Zanna Chase, IMAS
Time and date: 12:00 – 12:50 pm, Wednesday, 26th Oct
Venue: Seminar room, IMAS Sandy Bay
Abstract:
Biogenic particle flux was reconstructed using the Thorium-230 normalisation technique at two sites on the southern Chile margin. ODP Site 1233 at 41°S, 838 m depth is at the southern limit of the Peru-Chile upwelling system, where the northern extent of the Antarctic Circumpolar Current (ACC) impinges on the South American continent. ODP Site 1234, at 36°S, 1014 m depth, is located within the core of the coastal upwelling system. At 41°S, maximum organic carbon, opal and carbonate fluxes over the last 30 ka occurred during the last glacial period (26-20 ka). At 36°S, the pattern is very similar, except a second, larger maximum in organic carbon flux is observed during the late Holocene (~5 ka), without an accompanying peak in opal flux. These reconstructed fluxes at 36°S and 41°S fit within a larger latitudinal pattern of a poleward increase in the magnitude of opal flux during the glacial period. A similar gradient is observed in the magnitude of lithogenic flux.
The pattern of reconstructed productivity is consistent with several mechanisms, including: i) a more northerly position of the ACC during the last glacial period, bringing the core of high-nutrient waters to 41°S; ii) enhanced supply of Si from the Southern Ocean, as proposed by the Silicic Acid Leakage Hypothesis. and iii) enhanced macro or micro-nutrient delivery from land, driven by glaciation in the south. The pattern of reconstructed productivity also confirms that the less reducing conditions during the glacial interval, inferred from authigenic metal accumulation, were driven by increased ventilation by Antarctic Intermediate Water, rather than by increases in local productivity.
Biography:
Zanna Chase is a senior lecturer in IMAS. She is a chemical oceanographer interested in the interaction of chemical cycles with biological production in the ocean, on a range of spatial scales from estuaries to the open ocean, and a range of temporal scales, from glacial-interglacial variations to predictions of future changes. Before moving to UTas in June 2010, she was an assistant professor at Oregon State University in the College of Oceanic and Atmospheric Sciences. She received her PhD from Columbia University, USA and her MSc and BSc degrees from McGill University, Canada.