Deep-sea Research Part Ii-topical Studies in Oceanography最新文献

Many fish species have moved poleward with ocean warming, and species distribution shifts can occur because of adult fish movement, or juveniles can recruit to new areas. In the Bering Sea, recent studies document a dramatic northward shift in the distribution of Gadus macrocephalus (Pacific cod in English and tikhookeanskaya treska in Russian) during a period of ocean warming, but it is unknown whether the current northward distribution shift continues into the Chukchi Sea. Here, we use catch data from multiple gear types to present larval, age-0, and older Pacific cod distributions from before (2010 and 2012) and during (2017, 2018, and 2019) recent Chukchi Sea warming events. We also report on the habitat, diet, and condition of age-0 Pacific cod, which were present in the eastern Chukchi Sea in recent warm years (2017 and 2019), but were absent in a cold year (2012). We hypothesize that age-0 recruitment to the eastern Chukchi Sea is associated with recent warm temperatures and increased northward transport through the Bering Strait in the spring. Age-0 fish were present in both benthic and pelagic habitats and diets reflected prey resources at these capture locations. Age-1 Pacific cod were observed in the western Chukchi Sea in 2018 and 2019, indicating possible overwinter survival of age-0 fish, although there was little evidence that they survive and/or remain in the Chukchi Sea to age-2. Observed low lipid accumulation in age-0 Pacific cod from the Chukchi Sea suggests juvenile overwinter mortality may be relatively high compared to more boreal regions (e.g. Gulf of Alaska). Adult Pacific cod were also observed in the Chukchi Sea during 2018 and 2019. Although densities in the western Chukchi Sea were very low compared to the Bering Sea, the adults are the first known (to us) records from the Chukchi Sea. The increased presence of multiple age-classes of Pacific cod in the Chukchi Sea suggests poleward shifts in both nursery areas and adult summer habitat beyond the Bering Sea, but the quantity and quality (e.g. summer productivity and overwintering potential) of these habitats will require continued surveys.

Water renewal through the Bohai Strait largely dominates the water quality of the semi-enclosed Bohai Sea (BS), which connects only to the northern Yellow Sea (NYS) through the strait. Although the peak water transport through the Bohai Strait occurs in summer, the spatially averaged water residence time of the BS shows no significant decrease compared to other periods. A three-dimensional model is applied to unravel the detailed structure and dynamic processes of the summertime NYS water transport from the northern Laotieshan Channel to the BS interior. Model results from both climatological and hindcasting cases show that despite a large amount of the NYS water enters the strait, they are confined to the Laotieshan Channel between the Central Bank and Dalian surrounded by a strong Ω-shaped tidal front and could not move further north into the Liaodong Bay. The strong along-front flow steered by the topography forms a counter-clockwise circulation pattern in the strait zone, resulting in most of water southward movement east of the Central Bank, then join the outflow south of the strait and leave for the NYS. The Central Bank and the topographic sill north of the Laotieshan Channel act as a barrier that significantly reduces the water exchange between the strait zone and the BS interior, in particular the Liaodong Bay. Particle-tracking experiments suggest that less than 10% of particles released in the NYS could finally reach the BS interior, and among of them only a small portion of them could move further north into the Liaodong Bay. Momentum diagnostics suggest that the water transport northwest of the strait is dominated by geostrophic balance in the Ω-shaped frontal region. Sensitivity experiments indicate that tides promote the surface water transport from the NYS to the BS interior. The realistic wind forcing including synoptic events may facilitate the water transport from the strait to the BS interior by modulating the barotropic and baroclinic pressure gradient than that with the climatological wind case.

Four new species of vulcanellid sponges (Demospongiae: Tetractinellida), Poecillastra malyutini sp. nov., Vulcanella koltuni sp. nov., V. commander sp. nov. and V. grebelnyi sp. nov., are described from the Piip submarine volcano and adjacent area (the Bering Sea, North Pacific). This work includes materials sampled using the ROV Comanche 18 during the cruises of the RV Akademik M.A. Lavrentyev in 2016 and 2018. These specimens were studied and illustrated using light and electron (SEM) microscopy and micro-computed tomography (micro-CT). The distribution of species is characterized by pronounced vertical zoning. In areas of hydrothermal vents and on their periphery, Demospongiae are abundant with a pronounced dominance of a single species, V. koltuni sp. nov. The δ¹³C value for V. koltuni sp. nov. and P. malyutini sp. nov. from the volcano summits were almost 2-fold lower than for V. commander sp. nov. collected outside the areas of hydrothermal activity. These isotopic signatures indicate the organic matter of chemosynthetic origin in the diet of V. koltuni sp. nov. and P. malyutini sp. nov. Phylogenetic analysis based on 18S rDNA does not confirm the phylogenetic relationship of Lamellomorpha Bergquist, 1968 with the family Vulcanellidae Cárdenas, Xavier, Reveillaud, Schander & Rapp, 2011.

