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Three-dimensional numerical simulations of a tidally dominated estuary within the Gulf of Maine are performed using the Regional Ocean Modeling System (ROMS) and validated with observations of sea surface elevation and velocity time series obtained between 1975 and 2016. The model is forced at the ocean boundary with tidal constituents (M2, S2, N2, O1, K1), a time series of observed subtidal elevations and discharge from seven rivers that drain into the estuary. Harmonic analysis is used to determine the tidal dissipation characteristics and generation of overtides within the system. Amplitude decay and phase shift of the dominant semidiurnal (M2) tidal component shows good agreement with observations throughout the main channel of the Piscataqua River and over the channels and mudflats of the Great Bay. The model simulates harmonic growth of the overtides across the spectrum, and indicates a spatial evolution of the tide consistent with a shoaling wave that evolves from a skewed elevation profile with ebb dominance in the lower parts of the estuary, to a more asymmetric, pitched-forward shape consistent with flood dominance. The M4 constituent has spatial variation qualitatively similar to the observations but has magnitudes that are under-predicted in the complex bathymetric region of the Piscataqua River where much of the M2 tidal dissipation occurs. The M6 tidal constituent agrees well with the observations throughout the estuary suggesting that frictional effects on harmonic growth are well modeled. Root-mean-square model-data differences in velocities (~0.05 m/s) and sea surface elevation (~0.1 m) agree to within about 10% of the tidal amplitudes. Differences between model simulations with and without subtidal oscillations in the estuary are small, suggesting that interactions between the tide and other low frequency (subtidal) mean flows are weak and can be ignored when considering tidal dynamics. Including average fresh water discharge in the model does not affect the behavior of the tidal flows, but can generate high frequency baroclinic velocities potentially important to mixing within the estuary.

Field observations of current profiles and temperature, salinity, and density structure were used to examine vertical mixing within two pockmarks in Belfast Bay, Maine. The first is located in 21 m water depth (sea level to rim), nearly circular in shape with a 45 m rim diameter and 12 m rim-to-bottom relief. The second is located in 25 m water depth, more elongated in shape with an approximately 80 m (36 m) major (minor) axis length at the rim, and 17 m relief. Hourly averaged current profiles were acquired from bottom-mounted acoustic Doppler current profilers deployed on the rim and center of each pockmark over successive 42 h periods in July 2011. Conductivity–temperature–depth casts at the rim and center of each pockmark show warmer, fresher water in the upper water column, evidence of both active and fossil thermocline structure 5–8 m above the rim, and well-mixed water below the rim to the bottom. Vertical velocities show up- and down-welling events that extend into the depths of each pockmark. An observed temperature change at both the rim and center occurs coincident with an overturning event below the rim, and suggests active mixing of the water column into the depths of each pockmark. Vertical profiles of horizontal velocities show depth variation at both the center and rim consistent with turbulent logarithmic current boundary layers, and suggest that form drag may possibly be influencing the local flow regime. While resource limitations prevented observation of the current structure and water properties at a control site, the acquired data suggest that active mixing and overturning within the sampled pockmarks occur under typical benign conditions, and that current flows are influenced by upstream bathymetric irregularities induced by distant pockmarks.

Lippmann, T. C., J. Irish, and Hunt, J., 2013. Observations of the vertical structure of tidal currents in two inlets. In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 2029-2034, ISSN 0749-0208. Observations of the vertical structure of broad band tidal currents were obtained at two energetic inlets. Each experiment took place over a 4 week period, the first at Hampton Inlet in southeastern New Hampshire, USA, in the Fall of 2011, and the second at New River Inlet in southern North Carolina, USA, in the spring of 2012. The temporal variation and vertical structure of the currents were observed at each site with 600 kHz and 1200 kHz RDI Acoustic Doppler Current Profilers (ADCP) deployed on low-profile bottom tripods in 7.5 and 12.5 m water depths near the entrance to Hampton Inlet, and in 8 and 9 m water depth within and outside New River Inlet, respectively. In addition, a Nortek Aquapro ADCP was mounted on a jetted pipe in about 2.5 m water depth on the flank of the each inlet channel. Flows within the Hampton/Seabrook Inlet were dominated by semi-diurnal tides ranging 2.5 - 4 m in elevation, with velocities exceeding 2.5 m/s. Flows within New River inlet were also semi-diurnal with tides ranging about 1 – 1.5 m in elevation and with velocities exceeding 1.5 m/s. Vertical variation in the flow structure at the dominant tidal frequency are examined as a function of location within and near the inlet. Outside the inlet, velocities vary strongly over the vertical, with a nearly linear decay from the surface to near the bottom. The coherence between the upper most velocity bin and the successively vertically separated bins drops off quickly with depth, with as much as 50% coherence decay over the water column. The phase relative to the uppermost velocity bin shifts over depth, with as much as 40 deg phase lag over the vertical, with bottom velocities leading the surface. Offshore, rotary coefficients indicate a stable ellipse orientation with rotational directions consistent over the vertical. At Hampton, the shallower ADCP, but still outside the inlet, shows a rotational structure that changes sign in the vertical indicating a sense of rotation at the bottom that is opposite to that at the surface. Within the inlet, the flow is more aligned with the channel, the decay in amplitude over the vertical is diminished, the coherence and phase structure is nearly uniform, and the rotary coefficients indicate no sense of rotation in the flow. The observations are qualitatively consistent with behavior described by Prandle (1982) for shallow water tidal flows.

The University of New Hampshire is studying CO2 gas exchange, ocean acidification, air-sea dynamics, and associated biological processes in the western Gulf of Maine. Two buoys provide data supporting these studies. The UNH CO2 buoy has been deployed jointly with the National Oceanic and Atmospheric Administration (NOAA)’s Pacific Marine Environmental Laboratory northeast of the Isles of Shoals since 2006. The Jeffreys Ledge Moored Observatory is a development mooring testing new techniques and is deployed east of Gloucester, MA. This mooring is testing the direct covariance measurement of wind stress using a 3-D sonic anemometer with a motion package to remove buoy motion effects. A fast-rate atmospheric CO2 sensor is mounted by the anemometer to evaluate its potential for direct covariance gas flux measurements. Both buoys have additional meteorological and oceanographic sensors to provide supporting measurements. Six years of CO2 buoy data have helped quantify the seasonal air-sea flux cycle of CO2 in the Western Gulf of Maine. The buoy is now a node in near-term ocean carbon cycle process control experiments and longer-term ocean acidification monitoring. The Jeffreys Ledge buoy momentum flux measurements using wind and motion measurements indicate reasonable first-order buoy motion corrections can be made. Also, buoy-induced flow disturbance requires postmeasurement corrections. Rapid buoy azimuthal rotations were corrected with the addition of a steering vane. A vertical array of oxygen sensors captures phytoplankton bloom signatures and provides net community production estimates that augment in-water SAMI-CO2 measurements and add to a robust system to support process studies and improved biophysical modeling within this region.

