Sea Slope Research Articles

Corals, Canyons, and Conservation: Science Based Fisheries Management Decisions in the Eastern Bering Sea

When making science matter for conservation, marine conservation practitioners and managers must be prepared to make the appropriate decision based on the results of the best available science used to inform it. For nearly a decade, many stakeholders encouraged the North Pacific Fishery Management Council to enact protections for deep-sea corals in several canyons in the Eastern Bering Sea slope. In 2014, at the request of the Council, the National Marine Fisheries Service, Alaska Fisheries Science Center conducted a strip-transect survey along the Eastern Bering Sea slope to validate the results of a model predicting the occurrence of deep-sea coral habitat. More than 250,000 photos were analyzed to estimate coral, sponge, and sea whip abundance, distribution, height and vulnerability to anthropogenic damage. The results of the survey confirmed that coral habitat and occurrence was concentrated around Pribilof Canyon and the adjacent slope. The results also confirmed that the densities of corals in the Eastern Bering Sea were low, even where they occurred. After reviewing the best available scientific information, the Council concluded that there is no scientific evidence to suggest that deep-sea corals in the Eastern Bering Sea slope or canyons are at risk from commercial fisheries under the current management structure, and that special protections for deep-sea corals were not warranted.

Mineralogical, geochemical, and magnetic signatures of surface sediments from the Canadian Beaufort Shelf and Amundsen Gulf (Canadian Arctic)

AbstractMineralogical, geochemical, magnetic, and siliciclastic grain‐size signatures of 34 surface sediment samples from the Mackenzie‐Beaufort Sea Slope and Amundsen Gulf were studied in order to better constrain the redox status, detrital particle provenance, and sediment dynamics in the western Canadian Arctic. Redox‐sensitive elements (Mn, Fe, V, Cr, Zn) indicate that modern sedimentary deposition within the Mackenzie‐Beaufort Sea Slope and Amundsen Gulf took place under oxic bottom‐water conditions, with more turbulent mixing conditions and thus a well‐oxygenated water column prevailing within the Amundsen Gulf. The analytical data obtained, combined with multivariate statistical (notably, principal component and fuzzy c‐means clustering analyses) and spatial analyses, allowed the division of the study area into four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough‐Canadian Beaufort Shelf with high phyllosilicate‐Fe oxide‐magnetite and Al‐K‐Ti‐Fe‐Cr‐V‐Zn‐P contents; (2) Southwestern Banks Island, characterized by high dolomite‐K‐feldspar and Ca‐Mg‐LOI contents; (3) the Central Amundsen Gulf, a transitional zone typified by intermediate phyllosilicate‐magnetite‐K‐feldspar‐dolomite and Al‐K‐Ti‐Fe‐Mn‐V‐Zn‐Sr‐Ca‐Mg‐LOI contents; and (4) mud volcanoes on the Canadian Beaufort Shelf distinguished by poorly sorted coarse‐silt with high quartz‐plagioclase‐authigenic carbonate and Si‐Zr contents, as well as high magnetic susceptibility. Our results also confirm that the present‐day sedimentary dynamics on the Canadian Beaufort Shelf is mainly controlled by sediment supply from the Mackenzie River. Overall, these insights provide a basis for future studies using mineralogical, geochemical, and magnetic signatures of Canadian Arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late Quaternary climate and oceanographic changes.

Beluga whales in the western Beaufort Sea: Current state of knowledge on timing, distribution, habitat use and environmental drivers

The seasonal and geographic patterns in the distribution, residency, and density of two populations (Chukchi and Beaufort) of beluga whales (Delphinapterus leucas) were examined using data from aerial surveys, passive acoustic recordings, and satellite telemetry to better understand this arctic species in the oceanographically complex and changing western Beaufort Sea. An aerial survey data-based model of beluga density highlights the Beaufort Sea slope as important habitat for belugas, with westerly regions becoming more important as summer progresses into fall. The Barrow Canyon region always had the highest relative densities of belugas from July-October. Passive acoustic data showed that beluga whales occupied the Beaufort slope and Beaufort Sea from early April until early November and passed each hydrophone location in three broad pulses during this time. These pulses likely represent the migrations of the two beluga populations: the first pulse in spring being from Beaufort animals, the second spring pulse Chukchi belugas, with the third, fall pulse a combination of both populations. Core-use and home range analyses of satellite-tagged belugas showed similar use of habitats as the aerial survey data, but also showed that it is predominantly the Chukchi population of belugas that uses the western Beaufort, with the exception of September when both populations overlap. Finally, an examination of these beluga datasets in the context of wind-driven changes in the local currents and water masses suggests that belugas are highly capable of adapting to oceanographic changes that may drive the distribution of their prey.

