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Browsing by Author "Rother, H"

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The chronology of the last deglaciation from two New Zealand valleys and some climatic implications
(18th INQUA Congress, 2011-07-21) Shulmeister, J; Fink, D; Rother, H; Thackray, GD
We present Be-10 and Al-26 chronologies from the paleo-Rakaia glacier and the Clearwater lobe of the Rangitata glacier focussing on the transition from the last glaciation maximum (LGM) to the Holocene. From the Rakaia we demonstrate that the local glacial maximum preceded the global LGM by several thousand years at c. 25 ka. Over the succeeding 12,000 years the glacier retreated only about 10 km and although undated, geomorphic evidence suggests a continued steady retreat after this time. The Clearwater lobe of the Rangitata glacier provides the most detailed LGIT record from any New Zealand glacier because it the valley was protected from significant meltwater flow during the deglaciation. Between 16.4 ka and 13.7 ka the Clearwater ice lobe retreated only 12 km producing 23 closely spaced recessional ice positions. The geomorphology and chronology are categorical in demonstrating that no significant re-advance can have occurred during this period. The inboard termination of the record occurs where the Clearwater valley drops into the main Rangitata Valley and should not be interpreted as the start of the more significant retreat. We highlight that uncertainties in isotope production rates and other elements of cosmogenic age determination (e.g. geomagnetic corrections) means that while we have millenial scale precision on ages during the LGIT, the accuracy of the ages is not as high. Nevertheless, our data clearly demonstrate that the evacuation of ice from these east coast valleys in New Zealand was remarkably slow with glaciers extending to ~60% of their LGM extents at 14 kyr (or younger). There is no evidence for either an early LGIT ice collapse or rapid retreat and consequently no late LGIT major readvance. We contrast our findings with the interpretations of chronologies coming from the Mackenzie Basin and we conclude that the records are compatible, with the chronological differences created by the morphometry of the respective ice catchments.Copyright (c) 2011 INQUA 18
Cosmogenic 10Be and 26Al exposure ages of moraines in the Rakaia Valley, New Zealand and the nature of the last termination in New Zealand glacial systems
(Elsevier, 2010-09-01) Shulmeister, J; Fink, D; Hyatt, OM; Thackray, GD; Rother, H
New Zealand glaciers reached their last glacial maximum position at or before ~ 25 ka, and, as early as 23 ka, commenced a slow and continual retreat. New cosmogenic exposure ages and field mapping from the Rakaia Valley in the South Island suggest that extensive ice survived well into the latter half of the Last Glacial–Interglacial Transition (18–11 ka), with the post-15 ka period inferred to have near Holocene climate conditions based on ecological proxy data. By as late as ~ 15.5 ka, glacier termini had retreated as little as 5–10 km from glacial maximum positions. Numerous minor ice still-stand positions and oscillations are recognized, but the record specifically excludes evidence for either a major climatic amelioration at ~ 15–16 ka or a significant glacial re-advance during the Antarctic Cold Reversal (ACR) or the Younger Dryas (YD). We conclude that the currently widespread interpretation of an episodic New Zealand glacial record since the LGM is an artifact of valley-dependent retreat processes. Pro-glacial lake formation and local site conditions combined to give an apparent, but misleading, picture of glacial retreat punctuated by major, climatically driven, re-advances. © 2010, Elsevier Ltd.
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.
The early rise and late demise of New Zealand’s last glacial maximum
(Proceedings of the National Academy of Sciences of the United States of America, 2014-06-13) Rother, H; Fink, D; Shulmeister, J; Mifsud, C; Evans, M; Pugh, J
Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30–20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28–16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26–19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19–16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28–20 ka, and gradual deglaciation until at least 15 ka. © 2014, National Academy of Sciences of the United States of America.
Extent, timing and paleoclimatic significance of glaciation in the High Atlas, Morocco
(18th INQUA Congress, 2011-07-21) Hughes, PD; Fenton, C; Fink, D; Schnabel, C; Rother, H
Glacial geomorphological mapping, 10Be terrestrial cosmogenic isotope analyses and palaeoglacier-climate modelling in the highest peaks of the Atlas Mountains, Morocco (31.1°N, 7.9°W), provides new and novel data toward understanding the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple Pleistocene glaciations. The largest ice field and valley glaciers formed in the Toubkal massif. Here, the oldest moraines have yielded 10Be ages scattered in the range 74-31 ka. A later phase of glaciation is dated to c. 24 ka. Moraines belonging to a third phase of glaciation has yielded a series of very close exposure ages (within error) at around 12 ka, and falling within the Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The low altitude of the glaciations in all three glacial episodes indicate that climate was not only significantly cooler than today, but also very much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages. The findings are highly significant for understanding atmospheric circulation during pluvial phases recorded in the Sahara, such as during the African Humid Period at the Pleistocene/Holocene transition (15 to 6 ka). Glacier advance in the High Atlas during this interval provides insight into the seasonal distribution of precipitation and provides valuable insight into the respective roles of moisture supply from the North Atlantic depressions and the West African Monsoon. This in turn then has important bearing on the strengths of meridional vs. zonal circulation at mid-latitudes during pluvial phases. Copyright (c) 2011 INQUA 18
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.
