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Accurate estimation of the changes of tides is important for sea level prediction and fundamental for local coastal planning. Here we use a novel method, enhanced harmonic analysis (EHA), to extract temporal changes in the response of the nodal modulation of the M 2 tide in the Gulf of Maine. The results show that the temporal variations of nodal amplitudes at four stations in the Gulf of Maine are similar from 1970s to 2013. They all increase in the 1970s to peak values in the 1985s and in the 2000s they decrease to minimum values. The North Atlantic Oscillation (NAO), which is one of the major climate modes in the North Atlantic Ocean, may be responsible for temporal changes in the response of the nodal modulation of the M 2 tide from 1970s to 2013. Also, the results obtained by the new method indicate that the traditional method of harmonic analysis slightly underestimates the trend of M 2 amplitude in the Gulf of Maine. • Temporal changes in the response of the nodal modulation of the M2 tide is extracted by enhanced harmonic analysis. • The traditional method of harmonic analysis slightly underestimates the trend of M2 amplitude in the Gulf of Maine. • Temporal changes in the response of the nodal modulation of the M2 tide may be induced by the NAO and sea level rise. [ABSTRACT FROM AUTHOR]

Hydrographic variability and dynamics in the Gulf of Maine are examined through the investigation of δ18Ow and salinity properties of coastal surface waters. Data from Gulf of Maine waters sampled over a decade, from 2003 to 2015, including a suite of samples that were collected monthly from April 2014 to March 2015, are presented. These water samples fall on a mixing line between Maine River Water (MRW) and Scotian Shelf Water (SSW). However, slope waters likely also contribute to these surface waters. The seasonal variability in water samples collected during 2014 and 2015 indicates the strong influence of river runoff on coastal Gulf of Maine surface water properties. The coastal Gulf of Maine mixing line presented in this paper is a needed baseline for reconstructing hydrographic variability in bicarbonates using oxygen isotopes. [ABSTRACT FROM AUTHOR]

We report planktonic foraminiferal fluxes (accumulation rates) and oxygen isotopes (δ 18 O) from a nine-month sediment trap deployment, and δ 18 O from three sediment cores in Jordan Basin, Gulf of Maine. The sediment trap was deployed at 150 m, about halfway to the basin floor, and samples were collected every three weeks between August 2010 and May 2011. The planktonic foraminiferal fauna in the trap is dominated by Neogloboquadrina incompta that reached a maximum flux in the second half of October. Oxygen isotope ratios on that species indicate that on average during the collecting period it lived in the surface mixed layer, when compared to predicted values based on data from a nearby hydrographic buoy from the same period. New large diameter piston cores from Jordan Basin are 25 and 28 m long. Marine hemipelagic sediments are 25 m thick, and the sharp contact with underlying red deglacial sediments is bracketed by two radiocarbon dates on bivalves that indicate ice-free conditions began 16,900 calibrated years ago. Radiocarbon dating of foraminifera indicates that the basin floor sediments (270–290 m) accumulated at >3 m/kyr during the Holocene, whereas rates were about one tenth that on the basin slope (230 m). In principle, Jordan Basin sediments have the potential to provide time series with interannual resolution. Our results indicate the Holocene is marked by ~2°C variability in SST, and the coldest events of the 20th century, during the mid 1960s and mid 1920s, appear to be recorded in the uppermost 50 cm of the seafloor. [ABSTRACT FROM AUTHOR]

Abstract: Two independent methods were used to estimate particle export fluxes of metals in the Gulf of Maine and Scotian Shelf. The first method used measurements of particulate trace metals (Cd, Cu, Fe and Pb) and metal/234Th ratios on large (>53µm), rapidly sinking, particles together with prior estimates of 234Th/238U disequilibrium to quantify the particle export flux of these metals. The second method adopted a mass balance approach whereby measurements of the distribution of dissolved (<0.4µm) and fine particulate (0.4–53µm) trace metals (Cd, Cu, Fe, Pb, Mn, Ni and Zn) were combined with rates of water volume transport to determine advective metal fluxes in the Gulf of Maine and Scotian Shelf. Estimates were also made of rates of external supply of metals from atmospheric, riverine and municipal sewage sources. Imbalances between total input fluxes to the Gulf of Maine and Scotian Shelf and the removal fluxes by offshore advection were used to estimate metal export fluxes to the sediments. The mass balance model export fluxes are generally within, or close to, the range of values determined independently from the 234Th/238U method, indicating that metal transport through shelf/slope regimes can be reasonably characterized using relatively limited data sets. Specifically, these results indicate that ~40–60% of the Pb and Zn inputs to the Gulf of Maine and Scotian Shelf are scavenged and exported to the sediments, whereas only ~5–15% of the Ni and Cu inputs are removed by particle export, as would be anticipated based on their respective particle affinities. [Copyright &y& Elsevier]

