Catalan J., Pla-Rabes S., Garcia J., Camarero L. (2014) Air temperature-driven CO2 consumption by rock weathering at short timescales: Evidence from a Holocene lake sediment record. Geochimica et Cosmochimica Acta. 136: 67-79.LinkDoi: 10.1016/j.gca.2014.04.005
The role that air temperature plays in the interaction between atmospheric CO2 levels and continental rock weathering at relatively short time scales is still a matter of debate. Laboratory studies reveal a strong dependence of mineral dissolution on temperature, but field comparisons among watersheds under different climate conditions often indicate correlations with other environmental factors. Using a paleolimnological approach, here we show that there has been an extremely good coupling between rock weathering, water alkalinity (CO2 consumption), and air temperature during the last 10,000years at sub-millennial time scales in a small watershed of silicate bedrock and scarce vegetation. The calculation of apparent activation energy for the weathering reaction (as a means to describe the temperature dependence of the process) provides a value (Ea=67±7kJmol-1) that is comparable to those found for silicate rocks similar to those in the watershed in laboratory experiments and some field studies. Our results provide evidence that regulatory constraints between air temperature, atmospheric CO2 and silicate rock weathering can be fine-tuned at geological timescales and may not be negligible in the current context of global change. © 2014 Elsevier Ltd.
Cortizas A.M., Muniz I.R., Taboada T., Toro M., Granados I., Giralt S., Pla-Rabes S. (2014) Factors controlling the geochemical composition of Limnopolar Lake sediments (Byers Peninsula, Livingston Island, South Shetland Island, Antarctica) during the last ca. 1600 years. Solid Earth. 5: 651-663.LinkDoi: 10.5194/se-5-651-2014
We sampled a short (57 cm) sediment core in Limnopolar Lake (Byers Peninsula, Livingston Island, South Shetland Islands), which spans the last ca. 1600 years. The core was sectioned at high resolution and analyzed for elemental and mineralogical composition, and scanning electron microscope and energy dispersive X-ray spectrometer (SEM-EDS) analysis of glass mineral particles in selected samples. The chemical record was characterized by a contrasted pattern of layers with high Ca, Ti, Zr, and Sr concentrations and layers with higher concentrations of K and Rb. The former were also enriched in plagioclase and, occasionally, in zeolites, while the latter were relatively enriched in 2 : 1 phyllosilicates and quartz. This was interpreted as reflecting the abundance of volcaniclastic material (Ca rich) versus Jurassic-Lower Cretaceous marine sediments (K rich) - the dominant geological material in the lake catchment. SEM-EDS analysis revealed the presence of abundant volcanic shards in the Ca-rich layers, pointing to tephras most probably related to the activity of Deception Island volcano (located 30 km to the SE). The ages of four main peaks of volcanic-rich material (AD ca. 1840-1860 for L1, AD ca. 1570-1650 for L2, AD ca. 1450-1470 for L3, and AD ca. 1300 for L4) matched reasonably well the age of tephra layers (AP1 to AP3) previously identified in lakes of Byers Peninsula. Some of the analyzed metals (Fe, Mn, Cu, and Cr) showed enrichments in the most recent tephra layer (L1), suggesting relative changes in the composition of the tephras as found in previous investigations. No evidence of significant human impact on the cycles of most trace metals (Cu, Zn, Pb) was found, probably due to the remote location of Livingston Island and the modest research infrastructures; local contamination was found by other researchers in soils, waters and marine sediments on areas with large, permanent research stations. Chromium is the only metal showing a steady enrichment in the last 200 years, but this cannot be directly attributed to anthropogenic pollution since recent research supports the interpretation that climatic variability (reduced moisture content and increased wind intensity) may have resulted in enhanced fluxes of mineral dust and trace elements (Cr among them) to Antarctica. At the same time, some features of the chemical record suggest that climate may have also played a role in the cycling of the elements, but further research is needed to identify the underlying mechanisms. © Author(s) 2014.
Margalef O., Martinez Cortizas A., Kylander M., Pla-Rabes S., Canellas-Bolta N., Pueyo J.J., Saez A., Valero-Garces B.L., Giralt S. (2014) Environmental processes in Rano Aroi (Easter Island) peat geochemistry forced by climate variability during the last 70kyr. Palaeogeography, Palaeoclimatology, Palaeoecology. 414: 438-450.LinkDoi: 10.1016/j.palaeo.2014.09.025
We analyze the geochemistry of Rano Aroi mire record (Easter Island) using bulk peat composition (C, N, S) and stable isotopes (δ13C, δ15N, δ34S) and major, minor and trace elemental compositions obtained by ICP-AES (Al, Ti, Zr, Sc, V, Y, Fe, Mn, Th, Ba, Ca, Mg and Sr). Peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70kyr BP. Principal component analysis on ICP-AES data revealed that three main components account for the chemical signatures of the peat. The first component, characterized by lithogenic elements (combined signal of V, Al, Sc, Y, Cr, Cd, Ti, Zr and Cu), evidences long-term changes in the basal fluxes of mineral material into the mire. This component, in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the Rano Aroi watershed. The second component is identified by the signal of Fe, Mn, Th, Ba, Zr and Ti, and is indicative of strong runoff events during enhanced precipitation periods. The third component (tied mainly to Ca, Sr and Mg) reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts, sometime between 39 and 31kyr BP. Correlation coefficients and a multiple regression model (PCR analysis) between peat organic chemistry and the principal components of ICP-AES analysis were calculated. Isotope chemistry of the peat organic matter further contributes to define Rano Aroi environmental history: δ13C data corroborates a vegetation shift documented by the palynological record from C4 to C3 between 55 and 45calkyr BP; the δ15N record identifies periods of changes in mire productivity and denitrification processes, while the δ34S peat signature indicates a marine origin of S and significant diagenetic cycling. The geochemical and environmental evolution of Rano Aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70kyr BP. The coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions.
Soroczki-Pinter E., Pla-Rabes S., Magyari E.K., Stenger-Kovacs C., Buczko K. (2014) Late Quaternary Chrysophycean stomatocysts in a Southern Carpathian mountain lake, including the description of new forms (Romania). Phytotaxa. 170: 169-186.LinkDoi: 10.11646/phytotaxa.170.3.3
In this study we present results of a low-resolution chrysophyte stomatocyst analysis that followed a high-resolution diatom analysis of a mountain lake sediment sequence from the Retezat Mountains, in the south Carpathians (Romania). The stomatocyst assemblages of the previously distinguished ten diatom assemblage zones of Lake Gales were studied with the aim to describe stomatocyst composition and create a taxonomical basis for detailed stratigraphical analysis in the future. We report 83 stomatocyst forms, and 7 of them are formally described here as new for science. An abrupt shift in cyst as well as diatom assemblages were recorded around 9200 cal yr BP during the 15, 000 years long history of the Lake Gales. This Lake Gales event could be linked to the 9.3-ka widespread significant climatic anomaly, which was triggered by a melt water pulse into the North Atlantic. © 2014 Magnolia Press.
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