Optical Stimulated Luminescence Dating of Three Classic Sites on the South Island of New Zealand

(1)

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

(2)

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 a l , 2001) or 12.900-11.500 cal yr BP (Björck et al. 1998). The Y D 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 a l , 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 Y D 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 N A 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 a l , 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. A n 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 a l , 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 a l , 1976) impUed apparently synchronous advances with the Y D event in the Northem Hemisphere. I n 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 a l , 1998) and from Kettlehole Bog in the Cass Basin, central South Island (Turney et al., 2003; McGlone et a l , 2004). This could imply that ice advances i n 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 a l , I N PRESS). Which makes comparison with the North Atiantic extremely complex and difficuh to interpret. So the identification of an unambiguous Y D cold event in New Zealand remains problematical (McGlone, 1995).

(4)

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 a l , (1998). Corrections are necessary because the radiocarbon clock did not run at a uniform rate during the North Atlantic Y D time (Hughen et a l , 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 Y D 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 Y D 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 a l , 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.

(5)

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.

Fig. 1: Location of the Birch Hill sample site (43°48'50"S, 170°06'37"E) * Kilometer scale: 1:37795 (blue lines)

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).

The section being sampled for OSL dating is exposed on the northem 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.

(6)

B I R

C A N

C R

Ö O

" • " . . 0 D. • O • 7 d

ra:

G ra n ite I ^ U ^ Q ' . D i a m i c t o n O x i d a t e d g r a v e l D O | = r - H Ï ^ I m b r i c a t e d g r a v e l C o a r s e s a n d L a m i n a t e d s a n d C l a y e y silt O r g a n i c silt % % O S L s a m p l e s

Schematic sicetches ofthe three site iocations on the south Island in New Zealand: Birch Hill (BIR), Canavans Knob (CAN) and Cropp River (CR).

(7)

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 that rises approximately 120 m above the alluvial plane. The outcrop lies 1,6 km upstream from the actual Waiho Loop moraine and is surrounded by outwash deposits. These outwash deposits are interpreted to be of glacial

origin (Wardle, 1978). The section is being exposed on the northwestern side by a quarry. The sedimentological sequence of the section being sampled, figure 2, consists from bottom to top of granitic bedrock at the base, organic brown grey sih (0.13 m), grey clayey sih (0.16 m), organic brown grey sih (0.06 m), wood bearing grey clayey sih (0.22 m) and a coarse compact till (>3.30 m). The till is a very poorly sorted, matrix-supported diamicton with clasts up to 60 cm in diameter. Two duphcate tubes of sample for OSL were taken in the grey clayey sihs directly under the 0.06 m thick layer of organic brown grey sih. Because the OSL samples were taken in non-uniform stratum two samples were taken for estimation ofthe dose rate. Dose rate sample CAN#2 was from the grey clayey sihs directly surrounding the tubes, and dose rate sample CAN#3 was from the organic brown grey layer of sih directly above the tubes. Samples for radiocarbon dating were taken from the lowermost, 0.13 m thick layer of organic brown grey sih in the form of a small root imbedded with the sedmient, and from the wood bearing grey clayey silts above the tubes in the form of a piece of a large branch or small trunk.

1 ' I 1 ' • - r - .'^ • V f i U f r t r u J o s e t m a i a u '

Fig. 3: Location of lite Canavans Knob sample site (43 ° 22'50"S, 170° 09' 37"E) and the arcuate ridge ofthe Waiho Loop terminal moraine. * Kilometer scale: 1:47244 (blue lines)

Cropp River

Cropp River is located on the westem side of the main divide of the Southem Alps. The river has a drainage area of 28,5 km flowing into the Whitcombe River, which is a major tributary stream of the Hokitika River. Several peaks above 1500 m surround the drainage basin with Mt Beaumont being the highest peak at 2131 m above sea level.

(8)

cirque glacier remains on the northern side of Mt Beaumont.

The exposure being sampled lies on the southem side of the river a few hundred meters west of Tarkus Knob near two river gauges (Fig. 4). The section is schematically drawn in figure 2 and consists from bottom to top of grey-brown oxidated gravels (0,4 m), an alternation of grey clayey sihs and organic brown-grey clayey sihs (0,7 m), angular imbricated gravels (0,45 m), grey well-sorted coarse sands (0,3 m) and poorly sorted grey diamicton (> 2,8 m).

The altemated part consist in detail from bottom to top of organic grey-brown sihs imbedded with macros and wood (0,05 m), grey relatively coarse sihs with wood fragments (0,15 m), organic brown-grey silty clay with wood fragments (0,1 m) and a grey clayey sih with subtle banding (0,4 m) and a 175 cm long wooden branch at the top. The angular gravels are moderately too well rounded with two bedded lenses of silty sand, both 1 cm thick. The diamicton is matrix supported and contains in-egular and sub-rounded clasts up to 40 cm in diameter. Samples for OSL dating were taken in two different strata. Two duplicate tubes of sample (A) were taken from the lowermost layer of grey clayey sihs directly under the layer of organic grey brovm sihs. And two duphcate tubes of sample (B) were taken from the grey well-sorted coarse sands 15 cm under the grey diamicton. Only for sample (A) determination of the dose rate has been taken out. Dose rate sample CR-A #1 was from the lowermost grey brown oxidated gravels and dose rate sample CR-A #2 was from directly around the tubes. Sample for radiocarbon dating was taken from the 0,1 m thick layer of organic brown-grey clayey sihs above the lowermost tubes.

(9)

Methods

Optical Stimulated Luminescence dating

OSL dating relies on the fact that, when buried, grains are ex^osed^to an ionising radiation dose (dose-rate) from the radioactive decay of ^^^U, U , Th (and their daughter products) and ''^K in the deposh. This resuhs in the accumulation of a trapped-charge population. Exposure of the grains to sunlight, also known as bleaching, releases the hght-sensitive trapped charge, thereby resetting the OSL signal. So the time elapsed since the grains were last exposed to sunlight can be estimated by measuring the OSL signal within the grains, this signal is known as the burial dose or paleodose (PD), and the rate of exposure of the grains to the ionising radiation which is known as the dose rate (D,). The actual burial age can be calculated using the following formula:

Burial age = PD

D..

Gy

Gylka (1)

In the field sampling for luminescence dating was carried out by hammering two cylindrical PVC tubes horizontally into the vertical section ofthe sediment. The tubes were immediately packed in black plastic bags to avoid bleaching by sunlight. Separate dose-rate samples were being taken of each stiatum within 0,3 m of the paleodose samples. This aUows an approximate evaluation of the gamma dose-rate by calculation in cases of non-uniformity (Aitken, 1998). The dose-rate samples were determined at the CSIRO in Canberra.

Preparation ofthe samples used for determination of the paleodose was carried out at the OSL laboratory at the University of WoUongong under subdued laboratory red-hght conditions. The outer sides ofthe tubes are potentially bleached and thus used to determine the moisture content of the samples. The samples were wet-sieved to extiact the 90 to 300 \xm fraction. Samples were pre-treated with hydrochloric acid (10%) and hydrogen peroxide (50%) to remove carbonates and organic matter. Quartz and feldspar grains were isolated using Sodium Polytungstate (Na6(H2Wi204o)H20) under standard extraction procedures for sand-sized quartz, including etching in 40% hydrofluoric acid for 40 min (Aitken, 1998).