Abstract: The carbon isotope and lipid biomarker composition of suspended particles and surface sediment was measured to examine the impact of sediment supply, redistribution and post-depositional alteration processes on organic matter cycling in the Gulf of Maine, a semi-enclosed shelf sea in the northwest Atlantic. A beam attenuation profile revealed a >50m-thick benthic nepheloid layer (BNL) in the Jordan Basin at the time of sampling (April 2006). The relatively low radiocarbon content of suspended particulate organic carbon (POC) in the BNL indicates that up to 82% of the POC in this layer was supplied from resuspension of sediment. The concentration of alkenones normalized to POC increased with increasing depth in the water column and was highest in the surface sediment. In contrast to these markers of surface ocean photoautotrophy, the vertical profiles for the concentration and composition of short-chain (C14–C18) n-alkanoic acids provided evidence for enhanced heterotrophic processes near the top of the BNL. Suspended POC samples from two depths within the BNL exhibited marked differences in radiocarbon content and fatty acid composition, suggesting that biological activity and associated processes within the BNL are vertically heterogeneous. [Copyright &y& Elsevier]

Abstract: The hydrographic and optical properties in the Gulf of Maine (GOM) are controlled by an array of forces operating on local scales such as the distributed river system to global such as the North Atlantic Oscillation. Regional hydrographic and bulk optical relationships, however, are not always in concert revealing that variable forcing mechanisms operate separately on different water column characteristics leading to a complex set of interrelationships that vary on both vertical and horizontal spatial scales. In this study, we examined hydrographic and bio-optical variability during two seasonal surveys with an emphasis on the influence of regional phytoplankton variability on ocean color. GOM component optical variability suggested that the relatively invariant green ocean color of the GOM is related to the temporal and spatial invariance of the total absorption signal. This invariance, however, masked both variations in the relative magnitudes of the dissolved and particulate optical components (e.g. CDOM, phytoplankton, and non-algal particles) and the optical variations observed within these components. Component absorption variability between provinces of the GOM and between seasonal surveys was distinct with discernible differences. These temporal and regional differences were due in part to particle type and phytoplankton absorption spectral variability. Variability in phytoplankton size-class dominance in both fall and spring implied that phytoplankton size dependencies develop in response to variability in mixing, stratification, and stability which may occur independently within different regions of the GOM. However, depth dependent photoacclimation was not a driving factor indicating that mixing rates exceeded photoacclimation rates during both cruises. [Copyright &y& Elsevier]

Abstract: This study examines the effects of freshwater discharge from the St. Lawrence River (SLR) on the three-dimensional circulation and hydrography in Canada's Atlantic waters using a regional shelf circulation model based on the Princeton Ocean Model. The study region comprises the Gulf of St. Lawrence, the Scotian Shelf, and the Gulf of Maine. The model forcing includes atmospheric forcing at the sea surface; tidal elevation and currents at the lateral open boundaries; and freshwater discharge from the SLR and other major rivers in the region. The forcing at the lateral open boundaries also includes non-tidal currents as well as temperature and salinity fields produced by a coarse-resolution circulation model for the northwest Atlantic. The shelf circulation model is integrated for 5 years (1999–2003); the simulated hydrography and circulation during the last 4 years are compared to observations to assess the model's performance. Three additional model runs are made, called the climate, wet, and dry runs, in which the SLR discharge values specified in the model are respectively the long-term mean and the long-term mean plus or minus 3.5 standard deviations. Model results from the climate run demonstrate that the variability of freshwater flux in the St. Lawrence Estuary takes ∼100 days to reach Cabot Strait; ∼160 days to reach the central Scotian Shelf; and ∼220 days to reach the eastern Gulf of Maine. Within the Gulf of St. Lawrence, an increase in the SLR discharge results in a stronger Gaspé Current (up to ∼0.1ms−1 stronger in the wet run than in the dry run) as well as lower salinity in the western part of the gulf. In the winter, the effect of a higher SLR discharge extends along the Scotian Shelf and into the Gulf of Maine, with salinity in both areas lower by ∼0.1psu in the wet run than in the dry run. [Copyright &y& Elsevier]

