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It has been historically documented that deep, nutrient-rich, offshore slope waters that enter the Gulf of Maine through the Northeast Channel are the principal source of nutrients to the region. Silicate (Si(OH)4) and nitrate (NO3) in particular are potentially limiting nutrients for phytoplankton production. We examine here the extent to which nutrient variability in the region may be caused by internal recycling of organic material (i.e., chemical breakdown and dissolution of diatoms) versus variability in water mass sources, which can be identified by temperature and salinity properties. We present here the results from a gulf-wide survey conducted in October 2016. Nutrient samples were collected at 44 stations and compared to temperature, salinity, and beam attenuation profiles. Additionally, suspended particulate material in near-bottom waters was collected on filters at all stations and analyzed for biogenic silica. The results show that after being supplied via a slope water source, nitrate is likely to become depleted and silicate is likely to become enriched at any location in the gulf. We suspect that most of the nutrient variability is due to internal recycling, but there is evidence for an input of Scotian Shelf Water to the Jordan Basin region contributing nutrients at mid-depths and mixing with the deeper slope waters.

The dramatic marine environmental change seen today can be difficult to fully document and interpret without adequate, spatially and temporally comprehensive, baseline datasets of hydrographic properties. Here we present isotope data measured in water samples collected during a nine-day research cruise in October 2016 throughout the Gulf of Maine, a rapidly changing region of the world's oceans. A comparison of the oxygen isotopes of the water (δ18Owater) and salinity data reveal that water samples fall on a tight, linear mixing line between fresher shelf water and saltier slope waters, with the freshwater endmember originating from much higher latitudes (the Gulf of St. Lawrence and the Labrador Sea). Some subtle differences in freshwater endmembers are observed between the three different deep basins in the Gulf of Maine. These differences are likely reflecting differences in freshwater input and vertical mixing between the different basins. Additionally, these water samples have lower δ18Owater values for a given salinity value than previously published values of marine water mass endmembers. This offset may be related to systematic changesin water mass endmember values or year to year variability, as well as differences in the proportions of water masses entering the Gulf of Maine. Nitrogen and oxygen isotopes of dissolved nitrate (NO3−; δ15NNO3- and δ18ONO3-, respectively) measured in the water samples suggest a strong influence of phytoplankton assimilation near the surface in both isotopic systems. Combining these two datasets using Δ(15, 18) to look at the rates of fractionation between the two isotope systems reveals potential water column nitrification above 100 m in most places in the Gulf of Maine. This finding provides support for previous hypotheses of water column nitrification in the Gulf of Maine based on nutrient distribution and nitrogen box modeling. However, these calculations rely on the assumption that all nitrate is sourced from deeper waters. It is possible these results are instead caused by NO3− from different sources at the surface and therefore do not necessarily indicate the presence of nitrification.

The velocity and hydrographic structure across Broad Sound, a north-south orientated subsystem of Casco Bay, ME that lacks continuous coastal boundaries, were characterized using velocity observations from two moorings in late summer/fall of 2013 and velocity and density observations from a repeat-transect ship survey conducted over a tidal cycle during the same period. At tidal time scales, the system is dominated by a barotropic semidiurnal standing wave with a west to east decrease in tidal amplitude and relatively minimal phase change across the majority of the transect. The stratification (vertical differences of 0.5–1.0 kg m−3) was generally laterally uniform and stronger during the flood phase which is hypothesized to result from stronger offshore stratification. The mean circulation had strong lateral shear with inflow over the deepest point in the bathymetric cross section and eastern slope and outflow over the western slope. There was also vertical shearing of the horizontal velocities with stronger northward (or northward trending) velocities at depth. The depth-averaged subtidal fluctuations were relatively small (∼2–3 cm s−1) and uncorrelated between mooring sites suggesting the vertically uniform current response associated with remote wind forcing is of limited importance. On the other hand, the depth-dependent velocity fluctuations at the subtidal time scale were, in large part (∼36–72%), driven by wind forcing. The net flux ratio, a means of quantifying the relative importance of the vertical and lateral shear in the flow field, was typically ∼0.44 indicating the structure of the local wind response favored vertically sheared flow.

The Gulf of Maine, a semienclosed basin on the continental shelf of the northwest Atlantic Ocean, is fed by surface and deep water flows from outside the gulf: Scotian Shelf Water (SSW) from the Nova Scotian shelf that enters the gulf at the surface and slope water that enters at depth and along the bottom through the Northeast Channel. There are two distinct types of slope water, Labrador Slope Water (LSW) and Warm Slope Water (WSW); it is these deep water masses that are the major source of dissolved inorganic nutrients to the gulf. It has been known for some time that the volume inflow of slope waters of either type to the Gulf of Maine is variable, that it covaries with the magnitude of inflowing SSW, and that periods of greater inflows of SSW have become more frequent in recent years, accompanied by reduced slope water inflows. We present here analyses of a 10-year record of data collected by moored sensors in Jordan Basin in the interior Gulf of Maine, and in the Northeast Channel, along with recent and historical hydrographic and nutrient data that help reveal the nature of SSW and slope water inflows. We show that proportional inflows of nutrient-rich slope waters and nutrient-poor SSWs alternate episodically with one another on timescales of months to several years, creating a variable nutrient field on which the biological productivities of the Gulf of Maine and Georges Bank depend. Unlike decades past, more recent inflows of slope waters of either type do not appear to be correlated with the North Atlantic Oscillation (NAO), which had been shown earlier to influence the relative proportions of the two types of slope waters that enter the gulf, WSW and LSW. We suggest that of greater importance than the NAO in recent years are recent increases in freshwater fluxes to the Labrador Sea, which may intensify the volume transport of the inshore, continental shelf limb of the Labrador Current and its continuation as the Nova Scotia Current. The result is more frequent, episodic influxes of colder, fresher, less dense, and low-nutrient SSW into the Gulf of Maine and concomitant reductions in the inflow of deep, nutrient-rich slope waters. We also discuss evidence that modified Gulf Stream ring water may have penetrated to Jordan Basin in the summer of 2013.