Stanton, T. K., Chu, D., Jech, J. M., and Irish, J. D. 2010. New broadband methods for resonance classification and high-resolution imagery of fish with swimbladders using a modified commercial broadband echosounder. – ICES Journal of Marine Science, 67: 365–378. A commercial acoustic system, originally designed for seafloor applications, has been adapted for studying fish with swimbladders. The towed system contains broadband acoustic channels collectively spanning the frequency range 1.7–100 kHz, with some gaps. Using a pulse-compression technique, the range resolution of the echoes is ∼20 and 3 cm in the lower and upper ranges of the frequencies, respectively, allowing high-resolution imaging of patches and resolving fish near the seafloor. Measuring the swimbladder resonance at the lower frequencies eliminates major ambiguities normally associated with the interpretation of fish echo data: (i) the resonance frequency can be used to estimate the volume of the swimbladder (inferring the size of fish), and (ii) signals at the lower frequencies do not depend strongly on the orientation of the fish. At-sea studies of Atlantic herring demonstrate the potential for routine measurements of fish size and density, with significant improvements in accuracy over traditional high-frequency narrowband echosounders. The system also detected patches of scatterers, presumably zooplankton, at the higher frequencies. New techniques for quantitative use of broadband systems are presented, including broadband calibration and relating target strength and volume-scattering strength to quantities associated with broadband signal processing.

In conjunction with the GLOBEC (Global Ocean Ecosystems Dynamics) program, measurements of moored currents, temperature and salinity were made during 1994–1999 at locations in 76 m of water along the southern flank of Georges Bank and at the Northeastern Peak. The measurements concentrate on the biologically crucial winter and spring periods, and coverage during the fall is usually poorer. Current time series were completely dominated by the semidiurnal M2 tidal component, while other tidal species (including the diurnal K1 component) were also important. There was a substantial wind-driven component of the flow, which was linked, especially during the summer, to regional–scale response patterns. The current response at the Northeast Peak was especially strong in the 3–4 days period band, and this response is shown to be related to an amplifying topographic wave propagating eastward along the northern flank. Monthly mean flows on the southern flank are southwestward throughout the year, but strongest in the summertime. The observed tendency for summertime maximum along-bank flow to occur at depth is rationalized in terms of density gradients associated with a near-surface freshwater tongue wrapping around the Bank. Temperature and salinity time series demonstrate the presence, altogether about 25% of the time, of a number of intruding water masses. These intrusions could last anywhere from a couple days up to about a month. The sources of these intrusions can be broadly classified as the Scotian Shelf (especially during the winter), the Western Gulf of Maine (especially during the summer), and the deeper ocean south of Georges Bank (throughout the year). On longer time scales, the temperature variability is dominated by seasonal temperature changes. During the spring and summer, these changes are balanced by local heating or cooling, but wintertime cooling involves advective lateral transports as well. Salinity variations have weak, if any, seasonal variability, but are dominated by interannual changes that are related to regional- or basin-scale changes. All considered, Georges Bank temperature and salinity characteristics are found to be highly dependent on the surrounding waters, but many questions remain, especially in terms of whether intrusive events leave a sustained impact on Bank waters.

The Gulf of Maine Ocean Observing System (GoMOOS) was established in the summer of 2001 as a prototype real-time observing system that now includes eleven solar powered buoys with physical and optical sensors, four shore-based long-range HF radar systems for surface current measurement, operational circulation and wave models, satellite observations, inshore nutrient monitoring, and hourly web delivery of data. The observing system in the Gulf of Maine (GoM) is one of the most comprehensive and operational of the Integrated Ocean Observing Systems (IOOS) systems that have been established in the United States to date. It has also been a very successful system, with data returns routinely in the 85-95% range.The Gulf of Maine is a harsh operational environment. Winter storms pose severe challenges, including high waves and the build-up of sea ice on buoy sensors, superstructure, and solar panels, and in summer its productive waters present severe biofouling problems that can affect the optical sensors. The periods of most difficult field operations often coincide with periods of greatest data value in terms of marine safety, search and rescue, and monitoring biological productivity.The challenges of the Gulf of Maine physical environment were paired with the unexpected challenges of the funding environment that have been the hallmark of the turn of this century. Funding for the system has been chronically short and subject to the unpredictable fluctuations of the congressional appropriations process. The inadequacy and variability of funding has substantially hampered the operations of many of the Integrated Ocean Observing Systems, including GoMOOS, and has hindered technological advancements and maintenance measures. As a result, the design of the GoMOOS infrastructure is little improved from that developed almost a decade ago, and it has deteriorated with age, usage, and suboptimal replacement schedules. In the absence of an adequate and reliable funding stream, the system is fast approaching the end of its expected operational lifetime. Unless this trend is reversed, the system will no longer well serve the many citizens, organizations, and agencies that have come to rely on the data it provides.In this article, we present lessons learned by the scientific and technical groups that have been responsible for the data acquisition of GoMOOS. We believe that these lessons are generic, rather than peculiar to the GoMOOS system, and that they have value for others who are embarking on similar endeavors. However, it is important to make clear that these lessons are from the perspective of the scientists, and that the views of others involved in complementary aspects of GoMOOS, including public outreach, fundraising, and providing data and products to the more general user community, are not represented here.

