Fjords
Distribution
• Fjords formed by glaciers, consequently
occur at high latitudes
• Northern hemisphere: Canada, USA (one
fjord), Norway, Island, Greenland,
Scotland, Sweden (one fjord)
• Southern hemisphere: Chile, New Zealand
Topography
• Outer sill, sill depth and area at opening
essential for exchange with outer waters
• Polls, very shallow sill
• Fjords are deep; depth more important
characteristics than supply of freshwater
• Sognefjorden 1300 m
Sketch fjord
Transport (advection)
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Estuarine circulation
Exchange intermeditate layer
Deep water renewals
Tidal exchange
Estuarine circulation
• Supply of freshwater gives surplus of water which runs out of the
estuary/fjord
• Mixes with salt water, so that volume of outgoing water increases,
including outwards transport of salt water
• Results in an ingoing, compensation current of salt water
Example estuarine circulation; experiment
with hydroelectric power plant
Biological implication: brackish
water plankton
Oceanic fauna
In this situation estuarine circulation important,
but text books often give a misleading picture
of its importance in fjords
• Fjords are deep, and only a thin, upper layer
impacted by freshwater (though the most
productive vertical strata)
• The ”engine” in ES generally to weak
compared to other current systems
Exchange in the intermediate layer
may be very important
• Exchange between fjord and outer coastal
waters, beneath the brackish layer, but
above sill depth
• Importance of exchange in the
intermediate layer increases by depth and
area at fjord opening
Deep water/oxygen
Fish and krill in hypoxic waters
Bunnefjorden
• Oxygen reduced at depth, but still normally sufficient
oxygen also in the deep basin water (basin water =
beneath sill depth)
• Gradual dilution of deep water over time due to mixing
with upper layers, make the deep water less dense
• Replacement of the deep water when water at (above)
sill depth outside the fjord higher density than basin
water within the fjord
• Deep water renewals often during winter, due to
temperature, salinity (at sill depth) and wind conditions
• Frequencies of renewals varies among fjords
Nordfjord, many years between renewals, still
no oxygen deficiency at 400 m depth
Fjords of limited vaule for fisheries
• Aquaculture
• Sprat
• Overwintering herring
Fauna
• The fauna in fjords simlar to coastal and
oceanic fauna, no praticular fjord fauna
• The depth of fjords very important; large
depth facilitates presence of deep-sea
(mesopelagic) species otherwise only
found in the open ocean
• Fjords with different optical properties
have different fauna
Benthosema glaciale
Periphylla periphylla
Fjords as model systems
• Fjords can be used as model systems for
oceans
• Easy access to organisms which otherwise only
can be studied at large depths offshore
• Inexpensive, simple logistics
• Examples: mortality overwintering Calanus
exposed to different types of predators, the
ecology of krill, mesopelagic fish, deep sea
jellyfish