Cambios en el nivel marino y transformación ambiental del estuario de la Reserva de la Biosfera de Urdaibai (País Vasco, España) durante el Holoceno y Antropoceno

Abstract

In order to study the sea-level change process in the eastern Cantabrian coast during the last 8500 years based on the information registered in the coastal sedimentary sequences, 7 boreholes were drilled using a rotary drill until the pre-Quaternary basement was reached and 2 manual cores were obtained from different estuarine areas in the Urdaibai Biosphere Reserve. Sedimentological (grain size), micropalaeontological (benthic foraminifera) and geochemical (radioactive isotopes of geochronological interest) analyses were performed aiming to reconstruct the environmental transformation process of this coastal area and quantify the sea-level changes responsible for this environmental variation through time, both of natural origin (Holocene) or derived from human activities (Anthropocene). Sea-level changes show two main phases based on the analysis of SLIPs (sea-level index points) defined from the Holocene sedimentary sequences and the information previously published for this coastal area: 1- rapid relative sea-level rise of 9-12 mm yr-1 from -21 m to -5 m since 8500 cal yrs BP until 7000 cal yrs BP; 2- moderate sea-level rise of 0.3-0.7 mm yr-1 since 7000 cal yrs BP until 20th century. However, the recent sea-level rise rate reconstructed using microfossilbased transfer functions and instrumental records from tide gauges in the Bay of Biscay is 1.9± 0.3 mm yr-1 during the 20th century, which is three to six times higher than the sea-level rise rate registered during the last 7000 years, which is probably related to the human impact of global warming.