Cold-water ostracod fossils from the southern and eastern margins of the Japan Sea

The present study was carried out to describe the distribution of ophiuroids on the continental shelf and slope of the East Sea, off the Korean Peninsula. Three cruises were made from 1985 to 1987 in the area between 35 to 38°N and 129 to 130°E. A total of ten species was identified from the samples collected at 136 stations. Among them four species (Amphiodia craterodometa, Amphioplus macraspis, Ophiura leptoctenia and Ophiura sarsi) constituted more than 98% of abundance by number. The continental shelf off Gampo, near 35°40′N, could be considered to be the southern limit of cold-water species. The abundance of dominant ophiuroids changed according to depth. Three faunal zones, namely, the inner shelf, the shelf edge and the slope zones, coincided with the topographic divisions of continental shelf and slope. The major inhabitant of the inner shelf was A. craterodometa and that of the continental slope was O. leptoctenia. The shelf edge area revealed a transitional zone where all four species occurred, contributing to the total number of individuals with almost equal proportions. The temperature of bottom waters was considered to be a factor determining zonal distribution. The sediment characteristics were not closely related to ophiuroid distribution.

Gas-charged sediments on the inner continental shelf off western India

Paleoceanographic insights on meridional ventilation variations in the Japan Sea since the Last Glacial Maximum: A radiolarian assemblage perspective

Factors determining the spatial distribution of gas-charged sediments in the continental shelf off southeastern Korea

Magnetic and seismic-reflection surveys have revealed the presence of faults and basic intrusive rocks, two open-ended shelf basins, a drowned delta, unconformities, a distorted sediment zone, nonuniform prograding, and slumps and slides on the continental shelf off southwestern Sierra Leone. Dominant northeastward and northwestward magnetic trends coincide with the directions of structural features of the Liberian (about 2,700 m.y.) and Pan African (about 550 m.y.) thermotectonic episodes. A basement fracture and deformation pattern with associated volcanism, reflecting weakness lineaments of these older thermotectonic episodes, is believed to have been exploited by Mesozoic deformation.

Data from ichthyoplankton surveys between 1980 and 1990 are used to describe the distribution of bluefish (Pomatomus saltatrix) larvae along the continental shelf off southern Brazil (24º-35ºS). Only 46 larvae in 9 stations were found in 1026 oblique and horizontal tows taken with a 330 pm-mesh Bongo net. Larvae ranged in size from 3 to 10 mm, with the larger larvae distributed close to shore. There were no significant differences in size between larvae found in the northern and southern regions of the shelf. However, there was evidence of a gradual northward displacement of larval abundance towards winter. About 85% of the larvae occurred in the southernmost region of the shelf (below 32ºS) in January and February (summer), and the remaining larvae were caught further north from March to August. This pattern of larval distribution could be attributed to the northwards retreat of warmer (> 20ºC) and more saline (> 34) Brazilian coastal waters from the region. Results from this study suggest that bluefish spawn over a protracted period, following the seasonal displacement of Brazilian coastal waters along the continental shelf off southern Brazil, a pattern that is also consistent with the spawning migration proposed for bluefish in the north-western Atlantic.

A coupled approach based on grain size and geochemical elements is used to trace the provenance of surface sediments and to confirm the distribution patterns of grain size and elements on the continental shelf off western Guangdong Province and northeastern Hainan Island. The mean grain size ranges from 0.05 ϕ to 7.28 ϕ with a mean value of 5.60 ϕ. The average concentrations of major elements descend in the order of SiO2 >Al2O3 >CaO>Fe2O3 >K2O>MgO>Na2O>TiO2 >P2O5 >MnO, while those of trace elements exhibit a descending order of Sr>Rb >Zn>V>Cr>Pb>Ni>Cu>As>Cd. On the basis of the distribution patterns of elements and results of statistical analysis, the study area is classified into three zones. Zone I locates on the continental shelf off western Guangdong Province, and the sediments are mainly from Pearl River, Taiwanese rivers, and small rivers nearby. Zone II locates in the eastern exit of Qiongzhou Strait and the coastal area off Leizhou Peninsula, and the sediments are mainly from the erosion products of Qiongzhou Strait and Hainan Island. Zone III locates off the eastern Hainan Island and the continental shelf deeper than −50 m isobaths, and the sediments are mainly from Hainan Island and coral reef. The influence from open water should also be considered. Results indicate that the grain size is the main controlling factor for major and trace element contents and that anthropogenic impact and biological activity also play an important role in the distribution of these elements.

