7 Imprint of Climatic Zonation on Marine Sediments
7.1 Overall Zonation and Main Factors
7.1.1 The Zones. The chief factor in producing climatic zonation is the amount of
energy received from the sun - it is high in the tropics, low at the poles (Fig. 7.1). A
coarsely latitudinal zonation of the oceans generally employs the categories tropical,
subtropical, temperate, and polar, whereby the poleward part of temperate and the
more temperate part of polar could be distinguished as subpolar (Fig. 7.2).
The tropical zone has an excess of heat, which it exports. Seasonal fluctuations are
minimal; average temperatures are near 25°C, with sustained open ocean maxima
close to 30 0c. Near the equator, daily rainfall, cloud cover, and weak winds, lead to
excess precipitation over evaporation. At the equator proper (± 2° latitude) fertility is
high because of equatorial upwelling. Elsewhere it is low, except near continents.
The subtropical zone is the broad region between the tropics proper and the temperate areas. It is the desert belt, both on land and in the sea. Cloud cover is low,
evaporation rates are high, and salinities, therefore, attain values well above average.
This zone is invaded by the neighboring climate regimes depending on seasons.
Annual temperature ranges can be very high. Coastal areas show seasonal upwelling,
depending on wind strength.
The temperate zone is strongly influenced by seasonal change. Rainfall generally
exceeds evaporation, and salinities are correspondingly reduced. Being the transition
between the warm and the cold regions of the planet, the temperate zone has strong
temperature gradients, hence strong winds. These force mixing of surface waters with
(nutrient-rich) waters in the upper thermocline, along the west-wind drift. The temperate zones are fertile regions, therefore. In the poleward parts of the temperate
zones, mixing is further enhanced by seasonal break-down of the thermocline.
The polar areas, finally, take up the smallest portion of the globe, but they are of
prime importance as makers of climate. Their ice rim fixes the endpoint of the overall
temperature gradient, which ultimately controls winds, currents, and evaporation-precipitation patterns (Figs. 4.14 and 7.2).
The climatic zones are not exactly parallel to latitudes: note how the boundaries
are shifted by the currents of the subtropical gyres, especially the Gulf Stream and its
west-wind extension.
7.1.2 Temperature and Fertility are the most important climatic factors in the
ocean, as far as the production and distribution of biogenous sediments. In the
7.1 Overall Zonation and Main Factors
7.1.1 The Zones. The chief factor in producing climatic zonation is the amount of
energy received from the sun - it is high in the tropics, low at the poles (Fig. 7.1). A
coarsely latitudinal zonation of the oceans generally employs the categories tropical,
subtropical, temperate, and polar, whereby the poleward part of temperate and the
more temperate part of polar could be distinguished as subpolar (Fig. 7.2).
The tropical zone has an excess of heat, which it exports. Seasonal fluctuations are
minimal; average temperatures are near 25°C, with sustained open ocean maxima
close to 30 0c. Near the equator, daily rainfall, cloud cover, and weak winds, lead to
excess precipitation over evaporation. At the equator proper (± 2° latitude) fertility is
high because of equatorial upwelling. Elsewhere it is low, except near continents.
The subtropical zone is the broad region between the tropics proper and the temperate areas. It is the desert belt, both on land and in the sea. Cloud cover is low,
evaporation rates are high, and salinities, therefore, attain values well above average.
This zone is invaded by the neighboring climate regimes depending on seasons.
Annual temperature ranges can be very high. Coastal areas show seasonal upwelling,
depending on wind strength.
The temperate zone is strongly influenced by seasonal change. Rainfall generally
exceeds evaporation, and salinities are correspondingly reduced. Being the transition
between the warm and the cold regions of the planet, the temperate zone has strong
temperature gradients, hence strong winds. These force mixing of surface waters with
(nutrient-rich) waters in the upper thermocline, along the west-wind drift. The temperate zones are fertile regions, therefore. In the poleward parts of the temperate
zones, mixing is further enhanced by seasonal break-down of the thermocline.
The polar areas, finally, take up the smallest portion of the globe, but they are of
prime importance as makers of climate. Their ice rim fixes the endpoint of the overall
temperature gradient, which ultimately controls winds, currents, and evaporation-precipitation patterns (Figs. 4.14 and 7.2).
The climatic zones are not exactly parallel to latitudes: note how the boundaries
are shifted by the currents of the subtropical gyres, especially the Gulf Stream and its
west-wind extension.
7.1.2 Temperature and Fertility are the most important climatic factors in the
ocean, as far as the production and distribution of biogenous sediments. In the