DOI: 10.25921/2r0g-w315
title: NOAA/WDS Paleoclimatology - Carbon and nitrogen stable isotopes of bulk sediment, ICDP Laguna Potrok Aike

description: A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (d15N) and organic carbon (d13Corg) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina) for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before 8470 calibrated 14C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470-7400 cal. yrs BP), however, extremely high input of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte OM) to model OM variations and the model results were compared with quantitative microfossil data.
description: The age model for the record was published in: Haberzettl et al., 2007. The original dates of the age model are provided, rather than the calibrated ages used in the publication, because since then the radiocarbon calibration curve has changed substantially in the Late Glacial. The new INTCAL 6.0 calibration curve causes up to 640 years older ages in the basal layers of the record with respect to the calibration curve used in Haberzettl et al. 2007 (INTCAL 5.0.2). As the radiocarbon calibration curve is steadily improved, the original radiocarbon dates are presented. These allow to construct and update the age model for future studies.
Variable names: carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios in delta notations
Variable unit: per mil relative to the international standards VPDB (carbon) and AIR (nitrogen)
Data precision: Analytical precision (one standard deviation) was 0.08%. 
Bathymetry/elevation: core was recovered from 100 m water depth, lake surface is at 113 m a.s.l.. 
Additional information: Some layers of the record are considered redeposited. These are indicated ("redeposited yes") in the respective column (see Mayr et al., 2009 for further details). 
Contact Information: Christoph Mayr, Institute of Geography, University of Erlangen-Nuremberg, D-91054 Erlangen, Germany, christoph.mayr@fau.de, +49(0)9131-8522016.
Keywords Stable isotopes - Rock Eval analyses - Organic matter - Soil erosion - Isotope mixing model - South America - Late Quaternary - Lake sediments