An integrated nutrient observatory is being developed within the Northeastern Regional Association of Coastal Ocean Observing Systems (NERACOOS), capable of monitoring nutrient dynamics year-round at temporal and spatial scales necessary to address critical needs of stakeholders throughout the Northeast region. Nutrient levels and fluxes drive total biological productivity throughout the region, from phytoplankton to commercially exploited fish stocks. Nitrate sensors (Satlantic SUNAs) are being installed on existing mooring assets in western Long Island Sound, Narragansett Bay (Prudence Island), Great Bay in New Hampshire, Massachusetts Bay, three sites along the coastal shelf of the Gulf of Maine (GOM), at five depths in Jordan Basin in the interior GOM, and at two depths in the GOM Northeast Channel. Phosphate and ammonium sensors (WET Labs Cycle-PO4 and Cycle-NH4) are also being deployed at the three nearshore sites. The measurements from these sensors will extend the current sparse, long-term records of nutrients from discretely collected samples in the Northeast region and will dramatically improve temporal resolution and continuity of the data for use in studying potential impacts of climate change. Nearshore measurements will be used by NERACOOS stakeholders to help assess, regulate, and mitigate the adverse impacts on water quality associated with excessive pollutant loadings. Measurements throughout the GOM will be used to assess basin-wide nutrient variability and to initialize harmful algal bloom (Alexandrium fundyense) forecast models.

Rapidly expanding data collections from ocean observing systems create a need for new tools to process, to explore, and to analyze data. This article presents capabilities of the EventViewer in the context of exploring ocean observing system data. The EventViewer is a graphical user interface for visualizing and exploring patterns in events where events constitute changes of interest in a time series. The EventViewer allows users to make queries on events stored in an events database and explore various spatial, temporal, and thematic patterns in events. Once events are selected, the user can assign event spatial, temporal, and thematic categories to graphic display elements in the interface called bands, stacks, and panels. Selected events are displayed according to their associations with the user-specified categories. The spatial, temporal, and thematic categories can be directly manipulated and rearranged among the bands, stacks, and panels to change the view of events and highlight different patterns. The EventViewer supports exploration of periodic patterns, spatial and temporal trends, and event‐event relationships. The EventViewer functionality is illustrated with oceanographic events extracted from ocean observing system sensor data collected in the Gulf of Maine. Events were extracted from multiple time series variables collected at a number of locations and depths.

We used a coupled biophysical model to investigate larval transport and connectivity patterns in the Gulf of Maine lobster (Homarus americanus) population. Biological ‘particles’ were released at over 21 000 locations every 10 days over a 4-month hatching period, and were followed from hatching through late postlarval stage. In addition to circulation and dispersion, model calculations included spatial patterns of egg production, temporal patterns of hatching, temperature-dependent development, vertical distribution and mortality. We ran the model for three larval production seasons using the same hatching patterns and individual-based modeling parameters but different flow patterns in the coastal current system. Model results gave distribution and abundance patterns of competent postlarvae that closely resembled observed, alongshore patterns of lobster settlement density. We evaluated the relative contribution of all source regions to the total number of competent postlarvae in a series of medium-size zones along the coastal shelf, many of which are used in lobster management. Connectivity depended on many factors, including patterns of egg production and transport, and the location and size of the receiving zones. Self recruitment ranged from a few percent to >90% of competent postlarvae. Although it was common for postlarvae to come from many, often distant, sources, most of the competent postlarvae in a zone originated within one to two zones in the prevailing ‘up-stream’ direction, forming shorter connections along the coast than the energetic currents might otherwise suggest. Inshore migrations during summer hatching may contribute to these shorter patterns of connectivity. Transport in the prevailing ‘upstream’ direction was also indicated.

Two-hundred and twenty seven satellite-tracked drifters were deployed in the Gulf of Maine (GoM) from 1988 to 2007, primarily during spring and summer. The archive of tracks includes over 100,000 kilometers logged thus far. Statistics such as transit times, mean velocities, response to wind events, and preferred pathways are compiled for various areas of the coastal GoM. We compare Lagrangian flow with Eulerian estimates from near-by moorings and evaluate drifter trajectories using Ekman theory and 3-D ocean circulation models. Results indicate that the Gulf of Maine Coastal Current is a strong and persistent feature centered on the 94 ± 23 meter isobath, but that particles: a) deviate from the seasonal-mean core fairly regularly, and are often re-entrained; b) follow a slower (9 cm/s), less-constrained path in the western portion off the coast of Maine relative to the eastern (16 cm/s) section; and c) can be affected by wind events and small scale baroclinic structures. Residence times calculated for each ½ degree grid cell throughout the GoM depict some regions (Eastern Maine and Western Nova Scotia) as being relatively steady, flow-through systems, while others (Penobscot, Great South Channel) have more variable, branching pathways. Travel times for drifters that are retained within the coastal current along the entire western side of the Gulf of Maine are typically less than two months (55 days).

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.

The remarkable increase of Homarus Americanus (lobster) abundance in recent years has resulted in record landings throughout the states and provinces along the perimeter of the Gulf of Maine. A considerable amount of data on various life stages of lobsters has been collected for research, management and conservation purposes over the past 15 years. We have used these data sets to develop models that simulate lobster populations from newly hatched larval stage through settlement and recruitment to the fishery. This paper presents a part of the synthesis study that focuses on the early life history of lobsters. A coupled biophysical individual based model was developed that considers patterns of egg production (abundance, distribution and timing of hatch), temperature-dependent larval growth, stage-explicit vertical distributions of larvae, and mortality. The biophysical model was embedded in the realistic simulations of the physical environment (current and temperature) from the Gulf of Maine Nowcast/Forecast System. The predominant direction of larval movement follows the cyclonic Gulf of Maine Coastal Current (GMCC). Results show relatively low accumulation of planktonic stages along the eastern Maine coast and high accumulation along the western Maine coast. In years when the eastern branch of the GMCC turns offshore southeast of Penobscot Bay, more particles accumulate downstream of the branch point. Interannual variability is also apparent in development times that vary as a function of year-to-year water temperature variation. The larval stages tend to remain relatively near shore, but the final planktonic stage (the postlarva) resides near the sea surface, and the prevailing southwesterly winds in summer cause eastward and offshore drift of postlarvae. Thus, more settlement might take place earlier in the potentially long postlarval stage, and the timing and strength of the southwesterly winds are important in determining the population of potential settlers.

