scholarly journals Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere

2006 ◽  
Vol 2 (1) ◽  
pp. 11-19 ◽  
Author(s):  
H. Rother ◽  
J. Shulmeister
Keyword(s):  
New Zealand ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Late Quaternary ◽  
Synoptic Climatology ◽  
Balance Model ◽  
Last Glacial ◽  
Regional Flow ◽  
Quaternary Glaciations ◽  
The Last Glacial

Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40-55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand (NZ) and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glaciation in the temperate and hyperhumid Southern Alps of New Zealand can be generated with moderate cooling. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1-4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).

scholarly journals Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere

2005 ◽  
Vol 1 (3) ◽  
pp. 231-253 ◽  
Author(s):  
H. Rother ◽  
J. Shulmeister
Keyword(s):  
New Zealand ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Late Quaternary ◽  
Synoptic Climatology ◽  
Balance Model ◽  
Last Glacial ◽  
Regional Flow ◽  
Quaternary Glaciations ◽  
The Last Glacial

Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40–55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glacial advances in the temperate and hyperhumid Southern Alps of New Zealand can be generated with very little thermal forcing. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1–4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some Late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).

scholarly journals The glacial history of Tongariro and Ruapehu volcanoes, New Zealand

2021 ◽  
Author(s):  
◽  
Shaun Eaves
Keyword(s):  
New Zealand ◽  
Production Rate ◽  
Late Quaternary ◽  
Lateral Moraine ◽  
Glacial Cycle ◽  
Mountain Glacier ◽  
Last Glacial ◽  
Glacier Fluctuations ◽  
Exposure Ages ◽  
The Last Glacial

<p>Understanding the drivers and mechanisms of past, natural changes in Earth’s climate is a fundamental goal of palaeoclimate science. Recent advances in cosmogenic surface exposure dating and numerical glacier modelling have greatly improved the utility of geological glacial records for palaeoclimatic reconstruction. Here, I apply these techniques to investigate the timing and magnitude of late Quaternary mountain glacier fluctuations on Tongariro massif and Mt. Ruapehu volcanoes in central North Island, New Zealand (39°S).  First, I constrain the local cosmogenic ³He production rate, in order to compare my subsequent ³He moraine chronologies with other well-dated palaeoclimate records. I present a new radiocarbon age for a large debris avalanche event on the northwest slopes of Mt. Ruapehu that occurred at 10.4-10.6 cal. ka BP. Cosmogenic ³He concentrations in surficial boulders deposited during this event are consistent with that predicted by a global compilation of similar production rate calibrations. Thus, I conclude that this globally compiled production rate is suitable for cosmogenic ³He exposure age calculations in New Zealand.  Exposure ages from moraine boulders on both volcanoes constrain the timing of two periods of glaciation during the last glacial cycle, when the termini of valley glaciers reached c. 1200 m asl. The most recent of these events occurred between c. 31-17 ka, which corresponds with the global Last Glacial Maximum. During this period, the local equilibrium line altitude was depressed by c. 800-1100 m. Numerical model simulations of the glaciers, using a coupled energy balance/ice flow model, suggest that local atmospheric temperature was 4-7 °C colder than present. This palaeotemperature estimate is not greatly impacted by post-glacial topographic change on these active volcanoes. Surface exposure ages from a degraded lateral moraine on Tongariro massif indicate that an earlier period of glaciation, of similar extent to that at the LGM, culminated during Marine Isotope Stage 4.  During the last glacial-interglacial transition (c. 18-11 ka), glacial retreat on Mt. Ruapehu was interrupted by a re-advance during the late-glacial (c. 15-11 ka). Exposure ages for this event exhibit some scatter, likely due to surface processes. Accounting for these processes with a topographic diffusion model yields a best-estimate age of 14-13 ka, corresponding to the Lateglacial reversal in New Zealand. Glacier model experiments indicate this re-advance resulted from a temperature lowering of 2.5-3.4 °C relative to present. Comparison with other proxy records suggests that this cooling was most pronounced during summer. Due to its lower elevation, it is unlikely that glaciers were present on Tongariro massif at this time.  The results of this research provide the first direct age constraint and quantitative palaeoclimate reconstructions for late Quaternary glacier fluctuations in central North Island, New Zealand. The timing and magnitude of these changes are in good agreement with glacial records from the Southern Alps and South America. This suggests that glaciers in the southern mid-latitudes were responding to common climatic forcings at orbital- and millennial-timescales, during the last glacial cycle.</p>

scholarly journals Late Quaternary dynamics of Arctic biota from ancient environmental genomics

Nature ◽  
2021 ◽  
Author(s):  
Yucheng Wang ◽  
Mikkel Winther Pedersen ◽  
Inger Greve Alsos ◽  
Bianca De Sanctis ◽  
Fernando Racimo ◽  
...  
Keyword(s):  
Large Scale ◽  
Late Quaternary ◽  
Environmental Dna ◽  
Plant Genome ◽  
The Arctic ◽  
Last Glacial ◽  
Animal Diversity ◽  
Arctic Biota ◽  
The Last Glacial

