Coastal Mixing Research Articles

Sediment input, alongshore transport, and coastal mixing in the northeastern Gulf of Mexico based on detrital-zircon geochronology

We present detrital-zircon U–Pb geochronology from the Mississippi, Mobile, and Apalachicola rivers, as well as five beach and barrier island deposits to determine sediment sources, alongshore transport, and sediment mixing in the northeastern Gulf of Mexico. The Mississippi River has a distinct age spectrum defined by prominent Cenozoic and Mesozoic populations coupled with minor Appalachian (490-270 Ma), Grenville (1200-900 Ma), Granite-Rhyolite (1500-1300 Ma), and Yavapai-Mazatzal (1800-1600 Ma) populations. The Mobile and Apalachicola rivers exhibit age spectra containing few to no Cenozoic grains, are proportionately dominated by Appalachian and Grenville populations, and have minor populations consisting of Iaptian Rifting/Gondwanan (850-550 Ma), Granite-Rhyolite, and Yavapai-Mazatzal ages. Comparison of U–Pb age spectra and inverse mixing models shows that beach and barrier island deposits are primarily derived of material from the Apalachicola River, with Mobile River contribution being dependent on geographic position west of Mobile Bay. Minor Mississippi River contribution in coastal deposits results from shelf bypass to deep marine sinks and when present is likely associated with recycling of Coastal Plain strata. Metamorphic zircon grain abundance (14–36%) in coastal deposits and chemical-age relationships to southern Appalachian eastern Blue Ridge and Inner Piedmont provinces corroborate Apalachicola and or Mobile river system provenance. Results from this study suggest that anthropogenic influences and hurricanes have little to no effect on the detrital-zircon age spectra at a regional scale, and that the northeastern Gulf of Mexico can be used as an analog for older Cenozoic and Mesozoic source to sink investigations in the eastern Gulf Coastal Plain.

Nekton community dynamics within active and inactive deltas in a major river estuary: potential implications for altered hydrology regimes

High fisheries production within estuaries is associated with coastal upwelling, tidal mixing, and land-based runoff facing increasing impacts from climate and human activities. Active river deltas receive large riverine inflows compared to inactive river deltas, providing contrasting estuaries to compare impacts of river inflow on estuarine nekton. We quantified nekton assemblages and stable isotopes (δ13C, δ15N) of commercially important blue crab Callinectes sapidus Rathbun, 1896 within an active and inactive delta in coastal Louisiana to explore the impacts of differing riverine inflow. Crustaceans dominated estuarine assemblages, differing only by season and not delta type, with summer and fall supporting highest densities. Fish density and assemblages differed by the interaction of season and delta due to differences during the 2019 record high spring river inflow. During this period, the active delta supported reduced fish densities and richness compared to the inactive delta. Nekton densities across deltas and seasons reflect a combination of species life history characteristics and habitat conditions. The high spring river discharge in 2019 impacted habitat availability (reduced presence of submerged aquatic vegetation), water conditions (decreased temperature and salinity), and potentially displaced nekton to unsampled habitat areas (i.e. interior marsh surface) within the active delta. While differences in nekton density and assemblages were only evident during the high spring river discharge, δ15N values of blue crabs were approximately 1.5 times higher in the active delta, potentially indicating more terrestrial influence. Understanding how altered inflow impacts environmental variables supporting estuarine nekton production remains critical for supporting management within these hydrologically managed regions.

Coastal Langmuir circulations induce phase-locked modulation of bathymetric stress

The ocean boundary layer (OBL) is forced by atmosphere-ocean and sea ice-ocean momentum fluxes, wave dynamics, and buoyancy; in coastal zones, OBL dynamics are further complicated by additional shear from the seafloor. Among numerous other phenomena, coastal mixing affects dispersion of anthropogenic quantities, erosion and turbidity, and benthic sequestration. In the OBL, interaction of wind-induced shear and surface waves manifests so-called Langmuir turbulence and distinctive Langmuir cells under favorable conditions, which have implications for the aforementioned coastal processes. Large-eddy simulation was used to dynamically sample the flow during relative extremes in bathymetric stress and vertical velocity. Probability density functions of vertical velocity are bimodal, the signature of persistent upwelling and downwelling within Langmuir cells, and this attribute manifests itself in the bathymetric stress, revealing a phase-locked modulation. We report modulation between negative vertical velocity (downwelling) and relatively elevated bathymetric stresses, thereby revealing that coastal Langmuir turbulence has direct implications for erosion and turbidity.

