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Aaron E. Putnam - One of the best experts on this subject based on the ideXlab platform.
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millennial scale pulsebeat of glaciation in the Southern Alps of new zealand
Quaternary Science Reviews, 2019Co-Authors: Peter D Strand, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Tobias N B Koffman, Roseanne SchwartzAbstract:Abstract We undertook geomorphological mapping in conjunction with 10Be surface-exposure dating in a previously unstudied sector of the left-lateral moraine sequence of the ice-age Pukaki glacier in the Southern Alps of New Zealand. The mapping and dating approach enabled the identification of six distinct moraine belts that were formed during maxima of glacier extent during the last glaciation. The chronology implies that ice recession occurred during Northern Hemisphere Heinrich stadials, while expansion occurred between Heinrich stadials. The ages of the moraine belts identified here are 44,000 ± 1000 yrs; 41,800 ± 1100 yrs; 36,450 ± 940 yrs 26,730 ± 740 yrs; 20,030 ± 460 yrs; and 18,000 ± 400 yrs. This moraine chronology is consistent with previous dating results from other sectors of the Pukaki moraine sequence, except that the c. 44,000 yr old moraine belt has not previously been detected elsewhere in the Pukaki moraines. Collectively with previously published 10Be chronologies from the Pukaki glacier, and the adjacent Ohau glacier valley, the results demonstrate that there were several millennial-scale episodes of ice advance to full-glacial extent, and subsequent ice recession, during Marine Isotope Stages 3 and 2. This millennial-scale pulsebeat of oscillations of the Pukaki and Ohau glaciers in sympathy with the North Atlantic Heinrich episodes is further emphasized by rapid ice recession in the Southern Alps early in the last glacial termination, coeval with the onset of Heinrich stadial 1 (HS 1) in the Northern Hemisphere. That this pattern is widespread in mid-latitudes of the Southern Hemisphere is highlighted by similar chronologies of glacier variation for Andean ice lobes in the Chilean Lake District of South America.
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reconciling the onset of deglaciation in the upper rangitata valley Southern Alps new zealand
Quaternary Science Reviews, 2019Co-Authors: David J. A. Barrell, Aaron E. Putnam, George H. DentonAbstract:Abstract Enquiry into the detailed timing of paleoclimate events depends on well-resolved and reliable chronologies. A recently published set of 10Be surface-exposure ages for moraine boulders in the upper Rangitata valley was interpreted to indicate a gradual reduction in glacier surface height between c. 21 and c. 17 ka, without rapid glacier recession beginning c. 18 ka as reported from other valleys. The dating results were suggested to be consistent with moraine geomorphology and an interpreted lack of post-glacial lake formation in the valley. In contrast, we argue that the geomorphology is consistent with sustained glacier recession and we highlight evidence for a post-glacial lake. Furthermore, the upper Rangitata moraine chronology was encumbered by inaccurate altitude values assigned to many of the sample sites. Recalculation of the 10Be ages using accurate elevations produces values that are as much as 3000 years younger than originally reported. The recalculated values indicate no significant age difference across the c. 300-m relative altitudinal spread of sample locations, with mean age of all samples c. 17.7 ± 0.3 ka. The previous inference of slow late-glacial ice retreat is not supported by the recalculated chronology. Rather, the revised glacial chronology implies that substantial ice-surface lowering of the Last Glacial Maximum Rangitata glacier was in progress shortly after c. 18 ka. The revised upper Rangitata chronology is compatible with dating from other eastern valleys of the Southern Alps, indicating moraine formation at c. 18 ka, followed by sustained glacier recession associated with regional climatic amelioration.
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a beryllium 10 chronology of late glacial moraines in the upper rakaia valley Southern Alps new zealand supports Southern hemisphere warming during the younger dryas
Quaternary Science Reviews, 2017Co-Authors: Tobias N B Koffman, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Ann V Rowan, Robert C FinkelAbstract:Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination.
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warming and glacier recession in the rakaia valley Southern Alps of new zealand during heinrich stadial 1
Earth and Planetary Science Letters, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Bjorn G Andersen, Tobias N B Koffman, Ann V Rowan, R C FinkelAbstract:Abstract The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and Southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in Southern middle latitudes.
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the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau Southern Alps of new zealand
Quaternary Science Reviews, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Michael R Kaplan, Bjorn G Andersen, S D Birkel, Robert C FinkelAbstract:Abstract Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ∼26,500–∼19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the ‘local LGM’ (LLGM). We used 10 Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10 Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr −1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ∼520 m and ∼3.6 °C, respectively, between ∼18,000 and ∼13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed Southern LLGM is that Southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.
