First cosmogenic 10Be constraints on LGM glaciation ...

JOURNAL OF QUATERNARY SCIENCE (2008) 23(8) 707–712 Copyright ß 2008 John Wiley & Sons, Ltd. Published online 29 July 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jqs.1188

Rapid Communication First cosmogenic 10Be constraints on LGM glaciation on New Zealand’s North Island: Park Valley, Tararua Range MARTIN S. BROOK,1* JAMES SHULMEISTER,2 TYNE V. H. CROW1 and ALBERT ZONDERVAN3 1 Geography Programme, School of People, Environment and Planning, Massey University, Palmerston North, New Zealand 2 Department of Geological Sciences, University of Canterbury, Christchurch, New Zealand 3 National Isotope Centre, GNS Science, Lower Hutt, New Zealand Brook, M. S., Shulmeister, J., Crow, T. V. H. and Zondervan, A. 2008. First cosmogenic 10Be constraints on LGM glaciation on New Zealand’s North Island: Park Valley, Tararua Range. J. Quaternary Sci., Vol. 23 pp. 707–712. ISSN 0267-8179. Received 18 November 2007; Revised 6 March 2008; Accepted 14 March 2008

ABSTRACT: We report the first direct ages for late Quaternary glaciation on the North Island of New Zealand. Mt Ruapehu, the volcanic massif in the North Island’s centre, is currently glaciated and probably sustained glaciers throughout the late Quaternary, yet no numeric ages have been reported for glacial advances anywhere on the North Island. Here, we describe cosmogenic 10Be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the Tararua Range, part of the axial ranges of the North Island. Results indicate that a limited valley glaciation occurred, culminating in recession at the end of the last glacial coldest period (LGCP, ca. 18 ka). This provides an initial age for deglaciation on the North Island during the last glacial–interglacial transition (LGIT). It appears that glaciation occurred in response to an equilibrium-line altitude (ELA) lowering of 1400 m below the present-day mean summer freezing level. Ages for glaciation in the Tararua Range correspond closely to exposure ages for the last glacial maximum (LGM) from the lateral moraines of Cascade Valley in the South Island, and in Cobb Valley, in northern South Island. The corollary is that glaciation in the Tararua Range coincided with the phase of maximum cooling during MIS 2, prior to the Antarctic Cold Reversal (ACR), during the LGCP. Copyright # 2008 John Wiley & Sons, Ltd. KEYWORDS: North Island; Tararua Range; cosmogenic

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Be; late Quaternary; ELA.

Introduction Evidence of glaciation on New Zealand’s North Island is poor compared with the wider New Zealand region. Indeed, while the extent and chronology of mid-latitude glaciation in the Southern Hemisphere for Tasmania (e.g. Mackintosh et al., 2006), Chile (e.g. Fogwill and Kubik, 2005) and New Zealand’s South Island is emerging (e.g. Suggate and Almond, 2005; Alloway et al., 2007), the timing and degree of glaciation on the North Island are unknown. While the North Island’s central volcanoes such as Mt Ruapehu are thought to have been permanently glaciated during the late Quaternary (McArthur * Correspondence to: M. S. Brook, Geography Programme, School of People, Environment and Planning, Massey University, Private Bag 11222, Palmerston North, New Zealand. E-mail: [email protected]

and Shepherd, 1990), attention has only recently been drawn to the lack of direct glacial evidence on the axial ranges of the North Island (Brook et al., 2005). These axial ranges are oriented north–south along the Australian-Pacific convergent plate margin (Stratford and Stern, 2006), with the Tararua Range (southern) sector of the axial ranges reaching elevations of 1500 m. These mountains are much lower, and more northward, than those of the Southern Alps, and consequently glaciation was much more restricted. Only one previous study (McGlone and Topping, 1977) has provided an estimate of the timing of glacial retreat in the central North Island. This was based on tephra (Rerewhakaaitu) overlying a moraine on Mt Ruapehu, and provided a glacial retreat age of 14.7–17.5 ka. This paper reports the first cosmogenic radionuclide exposure (CRSE) ages of the timing of glaciation on the North Island’s axial ranges, within the Tararua Range (Fig. 1). We also probe possibilities regarding climate change necessary to produce glaciation in these mountains.

