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  • Print publication year: 2006
  • Online publication date: August 2009

5 - Shelf seas

Summary

Wherever possible, citations of references and data tables are given in the captions to figures to save repetition and to avoid interrupting the flow of the text. There are more comprehensive versions of Figures 5.1 and 5.6 on the linked website (indicated by ‘+ web’).

Introduction

The continental shelf includes the gently sloping sublittoral area from the open-sea shoreline to the shelf break where the inclination of sea floor increases with passage to the continental slope. The majority of shelves are shallower than 130 m but some reach depths of several hundred metres, as off Antarctica and in shelf basins. They are generally narrow along convergent plate margins where they border deep trenches (as around the Pacific Ocean), and wide along intraplate passive margins where they border a wide continental slope/rise (as around much of the Atlantic Ocean). Along the margin of California, USA, there is a transition zone from continental shelf to continental slope with deep elongated basins separated by ridges forming a continental borderland.

During the last glacial maximum (LGM) 18 000 years ago large areas of modern continental shelves were exposed as land and those at high latitudes were ice-covered. In some areas, for example, along the margins of the Norwegian–Greenland Sea, bordering mountains are cut by deep ice-gouged valleys that now form fjords. There are also large quantities of moraine deposits (e.g., off Newfoundland).