Paul Augustinus - One of the best experts on this subject based on the ideXlab platform.
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glacial valley cross profile development the influence of in situ rock stress and rock mass strength with examples from the Southern Alps new zealand
Geomorphology, 1995Co-Authors: Paul AugustinusAbstract:Abstract The evolution of the glacial valley cross-profile form is commonly attributed primarily to the glaciological variables that control the erosion of the channel. However, studies in the New Zealand Southern Alps suggest that the rock mass strength (RMS) of the eroded rock mass is a major control on slope stability, and hence on the final form of the trough. RMS of the slope rock will alter with time and erosional excavation and oversteepening of the valley slopes. The in situ rock stress field induced by: (1) the extreme topography in the axial ranges of the New Zealand Southern Alps, and (2) tectonically by collision of the Australian and Pacific crustal plates, may play a role in valley slope development by controlling the location of rock failure and reducing RMS. This provides weakened rock that may provide sites for selective glacial erosion of the rock mass. Hence, valley form evolution models should also take into account the RMS and the in situ stress field acting in the eroded rock mass. This study has implications for the development and modification of alpine glacial troughs in similar tectonic settings elsewhere.
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the influence of rock mass strength on glacial valley cross profile morphometry a case study from the Southern Alps new zealand
Earth Surface Processes and Landforms, 1992Co-Authors: Paul AugustinusAbstract:The erosional morphology in the vicinity of the Main Divide of the Southern Alps, and Fiordland, New Zealand, appears to be a product of the interaction between Alpine Fault-induced tectonic processes, rock mass strength of the uplifted and eroded bedrock, and the processes acting to denude the developing mountain landscape. The magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers, whilst the form of the trough is a direct consequence of the rock mass strength (RMS) properties of the slope rock. Realistic models of development of the cross-profile shape of glacial valleys must take into consideration the RMS properties of the eroded substrate.
Joerg M Schaefer - One of the best experts on this subject based on the ideXlab platform.
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millennial scale pulsebeat of glaciation in the Southern Alps of new zealand
Quaternary Science Reviews, 2019Co-Authors: Peter D Strand, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Tobias N B Koffman, Roseanne SchwartzAbstract:Abstract We undertook geomorphological mapping in conjunction with 10Be surface-exposure dating in a previously unstudied sector of the left-lateral moraine sequence of the ice-age Pukaki glacier in the Southern Alps of New Zealand. The mapping and dating approach enabled the identification of six distinct moraine belts that were formed during maxima of glacier extent during the last glaciation. The chronology implies that ice recession occurred during Northern Hemisphere Heinrich stadials, while expansion occurred between Heinrich stadials. The ages of the moraine belts identified here are 44,000 ± 1000 yrs; 41,800 ± 1100 yrs; 36,450 ± 940 yrs 26,730 ± 740 yrs; 20,030 ± 460 yrs; and 18,000 ± 400 yrs. This moraine chronology is consistent with previous dating results from other sectors of the Pukaki moraine sequence, except that the c. 44,000 yr old moraine belt has not previously been detected elsewhere in the Pukaki moraines. Collectively with previously published 10Be chronologies from the Pukaki glacier, and the adjacent Ohau glacier valley, the results demonstrate that there were several millennial-scale episodes of ice advance to full-glacial extent, and subsequent ice recession, during Marine Isotope Stages 3 and 2. This millennial-scale pulsebeat of oscillations of the Pukaki and Ohau glaciers in sympathy with the North Atlantic Heinrich episodes is further emphasized by rapid ice recession in the Southern Alps early in the last glacial termination, coeval with the onset of Heinrich stadial 1 (HS 1) in the Northern Hemisphere. That this pattern is widespread in mid-latitudes of the Southern Hemisphere is highlighted by similar chronologies of glacier variation for Andean ice lobes in the Chilean Lake District of South America.
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a beryllium 10 chronology of late glacial moraines in the upper rakaia valley Southern Alps new zealand supports Southern hemisphere warming during the younger dryas
Quaternary Science Reviews, 2017Co-Authors: Tobias N B Koffman, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Ann V Rowan, Robert C FinkelAbstract:Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination.
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warming and glacier recession in the rakaia valley Southern Alps of new zealand during heinrich stadial 1
Earth and Planetary Science Letters, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Bjorn G Andersen, Tobias N B Koffman, Ann V Rowan, R C FinkelAbstract:Abstract The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and Southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in Southern middle latitudes.