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Figure 1 (A) Location of Park Valley on North Island, New Zealand, relative to ocean cores MD97-2121 and MD97-2120 to the north and south of the Chatham Rise, and to the closest other known glacial sites of Cobb Valley, and Mt Ruapehu. (B) Detail of sampling area within Park Valley

Study area and previous work The last glacial cycle (ca. 74–11.5 ka) in New Zealand is locally known as the Otiran Glaciation (Suggate, 1990). Mix et al. (2001) considered that the most recent phase of extensive glaciation typically occurred during Marine Isotope Stage (MIS) 2, often referred to as the LGM, at ca. 24–18 ka. This roughly coincides with a more recent synthesis by Alloway et al. (2007) that used various tephras deposited since ca. 30 ka, to delineate the ’last glacial coldest period’ (LGCP) as extending from 28 ka to 18 ka. The Late Otiran glacial sequence (34–18 ka) in New Zealand is evident in moraine and outwash deposits on the west coast of the South Island (Fig. 1), which indicate early LGM cooling around 34 ka (Suggate and Almond, 2005), and this is mirrored by adjacent pollen profiles (Newnham et al., 2007). Studies of the last glacial interglacial transition (LGIT) on the

northern tip of the South Island (Fig. 1(A)) indicate the onset of glacial recession at ca. 20–19 ka, suggestive of 48C of cooling and an equilibrium line altitude (ELA) decline to 1380 m (Shulmeister et al., 2005). In contrast with the South Island (above), the glacial history on the North Island is poorly known. Adkin (1912) initially proposed a model of limited valley glaciation within the Tararua Range and this early work has remained largely unmodified, with no direct dating of glacial landforms anywhere on the North Island. From an analysis of digital terrain models and valley morphology, six valleys within the central Tararua Range probably sustained minor valley and cirque glaciers during the late Quaternary (Brook and Brock, 2005), with Park Valley the most impressive glacial site (Fig. 2). Recent attention has been drawn to the presence of a lateral moraine paralleling the true right side of the valley (Figs. 2 and 3), 250 m in length, and 15 m high (Brook and Crow,

Figure 2 The U-shaped, glacially eroded Park Valley, characterised by truncated spurs and trim-lines marking upper limits of glaciation (view to the south-west), with the lateral moraine arrowed (note lateral moraine asymmetry). The lower end is being degraded by stream erosion (arrowed)

Figure 3 The lateral moraine on the true right of the upper part of Park Valley, viewed from the western slope of Arete. Note the smooth surface and lower end degraded by erosion, and the erratic block perched on the ice proximal side of the moraine (arrowed)

Copyright ß 2008 John Wiley & Sons, Ltd.

J. Quaternary Sci., Vol. 23(8) 707–712 (2008) DOI: 10.1002/jqs

GLACIATION ON THE AXIAL RANGES OF NEW ZEALAND’S NORTH ISLAND

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measured at the GNS Science AMS facility in Lower Hutt, New Zealand. Methodology in calculating the ages followed Balco et al. (2008), with wrapper script version 1.1, main calculator version 1.2 and constant version 1.2 used.

Results

Figure 4 The rock outcrops where PV-01, PV-03 and PV-04 were sampled from (arrowed). This rock face lies at the confluence of two cirque basins at the head of the valley. The western-most cirque is in the foreground and the eastern-most cirque is in the middle distance, with the Wairarapa Plain and the Pacific Ocean in the far distance

2008). This is thought to be the only known glacial deposit on the North Island, other than on Mt Ruapehu, and is distinctive because of the lack of a corresponding lateral moraine on the opposing side of the valley. Possible reasons for this ’moraine asymmetry’ have been discussed in detail in Brook and Crow (2008).

Methods Exposure dating with cosmogenic nuclides provides a means of directly measuring the time elapsed since deposition of an erratic or erosion of a glacial landform (Gosse and Phillips, 2001). Three samples were obtained from a boulder perched on the ice-proximal side of the lateral moraine (Fig. 3), and three samples were obtained from rock knobs on the lower side-walls at the confluence of two cirques at the head of Park Valley (Figs. 1 and 4). The boulder and bedrock locations, respectively, are composed of quartzo-feldspathic metasediments, with some signs of plucking and striae, indicating their former erosion at the base of a glacier. The concentration of 10 Be in the six samples was measured in samples taken from the uppermost surfaces, to minimise problems relating to significant snow or vegetation coverage (e.g. Fogwill and Kubik, 2005). The isotope 10Be was selectively extracted from the whole rock sample following the standard procedures outlined by Kohl and Nishizumi (1992). The isotope ratios were