The spatial structure of the Caucasian chamois (Rupicapra rupicapra caucasica) population in the Tlyaratinskii Reserve (Dagestan)

The main environmental parameters that determine the spatial distribution of chamois in the high mountains of Dagestan in summer and winter were studied. The following landscape characteristics were studied: slope gradient, altitude above sea level, slope exposure, and additional parameters related to the defense of chamois (distances from detection sites to the nearest rocks, meadows, rhododendron bushes, etc.). The data on the localization and number of animals were analyzed. No seasonal differences in the distribution of chamois in relation to the slope gradient were revealed. In winter and summer, chamois prefers the slopes of 25°–35°. There were significant differences in the use of slope exposure by chamois depending on the season (χ2 = 71, p < 0.001). The distribution of chamois at different altitudes above sea level had no significant seasonal differences.

Depth-stratified community structure of Beaufort Sea slope zooplankton and its relations to water masses

Depth-stratified community structure of Beaufort Sea slope zooplankton and its relations to water masses

Erratum to: Closely related intertidal and deep-sea Halomonhystera species have distinct fatty acid compositions

The deep-sea free-living nematode Halomonhystera hermesi, dominant in the sulphidic sediments of the Hakon Mosby mud volcano (1280 m, Barent sea slope), is part of the mainly estuarine Halomonhystera disjuncta species complex consisting of five cryptic species (GD1–GD5). Cryptic species have a very similar morphology raising questions on their specific environmental differences. This study analyzed total fatty acid (FA) compositions of H. hermesi and GD1, one of H. hermesi’s closest relatives. Additionally, we experimentally investigated the effect of a temperature reduction, salinity increase and sulphide concentrations on GD1’s FA composition. Because nematodes are expected to have low amounts of storage FA, total FA compositions most likely reflect FA contents of cellular membranes. The deep-sea nematode H. hermesi had significantly lower saturation levels and increased highly unsaturated fatty acid (HUFAs) proportions due to the presence of docosahexanoic acid (DHA—22:6ω3) and higher eicosapentaenoic acid (EPA—20:5ω3) proportions. HUFAs were absent in H. hermesi’s food source indicating the ability and need for this nematode to synthesize HUFAs in a deep-sea environment. Our experimental data revealed that only a decrease in temperature resulted in lower saturated fatty acids proportions, indicating that the FA content of H. hermesi is most likely a response to temperature but not to sulphide concentrations or salinity differences. In experimental nematodes, EPA proportions were low and DHA was absent indicating that other factors than temperature, salinity and sulphides mediate the presence of these HUFAs in H. hermesi.

A hypothesis on variability of surface water &amp;lt;italic&amp;gt;p&amp;lt;/italic&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; under the rapid sea-ice retreat during summer in the Arctic Ocean