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the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau Southern Alps of new zealand
Quaternary Science Reviews, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Michael R Kaplan, Bjorn G Andersen, S D Birkel, Robert C FinkelAbstract:Abstract Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ∼26,500–∼19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the ‘local LGM’ (LLGM). We used 10 Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10 Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr −1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ∼520 m and ∼3.6 °C, respectively, between ∼18,000 and ∼13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed Southern LLGM is that Southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.
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last glacial maximum climate in new zealand inferred from a modelled Southern Alps icefield
Quaternary Science Reviews, 2012Co-Authors: Nicholas R Golledge, George H. Denton, Brian Anderson, Andrew Mackintosh, David J. A. Barrell, Marcus J Vandergoes, Kevin M Buckley, Alice M Doughty, Bjorn G Andersen, Joerg M SchaeferAbstract:Abstract We present a simulation of the New Zealand Southern Alps icefield at the Last Glacial Maximum (LGM, c. 30,000–20,000 calendar years ago (ka)) in an attempt to constrain the climate of that period. We use a 500 m-resolution ice-sheet model parameterised using empirical glaciological, climatological and geological data specific to the model domain to simulate the entire Southern Alps icefield. We find that an LGM cooling of at least 6–6.5 °C is necessary to bring about valley glaciers that extend beyond the mountains. However, climate–topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain, and in order to remain within geologically reconstructed LGM limits we find that the LGM cooling was most likely associated with a precipitation regime up to 25% drier than today. Wetter-than-present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence. These results perhaps indicate that either the westerly air masses affecting New Zealand during the LGM were drier than today, or that they were weaker or zonally displaced with respect to present.
George H. Denton - One of the best experts on this subject based on the ideXlab platform.
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millennial scale pulsebeat of glaciation in the Southern Alps of new zealand
Quaternary Science Reviews, 2019Co-Authors: Peter D Strand, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Tobias N B Koffman, Roseanne SchwartzAbstract:Abstract We undertook geomorphological mapping in conjunction with 10Be surface-exposure dating in a previously unstudied sector of the left-lateral moraine sequence of the ice-age Pukaki glacier in the Southern Alps of New Zealand. The mapping and dating approach enabled the identification of six distinct moraine belts that were formed during maxima of glacier extent during the last glaciation. The chronology implies that ice recession occurred during Northern Hemisphere Heinrich stadials, while expansion occurred between Heinrich stadials. The ages of the moraine belts identified here are 44,000 ± 1000 yrs; 41,800 ± 1100 yrs; 36,450 ± 940 yrs 26,730 ± 740 yrs; 20,030 ± 460 yrs; and 18,000 ± 400 yrs. This moraine chronology is consistent with previous dating results from other sectors of the Pukaki moraine sequence, except that the c. 44,000 yr old moraine belt has not previously been detected elsewhere in the Pukaki moraines. Collectively with previously published 10Be chronologies from the Pukaki glacier, and the adjacent Ohau glacier valley, the results demonstrate that there were several millennial-scale episodes of ice advance to full-glacial extent, and subsequent ice recession, during Marine Isotope Stages 3 and 2. This millennial-scale pulsebeat of oscillations of the Pukaki and Ohau glaciers in sympathy with the North Atlantic Heinrich episodes is further emphasized by rapid ice recession in the Southern Alps early in the last glacial termination, coeval with the onset of Heinrich stadial 1 (HS 1) in the Northern Hemisphere. That this pattern is widespread in mid-latitudes of the Southern Hemisphere is highlighted by similar chronologies of glacier variation for Andean ice lobes in the Chilean Lake District of South America.
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reconciling the onset of deglaciation in the upper rangitata valley Southern Alps new zealand
Quaternary Science Reviews, 2019Co-Authors: David J. A. Barrell, Aaron E. Putnam, George H. DentonAbstract:Abstract Enquiry into the detailed timing of paleoclimate events depends on well-resolved and reliable chronologies. A recently published set of 10Be surface-exposure ages for moraine boulders in the upper Rangitata valley was interpreted to indicate a gradual reduction in glacier surface height between c. 21 and c. 17 ka, without rapid glacier recession beginning c. 18 ka as reported from other valleys. The dating results were suggested to be consistent with moraine geomorphology and an interpreted lack of post-glacial lake formation in the valley. In contrast, we argue that the geomorphology is consistent with sustained glacier recession and we highlight evidence for a post-glacial lake. Furthermore, the upper Rangitata moraine chronology was encumbered by inaccurate altitude values assigned to many of the sample sites. Recalculation of the 10Be ages using accurate elevations produces values that are as much as 3000 years younger than originally reported. The recalculated values indicate no significant age difference across the c. 300-m relative altitudinal spread of sample locations, with mean age of all samples c. 17.7 ± 0.3 ka. The previous inference of slow late-glacial ice retreat is not supported by the recalculated chronology. Rather, the revised glacial chronology implies that substantial ice-surface lowering of the Last Glacial Maximum Rangitata glacier was in progress shortly after c. 18 ka. The revised upper Rangitata chronology is compatible with dating from other eastern valleys of the Southern Alps, indicating moraine formation at c. 18 ka, followed by sustained glacier recession associated with regional climatic amelioration.
