Überall, Sascha (2000) Holocene benthic foraminiferal assemblages from the SW Pacific : implications for a high resolution. (Diploma thesis), Aachen Technical University; GEOMAR, Aachen, Germany; Kiel, Germany, 84, XLIX pp.

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Abstract

The ocean between Australia/New Zealand and Antarctica is the major gateway for water mass exchange between the Indian and the Pacific Oceans. Thus, it is a key region of global oceanic circulation. As part of the paleoceanographical project TASQWA, this thesis presents a highresolution study and interpretation of the Holocene oceanographic and ecological variability of this area. The investigation concentrates on the abundance and faunal association of deep-sea benthic foraminifera. Short sediment cores were taken along two transects (South Tasman Rise and eastern Campbell Plateau) covering different water depths and water masses. The almost undisturbed sediments were continuously investigated in 1 cm intervals. The sediment record represents the entire Holocene period and is correlated to distinct climatic changes. However, evidence for erosional events and redepositional sedimentation is present. Multiple environmental factors are reflected by the investigated foraminiferal assemblages:
- Early diagenesis diminishes the abundance of certain arenaceous species in the uppermost cm of the sediment.
- Variations of nutrient flux have the major impact on the living fauna. Fursenkonia contemplata indicates high productivity at the South Tasman Rise, lasting until ~7500 years before present. The enhanced productivity might reflect the position of the Subtropical Front.
- A correlation between climatic changes (indicated by planktic δ18O isotope ratios) and benthic foraminifera species is described: Uvigerina peregrina is abundant in phases of warmer climate, Melonis pompilioides prefers phases of colder climate.
- Several distinct benthic foraminiferal assemblages, associated with certain water masses as published elsewhere, were found and described. A Nuttalides umbonifer association indicates strong influence of Antarctic Bottom Water (AABW). A Globocassidolina subglobosa association is described in samples recently bathed in the Circumpolar Deep Water (CPDW).
The variability in benthic foraminiferal assemblages indicates a change in bathymetric position of deep and bottom water masses:
The decreasing influence of the N. umbonifer association evolves into an abrupt change to the G. subglobosa association at the eastern Campbell Plateau at ~8000 years before present. This pattern is interpreted as a deepening of the water masses. The trend of the faunal associations at the South Tasman Rise is reverse: the influence of the N. umbonifer association increases throughout the last ~7500 years before present, while the significance of the G. subglobosa association decreases. A shallowing of the water mass body structure is assumed.

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