Constraints from monitoring on reconstruction of Gibraltar palaeoclimate in a speleothem record covering the last glacial period.

Ten years of comprehensive cave monitoring in Gibraltar provides a unique basis forinterpreting proxy records in speleothems, and in this study we discuss some of theopportunities and challenges in constructing an interpretive framework for long proxyrecords. We present a new trace element and stable isotope record spanning 30-110 kaobtained from two neighbouring speleothems from Ragged Staff Caves, Gibraltar. The agemodel is defined by over 100 U-Th dates with continuous micromilling for stable isotopes,and LA-ICPMS used for acquiring the trace element proxy record. These provide highlyresolved critical evidence for some of the main meteorological and environmental controls onpast western Mediterranean terrestrial climate at near decadal and sub-annual resolution,respectively. Our interpretations of the monitoring data highlight geochemical and hydrologicalprocesses critical to speleothem deposition. We conclude that δ13C and δ18O in speleothemcalcite are controlled by within-cave conditions that vary seasonally and are themselvescontrolled by the temperature and water balance at the ground surface. For interpretation oftrace elements, we utilize multi-annual monitoring of drip waters. The Gibraltar record showsvariations in δ13C and δ18O on timescales from multi-decadal to multi-millennial which wecompare with independently dated records of multiple proxies from marine cores,including vegetation and sea surface temperature (SST), and the Greenland ice corerecord. The precision of the Gibraltar speleothem chronology allows for greater confidence incorrelation with other records, and we particularly note a remarkable correspondence withδ18O in Greenland in the period 40-60ka, and similarity with SST records from the AlboranSea. We believe this reveals a dominant influence of North Atlantic climate at the gateway tothe Mediterranean. However, we note that in periods which there is weaker correspondencebetween speleothem and ice core δ18O, this may indicate changes in the dominant climatecontrols in the western Mediterranean. All comparisons of proxy records show a broad similarity with the cave recordover the longest timescales, i.e. δ13C and δ18O both display higher values in thecolder, drier climates of the mid-glacial, and generally lower values in the longinterstadials of the early glacial period. Superimposed on this trend are millennial-scalevariations with amplitudes of the same order of magnitude seen over stadial-interstadialtimescales. At times these fluctuations correspond closely to the variations seen in SST,pollen, and vegetation records while some excursions appear out of phase. We usemultiproxy marine core records to explore these phase differences, as the speleothemrecord may partially reflect other factors independent of those recorded throughSST and pollen proxies. Over centuries high frequency variations similar to thoseobserved on multi-annual timescales in cave monitoring and modern speleothemoccur, showing both the small and large scale applications of our monitoring data. [ABSTRACT FROM AUTHOR]