A study is conducted to validate a numerical model for calculating mooring system tensions of a large fish farm containing 20 net pens in the absence of waves. The model is forced using measured current velocity values obtained outside of the farm. Mooring line tensions calculated with the numerical model are compared with load cell field data sets. The approach considers current velocity reduction and load characteristics that occur through the net pen system for both clean and fouled net conditions. Without accounting for the reduction, the numerical model produces excessively conservative results. With reduction, a substantial improvement occurs. Understanding these differences will help to establish appropriate safety factors when designing large marine fish farms using the model. Additional validation studies should be conducted with wave and current forcing to investigate the modeling of large fish farms for exposed or open ocean sites.

Several experiments to measure postimpact burial of seafloor mines by scour and fill have been conducted near the Woods Hole Oceanographic Institution's Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). The sedimentary environment at MVCO consists of a series of rippled scour depressions (RSDs), which are large scale bedforms with alternating areas of coarse and fine sand. This allows simultaneous mine burial experiments in both coarse and fine sand under almost identical hydrodynamic forcing conditions. Two preliminary sets of mine scour burial experiments were conducted during winters 2001-2002 in fine sand and 2002-2003 in coarse sand with a single optically instrumented mine in the field of view of a rotary sidescan sonar. From October 2003 to April of 2004, ten instrumented mines were deployed along with several sonar systems to image mine behavior and to characterize bedform and oceanographic processes. In fine sand, the sonar imagery of the mines revealed that large scour pits form around the mines during energetic wave events. Mines fell into their own scour pits, aligned with the dominant wave crests and became level with the ambient seafloor after several energetic wave events. In quiescent periods, after the energetic wave events, the scour pits episodically infilled with mud. After several scour and infilling events, the scour pits were completely filled and a layer of fine sand covered both the mines and the scour pits, leaving no visible evidence of the mines. In the coarse sand, mines were observed to bury until the exposed height above the ripple crests was approximately the same as the large wave orbital ripple height (wavelengths of 50-125 cm and heights of 10-20 cm). A hypothesis for the physical mechanism responsible for this partial burial in the presence of large bedforms is that the mines bury until they present roughly the same hydrodynamic roughness as the orbital-scale bedforms present in coarse sand.

As wild fish stocks decline, marine aquaculture is expected to play an increasing role in satisfying the global need for seafood. Since the expansion of near-shore aquaculture is becoming more difficult because of multi-use issues and environmental impact concerns, the feasibility of moving aquaculture into the open ocean is being studied. To enable the optimum design and evaluation of fish cage and mooring performance in the energetic open ocean, physical and numerical modeling techniques are being utilized. To validate these methods, the dynamics of a fish cage and mooring system deployed in the Gulf of Maine are simulated with physical and numerical models and compared with field observations. Assuming that the system can be modeled as a linear system, a stochastic approach was used to analyze the motion response (heave, surge and pitch) characteristics of the fish cage and the load (tension) response in an anchor line to wave forcing. Transfer functions were calculated from field observations for storm events and used to understand the system dynamics and to validate the models for the deployed system. Fish cage heave and surge motions were found to be overdamped, while pitch exhibited a resonance at low frequencies (less than 0.1 Hz). Transfer functions for anchor line tension were consistent with observations over most of the wave frequencies. The physical model clearly revealed the pitch resonance, while the numerical model was better at predicting mooring line tension. Results also provided insight concerning dynamical processes that require further study, including fluid–net panel interaction, transfer function amplitude dependence and the nonlinear relationship between steady current and wave fluid velocity on drag and its effect on system geometry and therefore response.

The Woods Hole Oceanographic Institution (WHOI) and Dalhousie University conducted a sediment transport study at the LEO-15 observatory maintained by Rutgers University and WHOI engineers off the central New Jersey coast. This study was designed to take advantage of the unique capabilities (power and telemetry) provided at the site. The various sensing systems were attached to a bottom-mounted frame and connected by divers to the underwater-mateable guest ports on the LEO-15 node. The node supplied power for the various acoustic and electronic systems and provided telemetry for control of the remote instrumentation and acquisition of several GBytes of data per day. A shore-based support station of several PCs and workstations networked together and connected to the Internet was set up at Rutgers Tuckerton Field Station to receive, display and store this data. Instrumentation was deployed in mid-November 1999, remained active until Christmas 1999, and was recovered in January 2000. The methodology of using the LEO-15 observatory was different from previous approaches used by the WHOI and Dalhousie sediment transport teams and had some subtle problems not obvious until the equipment was set up and utilizing the observatory. A second LEO-15 node, on shore at the Tuckerton field station, facilitated testing of each subsystem and the fully integrated system before offshore deployment. One set of problems involved the node's ground fault detection system that was designed to shut down all scientific instrumentation to protect the node when a current leak to seawater was detected on any power or telemetry line. WHOI connected all their sensing systems together to provide an optimum test of any system problem. Dalhousie had isolated their instrumentation (power and communications) so the ground fault circuit only tested the cables from the LEO-15 node to their electronics. The WHOI instrumentation developed a slowly increasing ground fault in one line that resulted in some unnecessary data loss. The underwater-mateable connectors required at the LEO-15 sometimes showed a low ground fault level leakage that disappeared when they were reconnected. Because or the constant power source, the electronics on the tripod remained powered up and active during the deployment, and individual sensors were powered and burst-sampled once or twice an hour, collecting /spl sim/4 GBytes of data per day that was telemetered to shore. WHOI's high-speed link operated successfully at /spl sim/400 kbits/sec and Dalhousie's at 2 Gb/s. Dalhousie experienced some problems with their remote system suddenly stopping that may be associated with changes made to interface it with the LEO-15 observatory. All data were archived at the Tuckerton facility as the Internet link to WHOI and Dalhousie could only provide 1/3 of the required speed to transmit the data collected daily. In spite of these problems, the systems worked much of the time and collected many gigabytes of data on the suspended sediment transport and structure in relationship to bedform roughness, and wave and current forcing. Real-time sensor functionality and data acquisition operations were monitored over the Internet. The goal of plugging instruments into the LEO-15-node and obtaining continuous long time-series remotely with no interruptions is not yet fully realized. Someone had to monitor the connection to keep systems functioning optimally. However, we learned much of the methodology to move toward full remote operations in the future which will improve future observatories, such as the new Martha's Vineyard Coastal Observatory.