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a beryllium 10 chronology of late glacial moraines in the upper rakaia valley Southern Alps new zealand supports Southern hemisphere warming during the younger dryas
Quaternary Science Reviews, 2017Co-Authors: Tobias N B Koffman, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Ann V Rowan, Robert C FinkelAbstract:Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination.
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warming and glacier recession in the rakaia valley Southern Alps of new zealand during heinrich stadial 1
Earth and Planetary Science Letters, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Bjorn G Andersen, Tobias N B Koffman, Ann V Rowan, R C FinkelAbstract:Abstract The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and Southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in Southern middle latitudes.
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the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau Southern Alps of new zealand
Quaternary Science Reviews, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Michael R Kaplan, Bjorn G Andersen, S D Birkel, Robert C FinkelAbstract:Abstract Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ∼26,500–∼19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the ‘local LGM’ (LLGM). We used 10 Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10 Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr −1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ∼520 m and ∼3.6 °C, respectively, between ∼18,000 and ∼13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed Southern LLGM is that Southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.
David J. A. Barrell - One of the best experts on this subject based on the ideXlab platform.
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millennial scale pulsebeat of glaciation in the Southern Alps of new zealand
Quaternary Science Reviews, 2019Co-Authors: Peter D Strand, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Tobias N B Koffman, Roseanne SchwartzAbstract:Abstract We undertook geomorphological mapping in conjunction with 10Be surface-exposure dating in a previously unstudied sector of the left-lateral moraine sequence of the ice-age Pukaki glacier in the Southern Alps of New Zealand. The mapping and dating approach enabled the identification of six distinct moraine belts that were formed during maxima of glacier extent during the last glaciation. The chronology implies that ice recession occurred during Northern Hemisphere Heinrich stadials, while expansion occurred between Heinrich stadials. The ages of the moraine belts identified here are 44,000 ± 1000 yrs; 41,800 ± 1100 yrs; 36,450 ± 940 yrs 26,730 ± 740 yrs; 20,030 ± 460 yrs; and 18,000 ± 400 yrs. This moraine chronology is consistent with previous dating results from other sectors of the Pukaki moraine sequence, except that the c. 44,000 yr old moraine belt has not previously been detected elsewhere in the Pukaki moraines. Collectively with previously published 10Be chronologies from the Pukaki glacier, and the adjacent Ohau glacier valley, the results demonstrate that there were several millennial-scale episodes of ice advance to full-glacial extent, and subsequent ice recession, during Marine Isotope Stages 3 and 2. This millennial-scale pulsebeat of oscillations of the Pukaki and Ohau glaciers in sympathy with the North Atlantic Heinrich episodes is further emphasized by rapid ice recession in the Southern Alps early in the last glacial termination, coeval with the onset of Heinrich stadial 1 (HS 1) in the Northern Hemisphere. That this pattern is widespread in mid-latitudes of the Southern Hemisphere is highlighted by similar chronologies of glacier variation for Andean ice lobes in the Chilean Lake District of South America.
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reconciling the onset of deglaciation in the upper rangitata valley Southern Alps new zealand
Quaternary Science Reviews, 2019Co-Authors: David J. A. Barrell, Aaron E. Putnam, George H. DentonAbstract:Abstract Enquiry into the detailed timing of paleoclimate events depends on well-resolved and reliable chronologies. A recently published set of 10Be surface-exposure ages for moraine boulders in the upper Rangitata valley was interpreted to indicate a gradual reduction in glacier surface height between c. 21 and c. 17 ka, without rapid glacier recession beginning c. 18 ka as reported from other valleys. The dating results were suggested to be consistent with moraine geomorphology and an interpreted lack of post-glacial lake formation in the valley. In contrast, we argue that the geomorphology is consistent with sustained glacier recession and we highlight evidence for a post-glacial lake. Furthermore, the upper Rangitata moraine chronology was encumbered by inaccurate altitude values assigned to many of the sample sites. Recalculation of the 10Be ages using accurate elevations produces values that are as much as 3000 years younger than originally reported. The recalculated values indicate no significant age difference across the c. 300-m relative altitudinal spread of sample locations, with mean age of all samples c. 17.7 ± 0.3 ka. The previous inference of slow late-glacial ice retreat is not supported by the recalculated chronology. Rather, the revised glacial chronology implies that substantial ice-surface lowering of the Last Glacial Maximum Rangitata glacier was in progress shortly after c. 18 ka. The revised upper Rangitata chronology is compatible with dating from other eastern valleys of the Southern Alps, indicating moraine formation at c. 18 ka, followed by sustained glacier recession associated with regional climatic amelioration.
