Sedimentary stable carbon isotope evidence of late Quaternary vegetation and climate change in highland Costa Rica

Terrestrially Derivedn-Alkane δD Evidence of Shifting Holocene Paleohydrology in Highland Costa Rica

“…This finding, together with the close correspondence of C 25 and C 27 ␦D values through the LM1 sediment profile, lead us to consider that these two n-alkanes are originating from the same source and should be representative of the páramo environment surrounding LM1, where Chusquea subtessellata dominates in both cover and biomass. The comparatively different ␦D pattern observed for the longer-chain C 29 , C 31 , and C 33 n-alkanes in the LM1 sediments, and their relatively high abundance despite the dominance of C. subtessellata in the LM1 watershed (Lane et al, 2011) suggests that these alkanes reflect a different vegetation source. We conjecture that they may derive from montane forest ecosystems at lower elevations, where the waxes are abrasively removed by winds and transported upslope (Schefu␤ et al, 2003).…”

“…The sediments of core 1 are the focus of this study and of the bulk and compoundspecific carbon isotope analyses carried out by Lane et al (2011). All other proxy analyses, including pollen, microscopic charcoal, macroscopic charcoal, diatom, and basic geochemical analyses, were conducted using sediments from core 2 (Horn, 1993;Haberyan and Horn, 1999;League and Horn, 2000).…”

“…All other proxy analyses, including pollen, microscopic charcoal, macroscopic charcoal, diatom, and basic geochemical analyses, were conducted using sediments from core 2 (Horn, 1993;Haberyan and Horn, 1999;League and Horn, 2000). The chronology for LM1 core 1 is based on six AMS radiocarbon dates on bulk sediment (Lane et al, 2011). Radiocarbon dates were converted to calibrated years B.P.…”

“…Sachse et al (2006) identified this evaporative enrichment of meteoric waters prior to biosynthesis by terrestrial organisms as a potential proxy for ecosystem evapotranspiration, and Tierny et al (2008) and Niedermeyer et al (2010) subsequently employed it as an indicator of paleohydrologic variability on millennial timescales in tropical Africa. Lane et al (2011) presented bulk and compound-specific stable carbon isotope (␦ 13 C) data spanning the Holocene from Lago shifting to more negative ␦ 13 C values during the middle Holocene, and then returning to relatively higher ␦ 13 C values during the late Holocene, led Lane et al to speculate that the ␦ 13 C n-alkane record reflected drought stress in vegetation surrounding the lake and thus may track millennial-scale changes in circum-Caribbean precipitation. In this study, we test this interpretation by analyzing the more direct terrestrial n-alkane ␦D proxy of ecosystem evapotranspiration in samples from the same LM1 sediment core.…”

Topical advances and recent studies in paleolimnological research

“…These patterns were related to solar activity and ENSO, as well as to changes in strength and position of the Bolivian High. A study of a highland glacial lake in Costa Rica used stable carbon isotopes of n-alkanes from terrestrial plants to examine aridity and rainfall associated with the migration of the ITCZ during the late Pleistocene and Holocene (Lane et al, 2011). Enters et al (2010) used multiple lines of evidence (pollen, diatoms, C/N ratios, biogenic silica and δ 13 C) from laminated sediments in southeastern Brazil to describe Holocene precipitation patterns, and to assess how changes in terrestrial vegetation influenced erosion, nutrient inputs, and ultimately lake productivity.…”