Continental Shelf Break and Continental Shelf

Important Processes at the Shelf Break:

Shelf Break Fronts

Eddies and meanders

IntrusionsShelf Break Depth - Ekman DynamicsProperty exchange through Canyons

SHELF BREAK FRONTS

A hydrographic section through the shelf break front on the shelf of the Mid-Atlantic Bight, taken south of Rhode Island in April 1974. After Flagg and Beardsley (1975), adapted from Bowman and Esaias (1978).

© 1996 M. Tomczak

SHELF BREAK FRONTS

The shelf break front of Bass Strait. Left: Sea surface temperature (°C, top), salinity (middle) and density (bottom). Right: Vertical density sections across the front, south (top) and north-east (bottom) of the Cascade. As indicated by the 26.55 and 26.60 contours, the front is attached to the bottom south of the Cascade but lifted off the bottom, indicating movement down the slope, in the north. The approximate position of the two vertical sections is indicated by the black lines in the temperature map (a). Adapted from Tomczak (1985).

© 2000 M. Tomczak

EDDIES AND MEANDERS

Cause large cross-isobath flows

Frontal eddiesFrontal eddiesSmall cold-core cyclonic featuresEnhance shelf/ocean exchanges

Meanders

MEANDERS

WARM-CORE RINGS

COLD-CORE RINGS

Importance of shelf break depth on shelf/ocean exchange

Importance of canyons

Canyons favor injection of ocean materials to coastal environments

Sometimes really close to the coast

But they may also serve as conduits of terrigenous materials to the open ocean

Dynamics of Wind-Dominated Shelves (e.g. western coast of U.S.)

zu

Azx

pfv z

1

zu

Az

HxgfV

bsx x

Across-shelf

HygfU

bsy y

Along-shelf

zu

Azy

uA

yxu

Axx

pfv

zu

wyu

vxu

utu

zyx1

Across-shelf dynamics:

Integrating throughout the water column:

Continental Shelves Influenced by Freshwater (Large Scale)

zv

Azy

vA

yxv

Axy

pfu

zv

wyv

vxv

utv

zyx1

zu

Azx

pz

10 Along-shore

xp

fv

1

Across-shore

Semigeostrophic

Dynamics

Similar to

Shallow Shelves

CoherentCoastal Current

Mid-Atlantic Bight

Green

land

Norway

Iceland

Gaspé Peninsula

Québec

New Brunswick

Nova Scotia

Newfoundland

Anticosti Island

Gaspé Peninsula

Québec

Gaspé Peninsula

Québec

New Brunswick

Nova Scotia

Newfoundland

What is the transverse length scale?

xp

fv

1

zx

gx

gxp

1

HgLf x '22

2

2 'fHg

Lx

f

HgLx

'

zx

gvf

Reformulating in terms of the balance between baroclinic pressure gradient and Coriolis:

xx L

HgfLf '

Scaling:

fC

L ix

Internal radius of deformation orInternal Rossby radius

Continental Shelves Influenced by Fresh Water (small scale)

Non-linear effects may be influential

Coriolis not

Radial Plume - Pulsating

Radial Plume - Pulsating

Results by Neil Banas, U. of Washington

What if wind is important?

Component Non-linear

Coriolis Pressure

Gradient

Wind Stress

Other Stresses

Narrow and deep shelves

cross-shelf X XX X XX Xalong-shelf X X XX XX X

Shallow shelves cross-shelf X XX XX X Xalong-shelf X X XX XX XX

Shelves influenced by fresh water

cross-shelf X XX XX X X(large scale) along-shelf X X XX XX XXShelves influenced by fresh water

cross-shelf XX X XX X X(small scale) along-shelf XX X XX X X

Steady Dynamics Over Continental Shelves

XX - Dominant ForcingX - may be dominantX - weak