Coastal mixing in multiple-mouth deltas: A case study in the Po delta, Italy

Satellite imagery provides evidence of complex mixing dynamics in the coastal zone in front of multiple mouth deltas. One peculiar feature, identified in front of the Po Delta (Italy), consists in warmer water bulges present in some periods in the coastal zone between the river mouths. Such features are evident during both high and low river discharge.Through an integrated approach based on the analysis of satellite imagery, in situ field data and a high-resolution oceanographic model, representing the whole river-delta-sea system, we investigated the relative contribution of the different forcing in controlling coastal mixing of riverine waters. The results evidence that the occurrence of these warmer saltier water bulges is due to upwelling induced by the combined action of tides and wind regimes aligned along coastline. Winds from the land and along the coast drive the upwelling through the well-known mechanism described by Ekman. The presence of river discharge enhance the water column stratification, creating the conditions in which tidal action follows the tidal straining theory. Both processes are identified in modelling results. The occurrence of these localized coastal waters with peculiar thermohaline characteristics, detectable on satellite imagery of the area, can be relevant in the definition of the freshwater areas of influence and the mechanisms of riverine water mixing in the near coastal zone. This can shed some light, eventually, on characterizing the sediment dynamics, as well as the thermohaline properties of waters in the area, and also to identify eventual impacts on the local ecosystems and fishery.

Biological and Physical Effects of Brine Discharge from the Carlsbad Desalination Plant and Implications for Future Desalination Plant Constructions

Seawater reverse osmosis (SWRO) desalination is increasingly used as a technology for addressing shortages of freshwater supply and desalination plants are in operation or being planned world-wide and specifically in California, USA. However, the effects of continuous discharge of high-salinity brine into coastal environments are ill-constrained and in California are an issue of public debate. We collected in situ measurements of water chemistry and biological indicators in coastal waters (up to ~2 km from shore) before and after the newly constructed Carlsbad Desalination Plant (Carlsbad, CA, USA) began operations. A bottom water salinity anomaly indicates that the spatial footprint of the brine discharge plume extended about 600 m offshore with salinity up to 2.7 units above ambient (33.2). This exceeds the maximum salinity permitted for this location based on the California Ocean Plan (2015 Amendment to Water Quality Control Plan). However, no significant changes in the assessed biological indicators (benthic macrofauna, BOPA-index, brittle-star survival and growth) were observed at the discharge site. A model of mean ocean wave potential was used as an indicator of coastal mixing at Carlsbad Beach and at other locations in southern and central CA where desalination facilities are proposed. Our results indicated that to minimize environmental impacts discharge should target waters where a long history of anthropogenic activity has already compromised the natural setting. To ensure adequate mixing of the discharge brine desalination plants should be constructed at high-energy sites with sandy substrates, and discharge through diffusor systems.

A process study of the interaction of tidal currents, tidal mixing and density gradients in a region of freshwater influence

Abstract A three dimensional unstructured grid model of the west coast of Britain is used to study the process of the interaction of tidal currents, tidal mixing and density gradient in the Liverpool Bay region. Calculations with M 2 tidal forcing and omitting freshwater discharge show that tidal currents in the region are strong (of order 1 ms − 1 ), with tidal current ellipses essentially rectilinear in the surface and bottom. In the absence of tidal forcing, the freshwater is confined to a thin surface layer. With the inclusion of tidal mixing the surface layer thickens, and in the shallow water area mixed layer occupies the whole water depth. This has a significant effect of reducing its lateral spread. A detailed study of time series of velocity, salinity and turbulence reveals that at flood tide, more saline water is advected into the coastal region and rapid vertical mixing occurs, whereas at ebb tide, fresher water is advected over more saline water. The induced strong pycnocline uncouples surface and bottom layers leading to more circular tidal ellipses which rotate in opposite directions in the vertical, as found in observations. The three dimensional nature of the model reveals that this process involves both horizontal and vertical density gradients, and shows significant horizontal variability in the Liverpool Bay region.