Special issue Gabriel T. Csanady: Understanding the Physics of the Ocean.-- 22 pages, 6 figures Gabriel T. Csanady turned 80 in December 2005 and we celebrate it with this special Progress in Oceanography issue. It comprises 20 papers covering some of the many areas that Gabe contributed significantly throughout his professional career. In this introductory paper we briefly review Gabe’s career as an engineer, meteorologist and oceanographer, and highlight some of his major contributions to oceanography, both as a scientist as well as an educator. But we also use this opportunity to remember and thank Gabe, and his wife Joyce, for being such good friends and mentors to several generations of oceanographers. The authors of the collection of papers in this volume deserve special thanks for their efforts. We also are pleased to acknowledge the support of Progress in Oceanography’s editor, Detlef Quadfasel, and the many anonymous reviewers who generously contributed their time and expertise

A circulation nowcast/forecast system has been developed for the Gulf of Maine as an integral component of the Gulf of Maine Ocean Observing System (GoMOOS). It has been used daily since 2001 to produce short-term forecasts of the circulation and hydrographic properties in the Gulf of Maine. One of the expectations is that the nowcast/forecast system can provide consistent SST to fill in AVHRR data gaps and eventually produce reliable 3D temperature and flow fields for fisheries and other applications. The framework of the nowcast/forecast system is presented, including an algorithm for assimilating satellite-derived SST. Comparisons between the predicted and the observed temperature (both in situ and satellite-derived) and velocity are discussed. In general, the assimilation algorithm is stable and produces robust SST patterns. Seasonal variations in temperature and the coastal current are reasonably reproduced. Correlation between the modeled and observed fields in the synoptic band is summarized for individual buoys in monthly bins. The Root-Mean-Square (RMS) errors for the M2 tidal ellipse are estimated at 1.9 and 1.2 cm s−1 for the major and minor axis, respectively, while the RMS error in ellipse orientation is at 11°.

Exchange of water between eastern Casco Bay and the adjacent Gulf of Maine shelf is examined to assess the circulation processes that impact the distribution and occurrence of a toxic dinoflagellate, Alexandrium fundyense, in eastern Casco Bay. Over the inner shelf adjacent to the bay, tidal variance is weak, and the across-shelf current is highly coherent and in phase with the along-shelf wind stress. Although tidal current variance increases as one advances into the bay, non-tidal currents account for 30–40% of the across-shelf current variance at the bay entrance. Between the shelf and the bay interior is a transition region, where the circulation response to wind forcing changes as the wind adjusts to the changing orientation of the shoreline. Far from shore, the overall large-scale coastline orientation dominates the wind-driven response, but within a few internal Rossby radii, the local coastline clearly dominates the flow patterns and across-shelf wind becomes locally shore-parallel inside the bay. Within the bay interior, the across-shelf wind is highly coherent and in phase with the near-surface subtidal across-shelf current. The Kennebec River north of the study area supplies freshwater to eastern Casco Bay in all seasons. A pool of low-density, relatively fresh water at the entrance to the bay sets up an across-shelf density gradient that is reversed from a typical estuary, and likely contributes to the mean surface on-shelf transport in this region. Surface-drifter trajectories observed over the course of the study suggest that both the across-shelf wind and the across-shelf density gradient are important in driving surface up-bay transport and in the retention of surface-dwelling organisms in eastern Casco Bay.

Blooms of the toxic dinoflagellate, Alexandrium fundyense, are a common feature during the summer months in the Gulf of Maine, potentially resulting in paralytic shellfish poisoning when human beings consume shellfish that have ingested these dinoflagellates. Factors that control the dynamics of offshore blooms, including their timing, distributions and cell densities were investigated on three research cruises in the Gulf of Maine: 25 April to 3 May and 5–14 June, 2000, and 19–28 July, 2001; additional samples were collected by our colleagues on separate cruises in May and June, 2001. Measurements included hydrographic data, concentrations of phytoplankton chlorophyll, inorganic nutrients, cell densities of Alexandrium at standard depths, and near-surface densities of major phytoplankton taxa. The Alexandrium bloom in 2000 began sometime between the April–May cruise, when we observed low Alexandium cell densities (o200 cells L � 1 ), and June, when broad patches of 41000 cells L � 1 were observed. In July of 2001 we observed high cell densities of Alexandrium (410,000 cells L � 1 ), which were most abundant at subsurface depths. Vertical pump samples collected at 1-m resolution in July 2001 revealed high densities of Alexandrium cells in thin layers at depths corresponding to the pycnocline and nutricline. We present evidence that the distributions, abundances and timing of onset of the seasonal Alexandrium bloom may be related to oceanographic processes that control differences in the relative concentrations of dissolved inorganic nitrogen (DIN) and silicate. While by no means conclusive, results are suggestive of an allelopathic interference by diatoms on Alexandrium growth, which might impede the development of high densities of Alexandrium cells. r 2005 Elsevier Ltd. All rights reserved.

The Gulf of Maine Coastal Current (GMCC), which extends from southern Nova Scotia to Cape Cod Massachusetts, was investigated from 1998 to 2001 by means of extensive hydrographic surveys, current meter moorings, tracked drifters, and satellite-derived thermal imagery. The study focused on two principal branches of the GMCC, the Eastern Maine Coastal Current (EMCC) that extends along the eastern coast of Maine to Penobscot Bay, and the Western Maine Coastal Current (WMCC) that extends westward from Penobscot Bay to Massachusetts Bay. Results confirm that GMCC is primarily a pressure gradient-driven system with both principal branches increasing their transport in the spring and summer due to fresh-water inflows, and flowing southwestward against the mean wind forcing during this period. In the spring and summer the subtidal surface currents in the EMCC range from 0.15 to 0.30 ms 1 while subtidal WMCC currents range from 0.05 to 0.15 ms 1 . The reduction of southwestward transport near Penobscot Bay is accomplished via an offshore veering of a variable portion of the EMCC, some of which recirculates cyclonically within the eastern Gulf of Maine. The degree of summer offshore veering, versus leakage into the WMCC, varied strongly over the three study years, from nearly complete disruption in 1998 to nearly continuous through-flow in 2000. Observations show strong seasonal and interannual variability in both the strength of the GMCC and the degree of connectivity of its principal branches. r 2005 Elsevier Ltd. All rights reserved.

Analyses of CTD and moored current meter data from 1998 and 2000 reveal a number of mechanisms influencing the flow along the western coast of Maine. On occasions, the Eastern Maine Coastal Current extends into the western Gulf of Maine where it takes the form of a deep (order 100 m deep) and broad (order 20 km wide) southwestward flow with geostrophic velocities exceeding 20 cm s−1. This is not a coastally trapped flow, however. In fields of geostrophic velocity, computed from shipboard-CTD data, the core of this current is roughly centered at the 100 m isobath and its onshore edge is no closer than 10 km from the coast. Geostrophic velocity fields also reveal a relatively shallow (order 10 m deep) baroclinic flow adjacent to the coast. This flow is also directed to the southwest and appears to be principally comprised of local river discharge. Analyses of moored current meter data reveal wind-driven modulations of the coastal flow that are consistent with expectations from simple theoretical models. However, a large fraction of the near-shore current variance does not appear to be directly related to wind forcing. Sea-surface temperature imagery, combined with analysis of the moored current meter data, suggests that eddies and meanders within the coastal flow may at times dominate the near-shore current variance.