The continental shelf off New Hampshire (NH) in the Western Gulf of Maine (WGOM) is extremely complex and includes extensive bedrock outcrops, marine-modified glacial deposits, marine-formed shoals, seafloor plains, and associated features that are composed of a range of sediment types from mud to gravel. Furthermore, the physiography and composition of the seafloor frequently changes dramatically over relatively short distances (tens of meters). The complexity of the WGOM seafloor results from the interplay of glaciations, sea-level fluctuations, and marine processes (waves and currents). High-resolution multibeam echosounder (MBES) bathymetry and backscatter surveys, along with ground truth consisting of archived seismic reflection profiles, bottom sediment grain size data, vibracores, and video were used to develop surficial geology maps based on the Coastal and Marine Ecological Classification Standard (CMECS). The surficial geology maps cover ~3,250 km2 and extend from the coast of NH seaward ~50 km to Jeffreys Ledge and depict major geoforms (physiographic features) and seafloor substrate (sediment size) classifications. CMECS provides a sound basis for classifying the texture of the seafloor; however, the geoform classifications need to be broadened for paraglacial environments in future studies. The surficial geology maps presented here are a major refinement of the original maps produced in 2016 (see Ward et al., 2016a). The new maps reflect the results of a major field campaign conducted in 2016-2017 to obtain accurately located sediment samples and seafloor images to complement the original bottom sediment database. The new sites specifically targeted areas where high-resolution MBES bathymetry existed or where surficial features warranted further ground truth for evaluations. This work was designed to enhance the surficial geology mapping efforts and contribute to the development of new approaches for utilizing acoustics to remotely classify seafloor sediments and morphologic features (also supported by the University of New Hampshire Joint Hydrographic Center). The new surficial geology maps presented here depict the exposed bedrock, morphologic features, and sediment distribution on the continental shelf off NH, revealing features of the seafloor in exceptional detail that have not been previously described. An important finding of this study was the extent and importance of marine-modified glacial features on the WGOM continental shelf. Extensive glacial deposits including drumlins, eskers, outwash, and moraines have been eroded and modified by wave and tidal currents as sea level fluctuated over the last 12,000 years. These features are potential sources of sand and gravel for future beach nourishment projects; however, more detailed subbottom

Bryozoan faunal composition and community structure from the continental shelf off Cap de Creus (Northwestern Mediterranean)

Freshwater discharge drives latitudinal changes of phytoplankton composition on the continental shelf off Chilean Patagonia

