Block Island Sound Research Articles

Spatial and temporal genetic stock composition of river herring bycatch in southern New England Atlantic herring and mackerel fisheries

Anadromous river herring (alewife and blueback herring) persist at historically low abundances and are caught as bycatch in commercial fisheries, potentially preventing recovery despite conservation efforts. We used newly established single-nucleotide polymorphism genetic baselines for alewife and blueback herring to define fine-scale reporting groups for each species. We then determined the occurrence of fish from these reporting groups in bycatch samples from a Northwest Atlantic fishery over four years. Within sampled bycatch events, the highest proportions of alewife were from the Block Island (34%) and Long Island Sound (22%) reporting groups, while for blueback herring the highest proportions were from the Mid-Atlantic (47%) and Northern New England (24%) reporting groups. We then quantified stock-specific mortality in a focal geographic area (∼3500 km2, including Block Island Sound) of high bycatch incidence and sampling effort, where the most accurate estimates of mortality could be made. During this period, we estimate that bycatch took about 4.6 million alewife and 1.2 million blueback herring, highlighting the need to reduce bycatch mortality for the most depleted river herring stocks.

The Use of Baited Remote Underwater Video Systems (BRUVS) to Noninvasively Characterize a White Shark (Carcharodon carcharias) Nursery Area off Eastern Long Island, New York

AbstractUnderstanding if a discrete region fits three key criteria for shark nursery area designation is of utmost importance. Such a designation within United States territorial waters could result in the implementation of an Essential Fish Habitat (EFH) classification, a determination facilitating species protection. In this study, baited remote underwater video systems (BRUVS) were used to determine if they could effectively confirm a previously identified white shark (Carcharodon carcharias) nursery area south of Montauk, New York, so that the technique may be applied in other potential nursery areas. During experimentation, 1,348.32 h of video data were collected between Region A (Block Island Sound; 674.16 h), outside of the previously identified nursery area, and Region B (Atlantic Ocean; 674.16 h), within the identified nursery area. From the video data, 35 sightings of C. carcharias were recorded, with 31 unique individuals identified. Data associated with Region B fit all three nursery area criteria: (a) young-of-the-year (YOY) and juvenile sharks were more commonly found in this region over Region A (p < 0.001), (b) several YOY and juvenile sharks (n = 4) were resighted in this region within a given year (e.g., average resighting duration: 10.5 days), and (c) YOY and juvenile sharks exhibited repeated use of this region over multiple years. We conclude that BRUVS can be used for fine-scale analyses to help designate a discrete area(s) as a shark nursery, even in turbid New York waters. Therefore, using BRUVS to identify shark nursery areas is a viable and noninvasive approach that can contribute to species conservation.

Summertime Connecticut River Water Pathways and Wind Impacts

AbstractLong Island Sound is a large macrotidal estuary. Connecticut River as the primary freshwater source enters near the sound's mouth. The summertime pathways of river water under low discharge and mild wind conditions are studied through both numerical simulations with a passive dye pulse and field surface drifter observations. Within the 19‐day modeling analysis period a third of the river dye pulse remains in the eastern sound; another third of the pulse moves up‐estuary with the near‐bottom dense inflow into the central and western sound with a spring‐neap tidal modulation; and another third leaves the sound with the near‐surface outflow toward the continental shelf through Block Island Sound. The latter pathway is confirmed by field surface drifter tracks. Three scenarios of wind forcing are tested: a WRF‐ROMS Coupled case, a NARR data forcing case, and a No‐Wind case. The results show though that the sound is tidal mixing dominated, mild winds still alter the position and strength of the estuarine exchange flow, and either enhances by the cross‐estuary winds or lateral straining. On the shelf, winds play a more important role on the fresher estuarine water distribution. The sensitivities of circulation, salinity, and numerical drifter tracks to different atmospheric forcings also are studied. The results suggest that the coupled model has better performance to simulate surface drifter tracks.

Sediment Facies and Dispersal Systems in the Estuaries of Easternmost Long Island, New York, U.S.A.

ABSTRACT Coch, N.K., 2019. Sediment facies and dispersal systems in the estuaries of easternmost Long Island, New York, U.S.A. Journal of Coastal Research, 35(1), 165–176. Coconut Creek (Florida), ISSN 0749-0208. A multidecadal study of the estuarine systems of easternmost Long Island, New York, U.S.A. has provided detailed data on sediment facies, structures, and sediment dispersal patterns in this important estuarine–oceanic system. In addition, new data are presented on the unique morphology, sediment type, and distribution and geological history of the three deep channels connecting Block Island Sound and Long Island systems. Detailed sediment facies mapping has delineated six separate sediment dispersal systems in the study area.