The life cycle of dinoflagellates of the genus Alexandrium includes sexual reproduction followed by the formation of a dormant hypnozygote cyst, which serves as a resting stage. Negatively buoyant cysts purportedly fall to the benthos where they undergo a mandatory period of quiescence. Previous reports of cysts in the surficial sediments of the Gulf of Maine, where Alexandrium blooms are well documented, show a broad distribution of cysts, with highest concentrations generally in sediments below 100 m depth. We report here an exploration of cysts suspended in the water column, where they would be better positioned to inoculate springtime Alexandrium populations. During cruises in February, April, and June of 2000, water samples were collected at depths just off the bottom (within 5 m), at the top of the bottom nepheloid layer, and near the surface (1 m) and examined for cyst concentrations. Suspended cysts were found throughout the Gulf of Maine and westernmost Bay of Fundy. Planktonic cyst densities were generally greater in near-bottom and top of the bottom nepheloid layer samples than in near-surface water samples; densities were of the order of 10 2 cysts m −3 in surface waters, and 10 2 –10 3 cysts m −3 at near-bottom depths. Temporally, they were most abundant in February and least abundant in April. Reports by earlier workers of cysts in the underlying sediments were on the order of 10 3 cysts cm −3 . We present calculations that demonstrate the likelihood of cyst resuspension from bottom sediments forced by swell and tidal currents, and propose that such resuspended cysts are important in inoculating the seasonal bloom. We estimate that suspended cysts may contribute significantly to the annual vegetative cell population in the Gulf of Maine.

The University of Maine Ocean Observing System (UMOOS), a member of the Northeastern Regional Association of Coastal and Ocean Observing Systems (NERACOOS), has been operated by the University of Maine's Physical Oceanography Group (PhOG) since 2001. UMOOS currently maintains five real-time data buoys in the coastal Gulf of Maine (GoM) and two in the offshore GoM. Since September 2013, PhOG has been intermittently deploying Teledyne Webb Slocum G2 gliders to study spatial variability near, and between, several UMOOS data buoys in two principal branches of the Gulf of Maine Coastal Current, the Eastern Maine Coastal Current (EMCC) that extends along the eastern coast of Maine to Penobscot Bay, and the Western Maine Coastal Current (WMCC) that extends westward from Penobscot Bay toward outer Cape Cod. The gliders are equipped with a standard sensor suite that measures salinity, temperature, pressure, chlorophyll 470/695 nm), turbidity, and a dissolved oxygen optode. This manuscript evaluates two of the most recent sensor packages added to the potential payload of gliders: a Teledyne RDI 600 kHz phased-array ADCP and a wave module developed by PhOG in collaboration with Ocean Science and Technology (OST).

Paralytic shellfish poisoning (PSP) occurs nearly every year in the Gulf of Maine. In a study of dynamics of the causative organism, the toxic dinoflagellate Alexandrium sp., we conducted three surveys of the coastal and oshore waters of Gulf of Maine during the summer of 1998, sampling more than 200 stations during each cruise in June, July and August. Hydrographic data were collected and concentrations of phytoplankton chlorophyll, inorganic nutrients and densities of Alexandrium cells were measured in discrete water samples. The distributions of Alexandrium at the surface and in subsurface waters displayed maximum cell densities in the oshore waters of the Gulf on all three cruises. Highest cell densities in surface waters (ca. 5.510 3 cellsl ˇ1 ) were observed in two broad patches: one in the Bay of Fundy and another in shelf and oshore waters of the central and eastern Gulf of Maine in association with the Eastern Maine Coastal Current. Highest subsurface densities of cells appeared to be associated with the frontal edges beyond the cold surface waters associated with the Eastern Maine Coastal Current. As the summer progressed, the highest surface densities of Alexandrium receded toward the eastern portions of the Gulf and the Bay of Fundy. We suggest that the oshore distributions of relatively high densities of Alexandrium are naturally occurring and can be related to inorganic nutrient fluxes, and to the ambient light field as it varies seasonally and vertically. Locations of high cell densities were described and interpreted using a nondimensional light-nutrient parameter, computed as the ratio of the depth of the 10% surface irradiance to the depth of 4mMNO3 concentration. Possible mechanisms responsible for periodic development of PSP outbreaks in nearshore shellfish beds are discussed. # 2001 Elsevier Science Ltd. All rights reserved.

The Princeton Ocean Model is used to study the circulation in the Gulf of Maine and its seasonal transition in response to wind, surface heat flux, river discharge, and the M2 tide. The model has an orthogonal-curvature linear grid in the horizontal with variable spacing from 3 km nearshore to 7 km offshore and 19 levels in the vertical. It is initialized and forced at the open boundary with model results from the East Coast Forecast System. The first experiment is forced by monthly climatological wind and heat flux from the Comprehensive Ocean Atmosphere Data Set; discharges from the Saint John, Penobscot, Kennebec, and Merrimack Rivers are added in the second experiment; the semidiurnal lunar tide (M2) is included as part of the open boundary forcing in the third experiment. It is found that the surface heat flux plays an important role in regulating the annual cycle of the circulation in the Gulf of Maine. The spinup of the cyclonic circulation between April and June is likely caused by the differential heating between the interior gulf and the exterior shelf/slope region. From June to December, the cyclonic circulation continues to strengthen, but gradually shrinks in size. When winter cooling erodes the stratification, the cyclonic circulation penetrates deeper into the water column. The circulation quickly spins down from December to February as most of the energy is consumed by bottom friction. While inclusion of river discharge changes details of the circulation pattern, the annual evolution of the circulation is largely unaffected. On the other hand, inclusion of the tide results in not only the anticyclonic circulation on Georges Bank but also modifications to the seasonal circulation.

Cold surface temperatures, reflecting Scotian Shelf origins and local tidal mixing, serve as a tracer of the Eastern Maine Coastal Current and its offshore extensions, which appear episodically as cold plumes erupting from the eastern Maine shelf. A cold water plume emanating from the Eastern Maine Coastal Current in May 1994 was investigated using advanced very high resolution radiometer (AVHRR) imagery, shipboard surveys of physical and biochemical properties, and satellite-tracked drifters. Evidence is presented that suggests that some of the plume waters were entrained within the cyclonic circulation over Jordan Basin, while the major portion participated in an anticyclonic eddy at the distal end of the plume. Calculations of the nitrate transported offshore by the plume show that this feature can episodically export significant quantities of nutrients from the Eastern Maine Coastal Current to offshore regions that are generally nutrient depleted during spring-summer. A series of AVHRR images is used to document the seasonal along-shelf progression of the coastal plume separation point. We speculate on potential causes and consequences of plume separation from the coastal current and suggest that this feature may be an important factor influencing the patterns and overall biological productivity of the eastern Gulf of Maine.

