Changing dominance of high-latitude intermediate waters and its impact on the equatorial nutrient-budget - Implications from foraminiferal geochemistry

• Main Author: Rippert, Nadine
• Format: Thesis
• Language: unknown
• Published: 2016
• Subjects: Planktonic foraminifera; Southern Ocean
• Online Access: https://epic.awi.de/id/eprint/42872/; https://epic.awi.de/id/eprint/42872/1/Dissertation_Nadine-Rippert.pdf; https://hdl.handle.net/10013/epic.49413; https://hdl.handle.net/10013/epic.49413.d001

The equatorial Pacific holds the potential to investigate the climate variability of the Earth as it connects both hemispheres via the atmospheric and oceanic circulation. The modern Equatorial Pacific Intermediate Water (EqPIW) is fed by three end-member components: Southern Ocean Intermediate Water (SOIW), Pacific Deep Water (PDW) and, by a smaller proportion, North Pacific Intermediate Water (NPIW). This modern configuration of end-members in the EqPIW results in low productivity of siliceous phytoplankton in the Eastern Equatorial Pacific (EEP) today as SOIW is depleted in silicic acid compared to other nutrients. An increased primary production during glacials has often been attributed to an enhanced contribution of SOIW to equatorial sub-surface waters. However, there is growing debate over whether SOIW was capable of stimulating glacial equatorial productivity. This is in light of the fact that nutrients appear to have been trapped in glacial Southern Ocean waters. Furthermore, recent studies point towards a change in the lateral and vertical extent of both SOIW and NPIW during glacials, impacting the supply of nutrients to the EEP. Ultimately, the effect of these intermediate water mass changes on equatorial waters remains elusive. Most upper ocean water mass reconstructions are based on planktonic foraminifera tests. Different foraminiferal species preferentially dwell in distinct water depths and thus, the calcitic tests of these species can be used to infer past climate conditions. However, it has been shown that the Apparent Calcification Depths (ACDs) of foraminiferal species are spatially non-uniform. Today, there are no ACD reconstructions from the equatorial Pacific based on multinet data. This thesis assesses equatorial foraminiferal ACDs to identify a species suitable to trace nutrient inflow of extra-tropical intermediate water masses. Using this determined species, this thesis then reconstructs the effect of variable nutrient injections from extra-tropical water masses on the equatorial ...