The Arctic Ocean has been recognized to play an active role in global carbon cycle due to its potential to disproportionally take up CO2 from the atmosphere especially under a dwindling ice extent. It is estimated that the Arctic Ocean will be responsible for up to 5%–14% of the total global oceanic CO2 uptake even though it comprises only 3% of the world ocean surface area. Over the past decade, the sea ice in the Arctic Ocean has significantly retreated during summer. The rapid sea ice retreat is thought to cause corresponding changes in the distribution of p CO2 in the surface waters of Arctic Ocean. However, the response of carbon dynamics to a changing Arctic Ocean remains poorly quantified. It has been postulated that an ice-free condition in the Arctic Ocean basins would allow for uptake of a substantial amount of carbon dioxide (CO2) from the atmosphere as a result of sea ice melt and increasing primary productivity. However, the other direct observation-based study of high-resolution survey of sea-surface CO2 concentration across the Canada Basin, showing a great high p CO2 relative to earlier observations and predicted that the Arctic Ocean basin will not become a large atmospheric CO2 sink under ice-free conditions. Due to the existing quite different views, thus, there is an implication of observation-based learning in the variations of the surface seawater p CO2 under a scenario of rapid sea ice melting. In the summer of 2008, during the 3rd Chinese National Arctic Research Expedition (CHINARE) cruise, significant variability of p CO2 in surface water has been observed along a trans-Arctic section of 150°–160°W from the Chukchi Sea slope to 88°N in the western Arctic Ocean. We propose a hypothesis of “low-low-high” variation trend in surface water p CO2 levels along a decreasing ice-cover gradient across three different zones in the Arctic Ocean under a rapid sea ice melting scenario in the summer. Specifically, there are (1) “low” p CO2 levels of ~270–280 μ atm in the sea ice-covered zone (north of 84°N) with a high ice concentration >70%; (2) “low” p CO2 of ~250–270 μ atm in a sea ice melting zone (78°–81°N) with a medium ice extent of around 50%; and (3) “high” p CO2 of ~320–365 μ atm in an ice-free zone (72°–77°N) with a low ice concentration of p CO2 variation trend could be attributed to different driving forces. The low p CO2 in the heavily ice-covered northern basin is likely influenced by a combination of several processes, including mixing of various source waters, CO2 fixation by ice algae, ice-water gas exchange, and temperature change, although their relative roles remain to be quantified. The low p CO2 observed in the partially ice-covered northern Canada Basin could be primarily derived from biological CO2 fixation and the dissolution of CaCO3 precipitates, both of which consume CO2. Primary productivity enhanced by the early melting of sea ice plays an important role in the decreased sea-surface p CO2. In addition, sea ice melting also promotes the dissolution of authigenic CaCO3 in the form of ikaite within the sea ice. Finally, results of tracer data and model simulations suggest that the rapid CO2 invasion from the atmosphere and low biological export of CO2 owing to a shallow mixed-layer depth, strong subsurface water stratification, and limited nutrient supply to the surface water are both responsible for the observed high p CO2 values in the ice-free southern Canada Basin.

Sedimentary responses to sea-level rise and Kuroshio Current intrusion since the Last Glacial Maximum: Grain size and clay mineral evidence from the northern South China Sea slope

We analyzed the terrigenous fraction of a sediment core from the northern slope of the South China Sea, to better understand the depositional history of the region since the Last Glacial Maximum (LGM). Temporal variations in the grain size and clay mineral composition revealed a complex set of overlapping controls. Approximately 90% of terrigenous sediment throughout the core ranged in size from 5.5 to 8.5 Φ, with the 5.25–6.25 Φ size class being particularly sensitive to environmental changes. The proportion of this fraction decreased during deglacial, indicating a reduction in the supply of coarser grains due to coastline retreat. As the sea level rose toward its present position, the relative proportion of clay derived from Taiwan increased; however, the mass accumulation rate of Taiwan-derived clay decreased, suggesting a reduction in the westward bottom current intensity. In contrast, the relative contribution of clay from the Pearl River decreased from ~40% during the LGM, to ~5% when the sea level reached ~70m below its present position. The Pearl River contribution has remained consistently low throughout the Holocene, indicating that shore-parallel circulation patterns on the shelf resembled their present configuration by 13ka. Compared to Taiwan and the Pearl River, the proportion of clay derived from the area east of Pearl River (EPR) was relatively minor, and less variable. A local peak in the relative contribution from this area occurred during a Melt Water Pulse Event (MWP-1A), suggesting that a reservoir of smectite-rich clays residing in coastal bays was remobilized by this marine transgression. Spectral analysis of the relative contributions of the three major clay sources revealed a significant periodicity of ~380years, which may reflect changes in solar insolation modulating the flux of clay minerals from Taiwan and the Pearl River to the deposition site on a centennial scale.

