[Abstract] In an effort to understand how alpine environments from the western Mediterranean region responded to climate variations since the last glacial-interglacial transition, a detailed chronological control and sedimentological analysis, supported by magnetic susceptibility, total organic carbon and C/N data, were carried out on the sedimentary record of Laguna Seca (LS). This is a latitudinal and altitudinally (2259 masl) key alpine wetland site located in the easternmost area of the Sierra Nevada, southern Iberian Peninsula, where sediments accumulated during Heinrich Stadial 1, Bølling-Allerød (B-A) and the Younger Dryas (YD) - previously unrecorded in alpine Sierra Nevada. Climate controlled sedimentation in LS and three coarse-grained and one fine-grained facies association are differentiated, which help us decipher the paleoenvironmental evolution of LS: (1) subaerial cohesionless debris flows during a paraglacial stage; (2) till or nival diamicton during a small glacier/nivation hollow stage; (3) massive mudstone by suspension settling of clays into standing water during a lacustrine stage; and (4) frost-shattering breccia deposited inside the lacustrine stage, probably during the YD, and linked to a periglacial substage. The development of a previously existing small glacial cirque during the Last Glacial Maximum (LGM) in the LS basin at an elevation between 2500 and 2300 m could be supported by the important availability of slope sediments glacially-conditioned such as debris flows, reworked by paraglacial slope processes during the first deglaciation stages, confirming previous studies of landforms in the catchment area and the LGM-Equilibrium Line Altitude estimation above 2400 masl in Sierra Nevada. Mean sediment accumulation rates in the LS sedimentary units (4.21 and 0.28 mm/yr during the paraglacial - small glacier/nivation stage and the lacustrine stage, respectively) confirm that geomorphic activity accelerated just after glaciers retreated due to a slope adjustment and high availability of glacially conditioned sediments. An abrupt change in paleoenvironmental and paleoclimatic conditions occurred in LS at ∼ 15.7 cal kyr BP. This change was probably due to an increase in temperature and precipitation in the western Mediterranean region during the B-A. At LS, this resulted in significant ice-melt, forming a deep-water lake in LS with important organic matter contribution until the end of the Early Holocene (except in the YD when the lake level probably dropped), but elsewhere a general glacier recession in the Sierra Nevada and an expansion of the Mediterranean forest in the southern Iberian Peninsula. Finally, the general long-term aridification that occurred during the Middle Holocene until the present in the western Mediterranean region triggered an important environmental change transforming LS into an ephemeral wetland with an increase in aquatic productivity. This study is was supported by the I + D + i projects CGL2013-47038-R and CGL2017-85415-R funded by Ministerio Ciencia e Innovación/Agencia Estatal de Investigación/ 10.13039/501100011033/ and Fondo Europeo de Desarrollo Regional “Una manera de hacer Europa”, I + D + i projects B-RNM-144-UGR18 and P20_00059 of the action “Proyectos I + D + i del Programa Operativo FEDER - Junta de Andalucía - UGR” and the research group RNM-190. Alejandro López Avilés acknowledges the predoctoral fellowship BES-2018-084293 provide by the MCIN/ AEI/ 10.13039/501100011033/. Antonio García-Alix acknowledges the Ramón y Cajal fellowship RYC-2015-18966 provided by the MCIN/ AEI/ 10.13039/501100011033/. Fernando García García collaboration in this study was supported by the I + D + I project CGL2017-89618-R funded by MCIN/ AEI/ 10.13039/501100011033/ and FEDER “Una manera de hacer Europa” and the research group RNM-178. José Carrión collaboration in this study was supported by the I + D + I project PID2019-1049449 GB-I00 funded by MCIN/ AEI/ 10.13039/501100011033/ and FEDER “Una manera de hacer Europa” and the fellowship 20788/PI/18 of Fundación Séneca Junta de Andalucía; B-RNM-144-UGR18 Junta de Andalucía; P20_00059 Fundación Séneca; 20788/PI/18