Observations of cross-shelf sediment transport conducted in the winter of 1997–1998 as part of the STRATAFORM program reveal that gravitationally forced density flows of fluid mud trapped within the thin wave bottom boundary layer provide a mechanism for forming flood deposits on the Eel river continental shelf. The data from two moored tripods located on the 20 and 60 m isobaths combined with “rapid response” hydrographic surveys, indicate a process whereby the Eel River delivers sediment on to the inner shelf faster than dispersal and transport processes are able to move it offshore. The river does not deliver sediment beyond the inner shelf because the plume is trapped along the coast due to onshore surface flow associated with downwelling favorable winds. However, the final flood deposition region is located seaward of the 50-m isobath. Acoustic backscattering data taken on the 60-m isobath (in the historic flood deposit region) show two depositional events of 6 and 13 cm during a period of high river discharge and high waves in January of 1998. These depositional events are associated with fluid mud layers that scale in thickness with the wave boundary layer. Velocity profiles from a vertical array of current meters spanning the bottom 2 m of the water column show that the current meter closest to the seafloor has the largest offshore velocity during the depositional events, indicating an offshore flow of the fluid mud from the inner shelf to the flood deposit region. During periods of low concentration suspended sediment transport without fluid mud layers present, either no deposition or erosion was found indicating that the offshore flow of the fluid mud is the dominant depositional mechanism.

Studies and models of sediment transport in the bottom boundary layer require knowledge of the bottom roughness as a parameter affecting the suspension and transport of sediment. Knowledge of this has often been quite imprecise since measurements could only be made from diver observations or camera pictures at times when the water was clear. A self-contained, tripod-mounted rotating-beam sonar system has been developed, which allows bottom topography to be imaged on scales of a few square centimeters out to 4-m radius at regular intervals in time. Most importantly, this system produces images during high suspended sediment concentration transport events, when knowledge of the bottom structure and movement is most crucial. To accomplish this, a Simrad/Mesotech sonar head was adapted as the sensing element for remote use. A separate self-contained controller/recorder was constructed and housed in its own pressure case with sufficient battery and storage capacity for up to six months deployment with...

The LISST (Laser In Situ Scattering and Transmissometery) instrument was designed by Sequoia Scientific to measure the particle size distributions and concentrations of sediment suspensions in the field environment. To understand the LISST's performance with natural sediments from a variety of marine sources, several experiments were performed to compare the LISST's results to traditional sieving, filtering and weighing techniques. The LISST was able to correctly locate the peak of a unimodal particle size distribution and resolve the two peaks of a bimodal distribution if they are separated by at least 1φ for sediment sizes of 5 to 250 μm. Unlike a single frequency scattering sensor for sediment concentration, which require sediment size specific calibration constants, the LISST is able to accurately measure sediment concentration with a single calibration constant for varying size distributions within the size range of 5 to 250 μm. The LISST was also found to adequately represent the particle volumetric size distribution for two different samples from marine environments.

Energetic waves, strong bottom currents, and relatively high rates of sediment discharge from the Eel River combined to produce large amounts of suspended-sediment transport on the inner continental shelf near the Eel River during the winter of 1995–1996. Bottom-boundary-layer (BBL) measurements at a depth of ∼50 m using the GEOPROBE tripod showed that the strongest near-bottom flows (combined wave and current speeds of over 1 m/s) and highest sediment concentrations (exceeding 2 g/l at ∼1.2 m above the bed) occurred during two storms, one in December 1995 and the other in February 1996. Discharge from the Eel River during these storms was estimated at between 2 and 4×103 m3/s. Suspended-sediment flux (SSF) was measured 1.2 m above the bed and calculated throughout the BBL, by applying the tripod data to a shelf sediment-transport model. These results showed initially northward along-shelf SSF during the storms, followed by abrupt and persistent southward reversals. Along-shelf flux was more pronounced during and after the December storm than in February. Across-shelf SSF over the entire measurement period was decidedly seaward. This seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region. Sediment ripples and larger bedforms were observed in the very fine to fine sand at 50-m depth using a sector-scanning sonar mounted on the tripod. Ripple wavelengths estimated from the sonar images were about 9 cm, which compared favorably with photographs of the bottom taken with a camera mounted on the tripod. The ripple patterns were stable during periods of low combined wave–current bottom stresses, but changed significantly during high-stress events, such as the February storm. Two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement. These changes are thought to have been caused principally by the migration of low-amplitude, long-wavelength sand waves into the measurement area.

Observations of the temporal evolution of the geometric properties and migration of wave-formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements. Six weeks of bedform observations were taken at the sandy (medium to coarse sized sand) LEO-15 site located on Beach Haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar. During this period, six tropical storms, several of hurricane strength, passed to the east of the study site. Ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed. The predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3/4 of the wave orbital diameter. Although orbital diameters become larger than 130 cm during the maximum wave event, it is unclear if a transition to non-orbital scaling is occurring. Ripple migration is found to be directed primarily onshore at rates of up to 80 cm/day. Suspended transport due to wave motions, calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements, are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration. Thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near-bottom suspended transport. Bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates. Sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction, as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave-to-current velocities.

As part of the 1990–1991 Sediment TRansport Events on Shelves and Slopes (STRESS) experiment, a 5 MHz Acoustic BackScatter System (ABSS) was deployed in 90 m of water to measure vertical profiles of near-bottom suspended sediment concentration. By looking at the vertical profile of concentration from 0 to 50 cm above bottom (cmab) with 1 cm vertical resolution, the ABSS was able to examine the detailed structure of the bottom boundary layer created by combined wave and current stresses. The acoustic profiles clearly showed the wave-current boundary layer, which extends to (order) 10 cmab. The profiles also showed evidence of an “intermediate” boundary layer, also influenced by combined wave and current stresses, just above the wave-current boundary layer. This paper examines the boundary-layer structure by comparing acoustic data obtained by the authors to a 1-D eddy viscosity model formulation. Specifically, these data are compared to a simple extension of the Grant-Glenn-Madsen model formulation. Also of interest is the appearance of apparently 3-D “advective plume” structures in these data. This is an interesting feature in a site which was initially chosen to be a good example of (temporally averaged) 1-D bottom boundary-layer dynamics. Computer modeling and sector-scanning sonar images are presented to justify the plausibility of observing 3-D structure at the STRESS site. © 1997 Elsevier Science Ltd

