| dc.description.abstract | Fossils of planktic foraminifera found in marine sediments are used widely as a proxy for past ocean conditions. These unicellular marine zooplankton range from tropical to polar latitudes and are most abundant in the upper mixed layer of the ocean. During their lifespan they form a calcium carbonate ’shell’ around their cell. When they die, foraminifera lose their ability to control their buoyancy and their shells sink to the ocean floor. It is often assumed that the proxies derived from the shells found in sediment cores represent ocean conditions above the location of deposition. However, foraminifera are transported by ocean currents, both during and after their lifespan. Hence, the paleoclimatic conditions recorded from their shells may originate far from the core site, generating large footprints in foraminifera-based paleoclimatic proxies. In this project we have quantified the influence of the transport on the proxy signal of foraminifera found at core sites in the Uruguayan margin of the Argentine basin. This is a region where two western boundary currents, the southward flowing Brazil current and the northward flowing Malvinas current, meet and is thus well suited to serve as a case study for developing an understanding of transportation effects. This is done with use of a high resolution ocean general circulation model, in which pathways of virtual particles are traced and local oceanic conditions along their pathways captured.These model results are compared to proxy- and species analysis from the core sites. We have found that offsets in modeled proxy signals due to transportin the Uruguayan margin are strongly linked to the relative position of the core site to the Brazil-Malvinas confluence. These offsets are most pronounced in the tails of the temperature distributions where they can reach up to +/- 7°C at sites located in the confluence zone. Species analysis from core tops taken slightly north of this region show more cold water species than reflected by the modeled temperature distributions, suggesting biological activity and nutrient availability not taken into account in the model play an important additional role in the relative abundances of species. Our model simulations have provided both a first order insight into the potential proxy-signal offsets in highly dynamic ocean regions and show that understanding of the interplay between transportation effects and the biological activity of foraminifera is crucial for the20 interpretation of these proxies. | |