A periodic freshwater patch detachment process from the Block Island Sound estuarine plume

AbstractPrevious observations suggest periodic freshwater patches separating from the Block Island Sound (BIS) estuarine plume. In this study, the dynamics of the separation process is investigated through a series of numerical experiments using the Regional Ocean Modeling System (ROMS). In addition, we explore the seasonal variability of the freshwater patches and their response to river discharge and ambient current. The model results indicate that episodic freshwater patches are triggered by small changes in tidal currents over the spring‐neap tidal cycle. The spring‐neap variation in tidal currents causes significant, monthly fluctuations in turbulent mixing and vertical stratification in BIS, modulating the freshwater discharge thereby generating episodic freshwater patches that move both downstream along the southern shore of Long Island and toward Rhode Island Sound (RIS). The realistically configured model shows that the freshwater patches experience strong seasonal variability. They are largest in spring when the river discharge peaks, and smallest in summer due to the weak river discharge and a robust upstream ambient current from RIS. According to the analysis of the freshwater transport out of BIS, we conclude that such detachment occurs at tidal mixing fronts.

Dynamics of the periphery current in Rhode Island Sound

Observations reveal a near-surface circulation around the periphery of Rhode Island Sound (RIS) that occurs in summer stratified conditions and disappears in winter when weak solar insolation and wind stirring result in strong vertical mixing. According to a series of numerical simulations and theoretical analysis, we attribute the summer intensification of this “periphery current” to a circulation produced by seasonal bottom thermal fronts often observed from May to September. The strength of the thermal fronts is proportional to the surface solar radiation. Meanwhile, the simulations capture a continuous topographically rectified tidal residual current in RIS and a pair of opposite-sign headland eddies around Montauk Point in Block Island Sound (BIS). Our analysis suggests the importance of nonlinear vorticity advection and frictional torques in BIS. On the other hand, the vorticity balance shows the importance of velocity torque by contributing to the opposite headland gyres, while the effect by planetary vorticity stretching is negligible over BIS but important in RIS.

Trophic structure of a coastal fish community determined with diet and stable isotope analyses.

A combination of dietary guild analysis and nitrogen (δ(15) N) and carbon (δ(13) C) stable-isotope analysis was used to assess the trophic structure of the fish community in Rhode Island and Block Island Sounds, an area off southern New England identified for offshore wind energy development. In the autumn of 2009, 2010 and 2011, stomach and tissue samples were taken from 20 fish and invertebrate species for analysis of diet composition and δ(15) N and δ(13) C signatures. The food chain in Rhode Island and Block Island Sounds comprises approximately four trophic levels within which the fish community is divided into distinct dietary guilds, including planktivores, benthivores, crustacivores and piscivores. Within these guilds, inter-species isotopic and dietary overlap is high, suggesting that resource partitioning or competitive interactions play a major role in structuring the fish community. Carbon isotopes indicate that most fishes are supported by pelagic phytoplankton, although there is evidence that benthic production also plays a role, particularly for obligate benthivores such as skates Leucoraja spp. This type of analysis is useful for developing an ecosystem-based approach to management, as it identifies species that act as direct links to basal resources as well as species groups that share trophic roles.

Dynamics of the Block Island Sound Estuarine Plume

AbstractBuoyant discharge of freshwater from Long Island Sound (LIS) forms a seasonal buoyant plume outside Block Island Sound (BIS) between the coast of Long Island and the denser shelf waters. The plume’s seasonal variability and its response to tides, winds, and surface heating are investigated through a series of process-oriented experiments using the Regional Ocean Modeling System (ROMS). Results show the importance of river discharge, wind directions, and surface heating in the seasonal variation of the BIS buoyant plume. In winter and spring, the plume is intermediate with a large surface offshore extension detached from the bottom. From winter to spring, the river discharge increases; meanwhile, upwelling-favorable winds keep dominating. They compete with the increase of surface heating and generate a broader buoyant plume in spring than in winter. In summer, the plume is bottom advected with most of its width in contact with the bottom and is featured with the steepest isopycnals and narrowest plume, which is driven by a combination of strong insolation, weak buoyant discharge from LIS, and feeble winds. In fall, although the river discharge is comparable to that in winter, the upwelling-favorable wind is relatively weaker, corresponding to a narrower intermediate plume.