During the 1988–1989 Sediment Transport Events on Shelves and Slopes (STRESS) experiment, a 1-MHz acoustic backscatter system (ABSS), deployed in 90 m of water off the California coast measured vertical profiles of suspended sediment concentration from 1.5 to (nominally) 26 meters above bottom (m.a.b.). An 8-week-long time series was obtained, showing major sediment transport events (storms) in late December and early January. Comparison of the acoustics measurements from 1.5 m.a.b. are made with optical backscatter system (OBS) concentration estimates lower in the boundary layer (0.25 m.a.b.). Correlations between ABSS and OBS concentration measurements and the boundary layer forcing functions (waves, currents, and their non-linear interaction) provided a variety of insights into the nature of the sediment transport of the STRESS site. Transport rates and integrated transport are seen to be dominated by the largest storm events.

During the winter of 1990–1991 an Acoustic BackScatter System (ABSS), five Optical Backscatterance Sensors (OBSs) and a Laser In Situ Settling Tube (LISST) were deployed in 90 m of water off the California coast for 3 months as part of the Sediment Transport Events on Shelves and Slopes (STRESS) experiment. By looking at sediment transport events with both optical (OBS) and acoustic (ABSS) sensors, one obtains information about the size of the particles transported as well as their concentration. Specifically, we employ two different methods of estimating “average particle size”. First, we use vertical scattering intensity profile slopes (acoustical and optical) to infer average particle size using a Rouse profile model of the boundary layer and a Stokes law fall velocity assumption. Secondly, we use a combination of optics and acoustics to form a multifrequency (two frequency) inverse for the average particle size. These results are compared to independent observations from the LISST instrument, which measures the particle size spectrum in situ using laser diffraction techniques. Rouse profile based inversions for particle size are found to be in good agreement with the LISST results except during periods of transport event initiation, when the Rouse profile is not expected to be valid. The two frequency inverse, which is boundary layer model independent, worked reasonably during all periods, with average particle sizes correlating well with the LISST estimates. In order to further corroborate the particle size inverses from the acoustical and optical instruments, we also examined size spectra obtained from in situ sediment grab samples and water column samples (suspended sediments), as well as laboratory tank experiments using STRESS sediments. Again, good agreement is noted. The laboratory tank experiment also allowed us to study the acoustical and optical scattering law characteristics of the STRESS sediments. It is seen that, for optics, using the cross sectional area of an equivalent sphere is a very good first approximation whereas for acoustics, which is most sensitive in the region ka ∼ 1, the particle volume itself is best sensed. In concluding, we briefly interpret the history of some STRESS transport events in light of the size distribution and other information available. For one of the events “anomalous” suspended particle size distributions are noted, i.e. larger particles are seen suspended before finer ones. Speculative hypotheses for why this signature is observed are presented.

The University of New Hampshire (UNH), in collaboration with the University of Maine at Orono (UMO) and the University of Montana, has been monitoring surface ocean dissolved carbon dioxide and oxygen in the Northeast Channel, at a site on the northeast flank, of the Gulf of Maine for the last several years. UMO has maintained a buoy at this site (Buoy N) since 2004, and UNH has deployed two instruments (the SAMI-CO 2 Sensor (Sunburst Sensors, LLC) and an Aanderraa Instrument Oxygen Optode 3835) since March 2008. The controls on the CO 2 system are examined to determine the dominating biological seasonal influences that occur alongside physical processes. We evaluate several approaches to isolate these factors and processes using the buoy data and following previous studies. Preliminary results suggest measurable interannual biochemical variability may be attributed to water mass dynamics at this site.

[1] Ocean surface layer carbon dioxide (CO2) data collected in the Gulf of Maine from 2004 to 2008 are presented. Monthly shipboard observations are combined with additional higher-resolution CO2 observations to characterize CO2 fugacity (fCO2) and CO2 flux over hourly to interannual time scales. Observed fCO2 and CO2 flux dynamics are dominated by a seasonal cycle, with a large spring influx of CO2 and a fall-to-winter efflux back to the atmosphere. The temporal results at inner, middle, and outer shelf locations are highly correlated, and observed spatial variability is generally small relative to the monthly to seasonal temporal changes. The averaged annual flux is in near balance and is a net source of carbon to the atmosphere over 5 years, with a value of +0.38 mol m−2 yr−1. However, moderate interannual variation is also observed, where years 2005 and 2007 represent cases of regional source (+0.71) and sink (−0.11) anomalies. We use moored daily CO2 measurements to quantify aliasing due to temporal undersampling, an important error budget term that is typically unresolved. The uncertainty of our derived annual flux measurement is ±0.26 mol m−2 yr−1 and is dominated by this aliasing term. Comparison of results to the neighboring Middle and South Atlantic Bight coastal shelf systems indicates that the Gulf of Maine exhibits a similar annual cycle and range of oceanic fCO2 magnitude but differs in the seasonal phase. It also differs by enhanced fCO2 controls by factors other than temperature-driven solubility, including biological drawdown, fall-to-winter vertical mixing, and river runoff.

The University of New Hampshire is studying CO 2 gas exchange, ocean acidification, air-sea dynamics, and associated biological processes in the western Gulf of Maine. Three buoys and shipboard cruises have provided data to support these studies. The first, a CO 2 monitoring buoy, is deployed jointly with NOAA's Pacific Marine Environmental Laboratory and has been moored in 70 m of water northeast of the Isles of Shoals off the Maine coast during the last 4 years. The second, Jeffrey's Ledge Moored Observatory, is a development mooring testing new techniques and is deployed east of Gloucester, MA near our third platform, a dedicated 2D wave measurement buoy. The Jeffrey's Ledge mooring is testing the direct measurement of the wind stress from a discus buoy using a 3-D sonic anemometer along with a motion package to remove buoy motion effects. A fast-rate atmospheric CO 2 sensor is mounted next to the anemometer to evaluate the potential for direct covariance gas flux measurements. Both discus buoys have additional meteorological and oceanographic sensors to provide key supporting measurements and to augment our regional ocean observing system. Long-term data from the CO 2 buoy have helped to quantify the seasonal air-sea flux cycle of CO 2 in the Gulf of Maine, and this buoy site is now the central node for near-term Carbon cycle process control experiments and longer term ocean acidification monitoring in this region. Jeffrey's Ledge buoy momentum flux estimation results indicate reasonable first-order buoy motion corrections, likely flow disturbance leading to a non-zero mean vertical velocity, and possible artifacts due to large azimuthal rotations of the buoy. All aspects are under study. The paired sonic anemometer and open-path CO 2 sensor package shows promise for long-term measurements using solar power. Ten-minute resolution vertical water column oxygen profiles from this mooring show phytoplankton bloom signatures and permit robust net community production estimates in summer and fall 2009. Finally, all three buoys are providing information on mooring response, platform survival/servicing, sensor biofouling, and low-power data system and telemetry issues in the Gulf of Maine region.

