Shelf-slope frontal structure and cross-shelf exchange at the New England shelf-break

The shelf water over the outer edge of the Scotian Shelf and the shelf/slope water front at the shelf break south of Nova Scotia have been sampled with a Batfish cycling over a 3- to 110-m-depth range while measuring salinity, temperature, depth, chlorophyll a, and copepods. Plant production and copepod abundance were much higher at the front than in surrounding shelf and slope waters. Convergence at the front is invoked as a possible transport mechanism which results in the accumulation of copepods in a region of high food concentration. Copepods exhibit diel vertical migration in shelf water but not in the front itself, and possible mechanisms are examined. Most Batfish profiles (with ≈1-m-depth resolution) indicated that the copepod maximum was situated ≈10 m above the chlorophyll maximum. A series of vertical profiles consisting of chlorophyll a, estimated production, and copepod abundances indicate a high correlation between the copepod and production profiles and low correlation between either of these and chlorophyll. Possible relationships between copepod layer depths and the depths of high plant production are considered.Key words: copepods, batfish, chlorophyll, production, front, migration

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Life on the edge: environmental determinants of tilefish (Lopholatilus chamaeleonticeps) abundance since its virtual extinction in 1882

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu053 ◽

2014 ◽

Vol 71 (9) ◽

pp. 2371-2378 ◽

Cited By ~ 1

Author(s):

Jonathan A. D. Fisher ◽

Kenneth T. Frank ◽

Brian Petrie ◽

William C. Leggett

Keyword(s):

New England ◽

North Atlantic ◽

Marine Species ◽

Habitat Requirements ◽

The North ◽

Shelf Slope ◽

The North Atlantic ◽

Continental Shelf Slope ◽

The North Atlantic Oscillation ◽

Response To Environmental Change

Abstract Unlike many temperate marine species that alter spatial or depth distributions in response to environmental change, tilefish (Lopholatilus chamaeleonticeps) has such specific habitat requirements that off the coast of New England, USA, it is restricted to the normally warm-water, upper continental shelf slope, where it excavates and occupies burrows. In 1882, tens of millions of adult tilefish died suddenly following the intrusion of lethally cold Subarctic water into the tilefish habitat. Here we show that the same climate driver implicated in the 1882 event (the North Atlantic Oscillation: NAO) has also affected commercial tilefish landings throughout most of the 20th century by altering slope water temperatures and likely the tilefish's reproductive success. We also show that this temperature–landings relationship broke down in the 1970s coincident with dramatically increased exploitation. Reconstructions of decadal to millennial scale variations in slope water temperatures explain why no mass mortality occurred following the 2010 negative NAO anomaly, despite being similar in magnitude to the NAO anomaly that preceded the 1882 event.

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Internal Wave Reflection on Shelf Slopes with Depth-Varying Stratification

Journal of Physical Oceanography ◽

10.1175/jpo-d-11-0192.1 ◽

2013 ◽

Vol 43 (2) ◽

pp. 248-258 ◽

Cited By ~ 24

Author(s):

Rob A. Hall ◽

John M. Huthnance ◽

Richard G. Williams

Keyword(s):

Internal Wave ◽

Internal Waves ◽

Energy Flux ◽

Internal Tide ◽

Shelf Break ◽

Maximum Slope ◽

Near Surface ◽

Shelf Slope ◽

Linear Slope ◽

Horizontal Wavelength

Abstract Reflection of internal waves from sloping topography is simple to predict for uniform stratification and linear slope gradients. However, depth-varying stratification presents the complication that regions of the slope may be subcritical and other regions supercritical. Here, a numerical model is used to simulate a mode-1, M2 internal tide approaching a shelf slope with both uniform and depth-varying stratifications. The fractions of incident internal wave energy reflected back offshore and transmitted onto the shelf are diagnosed by calculating the energy flux at the base of slope (with and without topography) and at the shelf break. For the stratifications/topographies considered in this study, the fraction of energy reflected for a given slope criticality is similar for both uniform and depth-varying stratifications. This suggests the fraction reflected is dependent only on maximum slope criticality and independent of the depth of the pycnocline. The majority of the reflected energy flux is in mode 1, with only minor contributions from higher modes due to topographic scattering. The fraction of energy transmitted is dependent on the depth-structure of the stratification and cannot be predicted from maximum slope criticality. If near-surface stratification is weak, transmitted internal waves may not reach the shelf break because of decreased horizontal wavelength and group velocity.

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