Optical Stimulated Luminescence Dating of Three Classic Sites on the South Island of New Zealand: Investigation of interhemispheric synchroneity during the last deglaeiation. Niek de Jonge Research traineeship at the University of Wollongong, Australia December 2005 Supervisors Chris S. M. Turney Richard 'Bert' G. Roberts Table of Contents Introduction Site descriptions Choice of OSL sample location 5 Birch Hill 5 Waiho Loop / Canavans Knob 7 Cropp River 7 Methods - Optical Stimulated Luminescence dating 9 - Fine grains 10 - Anomalous Fading 10 - Radiocarbon dating H Results 12 Radiocarbon dating 12 Optical Stimulated Luminescence 13 - Dose rate 13 -Birch Hill 14 - Canavans Knob 18 - Cropp River 23 Discussion / Conclusion 24 Appendix A 27 Appendix B 29 References 31 Introduction The Younger Dryas Stadial (YD) was a brief but intense climatic deterioration that occurred during the last deglaeiation of the North Atlantic region. This 1300 yr long cold period also known as the YD chronozone or Greenland stadial 1 (GS-1) took place 12.800 to 11.500 ice-core years ago (Turney et al., 1997; Lowe et al, 2001) or 12.900-11.500 cal yr BP (Björck et al. 1998). The YD chronozone is widely recognized throughout the North Atlantic (NA) and involved temporarily reversion to glacial conditions during the transition ftom the Last Glacial Maximum (LGM) to the Holocene (ca. 18-10 ^"^C ka). The reversion included changes in mean summer temperature which dropped to approximately -5 °C (Atkinson et al, 1987), while periglaeial conditions prevailed in lowland areas, and icefields and glaciers formed in upland areas (Sissons, 1979). Nothing ofthe size, extent, or rapidity of this period of abrupt climate change has been experienced since (Alley, 2000). Although the YD is widely recognized in magnitude, timing and geographic extent throughout the North Atlantic, the mechanism behind the temporarily reversion is still poorly understood. Initially it was assumed that the Thermohaline Circulation (THC) of the NA region would induce globally synchronous climate change (Broecker, 2003). This view is supported by comparisons of some Antarctic and Greenland ice- core records (Steig et al, 1998). In contrast with this is the mechanism ofthe bipolar seesaw (Broecker, 1998), which drives warm periods like the Boiling-Allerod interstadial (GI-1, Greenland ice-core isotope stratigraphy) too coincide with cooling periods in the south (the Antarctic Cold Reversal, ACR), and vice versa (Blunier & Brook, 2001). With this the southem ocean potentially triggers an intensification of the THC in the North Atlantic (Knorr & Lohmann, 2003). This mechanism is thus supporting globally asynchronous climatic change. To get a better understanding of global climatic change more precise records of mid- latitude palaeoclimatic changes in the Southem Hemisphere are needed. An ideal location to record climatic changes on the Southern Hemisphere is New Zealand. This country has a high potential sensitivity to climate change due to the high mountains that support glaciers and the prevailing westerly airflow, which generates abmpt environmental and climatic gradients (Newnham et al, 1999). Previous work on dating glacial moraine deposits like the Waiho Loop at Franz Josef glacier (Denton & Hendy, 1994), Cropp River (Basher & McSaveney, 1989) and the Birch Hill moraine at the' Tasman glacier (BuiTows et al, 1976) impUed apparently synchronous advances with the YD event in the Northem Hemisphere. In contrast with this pollen- records, from the west coast ofthe South Island, show increased precipitation between ca 12.000 - 10.000 ^'^C yr BP, which Ukely reflects a strengthened westerly circulation and no unequivocal evidence of cooling (Vandergoes & Fitzsimons, 2003). This is supported by pollen and isotope data from the Cobb Valley in the northwest of the South Island (Singer et al, 1998) and from Kettlehole Bog in the Cass Basin, central South Island (Turney et al., 2003; McGlone et al, 2004). This could imply that ice advances in southem New Zealand are driven by increased precipitation instead of temperature decrease. This supports the assumption that the southwest Pacific is a region dominated by changes in moisture and not in temperature (Turney et al, IN PRESS). Which makes comparison with the North Atiantic extremely complex and difficuh to interpret. So the identification of an unambiguous YD cold event in New Zealand remains problematical (McGlone, 1995). A major problem with the comparison of records spanning the YD Stadial on both hemispheres is that the majority have been obtained from terrestiial records using the 3 radiocarbon (^''C) method. This method inhibits uncertainties in the Pre-Holocene calibrated radiocarbon time scale because of local and regional differences in marine reservoir ages (Stuiver et al, (1998). Corrections are necessary because the radiocarbon clock did not run at a uniform rate during the North Atlantic YD time (Hughen et al, 1998). These problems are