The Last Glacial Maximum in the central North Island, New Zealand: palaeoclimate inferences from glacier modelling

Abstract

Abstract. Quantitative palaeoclimate reconstructions provide data for evaluating the mechanisms of past, natural climate variability. Geometries of former mountain glaciers, constrained by moraine mapping, afford the opportunity to reconstruct palaeoclimate, due to the close relationship between ice extent and local climate. In this study, we present results from a series of experiments using a 2-D coupled energy balance-ice flow model that investigate the palaeoclimate significance of Last Glacial Maximum moraines within nine catchments in the central North Island, New Zealand. We find that the former ice limits can be simulated when present-day temperatures are reduced by between 4 and 7 • C, if precipitation remains unchanged from present. The spread in the results between the nine catchments is likely to represent the combination of chronological and model uncertainties. The majority of catchments targeted require temperature decreases of 5.1 to 6.3 • C to simulate the former glaciers, which represents our best estimate of the temperature anomaly in the central North Island, New Zealand, during the Last Glacial Maximum. A decrease in precipitation of up to 25 % from present, as suggested by proxy evidence and climate models, increases the magnitude of the required temperature changes by up to 0.8 • C. Glacier model experiments using reconstructed topographies that exclude the volume of post-glacial (< 15 ka) volcanism generally increased the magnitude of cooling required to simulate the former ice limits by up to 0.5 • C. Our palaeotemperature estimates expand the spatial coverage of proxy-based quantitative palaeoclimate reconstructions in New Zealand. Our results are also consistent with independent, proximal temperature reconstructions from fossil groundwater and pollen assemblages, as well as similar glacier modelling reconstructions from the central Southern Alps, which suggest air temperatures were ca. 6 • C lower than present across New Zealand during the Last Glacial Maximum.

Glacier‐based climate reconstructions for the last glacial–interglacial transition: Arthur's Pass, New Zealand (43°S)

“…6-6.5˚C to simulate the Southern Alps ice field at the LGM. This result is in good agreement with several catchment-scale modelling studies of LGM glaciers distributed across the Southern Alps and central North Island (Putnam et al, 2013a,b;Eaves et al, 2016a). The results of Golledge et al (2012) are also in good agreement with the LGM temperature estimates of Rother et al (2015), which are based on mass balance modelling of the former Waimakairiri glacier that drained eastwards from Arthur's Pass (Fig.…”

“…This model has been used to simulate late Quaternary glaciers in New Zealand at a number of locations (e.g. Kaplan et al, 2013;Doughty et al, 2013;Eaves et al, 2016a). We refer the reader to Doughty et al (2013) for a full model description.…”

“…Kaplan et al, 2010;Eaves et al, 2016b) and/or numerical glacial modelling (e.g. Doughty et al, 2013;Eaves et al, 2016a). Using the latter approach, Golledge et al (2012) modelled the LGM ice field in the Southern Alps, which achieved a best fit to the mapped limits (e.g.…”

Using Soil Stratigraphy and Tephrochronology to Understand the Origin, Age, and Classification of a Unique Late Quaternary Tephra-Derived Ultisol in Aotearoa New Zealand

“…A frequently occurring (c. 70% of years) late summer or early autumn soil moisture deficit, usually lasting several months (typically from c. 30 to 50 median annual days), is generally most pronounced north and northeast of Hamilton [73,150]: the potential summer soil moisture deficit for the Kainui soil is likely to be c. 170 mm; that for the Otorohanga soil is probably <c. 140 mm (after [54,73,151,152]). Generally, rainfall during glacial periods is reduced by up to c. 25% of that of the present, e.g., [153,154], and therefore halloysite formation rather than allophane is promoted in such times because of limited desilication, as evident in the middle to lower profile (below c. 0.9 m depth) of the Otorohanga soil ( Figure 8B). From c. 0.9 to 1.5 m depth, both allophane and halloysite have been formed in the Otorohanga soil, very likely during MOIS 3 and 2 when the parent tephras and tephric loess were being deposited and simultaneously weathered and altered by pedogenesis during a mainly (but not wholly) drier and cooler climate [54,102,[155][156][157].…”

“…Therefore, are 1-m-deep soils, such as the Otorohanga soil ( Figure 8B), formed by developmental upbuilding, destined to end up (in, say, another c. 50,000 years) as a rather homogenous-looking, welded, halloysite-rich clayey unit as seen throughout the Hamilton Ash (and Kauroa Ash) sequences? Churchman and Lowe [44] and Moon et al [149] (indirectly) addressed this question with respect to the likely clay mineral composition by considering longer timescales of glacial and interglacial cycles in temperate volcanic landscapes not directly glacierized, as was the case for most of North Island, e.g., [154,183]. They pointed out that the marine oxygen isotope records show that cooler and drier conditions associated with glaciations persisted c. 80-90% of the time whereas warmer and wetter conditions associated with interglaciations occurred only c. 10-20% of the time.…”