Central Santa Catarina coastal dunefields chronology and their relation to relative sea level and climatic changes

During the past decades, there have been contrarian explanations for the formation and stabilization of coastal dunefields: while many authors believe the dunes formation would be enhanced by falling sea level, others argue that a rising or stable sea level context would be favorable. For Brazilian coastal dunefields, the second hypothesis seems to be more consistent with the luminescence ages found so far; however, most of these data were obtained without using the SAR protocol. Another point of concern is the role of climate change in the aeolian system, which is still not very clear. The aim of this paper is to try to clarify these two questions. To this end, five coastal dunefields were selected in central Santa Catarina coast. The remote sensing and dating results allowed the discrimination and mapping of at least four aeolian generations. Their age distribution in relation to the global curve of relative sea level variation during the Late Pleistocene allows us to suggest that the formation of Aeolian dunefields in the coastal context is supported by stable relative sea level. However, relative sea level is not the only determinant for the formation and preservation of the aeolian coastal dunes. Evidences of climatic control indicate that the initiation of dunefields would be favored by periods of less humidity while their stabilization would occur preferably during the periods of rain intensification, connected to monsoon activity

Data for: The role of abrupt climate change in the formation of an open vegetation enclave in northern Amazonia

This file contains data from the age model, grain-size distruibution, magnetic susceptibility, and reflectance from the manuscript The role of abrupt climate change in the formation of an open vegetation enclave in northern AmazoniaTHIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

The effects of mid-Holocene fluvio-eolian interplay and coastal dynamics on the formation of dune-dammed lakes in NE Brazil

We analyzed the Late Quaternary coastal evolution of the easternmost tip of South America in Brazil in light of fluvial-eolian interactions controlled by relative sea-level, climate, and coastal physiography changes. The chronology obtained by OSL-SAR of 36 samples coupled with sedimentological analysis from stabilized dunes suggest that eolian activity was primarily controlled by episodes of sediment availability because prevailing SE trade winds have been steadily strong throughout the Holocene. Contrary to the most conventional view linking dune activity to aridity, dune buildup occurred in a period of increased humidity in NE Brazil between 11 ka and 6 ka when a rising relative sea level and higher rainfall enhanced sediment delivery benefiting the construction of transgressive dunefields. The interplay of these advancing dunes with the existing drainage pathways is here investigated using a modern regional analog and through the evolution of Boqueirao Lake formed by dune blockage. Analysis of a sediment core from this lake dated between 8.4 and 0.9 ka indicated changes over time in microfossil assemblages, organic geochemistry, and grain size data conforming to fluvial or lacustrine depositional conditions. Between 7.2 and 4.4 ka, during the predominantly regional humid climate, the high abundance of fluvial sponge species correlated with a framework of competent-flow drainage systems diverting from advancing dunes. An abrupt transition from a wetter to a drier climate at 4.4-4.0 ka stimulated episodes of fluvial damming as indicated by sharp changes from sandy to muddy sediments and anomalous concentration of sponge spicules concurrent with significant mortality rates of fluvial adapted species. From 3.9 ka to the present, the disappearance of sponge spicules and peaking diatom concentration attested to a predominant lacustrine environment. Thus, the formation of Boqueirao Lake is mainly a result of the regionally drier climate and not a consequence of increased humidity in coastal NE Brazil

The response of a dune succession from Lencois Maranhenses, NE Brazil, to climate changes between MIS 3 and MIS 2

In tropical Southern Hemisphere South America, late Quaternary marine core and speleothem records provide different proxies and accurate chronologies correlating millennial-scale intervals of increased precipitation with southward shifts of the Intertropical Convergence Zone (ITCZ). However, the climatic effect of these intervals on coastal landforms is poorly understood. Here we investigated the response of abrupt and long-lasting climate events during the Marine Isotope Stages 3 and 2 in a 13.8-m thick sand succession located in a large-scale coastal eolian system, the Lencois Maranhenses Dunefield, NE Brazil, where winds and precipitation are anti-phased and controlled by the single action of the ITCZ. A chronology of the sediment overburden determined by optically stimulated luminescence (OSL) dating of 14 sediment samples obtained at 1-m intervals showed ages between 132.2 +/- 7.0 and 12.9 +/- 0.6 thousand years ago in stratigraphic order. A multi-proxy approach based on grain size, surface grain texture, heavy minerals, thermoluminescence (TL) sensitivity, inorganic geochemistry, reflectance, and magnetic parameters from 268 sediment samples collected at 5-cm intervals indicated periods of dune building and stabilization. Significant stabilization periods are synchronous with Heinrich Stadials 6, 4, 3, 2, and 1, and Greenland Stadial 4, within age model uncertainties. Heavy mineral analysis indicated a steady sand source to the dune succession, while TL sensitivity analysis of quartz grains showed the input allochthonous sediments during stadials. The preservation of peak dune activity during the Last Glacial Maximum is attributed to the enduring precipitation brought by the subsequent Heinrich Stadial 1 event

The effects of mid-Holocene fluvio-eolian interplay and coastal dynamics on the formation of dune-dammed lakes in NE Brazil

We analyzed the Late Quaternary coastal evolution of the easternmost tip of South America in Brazil in light of fluvial-eolian interactions controlled by relative sea-level, climate, and coastal physiography changes. The chronology obtained by OSL-SAR of 36 samples coupled with sedimentological analysis from stabilized dunes suggest that eolian activity was primarily controlled by episodes of sediment availability because prevailing SE trade winds have been steadily strong throughout the Holocene. Contrary to the most conventional view linking dune activity to aridity, dune buildup occurred in a period of increased humidity in NE Brazil between 11 ka and 6 ka when a rising relative sea level and higher rainfall enhanced sediment delivery benefiting the construction of transgressive dunefields. The interplay of these advancing dunes with the existing drainage pathways is here investigated using a modern regional analog and through the evolution of Boqueir&atilde;o Lake formed by dune blockage. Analysis of a sediment core from this lake dated between 8.4 and 0.9 ka indicated changes over time in microfossil assemblages, organic geochemistry, and grain size data conforming to fluvial or lacustrine depositional conditions. Between 7.2 and 4.4 ka, during the predominantly regional humid climate, the high abundance of fluvial sponge species correlated with a framework of competent-flow drainage systems diverting from advancing dunes. An abrupt transition from a wetter to a drier climate at 4.4&ndash;4.0 ka stimulated episodes of fluvial damming as indicated by sharp changes from sandy to muddy sediments and anomalous concentration of sponge spicules concurrent with significant mortality rates of fluvial adapted species. From 3.9 ka to the present, the disappearance of sponge spicules and peaking diatom concentration attested to a predominant lacustrine environment. Thus, the formation of Boqueir&atilde;o Lake is mainly a result of the regionally drier climate and not a consequence of increased humidity in coastal NE Brazil.</p