Dinoflagellate proxies for surface water property changes in the Miocene Atlantic Ocean

• Main Author: Heinrich, Sonja
• Other Authors: Willems, Helmut, Henrich, Rüdiger
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2012
• Subjects: Dinoflagellates; Upwelling; Amazon; Central American Seaway; Oxygen Isotopes; 550; 550 Earth sciences and geology; ddc:550; Antarctic; Atlantik; Pacific; The Antarctic; Antarc*; Antarctica; North Atlantic Deep Water; North Atlantic; South Atlantic Ocean
• Online Access: https://media.suub.uni-bremen.de/handle/elib/388; https://nbn-resolving.org/urn:nbn:de:gbv:46-00102806-15

Oceanographic and environmental changes had a strong impact on the climate progression during the middle and late Miocene. The climatic cooling during this time interval, involving the glaciation of Antarctica and the development of the Antarctic Circumpolar Current, influenced the initiation of oceanographic features of the South Atlantic Ocean, such as the Benguela upwelling in the eastern South Atlantic Ocean. The initiation of the Benguela upwelling, together with the associated Benguela Current, specifically had a strong impact on the global heat budget. It represented an important pathway for heat transport from the South Atlantic across the equator into the North Atlantic. This heat transport, combined with the return path via the North Atlantic Deep Water, encompasses a significant part of the thermohaline circulation. Another important development during the Miocene that affected thermohaline circulation was the closure of the Central American Seaway. However, it is still a matter of intense debate if thermohaline circulation, particularly the portion regarding equatorial heat transport via the North Brazil Current as well as the production of North Atlantic Deep Water, was possible at times of an open seaway between the Atlantic and Pacific. Samples from ODP Site 1085 were investigated for changes in productivity as well as water quality with data derived from calcareous dinoflagellate cyst associations. Two distinct increases in productivity and corresponding decreases in upper water temperatures reflect upwelling pulses off Namibia in relation to the Miocene cooling events, Mi-5 and Mi-6. At about 11.1 Ma, productivity increased and the polar species Caracomia arctica was found for the first time. The occurrence of C. arctica implies a fundamental change in the water quality, which was likely related to the influence of subantarctic water and allowed upwelling to fully develop into modern conditions. C. arctica is constantly found in the association from about 10.4 Ma on, which indicates that the ...