed layer dynamics in a surrounding seasonally stratified Outer Shelf. There is a shift to a persistently stratified Outer Shelf during late May – early June, which thereafter holds the highest phytoplankton biomass and becomes nutrient limited in the upper layer. The Central Shelf chlorophyll accumulation becomes impeded around this transition, which is coincident with strong silicate drawdown. Subsequently, a succession of blooms can occur, and these coincide with nutrient enriching erosion of the Outer Shelf stratification and become terminated by re-establishments of the stratification. We hypothesize that the mixed layer dynamics of the Outer Shelf regulates the lateral nutrient fluxes to the Central Shelf.

Phenologically distinct phytoplankton regions on the Faroe Shelf - identified by satellite data, in-situ observations and model

Marked inter-annual fluctuations in the primary production on the Faroe shelf propagate to higher trophic levels and influence commercial fish stocks. This has previously been demonstrated based on weekly chlorophyll samples from a coastal station, dating back to 1997.However, the spatial extent, for which the coastal samples are representative, has not been well defined, and potential bio-geographical segregations of the shelf have not been considered. By integrating 18years of chlorophyll satellite data, supplemented by in-situ, model, and meteorological reanalysis data, we identify three regions with unique characteristics with regards to surface chlorophyll and vertical structure - the Central Shelf, the Outer Shelf and the Eastern Banks. The observed difference in timing of the spring bloom in these regions helps explain different spawning patterns of important fish stocks, and the spatial division of the Faroe Shelf should be considered when studying biology and hydrography in these waters.A positive correlation between annual means on the outer Faroe Shelf and parts of the outer northwest Scottish Shelf indicates similarities between these neighbouring regions.We suggest that this similarity arises from the commonality in nutrient composition of the water masses shared by these neighbouring regions.

Srednjojadranski prag – važnija istraživanja i metodologija obrade podataka

A methodological approach in the analyses of the seawater oceanographic states is determined by the purpose of the paper and general purpose of the research. In the recent decades the scientific work in this area has advanced thanks to computer data processing, particularly owing to modern technical and technological achievements that allow us to obtain important results, which significantly augment application of scientific results. This paper is a review of the research on the Central Adriatic shelf. Until now, papers dealing with geographical and oceanographic features regularly used the terms Palagruža Shelf and Jabuka concavity in the meaning of independent entities in the Adriatic basin which partly define physicogeographic features of water masses. However, such perception should be corrected. The Central Adriatic shelf is situated between the north Adriatic and the south Adriatic basin. Its length is greater than the width. Therefore, it deserves more attention and more cautious scientific approach. In this paper there are also evaluations of some methodologies used in the research and in the measuring of oceanographic parameter values, and also new technical solutions are proposed. The purpose of this paper is to analyse some methods of approach in the presentation of oceanographic states of seawater in the area of the Central Adriatic shelf. The purpose is also to introduce a succession of articles in which this maritime zone should be given its deserving significance from the geographic and oceanological aspects.

The distribution and inter-annual variation of water masses on the Bering Sea shelf in summer

On the basis of the CTD data obtained within the Bering Sea shelf by the Second to Sixth Chinese National Arctic Research Expedition in the summers of 2003, 2008, 2010, 2012 and 2014, the classification and interannual variation of water masses on the central Bering Sea shelf and the northern Bering Sea shelf are analyzed. The results indicate that there are both connection and difference between two regions in hydrological features. On the central Bering Sea shelf, there are mainly four types of water masses distribute orderly from the slope to the coast of Alaska: Bering Slope Current Water (BSCW), MW (Mixed Water), Bering Shelf Water (BSW) and Alaska Coastal Water (ACW). In summer, BSW can be divided into Bering Shelf Surface Water (BSW_S) and Bering Shelf Cold Water (BSW_C). On the northern Bering Sea shelf near the Bering Strait, it contains Anadyr Water (AW), BSW and ACW from west to east. But the spatial-temporal features are also remarkable in each region. On the central shelf, the BSCW is saltiest and occupies the west of 177°W, which has the highest salinity in 2014. The BSW_C is the coldest water mass and warmest in 2014; the ACW is freshest and mainly occupies the east of 170°W, which has the highest temperature and salinity in 2012. On the northern Bering Sea shelf near the Bering Strait, the AW is saltiest with temperature decreasing sharply compared with BSCW on the central shelf. In the process of moving northward to the Bering Strait, the AW demonstrates a trend of eastward expansion. The ACW is freshest but saltier than the ACW on the central shelf, which is usually located above the BSW and is saltiest in 2014. The BSW distributes between the AW and the ACW and coldest in 2012, but the cold water of the BSW_C on the central shelf, whose temperature less than 0°C, does not exist on the northern shelf. Although there are so many changes, the respond to a climate change is synchronized in the both regions, which can be divided into the warm years (2003 and 2014) and cold years (2008, 2010 and 2012). The year of 2014 may be a new beginning of warm period.