Geologic constraints and speleogenesis of Cova des Pas de Vallgornera, a complex coastal cave from Mallorca Island (Western Mediterranean)

The flat areas of eastern and southern Mallorca host a remarkable coastal karst, where Cova des Pas de Vallgornera stands out due to its length (more than 74 km) and its special morphological suite. The pattern of the cave is quite heterogeneous showing sharp differences produced by the architecture of the Upper Miocene reef: spongework mazes and collapse chambers dominate in the reef front facies, whereas joint-guided conduits are the rule in the back reef carbonates. Regarding the speleogenesis of the system, a complex situation is envisaged involving three main agents: coastal mixing dissolution, drainage of meteoric diffuse recharge, and hypogene basal recharge related to local geothermal phenomena. The cave system is disposed in two main tiers of passages, of which geomorphologic interpretations are derived from their elevation data. The evolutionary trends as well as the chronology of the different cave sections are difficult to establish owing to the frequent shifting of the coastal base level during the Plio-Quaternary. In this respect, the genesis and evolution of the cave were fully controlled by sea-level fluctuations in the Western Mediterranean basin, with the main phases of cave formation, based on vertebrate paleontological data, going back to mid-Pliocene times.

Laboratory experiments on mass transport by large amplitude mode-2 internal solitary waves

The existence of internal solitary waves (ISWs) in the coastal ocean is well established. Numerous observations of large amplitude (both mode-1 and mode-2) solitary waves have facilitated the identification of their unique properties; in particular they contain regions of internal recirculation (trapped cores) that enable mass transport over large distances. However, the basic physics of mode-2 ISWs is as yet not well understood. The present experiments and the associated numerical simulations are focused on providing the first quantitative measure of the extent of mass transported by mode-2 ISWs and insight into the potential effects of mass transport on coastal mixing and the distribution of biochemical material. The ISWs were generated by the release of fluid from an initially mixed volume. It was found that the amplitude and amount of mass transported by the leading and second, following ISW, was proportional to the level of forcing and was attenuated at an approximately uniform rate as the ISW propagated downstream. At the highest level of ISW forcing, over 40% of the mixed fluid was transported within the leading ISW. Excellent agreement was found with the numerical simulations of Salloum, Knio, and Brandt [“Numerical simulation of mass transport in internal solitary waves,” Phys. Fluids 24, 016602 (2012)] that were designed to replicate the present experimental configuration. In addition, evidence of a new ISW regime was identified, termed very-large amplitude ISW, which exhibited strong internal recirculation, a smooth front face, and local mixing at the aft end. The present data extend to larger amplitudes than prior studies and exhibit a second order dependence of wave speed and wavelength on amplitude.

Estimating Coastal Lagoon Tidal Flooding and Repletion with Multidate ASTER Thermal Imagery

Coastal lagoons mix inflowing freshwater and tidal marine waters in complex spatial patterns. This project sought to detect and measure temperature and spatial variability of flood tides for a constricted coastal lagoon using multitemporal remote sensing. Advanced Spaceborne Thermal Emission Radiometer (ASTER) thermal infrared data provided estimates of surface temperature for delineation of repletion zones in portions of Chincoteague Bay, Virginia. ASTER high spatial resolution sea-surface temperature imagery in conjunction with in situ observations and tidal predictions helped determine the optimal seasonal data for analyses. The selected time series ASTER satellite data sets were analyzed at different tidal phases and seasons in 2004–2006. Skin surface temperatures of ocean and estuarine waters were differentiated by flood tidal penetration and ebb flows. Spatially variable tidal flood penetration was evaluated using discrete seed-pixel area analysis and time series Principal Components Analysis. Results from these techniques provide spatial extent and variability dynamics of tidal repletion, flushing, and mixing, important factors in eutrophication assessment, water quality and resource monitoring, and application of hydrodynamic modeling for coastal estuary science and management.

Characteristic ichthyoplankton taxa in the separation zone of the East Australian Current: Larval assemblages as tracers of coastal mixing

Ichthyoplankton assemblages were compared between regions dominated by the oligotrophic East Australian Current (EAC) and the inner-shelf waters off southeastern Australia, to determine if the early life history of fish was related to the separation of the EAC from the coast, producing different water masses as well as characteristic taxa. Samples were collected at the surface and in sub-surface waters, at 50 and 100 m isobath stations, during two summer research voyages in November 1998 and January 1999. On both voyages the study region was characterized by coastal and EAC waters in the north (∼31°S), and in the south by topographically induced upwelling (∼31°S), associated with narrowing of the continental shelf and separation of the EAC from the coast. Among the 111 families of larval fish, we observed distinctive assemblages of ichthyoplankton associated with the two different water masses. A greater abundance of the Carangidae, Labridae, Lutjanidae, Microcanthidae, Myctophidae and Scombridae was associated with the nutrient poor EAC water mass, while the Callionymidae, Clupeidae, Platycephalidae and Sillaginidae were mostly found in the cooler and/or fresher inner-shelf water mass. We assessed these patterns with opportunistic samples from an unusual, wind-driven upwelling event in the north (∼31°S) earlier in the November voyage. The relative abundance of these 10 characteristic families distinguished this wind-driven upwelling event from the subsequent relaxation and predominance of the EAC assemblage at this location just 6 d later. Distinctive and abundant families such as larval clupeids, relative to larval carangids, could be a useful marker of inner-shelf, EAC and mixed water masses in the absence of robust hydrographic data. This and related studies indicate contrast in early life histories of Sardinops sagax and Trachurus spp., which appear to spawn respectively in the inner-shelf and outer-shelf waters. The post-flexion stages of S. sagax predominate in the outer-shelf and Tasman Front, while post-flexion Trachurus spp. predominate in inner-shelf water masses.