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a beryllium 10 chronology of late glacial moraines in the upper rakaia valley Southern Alps new zealand supports Southern hemisphere warming during the younger dryas
Quaternary Science Reviews, 2017Co-Authors: Tobias N B Koffman, George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Ann V Rowan, Robert C FinkelAbstract:Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination.
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warming and glacier recession in the rakaia valley Southern Alps of new zealand during heinrich stadial 1
Earth and Planetary Science Letters, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Bjorn G Andersen, Tobias N B Koffman, Ann V Rowan, R C FinkelAbstract:Abstract The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and Southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in Southern middle latitudes.
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the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau Southern Alps of new zealand
Quaternary Science Reviews, 2013Co-Authors: George H. Denton, Joerg M Schaefer, Aaron E. Putnam, David J. A. Barrell, Michael R Kaplan, Bjorn G Andersen, S D Birkel, Robert C FinkelAbstract:Abstract Determining whether glaciers registered the classic Last Glacial Maximum (LGM; ∼26,500–∼19,000 yrs ago) coevally between the hemispheres can help to discriminate among hypothesized drivers of ice-age climate. Here, we present a record of glacier behavior from the Southern Alps of New Zealand during the ‘local LGM’ (LLGM). We used 10 Be surface-exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well-preserved terminal moraines deposited during the LLGM near Lake Ohau on central South Island. We then used a glaciological model to estimate a LLGM glacier snowline and atmospheric temperature from the Ohau glacier record. Seventy-three 10 Be surface-exposure ages place culminations of terminal moraine construction, and hence completions of glacier advances to positions outboard of present-day Lake Ohau, at 138,600 ± 10,600 yrs, 32,520 ± 970 yrs ago, 27,400 ± 1300 yrs ago, 22,510 ± 660 yrs ago, and 18,220 ± 500 yrs ago. Recessional moraines document glacier recession into the Lake Ohau trough by 17,690 ± 350 yrs ago. Exposure of an ice-molded bedrock bench located inboard of the innermost LLGM moraines by 17,380 ± 510 yrs ago indicates that the ice tongue had receded about 40% of its overall length by that time. Comparing our chronology with distances of retreat suggests that the Ohau glacier terminus receded at a mean net rate of about 77 m yr −1 and its surface lowered by 200 m between 17,690 and 17,380 yrs ago. A long-term continuation of ice retreat in the Ohau glacier catchment is implied by moraine records at the head of Irishman Stream valley, a tributary of the Ohau glacier valley. The Irishman Stream cirque glacier advanced to produce a set of Lateglacial moraines at 13,000 ± 500 yrs ago, implying that the cirque glacier was less extensive prior to that advance. We employed a glaciological model, fit to these mapped and dated LLGM moraines, to derive snowline elevations and temperature parameters from the Ohau glacier record. The modeling experiments indicate that a snowline lowering of 920 ± 50 m and temperature depression of 6.25 ± 0.5 °C below modern values allows for the Ohau glacier to grow to an equilibrium position within the LGM moraine belt. Taken together with a glaciological simulation reported from the Irishman Stream valley, snowlines and temperatures increased by at least ∼520 m and ∼3.6 °C, respectively, between ∼18,000 and ∼13,000 yrs ago. Climate parameters derived from the Ohau glacier reconstruction are similar to those derived from glacier records from Patagonia, to air temperature indicators from Antarctica, as well as to sea-surface temperature and stratification signatures of the Southern Ocean. We think that the best explanation for the observed Southern LLGM is that Southern winter duration modulated Southern Ocean sea ice, which in turn influenced Southern Ocean stratification and made the surface ocean cooler. Orbitally induced cooling of the Southern Ocean provides an explanation for the LLGM in the Southern Alps having been coincident with the northern LGM. We argue further that the global effect of North Atlantic stadials led to disturbance of Southern Ocean stratification, southward shifts of the subtropical front, and retreat of Southern Alps glaciers. Collapse of Southern Ocean stratification during Heinrich Stadial-1, along with attendant sea-surface warming, triggered the onset of the Last Glacial termination in the Southern Alps of New Zealand.
