Browsing by Author "Schulmeister, J"

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    A cosmogenic glacial chronology of Lake Judd, southwest Tasmania and latitudinal shifts in the Roaring Forties
    (International Union for Quaternary Research (INQUA), 2019-07-27) Fink, D; Wilcken, KM; Simon, KJ; Schulmeister, J; Thackray, GD
    Limited attention has been paid to the glacial history of Tasmania (40-44 S). At the northern limits of today’s Westerly storm track (the Roaring Forties), it experiences precipitation changes due to shifts in the Southern Annular Mode and ITCZ. Cosmogenic dating in southwest Tasmania (Kiernan 2010) highlights the marginal nature of its glaciation where small precipitation or temperature changes cause large changes in mass balance. This makes southwestern Tasmania an excellent location to study Westerly flow through the Last Glacial Cycle. The prevailing idea is that during glacial times, Westerlies expand northward to lower Southern Ocean latitudes, delivering increased rainfall to Tasmania, whilst during interglacials, their migration polewards reduces precipitation. Somewhat counterintuitively, from a Tasmanian perspective of increased Westerly circulation and wind strength, maxima glaciation should coincide with peak global glacials. Although well preserved, extensive last glacial cycle moraine sequences are not common, a series of more than 20 terminal moraine ridges have been mapped over 3 km concentric with the southern margin of Lake Judd, in the SW wilderness corner of Tasmania. Morphologically, the Lake Judd sequence is believed to represent three phases; pre MIS-6, MIS 5-3 and MIS 2 (LGM), representing substantially different volumes of ice accumulation. Our first field campaign collected 16 dolerite samples (36Cl) from the three innermost concentric moraines adjacent to lake edge and 4 quartzite (10Be, 26Al) samples from the most distal moraines. Our aim is to test correlation of the long-term glacial history with records of westerly fluctuations from NZ speleothems (Whittaker et al., 2011) to determine whether the latitudinal variation in Westerly winds in the Australasian region are zonal during glacial times as they are demonstrated to be in interglacial intervals (Fletcher and Moreno, 2012). Preliminary exposure age calculations on the full set of 20 samples are in poor agreement with Kiernan’s age associations. The 10Be (and 26Al) ages on the distal moraine indicate a most probable MIS 4/5 affiliation (>50 ka), significantly younger than expected. In contrast, the 16 dolerite samples from the 3 innermost proximal moraines at lake edge gave a complex set of ages that ranged from MIS 3 to MIS 4 affiliation (45-25ka), somewhat older than predicted. To add further complexity, these 16 ages show no intra or inter moraine age trends with respect to their morphologic positions and ice flow direction. These results contrast with those from other Tasmanian glacial records and reveal the need for a concretive effort to apply cosmogenic exposure dating to the numerus glacial deposits already mapped throughout Tasmania.
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    Detailed surface exposure age chronology for last glacial sequences in the Rangitata and Waimakariri Valleys, South Island, New Zealand
    (GNS Science, 2009-05-15) Rother, H; Fink, D; Schulmeister, J; Evans, M
    The response of mid-latitude Southern Hemisphere glaciers to Quaternary climate forcing has become a prime research focus in the debate on the dynamics of global climate teleconnections. Of key importance in this research is the investigation of the timings of late Quaternary mountain glacier fluctuations in New Zealand relating both to last glacial ice maxima and ice decay signals. To address these questions we collected 62 rock samples from glacial moraine sequences in two major valley systems of the central Southern Alps for surface exposure dating (SED). Here we present geomagnetically corrected ages derived from cosmogenic 10Be isotope concentrations that provide absolute age control for glacial events in these valleys from 23.0 ka to 13.7 ka. Results show that recession from extended LGM positions commenced close to 22 ka followed by a slow ice retreat and ice margin stabilization at 19-18 ka. This sequence is similar to other New Zealand sites but commences several ka earlier than in the Northern Hemisphere. Our data also show that the largest of the LGM advances in the Waimakariri Valley extended much further than previously recognized and overran the so-called Avoca surface (previously OIS 8). Further slow ice retreat re-commenced at around 16.5 ka resulting in multiple closely spaced retreat positions over a ~10 km distance in both valleys that date to 14.5 - 16.0 ka (Blackwater III in Waimakariri; Spider Lake / Lake Emma in Rangitata). The youngest late glacial moraines date to 14.0 ka (Poulter, Waimakiriri) and 13.7 ka (Lake Clearwater, Rangitata). In summary our findings document that: (1) the period 23.0 – 13.7 ka is characterized by a slow and gradual ice retreat interrupted by stabilization phases but no major ice re-advances (2) very extensive valley glaciers of 30 – 50 km length survived in New Zealand until at least 14 ka (3) as a consequence of (2), either an accelerated retreat rate or a short-lived ice collapse would necessarily have occurred after 13.7 ka in order to restrict ice limits to upper valley positions prior to the onset of the Holocene.
