Geology Reference
In-Depth Information
• Aggregate grains (Sect. 4.2.7) are abundant in the
upper euphotic zone.
Morphological adaptions
• Morphological features that may be interpreted as
adaptions to light conditions occur in various inverte-
brates (e.g. eye reduction in ostracods and trilobites).
Algae and cyanobacteria
• Occurrence of calcareous algae. Depth distribution
patterns of green algae are much narrower than those
of red algae, which can utilize minimal light intensities
and specific wave lengths. Corallinacean red algae,
therefore, may also occur in deeper waters down to more
than 200 meters.
• Dasyclad algae are restricted to a few meters in
depth; the depth range of udoteacean green algae var-
ies between a few tens of centimeters to about 80 meters.
Since the fragments of calcareous green algae are of-
ten transported, some caution is needed when using the
occurrence of dasyclads as an indicator of the upper
euphotic zone.
• Because light conditions control the growth rates of
encrusting coralline algae, the thickness of the calci-
fied algal body can be used in evaluating relative water
depths (Sect. 10.2.1.2).
• The taxonomic composition of red algal oncoids
(rhodoids) reflects differences in light conditions.
Rhodoids offer a possibility of distinguishing shallower
and deeper parts of the euphotic zone.
• Cyanobacteria are aerobic phototrophs. They occur
in illuminated as well as in shadowy habitats and can
better tolerate changes in light, salinity, water tempera-
ture and other ecological factors than algae (Sect. 9.1).
Basics: Light
Aguirre, J., Riding, R., Braga, J.C. (2000): Late Cretaceous
incident light reduction: evidence from benthic algae. -
Lethaia,
33
, 205-213
Budd, D.A., Perkins, R.D. (1980): Bathymetric zonation and
paleoecological significance in Puerto Rican shelf and
slope sediments. - Journal of Sedimentary Petrology,
50
,
881-553
Glaub, I. (1994): Mikrobohrspuren in ausgewählten Ablage-
rungsräumen des europäischen Jura und der Unterkreide
(Klassifikation und Palökologie). - Courier Forschungs-
institut Senckenberg,
174
, 1-324
Jerlov, N.G. (1970): Light. - In: Kinne, O. (ed.): Marine ecol-
ogy. Vol. I (Environmental factors), part 1. - 95-102, Lon-
don (Wiley)
Liebau, A. (1980): Paläobathymetrie und Ökofaktoren: Flach-
meerzonierungen. - Neues Jahrbuch für Geologie und
Paläontologie, Abhandlungen,
160
, 173-216
Liebau, A. (1984): Grundlagen der Ökobathymetrie. - Palä-
ontologische Kursbücher,
2
, 149-184
Lüning, K. (1985): Meeresbotanik. Verbreitung, Ökophysio-
logie und Nutzung der marinen Makroalgen. - 375 pp.,
Stuttgart (Thieme)
Riedl, R. (1966): Biologie der Meereshöhlen. - 636 pp., Ham-
burg (Parey)
Further reading:
K168
12.1.5 Oxygen
Microborers
• Microorganisms boring in shells or hard lithified
substrates are excellent indicators of light conditions
and water depths (Fig. 9.16). Boring cyanobacteria,
algae and fungi are used to subdivide the euphotic and
dysphotic zones.
Oxygen is a bio-limiting element for marine metazoa
and one of the most important factors influencing spe-
cies diversity and abundance. The absence of oxygen
is generally considered to be essential for inhibiting
microbial decay and forming organic-rich sediments
(Allison et al. 1995).
Oxygen-controlled environments occur in tidal flats,
open to poorly enclosed shelf seas, upwelling areas,
filled basins, and hydrothermal vent and cold seep ar-
eas (Oschmann 1995). All these environments show
cyclic oxygen fluctuations.
Estimates of dissolved-oxygen levels in ancient
oceans contribute towards an understanding of the his-
tory of ocean circulation and paleoclimate. Paleo-oxy-
genation levels are based on fabrics (intensity of bio-
turbation), biota (foraminifera, bivalves) and geochemi-
cal criteria (organic carbon/sulfur ratio, sulfur isotopes,
rare element concentrations).
Organisms with photosymbionts
• Benthic larger foraminifera with green and red algal
symbionts are restricted to shallow euphotic areas (Sect.
10.2.2.1). Differences in light attenuation by the water
column are reflected by different wall structures
(Hohenegger 1999). Planktonic foraminifera with al-
gal endosymbionts occur in water depths down to 50
and 100 m.
• Various invertebrates (e.g. corals, some bivalves) are
characterized by photosymbiotic algae. Calcification
and distribution of zooxanthellate reef corals is greatly
determined by endosymbiotic algae. The symbiosis of
ancient corals and algae is inferred from the morpho-
logical criteria of the corals (e.g. integration and size
of corallites) and from stable isotope data.
The oxygen content is generally high in the surface
waters of the oceans. A
shallow oxygen maximum
(SOM)
occurs in the upper ocean layers (Hayward