The annual evolution of the geostrophic flow structure in the Gulf of Maine was studied with a combined set of moored pressure time-series measurements and five hydrographic surveys from August 1986 through September 1987. A series of quasi-synoptic dynamic height maps depicts a gulf flow structure whose typical spatial scales decrease from order 100 km during the winter to about half that in the summer, when the evolution of surface, intermediate, and deep water masses is most rapid and complex. The unusually large amount of freshwater in the gulf during 1987 was partially responsible for the establishment of a north–south across-gulf front during the summer. Year-long time series of bottom pressure and internal pressure (derived from temperature and conductivity measurements in Georges and Jordan basins) have been differenced with coastal synthetic subsurface pressures (SSP) to yield a history of the basin-scale geostrophic flow variability. The basin-scale geostrophic transport was dominated b...

The University of New Hampshire has been involved with an Open Ocean Aquaculture demonstration project for the last 10 years in the western Gulf of Maine. As part of an environmental monitoring program, a mooring has been deployed at the field site 10 km off the New Hampshire coast about 9 months each year. Since 2005, dissolved oxygen sensors have been deployed on the mooring. Oxygen was measured by Sea-Bird SBE-43 sensors powered and recorded by SBE-16 Plus SEACATs located ~22 m depth and ~2 m above the bottom. The sensors were calibrated and checked yearly by Sea-Bird. In-situ calibration of the moored oxygen sensors was also done with water samples and Winkler titrations about 6 times a year from 2005 to 2008. The difference between the moored and water sample oxygen concentrations showed a nearly linear drift with time. The drift rates during each of the years and for each sensor (at different depths) were not the same. As the SBE-43 sensors have no apparent zero drift, the drift was corrected by a time changing sensitivity which was applied to the data. The resulting time-series showed the dissolved oxygen variations with time over a year, and showed low values of dissolved oxygen in the deeper waters in late summer and fall. With the successful correction for the sensor drift, the climatology of the Western Gulf of Maine can be studied in more detail and related to the spring and fall plankton blooms, the biological cycles and health of the Gulf.

A collaboration has been established between the University of New Hampshire's (UNH) Joint Center for Ocean Observing Technology and NOAA's Pacific Marine Environmental Laboratory (PMEL) to adapt and deploy an autonomous carbon dioxide measurement system on a moored platform in the coastal Western Gulf of Maine. This buoy provides high-resolution timeseries measurements of atmospheric and oceanic CO2 values and is useful for the estimation of air-sea CO2 fluxes and monitoring coastal zone biochemistry dynamics. In addition, with its close location to the coast, it allows study of terrestrial air mass effects on marine air-sea CO2 exchange. This paper provides details on the overall system including field validation of buoy observations. This validation includes data from a nearby UNH AIRMAP atmospheric observing station on Appledore Island and a monthly shipboard cruise transect made by the UNH Center for Coastal Ocean Observing. These assets permit evaluation of dissolved oxygen and both air and water CO2 levels.

Open ocean aquaculture will be important in supplying fish as natural fish stocks decline due to environmental changes and overfishing. However, the technology needs to be developed to provide the equipment and methodology for such offshore operations. The University of New Hampshire has been developing and testing systems in the open Gulf of Maine, and has a number of years experience with a feed buoy moored to a fish cage via a stretch hose and elastic tethers. This configuration has survived the Gulf of Maine currents and waves, and continued to feed fish autonomously. The unique tri-mooring is studied via modeling, and observing the wear and behavior for years. The system is robust and has functioned well over the years and is a good candidate for aquaculture operations.

A new echosounder that exploits the resonance frequency of swimbladder-bearing fish is described. The system is a custom configuration of a commercial device originally developed for studying the seafloor and adapted for studying fish. The frequencies span the range 1.7 kHz to 100 kHz, with some gaps, with the lower portion of that range corresponding to the resonance frequency of common adult fish. Through pulse-compression processing of the broadband signals, the range resolution is greatly improved to about 20 cm at the lowest frequencies and about 3 cm at the highest frequencies. As a result of the resonance classification at these low frequencies, significant ambiguities that are normally associated with interpretation of high frequency echosounder data are eliminated. Summarized in this paper are the design and calibration of the system, as well as results from using the system to study schools of fish in the ocean.

This document describes data, sensors, and other useful information pertaining to the moorings that were deployed from the R/V Knorr from July 24th to August 4th, 2006 in support of the SWO6 experiment. The SWO6 experiment was a large, multi-disciplinary effort performed 100 miles east of the New Jersey coast. A total of 62 acoustic and oceanographic moorings were deployed and recovered. The moorings were deployed in a "T" geometry to create an along-shelf path along the 80 meter isobath and an across shelf path starting at 600 meters depth and going shoreward to a depth of 60 meters. A cluster of moorings was placed at the intersection of the two paths to create a dense sensor-populated area to measure a 3-dimensional physical oceanography. Environmental moorings were deployed along both along-shelf and across-shelf paths to measure the physical oceanography along those paths. Moorings with acoustic sources were placed at the outer ends of the "T" to propagate various signals along these paths. Five single hydrophone receivers were positioned on the across shelf path and a vertical and horizontal hydrophone array was positioned at the intersection of the "T" to get receptions from all the acoustics assets that were used during SW06.

