Palaeoclimatic interpretation of stable isotope data from holocene speleothems of the Waitomo district, North Island, New Zealand

Citation
Pw. Williams et al., Palaeoclimatic interpretation of stable isotope data from holocene speleothems of the Waitomo district, North Island, New Zealand, HOLOCENE, 9(6), 1999, pp. 649-657
Citations number
35
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
HOLOCENE
ISSN journal
0959-6836 → ACNP
Volume
9
Issue
6
Year of publication
1999
Pages
649 - 657
Database
ISI
SICI code
0959-6836(199911)9:6<649:PIOSID>2.0.ZU;2-F
Abstract
One straw stalactite and three stalagmites from the Waitomo district of Nor th Island, New Zealand, were examined for stable isotopes of oxygen and car bon with a view to interpreting their palaeoclimate signal. Dating was by u ranium series and AMS C-14 for the stalagmites and by gamma-ray spectrometr y for the straw. Records were thus established for about 100 years for the straw and 3.9, 10.1 and 10.2 ka for the stalagmites. The range of variabili ty in delta(18)O(c) and delta(13)C(c) this century is about two-thirds of t hat experienced over the entire Holocene, and is most simply explained in t erms of the oceanic source area of rain. Stable isotope variations in three stalagmites show some general similarities, but have significant differenc es in detail. which underlines the necessity to base palaeoclimatic interpr etations on more than one speleothem record. The delta(18)O(c) of each stal agmite varies positively with temperature. indicating the dominance of the ocean source of evaporation in determining the isotopic composition of prec ipitation and hence speleothem calcite in the Holocene. This conclusion is contrary to that of other authors working in New Zealand, who identified a negative relationship between delta(18)O(c) and temperature, while examinin g time periods extending across the Last Glacial Maximum. It is concluded h ere that, whereas the ice volume effect dominates the large climatic shifts of glacial-interglacial amplitude, the oceanic source effect becomes more important during the period of relatively stable sea level during the Holoc ene. Results also indicate a late-Holocene altitudinal effect of 0.2 parts per thousand delta(18)O(c) per 100 m and an associated temperature relation ship of about 0.26 parts per thousand per degrees C. The average of two rec ords identifies the postglacial climatic optimum to lie in the interval fro m prior to 10 ka BP to 7.5 ka BP, when delta(18)O(c) values were up to 0.6 parts per thousand less negative than present, implying an average annual m ean temperature that was up to 2.3 degrees C warmer. The average of three s peleothem records for the last 3900 years reveals the coldest period of the Holocene to have occurred about 3 to 2 ka BP, when delta(18)O(c) values we re typically 0.4 parts per thousand more negative than present and average temperatures may hate been 1.5 degrees C cooler. Mean annual temperature va riability of about 2 degrees C was sometimes experienced in little more tha n 100 years.