Abstract: Ocean color remote sensing has provided the scientific community with unprecedented global coverage of chlorophyll a, an indicator of phytoplankton biomass. Together, satellite-derived chlorophyll a and knowledge of Phytoplankton Functional Types (PFTs) will improve our limited understanding of marine ecosystem responses to physiochemical climate drivers involved in carbon cycle dynamics and linkages. Using cruise data from the Gulf of Maine and the Middle Atlantic Bight (N=269 pairs of HPLC and phytoplankton absorption samples), two modeling approaches were utilized to predict phytoplankton absorption and pigments. Algorithm I predicts the chlorophyll-specific absorption coefficient ( (m2 mgchla−1)) using inputs of temperature, light, and chlorophyll a. Modeled r 2 values (400–700nm) ranged from 0.79 to 0.99 when compared to in situ observations with ∼25% lower r 2 values in the UV region. Algorithm II-a utilizes matrix inversion analysis to predict (m−1, 400–700nm) and r 2 values ranged from 0.89 to 0.99. The prediction of phytoplankton pigments with Algorithm II-b produced r 2 values that ranged from 0.40 to 0.93. When used in combination, Algorithm I, and Algorithm II-a are able to use satellite products of SST, PAR, and chlorophyll a (Algorithm I) to predict pigment concentrations and ratios to describe the phytoplankton community. The results of this study demonstrate that the spatial variation in modeled pigment ratios differ significantly from the 10-year SeaWiFS average chlorophyll a data set. Contiguous observations of chlorophyll a and phytoplankton biodiversity will elucidate ecosystem responses with unprecedented complexity. [Copyright &y& Elsevier]

Abstract: The percent of Labrador Slope Water (%LSW) in the waters entering the Gulf of Maine at depth (150–200m) through the Northeast Channel is estimated from temperature/salinity measurements for the period 1964–2008. Comparison of the annual average %LSW with the North Atlantic Oscillation (NAO) lagged two years shows that both series have very similar, but opposite, long term trends. High %LSW in the 1960s decreased to low values in the 1990s as the NAO increased from low to high values over the same period. A regression of the residuals of the two series from their long term trends also is significant at the 5% level, indicating that the %LSW at the Northeast Channel has a persistent relationship on a year-to-year basis with the NAO over the full range of variation in the NAO. The response of the %LSW to the NAO, however, appeared substantially reduced after about 1990. Changes in the potential nutrient flux into the Gulf of Maine/Georges Bank system associated with changes in the %LSW cannot account for changes in chlorophyll a concentrations estimated for three multi-year stanzas during the sampling period. [Copyright &y& Elsevier]

Abstract: Recent oceanographic observations and a retrospective analysis of nutrients and hydrography over the past five decades have revealed that the principal source of nutrients to the Gulf of Maine, the deep, nutrient-rich continental slope waters that enter at depth through the Northeast Channel, may have become less important to the Gulf''s nutrient load. Since the 1970s, the deeper waters in the interior Gulf of Maine (>100m) have become fresher and cooler, with lower nitrate (NO3) but higher silicate (Si(OH)4) concentrations. Prior to this decade, nitrate concentrations in the Gulf normally exceeded silicate by 4–5μM, but now silicate and nitrate are nearly equal. These changes only partially correspond with that expected from deep slope water fluxes correlated with the North Atlantic Oscillation, and are opposite to patterns in freshwater discharges from the major rivers in the region. We suggest that accelerated melting in the Arctic and concomitant freshening of the Labrador Sea in recent decades have likely increased the equatorward baroclinic transport of the inner limb of the Labrador Current that flows over the broad continental shelf from the Grand Banks of Newfoundland to the Gulf of Maine. That current system now brings a greater fraction of colder and fresher deep shelf waters into the Gulf than warmer and saltier offshore slope waters which were previously thought to dominate the flux of nutrients. Those deep shelf waters reflect nitrate losses from sediment denitrification and silicate accumulations from rivers and in situ regeneration, which together are altering the nutrient regime and potentially the structure of the planktonic ecosystem. [Copyright &y& Elsevier]