Springtime distributions of phytoplankton chlorophyll a and nitrate + nitrite on Georges Bank were analyzed for three survey cruises: 17-26 May 1993,7-15 April 1994 and 12-20 May 1994. Results showed that nutrients become depleted over much of the Bank inside the 60 m isobath as a result of the spring phytoplankton bloom, after which relatively high nutrient concentrations were con- fined to the frontal regions around the periphery of the Bank. Highest nutrient concentrations and horizontal gradients occurred along the northern edge and the Northeast Peak, where cross-frontal, on-bank fluxes of new nitrogen onto the Bank were most pronounced. These data, and earlier obser- vations by others that show (i) high rates of primary production on the central Bank despite low nutri- ents, (ii) low f-ratios on the central Bank, (iii) anomalously low secondary production as compared with rates of primary production and (iv) average distributions of zooplankton and gadid spawning areas on the Bank, are interpreted in the context of nitrogen limitation of secondary production. Calculations of cross-bank nutrient fluxes suggest that Georges Bank is too large a geographical feature to function efficiently on nutrients delivered via fluxes from deeper waters around its periph- ery and therefore much of the primary production is recycled. Thus, it follows that production of higher trophic level biomass, from zooplankton to fish, is limited by the frequency and intensity of processes that drive fluxes of deep-water nitrogen onto the Bank.

Covering more than two-thirds of the Earth’s surface, the oceans are a central component of the global climate system. The oceans help to control the timing and regional distribution of the Earth’s response to climate change, primarily through their absorption of carbon dioxide (CO2) and heat. Changes to the physical and chemical properties of the oceans are already being observed. Sea surface temperatures are warming, sea level rise is accelerating, the oceans are becoming increasingly acidic, and the rate of sea ice melt is steadily increasing. The International Panel on Climate Change (IPCC) assessment released in 2007 projects that, due to the persistence of greenhouse gases in the atmosphere, it is highly likely that the oceans will continue to warm and the impacts will be felt for centuries (IPCC, 2007a). This section focuses on the physical and chemical changes currently being observed in the Earth’s oceans, including changes in temperature, stratification, salinity, sea ice, climate regimes, ocean circulation, and ocean acidification. Knowledge gaps and research needs will be discussed throughout. The aim is to assess the current state of knowledge related to how climate change may be interacting with, and in some cases, driving, the observed physical and chemical changes in the Earth’s oceans, and what that means for the U.S.

The hydrography and distributions of cod larvae on Georges Bank were surveyed during two research cruises in April and May 1993 in order to relate larval drift between cruises to the vernal intensification of the frontal component of the residual circulation. We observed the transport of two patches of cod larvae. One patch, which had maximum larval cod densities of 45 larvae 100 m −3 in April, appeared to have been advected south about 75 km between surveys, while the other, which had maximum larval cod densities of 20 larvae 100 m −3 in April, appeared to have been advected north-northeast about 25 km. Maximum larval densities in each patch sampled during the second cruise in May were 15 and 18 larvae 100 m −3 , respectively, and mean growth in total length for larvae in the two patches was approximately 5.5 mm and 4.5 mm, respectively, between the two cruises. During the April cruise there was a large volume of anomalous cold, fresh water, of Scotian Shelf origin, which occupied much of the eastern third of Georges Bank. During May, relatively cold, fresh water appeared in a band from the Northeast Peak along the Southern Flank, between Georges Bank water on the top of the Bank, and upper Slope Water offshore. The distribution of cold, fresh water suggests its participation in the general clockwise circulation around the Bank. The transport of cod larvae comprising the first patch appeared to become organized within, and move along, the frontal boundary established by the Scotian Shelf-like water mass, while larvae in the second patch, which we assumed to have moved to the north, may have been transported northward in an on-Bank flow of warmer and saltier upper Slope Water, which may have originated from a Gulf Stream Ring. Based upon observed transport of the first patch of larvae in relation to the frontal boundary, we present a conceptual model of frontal mixing currents on Georges Bank, where current velocities may reach 5 cm s −1 at the depth of the pycnocline. We suggest that this frontal component of the residual circulation, which is in addition to that resulting from tidal rectification, may be important in the transport of fish larvae, and that interannual variability in the degree of intrusion of extrinsic water masses may contribute to variable larval cod drift patterns, to variable larval cod retention on the Bank, and ultimately, to variable larval fish recruitment to the early juvenile stage.

The Gulf of Maine buoy array of the Northeastern Regional Association of Coastal Ocean Observing Systems (NERACOOS) has been providing continuous oceanographic measurements for over a decade. NERACOOS is one of the eleven regional associations of the US Integrated Ocean Observing System (IOOS). The buoys are deployed and maintained by the Physical Oceanography Group of the University of Maine, initially as part of the Gulf of Maine Ocean Observing System. Analysis of this large timeseries (over 105 samples for a single depth) shows statistically significant warming trends at all depths for all locations, providing the first depth-resolved rates of temperature variability for the U.S. East Coast from continuous data. Analysis steps include quality control of the data, calculation and averaging of daily means and anomalies, according to the decorrelation timescale (∼ 20 days) and calculation of rates of change with linear regression. Use of the decorrelation timescale allows for optimal determination of errors by assessing the number of unique samples within the large dataset, in which observations are closely correlated to adjacent records. There are significant relationships between temperature variability and time (p

Established conceptual models of the initiation and progression of spring phytoplankton blooms are reconsidered in light of recent observations. We use biological simulation modelling as a tool for the analysis of spring plankton blooms in shallow, coastal waters in temperate latitudes of the North Atlantic. The model shows that interannual variability in the timing of bloom initiation arises from year-to-year differences in incident irradiation, as determined by weather (cloudiness). This variability in timing results in some years when the spring bloom occurs in cold water temperatures near 0°C. Model results suggest that due to low temperature inhibition of heterotrophic consumption, more fresh organic material is delivered to the benthos in these cold-water blooms than when the bloom occurs in waters only 3°C warmer. Thus we suggest that variable bloom timing can be important to the trophodynamic fate of bloom products. We suggest that variability in timing of spring phytoplankton blooms in offshore and open ocean waters is also related to weather, through controls on the light field and wind mixing. Our analyses of wind-driven vertical mixing demonstrate such blooms can begin following the winter period of deep convection, and prior to the vernal development of stratification, provided that wind speed is below a certain, predictable threshold, which we estimate. In such cases, there may be several spring bloom pulses, each interrupted by self-shading light limitation or vertical mixing events. Eventually the seasonal thermocline develops and nutrient exhaustion curtails bloom production. This means that the spring phytoplankton bloom in offshore and open ocean areas may be significantly more productive, result in more export production, and be more important to the carbon cycle, than has been previously assumed. Furthermore, these features of temperate marine planktonic ecosystems are not only sensitive to annual variations in weather, but also any trends that might result from greenhouse warming or other factors that affect the climate system.

