41
Abstract There are boundaries in the ocean which are not fronts, such as the
pycnocline, the interface of water with the air, the sediments or the ice. These
boundaries pose distinctive biotic and abiotic conditions and are the preferred
living space for certain groups of organisms. Due to the gravitational stratification, vertical scales in the sea are highly compressed relative to horizontal scales,
so pycnoclines, and the interfaces between water and sediments; ice; and the
atmosphere are all nearly horizontal edges having much larger horizontal scales
than typical fronts. Most of these interfaces are layers of greatly reduced flows,
weakening plankton dispersion. Life tends to congregate at boundaries and such
non-frontal interfaces are places of locally elevated biological activity. However,
non-frontal interfaces lack mechanisms that persistently bring nutrients to promote phytoplankton production. Fronts concentrate more biological productivity
in narrower places, and their dynamics appear as more complex, characterized by
intense three dimensional flows. Such complexity could explain the wider range
of ecological properties of fronts compared to other interfaces.
Keywords Thermocline · Halocline · Marine interfaces · Abiotic conditions ·
Plankton concentration · Benthic boundary layer
5.1 The Pycnocline Interface
In several regions of the oceans the water column is stratified, that is, there is a low
density layer overlaying a denser layer. The density change between both layers
is abrupt and is referred to as a pycnocline (Fig. 5.1); most fronts are associated
or connected with pycnoclines (e.g. tidal fronts; estuarine fronts), but pycnoclines
exist independently of fronts. Pycnoclines may be driven by temperature (thermoclines) or by salinity (haloclines); or by both. Haloclines are more common
in coastal waters due to the continental runoff, while thermoclines are present
in coastal and offshore environments and are basically driven by the balance of
solar heating and wind mixing. In addition to temperature and salinity pycnoclines
Chapter 5
Comparisons of Fronts with Other
Boundaries at Sea
© The Author(s) 2015
E.M. Acha et al., Ecological Processes at Marine Fronts,
SpringerBriefs in Environmental Science, DOI 10.1007/978-3-319-15479-4_5
Abstract There are boundaries in the ocean which are not fronts, such as the
pycnocline, the interface of water with the air, the sediments or the ice. These
boundaries pose distinctive biotic and abiotic conditions and are the preferred
living space for certain groups of organisms. Due to the gravitational stratification, vertical scales in the sea are highly compressed relative to horizontal scales,
so pycnoclines, and the interfaces between water and sediments; ice; and the
atmosphere are all nearly horizontal edges having much larger horizontal scales
than typical fronts. Most of these interfaces are layers of greatly reduced flows,
weakening plankton dispersion. Life tends to congregate at boundaries and such
non-frontal interfaces are places of locally elevated biological activity. However,
non-frontal interfaces lack mechanisms that persistently bring nutrients to promote phytoplankton production. Fronts concentrate more biological productivity
in narrower places, and their dynamics appear as more complex, characterized by
intense three dimensional flows. Such complexity could explain the wider range
of ecological properties of fronts compared to other interfaces.
Keywords Thermocline · Halocline · Marine interfaces · Abiotic conditions ·
Plankton concentration · Benthic boundary layer
5.1 The Pycnocline Interface
In several regions of the oceans the water column is stratified, that is, there is a low
density layer overlaying a denser layer. The density change between both layers
is abrupt and is referred to as a pycnocline (Fig. 5.1); most fronts are associated
or connected with pycnoclines (e.g. tidal fronts; estuarine fronts), but pycnoclines
exist independently of fronts. Pycnoclines may be driven by temperature (thermoclines) or by salinity (haloclines); or by both. Haloclines are more common
in coastal waters due to the continental runoff, while thermoclines are present
in coastal and offshore environments and are basically driven by the balance of
solar heating and wind mixing. In addition to temperature and salinity pycnoclines
Chapter 5
Comparisons of Fronts with Other
Boundaries at Sea
© The Author(s) 2015
E.M. Acha et al., Ecological Processes at Marine Fronts,
SpringerBriefs in Environmental Science, DOI 10.1007/978-3-319-15479-4_5