AbstractDuring the last glacial–interglacial cycle, Arctic biotas experienced substantial climatic changes, yet the nature, extent and rate of their responses are not fully understood1–8. Here we report a large-scale environmental DNA metagenomic study of ancient plant and mammal communities, analysing 535 permafrost and lake sediment samples from across the Arctic spanning the past 50,000 years. Furthermore, we present 1,541 contemporary plant genome assemblies that were generated as reference sequences. Our study provides several insights into the long-term dynamics of the Arctic biota at the circumpolar and regional scales. Our key findings include: (1) a relatively homogeneous steppe–tundra flora dominated the Arctic during the Last Glacial Maximum, followed by regional divergence of vegetation during the Holocene epoch; (2) certain grazing animals consistently co-occurred in space and time; (3) humans appear to have been a minor factor in driving animal distributions; (4) higher effective precipitation, as well as an increase in the proportion of wetland plants, show negative effects on animal diversity; (5) the persistence of the steppe–tundra vegetation in northern Siberia enabled the late survival of several now-extinct megafauna species, including the woolly mammoth until 3.9 ± 0.2 thousand years ago (ka) and the woolly rhinoceros until 9.8 ± 0.2 ka; and (6) phylogenetic analysis of mammoth environmental DNA reveals a previously unsampled mitochondrial lineage. Our findings highlight the power of ancient environmental metagenomics analyses to advance understanding of population histories and long-term ecological dynamics.

scholarly journals A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

2019 ◽  
Vol 15 (6) ◽  
pp. 1939-1958
Author(s):  
Svante Björck ◽  
Jesper Sjolte ◽  
Karl Ljung ◽  
Florian Adolphi ◽  
Roger Flower ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Large Scale ◽  
Ice Cores ◽  
Oceanic Islands ◽  
South Atlantic ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Driving Mechanism ◽  
Last Glacial ◽  
The Last Glacial

Abstract. Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4–18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37∘ S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3–4 ∘C, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas.

scholarly journals The glacial history of Tongariro and Ruapehu volcanoes, New Zealand

2021 ◽  
Author(s):  
◽  
Shaun Eaves
Keyword(s):  
New Zealand ◽  
Production Rate ◽  
Late Quaternary ◽  
Lateral Moraine ◽  
Glacial Cycle ◽  
Mountain Glacier ◽  
Last Glacial ◽  
Glacier Fluctuations ◽  
Exposure Ages ◽  
The Last Glacial

<p>Understanding the drivers and mechanisms of past, natural changes in Earth’s climate is a fundamental goal of palaeoclimate science. Recent advances in cosmogenic surface exposure dating and numerical glacier modelling have greatly improved the utility of geological glacial records for palaeoclimatic reconstruction. Here, I apply these techniques to investigate the timing and magnitude of late Quaternary mountain glacier fluctuations on Tongariro massif and Mt. Ruapehu volcanoes in central North Island, New Zealand (39°S).  First, I constrain the local cosmogenic ³He production rate, in order to compare my subsequent ³He moraine chronologies with other well-dated palaeoclimate records. I present a new radiocarbon age for a large debris avalanche event on the northwest slopes of Mt. Ruapehu that occurred at 10.4-10.6 cal. ka BP. Cosmogenic ³He concentrations in surficial boulders deposited during this event are consistent with that predicted by a global compilation of similar production rate calibrations. Thus, I conclude that this globally compiled production rate is suitable for cosmogenic ³He exposure age calculations in New Zealand.  Exposure ages from moraine boulders on both volcanoes constrain the timing of two periods of glaciation during the last glacial cycle, when the termini of valley glaciers reached c. 1200 m asl. The most recent of these events occurred between c. 31-17 ka, which corresponds with the global Last Glacial Maximum. During this period, the local equilibrium line altitude was depressed by c. 800-1100 m. Numerical model simulations of the glaciers, using a coupled energy balance/ice flow model, suggest that local atmospheric temperature was 4-7 °C colder than present. This palaeotemperature estimate is not greatly impacted by post-glacial topographic change on these active volcanoes. Surface exposure ages from a degraded lateral moraine on Tongariro massif indicate that an earlier period of glaciation, of similar extent to that at the LGM, culminated during Marine Isotope Stage 4.  During the last glacial-interglacial transition (c. 18-11 ka), glacial retreat on Mt. Ruapehu was interrupted by a re-advance during the late-glacial (c. 15-11 ka). Exposure ages for this event exhibit some scatter, likely due to surface processes. Accounting for these processes with a topographic diffusion model yields a best-estimate age of 14-13 ka, corresponding to the Lateglacial reversal in New Zealand. Glacier model experiments indicate this re-advance resulted from a temperature lowering of 2.5-3.4 °C relative to present. Comparison with other proxy records suggests that this cooling was most pronounced during summer. Due to its lower elevation, it is unlikely that glaciers were present on Tongariro massif at this time.  The results of this research provide the first direct age constraint and quantitative palaeoclimate reconstructions for late Quaternary glacier fluctuations in central North Island, New Zealand. The timing and magnitude of these changes are in good agreement with glacial records from the Southern Alps and South America. This suggests that glaciers in the southern mid-latitudes were responding to common climatic forcings at orbital- and millennial-timescales, during the last glacial cycle.</p>

scholarly journals A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

2019 ◽  
Author(s):  
Svante Björck ◽  
Jesper Sjolte ◽  
Karl Ljung ◽  
Florian Adolphi ◽  
Roger Flower ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Ice Cores ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Driving Mechanism ◽  
Last Glacial ◽  
Climate Shifts ◽  
The Last Glacial

