Climate and environmental change in Southern Europe – the paleoecological record of Padul, Sierra Nevada (Western Mediterranean, Southern Iberian Peninsula)

Résumé

Extended abstract: There are large gaps in our understanding of natural climate variability and how the water cycle and ecosystems will respond to global climate warming. Several scientific reports show that in the near future the southern Iberian Peninsula and other Mediterranean areas will be affected by increased drought frequency. This will generate very important economic and social problems in this region, characterized by scarce water resources. However, climate prediction is still a challenge, due to lack of long databases with quantitative measurements (especially for precipitation and temperature) and studies of how the environment reacted to climate change before the historical record. To solve this problem we need long continuous paleoclimatic records that will allow us to predict ecosystem response to climate change at short and long term. The present PhD Thesis focuses on the paleoenvironmental reconstruction of the last two glacial-interglacial cycles (the last ~200,000 years) in southern Iberian Peninsula through the study of the Padul-15-05 core, a 42.64 m-long continuous continental record that was retrieved from the Padul wetland. This sediment core was studied using high-resolution multiproxy analyses, including lithology/sedimentology, physical properties, mineralogy, inorganic and organic geochemistry, paleontological analysis and chronological analysis. These multiproxy analyses have provided with high-quality data that can be used for local (Padul wetland) and regional (southern Iberian Peninsula) paleoenvironmental and paleoclimatic reconstructions. The obtained data allowed identifying environmental variability due to orbital- and sub-orbital scale climate changes, improving the comprehension of factors and patterns influencing the environment caused by past climate changes in this region. In this study, the age-depth model of the Padul sedimentary sequence was improved with respect to previously published studies from this site. This was done using high-resolution accelerator mass spectrometry (AMS) radiocarbon dating, amino acid racemization (AAR) dating and sediment accumulation rates (SAR). This allowed constructing a robust age-depth model that permitted a good understanding of the time frame for paleoenvironmental reconstructions from the Padul wetland and the southern Iberian Peninsula for the last two glacial-interglacial cycles. The detailed palynological analysis from the Padul-15-05 sediment core has provided with one of the longest and most exhaustive past vegetation record from the Mediterranean region. The expansion and contraction of the forest cover and vegetation changes in the study area were strongly related with changes in insolation at this latitude, which was forced by the orbital-scale precession and eccentricity parameters. In general, the evolution of the vegetation in Padul in the last two glacial-interglacial cycles agree with other continental pollen records from the Mediterranean region, but some differences can also be recognized. The abundance of temperate humid forest taxa together with Mediterranean forest in the Padul pollen record during the last interglacial period (MIS 5e) shows the highest moisture conditions of the last ~200,000 years in the study area. Mediterranean forest taxa are the main components of the forest cover during the Holocene and the MIS 5a. Thus, the recent Holocene interglacial period in Padul seems to be climatically more similar to the MIS 5a interstadial than to the last interglacial period. Lithological and sedimentological features of the Padul record were mostly related to lake level oscillations, which were dependent on the precipitation/evapotranspiration balance. Two lake level reconstructions carried out using different multiproxy data (i.e., compilation of inorganic and organic geochemistry and magnetic susceptibility data for the first reconstruction and palynological data for the second) presented very high correlation, indicating that both methods are good proxies for the lake level interpretation and useful for future water level reconstructions in other similar lakes and wetlands. Generally, warm interglacial/interstadial phases were characterized by negative precipitation/evapotranspiration balance, and therefore, low lake levels, while during cold glacial/stadial periods the absence of evapotranspiration resulted in a higher lake water level. Moreover, higher siliciclastic/detrital input in the lake/wetland occurred during cold/arid periods and minima in insolation, as result of increased soil erosion during periods of low forest cover. Therefore, insolation also seems to be the main factor controlling local and regional environmental changes in Padul and in the southern Iberian Peninsula. The organic biomarkers from the last 36 kyr BP provide information about local environmental changes in Padul with a close relationship with regional variability displayed by the pollen data, and therefore, also suggesting insolation as the main factor conditioning both paleoenvironmental signals. The high-resolution pollen analysis of the last 65 kyr BP from the Padul-15-05 sedimentary record show millennial- and centennial-scale vegetation and environmental changes in the southern Iberian Peninsula most-likely related to Heinrich Stadials (HSs) and Dangaard-Oeschger (D-O) variability. The Padul-15-05 record shows covariation with other paleoclimatic records from the western Mediterranean, pointing into a same millennial- and centennial-scale climatic control affecting environments in this climatically sensitive region. In addition, the amplitude of the observed short-scale climate variability (e.g., D-O cycles) was conditioned by insolation, presenting high-amplitude D-O interstadials during insolation maxima (e.g., D-O interstadials 17-14 and 8-5) and a buffered variability during insolation minima (e.g., D-O interstadial 13-12 and 4-2). The compilation of several marine and continental paleoclimatic records from southern Europe and the Mediterranean region reveal an early record of Heinrich Stadial 1 (HS1 between 17,780 and 15,080 cal yr BP) in the study area with respect to the correspondent Greenland Stadial 2.1a from Greenland ice core records (GS-2.1a; 17,480 – 14,692 cal yr BP). Moreover, high-resolution pollen analysis allowed identifying three main climatic phases during HS1 in the Padul record, i.e., HS1a (18,400 – 17,200 cal yr BP), HS1b (17,200 – 16,700 cal yr BP) and HS1c (16,700 – 15,600 cal yr BP), showing an overall arid(cold) – humid(cool) – arid(cold) trend. In addition, for the first time, seven centennial-scale sub-phases within HS1 (i.e., HS1a.1, HS1a.2, HS1a.3, HS1b, HS1c.1, HS1c.2 and HS1c.3) have been described, which seem to be related with solar activity.