Discovery of a spawning ground reveals diverse migration strategies in Atlantic bluefin tuna (Thunnus thynnus)

Atlantic bluefin tuna are a symbol of both the conflict between preservationist and utilitarian views of top ocean predators, and the struggle to reach international consensus on the management of migratory species. Currently, Atlantic bluefin tuna are managed as an early-maturing eastern stock, which spawns in the Mediterranean Sea, and a late-maturing western stock, which spawns in the Gulf of Mexico. However, electronic tagging studies show that many bluefin tuna, assumed to be of a mature size, do not visit either spawning ground during the spawning season. Whether these fish are spawning in an alternate location, skip-spawning, or not spawning until an older age affects how vulnerable this species is to anthropogenic stressors including exploitation. We use larval collections to demonstrate a bluefin tuna spawning ground in the Slope Sea, between the Gulf Stream and northeast United States continental shelf. We contend that western Atlantic bluefin tuna have a differential spawning migration, with larger individuals spawning in the Gulf of Mexico, and smaller individuals spawning in the Slope Sea. The current life history model, which assumes only Gulf of Mexico spawning, overestimates age at maturity for the western stock. Furthermore, individual tuna occupy both the Slope Sea and Mediterranean Sea in separate years, contrary to the prevailing view that individuals exhibit complete spawning-site fidelity. Overall, this complexity of spawning migrations questions whether there is complete independence in the dynamics of eastern and western Atlantic bluefin tuna and leads to lower estimates of the vulnerability of this species to exploitation and other anthropogenic stressors.

The Icelandic Low as a Predictor of the Gulf Stream North Wall Position

AbstractThe Gulf Stream’s north wall east of Cape Hatteras marks the abrupt change in velocity and water properties between the slope sea to the north and the Gulf Stream itself. An index of the north wall position constructed by Taylor and Stephens, called Gulf Stream north wall (GSNW), is analyzed in terms of interannual changes in the Icelandic low (IL) pressure anomaly and longitudinal displacement. Sea surface temperature (SST) composites suggest that when IL pressure is anomalously low, there are lower temperatures in the Labrador Sea and south of the Grand Banks. Two years later, warm SST anomalies are seen over the Northern Recirculation Gyre and a northward shift in the GSNW occurs. Similar changes in SSTs occur during winters in which the IL is anomalously west, resulting in a northward displacement of the GSNW 3 years later. Although time lags of 2 and 3 years between the IL and the GSNW are used in the calculations, it is shown that lags with respect to each atmospheric variable are statistically significant at the 5% level over a range of years. Utilizing the appropriate time lags between the GSNW index and the IL pressure and longitude, as well as the Southern Oscillation index, a regression prediction scheme is developed for forecasting the GSNW with a lead time of 1 year. This scheme, which uses only prior information, was used to forecast the GSNW from 1994 to 2015. The correlation between the observed and forecasted values for 1994–2014 was 0.60, significant at the 1% level. The predicted value for 2015 indicates a small northward shift of the GSNW from its 2014 position.

On the majestic seasonal upwelling system of the Arafura Sea

AbstractA three‐dimensional hydrodynamic model is applied to explore the development of phytoplankton blooms in the Arafura Sea during the southeast monsoon (June–November). Before this season, blooms are restricted to nearshore waters covering a total area of ∼25,000 km2. Satellite data indicate that the bloom area grows substantially to &gt;90,000 km2 during the southeast monsoon covering most of the northwestern Arafura Sea. Findings confirm that the southeast monsoon creates undercurrents via the classical lee effect driving nutrient‐rich Banda Sea slope water into this region. This nutrient‐rich slope water is driven over vast distances (∼300 km) into the northwestern Arafura Sea where it upwells and/or is entrained into the surface mixed layer. The associated overturning circulation is slow but continuous and it takes 1–2 months before nutrient‐rich water appears in surface waters of the region. The predicted pathways of nutrient‐rich inflows across the shelf break both north and south of the Ara Islands agree with observational evidence.

New deep ocean Iravadiidae of the genus Ceratia (Caenogastropoda: Truncatelloidea) from an underwater canyon and adjacent regions of the southwestern Atlantic (northeastern Brazil).