The University of New Hampshire has a submerged four grid mooring system off the coast of New Hampshire. To better understand the deployed grid system, a finite element model was built and field measurements of static tensions were taken. The purpose of the finite element model was to better understand the sensitivity of the system to anchor placement. An individual anchor was moved around the designed deployment location to better understand the grid tensions distribution. To take field measurements in the submerged system, a diver deployable instrument was designed. Field measurements reflect upon the accuracy of anchor placement and the effectiveness of the grid.

A critical part of an aquaculture operation is feeding the fish (at the right time, the right amount at the right rate) and monitoring the operation. The UNH Open Ocean Aquaculture demonstration project is working on its third and most ambitious automated, remote feeding buoy for offshore aquaculture operations. A central part of the feeders is a computer and software in the feed buoy, which controls and monitors the operations. This onboard processor has a large variety of tasks. It must start the generator in time for scheduled large power drain activities such as powering lights in the submerged fish cages to delay sexual maturation, and the feeding operations with its pumps, feed augers, feed dosers, etc. Also, the system must monitor of the status of each of these activity as they are taking place. This includes seeing that the generator started properly, that power is on the generator's power bus, and then switching it to the main system power bus. When activities such as feeding are taking place, the system must monitor the quantity of feed in the feed hopper, the rate that the feed is being delivered to the feed hose, and the pressure in the feed hose (to catch any blockages). The system also has a series of critical points that it monitors, such as any water in the buoy, the backup battery voltage, the rate of charge by any solar and wind power system and any critical problems with feeding or other activities. The system is programmed to respond to any problems, such as emergency shut down of the generator should it get too hot, the oil pressure too low, and the fuel level gets low. It will also terminate any feeding activity if the pressure in the feed hose rises indicating blockage. If water is detected in the buoy, indicating a leakage in the buoy itself or from one of the subsystems, the system sends an alert to shore as well as turns off any critical activities and making sure that all bilge pumps are active. The programmed activities are controlled by a series of files stored on compact flash in the computer. The system checks each hour to see if an activity is scheduled, then reads another control file (listed in the activities timing file) that will control the details of that activity. If it is feeding time, then it will read the feeding file specified which will tell how fast to feed, for what duration, and what sequence of pumps to use during the feeding process. By referring to different feeding control files, several feeding schedules can be run during one day, or on a weekly cycle. A feeding cycle may include putting a small amount of feed in the hose, then turning on a pump to wash it down to the fish cage, then waiting a little time for the fish to eat that food, and repeating the operation a number of times again. These systems are evolving with the third feed buoy, and lessons learned from the first two are being incorporated into the next

An extensive field study was conducted to investigate the current velocities and mooring system tensions in a 20-unit net pen fish farm located in Eastport Maine, USA, near the Bay of Fundy where extreme tides create strong currents loading fish farm components. To understand the flow characteristics at the site, currents meters were deployed at external and internal farm locations during three distinct operational conditions: (1) clean nets for smolts, (2) clean nets for standard grow out and (3) nets for standard grow out at the end of the stocking schedule, when the gear is fouled with biological material. Also, several load cells were deployed at the same time on important anchor leg and net pen attachment components to measure system loads. The current meter data sets provided evidence of velocity flow reduction through the farm by examining the current meter statistics and tidal harmonic constituents. Tidal analysis also showed substantial tidal harmonics or shallow water tides. The load cells measured maximum loads of 104 kN for anchor leg and 11 kN for net pen lines. The results are significant because few extensive fish farm engineering data sets exist, especially for different combinations of nets and levels of biological fouling. These results are being used in complementary studies to quantify flow reduction, to validate Morison equation type numerical models and as a baseline for specifying offshore fish farm gear.

Funding was provided by the Gulf of Maine Ocean Observing System (GoMOOS under ONR grant N0014-01-1-0999), NOAA-UNH CINEMAR (NOAA Grant Number NA16RP1718), and GLOBEC (NSF OCE93-13670 and OCE02-27679).

Funding was provided by the National Science Foundation under grant numbers OCE-93-13670, OCE-96-32348, OCE98-06379, OCE-98-06445 and OCE-02-27679.

[1] A field program detected direct “crossover” of Scotian Shelf Water (SSC) from Browns to Georges Bank during winter/spring 1999 using (1) moored measurements, (2) drogued drifters, and (3) satellite imagery. Statistics of the 30-day trajectories indicate that (18, 55) ± 17% of the drifters crossed the (100, 200) m isobaths on Georges Bank. Transit times ranged from 2 to 26 days. Four of the drifters crossed onto the Northeast Peak (NEP) coinciding with the detection of Scotian Shelf Water at the central NEP mooring. These events are deemed “significant” because they serve to deliver particles from the Scotian Shelf directly to the gadoid spawning grounds on Georges Bank. Depths of the SSC layers lie between 15 and 50 m, and “residence times” for the Scotian Shelf Water on the NEP are estimated at 3 to 4 weeks. Canonical correlation analysis of the NEP temperature and salinity records suggest that 10% of the correlation structure among the variables is related to SSCs, while 70% is associated with the annual cycle. A search for SSC driving mechanisms reveals that (1) interannual variability of the annual freshwater discharge from the Gulf of St. Lawrence is not a factor, (2) Ekman-like response of near-surface currents to southeast wind stress plays a role but is not the dominant factor, and (3) mesoscale baroclinic features penetrating Northeast Channel from offshore are the most likely cause. Furthermore, the incidence of SSCs may be related to offshore fronts whose proximity is positively correlated with the North Atlantic Oscillation index.

Within the last 2 years, a powerful new set of instruments have been developed which promise to address the measurement needs of the sediment transport community. The sediment transport researcher needs 3 measurements having to do with sediments: concentration of sediments with sufficient size resolution, the settling velocities of these size classes independently of each other, and the 'reference concentration' of these various size classes. The last of these lists the concentration at a small distance above the seafloor; it is the bottom boundary condition specifying the sediment concentration at, or flux off the bed in relationship to applied hydrodynamic stress. The suite of instruments described in this paper covers these needs, with only the continuing deficiency of assumed sphericity and homogeneity of individual particles. In this paper, the authors stress the engineering aspects, illustrating performance with data as available.