Abstract: In-situ observations and a coupled bio-physical model were used to study the germination, initiation, and development of the Gulf of Maine (GOM) Alexandrium fundyense bloom in 2006. Hydrographic measurements and comparisons with GOM climatology indicate that 2006 was a year with normal coastal water temperature, salinity, current and river runoff conditions. A. fundyense cyst abundance in bottom sediments preceding the 2006 bloom was at a moderate level compared to other recent annual cyst survey data. We used the coupled bio-physical model to hindcast coastal circulation and A. fundyense cell concentrations. Field data including water temperature, salinity, velocity time series and surface A. fundyense cell concentration maps were applied to gauge the model''s fidelity. The coupled model is capable of reproducing the hydrodynamics and the temporal and spatial distributions of A. fundyense cell concentration reasonably well. Model hindcast solutions were further used to diagnose physical and biological factors controlling the bloom dynamics. Surface wind fields modulated the bloom''s horizontal and vertical distribution. The initial cyst distribution was found to be the dominant factor affecting the severity and the interannual variability of the A. fundyense bloom. Initial cyst abundance for the 2006 bloom was about 50% of that prior to the 2005 bloom. As the result, the time-averaged gulf-wide cell concentration in 2006 was also only about 60% of that in 2005. In addition, weaker alongshore currents and episodic upwelling-favorable winds in 2006 reduced the spatial extent of the bloom as compared with 2005. [Copyright &y& Elsevier]

Abstract: 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 100,000km 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 nearby 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±23m isobath, but that particles: (a) deviate from the seasonal-mean core fairly regularly, and are often re-entrained; (b) follow a slower (9cm/s), less-constrained path in the western portion off the coast of Maine relative to the eastern (16cm/s) section; and (c) can be affected by wind events and small-scale baroclinic structures. Residence times calculated for each 1/2° 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). [Copyright &y& Elsevier]

Abstract: Observations suggest that the interannual variability of wintertime convection in Wilkinson Basin (WB) during 1977–2005 is related to the variation in the surface layer salinity in the western Gulf of Maine (wGOM). When the winter convection is stronger (weaker), the resulting deep-layer temperatures in the wGOM are colder (warmer), and the likelihood of deep winter mixing is greater when the wGOM salinities are high. This hypothesis was tested using a one-dimensional mixed layer model to simulate the water column structure over the cooling period. Comparisons were made between the convection potential for the range of observed late-fall salinity values. Model results indicated that the mixed layer depth could deepen by as much as 50% when the surface layer salinities in the wGOM were high. Sensitivity tests revealed that the surface layer salinity variability, and its influence on the water column density structure, was a significant factor, along with local climate variability, in determining the observed time series trend in springtime bottom layer temperatures. Density distributions in the wGOM in high salinity years suggested that winter-cooled water from the adjacent shallow coastal areas could become sufficiently dense to cascade into the deeper layers of WB and enhanced the convective cooling. The interannual variation in wintertime convection and in the resulting density structure has important implications for biological processes. The associated variation in deeper layer temperatures has been shown to influence the spatial distribution, timing of spawning, and growth rates of many demersal and mid-water fishery populations. [Copyright &y& Elsevier]