Comparison of measurement methods for radium‐226 on manganese‐fiber

Acrylic fibers impregnated with MnO2 (Mn‐fiber) have become a valuable tool for concentrating dissolved radium for oceanographic applications. With four naturally‐occurring radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) of vastly different half‐lives (3.6 days to 1600 years), radium can be a powerful tool for tracing terrestrial water discharges into the ocean and studying coastal mixing processes. Several techniques have been outlined in the literature describing the measurement of 226Ra on Mn‐fiber via its gaseous daughter, 222Rn. We present a proven, air‐tight cartridge design that allows one to use these measurement techniques. We then review the procedures for three radon‐based nondestructive measurement techniques for 226Ra on Mn‐fiber (via RAD7, RaDeCC, and Rn emanation line systems) and perform an intercomparison among them, using the standard technique of γ‐spectrometry as a reference. We find that all methods statistically agree in terms of measured activity. The Rn emanation line and the RaDeCC systems (both based on Lucas cell counting) provide the lowest measurement uncertainties and minimum detectable activities (MDAs) for a given counting time. The RAD7 technique, on the other hand, offers the advantage of being an automated system, thus requiring minimal user interaction. The standard γ‐spectrometry technique, while more time‐consuming and sample destructive, has the advantage of providing a simultaneous measurement for 228Ra.

Increases in the longwave photobleaching of chromophoric dissolved organic matter in coastal waters

Salinity effects on the photobleaching of chromophoric dissolved organic matter (CDOM) due to coastal mixing were investigated through a comparative study of surrogate and surface-water CDOM. Suwannee River humic acid (SRHA) and ultrafiltered river dissolved organic matter (UDOM) added to mixtures of river and seawater permeates (,1 kDa) that varied in salinity from 0 to 33 to mimic coastal mixing. Surface-water CDOM was collected from the Chesapeake Bay in January, June, and September 2002. Shortwave CDOM absorption loss (e.g., 280 nm) did not change with salinity; however, longwave CDOM absorption loss (e.g., 440 nm) often decreased by 10% to 40% with salinity. Apparent quantum yields for average absorption loss from 280 to 550 nm (Qavg) increased with salinity for both surrogate and surface-water CDOM, providing evidence for an effect of salinity independent of light absorption among different samples. Further, hydrogen peroxide photoproduction from UDOM increased from 15 to 368 nmol L 21 h 21 with salinity, even though pH values were circumneutral. A kinetic model demonstrated that, at circumneutral pH and iron concentrations expected for the Chesapeake Bay, photo-Fenton chemistry could not explain the increase in hydrogen peroxide production quantum yields (Qhp) with salinity. Using Qavg for the SRHA and UDOM surrogates, a model of the change in surface-water CDOM photoreactivity in the Chesapeake Bay as a function of salinity suggested additional CDOM inputs for the lower Chesapeake Bay. Because estuarine mixing increases photobleaching of longwave CDOM absorption, the modeling of absorption coefficients above 400 nm may underestimate dissolved organic matter in coastal waters.

Determination of transport rates in the Yellow River–Bohai Sea mixing zone via natural geochemical tracers