Funds provided in 2000 have resulted in creation of the Gulf of Maine Ocean Observing System (GoMOOS), which includes a technical program implemented by scientists at University of Maine, Bigelow Laboratory of Ocean Sciences, Bedford Institute of Oceanography-and Woods Hole-Oceanographic Institution, 10 buoys collecting real-time observations of the ocean and atmosphere, predictive models of waves and circulation testing of new technologies for monitoring nutrients and zooplankton, coordination of satellite measurements, a data management system, a website to disseminate the information a non-profit with over 30 institutions representing users and a headquarters in Portland, ME.

LONG TERM GOALS. The long-term goal of this project is to develop quantitative models of sediment transport, resuspension, deposition and accumulation on the continental margin. OBJECTIVES. The objectives of this research are 1) to characterize the structure of the river plumes and coastal currents in the western Adriatic Sea and their influence on sediment dispersal from Alpine and Apennine rivers; 2) to assess the relative contributions of Alpine and Apennine rivers to the clinoform development in the Adriatic, and to determine the delivery mechanism of these different sources; 3) to determine the mechanisms and rates of sediment resuspension and bottom-boundary-layer sediment transport in the western Adriatic; 4) to determine how bottom-boundary-layer processes influence the patterns of erosion and deposition in the western Adriatic.

Our goals are to understand the physics of acoustic/internal wave interaction on the world s continental shelves, the acoustic signal variability resulting from such interaction, and the dynamics of shelf internal waves.

As the aquaculture industry considers moving into the open ocean, understanding the dynamic response of fish containment structures becomes critical. Identification of possible resonant conditions and motion characteristics is necessary for system structural integrity and maximizing fish survivability. In this study, heave (vertical motion) free release tests of a central spar fish cage were conducted using a combination of physical and finite element models and field observations. These tests were performed to investigate the added mass, damping ratio and natural period of the system in the vertical direction. The test results were analyzed considering both linear and nonlinear damping. The comparison of these tests show that (1) the damped natural period of this fish cage is longer than 20 seconds, (2) the numerical model underestimates the damping and the cage oscillates longer and at a higher frequency than observed with the field tests and (3) the physical model is nearly critically damped near equilibrium due to Reynolds number effects at the model scale.Copyright © 2002 by ASME

Our research program focuses on identifying and quantifying sediment erosion, transport, and deposition processes on the continental shelf through state-of-the-art observational techniques in both fine grained and sandy environments. In sandy environments our goal is to understand the detailed interactions and feedbacks between hydrodynamics, bedforms, and the resulting sand transport. In fine-grained environments we have been investigating the role fluid mud flows as a depositional mechanism in areas with high deposition rates.

Fudning was provided by National Oceanic and Atmospheric Adminstration for the Open Ocean Aquaculture Project under Contract No. NA86RG0016 to the University of New Hampshire and under Subcontracts 00-394 and 01-442 to the Woods Hole Oceanographic Institution.

Funding was provided by the National Science Foundation under Grant Numbers OCE-98-06379 and OCE-98-06445.

Funding was provided by the Office of Naval Research under Grant Numbers N00014-01-1-0772, N00014-98-1-0413 and N00014-00-1-0206.

Fudning was provided by the National Oceanic and Atmospheric Adminstration for the Open Ocean Aquaculture Project under Contract No. NA86RG0016 to the Univesity of New Hampshire and under Subcontracts 00-394 and 01-442 to the Woods Hole Oceanographic Institution.

The overall goal of our research effort is to understand (1) the processes which govern sediment transport in the bottom boundary layer (including suspended, bedload and bedform transport), (2) the relationship of suspended and bedload transport to the bedforms and wave and current forcing, and (3) how these affect strata formation on the continental shelf. With a combined observational and theoretical approach, data is being obtained to improve models of suspended and bedload transport which will allow better predictions of sediment and contaminate transport. Our goal in STRATAFORM is to advance the understanding of the bottom sediment transport processes (resuspension and transport as suspended sediment and movement along the bottom in bedforms) and improve modeling of sediment transport, particularly the movement in the bottom meter of the water column, related to the cross shelf movement and deposition of sediment from the Eel river.

The Massachusetts Bays Program made bottom pressure and water velocity observations in Massachusetts and Cape Cod Bays during 1990 and 1991. In the Bays, the sea surface elevation appeared to rise and fall in phase with equal amplitudes at each diurnal or semidiurnal tidal frequency. There is some amplification in Boston and Provincetown harbors. The semidiurnal tides (particularly the M2 constituent) dominate. Massachusetts and Cape Cod Bays are part of the Gulf of Maine/Bay of Fundy system which is resonant near the semidiurnal tidal frequency. This resonance amplifies they importance of the semidiurnal tides so that diurnal and higher harmonic tides become negligible. The sea level tides force currents which move with the same frequencies, but whose amplitudes are affected by the bathymetry. The strongest currents exist in the channel between Race Point and Stellwagen Bank where tidal currents exceed 1 knot. Analysis of current records for their tidal signal is complicated by internal tides which contaminate the records. These internal waves at tidal frequency exist on the stratification in the water column, and disappear during winter well-mixed times. At other times they must be considered as a significant source of energy for mixing and resuspension of sediments.

A commercial system originally designed for surveying the seafloor has been adapted for measuring the swimbladder resonance of swimbladder‐bearing fish. The new towed system has three broadband active acoustic echosounders with nearly continuous coverage of the frequency band 2–110 kHz (with some gaps). The lower frequency bands are used for measuring the resonance, while the highest band can detect zooplankton. A pulse‐compression approach (cross correlating the transmit waveform with the echoes) is used to exploit the bandwidth through significantly improving the range resolution to 20, 10, and 2 cm (low‐, med‐, and high‐frequency bands, respectively). The system has been successfully deployed as deeply as 200 m and observed resonances at approximately 3 kHz for herring. Because of the 10–20‐cm range resolution at the low frequencies, fish near the towbody could be resolved from one another and fish swimming within 1 m of the seafloor could be distinguished from the seafloor. This system is compared with previous approaches of measuring swimbladder resonance. The potential of the resonance classification method for significantly reducing ambiguities associated with interpreting acoustic echo data compared with traditional high‐frequency narrow‐band systems (10’s to 100’s of kHz) is discussed.