Paleodoses were determined using a single-aliquot regenerative-dose (SAR) protocol, in which a dose-response curve is constructed for each grain using test dose OSL signals to correct for any sensitivity changes (Murray & Roberts, 1998; Galbraith et a l , 1999; MuiTay & Wintle, 2000; Yoshida et a l , 2000). In this protocol a measurement to check the reliability of the sensitivity correction is carried out by repeating the first regeneration dose after the principal regeneration. This is referred to as the recycling ratio (Murray & Wintie, 2000). A n other more stringent test is the "Dose Recovery Tesf', in which SAR is applied to an aUquot that has been given a laboratory dose following optical bleaching of the aliquot (Murray & Wintie, 2003). In this test the ratio ofthe measured and the given dose should be unity. These test are carried out on all the samples in this research. A l l the measurements were made on the RIS0 TL/OSL DA-15 reader No. 2 except for the quartz sample of CAN, these were measured on machine No. 3.

(10)

Fine grains

The sample of Canavans Knob consisted mainly of fme sihs and clay. The fme grain polymineral sample preparation v^as carried out following Frechen et al. (1996). After the pre-treatment with hydrochloric acid (10%) and hydrogen peroxide (50%) the sediment was wet sieved to separate the 63-90 ^m fraction and the <63 |j,m fraction. The 4-11 ym fraction was enriched using Stokes's law, whereby the <11 pm was separated under gravitational force and the 4-11 |im under centrifugation (Appendix A).

To isolate the quartz component, and thus remove unwanted feldspars in the polymineral sample, the sample was treated with 34 % fluorosilicic acid (HiSiFe) for 36 hours (Rees-Jones, 1995). Deposition of the fine grains on aluminium discs was carried out on two different ways (Appendix A). First an acetone suspension of the polymineral 4-11 |im fraction (~400mg/200ml) was poured in 41 smaU glass tubes with aluminium discs on the bottom and allowed to evaporate in a dry oven at 40 " C. A theoretical monolayer o f - l O m g with a mask size of 10 mm was achieved on each disc. In order to achieve smaller mask sizes material was scraped of the discs until 2mm and 1 mm squares were being left. Second a 5 pl drop of distilled water suspension with a proportion of 100ml water to 500 mg sample was deposited with a pipet on each aluminium disc. This resulted in a mask size of 2mm and with a rough estimation of 45.000 grains per disc.

Anomalous fading

K-feldspar grains are commonly affected by anomalous fading, which reflects the instability of some of the electron traps (Wintie, 1973). Since the detection of anomalous fading, K-feldspar grains were usually considered to be undatable (Aitken, 1985). When anomalous fading is present and not detected the calculated age will be too young, whereas i f detected the age can only be interpreted as a lower limh.

Anomalous fading can be detected by conducting fading tests on K-feldspar aliquots using the SAR technique (Auclah et a l , 2003). The anomalous fading is quantified by the g value, which corresponds to the percentage fading loss per decade of time (Aitken, 1985). The g value is calculated as the slope from a regression line through points of a graph plotting I/Ic versus logio(t*/tc). Where t* has taken into account that the sample suffers from fading even during irradiation (Auclair et al., 2003; Aitken, 1985, Appendix F). The g value can be expressed by combining Eq. (3) and Eq. (5) of Huntley & Lamothe (2001):

g = m

1

-• ln{io) (2)

where / is the IRSL intensity measured at time t after the irradiation, and Ic is the intensity when t = tc. The arbitiary time tc can be taken as the time of the prompt measurement.

To compare g values of different sets of measurement or different samples, the g values were normaUzed to a specified tc of 2 days (t2d) from Huntiey & Lamothe (2001). The normalised g value (g2d) is expressed by:

(11)

ëld =• g 100 g log 10 hd \ h j (3)

The actual correction to be made to an optical age, when anomalous fading is present, is carried out with the following formula after Eq. (A5) in the appendix of Huntley & Lamothe (2001):

T PD

g

m-LN

(10)

LN - 1 (4)

where T is the true age and PD is the paleodose, which are proportional (with the subscript ƒ indicating a value that is affected by fading).

Radiocarbon dating

Radiocarbon dating was carried out to supply the luminescence dates with an independent age control and to compare two different laboratory pre-treatment procedures. Mercer (1988) showed that small apparent differences in ages were obtained depending on the different pre-treatment protocols. This can be of critical importance when looking at evidence for a possible Younger Dryas timing in the Southern Hemisphere.

The samples being dated consist of wood ftom Canavans Knob and Cropp River. The sample ftom Canavans Knob was collected during fieldwork ftom the same quarry and lithological sequence as Mercer (1988) and Denton & Hendy (1994). The sample ftom Cropp River is ftom the same piece of wood as dated by Basher & McSaveney (1989). In the ^'*C-laboratory at the University of Wollongong the samples were treated to extract the holoceUulose and the alpha-cellulose fraction. The procedure of the holoceUulose extiaction consists of pre-treatment in HCl whereas the alpha-cellulose extraction also takes a tieatment of NaOH into account. The pre-treatment ofthe sample with NaOH gets rid of most of the humic acids in the sample. This is especially important for the samples from the west coast of New Zealand where precipitation rates are in the range of 5000 to 8000 mm/yr. The samples were exposed to huge amounts of run-off over time and thus possibly contaminated by younger humic acids from upstream, which give the samples a seemingly younger C age.

(12)

Results

Radiocarbon dating

The resuhs from the radiocarbon dates of Canavans iCnob and Cropp River are shown in table 1. A l l the radiocarbon ages were analysed at Lower Hutt, New Zealand. For Canavans Knob two sets of dates have been achieved. The pre-treatment of the first set was done in the ^'^C-laboratory at the University of Wollongong while the pre-freatment ofthe second set (NZA23559 and NZA23560) was done at Lower Hutt in New Zealand. With this set we're not 100 % sure which pre-treatment protocol has been used.

Location Treatment sample number Radiocarbon Age

Canavans Knob holoceUulose _ _{11440 ± 4 0 BP}

Canavans Knob alpha-cellulose - - 11640 ± 4 5 BP

Canavans Knob alpha-cellulose - - 11650 + 45 BP

Canavans Knob ?? NZA23559 -26.6 11056 ± 4 0 BP

Canavans Knob ?? NZA23560 -26.6 11098 ± 4 5 BP

Cropp River (Basher) alpha-cellulose - - 10120 ± 4 0 BP

Table 1: Radiocarbon ages for Canavans Knob and Cropp River

From the first set from Canavans Knob the holoceUulose age was 11440 ± 40 BP while the two alpha-cellulose samples came thi-ough as 11640 ± 45 BP and 11650 ± 45 BP. This shows a clear difference between the holoceUulose and the alpha-cellulose protocol. Though the second set which were supposed to be treated with the alpha-cellulose protocol show a much younger age of 11056 ± 40 BP and 11098 ± 45 BP. Still uncertainty exists about the pre-treatment being used by Lower Hutt. I f they used the alpha-cellulose treatment no clear difference exists between the two protocols. Though i f they used a different treatment, more radiocarbon ages should be achieved before conclusions can be made.

The radiocarbon date of Cropp River was pre-treated at the University of Wollongong and analysed at Lower Hutt, New Zealand. This sample was from the same piece of wood as used by Basher & McSaveney (1989). These authors got a radiocarbon age of 10250 ± 150 BP, which is consistent with the radiocarbon age of 10120 ± 40 BP that is been found here. Though this shows no age shift at all when using alpha-cellulose.