The Northeast U.S. (NEUS) continental shelf has experienced rapid warming in recent decades. Over the NEUS continental shelf, the circulation and annual cycle of heating and cooling lead to local variability of water properties. The mixed layer depth (MLD) is a key factor that determines the amount of upper ocean warming. A detailed description of the MLD, particularly its seasonal cycle and spatial patterns, has not been developed for the NEUS continental shelf. We compute the MLD using an observational dataset from the Northeast Fisheries Science Center hydrographic monitoring program. The MLD exhibits clear seasonal cycles across five eco-regions on the NEUS continental shelf, with maxima in January–March and minima in July or August. The seasonal cycle is largest in the western Gulf of Maine (71.9 ± 24.4 m), and smallest in the southern Mid-Atlantic Bight (34.0 ± 7.3 m). Spatial variations are seasonally dependent, with greatest homogeneity in summer. Interannual variability dominates long-term linear trends in most regions and seasons. To evaluate the sensitivity of our results, we compare the MLDs calculated using a 0.03 kg/m3 density threshold with those using a 0.2 °C temperature threshold. Temperature-based MLDs are generally consistent with density-based MLDs, although a small number of temperature-based MLDs are biased deep compared to density-based MLDs particularly in spring and fall. Finally, we compare observational MLDs to the MLDs from a high-resolution ocean reanalysis GLORYS12V1. While the mean values of GLORYS12V1 MLDs compare well with the observed MLDs, their interannual variability are not highly correlated, particularly in summer. These results can be a starting point for future studies on the drivers of temporal and spatial MLD variability on the NEUS continental shelf. • First MLD seasonal climatology for the entire Northeast U.S. Continental Shelf. • 38,340 hydrography from the Northeast Fisheries Science Center is analyzed. • State-of-the-art ocean reanalysis is evaluated against the new MLD climatology. [ABSTRACT FROM AUTHOR]

Abstract: Along the coast of the northeastern United States, strong winds blowing from the northeast are often associated with storms called northeasters, coastal storms that strongly influence weather. In addition to effects caused by wind stress, the sea floor is affected by bottom stress associated with these storms. Bottom stress caused by orbital velocities associated with surface waves integrated over the duration of a storm is a metric of storm strength at the sea floor. Near-bottom wave-orbital velocities calculated by using measurements of significant wave height and dominant wave period and the parametric spectral method described in Wiberg and Sherwood [Wiberg, P.L., Sherwood, C.R. Calculating wave-generated bottom orbital velocities from surface wave parameters. Computers in Geosciences, in press] compared well with observations in Massachusetts Bay. Integrated bottom-wave stress (called IWAVES), calculated at 30m water depth, and a companion storm-strength metric, integrated surface wind stress at 10m (called IWINDS), are used to provide an overview of the strength, frequency, and timing of large storms in Massachusetts Bay over a 17-year period from January 1990 through December 2006. These new metrics reflect both storm duration and intensity. Northeast storms were the major cause of large waves in Massachusetts Bay because of the long fetch to the east: of the strongest 10% of storms (n=38) ranked by IWAVES, 22 had vector-averaged wind stress from the northeast quadrant. The Blizzard of December 1992, the Perfect Storm of October 1991, and a December 2003 storm were the strongest three storms ranked by IWAVES and IWINDS, and all were northeasters. IWAVES integrated over the winter season (defined as October–May) ranged by about a factor of 11; the winters with the highest integrated IWAVES were 1992–1993 and 2004–2005 and the winter with the lowest integrated IWAVES was 2001–2002. May 2005 was the only month in the 17-year record that two of the nine strongest northeast storms ranked by IWINDS occurred in the same month or year; these were also the only storms of the nine strongest northeast storms to occur in the spring. [Copyright &y& Elsevier]

Abstract: Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50km wide and 100km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast (‘Northeasters’) generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave–current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin. [Copyright &y& Elsevier]

