Geology Reference
In-Depth Information
Pittman, J.S., Folk, R.L. (1971): Length-slow chalcedony after
sulphate evaporite minerals in sedimentary rocks. - Natu-
ral Physical Science,
230
, 64-65
Rye, D.M., Sommer, M.A. (1980): Reconstructing paleo-
temperature and paleosalinity regimes with oxygen iso-
topes. - In: Rhoads, D.C., Lutz, A.R. (eds.): Skeletal
growth of aquatic organisms. Biological records of envi-
ronmental change. - 169-202, New York (Plenum Press)
Spötl, C., Longstaffe, F.J., Ramseyer, K., Rüdinger, B. (1999):
Authigenic albite in carbonate rocks - a tracer of deep-
burial brine migration? - Sedimentology,
46
, 649-666
Yin, J. (1991): Stable carbon and oxygen isotopes in Jurassic
shells as palaeosalinity indicators. - Neues Jahrbuch für
Geologie und Paläontologie, Monatshefte,
1991
, 163-176
Yin, J., Fürsich, F., Werner, W. (1995): Reconstruction of
palaeosalinity using carbon isotopes and benthic associa-
tions: a comparison. - Geologische Rundschau,
84
, 223-
236
Further reading:
K155, K156 (trace elements), K158, K159
(stable isotopes), K170 (paleosalinity criteria).
production are largely confined to coastal regions of
the continental shelf due to the input of nutrients to-
gether with weathered materials from rocks on land and
upwelling of cold nutrient-rich waters from the deep.
Sediments associated with upwelling are rich in ma-
rine organic carbon, biologically produced silicon and
phosphorus.
In shallow depths plants photosynthesize faster than
they respire and more organic material is produced than
consumed. At the compensation depths photosynthesis
and respiration are equal. Below these depths respira-
tion exceeds photosynthesis and respiration by animals
as well as inorganic oxidation continues. Destruction
of organic matter frees nutrient elements that go back
into solution in seawater. This results in a low concen-
trations of nutrients at the surface and increasing con-
centration below the compensation depth. This basic
pattern is changed by vertical circulation. Some pri-
mary production occurs below the compensation depth
in deep waters by organisms using chemical energy.
Spectacular examples are bacteria that obtain their en-
ergy by oxidizing sulfide in hot vents. These bacteria
form the basis of an entire ecosystem.
The geographic variation in nutrient element con-
centration is influenced by global circulation patterns.
Areas of divergent currents usually exhibit high nutri-
ent element concentrations and high productivity. The
waters can also be enriched in nutrient elements by up-
welling water bodies. Areas of convergence in the cen-
ter of circulation gyres usually have low nutrient con-
centrations.
Nutrients may also be provided by
geothermal endo-
upwelling
(Rougerie and Wauthy 1986, 1993; Rougerie
et al. 1992): In this thermo-convective process in Pa-
cific atolls and barrier reefs remnant geothermal heat
from the volcanic foundation drives a continual upward
flow of deep oceanic waters (rich in nutrients) through
the overlying porous reef framework. The nutrients at
the reef surface support the high metabolism of the liv-
ing community. The importance of this mechanism has
been also stressed for ancient reefs (Rougerie and
Fagerstrom 1994).
12.1.8 Productivity and Nutrients
Nutrients are important controls on the rate of carbon-
ate production, bioerosion and the formation and de-
struction of carbonate platforms and reefs. Productiv-
ity collapse is regarded as a prime factor in major ex-
tinction events (e.g. Wood 1993; Caplan et al. 1996).
Productivity is the rate of production of organic
material by biological processes.
Primary productivity
refers to the production of energy-rich organic com-
pounds from inorganic materials predominantly by pho-
tosynthesis, but also by chemosynthetic bacteria, and
is expressed in terms of grams of carbon fixed per unit
area or volume of seawater per time interval. Prime
factors affecting primary productivity are light, nutri-
ents and vertical mixing of water, which is different in
temperate, tropical and polar seas.
Secondary produc-
tivity
designates the production of organic material by
animals utilizing preexisting plant and animal organic
matter.
Major texts concerning marine productivity are
listed under 'Basics'. Brasier (1995a, 1995b) gave a
concise summary of current thinking on the controls
and effects of nutrient levels on organisms and envi-
ronments.
Surface waters may be eutrophic or oligotrophic.
Eutrophic
conditions are characterized by high and os-
cillating levels of nutrient supply, and high net produc-
tivity. Good examples are the upwelling areas off the
west coast of Africa.
Oligotrophic
conditions are char-
acterized by low and stable nutrient supply and lower
net productivity. Examples are the coral reefs of the
Caribbean, and the Indian and Pacific Ocean.
Meso-
trophic
conditions are characterized by increasing nu-
trient supply favoring suspension feeders. Factors which
12.1.8.1 Nutrients
Bio-limiting nutrient elements are phosphorus, nitro-
gen, iron and silicon. In the presence of light and opti-
mal temperatures these elements control the primary
production by photosynthesis. Nutrient supply results
from terrestrial influx or organic matter, marine trans-
gression or upwelling. Optimal conditions for primary