(13)

Optical Stimulated Luminescence

Dose rate

The dose rates, necessary for the age model, were determined using the high-resolution gamma spectrometry for ^^^U, ^^^Ra, ^ ^ H , ^^^Ra, ^^^Th and % , and are listed in table 2. The moisture contents were calculated as the percentage of water compared to the dry sample (weight water (g)/ weight dry sample (g)).

Sample Code Moisture content (%)

U-238 se Ra-226 se Pb-210 se Ra-228 se Th-228 se K-40 se

CR-A#1 11.09 22.03 2.52 27.69 0.37 25.71 1.75 39.60 0.71 39.72 0.64 550.22 10.05 CR-A #2 43.02 39.06 1.92 42.55 0.49 41.84 2.21 61.42 0.92 63,93 0.89 927.79 14.81 CAN #2 48.23 32.17 1.68 34.44 0.43 34.29 2.00 47.15 0.79 48.63 0.74 694.63 11.91 CAN #3 58.48 39.27 1.89 39.84 0.47 35.28 2.10 57.47 0.89 60.04 0.86 936.64 14.95 BIR 11.57 30.38 2.83 32.79 0.58 33.65 3.27 50.18 1.26 50.13 0.97 735.10 16.97

Table 2: Dose rates and moisture contents for Cropp River (CR-A), Canavans Knob (CAN) and Birch Hill (BIR).

The cosmic ray dose rate is a function of altitude, geomagnetic latitude and the depth of the sample in the exposed deposit. The values of parameters used for calculating the cosmic ray dose rate are shown in table 3. These parameters were determined with figure 2 in Prescott & Hutton (1994).

C o s m i c d o s e rate Sample Cosmic latitude longitude altitude (m) F J H depht (cm) ray (Gy/ka)

CR-A -43.078 170.963 870 0.24 0.76 4.10 425 0.185

CAN -43.381 170.160 182 0.24 0.76 4,10 363 0.169

BIR -43.814 170.110 630 0.24 0.76 4.10 250 0.199

Table 3: Parameters usedfor calculating the cosmic ray dose rate for Cropp River (CR-A), Canavans Knob (CAN) and Birch Hill (BIR).

The relative gamma contribution m the dose rate for Canavans Knob (CAN) and Cropp River A (CR-A) had to be calculated because of inhomogeneous sttatum (fig. 2). The gamma effect for CR-A has not been calculated. For the C A N sample two dose rate samples have been taken. CAN#3 consisted of sample of the 6 cm horizontal layer of organic grown grey clay 1 cm above the tubes and CAN#2 consisted o f sample of the silty grey clay directly around the tubes and above the organic layer in a radius of 0.3 m. This resulted in a relative contribution of the total gamma radiation for CAN#3 and CAN#2 o f 11% and 89% respectively. The results o f t h e beta and gamma contribution to the dose rate are shown in table 4.

CAN U-aver. se-int. K - ' 4 0 s e 'Tli-«8 ' ' PD (Gy) se

beta spec gamma spec 37.00 0.36 37.68 0.37 694.63 11.91 721.25 12.24 48.63 0.74 49.89 0.75 48.4 4.3

Table 4: Calcidated gamma dose rate for Canavans Knob (CAN). The beta dose rate is the dose rate from CAN#2.

(14)

Birch Hill

IRSL of K-feldspar:

Quartz from North Westland in New Zealand is usually very dim and shows large changes in sensitivity during measurements (Preusser et al., 2005). So for the BIR-R sample the SAR technique was applied first for the K-feldspar grains. First a normal SAR test was applied on the 90-125 )j.m fraction using aliquots with Imm mask sizes. This showed a very bright IRSL-signal with consistently small error margins. Secondly a series of dose recovery tests were performed in order to achieve unity between measured and given dose. The aliquots were bleached for 250 sec using I R diodes (90%) at 0 °C and then given a known dose of 60 Gy. The SAR runs consisted of IR stimulation for 100 sec at 50 °C and a test dose of 30 Gy. The best resuhs were achieved using a preheat and cut heat of 250 °C for 60 sec (fig. 5).

CT)

d s : 3 g r : D e y e ; 1 . 0 4

4

( / i l l 1

0 3 1 0 6ie 9 2 9 1 2 3 8

Fig. 5: Typical dose recoveiy growth curve for a 1 mm mask of K-Fd grains for BIR-R. The stimulation dose was 60 Gy (619 sec) and the measured dose for this disc was 60.1 ±5.4 Gy.

After the dose recovery a normal SAR run was carried out. The run used the same measurement conditions as described for the dose recovery test. The results of this test are shown in figure 6. The central age model gave a paleodose of 144.27 ±20.6 Gy.

BIR-R normal SAR run

_{• R6/R1} _0T6n-n

, 231 \ 215 \ 199 \ 183

\

167 • 151 Ö 135 ₁

/

119 ' 103 25.00 12-50 a.33 6.25 0 1 2 3 4 5 6 7 disc no.

(15)

For these 6 ahquots of the BIR-R sample, anomalous fading has been detected by conducting fading tests on the K-feldspar aliquots using the SAR technique (Auclair et al., 2003). The used aliquots were artificially bleached using IR diodes (90%) at 0 °C for 250 sec. and given a dose of 150 Gy, preheated at 250 °C for 60 sec and stored for delayed periods of time to mduce the fading prior to IRSL measurement. The delayed storage times ranged from a prompt delay (0 pause), to more extended delays of 60 sec, 600 sec, -607860 sec (1 week) and -2696780 sec (1 month).

B I R - R F a d i n g test 180 170 160 150 140

I

130 120 110 100 90 80 8 « ? <> . i 5 Ö c > ! e c c > <

; I 1

> t » , t < 1 :

o No pause (prompt delay)

o pause 60 s e c o pause 600 s e c © pause - 607860 s e c • pause ~ 2696780 s e c 2 3 4 5 6 7 d i s c no. 8 9 10 11 12

Fig. 7: Results ofthe Fading test for the 6 K-Feldspar aliquots of Birch Hill (BIR-R).

The resuhs of the fading tests are shown in figure 7 and in Appendix B. The paleodoses of the prompt delayed measurements show approximate unity with the given dose of 150 Gy. Though the measured paleodoses with a pause of 600 sec or higher show significant lower signals, which accounts for anomalous fading ofthe K -feldspars.

The g values were calculated with formula (2) using the intensity (Ic) of the prompt measurement (tc or t*) and the intensity (l) of the -607860 sec (7 day) delayed measurement (0- To compare g values of different sets of measurement or different samples the g-2d value is calculated with formula (3). The faded paleodoses (PDf) of the normal SAR run (fig. 6) were used for making the actual age correction by calculating the paleodose (PD) prior to fading with formula (4). The calculated values are listed in table 5 and shown in figure 8.

disc PDf (Gy) se k g-value %/decade g-2day %/deoade PD (Gy) 1 141.30 18.31 0.030 6.973 8.282 258.63 3 195.72 21.88 0.029 6.762 7.987 355.42 5 131.19 10.56 0.026 5.969 6.903 212.74 7 253.39 32.64 0.022 5.092 5.756 383.93 9 122.44 11.54 0.024 5.574 6.380 189.88 11 84.05 7.52 0.032 7.368 8.846 156.62

(16)

CZJ P D l _ l PDf O g v a l u e 450 400 350 300 250 200 150 100 50 O 8 7 6 4 8_{u c}

I

O. (D 3 -S-2 1 O 3 5 7 disc no. 9 11

Fig. 8: Histogram of the faded paleodoses (PDf), paleodoses prior to fading and the g values of BIR-R.