Abstract. The period 36–18 ka was a dynamic phase of the last glacial, with large climate shifts in both hemispheres. Through the bipolar seesaw, the Antarctic Isotope Maxima and Greenland DO events were part of a global concert of large scale climate changes. The interaction between atmospheric processes and Atlantic meridional overturning circulation (AMOC) is crucial for such shifts, controlling upwelling- and carbon cycle dynamics, and generating climate tipping points. Here we report the first temperature and humidity record for the glacial period from the central South Atlantic (SA). The presented data resolves ambiguities about atmospheric circulation shifts during bipolar climate events recorded in polar ice cores. A unique lake sediment sequence from Nightingale Island at 37° S in the SA, covering 36.4–18.6 ka, exhibits continuous impact of the Southern Hemisphere Westerlies (SHW), recording shifts in their position and strength. The SHW displayed high latitudinal and strength-wise variability 36–31 ka locked to the bipolar seesaw, followed by 4 ka of slightly falling temperatures, decreasing humidity and fairly southern westerlies. After 27.5 ka temperatures decreased 3–4 °C, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly positioned SHW are correlated with periods of increased CO2 outgassing from the ocean. Changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, it shows that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial.

Polar Perspective of Late-Quaternary Climates in the Southern Hemisphere

1989 ◽  
Vol 32 (1) ◽  
pp. 60-71 ◽  
Author(s):  
Calvin J. Heusser
Keyword(s):  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Late Quaternary ◽  
Glacial Maximum ◽  
Small Scale ◽  
Time Interval ◽  
Climatic Fluctuations ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractLate-Quaternary paleoecological and glacial evidence from the higher latitudes of the Southern Hemisphere implies overall uniformity of large-scale glacial and interglacial climatic fluctuations for the past 40,000 yr. Climate of the last glacial maximum, variously dated between 30,000 and 11,000 yr B.P., was relatively cold and dry compared with the warmer, more humid climate of the Holocene and the interstade preceding the last glacial maximum. Conditions were apparently coldest during millennia centered around 20,000 yr B.P. and warmest in the early Holocene. Recorded small-scale fluctuations, frequently variable for any given time interval, are less consistent. A cold late-glacial episode, estimated as occurring between ca. 13,000 and 11,000 yr B.P. in Antarctica, possibly was coeval with the Younger Dryas Stade in northwestern Europe and may be correlative with a climatic episode in southern South America and perhaps in New Zealand and South Georgia; however, there is no evidence for the event in Tasmania. General atmospheric circulation models for the polar latitudes at the time of the last glacial maximum show an intensification of the southern westerlies, apparently a result of the expansion of ice cover in Antarctica and of sea ice in the Southern Ocean.

scholarly journals A palaeoenvironmental record of the Southern Hemisphere last glacial maximum from the Mount Cass loess section, North Canterbury, Aotearoa/New Zealand

2020 ◽  
pp. 1-15
Author(s):  
Peter C. Almond ◽  
Sándor Gulyás ◽  
Pál Sümegi ◽  
Balázs P. Sümegi ◽  
Stephen Covey-Crump ◽  
...  
Keyword(s):  
New Zealand ◽  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Climatic Variability ◽  
Glacial Maximum ◽  
Pollen Record ◽  
Good Correspondence ◽  
Last Glacial ◽  
Event Stratigraphy ◽  
Westerly Winds

Abstract Calcareous loess in North Canterbury, eastern South Island, New Zealand (NZ), preserves subfossil bird bone, terrestrial gastropods, and eggshell, whose abundances and radiocarbon ages allowed us to reconstruct aspects of palaeoenvironment at high resolution through 25 to 21 cal ka BP. This interval includes millennial-scale climatic variability during the extended last glacial maximum (30–18 ka) of Australasia. Our loess palaeoclimatic record shows good correspondence with stadial and interstadial climate events of the NZ Climate Event Stratigraphy, which were defined from a pollen record on the western side of South Island. An interstade from 25.4 to 24 cal ka BP was warm but also relatively humid on eastern South Island, and loess grain size may indicate reduced vigour of the Southern Hemisphere westerly winds. The subsequent stade (24–22.6 cal ka BP) was drier, colder, and probably windier. The next interstade remained relatively dry on eastern South Island, and westerly winds remained vigorous. The 25.4–24 ka interstade is synchronous with Heinrich stade 2, which may have driven a southward migration of the subtropical front, leading to warming and wetting of northern and central South Island and retreat of Southern Alps glaciers at ca. 26.5 ka.

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