Previous studies on the mollusks from Brazilian underwater canyons have addressed the record and description of new species of aplacophorans, bivalves, scaphopods and/or gastropods (Leal & Simone 2000; Absalão 2010; Corrêa et al. 2014). Leal & Simone (2000) described a new bathyal gastropod of the family Pseudococculinidae collected from the continental slope and Doce River Canyon (960 m) off the state of Espírito Santo (southeastern Brazil). Absalão (2010) reported a number of species of gastropods, bivalves and scaphopods from Campos Basin off the state of Rio de Janeiro (southeastern Brazil). It is likely that some of these species reported by Absalão (2010) were collected from underwater canyons in the northern portion of the Campos Basin. Corrêa et al. (2014) recorded two species of aplacophorans of the genus Falcidens Salvini-Plawen, 1968 obtained from the continental slope and underwater canyons of Campos Basin. Certainly more species of mollusks were studied from Brazilian underwater canyons, but not duly mentioned in publications (i.e., the region of canyons may have been referred to as the continental slope or deep sea).

Submarine gullies on the southern Weddell Sea slope, Antarctica

Submarine gullies are small-scale, confined channels on the order of tens of metres depth that form one of the most common morphological features of high-latitude continental slopes. Gully morphology varies in width, incision depth, length, sinuosity, branching order, shelf-incision, cross-sectional shape and gully spacing, with six distinct gully signatures recognized on high-latitude continental slopes (Gales et al. 2013 a , b ). Here we analyse the morphology of slope gullies off Halley and Filchner troughs in the southern Weddell Sea (Fig. 1a–f). Fig. 1. Multibeam bathymetry and along-slope profiles of gullies on the southern Weddell Sea continental margin. ( a ) Multibeam data showing V-shaped gullies at the mouth of Halley Trough. Acquisition system Kongsberg EM122. Frequency 12 kHz. Grid-cell size 30 m. ( b ) Sub-bottom profile of U-shaped gullies. VE×20. Location in (e). Acquisition system Kongsberg TOPAS PS 018. Frequency 18 kHz. Secondary beam frequency 1300–5000 Hz. ( c ) Along-slope profile through V-shaped gullies. Location in (a). VE×55. ( d ) Location of the study area (red boxes; map from IBCSO v. 3.0). FT, Filchner Trough; HT, Halley Trough. ( e ) Multibeam data showing U-shaped gullies at the mouth of Filchner Trough. Acquisition system Kongsberg EM120. Frequency 12 kHz. Grid-cell size 30 m. ( f ) Sub-bottom profile of U-shaped gullies. Location in (e). Acquisition …

Terrigenous supplies variability over the past 22,000 yr in the southern South China Sea slope: Relation to sea level and monsoon rainfall changes

Changing weathering intensity, sediment transport, and provenance variations over the past 22.0ka BP have been investigated by high-resolution clay mineralogy, grain-size and stable oxygen isotopes of planktonic foraminifera records along core CG2 recovered from the continental slope of the Sunda Shelf (southern South China Sea). Our results indicated that the reworking of older sediments outcropping on the Sunda Shelf exerted a great influence on the sediment supply during the last glacial and most of the last deglacial, modulated by sea level and monsoon rainfall changes. During the last 9.0ka BP, relative increased kaolinite and heavier δ18Oseawater values might reflect the higher influence of the tropical Indonesian Islands sources due to the reopen of southern straits, implying the formation of modern oceanic circulation and depositional patterns. High sediment fluxes in core CG2 during Heinrich stadial 1 might be a synthetic result of the intensified monsoon rainfall originated from the southward shift of the Intertropical Convergence Zone and the proximal location of the study core before the flooding of the Sunda Shelf. Fluctuations in smectite/(illite+chlorite) ratios correlated well with monsoon intensity, and periods of strong monsoon rainfall (lighter δ18Oseawater values) were associated with an intensification of erosion of pre-existing, more weathered materials on the Sunda Shelf. Finally, we concluded that sediment composition and mineralogy in the southern South China Sea slope were controlled by varying degrees of reworking on the Sunda Shelf, as well as climatically modulated sediment supply from the Mekong River and southern tropical islands over the last 22.0ka BP.