The coastal ocean observing system in the Gulf of Maine was deployed in the summer of 2001. The system operated a real-time data buoy array that collected oceanographic and meteorological measurements in a 24/7 operation at as many as 11 locations in the Gulf of Maine (GoM). The data return of the GoM sensor array has averaged approximately 90% over its first decade of operation. In addition to the hourly operational data delivery to several online websites, the University of Maine provides an archive of data and model output that are significantly advancing the scientific understanding of the GoM as a physical and ecological system. Over the decade of operation, the data have revealed marked seasonal and interannual variability of the circulation and physical properties of the gulf.

The Northeastern Regional Association of Coastal Ocean Observing Systems (NERACOOS), which began in 2008, includes the University of Maine’s comprehensive data buoy array in the Gulf of Maine (GoM). The University of Maine buoy system started in 2001 as part of the Gulf of Maine Ocean Observing System (GoMOOS). The buoys provide a wide variety of oceanographic and marine meteorological data in real time to scientists, environmentalists, the National Weather Service, the U.S. Coast Guard and Canadian Coast Guard, educators, regional natural resource managers, the GoM fishing and maritime industries, and the general public. The GoM observing system is presently undergoing a redesign of the buoy control system to enhance remote access and reduce operational costs. The enhancements will allow remote trouble-shooting and reprogramming of the buoys and subsurface sensors. The system will also accommodate sensors from other research groups and allow them post-deployment control without assistance from our buoy group.Over the near-decade of operation, the system has revealed marked seasonal and interannual variability of the circulation and physical properties of the GoM. In the fall of 2004 to spring of 2005, Doppler currents measured an outflow of deep salty slope waters that suggest a regime shift in the inflow and outflow of transports through the Northeast Channel. During the same period, a salinity anomaly event lowered salinity throughout the GoM by roughly 2 psu by the winter of 2005. In following years, the previously unusual slope outflow and reduced salinity have often reoccurred.

This paper presents capabilities of the EventViewer, a graphical user interface for visualizing and exploring patterns in events. The EventViewer supports queries on events stored in an events database and exploration of various temporal and spatial patterns in events. Interactions in the EventViewer interface allow users to select events from the database, assign spatial, temporal and thematic categories to graphic display elements called bands, stacks, and panels which causes events to be displayed according to their associations with the user selected categories. The spatial, temporal and thematic categories can be rearranged among the bands, stacks and panels thus changing the view of events and causing different patterns to become apparent. The EventViewer support exploration of periodic patterns, spatial and temporal trends, and event-event relationships. The EventViewer functionality is illustrated with oceanographic events extracted from the Gulf of Maine Ocean Observing system sensor data. Events are extracted from multiple time series variables collected at a number of locations and depths in the Gulf of Maine.

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 surface current systems, circulation and wave models, satellite observations, and hourly web delivery of data. The Gulf of Maine (GoM) is a harsh operational environment. Its winter storms pose severe challenges that include waves exceeding 10 m in height, and the build up of sea ice on buoy superstructure, solar panels, and sensors. In summer the productive waters of the GoM present severe biofouling problems that can affect the optical sensors. These periods of most difficult operations correspond to the periods of greatest data value, in terms of marine safety, search and rescue, and monitoring biological productivity.

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 surface current systems, circulation and wave models, satellite observations, and hourly web delivery of data. The Gulf of Maine is a harsh operational environment. Its winter storms pose severe challenges including 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 operations often coincide with periods of greatest data value in terms of marine safety, search and rescue, and monitoring biological productivity. GoMOOS scientists and engineers continue to refine system designs and operational procedures to moderate the environmental stresses on the sensors and systems.

The Gulf of Maine Ocean Observing System (GoMOOS) is a comprehensive prototype integrated coastal ocean observing system that was established in the summer of 2001. Its current configuration includes eleven solar-powered buoy-monitored locations 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. It serves a broad array of real-time oceanographic and marine meteorological data and data products to scientists, state and federal regulators, the National Weather Service, both the US and Canadian Coast Guards, the National Data Buoy Center, educators, regional natural- resource managers, the Gulf of Maine fishing and maritime industries, local airports and airlines, sailors, and the general public. The ocean observing system that can be thought of as consisting of four major subsystems: the data acquisition subsystem; the data handling, processing, and archiving subsystem; the system of numerical nowcast and forecast models; and a web-based data distribution/presentation subsystem. The Gulf of Maine is a harsh operational environment. Winter storms pose severe challenges including the build up of sea ice on buoy, its solar panels, and its meteorological sensors. In summer the productive waters of the gulf can present severe biofouling problems that affect the operation of optical sensors. Thus, the periods of most difficult field operations coincide with the periods of greatest data value in terms of marine safety, search and rescue, and the monitoring biological productivity. Never-the-less, the data returns for the GoMOOS ocean sensor array has averaged approximately 90% over the first seven years of operation. This unusually high rate of data return is due in large part to our operational six-month duty/maintenance cycle on all equipment. We have 22 buoys for 11 locations, and 22 complete sets of instrumentation that are rotated in and out of service on a six month schedule. The challenges of the Gulf of Maine physical environment were largely understood a priori, and were incorporated into the system design criteria and the blueprints for the service and maintenance protocols. However, there were unanticipated challenges in the funding process that have caused the greatest difficulties, and which continue to pose a serious threat to continued operation and success of this ocean observing system, as well as others observing systems in the United States. Funding for the system has been chronically short and subject to the unpredictable fluctuations of a US congressional appropriations process. The inadequacy and variability of funding has substantially hampered the operations of many of the Integrated Ocean Observing Systems (IOOS), including GoMOOS, and has hindered technological improvements. The funding crisis has deepened to the point that, unless this trend is quickly reversed, the number of monitoring stations will be substantially reduced and system will no longer be able to serve many of citizens, organizations, and agencies that have come to rely upon the data it currently provides. Ocean sensors, ocean platform technologies, and modeling and visualization techniques are in a period of rapid technical development. If stable funding can be achieved, the capabilities of operational ocean observing systems could increase dramatically over the next decade. Autonomous vehicles could become the fast response survey fleet of the IOOS, as well as taking on routine, sustained marine survey functions that are already prohibitively expensive to perform using ships, and will become even more costly as energy costs rise in the future. Practical autonomous vehicles will likely expand beyond gliders and AUVs to include surface sail vessels and energy-efficient autonomous aerial drones. The combination of time series measurements from profiling packages on buoy arrays with the repeatedly spatial surveys of the autonomous fleets will provide a new look at our coastal oceans that could transform coastal ocean science and management. Coupled with these new platform advances will be significant growth in the areas of real-time biochemical sensors, sensor miniaturization, high-speed data telemetry technologies, increases in onboard data processing capabilities, routine two-way communications with submerged sensors, and advances in data visualization techniques that will amount to virtual presence. The single greatest enabling factor of these broad improvements to ocean observing operations and science appears, at present, to be the establishment of an adequate, stable, and predictable funding process.

