Age frequency distribution and revised stable isotope curves for New Zealand speleothems: palaeoclimatic implications

Abstract

-X. 2010. Age frequency distribution and revised stable isotope curves for New Zealand speleothems: palaeoclimatic implications. International Journal of Speleology, 39(2), 99-112. Bologna (Italy). ISSN 0392-6672.The occurrence of speleothems in New Zealand with reversed magnetism indicates that secondary calcite deposition in caves has occurred for more than 780 thousand years (ka). 394 uranium-series dates on 148 speleothems show that such deposition has taken place somewhere in the country with little interruption for more than 500 ka. A relative probability distribution of speleothem ages indicates that most growth occurred in mild, moist interglacial and interstadial intervals, a conclusion reinforced by comparing peaks and troughs in the distribution with time series curves of speleothem δ 18 O and δ 13 C values. The stable isotope time series were constructed using data from 15 speleothems from two different regions of the country. The greater the number of overlapping speleothem series (i.e. the greater the sample depth) for any one region, the more confidence is justified in considering the stacked record to be representative of the region. Revising and extending earlier work, composite records are produced for central-west North Island (CWNI) and north-west South Island (NWSI). Both demonstrate that over the last 15 ka the regions responded similarly to global climatic events, but that the North Island site was also influenced by the waxing and waning of regional subtropical marine influences that penetrated from the north but did not reach the higher latitudes of the South Island. Cooling marking the commencement of the last glacial maximum (LGM) was evident from about 28 ka. There was a mid-LGM interstadial at 23-21.7 ka and Termination 1 occurred around 18.1 ka. The glacial-interglacial transition was marked by a series of negative excursions in δ 18O that coincide with dated recessional moraines in South Island glaciers. A late glacial cooling event, the NZ Late Glacial Reversal, occurred from 13.4-11.2 ka and this was followed by an early Holocene optimum at 10.8 ka. Comparison of δ 18 O records from NWSI and EPICA DML ice-core shows climatic events in New Zealand to lag those in Antarctica by several centuries to a thousand years. Waxing and waning of subantarctic and subtropical oceanic influences in the Tasman Sea are considered the immediate drivers of palaeoclimatic change.

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke

“…year BP the sea level has already attained its present-day position (Lowe et al 2008) and, thus, sea level related changes, such as a shallower aquifer depth for Lake Pupuke, can also be excluded for the time since then. Williams et al (2010) report diverging trends in d 18 O records from the Waitomo karst area (*170 km S of Lake Pupuke, Fig. 1) of the CWNI records and from the north-west South Island records from 10.5 kyr on.…”

“…year BP (Williams et al 2004;Lowe et al 2008). At 3.4-2.9 kyr the most negative d 18 O values of the CWNI record imply weakest effect of the subtropical gyre on the climate of the North Island (Williams et al 2010). This may have had also consequences for storm frequencies and direction of moisture-bringing air masses.…”

“…From that time point to around 3 kyr the CWNI record has increasingly negative d 18 O values attributed to the waning strength of the subtropical gyre west of New Zealand. This led to a reduction of poleward transport of subtropical waters into the Tasman Sea (Williams et al 2010). The consequence was a general cooling starting from around 6.4-6.2 kyr BP with increasing storm frequency after ca.…”

The river it goes right on: Post-glacial landscape evolution in the upper Waipaoa River basin, eastern North Island, New Zealand

“…These marine-derived terrestrial records indicate that the transition from dry, cold conditions to milder climates began~18.5 cal. ka BP, which is in broad agreement with terrestrial records derived from speleothems (Williams et al, 2010). Warmer, wetter conditions were reinstated after the termination of the cool (Antarctic Cold/New Zealand Late Glacial) reversal, from 12.5 cal.…”

“…Warmer, wetter conditions were reinstated after the termination of the cool (Antarctic Cold/New Zealand Late Glacial) reversal, from 12.5 cal. ka BP (Wright et al, 1995;McGlone, 2001;Hadjas et al, 2006;Williams et al, 2010); and the transition to a more variable climate occurred at~6.5 cal. ka BP.…”