Table 1 lists the cosmogenic 10Be radionuclide data, the location and type of sampling site and the conventional exposure ages of each sample. Similar ages within MIS 2 occur on both the lateral moraine boulder and the cirque side walls, varying between 17.1 1.1 ka and 23.9 1.7 ka. This most likely reflects a minimum age for glaciation of Park Valley, if one allows for the effects of surface weathering and possible shielding by seasonal snow, soils, vegetation or volcanic ash falls. By selecting from the upper surface of the boulder on the moraine and bedrock 10 m above the floor of the valley head sidewalls, we aimed to minimise the effect of any these shielding factors. The former Park Valley Glacier surface profile has been reconstructed by Brook et al. (2005), and these data are represented here by an area–altitude graph (Fig. 5). The ELA of the glacier was estimated using the accumulation area ratio (AAR) method, which assumes that the accumulation area assumed a fixed proportion of total glacier area (Ballantyne, 2007). For extant mid-latitude glaciers without significant debris cover, steady-state AARs typically lie in the range 0.55–0.65, and an AAR of 0.6 was used here as this is commonly used in ELA calculations (Ballantyne, 2007). Drawing firm conclusions from ELA reconstruction methods can be notoriously difficult (Benn and Evans, 1998), with a change in AAR from 0.6 to 0.5 yielding a 100 m rise in ELA in Park Valley, suggesting a minimum ELA uncertainty of 50 m. Using an AAR of 0.6 gives a Park Valley Glacier ELA of 1050 m 50 m (Fig. 5). The extent and ELA of valley glaciers is dependent on many variables including air temperature, precipitation, cloudiness, insolation, and near-surface wind velocity and humidity (e.g. Oerlemans, 1991). The degree of climate cooling during glacials is often determined by reconstructing ELA depression, and comparing this with present-day values within the same mountain range (e.g. Bakke et al., 2005). Following the approach of Mackintosh et al. (2006), we use the mean summer freezing level because of its close relationship with ELAs on contemporary glaciers (Ohmura et al., 1992). The mean summer freezing level was calculated as 2500 m using temperature data from 1990 and 1991 from Mt Bruce, 15 km

Table 1 Cosmogenic radionuclide data and exposure ages, Park Valley, Tararua Range, New Zealanda Sampleb

PV-01 PV-03 PV-04 PV-05 PV-07 PV-09

Altitude (m)

1377 1160 1152 1199 1199 1199

Latitude (8E)

175.2605 175.2579 175.2570 175.2564 175.2564 175.2564

Longitude (8S)

44.9191 44.9722 44.9173 44.8961 44.8961 44.8961

Be concentrations (atoms g1)

10

0.197 0.011 0.157 0.011 0.182 0.013 0.187 0.012 0.186 0.015 0.185 0.013

10 Be exposure age (ka)

Scaling factors Thickness

Shielding

Location

0968 0.952 0.960 0.960 0.952 0.960

0.788 0.787 0.650 0.910 0.825 0.825

2.925 2.482 2.467 2.467 2.558 0.2558

17.78 1.07 17.05 1.19 23.90 1.72 17.58 1.21 18.68 1.53 18.38 1.30

a All samples prepared at the Department of Geological Sciences, University of Canterbury, New Zealand, and analysed at the accelerator mass spectrometry (AMS) facility at GNS Science, Lower Hutt, New Zealand. b PV-01 to PV-03 are sidewall samples; PV-4 to PV-06 are from boulder on lateral moraine.



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Figure 5 Area-elevation plot of the former Park Valley Glacier. An accumulation area ratio (AAR) of 0.6 is used in this study, which is typical of valley glaciers (e.g. Ballantyne, 2007). Note the large variation in ELA (100 m) caused by a change in AAR from 0.5 to 0.6, which highlights the uncertainty with simple ELA calculations

east of Park Valley (National Institute for Water and Atmospheric Research, 2007) and a temperature lapse rate of 6.58C km1.

Discussion Fig. 6 show sea surface temperature (SST) reconstructions from IMAG core MD97-2121 (408 22.80 S, 1778 59.40 E) and DSDP-594 (458 31.410 S, 1748 56.880 E), located east of New Zealand to the north and south of the west–east trending submarine Chatham Rise, respectively (Fig. 1(A)). SSTs from these sites suggest that glaciation in the Tararua Range

Figure 6 Exposure ages of glacial landforms in Park Valley. These data are compared with wider proxy records of climatic changes including sea surface temperatures reconstructed for DSDP-594 (Barrows et al., 2007), a marine core of the south-east coast of New Zealand (458 S), and for MD97-2121 (Pahnke and Sachs, 2006) from the north Chatham Rise (408 S), east of the North Island. The deuterium record (hashed line) from the Vostok ice core from central Antarctica (Petit et al., 1999) is included, together with the Antarctic Cold Reversal (ACR) event (Blunier et al., 1997) and last glacial coldest period (LGCP) as defined by Alloway et al. (2007) Copyright ß 2008 John Wiley & Sons, Ltd.

