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The approach commonly used to assess the potential for climate reconstruction is to use linear regressions to compare the isotopic signal stored in archives to instrumental climatic data sets. A new method is proposed that combines statistical and mechanistic approaches to extract climatic information from δ13C records in organic matter. Both a spatial and a temporal gradient of 13C discrimination in a moss species commonly found in temperate and tropical peat bogs are compared to meteorological records. The relevance of fossil and modern analogues to elucidate palaeoenvironment records are tested. It was found that the magnitude and, in some cases, the direction of the impact of temperature, humidity and CO2 atmospheric concentration on 13C discrimination depend on the calibration set considered. The use of a mechanistic model is shown to help greatly in specifying the joint influence of the climatic variables. [ABSTRACT FROM AUTHOR]

We present a new set of 14C ages obtained by accelerator mass spectrometry (AMS) on planktonic foraminifera from a deep-sea core collected off the Iberian Margin (MD952042). This site, at 37°N, is distant from the high-latitude zones where 14C reservoir age is large and variable. Many independent proxies — alkenones, magnetic susceptibility, ice-rafted debris, foraminifera stable isotopes, abundances of foraminifera, pollen, and dinoflagellates — show abrupt changes correlative with Dansgaard-Oeschger and Heinrich events of the last glacial period. The good stratigraphic agreement of all proxies — from the fine to the coarse-size fractions — indicates that the foraminifera 14C ages are representative of the different sediment fractions. To obtain reliable 14C ages of foraminifera beyond 20,000 14C yr B.P., we leached the shells prior to carbonate hydrolysis and subsequent analysis. For a calendar age scale, we matched the Iberian Margin U37K′ profile with that of Greenland Summit δ18O. Both are proxies for temperature, which in models varies synchronously in the two areas. The match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points. Except for ages older than 40,000 14C yr B.P., Greenland''s GISP2 and GRIP records yield similar calendars. The 14C and imported calendar ages of the Iberian Margin record are then compared to data — from lacustrine annual varves and from corals and speleothems dated by U–Th — previously used to extend the calibration beyond 20,000 14C yr B.P. The new record follows a smooth pattern between 23,000 and 50,000 cal yr B.P. We find good agreement with the previous data sets between 23,000 and 31,000 cal yr B.P. In the interval between 33,000 and 41,000 cal yr B.P., for which previous records disagree by up to 5000 cal yr, the Iberian Margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the Lake Suigetsu and the Bahamian speleothem data sets. [Copyright &y& Elsevier]