The central age model for the corrected true paleodoses gave a value of 245.34 ± 32.33 Gy. The calculated dose rate for the K-feldspars was 3.92 ± 0.11 Gy/ka. Using formula (1) this results in a burial age of 62.51 ± 8.51 ka.

OSL of Quartz (preliminarv data):

When the measurements on the K-Feldspar grains didn't give appropriate resuhs the OSL signal ofthe 90-125 fxm fraction of quartz was measured with several different preheat and cut heat temperatures. First a series of dose recovery tests were performed in order to achieve unity between measured and given dose. The aliquots were bleached for 250 sec using Blue LED diodes (50%) at 0 °C and then given a known dose of 50 Gy. The SAR runs consisted of stimulation with Blue LED diodes (50%)) for 100 sec at 125 °C and an infrared wash with IR diodes (90%)) for 100 sec at 125 "C. The test dose being used was 30 Gy. The different cut heat temperatures being tested for were 160 °C for 0 sec, 200 °C for 0 sec, 220 °C for 10 sec and 290 °C for 10 sec. With this different preheat temperatures were carried out. The cut heat of 200 °C for 0 sec and a preheat of 260 °C for 10 sec gave approximately unity between measured and given dose.

After the dose recovery tests normal SAR runs were carried out using the same conditions as described above. Figure 9 shows the radial plots for the resuhs of the SAR run measured on 1mm mask sizes and on 3nim mask sizes. The paleodoses of the 1mm mask size shows a higher spread around the mean due to higher standard errors even after deletion of the inaccurate discs. More SAR runs will be carried out for the 3nmi mask sized aliquots. The data shown here is taken as preliminary data for the moment.

The central age model for the aliquots of the 1mm mask sizes after deletion gave a paleodose of 61.56 ± 8.91 Gy. The calculated dose rate for Birch HiU was 3.65 ± 0.072 Gy/ka. Using formula (1) this resuhs in a burial age of 16.86 ± 2.49 ka. On the other hand the ahquots of the 3mm mask sizes had a paleodose of 56.25 ± 4.58 Gy. Using formula (1) this results in a burial age of 15.41 ± 1.33 ka. So the 3mm mask

(17)

size show clearly more accurate results than the 1mm mask size. Awaiting more data this will become even more accurate.

All Aliquots Imm mask After deletion 1 mm mask All Aliquots 3mm mask I ^1 \ 70

\

66

\

63 \ - 60 • 57 Ö 54 ₁ • 50 • 47 Relative Error C/o)

33.33 I6.CT 11.11 8.33 Relative Error (%) 33.33 16.67 11.11 8.33 Relative EiTOrf/o) 33.33 16.67 I l . l l 8.33 0 3 6 9 12 Predsioa

common age model avcom 63.254 std err 2.673 4.23% central age model

central 63.608 so 11.665 21.760% Sigma 0.879 se 0.160 18.22% common ag e model avconn 64.707 std err 2.903 4.49% central ar|e nodel

central 61.558

se 8.906 14.468% slgniH 0.480

0.110 22.90%

common age model avcom 54.351 std err 2.369 4.36% central age model

ceiilial 56.252 se 4.581 8.144% Sigma 0.192 so 0.069 35.82%|

Fig. 9: Radial plots of the 1 mm masks size of the 90-125 /jm fraction of quartz for Birch Hill (BIR-R).

(18)

Canavans Knob

Fine grains preliminarv data:

For Canavans Knob optical dating of the fine-grained (4-11 |am) polymineral sample was carried out because this grain size was most abundant (Appendix A). The grain sizes are too smaU for isolation of the different minerals with Sodium Polytungstate. So to isolate the feldspar signal different filter combinations are carried out whereas the quartz component is isolated through chemical pre-treatment. The probability of an optical age exceeding the true age of deposition increases with the number of grains on an ahquot (OUey et al., 2004). So various mask sizes were tried to get a better estimation of the true age.

First of all normal SAR runs were carried out with different filter combinations and mask sizes, these resuhs are shown in figure 10. Secondly dose recovery test were carried out, these resuhs are shown in figure 11. The tables in the figures show the names ofthe different data files ofthe different runs. Table 6 shows the different fiher combinations for the different data files. For aU the runs the mask sizes are 10 mm (lOmg) except for Wsg0422 and Wsg0424+Wsg0426, these are 2nim and 1mm respectively.

Run Filters Signal Treatment

Wsg0413 (SAR) Kopp 5-60 Wsg0416 (DR) (4.4mm) Wsg0416 BG-39 (3mm) Feldspar N O H F Wsg0422 2mm mask!! Wsg0424 (DR) 1 mm mask!! Wsg0426 1mm dot mask Wsg0414 (SAR) _{- Kopp 5-60} Wsg0417 (DR) (4. 4m m) BG-39 (3mm) G G 400 Wsg0417 (DR) (4. 4m m) BG-39 (3mm) G G 400 Feldspar N O H F Wsg0415 (SAR) Wsg0420 (DR) -U-340 (7.5mm) Quartz N O H F Wsg0419 (SAR) H F U -U-340 (7.5mm) Quartz H F U

Table 6: The different fllter combinations and pre-treatment for the different datafiles of Canavans Knob (CAN).

The SAR run for the felspar signal consisted of stimulation for 100 sec at 50 °C with IR diodes (90%) and a test dose of 30 Gy, using a preheat and cut heat of 250 °C for 60 sec. The SAR run for the quartz signal consisted of stimulation for 100 sec at 125 °C with Blue LED diodes (50%) and an infrared wash for 100 sec at 125 °C with IR diodes (90%), a test dose of 30 Gy, using also a preheat and cut heat of 250 °C for 60 sec. The dose recoveries consisted of a bleach for 250 sec at 0 °C using IR diodes (90%) or Blue LED diodes (50%) for the feldspar and quartz signal respectively. The given dose was 84 Gy.

The SAR runs (fig. 10) and the dose recovery tests (fig. 11) show no significant differences in paleodoses when using only the Kopp 5-60 (4.4mm) and BG-39 (3mm)

(19)

the recychng ratio (R6/R1) and the test dose correction (T6/Tn) are consistent with unity. Though the quartz signal of Wsg0415, with the UB-340 (7.5mm) filter, shows a significant lower paleodose than the feldspar signals while the associated infrared wash (Wsg0415 IR) is consistent with the feldspar signals. The higher paleodoses in the feldspars could be contributed to partially bleaching of the feldspars prior to burial, which is possibly also shown with the BIR-R sample.

The dose recoveries show a consistently higher measured dose than the given dose of 84 Gy. The dose recovery of the quartz signal (Wsg0420) is not shown in figure 11 because ofthe huge errors and inaccurate growth curves. This could be contributed to wrong preheat and cut heat temperatures to isolate the quartz signal.

C A N SAR for different filter combinations

200 180 160 140 120 ^ 1 0 0 Q °- 80 60 40 20 0

WW-

j

-1 -1 o W s g 0 4 1 3 ®Wsg0414 0WsgO415 © W s g 0 4 1 5 IR O Wsg0422 {2mm mask) o W s g 0 4 2 6 (1mm dot) 0 5 10 15 20 25 30 35 40 45 50 55 disc no. R6/R1 6 10 16 20 26 3D 35 diseno. T6/Tn 40 46 50 65 1.7 1.5 1.3 1.1 0.9 0.7 -Q2 5 -20 26 30 35 disc no. 40 46 50 65

Fig. 10: Preliminary data of SAR runs with different fllter combinations and mask sizes for the polymineral fine grains of Canavans Knob. The left hand graph shows the values of the paleodoses, the upper right hand graph shows the associated recycling ratios (R6/R1) and the lower right hand graph the test dose corrections (T6/Tn).

