Browsing by Author "Rittenour, TM"

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    Comment on Barrell et al. “Reconciling the onset of deglaciation in the Upper Rangitata valley, Southern Alps, New Zealand” (Quaternary Science Reviews 203 (2019), 141–150.)
    (Elsevier, 2019-09-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TM
    Recently, Barrell et al. (2019) published an article that responded to our article (Shulmeister et al., 2018a) on gradual evacuation of ice from the Upper Rangitata Valley, South Island, New Zealand, during the last glaciation. They base their contrasting interpretation of substantial and rapid ice-lowering of Rangitata glacier shortly after 18 ka on a revision of our 10Be cosmogenic radionuclide (CRN) chronology and by reference to published sources (e.g. Mabin, 1980, 1987). Their interpretation relies on glacial landform features extracted from a geomorphology map of the central Southern Alps by Barrell et al. (2011). Barrell et al. (2019) highlight that rapid ice recession of the Rangitata glacier is compatible to their results from Mackenzie Basin and Rakaia Valley (Putnam et al., 2013a, b). We highlight four points in response to Barrell et al. (2019). © 2019 Elsevier Ltd.
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    Corrigendum to “Evidence for slow late-glacial ice retreat in the upper Rangitata Valley, South Island, New Zealand” [Quat. Sci. Rev. 185 (2018) 102–112]
    (Elsevier, 2019-09-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TM
    It has been brought to our attention, following a recent publication by Barrell et al. (2019), that the elevations for 12 of 23 boulders reported in our publication, Shulmeister et al., v185, 102–112 (2018) are incorrect. For these 12 samples, the true elevations are higher and hence all exposure ages based on their respective 10Be concentration measurements require a downward correction of between 10 and 15%. This change in age does not alter our main conclusions but does have some implication for the initiation and pace of deglaciation. © 2019 Elsevier Ltd.
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    Evidence for slow late-glacial ice retreat in the upper Rangitata Valley, South Island, New Zealand
    (Elsevier, 2018-04-01) Shulmeister, J; Fink, D; Winkler, S; Thackray, GD; Borsellino, R; Hemmingsen, M; Rittenour, TM
    A suite of cosmogenic radionuclide ages taken from boulders on lateral and latero-terminal moraines in the Rangitata Valley, eastern South Island, New Zealand demonstrates that relatively thick ice occupied valley reaches inland of the Rangitata Gorge until c. 21 ka. Thereafter ice began to thin, and by c. 17 ka it had retreated 33 km up-valley of the Rangitata Gorge to the Butler-Brabazon Downs, a structurally created basin in the upper Rangitata Valley. Despite its magnitude, this retreat represents a minor ice volume reduction from 21 ka to 17 ka, and numerous lateral moraines preserved suggest a relatively gradual retreat over that 4 ka period. In contrast to records from adjacent valleys, there is no evidence for an ice-collapse at c. 18 ka. We argue that the Rangitata record constitutes a more direct record of glacial response to deglacial climate than other records where glacial dynamics were influenced by proglacial lake development, such as the Rakaia Valley to the North and the major valleys in the Mackenzie Basin to the south-west. Our data supports the concept of a gradual warming during the early deglaciation in the South Island New Zealand. © 2018 Elsevier Ltd.
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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.
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    The timing and nature of the last glacial cycle in New Zealand
    (Elsevier, 2019-02-15) Shulmeister, J; Thackray, GD; Rittenour, TM; Fink, D; Patton, NR
    This paper constitutes a review of the last (Otiran) glaciation in New Zealand, spanning marine isotope stages (MIS) 4-2. We highlight the nature of glaciation, which is characterised by exceptional sedimentation, relatively mild maritime climatic conditions and the widespread presence of water associated with proglacial settings. These conditions produce glacial systems characterised by extensive outwash fans and relatively small terminal moraines. Extensive recent geochronological work allows us to recognise at least eight glacial advances during the Otiran. These occurred at 65 ± 3.25ka, 47.5 ± 3 ka, 38.5 ± 2 ka, 31.5 ± 3 ka, 26.5 ± 2 ka, 20.5 ± 2 ka, 17 ± 2 ka and 13 ± 1 ka, which we term the Otira 1 to 8 advances, respectively. Though the analytical uncertainty ranges for some of these advances overlap, all are independently distinguished through moraine morphologic relationships and/or stratigraphic relationships in outcrop. Major advances appear to be associated with climate influences such as periods of Southern Hemisphere insolation minima (65ka, and 31.5 ka advances), the last glacial maximum cooling (LGM) (20.5 ka) and periods of Antarctic cooling (13ka). 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 ka) were greatest in the central South Island. In the northern South Island and the North Island, MIS 4, MIS 3/2, and the last glacial maximum appear to be equivalent in extent. We attribute these spatio-temporal variations in the timing of maximum glaciation to precipitation changes related to a northward shift in the track of the westerlies. © 2018 Elsevier Ltd.