compounded by temporal variations in atmospheric ^"^C content and cause near constant ^"C ages, known as a radiocarbon age plateaus. Calendar ages at a radiocarbon age plateau can vary over several centuries (Lowe et al., 2001). The North Atlantic YD took place during such a radiocarbon age plateau. Age uncertainties from the radiocarbon ages obtained during this period are thus consequently too large to test for Interhemispheric Synchroneity. This study is aimed at answering one of the key questions in global cUmate change: "Whether the deglaeiation of the LGM happened synchronous or asynchronous on hoth hemispheres." In order to answer this question an alternative approach is used focussing in particular on the anomalous North Atlantic YD event. Optically stimulated luminescence (OSL) properties of quartz and feldspar sediments (Huntley et al., 1985) are used to date glacial moraine deposits of three classic sites on the South Island, New Zealand: the Birch Hill Moraines (Burrows et al, 1976), the Waiho Loop terminal moraine (Denton & Hendy, 1994; Mercer, 1988) and Cropp River (Basher & McSaveney, 1989). Relatively high precision ages are obtained for these glacial advances in order to test for an interhemispheric synchroneity. 4 Site descriptions Choice of OSL sample location Sediment suitable for OSL dating needs to be sufficiently bleached at or shortly before deposition and be in the range of fine sand (90-300 |im) to sih (4-63 ^m). The importance of fully bleaching (zeroing) sediment grains prior to burial is a fundamental requirement of OSL dating. OSL samples were taken in glaciofluvial or glaciolacustiine deposits. These deposits are expected to be most sufficiently bleached due to the transport distance between the glacier margin and the point of deposition. For the sediment grains to get bleached by sunlight, the grains need to have undergone supra-glacial transport. A good indication of transport is well-sorted and laminated sediment. Lenses of glaciofluvial or glaciolacustrine material within diamicton are most desirable because ofthe direct relationship with the glacial event (Richards, 2000). With regard to this the most appropriate locations are obtained for all the three classic sites. Birch Hill The Birch Hill moraines are situated in the Tasman Valley on the eastern side of the alpine fauh. The moraine deposits lie about 11 km in front of the present terminus of the Tasman glacier in the north. The moraines consist of hummocks and are roughly up to 30 m in height. They form an erosion relict on the westem side of the braided Tasman River floodplain (Fig. 1). Fig. 1: Location of the Birch Hill sample site The section being sampled for OSL (43°48'50"S, 170°06'37"E) dating is exposed on the northem * Kilometer scale: 1:37795 (blue lines) side of a hummocky moraine and is schematically drawn in figure 2. The sequence consists from bottom to top of a compact till (> 3m), laminated sands (l,7m-3m), coarse grey till (0,7m-l,7m) and a clayey poorly sorted top soil (0m-0,7m). The bottom till is a matrix-supported, non- stratified diamicton with sub-rounded clasts up to 10 cm in diameter. The laminated sands are well sorted and consist of fine grained (2m-3m) and medium grained sands (l,7m-2m) and are interpreted as glaciofluvial sediments. The overlying till has an erosion surface with the underlaying sands, clasts up to 50 cm in diameter and seems to be coarser at the base. Superimposition of the laminated sands on the glacial till is interpreted as an indication of supra-glacial transport whereas the overlying glacial till shows the laminated sands to have a direct relationship with the glacial event. Two duplicate tiibes of sample for OSL dating were taken in the fine-grained laminated sands (2.5 m). Sediment for the estimation of the dose rate was taken directly from around the tubes. 5 BIR CAN CR " • " . Ö O D. .0 •O •7d ra: G ra n ite Laminated sand I^U^Q'. Diamicton Clayey silt DO Oxidated gravel Organic silt |=r-HÏ^ Imbricated gravel %% OSL samples Coarse sand Schematic sicetches ofthe three site iocations on the south Island in New Zealand: Birch Hill (BIR), Canavans Knob (CAN) and Cropp River (CR). Waiho Loop / Canavans Knob The Waiho Loop terminal moraine is situated 10 km downstream of the Franz Josef Glacier on the west coast of the Southern Island, New Zealand. The terminal moraine forms the most conspicuous late-glacial moraine in the Southern Alps. The moraine is a 6 km long, steep-sided arcuate ridge rising over 100 m above the adjacent alluvial plain of the Waiho River and it's tributary, the Tatare Stream (Fig. 3). Canavan Knob is a bedrock outcrop consisting of granite forming a hill 1 ' I 1 '•-r- .'^ • VfiUfrtruJosetmaiau' that rises approximately 120 m above the alluvial plane. The outcrop lies 1,6 km upstream from the actual Waiho Fig. 3: Location of lite Canavans Knob sample site (43 ° 22'50"S, 170° 09' 37"E) and the arcuate Loop moraine and is surrounded by ridge ofthe Waiho Loop terminal moraine.