| Abstract: | Key environmental parameters influencing benthic communities
are food and oxygen. The main source of food for oxygen
minimum communities in modern ocean is carbon flux from
surface primary production. Amount, composition of export
production as well as transport and decay processes within
the water column and at the sea floor are thus the main
controls on the composition of the benthic community in the
modern oceans. Consequently, the distribution record of
benthic foraminifers in the modern ocean can be used to
quantitatively reconstruct primary production and carbon
flux. Trophic chains may have been signifcantly different
during Jurassic and Cretaceous OAEs: the composition of
primary producers may have been different (i.e. diatoms may
have been a less important component in the food chain),
transfer mechanisms of organic carbon to the deep-sea may
have been fundamentally different in a warm saline ocean and
benthic sources of organic carbon (i.e. chemosynthetic
bacteria) may have played a more important role.
To decode the organic carbon flux and water mass oxygenation
signals embedded in the fossil record of benthic
foraminifera we thus have to consider processes on three
different timescales. These timescales correspond to the
duration of species (evolutionary, million of years),
populations (paeloecological, thousands of years) and
individuals (life histories). Life histories of benthic
foraminifera in modern high carbon flux/oxygen minimum
environments vary on time scales of days, seasons, or years,
depending on the ecological niche, feeding strategy,
reproduction cycle, and population dynamics of individual
species. The short-term extreme with reproduction cycles and
life histories in the range of days or weeks and extremely
fluctuating high population densities is represented by
phytodetritus exploiting species, whereas detritus feeders
can live over several years in small populations, that are
controlled by the available oxygen or food resources.
A comparsion of benthic foraminiferal communities from
Jurassic, early Cretaceous and late Cretaceous OAEs and
different types of modern oxygen minima shows, that the
modern analogue may be applicable to the late Cretaceous
OAE2 and OAE3, but significantly different life cycles and
reproduction strategies may have prevailed during the Jurassic and Lower
Cretaceous OAEs. |