The formation of the cold ridge, a seasonal mid-shelf upwelling feature on the Agulhas Bank, is investigated from a combination of satellite-tracked surface drifters, in situ current and temperature data, as well as satellite sea surface temperature (SST) and chlorophyll-a (Chl-a). The observational data showed coastal upwelling along the Tsitsikamma coast to be induced by the easterly wind in austral summer, with a coexistent westward flowing coastal current. Under this wind and current regime, surface drifters moved west and onto the mid-shelf with the cold water, thereafter following the southward-curved 100 m isobath. Satellite observations in March–April 2008 showed increased south-westward advection of wind-driven upwelled water during an Agulhas Current intrusion that resulted in the formation of a classically shaped cold ridge. Also of interest was the passing of a Natal Pulse along the south-eastern shelf edge of the Agulhas Bank in July 2007. This generated a large cyclonic eddy in the Agulhas Bight with an attendant warm water plume that swept over the adjacent shelf. Two idle drifters positioned on the mid-shelf at the time, immediately west of the Natal Pulse, were rapidly advected offshore along the curved 100 m isobath, confirming the long-thought association of the cold ridge with an Agulhas Bight cyclone. A moored current meter adjacent to the Tsitsikamma coast (1.5 km offshore) showed the effect of the Natal Pulse on the nearshore. Drifter trajectories show accelerated south-westward flow on the offshore side of the cold ridge and recirculation towards the east on its shoreward side. These findings strongly support the Westward Transport Hypothesis where squid paralarvae are advected westward from the inshore breeding grounds, to the food maxima on the interior of the central Agulhas Bank, to improve their chances of survival and can therefore have important implications for the management of the South African chokka squid fishery.

Mesoscale eddies play an essential role in the freshwater transport, ocean circulation and climate. Although there is no completely objective eddy dataset, observations can better reproduce the eddies in the ocean as data resolution is improved and eddy detection methods are developed to some extent. This study uses satellite altimeter data and compares the Mesoscale Eddy Trajectory Atlas Product (META) with the Global Ocean Mesoscale Eddy Atmospheric-Oceanic-Biological Interaction Observational Dataset (GOMEAD) to analyze the mesoscale eddy characteristics in the oceanic pathways in the Agulhas Leakage (AL) region at the intersection of the Indian and Atlantic Oceans, and the Tasman Leakage (TL) region between the Indian and Pacific Oceans. Here we show that, the META dataset is more applicable for the detection of small-radius eddies, but this product increases the risk of over-detection. The GOMEAD dataset offers precise eddy boundaries and is useful for identifying large diameter eddies. The characteristics of eddies in the AL and TL regions are analyzed, and the results indicate that GOMEAD is more suited for eddy detection and analysis in the AL, while the META dataset is better suited for studies of mesoscale eddies of the TL region. Choosing the appropriate dataset is important for understanding the role of mesoscale eddies of different areas in a changing climate.

Recently, sea surface temperatures (SSTs) near the Korean Peninsula have increased rapidly due to global warming; this phenomenon can lead to high water temperatures and extensive damage to Korean fish farms. To reduce such damage, it is necessary to predict high water temperature events in advance. In this study, we developed a method for predicting high water temperature events using time series SST data for the Korean Peninsula obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 product and a long short-term memory (LSTM) network designed for time series data prediction. First, the SST prediction model was used to predict SSTs. Predicted SSTs exceeding 28 °C, which is the Korean government standard for issuing high water temperature warnings, were designated as high water temperatures. To evaluate the prediction accuracy of the SST prediction model, 1-to 7-day predictions were evaluated in terms of the coefficient of determination (R²), root mean square error (RMSE), and mean absolute percentage error (MAPE). The R², RMSE, and MAPE values of the 1-day prediction SST model were 0.985, 0.14 °C, and 0.38%, respectively, whereas those of the 7-day prediction SST model were 0.574, 0.74 °C, and 2.26%, respectively. We also calculated F1 scores to evaluate high water temperature classification accuracy. The F1 scores of the 1- and 7-day SST prediction models were 0.963 and 0.739, respectively.

Baseline surveys of offshore pelagic fishes in the eastern Chukchi Sea in 2012 and 2013 found that age-0 Arctic cod (Boreogadus saida) dominated the pelagic fish community in summer, with relatively few adults present in the region. Since this time, drastic changes in the ocean-atmosphere-ice feedback loop have led to continued warming, further reducing ice cover, and increased northward transport has led to an increase in Pacific-origin waters on the Chukchi shelf in summer. To examine potential bottom-up effects of these environmental changes on pelagic fishes in this rapidly changing environment, we extended a time series of large-scale acoustic-trawl surveys with additional surveys in 2017 and 2019. Age-0 Arctic cod were the most abundant pelagic fish in all four survey years, comprising 68–93% of fish abundance. However, age-0 walleye pollock (Gadus chalcogrammus), which were scarce (<0.1% of fishes) and confined to the southern Chukchi in 2012 and 2013, were present in high abundance (>21% of fish abundance) throughout the Chukchi shelf in 2017 and 2019. Age-0 Arctic cod were substantially more abundant in 2017 than in other years, possibly due to increased survivorship of larvae under warm conditions. Unlike in 2017, Arctic cod and pollock were spatially separated in 2019 due to enhanced transport, with Arctic cod primarily present in the northeastern portion of the survey area, which was characterized by cool surface and bottom temperatures. The substantial increase in abundance of age-0 pollock in recent years suggests that environmental conditions now allow this species to extend its northern range into the southern and central Chukchi Sea, at least on a seasonal basis. The changes in abundance and species composition of pelagic fishes in the 2012–2019 time series are tightly coupled to recent changes in sea ice, temperature, and the increasing transport of Bering Sea waters through Bering Strait into the Chukchi Sea. Given that the environment is expected to experience further warming and increased transport, these northward shifts in species distribution are likely to persist in the future.

