2 research outputs found
Millennial surface water dynamics in the RĂa de Vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers
13 pages, 7 figures, 2 tables.-- Printed version published Mar 10, 2005.A combined study of coccolith assemblages and biomarkers in a gravity core collected from the RĂa de Vigo (NW Spain) allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years. The quantitative distribution of coccolithophore species points to three different intervals within the core, dated by AMS radiocarbon measurements. The first interval (ca. 975 BCâ252 AD), characterized by high abundances of Calcidiscus leptoporus and Gephyrocapsa muellerae, is thought to represent moderate water temperatures, suggesting a transition from a warmer to a cooler period. The second interval (ca. 252â1368 AD), characterized by the dominance of Coccolithus pelagicus, Helicosphaera carteri and Syracosphaera spp., and a high concentration of hexacosanol linked to terrestrial input, is interpreted as having been a humid period with fluvial input. The third interval (ca. 1368 ADâ1950) is characterized by a high abundance of Gephyrocapsa oceanica, high alkenone values and low values of hexacosanol, and is thought to represent a period dominated by oceanic conditions within the RĂa.Taking into account the oceanâatmospheric system affecting the region studied, here we propose an alternation in the mean state of North Atlantic Oscillation (NAO) at millennial time scales. A well-developed upwelling system and an active RĂaâocean connection during the warmer interval I suggest a NAO+ phase influenced by a Hypsithermal period. The occurrence of the humid and relatively warm interval II is consistent with a negative phase in the NAO, as well as a relative restriction in oceanâRĂa exchange. Interval III, which was drier and more productive, again suggests the dominance of a positive phase in the NAO, with a more intense oceanic connection and more energized upwelling.Research grants ABRUMIS REN2003-08642-C02-02/CLI, BTE2002-04670 (Ministerio de Ciencia y TecnologĂa) and SA088/04 (Junta de Castilla y LeĂłn) supported this study.Peer reviewe
Millennial surface water dynamics in the Ria de Vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers
A combined study of coccolith assemblages and biomarkers in a gravity core collected from the RĂa de Vigo (NW Spain) allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years. The quantitative distribution of coccolithophore sp