Circulation of slopewater

doi:10.1016/0278-4343(88)90068-4

Continental Shelf Research

Volume 8, Issues 5–7, May–July 1988, Pages 565-624

https://doi.org/10.1016/0278-4343(88)90068-4 Get rights and content

Abstract

The recently conducted Mid-Atlantic Slope and Rise (MASAR) experiment yielded much new information on the structure and behavior of slopewater, the water mass occupying the upper “Slope Sea”, a narrow band of ocean between the Gulf Stream and the continental shelf from Cape Hatteras to the Grand Banks. The results of this experiment, combined with earlier evidence, have been used to construct a new empirical schema of slopewater circulation. Key features are: (1) inflow of Coastal Labrador Sea Water (CLSW) across the Grand Banks at the rate of 4 × 10⁶ m³ s⁻¹, and isopycnal advection from the Gulf Stream thermocline at the rate of 6 × 10⁶ m³ s⁻¹, the total draining eastward; (2) a closed cyclonic gyre in the western Slope Sea, transporting approximately 3 × 10⁶ m³ s⁻¹ along the New Jersey coast southward; and (3) seasonal formation of a pycnostad by convective overturn and its flushing in approximately 6 months.

Some of the CLSW inflow retroflects and turns eastward following entry into the Slope Sea, but a significant fraction flows westward along the coast and rounds the western gyre before draining eastward.

The circulation just described reaches to an approximate depth of 500 m. Deeper layers move through the Slope Sea southwestward. The layers of the Gulf Stream thermocline in contact with slopewater along isopycnals encompass the Antarctic Intermediate Water (AAIW) core, as well as the nutrient maximum and oxygen minimum layers. Shoreward advection of these layers and seasonal overturn to 200 m establish conditions favoring productivity in the upper slopewater, as well as on the shelf.

References (68)

FuglisterF.C.
Gulf Stream '60
Progress in Oceanography
(1963)
MannC.R.
The termination of the Gulf Stream and the beginning of the North Atlantic Current
Deep-Sea Research
(1967)
RichardsonP.L.
On the crossover between the Gulf Stream and the Western Boundary Undercurrent
Deep-Sea Research
(1977)
RichardsonP.L. et al.
Gulf Stream and western boundary undercurrent observations at Cape Hatteras
Deep-Sea Research
(1971)
WorthingtonL.V.
Evidence for a two gyre circulation system in the North Atlantic
Deep-Sea Research
(1962)
BaumgartnerA. et al.
The World water balance
BeardsleyR.C. et al.
On the mean circulation in the Mid-Atlantic Bight
Journal of Physical Oceanography
(1979)
BeardsleyR.C. et al.
The Nantucket Shoals Flux Experiment (NSFE79). Part I: A basic description of current and temperature variability
Journal of Physical Oceanography
(1985)
BisagniJ.J.
Passage of anticyclonic Gulf Stream eddies through deep water dumpsite 106 during 1974 and 1975
BowerA.S. et al.
The Gulf Stream—Barrier or Blender?
Journal of Physical Oceanography
(1985)

BrownO.B. et al.

Blooming off the U.S. East Coast: A satellite description

BumpusD.F.

A description of the circulation on the continental shelf of the east coast of the United States

BunkerA.F. et al.

Energy exchange charts of the North Atlantic Ocean

Bulletin of the American Meteorological Society

(1976)

ChamberlinJ.L.

Monitoring effects of Gulf Stream meanders and warm core eddies on the continental shelf and slope

Int. Comm. Northwest Atlantic Fisheries, Selected Papers No. 2

(1977)

ChapmanD.C. et al.

On the continuity of mean flow between the Scotian Shelf and the Mid-Atlantic Bight

Journal of Physical Oceanography

(1986)

ClarkeR.A. et al.

Current system south and west of the Grand Banks of Newfoundland

Journal of Physical Oceanography

(1980)

CsanadyG.T.

Mean circulation in shallow seas

Journal of Geophysical Research

(1976)

CsanadyG.T.

The pressure field along the western margin of the North Atlantic

Journal of Geophysical Research

(1979)

CsanadyG.T.

Long-term mixing processes in slope water

CsanadyG.T.

The influence of wind stress and river runoff on a shelf-sea front

Journal of Physical Oceanography

(1984)

DeardorffJ.W.

Convective velocity and temperature scales for the unstable planetary boundary layer and for Rayleigh convection

Journal of Atmospheric Science

(1970)

DeardorffJ.W.

A multi-limit mixed layer entrainment formulation

Journal of Physical Oceanography

(1983)

DefantA.

Dynamik stationärer ozeanischen Ströme im Lichte der experimentellen Strömungslehre

Ann. der Hydrogr. und Mar. Meteorologie

(1937)

EkmanV.W.