Benthic communities of the hydrothermally active submarine Piip Volcano (55°445 N, 167°263 E, 368–495 m, the southwestern Bering Sea) were explored during the 75th and 82nd cruises of the RV Akademik M.A. Lavrentyev using the ROV Comanche 18. The Piip Volcano is the northernmost hydrothermal region in the Pacific. Macrofauna composition and community structure were investigated based on qualitative and relative abundance samples along with still images and video records. In total, 130 species of macro- and megafauna were found, of which ∼25% are new to science. Of the fauna, 9 species (7%) are obligate or potentially obligate to environments with access to reduced chemicals. These species are the bivalve Calyptogena pacifica (Vesicomyidae: Pliocardiinae), the gastropods Parvaplustrum wareni (Parvaplustridae) and Provanna sp. (Provannidae), the amphipod Onesimoides sp. (Tryphosidae), the leptostracan Nebalia piipensis (Nebaliidae), the isopod Eurycope andreyi (Munnopsidae), and the polychaetes Neosabellides uschakovi (Ampharetidae), Ophryotrocha beringiana (Dorvilleidae) and Harmothoe globosa (Polynoidae).

The total species richness of the Northern and Southern summits was almost identical (90 species and 85 spp respectively), but the number of species on sites without bacterial mats on the Northern Summit (81 spp) was almost 1.5 times higher than on the Southern Summit (57 spp). At the same time the species richness was almost twice higher in habitats with bacterial mats and/or clam beds on the Southern Summit (58 spp) compared to the Northern one (32 spp). The main faunal difference was the absence of Calyptogena pacifica on the Northern Summit. The factors that may explain differences of the faunal communities of the Northern and Southern summits are discussed.

The distinctive features of macro- and megafaunal communities of the Piip Volcano were the significant number of taxa, obligate for reducing habitats, of different taxonomic levels including family and subfamily levels and plentiful abundances of sedentary organisms, including the sea anemone Corallimorphus cf. pilatus, the demosponge Vulcanella koltuni, calcareous sponges and benthopelagic Trachimedusa, all of them presumably utilizing the rich food resources of reducing habitats.

To further understand the processes of wave-turbulence interactions under nonhydrostatic conditions and to gain insight into the selection of second-moment closure models in subsequent nonhydrostatic ocean models, a newly developed nonhydrostatic ocean model is coupled with the General Ocean Turbulence Model (GOTM) to form a robust version of the Marine Environment Research and Forecasting Model (MERF). On this basis, internal lee wave simulation with various turbulent mixing schemes is investigated for an idealized two-dimensional supercritical sea slope topography with high-resolution (100 m). First, the LES-type simulation based on a 3D Smagorinsky diffusivity scheme can reproduce well the characteristics of lee waves, serving as a benchmark for comparison. Second, the Mellor and Yamada (MY) scheme and the quasi-equilibrium scheme are able to effectively simulate the effects of internal waves on large-scale structures, while small-scale dynamic processes are partially suppressed by turbulent mixing. However, the K-ε model and the one-equation model further suppress the small-scale dynamic processes and weaken the propagation of internal lee waves due to overly strong turbulence mixing. Finally, the generation of a lee wave changes the instantaneous temperature field, and the use of the second-moment closure models converts more energy into irreversible mixing. Enhancing the model resolution can slightly improve the accuracy of the simulation in exchange for paying considerable computation.

Velocity records from 8 mooring sites (2010–2019) and trajectories of drogued drifters (2012–2020) are used to evaluate patterns of flow on the Chukchi Sea continental shelf, with an emphasis on the latter three years (2016–2019). Together, these data provided insight into the temporal and spatial variability of the currents over this shelf. These data extend previous observations by five years and include three previously unoccupied sites, two of which span the Central Channel. Bathymetry directs a significant portion of the northward flow in Central Channel eastward across the Chukchi shelf where it joins the coastal flow prior to exiting Barrow Canyon and entering the Beaufort Sea. In addition, shelf-wide volume transport estimated from three mooring sites located off Icy Cape is modified from earlier analysis and extended in time. The resulting transport is highly correlated with that flowing through Central Channel, with similar magnitude. Icy Cape transport varies seasonally with variations in atmospheric forcing, as well as inter-annually, with an annual low of 0.24 Sv (September 2011–August 2012) to a annual high of 0.64 Sv (September 2017–August 2018), and a 9-year average of 0.43 Sv, or approximately 40% of the flow through Bering Strait. This nearly decade-long Icy Cape volume transport record also exhibits an increasing, although not significant, trend of ∼0.03 Sv/year.