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    Glacial chronologies across Southern Hemisphere latitudes during the past 30 ka and correlations to Antarctic ice cores
    (Australasian Quaternary Association, 2006-02-10) Fink, D; Williams, P; Augustinus, PC; Schulmeister, J
    On orbital time scales of glacial cycles (≈120 ka), Southern Hemisphere ice caps and alpine glacial systems appear to be in phase with major Northern Hemisphere ice sheet changes. However, recent advances in exposure dating of cirque and moraine sequences in Tasmania, New Zealand and Patagonia on sub-orbital timescales reveal a glacial variability that may respond to different forcing mechanisms.
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    The last deglaciation in New Zealand ; new 10Be production rates from Misery moraines, Arthur’s Pass, Southern Alps
    (International Union for Quaternary Research (INQUA), 2019-07-29) Fink, D; Rother, H; Woodward, C; Schulmeister, J; Wilcken, KM; Fujioka, T
    Recent debate on mid-latitude New Zealand glaciation has focused on reconstructing paleo-climate conditions leading into the (global) Last Glacial Maximum and subsequent deglaciation dynamics during the last termination. Paleo-environmental evidence coupled with reliable glacial chronologies confirms significant differences from that observed in northern hemisphere signatures of glacial change. The New Zealand glacial record does not show glacial readvance and strong cooling commensurate with Younger Dryas timing (~11.7-12.9 ka) and many lake pollen records suggest a minor cooling or hiatus in warming during the period from ~14.5 – 12.0 ka that is more commonly associated with the Antarctic Cold Reversal (ACR) (~14.7 - 13.0 ka). The Arthur’s Pass Moraine complex at 950 masl, deposited by an alpine glacier advancing out of the Otira Valley splaying east and westward over the divide of the Southern Alps in New Zealand, exhibits a full post-LGM glacial chronology. We have determined paired 10-Be and 26-Al exposure ages from 58 greywacke samples taken from all major moraines. Calculated exposure ages (using accepted local NZ production rates) show that the Arthur’s Pass moraine system spans a period of 19.5 ka to 12.0 ka with mean recessional moraine ages in chrono-stratigraphic sequence. The overall timing of deglaciation after peak LGM conditions is similar to the glacial systems we have dated in the Rakaia, Waimakariri and Rangitata Valleys. The Misery sequence shows ice retreat at the end of the ACR and no major advance during the YD period. Multiple cores from two intermorainal bog (Lances and Misery Tarns), separated by ~1 km and constrained by the terminal Dobson and Misery moraines, have been recovered for paleo-climate study. Basal glacial silts and organic matter have provided radiocarbon ages representing a minimum age for glacial retreat. Combined with the Misery moraine cosmogenic concentrations, new 10Be and 26Al production rate calibrations can be made for New Zealand to improve exposure age accuracy.
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    Late-glacial re-advance during the Last Glacial-Interglacial Transition; revisiting the Misery moraines in the Southern Alps of New Zealand
    (GNS Science, 2009-05-15) Fink, D; Rother, H; Schulmeister, J
    Locating evidence for or against a glacial readvance commensurate with Northern Hemisphere YD-time (~11-13 ka) in Southern Hemisphere glacial systems is a key aspect in addressing millennial-scale hemispheric climate linkages during the late Quaternary. Paleo-environmental evidence from New Zealand pollen records suggest a minor cooling or hiatus in warming during the period from ~14.5 – 12.0 ka that predates the onset but overlaps with the YD chron, and is more commonly associated with the Antarctic Cold Reversal (ACR). Evidence for a glacial re-advance during the YD chron has been proposed previously (Waiho Loop moraine, Denton and Hendy, 1994) and more recently based on a limited exposure age sample set (n=4, 11.7 ± 0.3 ka) from the Misery moraine sequence at Arthur’s Pass (~950 masl), Southern Alps, NZ (Ivy-Ochs et al 1999). The full group of moraines comprises a set of discontinuous latero-terminal moraines and elevated kame terraces (McGrath moraines) positioned on the eastern flanks of the Pass up to 3 kilometres down valley from the proximal Misery moraines within the Otira Gorge. However, a recalculation of the original data set (Ivy-Ochs et al 1999), based on revised 10-Be production rates, updated production rate scaling schemes and a remeasure of horizon site shielding, shifts the mean age from 11.7 ± 0.3 ka to 14.0-14.5 ka – a result more in line with other deglaciation ages (~14-16 ka) from proximal and cirque moraine sequences in NZ, Tasmania and southern South America. To further investigate this issue, we have determined paired 10-Be and 26-Al exposure ages from 38 greywacke samples taken from all major moraines throughout the Arthur’s Pass area and including repeat sampling from the Otira Gorge (Misery) moraine complex. The new exposure ages show that the Arthur’s Pass moraine system represents a glacial chronology for the last deglaciation spanning a period of 18.8 ka (at distal sites) to 10.4 ka (at proximal sites) (maximum to minimum sample age) with mean moraine ages following in chrono-stratigraphic sequence with ice flow direction. Although our new age for the proximal Misery moraine complex does not revise the conclusion reached by Ivy Ochs et al (1999) (though it does challenge the validity of the measurement) our more comprehensive sampling regime and extensive data set provides a different interpretation. The timing of deglaciation at Arthur’s Pass is similar to that observed at more distal down-valley terminal positions of the Rakaia and Rangitata Valleys and suggests that the scale of any late glacial readvance, as evidenced at the Misery moraine site, was insignificant in comparison to the magnitude of ice volume at the end of the LGM in New Zealand. Details regarding age interpretation, the importance of production-rate corrections necessary to provide a robust and reliable glacial chronology at the required sub-millennial resolution will be presented.