Neuere Ergebnisse und Probleme zur Theorie der Konvektionsströme in Meere

Gerlands Beitraege zur Geophysik, Suppl, 4, Ergebnisse der Kosmischen Physik

(1939)

FairbanksR.G.

The origin of continental shelf and slope water in the New York Bight and Gulf of Maine: Evidence from H₂¹⁸/H₂¹⁶ O radio measurements

Journal of Geophysical Research

(1982)

FisherA.

Entrainment of shelf water by the Gulf Stream northwest of Cape Hatteras

Journal of Geophysical Research

(1972)

FlaggC.N. et al.

Interpretation of the physical oceanography of Georges Bank

EG&G Environmental Consultants, Report prepared for BLM

(1982)

FlierlG.R.

Simple models of waste disposal in a gyre circulation

FofonoffN.P. et al.

Estimates of mass, momentum and kinematic energy fluxes of the Gulf Stream

Journal of Physical Oceanography

(1983)

FordW.L. et al.

On the nature, occurrence and origin of cold low salinity water along the edge of the Guif Stream

Journal of Marine Research

(1952)

GatienM.G.

A study in the slope water region south of Halifax

Journal of the Fisheries Research Board of Canada

(1976)

HellermanS. et al.

Normal monthly wind stress over the world ocean with error estimates

Journal of Physical Oceanography

(1983)

HorneE.P.W.

Interleaving at the subsurface front in the slope water off Nova Scotia

Journal of Geophysical Research

(1978)

HoughtonR.W. et al.

Observation of an anticyclonic eddy near the continental shelf break south of New England

Journal of Physical Oceanography

(1986)

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^*: Present address: Department of Oceanography, Old Dominion University, Hampton Boulevard, Norfolk, VA 23508, U.S.A.

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Circulation of slopewater

Abstract

Progress in Oceanography

Deep-Sea Research

Deep-Sea Research

Deep-Sea Research

Deep-Sea Research

The World water balance

On the mean circulation in the Mid-Atlantic Bight

Journal of Physical Oceanography

The Nantucket Shoals Flux Experiment (NSFE79). Part I: A basic description of current and temperature variability

Journal of Physical Oceanography

Passage of anticyclonic Gulf Stream eddies through deep water dumpsite 106 during 1974 and 1975

The Gulf Stream—Barrier or Blender?

Journal of Physical Oceanography

Blooming off the U.S. East Coast: A satellite description

A description of the circulation on the continental shelf of the east coast of the United States

Energy exchange charts of the North Atlantic Ocean

Bulletin of the American Meteorological Society

Monitoring effects of Gulf Stream meanders and warm core eddies on the continental shelf and slope

Int. Comm. Northwest Atlantic Fisheries, Selected Papers No. 2

On the continuity of mean flow between the Scotian Shelf and the Mid-Atlantic Bight

Journal of Physical Oceanography

Current system south and west of the Grand Banks of Newfoundland

Journal of Physical Oceanography

Mean circulation in shallow seas

Journal of Geophysical Research

The pressure field along the western margin of the North Atlantic

Journal of Geophysical Research

Long-term mixing processes in slope water

The influence of wind stress and river runoff on a shelf-sea front

Journal of Physical Oceanography

Convective velocity and temperature scales for the unstable planetary boundary layer and for Rayleigh convection

Journal of Atmospheric Science

A multi-limit mixed layer entrainment formulation

Journal of Physical Oceanography

Dynamik stationärer ozeanischen Ströme im Lichte der experimentellen Strömungslehre

Ann. der Hydrogr. und Mar. Meteorologie

Neuere Ergebnisse und Probleme zur Theorie der Konvektionsströme in Meere

Gerlands Beitraege zur Geophysik, Suppl, 4, Ergebnisse der Kosmischen Physik

The origin of continental shelf and slope water in the New York Bight and Gulf of Maine: Evidence from H218/H216 O radio measurements

Journal of Geophysical Research

Entrainment of shelf water by the Gulf Stream northwest of Cape Hatteras

Journal of Geophysical Research

Interpretation of the physical oceanography of Georges Bank

EG&G Environmental Consultants, Report prepared for BLM

Simple models of waste disposal in a gyre circulation

Estimates of mass, momentum and kinematic energy fluxes of the Gulf Stream

Journal of Physical Oceanography

On the nature, occurrence and origin of cold low salinity water along the edge of the Guif Stream

Journal of Marine Research

A study in the slope water region south of Halifax

Journal of the Fisheries Research Board of Canada

Normal monthly wind stress over the world ocean with error estimates

Journal of Physical Oceanography

Interleaving at the subsurface front in the slope water off Nova Scotia

Journal of Geophysical Research

Observation of an anticyclonic eddy near the continental shelf break south of New England

Journal of Physical Oceanography

The origin of continental shelf and slope water in the New York Bight and Gulf of Maine: Evidence from H₂¹⁸/H₂¹⁶ O radio measurements