Pelagic Productivity and Food Chains in Fjord Systems

The fjord systems of the world are all quite young in evolutionary time, yet they offer opportunities that are unique among coastal systems. Their common origin as glaciated coastal valleys and the common hydrographic conditions documented elsewhere in this volume give them a number of characteristic features. From a marine biological point of view the most important of these are: a) Topography i) A deep basin connecting directly or indirectly with the open sea at one end over a relatively shallow sill, typically one half to one tenth basin depth. ii) A length many times greater than the width. b) Climate and hydrography iii) Pronounced seasonal change, particularly in temperature and fresh-water run-off, as found at middle and high latitudes. iv) Development of a halocline, typically in summer and autumn, between brackish surface water and fully saline subsurface water. c) Hydrodynamics v) Vertical mixing (see Pollard, 1980, this volume) at certain times of year, particularly the autumn.