Surface circulation in Block Island Sound and adjacent coastal and shelf regions: A FVCOM-CODAR comparison

CODAR-derived surface currents in Block Island Sound over the period of June 2000 through September 2008 were compared to currents computed using the Northeast Coastal Ocean Forecast System (NECOFS). The measurement uncertainty of CODAR-derived currents, estimated using statistics of a screened nine-year time series of hourly-averaged flow field, ranged from 3 to 7cm/s in speed and 4° to 14° in direction. The CODAR-derived and model-computed kinetic energy spectrum densities were in good agreement at subtidal frequencies, but the NECOFS-derived currents were larger by about 28% at semi-diurnal and diurnal tidal frequencies. The short-term (hourly to daily) current variability was dominated by the semidiurnal tides (predominantly the M2 tide), which on average accounted for ∼87% of the total kinetic energy. The diurnal tidal and subtidal variability accounted for ∼4% and ∼9% of the total kinetic energy, respectively. The monthly-averaged difference between the CODAR-derived and model-computed velocities over the study area was 6cm/s or less in speed and 28° or less in direction over the study period. An EOF analysis for the low-frequency vertically-averaged model current field showed that the water transport in the Block Island Sound region was dominated by modes 1 and 2, which accounted for 89% and 7% of the total variance, respectively. Mode 1 represented a relatively stationary spatial and temporal flow pattern with a magnitude that varied with season. Mode 2 was characterized mainly by a secondary cross-shelf flow and a relatively strong along-shelf flow. Process-oriented model experiments indicated that the relatively stationary flow pattern found in mode 1 was a result of tidal rectification and its magnitude changed with seasonal stratification. Correlation analysis between the flow and wind stress suggested that the cross-shelf water transport and its temporal variability in mode 2 were highly correlated to the surface wind forcing. The mode 2 derived onshore and offshore water transport, and was consistent with wind-driven Ekman theory. The along-shelf water transport over the outer shelf, where a large portion of the water flowed from upstream Nantucket Shoals, was not highly correlated to the surface wind stress.

Comparison of surface chlorophyll, primary production, and satellite imagery in hydrographically different sounds off southern New England

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 535:29-45 (2015) - DOI: https://doi.org/10.3354/meps11386 Comparison of surface chlorophyll, primary production, and satellite imagery in hydrographically different sounds off southern New England Lindsey Fields1,5,*, Jeffrey Mercer1, Kimberly J. W. Hyde2, Mark Brush3, Scott W. Nixon1, Candace Oviatt1, Malia L. Schwartz4, David Ullman1, Daniel Codiga1 1Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA 2NOAA/NMFS, Narragansett, RI 02882, USA 3Virginia Institute of Marine Science, College of William & Mary, PO Box 1346, Gloucester Point, VA 23062, USA 4University of Rhode Island, Kingston, RI 02881, USA 5Present address: Department of Marine Sciences, University of Georgia, 325 Sanford Drive, Athens, GA 30602, USA *Corresponding author: lfields@uga.edu ABSTRACT: Block Island Sound (BIS) and Rhode Island Sound (RIS) are adjacent inner continental shelf ecosystems with contrasting hydrographic regimes. BIS exhibits more energetic tidal mixing, and water column stratification remains weak but persists year-round due to nearby estuarine exchange flow; RIS is less influenced by estuaries, and more seasonal with strong stratification in summer. We compared annual cycles of phytoplankton biomass and primary production in BIS and RIS using measurements (surface chlorophyll, 14C primary production), primary production models (Webb/Platt and BZE models), and satellite ocean color products. During 22 mo of sampling, measured surface chlorophyll was not significantly different between BIS (mean = 1.86 mg m-3) and RIS (1.69 mg m-3), and bimodal peaks of phytoplankton biomass and production occurred concurrently in both Sounds. In contrast, a 12 yr ocean-color based chlorophyll time series indicated higher long-term average surface chlorophyll in the more well-mixed system (BIS, mean = 1.50 mg m-3; RIS, mean = 0.86 mg m-3). BIS annual primary production (318 to 329 g C m-2 yr-1) was higher than RIS (239 to 256 g C m-2 yr-1; p < 0.001). These differences were most apparent during the summer, concurrent with the largest differences in water column stratification. Phytoplankton bloom phenology was driven by physical processes, with chlorophyll significantly related to water column stratification (r = -0.51, p = 0.01), depth of the euphotic zone (r = -0.54, p = 0.05), and surface water salinity (r = 0.54, p = 0.04). Primary production was correlated with surface water temperature (r = 0.57, p = 0.03) but the mechanisms underlying production differences between the Sounds remain unresolved. We hypothesize that different hydrographies give rise to different productivity between the Sounds. KEY WORDS: Chlorophyll a · Primary production · Continental shelf · Stratification · Remote sensing · Empirical model Full text in pdf format PreviousNextCite this article as: Fields L, Mercer J, Hyde KJW, Brush M and others (2015) Comparison of surface chlorophyll, primary production, and satellite imagery in hydrographically different sounds off southern New England. Mar Ecol Prog Ser 535:29-45. https://doi.org/10.3354/meps11386 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 535. Online publication date: September 15, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Benthic metabolism and nutrient regeneration in hydrographically different regions on the inner continental shelf of Southern New England