Dose recovery for different filter combinations

and mask sizes

R6/R1 115 110 _ 105 O X 100 Q CL 95 90 85 0 O O

oö"~ o

-_ . . O - i ó -b¬

i 1 1

oWsg0416 ® W s g 0 4 1 7 O Wsg0422 (2mm mask) O Wsg0424 (1mm mask) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 1.30 1.20 1.00 0.90

oqCDpo opp.

O 5 10 15 20 25 30 no. 1.00 0.90 0.80 0.70 T6n-n — O— — 15 20 25 30 no.

(20)

Two different pre-treatment procedures were also carried out to isolate the quartz signal in the polymineral sample. The first one consisted of a pre-treatment of the sample in diluted hydrofluoric (HF) acid (10%) for 80 mmutes (Mauz & Lang, 2004). The results for the SAR run of Wsg0419 are not shown because of the very high errors and inaccurate growth curves.

The second pre-treatment consisted of treatment of the sample with 34 % fluoro silicic acid (HaSiFe) for 36 hours (Rees-Jones, 1995). With this pre-treatment a mask size of 2nim with approximately 45.000 grains was achieved by deposition with pipet (Appendix A ) . The resuhs for this showed a measured quartz signal with a paleodose close to 1.58 ± 0.41 Gy. Though the infrared wash showed a weighted mean paleodose of 110.98 ± 3.33 Gy. This huge difference can be contributed to the pre-treatment with HiSiFe or to the mask size of the aliquots. Also rose recoveries and SAR's with less then 1000 grains per aliquot were achieved. The Dose recoveries gave unity between given and measured dose. Though the SAR runs show no natural signals. This shows that the sample is partially bleached with only a few bright grains on tens of thousand of dim or dead grains.

OSL of Quartz:

After the silt-sized polyminerals gave no satisfactory resuhs measurement of the 90¬ 125 fam grain size fraction of quartz was carried out. (Note that all the measurements on this fraction were made on riso machine no. 3). First of all dose recovery test were achieved in order to find the right preheat and cut heat temperatures. The right dose recovery consisted of a bleach of 250 sec at 0 °C using Blue LED diodes (50%), stimulation for 100 sec at 125 °C with Blue LED diodes (50%) and an infrared wash for 100 sec at 125 °C with IR diodes (90%), a test dose of 30 Gy and a preheat of 240

°C for 10 sec and a cut heat of 220 °C for 10 sec. The given dose was 50 Gy with a

resulting central age of the measured dose of 56.65 ± 4.47 Gy.

These same measurement settings of the dose recovery were used for the SAR run. The resuhs o f t h e SAR run are shown in figure 12. In order to get an accurate age estimation aliquots with a recycling ratio smaller than 0.8 or greater than 1.2 were deleted. Besides this two more aliquots were deleted. Aliquot 49 had too large errors while aliquot 61 was significant different from the population.

• 0.8<R6/R1 <1.2 • D E L E T E D 400 360 300 _ 260 - 200 160 100 50 0 T T 1 T 1

\ „

# 1 1 i T [ i i 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 disc no. ' ' " T W

(21)

All aliquots 0 . 8 < R 6 / R 1 < 1 . 2 0 . 8 < R 6 / R 1 < 1 . 2 + delete of d i s c 49 a n d 61 w 2 , 1 o] Relative Eiror (%) 50.00 25.00 16,67 12.50 2 4 6 8 Precision

Relative Error C/e) 50.00 25.00 16.67 12.50 0 2 4 6 Precision 320 zo4 200 136 104 72 56 40 32 Relative Error C/o)

50.00 25.00 16.67 12.50 2 4 6 8

Precision

central age model

central 48.664

se 5.840 12.000%

Sigma 0.723

0.093 12.80%

central age model

central 43.927

se 5.929 13.497%

Sigma 0.674

se 0.105 15.58%

cenlral age model

central 48.417

se 4.337 8.959%;

Sigma 0.373

s e 0.079 21.29%

Fig. 13: Radial plots for the 90-125 jjin grain size fraction of quartz for Canavans Knob.

Figure 13 shows radial plots and the associated central age models for all aliquots and the two deletion steps. The lowermost data point is aliquot 61, which has a significant weight on the central age of the total population. The central age models of the two deletion steps show a significant decrease in the standard error going firom 5.8 too 4.3 and in the sigma going from 0.72 too 0.37. This will resuh in a lower error margin with the final age calculation.

Six aliquots of the population were tested for anomalous fading in the quartz signal using the SAR technique (Auclair et al., 2003). Anomalous fading in the quartz signal can be detected i f fading feldspar contaminates the quartz, which are not removed by the infrared wash. The used aliquots were artificially bleached using Blue LED diodes (50%) at 0 "C for 250 sec. and given a dose of 50 Gy, preheated at 240 °C for 10 sec and stored for a delayed period of -508900 sec (~7 days) to induce the fading prior to OSL measurement.

Figure 14 shows no fading for the OSL signal of the quartz and some fading for the infrared wash. Thus fading does not influence the OSL signal.

Fading test voor Qz signal In CAN (90-126 um)

• I T 1 ' ' « I T Ï J, I L I ® NO pause #pau5a - 50E 10 12 14 disc no. 18 20 22 24

Fading test voor IR wash in CAN (90-125 um)

i NO pause

^ pause - 50B900 sec 10 12 14

disc no.

16 18 ZO 22 24

(22)

With no detected fading the fmal age calculation for the 90-125 \xm grain size fraction of quartz for Canavans Knob can be carried out. The central age model after deletion ofthe inaccurate ahquots gave a paleodose of 48.4 ± 4.3 Gy. The calculated effect o f the gamma particles and the beta particles are shovm in table 4. This results in a dose rate of 3.72 ± 0.16. The moisture content used v^ith this calculation is 20 ± 5 %. Using formula (1) this resuhs in a burial age of 14.79 ± 1.53 ka.

(23)

Cropp River

Preliminary data:

The Cropp River samples consisted of two duplicates in two different layers. Only the right-hand sample of the lower layer (A), CR-A-R, is measured to detect a OSL signal. A series of dose recovery tests were performed on the 90-125 ym fraction of quartz using aliquots with 3mm mask sizes. The aliquots were bleached for 250 sec using Blue LED diodes (50%) at 0 °C and then given a known dose of 50 Gy. The SAR runs consisted of an IR wash (90%) for 100 sec at 125 °C before the Blue LED stimulation for 100 sec at 125 °C and a test dose of 30 Gy. The preheat and cut heat temperatures were varied to achieve unity between the measured and given dose. A cut heat of 160 °C for 0 sec showed consistently larger errors for the measured doses than a cut heat of 220 °C for 10 sec (fig. 15). Secondly the best resuhs for the recycling ratio (R6/R1) were achieved with a pre heat of 240 °C for 10 sec, whereas the test dose correction (T6/Tn) is best for a preheat of 200 °C for 10 sec.

