Comunicación oral en XXI INQUA Congress. Rome (Italy). 14-20th july 2023Laguna Seca lake at 2259 masl has provided the longest alpine sedimentary record in southern Iberia, registering the last ~18 kyr in a ~14-meter-long sediment core. The oldest part of the sedimentary record represents a phase of subaerial debris flows and a small glacier/nivation hollow. The sediment characteristics abruptly changed at ~15.7 cal kyr BP, when a lake environment was established. A multi-proxy approach (magnetic susceptibility, organic geochemical analyses in bulk sediment, XRF core scanner data, and algae identification) has allowed the characterization of three different environmental phases in this lake. Deep lake conditions are identified from ~15.7 to ~10.6 cal kyr BP, agreeing with overall increasing precipitation in southern Iberia coinciding with augmenting summer insolation. This part of the record is characterized by grey lutites with high total organic carbon (TOC) content, high algae productivity, high vascular plant inputs (high C/N ratio) from the catchment and low Fe/S ratio, suggesting low oxygen conditions in the water-sediment interphase. Between ~10.6 and 8.2-8.0 cal kyr BP higher TOC and low Fe/S ratio are also recorded as well as higher algae content and low C/N ratio suggesting high aquatic production and more algae contribution to the local organic matter pool. This period registered the highest lake levels agreeing with summer insolation maximum and highest precipitation in southern Iberia. An abrupt lowering of the lake level is recorded after 8.0 cal kyr BP in the area. This is deduced by the decrease in TOC and algae in the sediments and more siliciclastic contribution from the catchment basin, evidenced by a high increase in siliciclastic elements (Si, Al, K, Ti, among others), with increased oxic conditions in the water-sediment interphase pointed out by the high increase in Fe/S ratio. Additionally, a potential increase in north African aeolian inputs (rich in Fe cations and Fe compounds) can be interpreted for the Middle and Late Holocene, evidenced by high Fe/Al values. This environmental change agrees with an aridification trend previously observed in the southern Iberian Peninsula
