DOI: 10.25921/1ay7-ts70
title: NOAA/WDS Paleoclimatology - Northern Spain 4000 Year Stalagmite d13C and Temperature Reconstruction

description: The surface temperature changes for the last 4000 years in northern inland Iberia (an area particularly sensitive to climate change) are determined by a high resolution study of carbon stable isotope records of stalagmites from three caves (Kaite, Cueva del Cobre, and Cueva Mayor) separated several tens of kilometers away in N Spain. Despite the local conditions of each cave, the isotopic series show a good overall coherence, and resulted to be strongly sensitive to surface temperature changes. The record reflects alternating warmer and colder intervals, always within a temperature range of 1.6 °C. The timing and duration of the intervals were provided by 43 230Th-234U (ICP-MS) ages. Main climatic recognized periods are: (1) 3950-3000 yr BP: warm period punctuated by cool events around ~3950, 3550 and 3250 yr BP; (2) 2850-2500 yr BP cold interval (Iron Age Cold Period); (3) 2500-1650 yr BP moderate warm period (Roman Warm Period), with maximum temperatures between 2150 and 1750 yr BP; (4) 1650-1350 yr BP cold interval (Dark Ages Cold Period), with a thermal minimum at ~1500 yr BP; (5) 1350-750 yr BP warm period (Medieval Warm Period) punctuated by two cooler events at ~1250 and ~850 yr BP; (6) 750-100 yr BP cold period (Little Ice Age) with extremes occurring at 600-500 yr BP, 350-300 yr BP, and 150100 yr BP; and (7) the last 150 years, characterized by rapid but no linear warming (Modern Warming).  Remarkably, the presented records allow direct comparison of recent warming with former warm intervals such as the Roman or the Medieval periods. That comparison reveals the 20th century as the time with highest surface temperatures of the last 4000 years for the studied area.  Spectral analysis of the time series shows consistent climatic cycles of ~400, ~900 and ~1300 yr, comparable with those recognized in the North Atlantic marine record, the Greenland ice cores, and other terrestrial records for the middle-late Holocene, suggesting common climate forcing mechanisms related to changes in solar irradiance and North Atlantic circulation patterns.
description: Carbon stable isotope stacked series for the last 4000 years 
derived from three stalagmites of three caves of N Spain 
(Kaite, Cobre, and Cueva Mayor). Age model is based in 43 230Th 
absolute ages. Analyses for age-dating were conducted at the 
University of Minnesota by means of ICP-MS. Carbon isotope data 
are expressed as absolute deviation values i.e., the absolute 
difference between that each d13C(V-PDB) value and a reference 
value for each stalagmite. This reference value is the average 
d13C of each stalagmite for the time interval between 1570 
and 670 yr BP - the longest interval of continuous and 
simultaneous growing of the three stalagmites.  For each 
measurement, approximately 100ug of powder sample were drilled 
from petrographical thin sections of the axial part of the 
stalagmites, and analyzed with an on-line, automated, carbonate 
preparation system (Kiel III), linked to a Finnigan MAT-252 ratio 
mass spectrometer at the University of Minnesota Isotope Lab. 
The 13C data is translated into relative temperature estimates 
by means of a transfer function based in cross correlation 
between instrumental series of temperatures and d13C values 
in stalagmite SLX1 (estimated error ±0.26 °C).