Climate changes in interior semi-arid Spain from the last interglacial to the late Holocene

Abstract

Abstract. The El Cañizar de Villarquemado sequence provides a palaeoenvironmental record from the western Mediterranean Basin spanning the interval from the last part of MIS6 to the late Holocene. The pollen and sedimentological records provide qualitative information about changes in temperature seasonality and moisture conditions. We use Weighted Averaging Partial Least-Squares (WA-PLS) regression to derive quantitative reconstructions of winter and summer temperature regimes from the pollen data, expressed in terms of the mean temperature of the coldest month (MTCO) and growing degree days above a baseline of 0 °C (GDD0) respectively. We also reconstruct a moisture index (MI), the ratio of annual precipitation to annual potential evapotranspiration, taking account of the effect of low CO2 on water use efficiency. We find a rapid summer warming at the transition to MIS5. Summers were cold during MIS4 and MIS2, but some intervals in MIS3 were characterized by summers as warm as the warmest phases of MIS5 or the Holocene. However, MIS3 was not significantly warmer in winter than other intervals, and there was a gradual decline in winter temperature from MIS4 through MIS3 to MIS2. The pronounced changes in temperature seasonality during MIS5 and MIS1 are consistent with changes in summer insolation. The ecophysiological effects of changing CO2 concentration through the glacial cycle has a significant impact on reconstructed MI. Conditions became progressively more humid during MIS5 and MIS4 was also relatively humid, while MIS3 was more arid. High MI values are reconstructed during the deglaciation and there was a pronounced increase in aridity during the Holocene. Changes in MI are anti-correlated with changes in GDD0, with increased MI during intervals of summer warming indicating a strong influence of temperature on evapotranspiration. Although our main focus here is on longterm changes in climate, the Villarquemado record also shows millennial-scale changes corresponding to Dansgaard-Oeschger cycles.

Early Holocene Thermal Maximum recorded by branched tetraethers and pollen in Western Europe (Massif Central, France)

“…Mathematical transfer functions such as the Weighted Averaging Partial Least Squares method (WAPLS) developed by ter Braak and Juggins (1993) are based on statistical calibration. However, new methods based on pollen data and vegetation modelling have also been recently developed and allow consideration of the direct effect of CO2 on vegetation and climate changes (Guiot and Kaniewski, 2015;Wei et al, 2019). Reconstructions of temperature variations in Europe during the Holocene derived from brGDGTs are uncommon and comparison between pollenand brGDGT-inferred temperatures are rare (Holtvoeth et al, 2017;Miller et al, 2018;Watson et al, 2018).…”

The impact of methodological decisions on climate reconstructions using WA-PLS

“…The modern climate data at each of the SMPDS sites (Harrison, 2020) are available online (doi: 10.5281/zenodo.3605003). Partial CCA carried out using each climate variable in turn, with the other two as covariates, shows that each variable has a highly significant effect ( p < 0.001) that is independent of the others (Wei et al, 2019a).…”

“…1), which we refer to as SMPDS, was constructed by combining records from the European Modern Pollen Database (EMPD) v3.0 (Davis et al, 2013), the Eastern Mediterranean-Black Sea-Caspian Corridor Biomes (EMBSeCBIO, which we abbreviate as EMB) database (Marinova et al, 2018), additional published records (see Supplementary Table 1) from the European Pollen Database (http://www.europeanpollendatabase.net/) or taken from Pangaea (https://www.pangaea. de/), and 73 modern surface samples from northern Spain (Wei et al, 2019a). About two-thirds of the sites (4575) were derived from the EMPD v3.0 (Davis et al, 2013), and a further 1088 sites were derived from the EMBSeCBIO database (Marinova et al, 2018).…”

“…MTCO is a surrogate for extreme winter temperatures and influences the survival of woody plants through a wide range of low temperature-tolerance mechanisms, GDD 0 is a combined measure of the length and warmth of the growing season that determines potential annual carbon accumulation, and MI is a measure of plant-available moisture (Harrison et al, 2010). Canonical correspondence analysis (CCA) applied to the SMPDS data set (Wei et al, 2019a) showed a strong correlation between species abundance and these climate variables. The modern climate data at each of the SMPDS sites (Harrison, 2020) are available online (doi: 10.5281/zenodo.3605003).…”

“…MTCO and GDD 0 were not transformed. We do not include interactions among the climate variables since previous analyses (Wei et al, 2019a) have shown that they each have a significant and independent influence on the distribution of plant taxa and vegetation types. For visualisation purposes, we show 2D slices (MTCO and MI) through the fitted 3D response surfaces at low, medium, and high values of GDD 0 .…”