coincided with the phase of maximum cooling during MIS 2 (Fig. 6), prior to the Antarctic Cold Reversal (ACR), during the LGCP as defined by Alloway et al. (2007). This also coincides with variations in the d18O record of the Vostok ice core (Petit et al., 1999). Process-based models of maritime glaciers in New Zealand suggest glaciers are sensitive to temperature changes (Anderson et al., 2006), and we speculate that glaciation in the Tararua Range does reflect past temperature change. Comparison with other glacial studies in New Zealand shows that the ages in Park Valley closely mirror those of the LGM reported for Cascade Valley on the west coast of the South Island (Sutherland et al., 2007), where CRSE ages of 22–19 ka from lateral moraines have been reported. Park Valley glaciation also coincides with the final two LGM advances at 21.5 ka and 19 ka identified by Suggate and Almond (2005) from the South Island. The closest other glacial site with age constraints is Cobb Valley on the northern tip of the South Island, where Shulmeister et al. (2005) concluded that the onset of glacial recession was at 20–19 ka, with dramatic warming at 16–15 ka. Our cosmogenic ages appear to confirm this, although further exposure age dating is needed to test this hypothesis. A palynological record from Pohehe Swamp (McLea, 1990), 25 km to the north-east of Park Valley reported a decline in Nothofagus taxa (southern beeches) at 24 ka, thought to represent a temperature decline between 3 and 4.58C. Comparing the present-day calculated ELA of 2500 m at Park Valley with the palaeo-ELA of 1050 m, using a simple lapse rate of 6.58C km1 implies cooling of up to 88C during MIS 2 in Park Valley. This is similar to the temperature decline of up to 78C reported from Lake Poukawa, 150 km to the north-east (Shulmeister et al., 2001). It is also similar to the 88C decline identified by Barrows et al. (2007) from DSDP-594 off the east of the South Island, where rapid temperature fluctuations of 68C over a few centuries have been identified. However, ocean cores closer to the study site off the eastern North Island show less severe temperature depression during the LGCP. Indeed, from analysis of alkenone, Pahnke and Sachs (2006) report a cooling of 68C from during the LGCP from MD97-2121. McGlone (2001) reports more moderate cooling of 48C from a palynological analysis of ocean core P69, adjacent to MD97-2121. The 88C cooling for Park Valley is also higher than the 4.6–5.98C cooling for the LGM reported by McGlone and Topping (1983), based on vegetational analysis of sites around Mt Ruapehu (Fig. 1), and the altitude of a cirque basin on the slopes of Mt Tongariro, to the north of Mt Ruapehu. Our palaeo-ELA of 1050 m is significantly lower than the 1500–1600 m estimated for Mt Ruapehu to the north (McArthur and Shepherd, 1990) and the 1380 m reported for Cobb Valley to the south. That the Park Valley palaeo-ELA is lower than that for Cobb Valley is intriguing, J. Quaternary Sci., Vol. 23(8) 707–712 (2008) DOI: 10.1002/jqs

GLACIATION ON THE AXIAL RANGES OF NEW ZEALAND’S NORTH ISLAND

though we suspect it could represent the effect of precipitation variation between sites (e.g. Lamont et al., 1999), and errors inherent in the calculation of ELAs (e.g. Benn and Evans, 1998). Indeed, McGlone and Topping (1983) highlighted that low temperatures alone did not account for the transition from dense podocarp–hardwood forest to sparse grassland–shrubland, citing precipitation and wind direction as being important factors. Recent work (Hooker and Fitzharris, 1999; Purdie et al., 2008) has demonstrated that contemporary glaciers on the western side of the Southern Alps respond to the regional airflow pattern over New Zealand, with temperature perhaps being a secondary effect. Enhanced southwesterly airflow during summer and winter reduces ablation and increases precipitation, causing glacial advances, whereas enhanced northerly flows and high pressures reduce precipitation and increase ablation, causing retreat (Shulmeister et al., 2005).

