Climate Impacts of the Common Era on Aquatic Systems in NW Spain: preliminary results

Abstract

Ecological resistance and resilience of freshwater ecosystems is intimately linked to climate variability. To the extent of our knowledge, this issue has never been addressed using a long-term paleoecological perspective in Galicia (NW Spain). Project IMPACOM (Climate Impacts of the Common Era on Aquatic Systems in NW Spain, Spanish Ministry of Science and innovation, PID2019-107424RB-I00) is intended to study the impacts of changes in the precipitation regime and storm conditions, among other climate forcing factors, on coastal lakes and their enclosing barriers, as well as on bogs and mountain lakes in the region during the Common Era (CE, last 2,000 yr). To identify and precisely date the major ecological transitions of the CE we use a multidisciplinary approach which includes sedimentological facies analysis, inorganic bulk geochemical analyses (from X-ray fluorescence analysis, core scanning, Fourier-transform infrared spectroscopy, estimation of humification indexes, elemental and isotopic analyses of organic matter, biogenic silica), biological proxies (diatoms, pollen, plant macrofossils, testate amoeba and chironomids), as well as a set of geochronological techniques (AMS radiocarbon dating, concentrations of fallout 137Cs, 210Pb, 214Pb and 241Am, OSL dating)

The study of the lacustrine sedimentary record of the coastal Lake Doniños, as well as of the sand barrier which encloses this lake and that of the wetland of Pantín, both in A Coruña province, shows a history of breaching and overwashing linked to the intensification of storms and enhanced precipitation over the last 4,500-4,000 yr. For the case of the last 2,000 yr, catastrophic emptying of Lake Doniños took place during the Dark Ages (DA, 350-750 CE) and the Little Ice Age (LIA, 1500-1930 CE). The transition from the Medieval Climate Anomaly (MCA) to the LIA involved in this lake a gradual 200 yr long transformation from an isolated lake to an intermittent tidal lagoon until the LIA breaching episode. Lake Ocelo, an oligotrophic mountain lake located in the Trevinca Massif (Ourense province) shows a net eutrophication trend since the termination of the Subatlantic period. This trend was however interrupted by oligotrophication events in the warm/cold transitions of the Roman Warm Period to the DA, lasting 500 years, and the MCA to LIA, which lasted 600 years. Extended ice cover during the LIA, as suggested by the preliminary diatom data, involved stronger denitrification processes associated to longer periods of anoxia, indicated by the nitrogen isotopic record. Anticipation of the oligotrophication events to the known chronologies for the onset of the DA and the LIA suggests that these two phases occurred approximately 100 and 200 years earlier than expected, according to other mountain lake record of the W Iberian Peninsula. Our preliminary data also show significant discrepancies in the timing of the ecological impacts of Recent Climate Changes (RCCs) taking place in the last 2,000 yr in coastal and mountain areas over a short longitudinal gradient which needs further exploration