We examined the effect of hydrography on benthic-pelagic coupling in a transitional inner continental shelf area. From Oct 2009 to Jul 2012, we measured sediment oxygen demand (SOD), benthic inorganic nutrient fluxes, and sediment characteristics (e.g. chl a and phaeopigment content, grain size, etc.) in two regions of the Southern New England continental shelf: a relatively well mixed ecosystem (Block Island Sound, BIS), and an adjacent, seasonally stratified ecosystem (Rhode Island Sound, RIS). Despite a higher rate of euphotic zone primary production in BIS, benthic metabolism (measured as SOD) was not significantly different between the two areas (BIS = 953.8 ± 88.2 μmol m−2 h−1; RIS = 912.2 ± 69.1 μmol m−2 h−1). We speculate that the similarity of SOD at these two sites was due to differences in water column hydrography between the Sounds, where the energetic water column mixing in BIS could potentially resuspend organic matter back to the water column to be decomposed before reaching the benthos. Additionally, we think that the seasonal presence of a strong pycnocline in RIS prevented mixing of regenerated DIN and DIP to surface waters for use by phytoplankton. Apparent differences in benthic macrofaunal abundance between Block Island Sound and Rhode Island Sound translated to differences in dissolved inorganic nutrient fluxes between the two areas. Excretion and irrigation activities by the dense amphipod communities in BIS likely caused higher effluxes of DIN (NH4+ = 36.9 ± 7.7 μmol m−2 h−1; NOX = 23.5 ± 3.4 μmol m−2 h−1) and DIP (7.2 ± 1.4 μmol m−2 h−1) compared to fluxes in RIS (NH4+ = 22.8 ± 4.5 μmol m−2 h−1; NOX = 11.1 ± 5.5 μmol m−2 h−1; DIP = 3.2 ± 0.8 μmol m−2 h−1). These findings indicate that the hydrographic regime of the water column may exert a strong influence on benthic-pelagic coupling dynamics on the Southern New England shelf and in other inner continental shelf ecosystems.

Fine-scale spatial patterns in the demersal fish and invertebrate community in a northwest Atlantic ecosystem

The abundance, biomass, diversity, and species composition of the demersal fish and invertebrate community in Rhode Island Sound and Block Island Sound, an area identified for offshore renewable energy development, were evaluated for spatial and seasonal structure. We conducted 58 otter trawls and 51 beam trawls in the spring, summer and fall of 2009–2012, and incorporated additional data from 88 otter trawls conducted by the Northeast Area Monitoring and Assessment Program. We used regionally-grouped abundance, biomass, diversity, and size spectra to assess spatial patterns in the aggregate fish community, and hierarchical cluster analysis to evaluate trends in species assemblages. Our analyses revealed coherent gradients in fish community biomass, diversity and species composition extending from inshore to offshore waters, as well as patterns related to the differing bathymetry of Rhode Island and Block Island Sounds. The fish communities around Block Island and Cox's Ledge are particularly diverse, suggesting that the proximity of hard bottom habitat may be important in structuring fish communities in this area. Species assemblages in Rhode Island and Block Island Sounds are characterized by a combination of piscivores (silver hake, summer flounder, spiny dogfish), benthivores (American lobster, black sea bass, Leucoraja spp. skates, scup) and planktivores (sea scallop), and exhibit geographic patterns that are persistent from year to year, yet variable by season. Such distributions reflect the cross-shelf migration of fish and invertebrate species in the spring and fall, highlighting the importance of considering seasonal fish behavior when planning construction schedules for offshore development projects. The fine spatial scale (10 s of kms) of this research makes it especially valuable for local marine spatial planning efforts by identifying local-scale patterns in fish community structure that will enable future assessment of the ecological impacts of offshore development. As such, this knowledge of the spatial and temporal structure of the demersal fish community in Rhode Island and Block Island Sounds will help to guide the placement of offshore structures so as to preserve the ecological and economic value of the area.