Conclusions Our 10Be data provide the first direct dating of glaciation on the North Island of New Zealand. The exposure ages (17.05–23.9 ka) suggest the glacier advance culminated during MIS 2, a time when most regional records indicate cooling. The advance of the Park Valley glacier developed a U-shaped valley cross-section, typical of glaciated mountain regions, and formed a lateral moraine on the true right of the valley. It appears the valley glacier would have been fed by two smaller cirque glaciers. Glacial activity in Park Valley was associated with an ELA reduction of 1400 50 m and a possible temperature reduction of 88C, though we caution this is the absolute upper limit of cooling, compared with other published work. Indeed, most other recent research reports temperature depression of the order of 4–68C. Glacial advances across New Zealand’s South Island occurred during glaciation of Park Valley, and ocean cores including DSDP-594, MD97-2121 and P69, together with pollen records from the North Island, provide further evidence of cooling. Further work may wish to explore the possibility of glacial activity at other sites on the axial ranges of the North Island, and the 2518 m high Mt Taranaki, 140 km to the west of Mt Ruapehu. Acknowledgements We thank Massey University for funding this project (MURF 04/2022, 05/2059), and the Department of Conservation for providing accommodation in the Tararua Range at Arete Bivouac and Te Matewai Hut. Advice from Dr Mike Shepherd was invaluable at the beginning of this project, and the assistance of Rob Spiers is gratefully acknowledged for sample preparation.

References Adkin GL. 1912. The discovery and extent of former glaciation in the Tararua Ranges, North Island, New Zealand. Transactions of the New Zealand Institute 44: 308–316. Alloway BV, Lowe DJ, Barrell DJA, Newnham RM, Almond PC, Augustinus PC, Bertler NAN, Carter L, Litchfield NJ, McGlone MS, Shulmeister J, Vandergoes MJ, Williams PW. 2007. Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ-INTIMATE project). Journal of Quaternary Science 22: 9–35. Anderson B, Lawson W, Owens I, Goodsell B. 2006. Past and future mass balance of ’Ka Roimata o Hine Hukatere’ Franz Josef Glacier, New Zealand. Journal of Glaciology 52: 597–607.


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Bakke J, Dahl SO, Paasche O, Lovlie R, Nesje A. 2005. Glacier fluctuations, equilibrium-line altitudes and palaeoclimate in Lyngen, northern Norway, during the Lateglacial and Holocene. Holocene 15: 518–540. Balco G, Stone JO, Lifton NA, Dunai TJ. 2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements. Quaternary Geochronology (in press). Ballantyne CK. 2007. The Loch Lomond readvance on North Arran, Scotland: glacier reconstruction and palaeoclimatic implications. Journal of Quaternary Science 22: 343–359. Barrows TT, Juggins S, De Dekker P, Calvo E, Pelejero C. 2007. Long-term sea surface temperature and climate change in the Australian–New Zealand region. Paleoceanography 22(2): PA2215. Benn DI, Evans DJA. 1998. Glaciers and Glaciation. Arnold: London. Blunier T, Schwander J, Stauffer B, Stocker T, Dallenbach A, Indermuhle A, Tschumi J, Chappellaz J, Raynaud D, Barnola JM. 1997. Timing of the Antarctic cold reversal and the atmospheric CO2 increase with respect to the Younger Dryas event. Geophysical Research Letters 24: 2683–2686. Brook MS, Brock BW. 2005. Valley morphology and glaciation in the Tararua Range, southern North Island, New Zealand. New Zealand Journal of Geology and Geophysics 48: 717–724. Brook MS, Crow TVH. 2008. A debris ridge in Park Valley, Tararua Range, New Zealand, as evidence for Pleistocene glaciation. New Zealand Journal of Geology and Geophysics 51: 23–28. Brook MS, Purdie HL, Crow TVH. 2005. Valley cross-profile morphology and glaciation in Park Valley, Tararua Range, New Zealand. Journal of the Royal Society of New Zealand 35: 399–407. Fogwill CJ, Kubik PW. 2005. A glacial stage spanning the Antarctic Cold Reversal in Torres del Paine (51 degrees S), Chile, based on preliminary cosmogenic exposure ages. Geografiska Annaler 87A: 403–408. Gosse JC, Phillips FM. 2001. Terrestrial in situ cosmogenic nuclides: theory and application. Quaternary Science Reviews 20: 1475–1560. Hooker BL, Fitzharris BB. 1999. The correlation between climatic parameters and the retreat and advance of Franz Josef Glacier, New Zealand. Global and Planetary Change 22: 39–48. Kohl CP, Nishizumi K. 1992. Chemical isolation of quartz for measurement of in situ produced cosmogenic nuclides. Geochemica et Cosmochemica Acta 56: 3583–3587. Lamont GN, Chinn TJ, Fitzharris BB. 1999. Slopes of glacier ELAs in the Southern Alps of New Zealand in relation to atmospheric circulation patterns. Global and Planetary Change 22: 209–219. Mackintosh A, Barrows TT, Colhoun EA, Fifield LK. 2006. Exposure dating and glacial reconstruction at Mt Field, Tasmania, Australia, identifies MIS 3 and MIS 2 glacial advances and climatic variability. Journal of Quaternary Science 21: 363–376. McArthur JL, Shepherd MJ. 1990. Late Quaternary glaciation of Mt Ruapehu, North Island, New Zealand. Journal of the Royal Society of New Zealand 20: 287–296. McGlone MS. 2001. A late Quaternary pollen record from marine core P69, southeastern North Island, New Zealand. New Zealand Journal of Geology and Geophysics 44: 69–77. McGlone MS, Topping QQ. 1977. Aranuian (post-glacial) pollen diagrams from the Tongariro region, North Island, New Zealand. New Zealand Journal of Botany 15: 749–760. McGlone MS, Topping WW. 1983. Late Quaternary vegetation, Tongariro region, central North Island, New Zealand. New Zealand Journal of Botany 21: 53–76. McLea WL. 1990. Palynology of Pohehe Swamp, northwest Wairarapa, New Zealand: a study of climatic and vegetation changes during the last 41 000 years. Journal of the Royal Society of New Zealand 20: 205–220. Mix AC, Bard E, Schneider R. 2001. Environmental processes of the ice age: land, oceans, glaciers (EPILOG). Quaternary Science Reviews 20: 627–657. National Institute for Water and Atmospheric Research. 2007 http:// cliflo.niwa.co.nz/ [14 November 2007]. Newnham RM, Vandergoes MJ, Hendy CH, Lowe DJ, Preusser F. 2007. A terrestrial palynological record for the last two glacial cycles from southwestern New Zealand. Quaternary Science Reviews 26: 517–535.


