100
Chapter 6: Biomes: The Primary Partition
Here, tidal streams and water depth control in the same manner where tidally mixed
and stratified shelf regions should occur, and the consequences of the flow of silty,
nutrient-rich river water out across the shelf are very similar everywhere. With some
exceptions that shall be noted, sedimentary regimes and the nature of deposits is rather
uniform and the ecological interaction between benthic and pelagic biota follows rather
similar logic everywhere. The strong interaction between the oceanography of any continental shelf and that of the adjacent oceanic biome that undoubtedly exists everywhere
is, nevertheless, of secondary importance to regional ecology compared with the physical
processes over the shelf.
The concept of a coastal boundary zone in the ocean was introduced by Mittelstaedt
(1991) and defines what many oceanographers regard as the critical regional distinction
between processes over continental shelves and those in the open oceans. The width of
the coastal boundary will tend to be a function of latitude, if topography permits, because
(as discussed in Chapter 4) the Rossby radius of deformation is a function of the relative
strength of the Coriolis acceleration, itself a function of latitude.
Continental shelves, the fundamental habitat of the Coastal biome, reflect the geomorphology of the continent of which they form the margin so that not only the width,
depth, orientation, and topography of the continental shelf are significant, but also the
nature of the coastline itself. Rias and fjordlands, shallow sedimentary regions (with or
without fringing mangroves), and the existence of major rivers are some of the characteristics that will determine the nature of the regional coastal ecosystem. Finally, the
discharge of silt by rivers onto the shelf is much greater in low than high latitudes.
Three-quarters of all silt delivered by all rivers comes from the Amazon/Orinoco (11%)
and from the rivers that enter the Bay of Bengal, the South China Sea, and the basins of
the Indo-Pacific archipelago (65%). In these regions, then, we may expect to find greater
areas of continental shelf dominated by silty, organic-rich deposits, and so it is. Shallow
seas in regions such as the Gulf of Thailand have almost entirely soft, muddy deposits.
Nevertheless, there is significant commonality in the ecology of muddy bottoms at all
latitudes, and whether the facies is small or is extensive.
The concept of shelf and slope water regimes, originally applied only to wide midlatitude shelves, is probably relevant at all latitudes. Shelf-break fronts are not only a useful
defining feature for the boundaries of this biome but, as discussed in Chapter 2, they
also have consequences for algal growth that are likely to be of importance everywhere,
and they will require special attention.
Coastal upwelling, and nutrient enrichment, occurs off all coasts and at all latitudes, seasonally forced by interaction among local topography, coastal currents, wind, and Kelvin
waves induced by distant wind stress. However, with the exception of the Somali-Omani
upwelling, all these are minor compared with upwelling in the California, Humboldt,
Canary, and Benguela current systems, and it is toward these that the attention of the
biological oceanography community has been largely directed. The wide range of conditions in these sites invites study by the comparative method, and this has been a feature of
research here: their individual characteristics will be discussed in later chapters.
Over the eastern boundary currents, the equatorward trade wind field has two maxima.
One of these, at 100–300 km from the coast, is also the line of zero wind curl so that
cyclonic curl (upward Ekman motion) occurs landward of the wind maximum, and
anticyclonic curl (downward Ekman motion) seaward. The offshore current velocity
maximum is also coincident with this offshore maximum in the wind field. A second
equatorward wind velocity maximum often occurs at the coast and is the boundary-layer
response of the eastward component of the oceanic wind field to its encounter with
coastal topography. Coastal winds also have a greater diel component than the oceanic
wind field, forced by the opposition of daytime solar heating and evening wind mixing,
and this phenomenon may give rise to diel changes in near-shore water column stability.
Chapter 6: Biomes: The Primary Partition
Here, tidal streams and water depth control in the same manner where tidally mixed
and stratified shelf regions should occur, and the consequences of the flow of silty,
nutrient-rich river water out across the shelf are very similar everywhere. With some
exceptions that shall be noted, sedimentary regimes and the nature of deposits is rather
uniform and the ecological interaction between benthic and pelagic biota follows rather
similar logic everywhere. The strong interaction between the oceanography of any continental shelf and that of the adjacent oceanic biome that undoubtedly exists everywhere
is, nevertheless, of secondary importance to regional ecology compared with the physical
processes over the shelf.
The concept of a coastal boundary zone in the ocean was introduced by Mittelstaedt
(1991) and defines what many oceanographers regard as the critical regional distinction
between processes over continental shelves and those in the open oceans. The width of
the coastal boundary will tend to be a function of latitude, if topography permits, because
(as discussed in Chapter 4) the Rossby radius of deformation is a function of the relative
strength of the Coriolis acceleration, itself a function of latitude.
Continental shelves, the fundamental habitat of the Coastal biome, reflect the geomorphology of the continent of which they form the margin so that not only the width,
depth, orientation, and topography of the continental shelf are significant, but also the
nature of the coastline itself. Rias and fjordlands, shallow sedimentary regions (with or
without fringing mangroves), and the existence of major rivers are some of the characteristics that will determine the nature of the regional coastal ecosystem. Finally, the
discharge of silt by rivers onto the shelf is much greater in low than high latitudes.
Three-quarters of all silt delivered by all rivers comes from the Amazon/Orinoco (11%)
and from the rivers that enter the Bay of Bengal, the South China Sea, and the basins of
the Indo-Pacific archipelago (65%). In these regions, then, we may expect to find greater
areas of continental shelf dominated by silty, organic-rich deposits, and so it is. Shallow
seas in regions such as the Gulf of Thailand have almost entirely soft, muddy deposits.
Nevertheless, there is significant commonality in the ecology of muddy bottoms at all
latitudes, and whether the facies is small or is extensive.
The concept of shelf and slope water regimes, originally applied only to wide midlatitude shelves, is probably relevant at all latitudes. Shelf-break fronts are not only a useful
defining feature for the boundaries of this biome but, as discussed in Chapter 2, they
also have consequences for algal growth that are likely to be of importance everywhere,
and they will require special attention.
Coastal upwelling, and nutrient enrichment, occurs off all coasts and at all latitudes, seasonally forced by interaction among local topography, coastal currents, wind, and Kelvin
waves induced by distant wind stress. However, with the exception of the Somali-Omani
upwelling, all these are minor compared with upwelling in the California, Humboldt,
Canary, and Benguela current systems, and it is toward these that the attention of the
biological oceanography community has been largely directed. The wide range of conditions in these sites invites study by the comparative method, and this has been a feature of
research here: their individual characteristics will be discussed in later chapters.
Over the eastern boundary currents, the equatorward trade wind field has two maxima.
One of these, at 100–300 km from the coast, is also the line of zero wind curl so that
cyclonic curl (upward Ekman motion) occurs landward of the wind maximum, and
anticyclonic curl (downward Ekman motion) seaward. The offshore current velocity
maximum is also coincident with this offshore maximum in the wind field. A second
equatorward wind velocity maximum often occurs at the coast and is the boundary-layer
response of the eastward component of the oceanic wind field to its encounter with
coastal topography. Coastal winds also have a greater diel component than the oceanic
wind field, forced by the opposition of daytime solar heating and evening wind mixing,
and this phenomenon may give rise to diel changes in near-shore water column stability.