Environmental controls of anammox and denitrification in southern New England estuarine and shelf sediments

We measured denitrification and anammox potential rates in homogenized sediments over two annual cycles from two estuarine sites (Providence River estuary and Narragansett Bay) and two continental shelf sites (Block Island and Rhode Island sounds). Denitrification varied both spatially and seasonally, but anammox only varied spatially. Denitrification ranged from 2.5 to 112 nmol N h−1 mL−1 sediment, and anammox from 0 to 8.7 nmol N h−1 mL−1 sediment, with the contribution of anammox to N2 fluxes (ra) ranging from undetectable to 4% in estuarine sites and 8–42% on the shelf. Oxygen microprofiles were analyzed in intact cores and concentrations of nitrate, nitrite, and ammonium were measured in the sediment slice corresponding to the depth layer in which potential rates were measured. Denitrification rates correlated positively with diffusive O2 consumption and temperature and potential anammox rates correlated positively with pore‐water concentrations. Anammox was positively correlated with denitrification in shelf sediments where anammox was regularly detected, but not in estuarine sediments. ra was negatively correlated with diffusive O2 consumption and positively correlated with pore‐water nitrate. Both organic matter and nitrate were important factors regulating the contribution of anammox to N2 production. As a whole, our results demonstrate that incorporating processes that control these two factors into models of N cycling, rather than focusing on organic matter availability alone, may improve predictions of the relative importance of anammox to N2 production in marine sediments.

Glaciotectonic deformation associated with the Orient Point–Fishers Island moraine, westernmost Block Island Sound: further evidence of readvance of the Laurentide ice sheet

High-resolution seismic-reflection profiles collected across pro-glacial outwash deposits adjacent to the circa 18 ka b.p. Orient Point–Fishers Island end moraine segment in westernmost Block Island Sound reveal extensive deformation. A rhythmic seismic facies indicates the host outwash deposits are composed of fine-grained glaciolacustrine sediments. The deformation is variably brittle and ductile, but predominantly compressive in nature. Brittle deformation includes reverse faults and thrust faults that strike parallel to the moraine, and thrust sheets that extend from beneath the moraine. Ductile deformation includes folded sediments that overlie undisturbed deposits, showing that they are not drape features. Other seismic evidence for compression along the ice front consists of undisturbed glaciolacustrine strata that dip back toward and underneath the moraine, and angular unconformities on the sea floor where deformed sediments extend above the surrounding undisturbed correlative strata. Together, these ice-marginal glaciotectonic features indicate that the Orient Point–Fishers Island moraine marks a significant readvance of the Laurentide ice sheet, consistent with existing knowledge for neighboring coeval moraines, and not simply a stillstand as previously reported.

Turbulence in coastal fronts near the mouths of Block Island and Long Island Sounds

Measurements of turbulence were performed in four frontal locations near the mouths of Block Island Sound (BIS) and Long Island Sound (LIS). These measurements extend from the offshore front associated with BIS and Mid-Atlantic Bight Shelf water, to the onshore fronts near the Montauk Point (MK) headland, and the Connecticut River plume front. The latter feature is closely associated with the major fresh water input to LIS. Turbulent kinetic energy (TKE) dissipation rate, ε, was obtained using shear probes mounted on an autonomous underwater vehicle. Offshore, the BIS estuarine outflow front showed, during spring season and ebb tide, maximum TKE dissipation rate, ε, estimates of order 10 − 5 W/kg, with background values of order 10 − 6 to 10 − 9 W/kg. Edwards et al. [Edwards, C.A., Fake, T.A., and Bogden, P.S., 2004a. Spring–summer frontogenesis at the mouth of Block Island Sound: 1. A numerical investigation into tidal and buoyancy-forced motion. Journal of Geophysical Research 109 (C12021), doi:10.1029/2003JC002132.] model this front as the boundary of a tidally driven, baroclinically adjusted BIS flow around the MK headland eddy. At the entrance to BIS, near MK, two additional fronts are observed, one of which was over sand waves. For the headland site front east of MK, without sand waves, during ebb tide, ε estimates of 10 − 5 to 10 − 6 W/kg were observed. The model shows that this front is at the northern end of an anti-cyclonic headland eddy, and within a region of strong tidal mixing. For the headland site front further northeast over sand waves, maximum ε estimates were of order 10 − 4 W/kg within a background of order 10 − 7 –10 − 6 W/kg. From the model, this front is at the northeastern edge of the anti-cyclonic headland eddy and within the tidal mixing zone. For the Connecticut River plume front, a surface trapped plume, during ebb tide, maximum ε estimates of 10 − 5 W/kg were obtained, within a background of 10 − 6 to 10 − 8 W/kg. Of all four fronts, the river plume front has the largest finescale mean-square shear, S 2 ~ 0.15 s − 2 . All of the frontal locations had local values of the buoyancy Reynolds number indicating strong isotropic turbulence at the dissipation scales. Local values of the Froude number indicated shear instability in all of the fronts.