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.
Re-evaluating the deglacial sequence in New Zealand – part 2 - sudden ice collapse or gradual retreat?
(GNS Science, 2009-05-15) Shulmeister, J; Fink, D; Hyatt, OM; Thackray, GD; Rother, H
New data on moraine formation and glacial valley chronology challenges the existing understanding of the nature of deglaciation in New Zealand. When the glaciers retreat from glacial maximum limits they drop behind their fan heads and this creates accommodation space. This almost invariably leads to the formation of a pro-glacial lake system during retreat. Where the glacier trough is well developed deep lakes are formed. This results in an apparent collapse of the ice margin as floating ice leaves no terminal moraines. In contrast, if an over-deepened trough is not present, the glacier retreats in a stepwise fashion up valley with many terminal positions created (though not always preserved). At Rakaia Valley ice retreated less than 10 km in 10,000 years from its glacial maximum position. In dated east coast systems, the subsequent timing of ‘ice collapse’ differs from valley to valley. The chronology of deglaciation in New Zealand indicates that apparent ice collapse occurred at different times in different valleys during the deglaciation but this is largely an artifact of the timing of proglacial lake formation. Instead of ice collapse during the early part of the deglaciation followed by a significant very late glacial (ACR/YD) re-advance, we propose that extended ice remained in valleys with high elevation catchments until after ~15 ka. There is no major ice collapse prior to this time. Subsequently a minor ice re-advance occurred in these systems, which might relate in timing to either the ACR or YD. It may alternatively reflect a change from a calving terminus into a proglacial lake back to an outwash fan head system. In either case this event is of minor significance.
Stratigraphy, timing and climatic implications of glaciolacustrine deposits in the middle Rakaia Valley, South Island, New Zealand.
(Elsevier, 2010-08) Shulmeister, J; Thackray, GD; Rieser, U; Hyatt, OM; Rother, H; Smart, CC; Evans, DJA
Stratigraphic interpretations and infrared stimulated luminescence (IRSL) ages document the glacial history of the Middle Rakaia Gorge section of the Rakaia Valley, Canterbury, New Zealand, during the last two glacial cycles. Sheets of glaciolacustrine sediments several tens of metres in thickness can be traced at least 10 km upstream of the Rakaia Gorge. The stratigraphic package is capped by outwash gravels associated with the last glacial maximum (LGM) advances. The dominant inferred sedimentary environments in the sequence are 1) pro-glacial and paraglacial lake beds, 2) sub-aqueous ice-contact fans, 3) sub-aqueous mass flow deposits 4) supraglacial dump material and 5) outwash gravels. Syndepositional deformation, associated with glacitectonic deformation, is common. The stratigraphy records glacier margin oscillations, including six significant advances. These occurred in early MIS 6, mid-MIS 6, MIS 5b (c100–90 ka), MIS 5a/4 (c 80 ka), mid-MIS 3 (c 48 ka), and late MIS 3 (c 40ka). All the post-MIS 6 advances can be corroborated from other sites in New Zealand and the timings appear to coincide with both Southern Hemisphere insolation minima and maxima, suggesting variable combinations of climatic forcing in New Zealand glaciation. © 2010, Elsevier Ltd.
Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance
(Elsevier, 2015-11-01) Rother, H; Shulmeister, J; Fink, D; Alexander, D; Bell, D
During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages. © 2015, Elsevier B.V.
Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia
(Elsevier, 2014-09) Rother, H; Lehmkuhl, F; Fink, D; Nottebaum, V
This study presents results from geomorphological mapping and cosmogenic radionuclide dating (10Be) of moraine sequences at Otgon Tenger (3905 m), the highest peak in the Khangai Mountains (central Mongolia). Our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during Marine Oxygen Isotope Stage (MIS) 3. Large ice advances also occurred during MIS-2 (at ~ 23 and 17–16 ka), but these advances did not exceed the limits reached during MIS-3. The results indicate that climatic conditions during MIS-3, characterized by a cool-wet climate with a greater-than-today input from winter precipitation, generated the most favorable setting for glaciation in the study region. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2, and again during the last glacial–interglacial transition when precipitation levels increased. Viewed in context of other Pleistocene glacial records from High Asia, the pattern of glaciation in central Mongolia shares some features with records from southern Central Asia and NE-Tibet (i.e. ice maxima during interstadial wet phases), while other features of the Mongolian record (i.e. major ice expansion during the MIS-2 insolation minimum) are more in tune with glacier responses known from Siberia and western Central Asia. © 2014, University of Washington.

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