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Iacopo Trattenero, Università degli Studi di Pavia (Italy)
Claudia Lupi, Università degli Studi di Pavia (Italy)
Nicoletta Mancin, Università degli Studi di Pavia (Italy)
Miriam Cobianchi, Università degli Studi di Pavia (Italy)
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The present work is based on the integrated study of calcareous nannofossil and benthic foraminiferal assemblages from the IMAGES site MD97-2114 (East New Zealand, Pacific Ocean) and aims to reconstruct the climate and oceanographic events occurred in this area during the Pleistocene. The site studied is located at bathyal water depth northeast of the Chatham Rise, a submarine plateau which extended for 300 Km eastern of New Zealand. This core records the last 1.07 My with substantial continuity of sedimentation as inferred by magneto-biostratigraphical data. Finally, the importance of the proposed site is also related to its peculiar position along the trajectory of the Deep Western Boundary Current (DWBC) that is the most important bottom current from the Antarctic sinking regions to the Pacific Ocean. Otherwise, the subtropical front lies upon the rise itself and separates the Subtropical Waters from the Subantarctic Waters, therefore this site is a good case history to check this topic.
Micropaleontological data have been collected through standard methodologies and processed using the most common and useful statistical methods of mono and multivariate analyses. The Principal Component Analysis, driven of the relative abundances of the most abundant benthic foraminiferal species, shows that the distribution patterns are mainly driven by primary productivity. In fact, benthic assemblages are alternatively dominated by indices indicative of conditions of very high to moderate food supply. In particular, the lower portion of the IMAGES core is characterized, up to MIS 18, by benthic foraminiferal assemblages indicative of mesotrophic conditions. In the central part of the core, a slow increase of the relative abundances of eutrophic taxa, which persists up to the MIS 10/MIS 9 transition, is documented. Than, after a period of re-establishment of mesotrophic conditions (up to MIS 7), a new trend of increasing productivity characterises the upper part of the core.
Calcareous nannofossil data are mainly consistent with benthic foraminiferal results. In fact, in the lower part of the core (up to MIS 18) calcareous nannofossil assemblages indicate stratified water column predominantly characterised by meso-oligotrophic conditions (e.g. occurrence of Oolithotus fragilis), whereas from MIS 14 to MIS 8, high abundance of Gephyrocapsa caribbeanica suggests enhanced nutrient levels. Finally, from MIS 8 to the core top, nannofossil assemblages are indicative of relative meso-oligotrophic conditions. The variations in food supply to the sea floor, related to shallow water primary productivity, appear to be the main factor controlling benthic foraminiferal distribution, otherwise those variations are probably to be linked to the DWBC dynamic and to its paleoceanographic history during the last 1 Myr.
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