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    Southern Hemisphere millennial glaciations during the past 30 ka driven by Antarctic ice sheet variability
    (GNS Science, 2009-05-15) Fink, D; Williams, P; Augustinus, PC; Schulmeister, J
    Recent exposure dating of last-glacial cycle deposits in Tasmania, New Zealand and Patagonia reveal a temporal and spatial variability of glacial advances different to that apparent in the Northern Hemisphere. Interhemispheric correlation of millennial-scale glaciations is presently the centre of much debate (e.g., Younger Dryas (YD) versus Antarctic Cold Reversal (ACR) cooling, timing of ‘global’ Last Glacial Maximum (LGM), relative strength of MIS-2 to MIS-6 glaciations). However, the role of Antarctica in Southern Hemisphere glaciations during the late Pleistocene is difficult to assess. Exposure ages from six alpine valley systems in Tasmania and three in New Zealand reveal similar trends: (1) MIS-3 (~30-40 ka) advances are of limited extent in Tasmania and less extensive than New Zealand MIS-2 advances; (2) peak glacial cold conditions (‘LGM’) occur between ~24-29 ka; (3) amelioration of LGM conditions and glacial retreat commenced ~19-22 ka; (4) deglaciation inferred from recessional moraine sequences continued to 14-15 ka; (5) there is little evidence for a major late glacial readvance younger than 14-15 ka with lower valley regions devoid of ice. This moraine chronology suggests that following a ‘weak’ MIS 3 cool phase, the Southern Hemisphere, or ‘local’ LGM, peaked and was followed by warming a few thousand years prior to that apparent in the Northern Hemisphere. These moraine ages from New Zealand and Tasmania for the LGM–LGIT (ca 30 to 11 ka) show a remarkable similarity to the glacial chronology emerging from Lagos Buenos Aires in Patagonia. A near-complete record of glacial expansion phases over the last glacial cycle is preserved in the series of 10 glacial moraine benches (8 of which have been exposure dated) that flank the slopes of Mt Murchison above Lake Te Anau, Fiordland, New Zealand. The ages span from 15-80 ka with the highest bench dated to MIS 4 (ca 65- 75 ka) and suggests that MIS 4 may have generated by far the largest glacial expansion of the last glacial cycle. Five other glacial advance phases are recorded as distinct benches with ages decreasing with altitude from LGM peak (27.2 ka, 830masl), recessional phases (24.4, 19.9, 20.7 and 17.2 ka) with the youngest terrace just above the lake (15.8 ka, 220 masl). This deglaciation chronology correlates well with δ18O variability apparent in the ice core records from Byrd and Law Dome in Antarctica, each of which display most depleted δ18O values from 30 to 20 ka, followed by general warming to 10 ka. Over this period, Byrd displays δ18O inferred cooling at 29, 27 and 22 ka, with hiatuses in warming at 18.9, 17.8, 16.8 and 15.9 ka. The latter phases can be matched to the Te Anau exposure dated moraine benches with an ca 1-3 ka delay between the polar warming phases and response of the Fiordland glaciers. Hence, the general character of Antarctic climate variability as observed in δ18O trends from the ice cores appear to be reflected in the Southern Hemisphere mid-latitude terrestrial deglaciation chronologies determined by cosmogenic exposure dating.
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    Timing and causes of MIS 4 and MIS 3 glacial advances in South Island, New Zealand
    (International Union for Quaternary Research (INQUA), 2019-07-27) Schulmeister, J; Thackray, GD; Rittenour, TM; Fink, D; Patton, NR
    This poster summarises information on the timing and possible causes of glaciation in New Zealand prior to the LGM (26.5-19 ka). We recognise five regionally identifiable advances in MIS 4 and MIS 3 in South Island, NZ, including one which may mark the start of the LGM, but may also precede it. These advances, all secured by CRN and/or luminescence chronologies, occurred at 65 ± 3 ka, 47.5 ± 3 ka, 38.5 ± 2 ka, 31.5 ± 3 ka, and at 26.5 ± 2 ka. Not all advances have clear linkages to climate but some are coincident with periods of Southern Hemisphere insolation minima (65ka, and 31.5 ka advances), while another occurs during a notably cold phase (38.5 ka) and precipitation may play a role (65 ka and 26.5 ka advances). The timing of greatest glacial extent in the last glacial cycle is not simultaneous across New Zealand. The MIS 4 advance was the greatest in the southern South Island, while the MIS 3/2 advances (26.5-25 ka) were greatest in the central South Island. We attribute these spatio-temporal changes in the timing of maximum glaciation to precipitation changes related to a northward shift in the track of the southern-hemisphere westerlies.