The biology of Benthosema glaciale and Ceratoscopelus maderensis (Myctophidae) in the Slope Sea off Nova Scotia, Canada

The myctophid species Benthosema glaciale and Ceratoscopelus maderensis were predominant in the catches of 10 mesopelagic fish surveys conducted in the Slope Sea, south and southeast of Nova Scotia. The area surveyed included both cold northeastern (Labrador Slope Water – LSW) and warm southwestern (Warm Slope Water – WSW) components of this water mass. The sub-polar-temperate species, B. glaciale, was found to be only about 15% as abundant in WSW as in LSW. Nonetheless, it occurred throughout WSW and reproduced there, maturing at a younger age than in LSW. The temperate species, C. maderensis, the predominant myctophid caught in WSW, had a life cycle of 1yr in most cases, but a small proportion lived for a second year and these occurred primarily in LSW. These larger animals matured sexually and contributed to spawning in the LSW/WSW boundary area, but their reproductive contribution elsewhere in LSW and in continental slope waters remains to be established. Both species had diverse diets, the taxonomic compositions of which overlapped substantially.

Undercurrent‐driven upwelling in the northwestern Arafura Sea

AbstractA three‐dimensional process‐oriented model is applied to explore the circulation in the Arafura Sea during the southeasterly monsoon. During this period, widespread phytoplankton blooms develop in a large area (300 km × 300 km) in the northwestern Arafura Sea. The model findings indicate that undercurrents are the principal source of nutrient‐rich Banda Sea slope water for the region. It is demonstrated that these undercurrents operate to flush the northwestern Arafura Sea with Banda Sea slope water on a time scale of 1–3 months, which is consistent with observational evidence. The simulated undercurrents are the signature of the classical lee effect, frequently observed in lakes, that comes into play in the Arafura Sea given its bay‐like geometry, shallow‐water depth (40–50 m), and close vicinity to the equator. It is also shown that density stratification and rotational effects have important influences on the pathway and intensity of the overturning circulation in the northwestern Arafura Sea, which needs to be further explored in the future.

Geochemical records of Taiwan-sourced sediments in the South China Sea linked to Holocene climate changes

We present a multi-proxy geochemical analysis of core KNG5 retrieved from the northern South China Sea slope spanning the last 13.0ka BP to assess the response of weathering and erosion processes in the Southwestern Taiwan River basin to climate change. A provenance analysis indicates that the core sediments were primarily derived from the Southwestern Taiwan River, and can be used to reconstruct the erosion and/or weathering history of this river basin. The chemical index of alteration, the plagioclase index of alteration, Rb/Sr, Al/Ti, principle component 1, and K/Al combined with terrigenous mass accumulation rates and the proportion of clay exhibit sharp excursions from 12.0 to 5.5ka, peaking at 10.0ka, which suggests strong chemical weathering and physical erosion during the Early-Mid Holocene, the period of the maximum summer monsoon. Abrupt falling weathering trends during 5.2 and 3.5ka BP correlate with a weaker monsoon. After 3.5ka BP, a stable lower weathering trend to the present day was evident, indicating the deposition of less weathered sediments in the slope when the monsoon rainfall was weakening. A good correlation between our proxy records of chemical weathering and variations of the monsoon intensity in South China emphasizes that variation in monsoon intensity is most likely the primary drive of the intensity of weathering and erosion in Southwestern Taiwan River sediments over the last 13.0ka BP. Finally, we concluded that geochemical parameters can be used as reliable proxies for climate variation on a millennial-centennial time scale in such areas as Taiwan, where weathering-limited regimes exist.