200 180 160 140 120 o 100 o 0. 80 60 40 20 0

CR-A-R Dose recovery CH&PH-test r 6 ; r i

0 OH=160/0seo « PH=200/10sec O CH=160;0sec & PH=240/10seo A CH=220;0seo & PH=20o;iOsec A CH=220/05eo & PH=240/10seo

f 1 X T T I { T T l l l l Ï ^ ] Ï 15 20 disc no. < T T — —frx— > - 1 _a_ê^4-g s

Fig. 15: Plot of measured doses for different cut heat and preheat temperatures for sample CR-A-R..

More dose recoveries were carried out with a cut heat of 220 °C for 10 sec and a preheat of 240 °C for 10 sec on riso-reader 3. These resuhs however were inconsistent with the resuhs ftom riso-reader 2, showing significantly larger errors. More dose recoveries need to be carried out, in order to make sure to get unity between measured and given dose, before running actual SAR's.

(24)

Discussion / Conclusion

For years scientist have been trying to date the Waiho Loop terminal moraine. Until today though no suhable outcrop exists on the terminal moraine hself. Wardle (1978) was the first to discover, by quarrying operations uncovered, wood embedded in fine sih beneath 1,5 m of till. These outwash deposits were found on the northwestern side of a bedrock outcrop lying 1,6 km inside the Waiho Loop moraine, called Canavan Knob. The author got a single age of 11.450 ± 200 ^'^ C yr BP and interpreted the age to predate the age of the glacial advance. Wardle concluded that the silt had been deposited when the advancing glacier first impounded an ice-marginal pond and suggested that the Franz Josef Glacier had advanced the remainmg 1.6 km beyond Canavan Knob to build the Waiho Loop moraine around 11.000 ^'^ C years ago, precluding the North-Atlantic Younger Dryas event. In contrast to this Burrows & Gellatly (1982) suggested that the glacier could have been retreating from the Waiho Loop. This implies that the moraine could be even older than the dated wood.

Mercer (1988) dated an 80 mm thick log of wood embedded near the base of 2.5 m o f bouldery till on gramtic bedrock in the same quarry on Canavans Knob. Mercer showed a clear difference in ages depending on the laboratory pre-treatment of the samples. The samples pre-treated to boiling i n distilled water have a mean age o f 11.600 ^'^ C yr BP whereas the samples pre-treated with hot alkali and hot acid ^hot dilute HCl and NaOH), the alpha-cellulose fraction, showed a mean age of 12.440 C yr BP. He concluded that an unequivocal age for the Waiho Loop couldn't yet be determined, but that h was clear the advance didn't occm- during the North-Atiantic Younger Dryas event.

Denton & Hendy (1994) obtained 36 radiocarbon dates, ofthe holoceUulose fraction, on 25 individual wood samples from the wood bearing diamicton from Canavans Knob, with an error weighted mean age of 11.150 ± 14 ^'*C yr BP. A correction of 100 yr for the wood transport time is taken into account and thus they place the advance o f the Franz Josef glacier at 11.050 ± 14 ^'^C yr BP, synchronous with the North Atiantic YD event.

In this study a radiocarbon age ofthe holoceUulose fraction of 11.440 ± 40 ^'*C yr BP was achieved while two alpha-cellulose fractions came through as 11.640 ± 45 BP and 11.650 ± 45 BP. The holoceUulose date is still i n the upper limhs of the Denton & Hendy (1994) age but the alpha-cellulose dates are significantiy older. An OSL age o f 14.79 ± 1.53 cal. ka (1 sigma) ofthe same sfrata as these radiocarbon dates implies a significant older advance ofthe glacier. A l l this bearing in mind that the sediments at Canavans Knob were deposited before the deposition of the Waiho Loop terminal moraine. As Burrows & Gellatly (1982) suggested the deposhs at Canavans Knob could have been deposhed after the forming of the Waiho Loop, with a refreating glacier, which would shift the age of the Waiho Loop even further back in time. From the OSL date alone h could be concluded that the Waiho Loop terminal moraine was formed during the Antarctic Cold Reversal (ACR) or North Atlantic Bölhng-AUerod interstadial (GI-1). In this scenario the radiocarbon dates could have been contaminated with younger humic acids, due to the highly precipitous conditions of the West coast, resuhing in a too young radiocarbon age.

The other scenario could be that the OSL age is overestimated due to incomplete bleaching of the quartz grains. The radiocarbon ages in this study would then place the Waiho Loop at the beginning of the North Atiantic Y D event. Though these

(25)

Hendy (1994) dates. So the first scenario, implying the Waiho Loop terminal moraine being formed during the ACR, is most likely. Though an unequivocal age for the Waiho Loop can't yet be determined.

The Birch Hill moraines are generally thought to be a possible correlative of the Waiho Loop, because their position is similar, allowing the differences in the size o f the glaciers (Burrows & Gellatly, 1982). Until now the only age estimation for these moraines are based on morphological evidence that mainly includes comparison with moraines formed during the Last Glacial Maximimi (LGM) throughout different valleys in the South Island. According to Porter (1975) the Birch Hill moraines are thought to be older than 5590 yr BP. Also the Birch Hill moraines must be younger than the LGM based on the location upstream of the big LGM moraines. Burrows et al. (1976) places the Birch Hill advance close to the Pleistocene-Holocene boimdary at 10.000 yr BP. This is based on radiocarbon dates of buried soils in nearby valleys. In this study two luminescence ages have been obtained of the Birch Hill moraines. The samples are taken from laminated sands in between glacial till deposhs clearly indicating a direct relationship with the glacial advance. The first age obtained is an IRSL age of 62.51 ± 8.51 ka (1 sigma). Because of the position of the Birch Hill moraines compared to the LGM moraines this age must be highly overestimated. This is most likely due to incomplete bleaching of the feldspar grains. The second age obtained is from preliminary data of the OSL signal of quartz. With a mask size of 1 mm an age of 16.86 ± 2.49 ka (1 sigma) was obtained, whereas with a mask size of 3 mm a more accurate age of 15.41 ± 2.49 ka (1 sigma) is obtained. So h looks like the quartz grains have been bleached more effectively than the feldspars. According to Wallinga et al. (2001) the quartz OSL signal is likely to be zeroed (bleached) more effectively than feldspars and is therefore the preferred mineral when dating fluvial (alluvial) deposits.

So far it can already be concluded that the Birch Hill moraines clearly predate the North Atlantic Y D event. The Birch Hill advance occurred close to the onset of the Antarctic Cold Reversal (ACR) or North Atlantic BöUing-Allerod interstadial (GI-1). It can thus be concluded that the Birch Hill moraines are no indication of an Interhemispheric synchroneity of the last deglaeiation.

Now we can turn to the key question of this study: Whether the deglaeiation of the

LGM happened synchronous or asynchronous on both hemispheres! In order to

answer this question we have to look at the three classic sites and compai-e them with the North Atlantic period of deglaeiation.

Although no OSL date has yet been obtained for the Cropp River site, the radiocarbon age of 10120 ± 40 ^'^C yr BP is consistent with the radiocarbon age of 10250 ± 150

C yr BP as foimd by Basher & McSaveney (1989). This suggests a glacial advance

synchronous with the North Atlantic Y D system. In comparison with this the Franz Josef glacier, forming the Waiho Loop terminal moraine, could have been advancing at the same time according to the radiocarbon dates achieved by Denton & Hendy (1994). On the other hand the OSL date of 14.79 ± 1.53 cal. ka suggests a significantly older advance of the Franz Josef glacier, putting the advance at the time of the ACR. So an unequivocal widespread advance of glaciers on the South Island can't still be determined.