Abstract: The Boston Harbor, Massachusetts Bay and Cape Cod Bay system (MBS) is a semi-enclosed coastal embayment located in the western Gulf of Maine (GOM). The strength of the spring bloom in the MBS varies dramatically and the underlying mechanisms are not well understood. It has been hypothesized that the weak (or missing) 1998 spring bloom was due to increased zooplankton grazing pressure after a relatively warmer winter that led to earlier development of zooplankton populations. However, chlorophyll concentrations were low in the entire GOM region during the spring bloom period of 1998. These low chlorophyll waters would enter the MBS by persistent intrusion from the GOM and affect the MBS spring bloom by reducing the accumulation of phytoplankton biomass, suggesting an alternative explanation for the missing bloom. In this study, the influences of the intruding GOM waters on the MBS spring bloom are examined using numerical simulations and observations to compare two contrasting spring blooms (a weak bloom in 1998 versus a strong bloom in 2000). The results indicate that intruding waters from the GOM significantly reduced the strength of spring bloom in 1998, but enhanced the spring bloom in 2000. A theoretical analysis suggests that the influence of the intrusion on the MBS spring bloom is mostly limited to the northern portion of the MBS, and the impact area is determined by local net growth, velocity of intruding flow and horizontal mixing. The intrusion of GOM waters carries the signal of long-term variability in the GOM region and thus may be an important oceanic pathway for climate changes to impact the MBS ecosystem. [Copyright &y& Elsevier]

Abstract: Observations of turbulence avoidance in zooplankton are compared to estimates of the wind-driven turbulence in the upper ocean. Plankton that avoid wind-driven turbulence by moving deeper are no longer transported by the wind-driven Ekman currents near the surface because they are no longer near the surface. Here, a threshold level of turbulence that triggers an avoidance response is estimated, and is used to infer the wind speed and water column stratification conditions that would lead to zooplankton leaving the Ekman layer. Turbulence avoidance is argued to lead to near-shore retention in wind-driven upwelling systems, and to a reduction of the delivery of zooplankton to Georges Bank from the deeper waters of the Gulf of Maine. [Copyright &y& Elsevier]

Abstract: Analyses of long time series of hourly tide-gauge data at four stations in the Gulf of Maine reveal that the amplitude of the M tide underwent a nearly linear secular increase throughout most of the 20th century. In the early 1980s, however, the amplitude of M abruptly dropped. Sea level changes alone appear inadequate to explain either the long-term trend or the recent trend discontinuity. Tidal models that account for Holocene sea level rise do predict an amplification of M, but much smaller than the currently observed trends. Nor do recent annual mean sea levels correlate with the recent trend discontinuity. Some unknown fraction of the open Atlantic may be similarly affected, since the M discontinuity, but not the long-term secular increase in the tide, is evident also at Halifax. [Copyright &y& Elsevier]

Abstract: 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 1.2cms−1 for the major and minor axis, respectively, while the RMS error in ellipse orientation is at 11°. [Copyright &y& Elsevier]

The first 4 years of SeaWiFS ocean color data (September 1997–August 2001) provide the first synoptic quantification of seasonal and interannual phytoplankton chlorophyll variability in the Gulf of Maine. Climatological monthly means show spatial patterns associated with the annual cycle. Concentrations are elevated throughout the year in coastal regions and over shallow banks (Georges Bank, Nantucket Shoals and Browns Bank) with a spring and fall bloom superimposed. Over deeper basins and the Scotia Shelf, a canonical North Atlantic seasonal cycle is present with low (< 1 mg m−3) winter (December–February) concentrations, an annual maximum in March–April (>2 mg m−3), reduced concentrations in summer and a fall bloom beginning as early as September in Jordan Basin but in October–November over other regions. Strong interannual variability over the 4-year time series shows the climatological seasonal features are often a biased picture of both timing and magnitude. The clearest interannual signal is of reduced chlorophyll concentrations throughout 1998, including weak spring and fall blooms. A connection between low concentrations in 1998 and local wind forcing is not evident. However, the low concentrations are coincident with negative anomalies in satellite surface temperature fields and follow the intrusion of relatively cold, low salinity slope water into the Northeast Channel which previous authors have argued is linked to changes in Labrador slope water transport induced by the North Atlantic Oscillation. Reduced concentrations in 1998 are consistent with both lower nitrate/nitrite concentrations in the intruding water as well as reduced subsurface stratification which would delay or reduce the onset of the spring bloom. [Copyright &y& Elsevier]

