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Speleothem Climate Capture

   In April 2010, Lancaster University student Andi Smith under Dr Phil Wynn and Prof Phil Barker (Lancaster University) and Prof Melanie Leng and Dr Steve Noble (British Geological Survey) started a programme of cave monitoring in Cueva Asiul to characterise cave microclimate (specifically temperature, humidity and carbon dioxide). Drip rate monitors have been installed to understand the nature of the hydrological system feeding the speleothem formations along with a rain gauge above (Video).
   These studies have resulted in a very complete and high resolution record for climate change in the area. Andi has completed a PhD thesis: Speleothem Climate Capture - A Holocene Reconstruction of Northern Iberian Climate and Environmental Change which challenges current understanding of North Atlantic Oscillation (NAO) dynamics and the exact timing of initial NAO development.

A "Latest News" page on the BGS web site has the following summary:
June 2014 - Well done to Andi Smith on the successful defence of his PhD thesis:
Speleothem Climate Capture - A Holocene Reconstruction of Northern Iberian Climate and Environmental Change.

An extensive 4 year cave monitoring program has been undertaken at Asiul Cave, a previously unstudied site in Cantabria (Spain). Monitoring indicates that this cave has the potential for long term speleothem development and that stalagmites are ideal for the reconstruction of palaeoclimatic conditions, including importantly palaeorainfall amount reconstruction. Two speleothem samples were therefore removed from the cave and analysed for a suite of geochemical proxies. Coeval oxygen isotope records from Asiul Cave indicate that northern Iberia has experienced considerable deviations in rainfall during the last 12,500 years. These high resolution records are strongly coupled with changes in other regionally important climate archives, helping to add to our understanding of northern Iberian climate evolution. The Asiul speleothem records however, go beyond explaining local changes in environmental conditions by exhibiting a strong coupling between atmospheric conditions, in the form of the North Atlantic Oscillation (NAO) and North Atlantic Ocean circulation. These speleothem archives indicate that the NAO controls not only the positioning of atmospheric storm tracks throughout Europe but through interactions with the surface layer of the ocean can cause major changes in oceanic circulation. These NAO controlled changes in North Atlantic Ocean circulation have been shown to cause significant cooling within the northern North Atlantic and the southerly transport of ice rafted debris, with a millennial periodicity of ~1500 years. The Asiul cave speleothem record is one of the first convincing archives of a millennial scale NAO system which has the capacity to force changes in oceanic circulation. These speleothems also act to extend existing archives of the NAO back into the Younger Dryas; in doing so the Asiul records challenge our current understanding of NAO dynamics and the exact timing of initial NAO development.

A paper summarising early results can be seen here.
An abstract of the talk given by Andi Smith at A BCRA Science Symposium is found on page 143 of Cave & Karst Science 41(3), 2014.

Drip water electrical conductivity as an indicator of cave ventilation at the event scale is a paper by Andi Smith et al documenting more research information from Cueva de Asiul (site 61).
Due to copyright, the paper (pdf) can be downloaded from the ScienceDirect site until August 8th 2015 and then may be available from the Matienzo website 2 years later.

The use of speleothems to reconstruct past climatic and environmental change through chemical proxies is becoming increasingly common. Speleothem chemistry is controlled by hydrological and atmospheric processes which vary over seasonal time scales. However, as many reconstructions using speleothem carbonate are now endeavouring to acquire information about precipitation and temperature dynamics at a scale that can capture short term hydrological events, our understanding of within cave processes must match this resolution. Monitoring within Cueva de Asiul (N. Spain) has identified rapid (hourly resolution) changes in drip water electrical conductivity (EC), which is regulated by the pCO2 in the cave air. Drip water EC is therefore controlled by different modes of cave ventilation. In Cueva de Asiul a combination of density differences, and external pressure changes control ventilation patterns. Density driven changes in cave ventilation occur on a diurnal scale at this site irrespective of season, driven by fluctuations in external temperature across the cave internal temperature threshold. As external temperatures drop below those within the cave low pCO2 external air enters the void, facilitating the deposition of speleothem carbonate and causing a reduction in measured drip water EC. Additionally, decreases in external pressure related to storm activity act as a secondary ventilation mechanism. Reductions in external air pressure cause a drop in cave air pressure, enhancing karst air draw down, increasing the pCO2 of the cave and therefore the EC measured within drip waters. EC thereby serves as a first order indicator of cave ventilation, regardless of changes in speleothem drip rates and karst hydrological conditions. High resolution monitoring of cave drip water electrical conductivity reveals the highly sensitive nature of ventilation dynamics within cave environments, and highlights the importance of this for understanding trace element incorporation into speleothem carbonate at the event scale.

Cave monitoring and the potential for palaeoclimate reconstruction from Cueva de Asiul, Cantabria (N. Spain)
A paper by Smith A.C., Wynn P.M., Barker P.A., Leng M.J., Noble S.R. and Stott A, published in the International Journal of Speleology, 45 (1), 1-9. Tampa, FL (USA) ISSN 0392-6672. The full paper can be read here.

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 +13.7°C, with a maximum range of 1°C, 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 (δ18O, δ2H) 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.

North Atlantic forcing of moisture delivery to Europe throughout the Holocene
A paper by Andrew C. Smith, Peter M. Wynn, Philip A. Barker, Melanie J. Leng, Stephen R. Noble & Wlodek Tych, published in nature.com/scientific reports, http://www.nature.com/srep/2016/160420/srep24745/full/srep24745.html. The full paper pdf can also be read here with supplementary material. Citation: Smith, A. C. et al. North Atlantic forcing of moisture delivery to Europe throughout the Holocene. Sci. Rep. 6, 24745; doi: 10.1038/srep24745 (2016). This work is licensed under a Creative Commons Attribution 4.0 International License.

Century-to-millennial scale fluctuations in precipitation and temperature are an established feature of European Holocene climates. Changes in moisture delivery are driven by complex interactions between ocean moisture sources and atmospheric circulation modes, making it difficult to resolve the drivers behind millennial scale variability in European precipitation. Here, we present two overlapping decadal resolution speleothem oxygen isotope (δ18O) records from a cave on the Atlantic coastline of northern Iberia, covering the period 12.1 - 0 ka. Speleothem δ18O reveals nine quasi-cyclical events of relatively wet-to-dry climatic conditions during the Holocene. Dynamic Harmonic Regression modelling indicates that changes in precipitation occurred with a ~1500 year frequency during the late Holocene and at a shorter length during the early Holocene. The timing of these cycles coincides with changes in North Atlantic Ocean conditions, indicating a connectivity between ocean conditions and Holocene moisture delivery. Early Holocene climate is potentially dominated by freshwater outburst events, whilst ~1500 year cycles in the late Holocene are more likely driven by changes internal to the ocean system. This is the first continental record of its type that clearly demonstrates millennial scale connectivity between the pulse of the ocean and precipitation over Europe through the entirety of the Holocene.