Distribution of early life Pacific halibut and comparison with Greenland halibut in the eastern Bering Sea

ABSTRACT Information about spatial distribution patterns during early life stages of fish is key to understanding dispersal trajectories and connectivity from spawning to nursery areas, as well as adult population dynamics. More than 30 years of historical field data were analyzed in order to describe the horizontal and vertical distributions of Pacific halibut early life stages (larvae to juveniles) in the eastern Bering Sea and to compare the distributions between Pacific halibut and Greenland halibut. Our results indicate that spawning for both species likely occurred in Bering and Pribilof canyons, along the slope between the two canyons, and on the eastern side of the Aleutian Islands during winter, but Pacific halibut spawning was protracted until early spring. Larvae of both species rose to shallower depths in the water column as they developed, but Pacific halibut larvae had an abrupt movement toward shallower depths. Geographically, larvae for both species either advected northwestward along the Bering Sea Slope or crossed onto the shelves from the slope regions, but the timing in Pacific halibut larval progression onto the shelf and along the slope was earlier than for Greenland halibut larvae. Pacific halibut juveniles (≤ 90 mm total length (TL)) were mostly found in the inner shelf between Bristol Bay and Nunivak Island, along the Alaskan Peninsula, and in the vicinity of the Pribilof Islands. The range of Greenland halibut juvenile (≤ 90 mm TL) distribution was expanded to south of the Pribilof Islands in the middle shelf and to the inner shelf. Although the two species share some attributes (i.e., spawning location) during early life stages, there were species-specific differences associated with spatial distribution (vertically and horizontally), timing differences in larval progression onto the shelves, pelagic larval duration, and juvenile nursery areas.

Effect of non-Gaussian properties of the sea surface on the low-incidence radar backscatter and its inversion in terms of wave spectra by an ocean wave spectrometer

The principle of ocean wave spectrometers was first presented several decades ago to detect the directional wave spectrum with real-aperture radar (Jackson, 1981). To invert wave spectra using an ocean wave spectrometer, for simplicity, the hydrodynamic forcing and wave-wave interaction effect are neglected and a Gaussian slope probability density function (pdf) is used to calculate the normalized backscattering cross-section (σ0) of the ocean surface. However, the real sea surface is non-Gaussian. It is not known whether the non-Gaussian property of the sea surface will affect the performance of the inversion of the wave spectrum if following existing inversion steps and methods. In this paper, the pdf of the sea surface slope is expressed as a Gram-Charlier fourth-order expansion, which is quasi-Gaussian. The modulation transfer function (MTF) is derived for a non-Gaussian slope pdf. The effects of non-Gaussian properties of the sea surface slope on the inversion process and result are then studied in a simulation of the SWIM (Surface Waves Investigation and Monitoring) instrument configuration to be used on the CFOSAT (China-France Oceanography Satellite) mission. The simulation results show that the mean trend of σ0 depends on the sea slope pdf, and the peakedness and skewness coefficients of the slope pdf affect the shape of the mean trend of σ0 versus incidence and azimuth; owing to high resolution of σ0 in the range direction, MTF obtained using the mean trend of σ0 is almost as accurate as that set in the direct simulation; in the inversion, if ignoring the non-Gaussian assumption, the inversion performances for the wave spectrum decrease, as seen for an increase in the energy error of the inverted wave slope spectrum. However, the peak wavelength and wave direction are the same for inversions that consider and ignore the non-Gaussian property.

Sedimentary responses to the Indian Summer Monsoon variations recorded in the southeastern Andaman Sea slope since 26 ka

Paleoenvironment and paleoclimate change in the Andaman Sea during the last 26ka were reconstructed from high-resolution records of grain-size, major elements and Sr–Nd isotopes in core ADM-9. The values of εNd(0) and 87Sr/86Sr were in good agreement with those of Irrawaddy River sediments, indicating a common source of origin. Two sensitive grain-size intervals (3.4–7.5 and 16.8–21.2μm) were identified; the former was controlled primarily by sea-level change, whereas the latter was related to Irrawaddy River discharge and South-west Current transport driven by the Indian Summer Monsoon (ISM). Proxies of chemical weathering (K/Al) and terrigenous input (Ti/Ca) coupled with sensitive grain-size interval (16.8–21.2μm population) revealed that the ISM was weak during ∼15–26ka BP and then strengthened gradually to a maximum during ∼7–9ka BP; subsequently, the ISM exhibited a generally declining trend to ∼2ka BP. The variation in the ISM recorded in this work is consistent with ISM variations observed in an open area in the northern Indian Ocean and adjacent continents, implying the evolution of the Asia Summer Monsoon since 26ka.