Estimating tidal current amplitudes outside estuaries and characterizing the zone of estuarine tidal influence

Tidal currents within many estuaries are stronger than on the adjacent continental shelf. Estuarine tidal influence extends onto the shelf elevating tidal amplitudes above ambient shelf levels over a region outside the estuary. In this paper, a kinematic theory that describes tidal flow in these estuary–shelf tidal interaction zones is derived and tested. Using these results, tidal current amplitudes outside estuaries are estimated and the range and intensity of estuarine tidal influence is characterized. The estimates for the tidal current amplitudes ( u tide) of the dominant constituent are appropriate for linear or weakly nonlinear systems with predominantly barotropic tides; the ratio of tidal height to water depth is small ( η/ h≪1) in linear or weakly nonlinear regimes. Within tidal interaction zones, the tidal current amplitude is composed of an ambient shelf part ( u a) and an estuary-induced part ( u e). The characteristic shelf amplitude far from the estuary is used to set u a. Continuity arguments indicate that u e (averaged over a control volume arc centered on the mouth with radius r and a swath angle of γπ) approximately equals the ratio of the tidal volume flux through the mouth ( V m) and the cross-sectional area of any control volume arc ( u e ≈ V m / γ π r h ¯ ) . This approximation holds where the squared product of the tidal wave number and radial distance is small: ( kr) 2≪1. For a shelf with constant slope α and small coastal wall depth, the arc-averaged depth is h ¯ ≈ sr (where s=2 α/ pi for γ=1). For this shelf bathymetry, u e decays with squared radial distance from the estuary mouth. Theoretical predictions are consistent with observed tidal current amplitudes outside the Delaware Bay and Block Island Sound. In both test cases, the estimated and observed amplitudes exhibit an r −2 dependence and decay over a similar distance. The relative importance of estuarine tidal influence is assessed with the tidal interaction index ( T i= u e/ u a). The intensity of estuarine influence is characterized by the value of T i at the mouth ( T im). The extent of an estuary–shelf tidal interaction zone is measured by the interaction radius r i (where T i=1) and by r ∞ (where T i=0.1). These metrics are used to compare the tidal interaction zone characteristics for the Delaware Bay, Block Island Sound, several other major estuaries, and a small tidal inlet. The kinematic theory can be applied outside other estuaries where only limited tidal information is available or used to interpret observed patterns in tidal amplitudes and characterize the degree of estuarine influence.

Comparison of observed (HF radar, ADCP) and model barotropic tidal currents in the New York Bight and Block Island Sound

A three-dimensional, primitive-equation model is used to simulate the barotropically-forced semidiurnal tidal currents in the New York Bight (NYB) and Block Island Sound (BIS). Model tidal velocity ellipses are verified at historical current meter locations and with measurements from acoustic Doppler current profilers (ADCPs) and HF radar (CODAR). The model reproduces well the regional tidal flow pattern as well as the vertical tidal velocity structure. The model misfits typically are 2–4 cm/s in amplitude and 5–7° in orientation. Through comprehensive skill assessment, the model's capacity of simulating the three-dimensional barotropic tidal currents is clearly demonstrated. Moreover, it is shown that the integrity of HF radar measurements can be assured by verifying with model tidal ellipses.

