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Iberian high-resolution terrestrial archives: timing and mechanisms of abrupt climate change during the Holocene

Final Activity Report Summary - IBERABRUPT (Iberian high-resolution terrestrial archives: timing and mechanisms of abrupt climate change during the Holocene)

Last results presented by the IPCC on the causes of climate change have found crucial the study of abrupt climate changes in the recent past since they have significant implications for understanding future manifestations of similar forcings under late Holocene boundary conditions. The 'Iberian high-resolution terrestrial archives: timing and mechanisms of abrupt climate change during the Holocene' (IBERABRUPT) proposal was placed in the framework of the Paleoclimate research and aimed to understand the structure and timing of rapid climate changes during last millennia in the northern Iberian Peninsula. Two different paleoclimate archives (lake records and speleothems) were selected in two high-altitude areas, the Pyrenees and the Cantabrian mountains. We expected to supply the scientific paleoclimate community with a high-resolution multi-proxy record that served as a reference of abrupt climate change during the last millennia on land for Southern Europe.

The Pyrenees
The studied speleothems constitute the first samples analysed for the Spanish Pyrenees (5 de Agosto cave, 1600 m asl). The growing period of these samples occur during interglacial periods (warmer and wetter intervals that take place roughly every 100 000 years when northern hemisphere ice sheets were reduced to their minima expansion): Holocene (last 11 kyr), oxygen isotope stage (OIS 7, 180-200 kyr), OIS 9 (320-340 kyr) and OIS 11 (380-400 kyr). This result allows to identify warmer and wetter intervals and to compare their duration and characteristics. Although there are not yet available long lake records in the Pyrenees, the collaboration in the study of other lake sediments from Estanya Lake in the Pre-Pyrenees provides important information for the last 20 kyr. The Estanya record documents arid conditions during lateglacial times, intensified during the Mystery Interval (17.5-14.5 kyr), the Younger Dryas (13.3-11.6 kyr) and prior to the Holocene (11.6-9.4 kyr), revealing a high impact of suborbital global climate fluctuations in lake hydrology.

The Cantabrian mountains
The nearly continuous speleothem record obtained from El Pindal cave, from 25 000 to 7 000 years BP, documents with high resolution and precise chronology the climate change in NW Iberia from the Late Glacial period through the Early Holocene by combining trace element indicators of aridity with oxygen and carbon isotopic tracers sensitive to temperature and moisture-source. Stalagmite growth ceases only during the mystery interval, thus indicating that this is potentially the coldest and driest interval of the presented record. Cold interludes in the North Atlantic region, such as Heinrich event 2, were characterised by more arid and cold conditions in NW Iberian Peninsula. The major glacial-interglacial transition occurred gradually between 15.4 to 13.4 ky BP while the Younger Dryas represents a return to more arid conditions. The Early Holocene interval is punctuated by rapid dry spells, in correlation with cold North Atlantic cycles. In combination with the speleothem record, the Enol Lake sedimentary sequence provides a paleoclimate reconstruction for the last 40 kyrs indicating that an early deglaciation took place in synchrony with other Southern European mountains. The upper part of the sequence is characterised by four distinct stages: a cold and dry episode coinciding with the Younger Dryas event (13.5-11.6 kyr); a humid and warmer period characterising the onset of the Holocene (11.6-8.7 kyr); a tendency towards drier climate during the Middle Holocene (8.7-4.6 kyr) and a final recovery of humidity when the landscape is already modified by human activity (4.6-2.2 kyr).

The IBERABRUPT project has therefore allowed identifying and characterising the main intervals of rapid climate change in northern Iberian Peninsula for the last millennia. These events offer the opportunity to study the climate responses to natural forcing mechanisms in the absence of significant human influences.