Traditional means of observing the ocean, like fixed mooring stations and radar systems, are difficult and expensive to deploy and provide coarse-grained and data measurements of currents and waves. In this paper, we explore the use of inexpensive wireless drifters as an alternative flexible infrastructure for fine-grained ocean monitoring. Surface drifters are designed specifically to move passively with the flow of water on the ocean surface and they are able to acquire sensor readings and GPS-generated positions at regular intervals. We view the fleet of drifters as a wireless ad-hoc sensor network with two types of nodes:i) a few powerful drifters with satellite connectivity, acting as mobile base-stations, and ii)a large number of low-power drifters with short-range acoustic or radio connectivity. Using real datasets from the Gulf of Maine (US) and the Liverpool Bay (UK), we study connectivity and uniformity properties of the ad-hoc mobile sensor network. We investigate the effect of deployment strategy, weather conditions as well as seasonal changes on the ability of drifters to relay readings to the end-users,and to provide sufficient sensing coverage of the monitored area. Our empirical study provides useful insights on how to design distributed routing and in-network processing algorithms tailored for ocean-monitoring sensor networks.

Detailed field testing of a bottom-mounted Aanderaa RDCP600 Doppler profiler was conducted at a protected coastal embayment. The RDCP600 was compared for 30 days to a string of seven moored Aanderaa RCM9 MKII in situ Doppler current meters, and an RDI 600 kHz workhorse ADCP. The test buoy was equipped with outriggers to allow measurements very close to the surface and to examine the acoustic and wake effects of the buoy on the performance of the RCM9 standard. The two 600 kHz Doppler profilers were deployed on the same bottom frame in order to ensure the same tilt and distance (approximately 50 m) from the moored RCM9 current meters. The Doppler profilers were programmed to sample during alternating time windows within a 20-minute sampling interval in order to avoid acoustic cross talk and interference. A common time base was achieved via post-deployment linear interpolation. Results of vector correlations and difference statistics show excellent agreement between all of the current measurement devices. Mean differences were generally less than 0.005 m s' and the RMS differences were on the order of 0.02 m s/sup -1/.

The Gulf of Maine Ocean Observing System (GoMOOS) was established in the summer of 2001 as a real-time pilot integrated observing system that includes a comprehensive array of moored physical and optical sensors, shore based long-range HF radar systems, circulation and wave modeling, satellite observations, and Web delivery of data and data products. The system is automated and operational. The GoMOOS moored buoy array presently consists of 10 solar-powered, automated buoy systems that telemeter data hourly via cellular/iridium phone and GOES satellite transmitters. The operational protocol is that 20 buoys and instrument suites are rotated through the 10 locations on a six-month cycle. Current measurements are made at 2 m depth using Aanderaa RCM9 in situ Doppler current meters, and subsurface currents are made with downward-looking RIM Doppler profilers. In addition, near-surface currents in the Gulf of Maine are being measured using a 5-megahertz long-range HF radar system manufactured by CODAR Ocean Systems Inc. Comparisons of the three current measurement systems are presented, and the operational logistics of current monitoring using these technologies in the challenging Gulf of Maine environment is discussed.

The performance of a prototype Doppler Acoustic Profiling Current Meter has been evaluated by comparison with state-of-the-art conventional current meter moorings in the Coastal Ocean Dynamics Experiment and also by consistency checks comparing velocities calculated from data from different combinations of acoustic beams. The RDI Doppler profiler generally yeilds high (lower) speeds than moored VMCM's (VACM's). Comparisons with laboratory calibrations of the mechanical current meters suggest that a large portion of the differences observed in the near-surface region could result from mooring motion and self-wake contamination experienced by the mechanical sensors in oscillatory flow.

The Gulf of Maine Ocean Observing System (GoMOOS) was established in the summer of 2001 as a prototype real-time observing system that includes a comprehensive array of moored physical and optical sensors, shore-based long-range HF radar systems, circulation and wave modeling, satellite observations, and hourly Web delivery of data and data products. The GoMOOS moored buoy array presently consists of 10 solar-powered, automated buoy systems that telemeter data hourly via cellular/iridium phone and GOES satellite transmitters. The locations of the buoys, which are replaced on a six-month maintenance schedule, range from bays and estuaries, the continental shelf, and the open Gulf of Maine. The buoys systems and their sensors are subjected to a broad range of wind, wave, bio-fouling, and icing conditions that have presented a significant challenge to the establishment of an operational integrated ocean observing system. Mounted on the surface buoys are sensors that measure wind speed and direction, atmospheric pressure, air temperature, visibility, solar insolation, and surface wave height and period. Subsurface measurements include near-surface currents, Doppler current profiles, temperature, conductivity, dissolved oxygen, spectral upwelling radiance and downwelling irradiance, chlorophyll fluorescence, and mufti-wavelength light attenuation, absorption, and backscattering. Data from deep sensors are telemetered up the mooring cable via an inductive modem to the buoy data system. The buoy system is designed with a flexible and modular architecture that is capable of handling on the order of one hundred sensors, and has relatively simple troubleshooting and maintenance procedures. The Gulf of Maine is a harsh and exacting environment in which to attempt to establish sustained real-time operations. The extreme cold, freezing spray, and high waves of winter have posed significant challenges to the wind and atmospheric pressure measurements, and to the dual telemetry system. In addition, the build up of sea ice on the buoy superstructure and on the solar panels has affected both the power systems and the buoy's wave response and sea-keeping ability. During spring and summer seasons, the productive waters of the Gulf of Maine often present a severe biofouling challenge, particularly to the optical sensors. The reality of the Integrated Ocean Observing System (IOOS) movement is that the conditions during which real-time data may be of greatest value, in terms of marine safety and search and rescue, correspond to the times of greatest difficulty in obtaining and transmitting those data. Similarly, the optical data are often of greatest interest during the season of highest productivity and biofouling. GoMOOS scientists and engineers have experienced successes and failures, and have developed strategies for dealing with environmental stresses to the sensors and systems.