In light of the current problems facing the Yellow River and surrounding areas (e.g., periods of zero river discharge, increasing nitrate concentrations of the Bohai Sea), we examined the coastal mixing dynamics around the mouth of the Yellow River. Naturally occurring radium isotopes ( 223Ra, 224Ra, 226Ra, and 228Ra) and other geochemical tracers (Ba, Si, and salinity) were employed to determine river plume transport scales and rates. Barium and radium exhibit elevated concentrations within the salinity gradient where they are desorbed from particles via ion-exchange. Once they are added to the system, they decrease offshore from dilution with lower concentration Bohai Sea water, and in the case of 224Ra and 223Ra, by radioactive decay. Using radium “ages” to assess the dissolved material transport scales and rates proved to be a useful tool in this environment. The ages based on the 224Ra/ 228Ra activity ratio increased gradually until salinities reached ∼25 when they rapidly increased due to decreased mixing at higher salinities. Integrated net transport rates through the salinity front ranged from 1.4 to 1.6 cm/s and did not vary significantly with river discharge. Thus, tidal mixing appears to dominate in this system, at least over the range of discharges investigated (80–600 m 3/s). Determining the temporal scale of flow across the coastal zone in this region is a valuable first step toward examining whether the Yellow River is contributing to the increasing inorganic nitrogen concentrations in the central Bohai Sea.

Comparison of observed and model‐computed low frequency circulation and hydrography on the New England Shelf

The finite volume coastal ocean model (FVCOM) is configured to study the interannual variability of circulation in the Gulf of Maine (GoM) and Georges Bank. The FVCOM‐GoM system incorporates realistic time‐dependent surface forcing derived from a high‐resolution mesoscale meteorological model (MM5) and assimilation of observed quantities including sea surface temperature and salinity and temperature fields on the open boundary. An evaluation of FVCOM‐GoM model skill on the New England shelf is made by comparison of computed fields and data collected during the Coastal Mixing and Optics (CMO) Program (August 1996–June 1997). Model mean currents for the full CMO period compare well in both magnitude and direction in fall and winter but overpredict the westward flow in spring. The direction and ellipticity of the subtidal variability correspond but computed magnitudes are around 20% below observed, partially due to underprediction of the variability by MM5. Response of subtidal currents to wind‐forcing shows the model captures the directional dependence, as well as seasonal variability of the lag. Hydrographic results show that FVCOM‐GoM resolves the spatial and temporal evolution of the temperature and salinity fields. The model‐computed surface salinity field compares well, except in May when there is no indication of the fresh surface layer from the Connecticut River discharge noted in the observations. Analysis of model‐computed results indicates that the plume was unable to extend to the mooring location due to the presence of a westward mean model‐computed flow during that time that was stronger than observed. Overall FVCOM‐GoM captures well the dynamics of the mean and subtidal flow on the New England shelf.

Importance of coastal nutrient supply for global ocean biogeochemistry

The coastal ocean provides nutrients to the open ocean in accounts that are poorly quantified. We use an ocean biogeochemistry model to assess the importance of the coastal nutrient supply to global ocean biogeochemistry. The model includes full cycles of P, Si, and Fe, as well as the representation of two phytoplankton groups, two zooplankton groups, and two organic detritus pools. When coastal mixing is enhanced to reproduce the action of tides and storms, primary production and chlorophyll‐a (Chla) concentrations show a large increase at the coast and a smaller increase in the open ocean. When coastal nutrient supply is enhanced to reproduce sediment resuspension or river supply, both the coastal ocean and the open ocean primary production and Chla concentration increase in comparable amounts. In agreement with the definition of nutrient limitation areas in the model, coastal export of P‐excess impacts mainly the subtropical oligotrophic areas, Si‐excess impacts the Arctic Ocean and some coastal areas, and Fe‐excess impacts the east equatorial Pacific, North Atlantic and North Pacific, and the Southern Ocean. Modeled Chla is closest to observations when the input ratio of Fe to P and Si is enhanced.

Uncertainties associated with 223Ra and 224Ra measurements in water via a Delayed Coincidence Counter (RaDeCC)

The short-lived radium isotopes, 223Ra ( T 1/2 = 11.4 days) and 224Ra ( T 1/2 = 3.66 days), have been successfully used as tracers of several environmental processes, e.g., submarine groundwater discharge, coastal mixing processes, and water residence times. In this paper, the uncertainties associated with 223Ra and 224Ra measurements using a Radium Delayed Coincidence Counter are determined on a detailed error propagation basis with a confidence interval of 1 σ. From the data analyses of several groups of coastal water samples, the calculated relative uncertainties averaged 12% for the 223Ra and 7% for the 224Ra. These uncertainties can decrease for radium-enriched groundwater samples although asymptotic limits have been found at 7% relative uncertainty for 223Ra and 4% for 224Ra. In this paper, the influence of sampling and measurement parameters on the final radium uncertainties is evaluated in order to provide guidance to optimize these factors and obtain more reliable results.

