Calibrating biogeochemical and physical climate proxies from non-varved lake sediments with meteorological data: methods and case studies

Abstract

Lake sediment records are underrepresented in comprehensive, quantitative, high-resolution (sub-decadal), multi-proxy climate reconstructions for the past millennium. This is largely a consequence of the difficulty of calibrating biogeochemical lake sediment proxies to meteorological time series (calibration-in-time). Thanks to recent methodological advances, it is now possible. This paper outlines a step-by-step, specifically tailored methodology, with practical suggestions for calibrating and validating biogeochemical proxies from lake sediments to meteorological data. This approach includes: (1) regional climate data; (2) site selection; (3) coring and core selection; (4) core chronology; (5) data acquisition; and (6) data analysis and statistical methods. We present three case studies that used non-varved lake sediments from remote areas in the Central Chilean Andes, where little a priori information was available on the local climate and lakes, or their responses to climate variability. These case studies illustrate the potential value and application of a calibration-in-time approach to non-varved lake sediments for developing quantitative, high-resolution climate reconstructions.

Late Holocene summer temperatures in the central Andes reconstructed from the sediments of high-elevation Laguna Chepical, Chile (32° S)

“…In absence of long local meteorological data series the reanalysis temperature data (HadCRU TS3, extracted for the 0.5 • × 0.5 • grid cell representing the study area; Mitchell and Jones, 2005) had to be used for the proxy -climate calibration. This procedure has been successfully applied and the representativeness of the reanalysis temperature data has been tested in other remote areas in Central Chile (von Gunten et al, 2012). For the calibration and reconstruction the temperature anomalies were calculated with reference to the 20th century mean.…”

“…The proxy -climate calibration followed the procedure described by von Gunten et al (2012). To allow for a comparison of meteorological data with proxy data, the VIS-RS proxy data (2 mm resolution) were regularized to annual resolution.…”

“…To take into account dating uncertainties and sediment bioturbation during the calibration period, the correlation coefficients and adjusted p values were calculated for 3 yr and 5 yrfiltered reanalysis and proxy data (De Jong and Kamenik, 2011;von Gunten et al, 2012). The performance of the inverse linear regression model (reduction of error RE and coefficient of efficiency CE) was assessed by splitting the calibration period into a calibration (AD 1960(AD -2004 and validation (AD 1901(AD -1960 period.…”

“…Obviously, this assumption introduces an unknown amount of uncertainty to the reconstruction, since changes in environmental factors and lake sediment responses cannot be ruled out, in particular over such long time periods. However, this basic assumption is part of all proxy-based environmental reconstructions, regardless whether calibration-in-time (von Gunten et al, 2012) or Transfer Functions (calibration-in-space) are used . Additional reconstructions from this high altitude region are required to verify the patterns reconstructed in this study, in particular further back in time.…”

Hyperspectral imaging spectroscopy: a promising method for the biogeochemical analysis of lake sediments

“…In these cases, spectral data could be used as high-resolution proxies for quantitative climate reconstructions. [26][27][28][29][30][31][32] In this study, we use a VNIR imaging spectrometer designed for use as a sediment core-scanning system and present a case study for spectral analysis of fresh lake sediments. First, we describe the technical equipment and the general methodology (workflow) that was used to acquire and process the spectral data.…”