In 2016, an unprecedented Pseudo-nitzschia australis bloom in the Gulf of Maine led to the first shellfishery closures due to domoic acid in the region's history. In this paper, potential introduction routes of P. australis are explored through observations, a hydrodynamic model, and a Lagrangian particle tracking model. Based on particle tracking experiments, the most likely source of P. australis to the Gulf of Maine was the Scotian Shelf. However, in 2016, connectivity between the Scotian Shelf and the bloom region was not significantly different from the other years between 2012 and 2019, nor were temperature conditions more favorable for P. australis growth. Observations indicated changes on the Scotian Shelf in 2016 preceded the introduction of P. australis : increased bottom salinity and decreased surface salinity. The increased bottom salinity on the shelf may be linked to anomalously saline water observed near the coast of Maine in 2016 via transport through Northeast Channel. The changes in upstream water mass properties may be related to the introduction of P. australis , and could be the result of either increased influence of the Labrador Current or increased outflow from the Gulf of St. Lawrence. The ultimate source of P. australis remains unknown, although the species has previously been observed in the eastern North Atlantic, and connectivity across the ocean is possible via a subpolar route. Continued and increased monitoring is warranted to track interannual Pseudo-nitzschia persistence in the Gulf of Maine, and sampling on the Scotian Shelf should be conducted to map upstream P. australis populations. • P. australis bloomed in the Gulf of Maine in 2016 and has bloomed annually since. • The most likely source of P. australis to the Gulf of Maine was the Scotian Shelf. • Connectivity and growth potential were not significantly different in 2016. • P. australis was concurrent with decreased surface salinity on the Scotian Shelf. • A subpolar route likely connected P. australis from the eastern N. Atlantic to the GOM. [ABSTRACT FROM AUTHOR]

Tides are one of the basic types of ocean water motions. Previous studies have reported that the M 2 constituent exhibits seasonal variations (annual cycles) in some regions. However, based on the newly proposed method of modified two-step harmonic analysis (HA) and its application at 240 global tide gauges, we find that the M 2 constituent as well as the S 2 and K 1 do not have significant seasonal variations at these tide gauges. The seasonal variations of the M 2 constituent reported in previous studies are caused by its satellites, the H 1 and H 2 constituents, which are not resolved in these studies due to the short time window (one month or three months) used in HA. Because the frequency of the H 1 (H 2) constituent is equal to that of the M 2 minus (plus) the frequency of annual cycles, the superposition of the M 2 , H 1 and H 2 constituents with constant amplitudes is equivalent to the M 2 constituent with seasonally varying amplitudes. Compared with the new method, some adaptations to traditional HA aiming to capture variations in amplitudes and phase lags of constituents have some limitations, because they either neglect some satellites of the major constitutes or introduce spurious fluctuations resulting from an unreasonably large number of independent points. The nodal modulations of predominant constituents are also explored in this study. On the global scale, the nodal modulations of the M 2 , K 1 and O 1 constituents agree with the theoretical predictions, except a cold spot region with reduced nodal modulation in the Gulf of Maine and a hot spot region with enhanced nodal modulation in the South China Sea for the M 2. Nodal modulation is also found for the S 2 constituent (in theory, the S 2 has no nodal modulation), which is 0.8% averaged at 164 tide gauges where the S 2 is not too weak. • The M 2 , K 1 and S 2 do not show significant seasonal variations at 240 tide gauges. • Unresolved constituents can cause unrealistic variations for predominant constituents. • Nodal modulation of the M 2 is reduced in Gulf of the Maine and enhanced in the SCS. • Nodal modulation is found for the S 2. [ABSTRACT FROM AUTHOR]

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 (δ18O water) 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 δ18O water 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 (NO 3 −; δ15N NO3- and δ18O NO3- , 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 NO 3 − from different sources at the surface and therefore do not necessarily indicate the presence of nitrification. • Differences in d18O water in different Gulf of Maine basins suggest differences in vertical mixing and freshwater input. • d15N NO3- and d18O NO3- values of Gulf of Maine water samples suggest significant influence of phytoplankton assimilation. • The Δ(15, 18) variable suggests nitrification is occurring in the upper water column throughout much of the Gulf of Maine. [ABSTRACT FROM AUTHOR]

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 (NO 3) 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. • Nutrient distributions in the Gulf of Maine are affected by multiple internal biogeochemical processes. • Silicate accumulates in bottom waters while nitrate becomes depleted. • Evidence for shelf sources delivering silicate at mid-depths. [ABSTRACT FROM AUTHOR]