Enhanced chlorophyll at the shelfbreak of the Mid‐Atlantic Bight and Georges Bank during the spring transition

Ryan, John P.; Yoder, James A.; Cornillon, Peter

doi:10.4319/lo.1999.44.1.0001

Cited by 77 publications

(57 citation statements)

References 51 publications

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“…From June through October, a tongue of relatively low chlorophyll concentration separates high concentrations immediately adjacent to the southwestern Nova Scotia coast from high concentrations further offshore near the 100 m isobath. Elevated chlorophyll concentrations along a shelf-break front south of Georges Bank shown by Ryan et al (1999) in spring data are temporally/spatially persistent enough to be present in the climatological data (March-May) and are also shown here to be present in the fall (October). Fig.…”

Section: Seasonal Variabilitymentioning

confidence: 68%

“…Over Georges Bank, March imagery showed smaller increases followed by a large increase in April. Examination of the full 7.5-year time series of CZCS imagery at the shelf break (Ryan et al, 1999) documents a strong annual enhancement of spring pigment over the southern flank of Georges Bank associated with the shelf break front. Yoder et al (2001) use the same data to show that in US Atlantic coastal and shelf waters, a simple seasonal cycle, maximum in winter, dominates chlorophyll variability.…”

Section: Introductionmentioning

confidence: 99%

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Satellite-measured phytoplankton variability in the Gulf of Maine

Thomas

Townsend

Weatherbee

2003

Continental Shelf Research

108

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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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Section: Seasonal Variabilitymentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Satellite-measured phytoplankton variability in the Gulf of Maine

Thomas

Townsend

Weatherbee

2003

Continental Shelf Research

108

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“…With the onset of stratification a spring bloom generally occurs in March-April, followed by surface nutrient depletion and highly stratified summer conditions with a pronounced subsurface Chl a maximum. As described by Ryan et al [1999a], during the transition between the spring bloom and summer stratification a band of enhanced surface Chl a concentration often develops along the shelfbreak (in the vicinity of the 100 m isobath). This feature is an apparent response to along-isopycnal upwelling of nutrients in deep shelf waters forced by meanders of the shellbreak front [Marra et al, 1990;Ryan et al, 1999b].…”

Section: Spectral Variationsmentioning

confidence: 99%

Temporal and vertical variability in optical properties of New England shelf waters during late summer and spring

Sosik¹,

Green²,

Pegau³

et al. 2001

J. Geophys. Res.

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Abstract. Relationships between optical and physical properties were examined on the basis of intensive sampling at a site on the New England continental shelf during late summer 1996 and spring 1997. During both seasons, particles were found to be the primary source of temporal and vertical variability in optical properties since light absorption by dissolved material, though significant in magnitude, was relatively constant. Within the particle pool, changes in phytoplankton were responsible for much of the observed optical variability. Physical processes associated with characteristic seasonal patterns in stratification and mixing contributed to optical variability mostly through effects on phytoplankton. An exception to this generalization occurred during summer as the passage of a hurricane led to a breakdown in stratification and substantial resuspension of nonphytoplankton particulate material. Prior to the hurricane, conditions in summer were highly stratified with subsurface maxima in absorption and scattering coefficients. In spring, stratification was much weaker but increased over the sampling period, and a modest phytoplankton bloom caused surface layer maxima in absorption and scattering coefficients. These seasonal differences in the vertical distribution of inherent optical properties were evident in surface reflectance spectra, which were elevated and shifted toward blue wavelengths in the summer. Some seasonal differences in optical properties, including reflectance spectra, suggest that a significant shift toward a smaller particle size distribution occurred in summer. Shorter timescale optical variability was consistent with a variety of influences including episodic events such as the hurricane, physical processes associated with shelfbreak frontal dynamics, biological processes such as phytoplankton growth, and horizontal patchiness combined with water mass advection.

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“…Seaward flow of shelf water is the fundamental process associated with all shelf break chlorophyll enhancement observed by the CZCS during late spring [Ryan et al, 1999] Biological effects of frontal processes, particularly those inferred from satellite remote sensing, require interpretation within the context of seasonal changes in stratification. This late spring chlorophyll enhancement developed within the context of the seasonal progression toward stratification of the upper water column.…”

mentioning

confidence: 99%

Chlorophyll enhancement and mixing associated with meanders of the shelf break front in the Mid‐Atlantic Bight

Ryan¹,

Yoder²,

Barth³

et al. 1999

J. Geophys. Res.

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Abstract. Meanders of the shelf break front in the Mid-Atlantic Bight (MAB)during April and May of 1997 were associated with chlorophyll enhancement along a hydrographic and a topographic feature. The hydrographic feature was the surface outcrop of the front, which ranged from ,.•10 to •100 km seaward of the shelf break owing to the meanders. The topographic feature was the shelf break (100-m isobath). Chlorophyll enhancement was observed by a satellite instrument, the ocean color and temperature sensor, and by a fiuorometer in situ. It developed in near-surface waters typically nutrient depleted during late spring, thus local nutrient enrichment of near-surface waters was probable. Observations of sufficient resolution to define processes were available only for the region of shelf break chlorophyll enhancement. Along two meander troughs (shoreward extremities near the shelf break), we observed shoaling of cold shelf water. Shelf water shoaled•20 m along frontal isopycnals, and phytoplankton absorption maxima coincided directly with the shoaled water. Thus local nutrient enrichment by along-isopycnal upwelling was the supported mechanism of chlorophyll enhancement at the shelf break. The basis for along-isopycnal upwelling was seaward flow of shelf water forced by meander circulation near the shelf break. Strong cross-isobath flow and mixing developed as these meanders propagated along the shelf break front of the MAB at a relatively constant rate of ,.•9 km day -1.

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Enhanced chlorophyll at the shelfbreak of the Mid‐Atlantic Bight and Georges Bank during the spring transition

Cited by 77 publications

References 51 publications

Satellite-measured phytoplankton variability in the Gulf of Maine

Satellite-measured phytoplankton variability in the Gulf of Maine

Temporal and vertical variability in optical properties of New England shelf waters during late summer and spring

Chlorophyll enhancement and mixing associated with meanders of the shelf break front in the Mid‐Atlantic Bight

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