Even when the Waiho Loop and Cropp River moraines would be placed at an age synchronous with the North Atlantic Y D event this still wouldn't imply evidence for

(26)

glaciers are associated with periods of enhanced westerly flow (Hessel, 1983; Fitzharris et al., 1992), causing high precipitation rates. So the advancing glaciers could have been a result of increased precipitation instead of decreased temperatures. This is supported by various pollen sequences around the South Island (McGlone, 1995; Vandergoes & Fhzsimons, 2003; Turney et al., 2003; McGlone et a l , 2004). On the other hand glaciers on the relative dry eastern side of the Southern Alps would experience less high precipitation rates induced by the westerly flow. So glacial advances on this side of the mountain range would be more an indication of cooling than of higher precipitation rates. The Birch Hill moraines are situated on the eastem side o f t h e Southern Alps. A n OSL date of 15.41 ± 2.49 cal. ka places this glacial advance at the time of the ACR, which is a period of cooling on the Southem Hemisphere.

So the Birch Hill moraine supports the bipolar seesaw mechanism (Broecker, 1998) which drives warm periods on the northem hemisphere too coincide with cooling periods in the southem hemisphere and vice versa. It can thus be concluded that the deglaeiation of the L G M happened asynchronous on both hemispheres.

(27)

Appendix A:

Fine grain sample preparation

The fine grain sample preparation was carried out following Frechen et al. (1996). I n the preparation the 4-11 )j,m grain size is isolated. In order to achieve this the sample is first treated with hydrochloric acid (10%) and hydrogen peroxide (50%) as any other sample. Then the sample is wet sieved to separate the < 63 |im Iraction. After that the < 11 ^m grain size fi-action is separated by settling in distilled water under the gravitational field using Stokes's law. The settling time t is calculated from the formula of Stokes using:

where rjo is the viscosity coefficient of distilled water, h is the height ofthe water i n the beaker, p and po are the density of the sediment and the water respectively, g is the acceleration by gravity and d is the diameter ofthe grain.

The next step is to remove the clay content (< 4 ^m) ofthe sample. This is done by centrifiigation. The time of centriftigation is calculated using the following formula:

t = — —

7t\p-p,).dLu' 1.62 4 0 (2)

where U is the revolution per minute of the centrifuge, R is the distance between rotation axis and bottom of the tube and VQ is the distance between the rotation axis and the surface of the water level in the tube.

< 11 \xm. separation: a beaker with a content of 600 ml and a relative large surface area was used with h = 0.06 m, g = 9.81 m s"^, d = 11 |am, p - 2650 kg m"^ and po = 1000 kg m ' ^ The settling times are dependent on the viscosity ofthe water, which i n turn is dependent on the temperature of the water. In table 1 are the calculated settling times given in relation to the different temperatures ofthe water (Eq. 1).

Temp, r C ) Temp. (" F ) llo 10-^ (kg m-' Time

16 60.8 1.109 10ml2s 17 62.6 1.081 9m56s 18 64.4 1.053 9m41s 19 66.2 1.027 9m26s 20 68 1.002 9ml3s 21 69.8 0.9779 8m59s 22 71.6 0.9548 8m46s 23 73.4 0.9325 8m34s 24 75.2 0.9111 8m22s 25 77 0.8904 8ml Is

(28)

With a water temperature of 21 ° C, a settling time of 8 min 59 s is needed to optimize the grain size separation. After the settling time the < 11 [im fraction is tipped into a separate beaker leaving ~2 cm of water. This is done to avoid coarser material to be stirred up from the bottom. This process is repeated about five times.

< 4 nm separation: the < 11 \xm fraction is poured into cenfrifugation tubes with h = 0.1 m with this time using d = 4 |am. The settling time is calculated using Eq. (2) with R = 0.137 m, ro = 0.037 m and U = 800 rpm (depending on type of centrifuge). A settling time of ~2 minutes was used.

The 4-11 |am fraction is enriched at the bottom of the tube and the water with the clay content is poured away. The tube is refilled up to the used water height, stirred and centrifiiged. This is repeated until the water in the tube is clear.

Fine grain disc deposition

The polymineral fme grains are deposited on alvmiinium discs on two different ways. The first method is through settling in suspension. With this method a acetone suspension of the fme grains (~400mg/200ml) is poured in 40 small glass tubes and allowed to evaporate in a dry oven at 40 ° C. This results in a ~10 mg monolayer of grains on each disc.

The second method is usefiil to allow a smaller mask size and thus reduce the amount of grains deposited on each disc. A suspension of distilled water with sample is prepared in a desired proportion depending on the number of grains wanted on each disc. The number of grains on a disc N is calculated with the following formula assuming the grains are idealized spheres:

W

N = ^ ^ (3)

-•TT-r -p

where W is the total weight of the grains on a disc, r is the mean radius of a single grain and p is the density of the sample. For the r a mean diameter of 7,5 ]xm is used which resuhs in a radius of 3,75 |tm. The total weight of the grains on a disc is achieved with the following formula:

W

W - V ^ , . r - f ^ (4)

waler

where Vpjpet is the volume (ml) of the water droplet i n a pipet, V^^ater is the volume

(ml) of distilled water in the beaker and Wsample is the amount of sample (mg). By

changing the amount of water and sample in the suspension, and the volume of the pipet, the total weight of the grains on a disc (Eq. 4) and thus the number of grains on a disc (Eq. 3) can be calculated. The volume of the pipet can control the mask size of the disc. A pipet with a volume of 5 \x\ results in mask sizes of approximately 2 mm.

(29)

Appendix B:

Anomalous fading data for BIR-R

Disc irrad. time (s) Pause (s) tl t2 t* tVtc log(t*/tc) |i se i/ic

1 1550 0 160 1710 935 1 0 3.82 0.218 1.00 1550 0 160 1710 935 1 0 3.85 0,245 1.01 1548 60 220 1768 994 1.06 0.03 3.83 0.286 1,00 1548 60 220 1768 994 1.06 0.03 3.69 0,211 0,97 1548 600 760 2308 1534 1.64 0.22 3.47 0.197 0.91 1548 600 760 2308 1534 1.64 0.22 3.48 0.201 0.91 1550 610860 611020 612570 611795 654.33 2.82 3.07 0.186 0,80 1550 2699820 2699980 2701530 2700755 2888.51 3.46 2.82 0.171 0,74

Irrad. time (s) Pause (s) t1 t2 t* t*/tc log(t*/tc) |l se l/ic Disc 1550 0 160 1710 935 1 0 3.94 0.222 1.00 3 1550 0 160 1710 935 1 0 3.96 0.239 1,01 1548 60 220 1768 994 1.06 0.03 3.86 0.220 0,98 1548 60 220 1768 994 1.06 0.03 3.75 0.210 0,95 1548 600 760 2308 1534 1.64 0.22 3.58 0.206 0,91 1548 600 760 2308 1534 1.64 0.22 3.56 0.200 0,90 1550 609660 609820 611370 610595 653.04 2.81 3.19 0.186 0,81 1550 2698620 2698780 2700330 2699555 2887.22 3.46 2.99 0.173 0,76

