Cave monitoring and the potential for palaeoclimate reconstruction from Cueva de Asiul, Cantabria (N. Spain)

Abstract

Abstract:Palaeoclimate records from northern Iberia are becoming increasingly sought after as this region is one of the most southerly terrestrial locations in Europe to have its climate dictated principally by the North Atlantic. Terrestrial records therefore have the potential to offer insights into changing oceanic and atmospheric circulation in the wider North Atlantic region. Cave speleothems offer one of the most promising archives from northern Iberia due to their wide geographic distribution and potential for accurately dated climate reconstruction. Cueva de Asiul, situated in Cantabria (N. Iberia; 43°19'0.63''N, 3°35'28.32''W; 285 m.a.s.l) within the Matienzo karst depression is one such site that offers the potential for palaeoclimate reconstructions. Here we present three years of climate and cave monitoring from Cueva de Asiul, giving detailed insight into local meteorology, hydrology and cave ventilation dynamics. In doing so, this paper presents a background to high resolution, Holocene duration speleothem records which have been extracted from this cave. Annual average cave temperatures are +13.7ºC, with a maximum range of 1ºC, reflecting the seasonality of external air temperature (average external temperature +13.8°C). Cave ventilation is controlled by changes in external air temperature and variations in external air pressure during low pressure events. Local rainfall measurements show an average of 1400 mm/year with the majority of rainfall occurring during the winter, with periods of water excess between October and April. Speleothem drip rates are characterised by summer lows and a rapid transition to higher rates at the onset of the winter season. Stable isotope analysis (δ 18 O, δ 2 H) indicate that aquifer water is derived predominantly from the previous year's rainfall and the rainfall feeding the karst system is controlled by a strong amount effect. Speleothems from this site are potentially suited to preserving extended records of rainfall amount in northern Spain and therefore have the potential to inform more clearly about Holocene scale changes in the rainfall source region, the North Atlantic.

Transfer of environmental signals from the surface to the underground at Ascunsă Cave, Romania

“…17), but with a muted signal when compared to that of rain water, an indication of a well-mixed aquifer (Riechelmann et al, 2011;Smith et al, 2014). A similar variability is seen in drip water at Green Lake in Isverna Cave too, although here the values are higher, an expected result of the altitude effect.…”

North Atlantic forcing of moisture delivery to Europe throughout the Holocene

“…Here, we add to this debate by reconstructing precipitation delivery to northern Spain during the last 12.1 ka, using a carbonate oxygen isotope (δ 18 O) record derived from speleothems contained within Cueva de Asiul (43° 19′ 0.63″ N, 3° 35′ 28.32″ W; 285 m.a.s.l) situated in the Matienzo depression (Cantabria), N. Spain 19 ( Fig. 1 ).…”

“…1 ). At this location, approximately 80% of the region’s annual precipitation is derived from an Atlantic source, associated with westerly frontal systems 19 20 21 22 . The monthly isotope composition of modern rainfall (monthly weighted mean) is controlled by a rainfall amount effect (r 2 = 0.51 p < 0.01), with lower δ 18 O related to higher rainfall totals 19 .…”

“…At this location, approximately 80% of the region’s annual precipitation is derived from an Atlantic source, associated with westerly frontal systems 19 20 21 22 . The monthly isotope composition of modern rainfall (monthly weighted mean) is controlled by a rainfall amount effect (r 2 = 0.51 p < 0.01), with lower δ 18 O related to higher rainfall totals 19 . At such mid-latitudes, it is variations in the mode of the NAO, defined as the difference in pressure between the Icelandic low and the Azores high 23 , which are the primary control over the relative positioning of westerly wind tracks across Europe 24 25 26 27 28 ( Fig.…”

“…The two speleothems used in this study (ASR and ASM) grew just 5 m apart, in the Cueva de Asiul system in a stable cave environment (air temp 13.7 ± 0.5 °C) 19 31 (75 m in length, 40 m rock overburden) and were both actively depositing calcite at the time of removal. The cave’s hydrological system is recharged primarily by winter rainfall (1400 mm/year), resulting in cave drip waters that reflect a bulk winter rainfall δ 18 O composition from the preceding year 19 . The analysis of modern carbonates indicates a minimal level of isotopic disequilibrium within the system 19 32 .…”