712


Oerlemans J. 1991. A model for the surface balance of ice masses. Part 1: Alpine glaciers. Zeitschrift fu¨r Gletscherkunde und Glazialgeolgie 27: 63–83. Ohmura A, Kasser P, Funk M. 1992. Climate at the equilibrium line of glaciers. Journal of Glaciology 38: 397–411. Pahnke K, Sachs JP. 2006. Sea surface temperatures of southern midlatitudes0-160 kyr BP. Paleoceanography 21(2): PA2003. Petit JR, Jouzel J, Raynaud D, Barkov NI, Barnola JM, Basile I, Bender M, Chappellaz J, Davis M, Delaygue G, Delmotte M, Kotlyakov VM, Legrand M, Lipenkov VY, Lorius C, Pepin L, Ritz C, Saltzman E, Stievenard M. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429–436. Purdie HL, Brook MS, Fuller IC. 2008. Seasonal variation in ablation and surface velocity on a temperate maritime glacier: Fox Glacier, New Zealand. Arctic, Antarctic and Alpine Research 40: 140– 147. Shulmeister J, Fink D, Augustinus PC. 2005. A cosmogenic nuclide chronology of the last glacial transition in North-West Nelson, New


Zealand: new insights in Southern Hemisphere climate forcing during the last deglaciation. Earth and Planetary Science Letters 233: 455–466. Shulmeister J, Shane P, Lian OB, Okuda M, Carter JA, Harper M, Dickinson W, Augustinus P, Heijnis H. 2001. A long late-Quaternary record from Lake Poukawa, Hawke’s Bay, New Zealand. Palaeogeography, Palaeoclimatology, Palaeoecology 176: 81–107. Stratford WR, Stern TA. 2006. Crust and upper mantle structure of a continental backarc: central North Island, New Zealand. Geophysical Journal International 166: 469–484. Suggate RP. 1990. Late Pliocene and Quaternary glaciations of New Zealand. Quaternary Science Reviews 9: 175–197. Suggate RP, Almond PC. 2005. The Last Glacial Maximum (LGM) in western South Island, New Zealand: implications for the global LGM and MIS 2. Quaternary Science Reviews 24: 1923–1940. Sutherland R, Kim K, Zondervan A, McSaveney M. 2007. Orbital forcing of mid-latitude Southern Hemisphere glaciation since 100 ka inferred from cosmogenic nuclide ages of moraine boulders from the Cascade Plateau, southwest New Zealand. Geological Society of America Bulletin 119: 443–451.