Jurassic failed rift system below the Filchner-Ronne-Shelf, Antarctica: New evidence from geophysical data

During the austral summer of 1994/95, reasonable ice conditions in the Weddell Sea allowed the acquisition of new high quality seismic refraction data parallel to the Filchner-Ronne Ice Shelf (FRS), Antarctica. Although pack ice conditions resulted in some data gaps, the final velocity-depth/2D-density models cover the entire FRS in E-W direction using all available deep seismic data/picks from this remote area. The velocity-depth model shows a sedimentary basin with a thickness up to 12km and a large velocity inversion in the lowermost sedimentary unit. The crustal thickness reaches a maximum of 40km along the basin's margins in the Antarctic Peninsula and East Antarctica. In the central shelf area, numerous interfering seismic phases occur from the crust-mantle boundary at decreasing distances indicating a thinning of the crust. Here, the modelled velocities and densities reveal a thickness of 20km for the igneous crust. This corridor of overthickened oceanic or close to oceanic crust is 160km wide. The corridor is characterized by weak, but in general continuous magnetic anomalies, which we interpret as isochrons developed during the rifting or the initial formation of oceanic crust. If the crustal composition represents an old stripe of oceanic crust, a minimum estimate for the early formation of the oceanic crust is 145/148Ma (Late Jurassic). However, based on the velocity of rift propagation during the initial opening of the adjacent Weddell Sea the oceanic crust is likely to have formed around 160Ma. The onset of rifting and development of a thick igneous crust can be related to stresses developed between the interior and the southwestern paleo-Pacific subduction margin of the fragmenting Gondwana supercontinent in combination with additional melt supply from a deeper mantle source that arrived and spread in the period 183–155Ma.

The characteristics of warm water inflowing and its temporal and spatial variation on the Prydz Bay continental shelf, Antarctic

Hydrographic observations collected by conductivity-temperature-depth (CTD) and instrumented elephant seals on the Prydz Bay continental shelf during 2012 and 2013 are used to characterize the intrusion of modified circumpolar deep water. As a regular occurrence, modified circumpolar deep water (MCDW) intrudes onto the shelf mainly between 150–300 m layer of 73°–75°E and then turns southeast affected by the cyclonic gyre of the Prydz Bay. The southernmost point of the warm water signal is captured on the east front of Amery Ice Shelf during March 2012. In terms of vertical distribution, MCDW occupies the central layer of 200 m with about 100 m thickness in the austral summer, but when to winter transition, the layer of MCDW deepens with time on the central shelf.

Distribution and composition of authigenic minerals in surface sediments of the western Gulf of Thailand

Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the MnO content in siderite decreases, but Fe2O3 and MgO content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains, which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The K2O content of glauconite is low or absent, indicating its short formation time.

Spatial dynamics of the bearded goby and its key fish predators off Namibia vary with climate and oxygen availability.

