Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 12, 623-634, 2016
http://www.clim-past.net/12/623/2016/
doi:10.5194/cp-12-623-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Mar 2016
Variability in terrigenous sediment supply offshore of the Río de la Plata (Uruguay) recording the continental climatic history over the past 1200 years
Laura Perez1,4, Felipe García-Rodríguez1,4, and Till J. J. Hanebuth2,3 1Sección Oceanología, Facultad de Ciencias, Universidad de la República, Iguá 4225, Montevideo 11400, Uruguay
2School of Coastal and Marine Systems Sciences, Coastal Carolina University, SC 29528, USA
3MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Straße, 28359 Bremen, Germany
4Centro Universitario Regional Este, CURE-Rocha, Ruta 9 intersección Ruta 15, Rocha, Uruguay
Abstract. The continental shelf adjacent to the Río de la Plata (RdlP) exhibits extremely complex hydrographic and ecological characteristics which are of great socioeconomic importance. Since the long-term environmental variations related to the atmospheric (wind fields), hydrologic (freshwater plume), and oceanographic (currents and fronts) regimes are little known, the aim of this study is to reconstruct the changes in the terrigenous input into the inner continental shelf during the late Holocene period (associated with the RdlP sediment discharge) and to unravel the climatic forcing mechanisms behind them. To achieve this, we retrieved a 10 m long sediment core from the RdlP mud depocenter at 57 m water depth (GeoB 13813-4). The radiocarbon age control indicated an extremely high sedimentation rate of 0.8 cm per year, encompassing the past 1200 years (AD 750–2000). We used element ratios (Ti  / Ca, Fe / Ca, Ti / Al, Fe / K) as regional proxies for the fluvial input signal and the variations in relative abundance of salinity-indicative diatom groups (freshwater versus marine-brackish) to assess the variability in terrigenous freshwater and sediment discharges. Ti / Ca, Fe / Ca, Ti /  Al, Fe /  K and the freshwater diatom group showed the lowest values between AD 850 and 1300, while the highest values occurred between AD 1300 and 1850.

The variations in the sedimentary record can be attributed to the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA), both of which had a significant impact on rainfall and wind patterns over the region. During the MCA, a weakening of the South American summer monsoon system (SAMS) and the South Atlantic Convergence Zone (SACZ), could explain the lowest element ratios (indicative of a lower terrigenous input) and a marine-dominated diatom record, both indicative of a reduced RdlP freshwater plume. In contrast, during the LIA, a strengthening of SAMS and SACZ may have led to an expansion of the RdlP river plume to the far north, as indicated by higher element ratios and a marked freshwater diatom signal. Furthermore, a possible multidecadal oscillation probably associated with Atlantic Multidecadal Oscillation (AMO) since AD 1300 reflects the variability in both the SAMS and SACZ systems.


Citation: Perez, L., García-Rodríguez, F., and Hanebuth, T. J. J.: Variability in terrigenous sediment supply offshore of the Río de la Plata (Uruguay) recording the continental climatic history over the past 1200 years, Clim. Past, 12, 623-634, doi:10.5194/cp-12-623-2016, 2016.
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Short summary
The observed changes in the presented proxy records indicate variations in both the continental runoff and the marine influence, related to regional climatic variability. Therefore, we put forward the suggestion that global atmospheric changes (related to changes in SAMS and SACZ intensity) have made an impact on the hydrodynamics and, consequently, on the local sedimentation regime and the inner Uruguayan continental shelf over the past 1200 cal yr BP (AD 750–2000).
The observed changes in the presented proxy records indicate variations in both the continental...
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