Disc Irrad. time (s) Pause (s) tl t2 t* t*/tc iog(t*/tc) |l se i/lc

5 1550 0 160 1710 935 1 0 3.81 0.207 1,00 1550 0 160 1710 935 1 0 3.78 0.213 0,99 1548 60 220 1768 994 1.06 0.03 3.61 0.189 0,95 1548 60 220 1768 994 1.06 0.03 3.56 0.200 0.94 1548 600 760 2308 1534 1.64 0.22 3.61 0.194 0,95 1548 600 760 2308 1534 1.64 0.22 3.57 0.202 0.94 1550 608460 608620 610170 609395 651.76 2.81 3.17 0.180 0,83 1550 2697420 2697580 2699130 2698355 2885.94 3.46 3.28 0.189 0.86

Disc Irrad. time (s) Pause (s) t1 t2 t* t*/tc log(t*/tc) |l se I/Ic

7 1550 0 160 1710 935 1 0 3.70 0.216 1,00 1550 0 160 1710 935 1 0 3.76 0.210 1.02 1548 60 220 1768 994 1.06 0.03 3.71 0.217 1,00 1548 60 220 1768 994 1.06 0.03 3.66 0.202 0,99 1548 600 760 2308 1534 1.64 0,22 3.57 0.201 0,97 1548 600 760 2308 1534 1.64 0.22 3.50 0.204 0,95 1550 607260 607420 608970 608195 650.48 2.81 3.17 0.188 0,86 1550 2696160 2696320 2697870 2697095 2884.59 3.46 3.24 0.187 0,88

Disc Irrad. time (s) Pause (s) t1 t2 t* t*/tc log(t*/tc) |l se I/Ic

9 1550 0 160 1710 935 1 0 3.70 0.216 1,00 1550 0 160 1710 935 1 0 3.81 0.206 1,03 1548 60 220 1768 994 1.06 0.03 3.69 0,220 1,00 1548 60 220 1768 994 1.06 0.03 3.69 0,198 1,00 1548 600 760 2308 1534 1.64 0.22 3.60 0,191 0,97 1548 600 760 2308 1534 1.64 0.22 3.59 0,201 0,97 1550 606060 606220 607770 606995 649.19 2.81 3.12 0,173 0,84 1550 2694960 2695120 2696670 2695895 2883.31 3.46 3.01 0,170 0,81

Disc irrad. time (s) Pause (s) t1 t2 t* t*/tc log(t*/tc) |i se l/ic

11 1550 0 160 1710 935 1 0 3.91 0.223 1.00

1550 0 160 1710 935 1 0 3.92 0.221 1,00

1548 60 220 1768 994 1.06 0.03 3.76 0.210 0,96

1548 60 220 1768 994 1.06 0.03 3.81 0.210 0,97

(30)

I R S L intensity plots: 1.30 -1-10 -too f 0.90 Orse-^ 0 . 7 0 - 0 . 4 0.6 Disci - 0 . 0 6 5 7 X + 0.9727 R2 = 0.8862 1.6 log ( t * / t c ) 2.6 1.30 1.20 kifr k e e ^ OiSfr 0.80 0.70 MO" - 0 . 4 0.6 Discs y = - 0 . 0 3 6 3 X + 0.9624 R2 = 0.7961 1.6 log ( t * / t c ) 2 . 6 3.6 1.30 ^ T 2 0 -1.10 0 . 9 0 0 . 8 0

0-70-•

D i s c s •• - 0 . 0 5 8 7 X + 0.9645 R2 = 0.8674 D i s c ? - 0 . 4 0 . 6 1.6 2.6 3 . 6 log ( t * / t c ) 1.30 1.20 1.10 1 0 0 I O r g e - lerse0 . 7 lerse0 -IOT BO-y = -0.0391x +0.9903 R2 = 0.858 - 0 . 4 0 . 6 1.6 2.6 log ( f / t c ) 3 . 6 1.30-- 1 ; 2 0 ^ ^ -Mo| 0:90¬ 0.80 '\ J 0 . 7 0 -- 0 . 4 D i s c s y = - 0 . 0 5 4 7 X + 0.9994 R2 = 0.964 0 . 6 1.6 2 . 6 log ( t * / t c ) 3.6 Disc 11 1r30 • 1.20 -4r10-0 . 9 -4r10-0 0 . 8 0 0 r 7 0 -- 0 . 4 y = - 0 . 0 4 9 6 X + 0.971 R2 = 0.8581 1.6 log ( t * / t c ) 2 . 6 3 . 6

(31)

References

Alley RB. 2000. The Younger Dryas cold interval as viewed from central Greenland.

Quaternary Science Reviews 19: 213-226.

Aitken MJ. 1985. Thermoluminescence Dating. Academic Press, London.

Aitken MJ. 1998. An Introduction to Optical Dating. Oxford University Press, Oxford. Atkinson TC, Briffa KR, Coope GR. 1987. Seasonal temperatures in Britain during the

past 22.000 years reconstructed using beetle remains. Nature 352: 587-592. Auclair M , Lamothe, M , Huot S. 2003. Measurement of anomalous fading for feldspar

IRSL using SAR. Radiation Measurements 38: 487-492.

Basher LR, McSaveney MJ. 1989. An early Aranuian glacial advance at Cropp River, central Westland, New Zealand. Journal of the Royal Society New Zealand 19: 263-268.

Blunier T, Brook EJ. 2001. Timing of Millennial-Scale Climate Change in Antarctica and Greenland During the Last Glacial Period. Science 291: 109-112.

Björck S, Walker MJS, Cwynar LC, Johnsen S, Knudsen K, Lowe JJ, Wohlfahrt B, INTIMATE members. 1998. An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: A proposal by the INTIMATE Group. Journal of Quaternary Science 13: 283-292.

Broecker WS. 1998. Paleocean circulation during the last deglaeiation: A bipolar seesaw?

Paleoceanographic Currents 13: 119-121.

Broecker WS. 2003. Does the Trigger for Abrupt Climate Change Reside in the Ocean or in the Atmosphere? Science 300: 1519-1522.

Burrows CJ, Gellatly AF. 1982. Holocene glacier activity in New Zealand. Striae 18: 41¬ 47.

Burrows CJ, Chinn T, Kelly M . 1976. Glacial activity in New Zealand near the Pleistocene-Holocene boundary in the light of new radiocarbon dates. Boreas 5: 57-60.

Denton GH, Hendy CH. 1994. Younger Dryas Age Advance of Franz Josef Glacier in the Southern Alps of New Zealand. Science 264: 1434-1437.

Fitzharris BB, Hay JE, Jones PD. 1992. Behaviour of New Zealand glaciers and atmospheric circulation changes over the past 130 years. The Holocene 2: 97-106. Frechen M , Schwehzer U, Zander A. 1996. Improvements in sample preparation for the

fme grain technique. Ancient TL 14: 15-17.

Galbraith RF, Roberts RG, Laslett GM, Yoshida H, OUey JM. 1999. Optical dating of single and multiple grains of quartz from Jinmium rock sheher, northern Australia: Part 1, experimental design and statistical models. Archaeometry 41: 339-364.

Hessel JWD. 1983. Climatic effects on the recession of the Franz Josef Glacier. New

Zealand Journal of Science 26: 315-320.

Hughen KA, Overpeck JT, Lehman SJ, Kashgarian M , Southon J, PetersonLC, Alley R, Sieman D M . 1998. Deglacial changes in ocean circulation from an extended radiocarbon calibration. Nature 391: 65-68.

Huntley DJ, Lamothe M . 2001. Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating. Canadian Journal of Earth

Optical Stimulated Luminescence Dating of Three Classic Sites on the South Island of New Zealand