[1] The Princeton Ocean Model is used to study the circulation in the South China Sea (SCS) and its seasonal transition. Kuroshio enters (leaves) the SCS through the southern (northern) portion of the Luzon Strait. The annually averaged net volume flux through the Luzon Strait is ∼2 Sv into the SCS with seasonal reversals. The inflow season is from May to January with the maximum intrusion of Kuroshio water reaching the western SCS during fall in compensation of summertime surface offshore transport associated with coastal upwelling. From February to April the net transport reverses from the SCS to the Pacific. The intruded Kuroshio often forms an anticyclonic current loop west of the Luzon Strait. The current loop separates near the Dongsha Islands with the northward branch continuously feeding the South China Sea Warm Current (SCSWC) near the shelf break and the westward branch becoming the South China Sea Branch of Kuroshio on the slope, which is most apparent in the fall. The SCSWC appears from December to February on the seaward side of the shelf break, flowing eastward against the prevailing wind. Diagnosis shows that the onshore Ekman transport due to northeasterly monsoon generates upwelling when moving upslope, and the particular distributions of the density and sea level associated with the cross shelf motion supports the SCSWC.

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.

As part of the Gibraltar Experiment, acoustic Doppler current profilers were deployed in the Tarifa Narrows section of the Strait of Gibraltar. Analysis of data from a Doppler profiler deployed near midstrait has shown that the passage of large amplitude nonlinear internal waves exerts profound influence on both the transient and mean flow structures in this section of the strait. Direct current measurements in the Tarifa Narrows yield an inflow transport estimate of one Sverdrup in the Atlantic layer. Of this total approximately 60% is associated with the internal bore, and only 40% is due to the steady circulation.

A turbidity maximum has been observed in the Kennebec estuary during mode rate and low flow conditions near the upstream limit of salinity intrusion. Hydrographic, ADCP, and transmissometer data were collected at different river flow levels and seasons during 1995–1998. The location of the tip of the salt intrusion changes dramatically and during high runoff may be flushed from the channel of the estuary along with the accumulated particles in the turbidity maximum. It is hypothesized that the estuarine turbidity maximum (ETM) was absent 18% of the time with occurrences in all seasons during 1993–1999 based on river flow volumes from the Kennebec and Androscoggin Rivers throughout the study period. When the flow is moderate and low, which occurred 73% of the time on average, a region of high turbidity can be found as far as 40 km upstream of the mouth. Suspended particulate loads are low in the ETM, on the order of tens of mg l−1 and may vary with the length of time that the ETM has been present.

Somes Sound has been described as the only example of a fjord on the east coast of the United States. On a small scale, and from a morpho? logical point of view, the Sound has key features normally associated with fjords, including pronounced subaerial topographic relief, submarine sills, and the U-shaped cross-section typical of glacially-carved troughs. However, based on its salinity distribution, which is related to the mixing and circulation processes used to characterize estuarine types from an oceanographic point of view, Somes Sound is a vertically well-mixed estuary that does not exhibit the strong stratification typical of fjords. While its geomorphology is unique, the oceanographic processes operating in the embayment are essentially the same as those in other shallow Maine estuaries with low fresh water input. In these estuaries, as well as in Somes Sound, tidal mixing is dominant over freshwater inflow in determining the circulation and the vertical stratification of the water column. Somes Sound, a narrow cut that nearly divides Mount Desert Island in two (Fig. 1), is morphologically unique among coastal embayments and estuaries along the eastern seaboard of the United States. The coastal embayments of Maine were altered by glacial erosion of the Pleistocene ice sheets and postglacial changes in sea level creating the typical low rolling relief best characterized as a fjard or firth coastline (Belknap et al. 1986; Kjerfve 1989). On the other hand, topographic relief in the Mount Desert region is decidedly more pronounced, and the eastern shore of Somes Sound rises at one point to more than 250 m above sea level. In addition to the spectacular subaerial relief, the submarine topogra? phy of the Sound displays the U-shaped channel cross-section and shallow terminal sill that characterize glacially-carved and deepened valleys. Based on these and other geological characteristics, Johnson (1925) concluded that Somes Sound represents the only "possible ex? ception to the statement that the term fjord cannot be properly applied to the coast of Maine." * Department of Oceanography, University of Maine, Orono, ME 04469-5741; ** Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME 04575 This content downloaded from 157.55.39.178 on Fri, 05 Aug 2016 04:51:03 UTC All use subject to http://about.jstor.org/terms 36 Northeastern Naturalist Vol. 4, No. 1 Figure 1. Mt. Desert Island

An easily implemented extension of the standard response method of tidal analysis is outlined. The modification improves the extraction of both the steady and the tidal components from problematic time series by calculating tidal response weights uncontaminated by missing or anomalous data. Examples of time series containing data gaps and anomalous events are analyzed to demonstrate the applicability and advantage of the proposed method.

Observations of wave crest elevation, wave trough elevation, and wave celerity have been made in the surf zone on a natural beach. A series of 22 wave poles having vertical gradations of 7 cm (near shore) and 11 cm (off shore) were placed across the surf zone from outside the break point to the swash zone. Movements of 10 individual waves all having a break point within one wave pole spacing of each other have been photographed, and the data on wave height changes and wave speed changes have been analyzed. Wave celerity within the surf zone, given as a ratio M to solitary wave celerity, shows a systematic increase of wave speeds near the break point to a peak of M ≃ 1.2, thence a decrease farther shoreward to M ≃ 0.8, and finally a second increase where M > 1. Wave height decay after breaking follows the theory of turbulent dissipation recently presented by Sawaragi and Iwata (1974). The wave height to water depth ratio within the surf zone is a function of distance from the break point and ranges from 2.0 to 0.6. The results indicate that the use of linear and nonlinear nonviscous wave theories to quantify surf zone wave characteristics is misleading insofar as quantitative prediction is concerned.

The Nantucket Shoals Flux Experiment (NSFE) was a collaborative effort to measure the alongshelf transport of mass, heat, salt and nutrients from March 1979 through April 1980 with a dense army consisting of moored current, temperature and bottom pressure instruments in an across-shelf and upper-slope transect south of Nantucket Island. The pressure component of that experiment is described here. Bottom pressure recorders were deployed at stations N1 (46 m), N2 (66 m), N4 (105 m), and N5 (196 m) during two half-year periods. spring–summer 1979 (SUMMER) and fall–winter 1979/80 (WINTER). A synthetic subsurface pressure (SSP) record was formed from atmospheric pressure and sea level observations at Nantucket Island. The low-pass filtered (periods > 36 h) or subtidal pressures were used for the subsequent analysis. It was found that Nantucket SSP and BP are very nearly equivalent for fluctuation periods less than about 50 days if steric changes in sea level, due to density changes above the seasonal ...