Aeolian dust has a significant environmental impact on the ocean biogeochemical cycles in different timescales. However, spatial and temporal variations of dust transported on long distances in the upper troposphere by the westerly jet, in particular over orbital-millennial timescales, have not been resolved yet. In this study, we present the evidence for changes in the main axis and path of westerly jet over East Asia at millennial-orbital scale during the last glacial period (~60 ka). We examine the grain size characteristics of sediment core LV53-23 collected from the central Japan (East) Sea, which lies the downwind of westerly jet to discuss the evolution of westerly jet since the last glacial period. Our results show that core sediments are composed mainly of silt characterized of eolian dust, which is consistent with those sediment cores discussed in previous studies from the Japan Sea. The median grain-size of silt fraction has similar pattern with environmentally sensitive grain size extracted by standard deviation/grain-size method. The median grain size in silt fraction increased in stadial periods and decreased in interstadial periods, which might be related to changes in the path of westerly jet. During the stadial, the westerly jet mostly located in the the south of the Tibetan Plateau. It can influence the northern part of the Tibetan Plateau extending to 50°N with high speed, which is prerequisite of dust raised to westerlies in northern China and thus carried the coarser dust from nearby Mongolian Gobi and northeastern China to the Japan Sea. During the interstadial, the provenance of the finer aeolian dust was from Taklimakan Desert when westerly jet migrated northward and concentrated within a narrow band at northern Tibetan Plateau with a longer duration. We found the multi-millennial time scales variations during DOI 8, 12, 14, 16 in cores LV53-23 and MD01-2407 located in the southwestern Japan Sea based on the results of NGRIP and GISP 2 Greenland ice cores. Contrasting with grain size variations of the loess-paleosol records (e.g., Gulang Loess sequence), the lowest grain size during the Last Glacial Maximum confirm that the silt fraction of Japan Sea sediment was mostly transported by westerlies instead of East Asian Winter Monsoon. The mechanism driving the orbital scale variability in grain size of aeolian dust in the Japan Sea is mainly forced by variations of ice volume due to summer insolation in the Northern Hemisphere. A southward migration in the main axis of westerly jet and its influential area was affected by a decrease of summer insolation and increase of ice volume in Northern Hemisphere. During the Last Glacial Maximum, although the cold surges and dust storms were intensive, the southward path of westerly jet may decreased the dust entrainment ability transported by westerlies so that downwind received finer grain size eolian dust. This argument is consistent with findings showing that the location of subarctic front in North Pacific during the Last Glacial Maximum was caused by a southward shift of the path of Kuroshio Current which is controlled by westerly jet. During the glacial period, the decreasing grain size of dust in northern site is explained by weaker westerlies in higher latitudes (40°–50°N) caused by the southward shift of westerly jet main axis, while the increase grain size in the southern site is controlled by the increasing of dust transport path because of westerlies speed in lower latitudes.

As interest of operating sonar system in the littoral area increases, study of reverberation on a continental shelf is needed. In this study, an incoherent reverberation on a continental shelf was simulated using a 2-D propagation model based on ray theory with scattering strength formula based on various theories. Each scattering cross section was modified for application to von Karman roughness spectrum, which was observed during an experiment on the continental shelf off of New Jersey. Various reverberation patterns were shown according to each scattering cross section. By comparing the results from the model and experimental data, an adequate scattering strength was found for each source frequency, and the dominant mechanism of the reverberation on the continental shelf was identified for each time step. In case of the monostatic reverberation measurement, the source and receiver were located on the border between slopes. So both slopes affected the reverberation. In case of the bistatic reverberation, scattered signal from each slope affected the reverberation at different times. The characteristic of bistatic reverberation was different from that of monostatic reverberation. The effect of source-receiver separation on the reverberation of a continental shelf was studied through simulating monostatic and bistatic reverberations.

Patos Lagoon outflow within the Río de la Plata plume using an airborne salinity mapper: Observing an embedded plume

Sediment distribution and provenance on the continental shelf off the Mekong River, SE Vietnam: Insights from heavy mineral analysis

The authors objective was to characterize distributions of chloropigment fluorescence in relation to physical processes in the benthic boundary layer in support of the Department of Energy (DOE) Ocean Margins Program`s (OMP) goal of quantifying carbon transport across the continental shelf. Their approach involved participation in the Ocean Margins Program (OMP) field experiment on the continental shelf off Cape Hatteras by conducting multi-sensor fluorescence measurements of photosynthetic pigments. Specific tasks included (1) pre- and post-deployment calibration of multiple fluorescence sensors in conjunction with Woods Hole personnel; (2) collection and analysis of photosynthetic pigment concentrations and total particulate carbon in water column samples to aid in interpretation of the fluorescence time-series during the field experiment; (3) collaboration in the analysis and interpretation of 1994 and 1996 time-series data in support of efforts to quantify pigment and particulate organic carbon transport on the continental shelf off Cape Hatteras. This third component included analysis of data obtained with a multi-sensor fiber-optic fluorometer in the benthic boundary layer of the inner shelf off Cape Hatteras during summer 1994.