Near-Inertial Waves on the New England Shelf: The Role of Evolving Stratification, Turbulent Dissipation, and Bottom Drag

Abstract Energetic variable near-inertial internal waves were observed on the springtime New England shelf as part of the Coastal Mixing and Optics (CMO) project. Surface warming and freshwater advection tripled the average stratification during a 3-week observational period in April/May 1997. The wave field was dominated by near-inertial internal waves generated by passing storms. Wave evolution was controlled by a balance among wind stress, bottom drag, and turbulent dissipation. As the stratification evolved, the vertical structure of these near-inertial waves switched from mode 1 to mode 2 with associated changes in the magnitude and location of wave shear. The growth of mode-2 waves was attributable to a combination of changing wind stress forcing and a nonlinear coupling between the first and second vertical modes through quadratic bottom stress. To explore both forcing mechanisms, an open-ocean mixed layer model is adapted to the continental shelf. In this model, surface wind stress and bottom stress are distributed over the surface and bottom mixed layers and then projected onto orthogonal vertical modes. The model replicates the correct magnitude and evolving modal distribution of the internal waves and confirms that bottom stress can act to transfer energy between internal wave modes.

Stirring by Small-Scale Vortices Caused by Patchy Mixing

Abstract Evidence is presented that lateral dispersion on scales of 1–10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small-scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events. Dye-release experiments conducted during the recent Coastal Mixing and Optics (CMO) experiment provide estimates of diapycnal and lateral dispersion. Microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1–10 m and horizontal scales of a few hundred meters to a few kilometers. Momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events. It is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal Rossby radius of deformation, which seems to have been the case for CMO. For parameter values relevant to CMO, lower-bound estimates of the effective lateral diffusivity by this mechanism ranged from 0.1 to 1 m2 s−1. Revised estimates after accounting for the possibility of long-lived motions were an order of magnitude larger and ranged from 1 to 10 m2 s−1. The predicted dispersion is large enough to explain the observed lateral dispersion in all four CMO dye-release experiments examined.

Oceanographic features related to northern fur seal migratory movements

Northern fur seals breeding on the Pribilof Islands are characterized by pelagic migrations that begin each fall and last approximately eight months. Previous studies have examined the early phases of the migration with respect to timing, location, and effects of ocean surface currents on movement. We used satellite telemetry and remotely sensed satellite data to examine relationships between oceanographic features and the movements of adult female fur seals in the Bering Sea and North Pacific Ocean during early, middle and late portions of their winter migration. Physical locations of 13 female fur seals were monitored during 2002–2003, and diving data were collected on a subset of the animals. Remotely sensed data were obtained to assess sea-surface temperatures, chlorophyll a concentrations, and seasurface height anomalies encountered by the fur seals. Data from historical pelagic collection of fur seals also were summarized to describe winter diet and the distribution of different age and sex classes of the general migration of fur seals to the eastern North Pacific. Seals departed from the Pribilof Islands in November and moved in a southeasterly direction over the continental shelf as they left the Bering Sea. Their travel routes did not follow coastal or bathymetric features as they crossed the North Pacific Ocean, but instead corresponded to complementary water movement of the Alaska Gyre and the North Pacific Current. Winter foraging areas varied geographically and were associated with eddies, the subarctic–subtropical transition region, and areas that undergo coastal mixing due to the California Current. The results indicate that fur seals may cue on a variety of oceanographic features that aid in reducing energetic expenditures and optimize foraging opportunities. Published by Elsevier Ltd.

Internal solitary waves in the Coastal Mixing and Optics 1996 experiment: Multimodal structure and resuspension

Observations of internal solitary waves (ISWs) and of their role in sediment resuspension during the Coastal Mixing and Optics 1996 (CMO 96) experiment are reported. The largest resuspension events observed in the experiment can be related to retarded flow under the wave footprint. Two distinctly different periods of resuspension events could be distinguished based on the prevailing atmospheric conditions: a calm period, which we consider characteristic of nominal conditions, and an energetic period, during which two major storms occurred. ISWs arrived at the mooring site from a variety of sources, though a common intermodal dynamics seemed to occur repeatedly. Both mode 1 and mode 2 ISWs have been observed. The present analysis of the month‐long portion of the CMO 96 data set constitutes the first reported observations, insofar as we are aware, of mode 2 waves on the continental shelf. Both mode 1 and mode 2 ISWs were found to stimulate resuspension. The mode 2 waves seem to be generated locally by resonant or topographic interactions with mode 1 ISWs. Internal wave fields of the type described here are expected to exist in a variety of other shallow seas as well.