Hypoxia [O2 < 2.0 mL L−1 (87 μmol kg−1)] and severely hypoxic water masses [O2 < 0.5 mL L−1 (21.8 μmol kg−1)] are increasing in coastal marine ecosystems due to eutrophication and warming. Here, we investigate the response of the suboxic-tolerant endemic fish, Sufflogobius bibarbatus, to variations in the thermal and oxygen environment, as well as to predation pressure, using 22 yr worth of satellite and in situ data. We show that environmental variation and predation pressure affect the goby population, which has expanded over the last decade while that of horse mackerel has contracted. These changes co-occurred with a general warming in the north and central shelf areas (north of 24.5°S). Spring warming positively affected both goby and hake abundances, but not the horse mackerel, suggesting different responses to surface temperature. The goby habitat contracted when predators were abundant, particularly in the north, which is the fringe of its distributional area. The implications of the differential tolerance of gobies and their predators for climate variations are discussed.

Shore-Based Video Observations of Nonlinear Internal Waves across the Inner Shelf *,+

Abstract Shore-based video remote sensing is used to observe and continually monitor nonlinear internal waves propagating across the inner shelf. Month-long measurements of velocity from bottom-mounted acoustic Doppler current profilers and temperature from thermistor chains at the 10- and 20-m isobaths are combined with sea surface imagery from a suite of cameras (Argus) to provide a kinematic description of 11 borelike internal waves as they propagate across the central Oregon inner shelf. The surface expression of these waves, commonly seen by eye as alternating rough and smooth bands, are identified by increased pixel intensity in Argus imagery (average width 39 ± 6 m), caused by the convergence of internal wave-driven surface currents. These features are tracked through time and space using 2-min time exposure images and then compared to wave propagation speed and direction from in situ measurements. Internal waves are refracted by bathymetry, and the measured wave speed (~0.15 m s−1) is higher than predicted by linear theory (&amp;lt;0.1 m s−1). Propagating internal waves are also visible in subsampled Argus pixel time series (hourly collections of 17 min worth of 2-Hz pixel intensity from a subset of locations), thus extending the observational record to times without an in situ presence. Results from this 5-month record show that the preferred sea state for successful video observations occurs for wind speeds of 2–5 m s−1. Continued video measurements and analysis of extensive existing Argus data will allow a statistical estimate of internal wave occurrence at a variety of inner-shelf locations.

Stable carbon and oxygen isotopes distribution in carbonates from the Central Barents Sea shelf sediments

Carbonate macrofaunal remains and diagenetic tubes collected from a number of structures in the Central Barents Sea area during the 18th TTR (Training Through Research) cruise were subdivided into three groups according to the results of stable carbon and oxygen isotopes analysis. The first group includes carbonates that were formed from bicarbonate only from surrounding sea waters. The carbonates of the second group were formed during diagenesis with use of mixed sources of bicarbonate. The fourth group includes methane-derived carbonates that were formed as a result of anaerobic oxidation of methane (AOM).

Circulation on the central Bering Sea shelf, July 2008 to July 2010

We examine the July 2008 to July 2010 circulation over the central Bering Sea shelf using measurements at eight instrumented moorings, hindcast winds and numerical model results. At sub‐tidal time scales, the vertically integrated equations of motion show that the cross‐shelf balance is primarily geostrophic. The along‐shelf balance is also mainly geostrophic, but local accelerations, wind stress and bottom friction account for 10–40% of the momentum balance, depending on season and water depth. The shelf exhibits highly variable flow with small water column average vector mean speeds (&lt;5 cm s−1). Mean/peak speeds in summer (3–6 cm s−1/10–30 cm s−1) are smaller than in winter and fall (6–12 cm s−1/30–70 cm s−1). Low frequency flows (&lt;1/4 cpd) are horizontally coherent over distances exceeding 200 km. Vertical coherence varies seasonally, degrading with the onset of summer stratification. Because effects of heating and freezing are enhanced in shallow waters, warm summers increase the cross‐shelf density gradient and thus enhance northward transport; cold winters with increased ice production and brine rejection increase the (now reversed) cross‐shelf density gradient and enhance southward transport. Although the baroclinic velocity is large enough to influence seasonal transports, wind‐forced Ekman dynamics are primarily responsible for flow variations. The system changes from strong northward flow (with coastal convergence) to strong southward flow (with coastal divergence) for northerly and easterly winds, respectively. Under northerly and northwesterly winds, nutrient‐rich waters flow toward the central shelf from the north and northwest, replacing dilute coastal waters that are carried south and west.