Abstract
Paleoecological and paleoenvironmental analysis of benthic and planktonic
foraminiferal associations from sediments from the northern Adriatic Sea, the Kau
Basin (Halmahera) and the Molucca Sea shed new light on the way in which various
environmental factors influence foraminiferal distribution patterns. The qualitative
and quantitative analyses on the faunas from these areas are presented and
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the
results discussed in eight separate papers, compiled as chapters 1 - 8 of this thesis.
In a series of three papers on the seasonally productive northern Adriatic
Sea (chapters 2-4), the influence of oxygenation and food supply on the size and
composition of benthic foraminiferal communities is emphasized. The paper on
benthic foraminiferal microhabitat selection (chapter 2) shows that three categories
of species can be distinguished on the basis of their vertical distribution patterns
in the sediment. These categories include epifaunal, predominantly infaunal and
potentially infaunal groups of taxa; the habitat selection appears to be closely
related to the degree of oxygenation of the sea-bottom environment.
From the distribution of living benthic foraminifera in fourteen sample
stations in the northern Adriatic Sea (chapter 3) it is concluded that the downward
organic flux is the most important factor determining the overall distribution
patterns. This flux controls the complex relation between food and oxygen
availability in the benthic environment.
Chapter 4 deals with a study on the benthic foraminiferal record
documenting the eutrophication history of the northern Adriatic Sea during the last
160 years. Three time-successive changes in benthic foraminiferal assemblages can
be attributed to the impact of man-induced changes in sedimentation rates, food
and oxygen availability in front of the Po delta. Anoxic, pollution-related events
occurred with increasing frequency since 1960, whereas the effects these events
had became even more from about 1980 onwards.
The two papers on the Kau Basin, Halmahera (chapters 5 and 6) give a
detailed account of its environmental evolution since the latest Pleistocene. Kau
Basin, which was a freshwater lake during the last glacial maximum, became
reconnected with the open ocean about 10 ka SP, due to the sea level rise at the
Pleistocene - Holocene transition. Dysoxic bottom conditions prevailed throughout
the Holocene. The surface waters were homothermal over the last 8 ka, as evidenced
by the composition of the low-diversity planktonic associations. Changes
in surface water productivity were most probably related to variations in river
discharge. Palynological, planktonic foraminiferal and stable isotope data from a
piston core off Halmahera are used to reconstruct glacial! interglacial contrasts in
the northern Molucca Sea (chapter 7). The inferred environmental changes are
interpreted in terms of changes in monsoonal circulation, lapse rate, and water
exchange between the Pacific and Indian Oceans. It is concluded that the glacial
climate was drier than today and that surface water temperatures were between
oand 2.5° C lower than at present.
In chapter 8, where benthic foraminiferal assemblages from food- enriched
areas are discussed, fluctuations in relative numbers of groups of opportunistic inand
epifauna from the Holocene of the Kau Basin are explained by applying the
microhabitat model established for the northern Adriatic Sea. It is shown that the
temporal and spatial relationships between the benthic faunas mainly mirror the
effects of changes in oxygenation of the bottom environments, which, in turn, can
be related to the Holocene climatic evolution
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