Observations of the Eastern Maine Coastal Current and its offshore extensions in 1994

Pettigrew, Neal R.; Townsend, David W.; Xue, Huijie; Wallinga, John; Brickley, Peter; Hetland, Robert D.

doi:10.1029/98jc01625

Cited by 86 publications

(95 citation statements)

References 20 publications

(14 reference statements)

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“…1) at the northeastern section of the sampling domain is complex, with a branch point near Penobscot Bay where the EMCC is commonly deflected offshore because of the influence of the Jordan Basin gyre (Brooks and Townsend 1989;Bisagni et al 1996;Pettigrew et al 1998). However, portions of the EMCC flow can continue alongshore into the western GOM to form the WMCC (Lynch et al 1997), augmented by the river outflow.…”

Section: Discussionmentioning

confidence: 99%

Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited

et al. 2005

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The plume advection hypothesis links blooms of the toxic dinoflagellate Alexandrium fundyense in the western Gulf of Maine (GOM) to a buoyant plume derived from river outflows. This hypothesis was examined with cruise and moored-instrument observations in 1993 when levels of paralytic shellfish poisoning (PSP) toxins were high, and in 1994 when toxicity was low. A coupled physical-biological model simulated hydrography and A. fundyense distributions. Initial A. fundyense populations were restricted to low-salinity nearshore waters near Casco Bay, but also occurred in higher salinity waters along the plume boundary. This suggests two sources of cells-those from shallow-water cyst populations and those transported to shore from offshore blooms in the eastern segment of the Maine coastal current (EMCC). Observations confirm the role of the plume in A. fundyense transport and growth. Downwelling-favorable winds in 1993 transported the plume and its cells rapidly alongshore, enhancing toxicity and propagating PSP to the south. In 1994, sustained upwelling moved the plume offshore, resulting in low toxicity in intertidal shellfish. A. fundyense blooms were likely nutrient limited, leading to low growth rates and moderate cell abundances. These observations and mechanisms were reproduced by coupled physical-biological model simulations. The plume advection hypothesis provides a viable explanation for outbreaks of PSP in the western GOM, but should be refined to include two sources for cells that populate the plume and two major pathways for transport: one within the low-salinity plume and another where A. fundyense cells originating in the EMCC are transported along the outer boundary of the plume front with the western segment of the Maine coastal current.Toxic dinoflagellate blooms are a serious economic and

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Section: Discussionmentioning

confidence: 99%

Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited

et al. 2005

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“…Elevated chlorophyll concentrations extend offshore into more oligotrophic portions of the central Gulf of Maine from the coastal region immediately south of Penobscot Bay during spring-summer. This region is where colder, nutrient-rich surface waters of the Eastern Maine Coastal Current turn cyclonically offshore (Townsend et al, 1987;Bisagni et al, 1996;Pettigrew et al, 1998). Relatively low concentrations are evident over the deeper basin at the mouth of the Bay of Fundy from October through March.…”

Section: Seasonal Variabilitymentioning

confidence: 99%

“…Spatial patterns of this seasonality reflect bathymetry ( Fig. 1) and residual circulation (Brooks, 1985;Pettigrew et al, 1998). Concentrations over Georges Bank, although elevated throughout the year, weaken in winter and late summer.…”

Section: Seasonal Variabilitymentioning

confidence: 99%

“…The vernal circulation in the Gulf of Maine inferred from June 1983 hydrography surveys (Brooks, 1985) shows separated cyclonic flows around all three major basins. A coastal current, usually divided into the Eastern Maine Coastal Current (EMCC) and the Western Maine Coastal Current (WMCC), makes up the nearshore portion of the cyclonic flow with a branch of the EMCC often observed turning offshore into the interior of the Gulf in the vicinity of Penobscot Bay (Brooks and Townsend, 1989;Pettigrew et al, 1998). Surface thermal signatures of both the vertical mixing and residual circulation are reflected in patterns evident in satellite surface temperature data (Bisagni et al, 1996(Bisagni et al, , 2001).…”

Section: Introductionmentioning

confidence: 99%

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Satellite-measured phytoplankton variability in the Gulf of Maine

Thomas

Townsend

Weatherbee

2003

Continental Shelf Research

Self Cite

107

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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 (o 1 mg m À3 ) winter (December-February) concentrations, an annual maximum in March-April (>2 mg m À3 ), reduced concentrations in summer and a fall bloom beginning as early as September in Jordan Basin but in OctoberNovember 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. r

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“…At this point the current branches into two segments, one that continues along the coast and another that veers offshore around the Jordan Basin Gyre. Potential mechanisms affecting the path of this offshore branch include topographic effects, offshore steering along the southwestern flank of the cyclonic gyre over Jordan Basin (Bisagni et al, 1996;Brooks and Townsend, 1989), and inshore influences of the Penobscot river plume that tend to push the current offshore (Brooks, 1994;Pettigrew et al, 1998;Xue et al, 2000). The Western segment of the MCC is fed by the inshore branch of the eastern segment together with the outflow of the Penobscot River.…”

Section: Circulation Modelmentioning

confidence: 99%

Mechanisms regulating large-scale seasonal fluctuations in Alexandrium fundyense populations in the Gulf of Maine: Results from a physical–biological model

McGillicuddy

Anderson

Lynch

et al. 2005

Deep Sea Research Part II: Topical Studies in Oceanography

148

132

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Observations of Alexandrium fundyense in the Gulf of Maine indicate several salient characteristics of the vegetative cell distributions: patterns of abundance are gulf-wide in geographic scope; their main features occur in association with the Maine Coastal Current; and the center of mass of the distribution shifts upstream from west to east during the growing season from April to August. The mechanisms underlying these aspects are investigated using coupled physical-biological simulations that represent the population dynamics of A. fundyense within the seasonal mean flow. A model that includes germination, growth, mortality, and nutrient limitation is qualitatively consistent with the observations. Germination from resting cysts appears to be a key aspect of the population dynamics that confines the cell distribution near the coastal margin, as simulations based on a uniform initial inoculum of vegetative cells across the Gulf of Maine produces blooms that are broader in geographic extent than is observed. In general, cells germinated from the major cyst beds (in the Bay of Fundy and near Penobscot and Casco Bays) are advected in the alongshore direction from east to west in the coastal current. Growth of the vegetative cells is limited primarily by temperature from April through June throughout the gulf, whereas nutrient limitation occurs in July and August in the western gulf. Thus the seasonal shift in the center of mass of cells from west to east can be explained by changing growth conditions: growth is more rapid in the western gulf early in the season due to warmer temperatures, whereas growth is more rapid in the eastern gulf later in the season due to severe nutrient limitation in the western gulf during that time period. A simple model of encystment based on nutrient limitation predicts deposition of new cysts in the vicinity of the observed cyst bed offshore of Casco and Penobscot Bays, suggesting a pathway of re-seeding the bed from cells advected downstream in the coastal current. A retentive gyre at the mouth of the Bay of Fundy tends to favor re-seeding that cyst bed from local populations.

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Observations of the Eastern Maine Coastal Current and its offshore extensions in 1994

Cited by 86 publications

References 20 publications

Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited

Toxic Alexandrium blooms in the western Gulf of Maine: The plume advection hypothesis revisited

Satellite-measured phytoplankton variability in the Gulf of Maine

Mechanisms regulating large-scale seasonal fluctuations in Alexandrium fundyense populations in the Gulf of Maine: Results from a physical–biological model

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