An LNG release, transport, and fate model system for marine spills

LNGMAP, a fully integrated, geographic information based modular system, has been developed to predict the fate and transport of marine spills of LNG. The model is organized as a discrete set of linked algorithms that represent the processes (time dependent release rate, spreading, transport on the water surface, evaporation from the water surface, transport and dispersion in the atmosphere, and, if ignited, burning and associated radiated heat fields) affecting LNG once it is released into the environment. A particle-based approach is employed in which discrete masses of LNG released from the source are modeled as individual masses of LNG or spillets. The model is designed to predict the gas mass balance as a function of time and to display the spatial and temporal evolution of the gas (and radiated energy field). LNGMAP has been validated by comparisons to predictions of models developed by ABS Consulting and Sandia for time dependent point releases from a draining tank, with and without burning. Simulations were in excellent agreement with those performed by ABS Consulting and consistent with Sandia's steady state results. To illustrate the model predictive capability for realistic emergency scenarios, simulations were performed for a tanker entering Block Island Sound. Three hypothetical cases were studied: the first assumes the vessel continues on course after the spill starts, the second that the vessel stops as soon as practical after the release begins (3 min), and the third that the vessel grounds at the closest site practical. The model shows that the areas of the surface pool and the incident thermal radiation field (with burning) are minimized and dispersed vapor cloud area (without burning) maximized if the vessel continues on course. For this case the surface pool area, with burning, is substantially smaller than for the without burning case because of the higher mass loss rate from the surface pool due to burning. Since the vessel speed substantially exceeds the spill spreading rate, both the thermal radiation fields and surface pool trail the vessel. The relative directions and speeds of the wind and vessel movement govern the orientation of the dispersed plume. If the vessel stops, the areas of the surface pool and incident radiation field (with burning) are maximized and the dispersed cloud area (without burning) minimized. The longer the delay in stopping the vessel, the smaller the peak values are for the pool area and the size of the thermal radiation field. Once the vessel stops, the spill pool is adjacent to the vessel and moving down current. The thermal radiation field is oriented similarly. These results may be particularly useful in contingency planning for underway vessels.

Seafloor character and sedimentary processes in eastern Long Island Sound and western Block Island Sound

Multibeam bathymetric data and seismic-reflection profiles collected in eastern Long Island Sound and western Block Island Sound reveal previously unrecognized glacial features and modern bedforms. Glacial features include an ice-sculptured bedrock surface, a newly identified recessional moraine, exposed glaciolacustrine sediments, and remnants of stagnant-ice-contact deposits. Modern bedforms include fields of transverse sand waves, barchanoid waves, giant scour depressions, and pockmarks. Bedform asymmetry and scour around obstructions indicate that net sediment transport is westward across the northern part of the study area near Fishers Island, and eastward across the southern part near Great Gull Island.

Interplay of Wind Forcing and Buoyant Discharge off Montauk Point: Seasonal Changes to Velocity Structure and a Coastal Front

Abstract Seasonal-mean currents in fall, winter, and spring on the bathymetrically complex continental shelf 15–65 m deep off Montauk Point, outside Block Island Sound, are analyzed using moored profiling current-meter records from a 2.5-yr period. A sharp boundary, or coastal front, occurs where strong, shallow, generally southwestward flow that weakens nearly linearly with increasing depth meets deeper flow nearly opposite in direction (fall/winter) or markedly weaker (spring). Velocities veer clockwise (counterclockwise) with increasing depth inshore (offshore) of the front. Evidence is presented that thermal wind balance holds without major frictional modification: it accounts for the veering, and the seasonal-mean horizontal density gradients it implies are generally toward the southeast quadrant in agreement with limited hydrographic measurements. Substantial seasonal changes in flow and frontal attributes occur because of the interplay of annual cycles in wind forcing and buoyant discharge. In fall and winter, upwelling-favorable wind causes nearshore setdown of sea surface height and an inshore-directed barotropic pressure gradient: shallow down-coast (alongshore to the south and west) currents weaken, and deep currents are up-coast. In spring, buoyant discharge peaks and winds weaken: shallow down-coast flow strengthens and deep flow weakens. The front extends to the seafloor, with attachment depth shallowest in winter, deepest in spring, and intermediate in fall; its width is smaller in fall than in winter. Buoyant discharge theory based on bottom boundary layer density advection dynamics captures these seasonal shifts. Cross-shelf circulation includes offshore (onshore) shallow (deep) motion; deep onshore motion appears enhanced near a canyon and persistent through all three seasons, suggesting wind-driven upwelling is not solely responsible.