scholarly journals Delayed and rapid deglaciation of alpine valleys in the Sawatch Range, southern Rocky Mountains, USA

2020 ◽  
Author(s):  
Joseph P. Tulenko ◽  
William Caffee ◽  
Avriel D. Schweinsberg ◽  
Jason P. Briner ◽  
Eric M. Leonard
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
North American ◽  
Rocky Mountains ◽  
Ice Sheets ◽  
Last Glacial ◽  
Southern Rocky Mountains ◽  
The North ◽  
The North Atlantic ◽  
Sawatch Range

Abstract. We quantify retreat rates for three alpine glaciers in the Sawatch Range of the southern Rocky Mountains following the Last Glacial Maximum using 10Be ages from ice-sculpted, valley-floor bedrock transects and statistical analysis via the BACON program in R. Glacier retreat in the Sawatch Range from at (100 %) or near (~ 83 %) Last Glacial Maximum extents initiated between 16.3 and 15.6 ka and was complete by 14.2–13.7 ka at rates ranging between 9.9 and 19.8 m a−1. Deglaciation in the Sawatch Range commenced ~ 2–3 kyr later than the onset of rising global CO2, but approximately in-step with rising temperatures observed in the North Atlantic region at the Heinrich Stadial 1/Bølling transition. Our results highlight a possible teleconnection between the North Atlantic sector and the southern Rocky Mountains. However, deglaciation in the Sawatch Range also approximately aligns with the timing of Great Basin pluvial lake lowering. Recent data-modeling comparison efforts highlight the influence of the large North American ice sheets on climate in the western United States, and we hypothesize that recession of the North American ice sheets may have influenced the timing and rate of deglaciation in the Sawatch Range. While we cannot definitively argue for exclusively North Atlantic forcing or North American ice sheet forcing, our data demonstrate the importance of regional forcing mechanisms on past climate records.

scholarly journals Delayed and rapid deglaciation of alpine valleys in the Sawatch Range, southern Rocky Mountains, USA

Geochronology ◽  
2020 ◽  
Vol 2 (2) ◽  
pp. 245-255
Author(s):  
Joseph P. Tulenko ◽  
William Caffee ◽  
Avriel D. Schweinsberg ◽  
Jason P. Briner ◽  
Eric M. Leonard
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
North American ◽  
Rocky Mountains ◽  
Ice Sheets ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Southern Rocky Mountains ◽  
The North ◽  
Sawatch Range

Abstract. We quantify retreat rates for three alpine glaciers in the Sawatch Range of the southern Rocky Mountains following the Last Glacial Maximum using 10Be ages from ice-sculpted, valley-floor bedrock transects and statistical analysis via the BACON program in R. Glacier retreat in the Sawatch Range from at (100 %) or near (∼83 %) Last Glacial Maximum extents initiated between 16.0 and 15.6 ka and was complete by 14.2–13.7 ka at rates ranging between 35.6 and 6.8 m a−1. Deglaciation in the Sawatch Range commenced ∼2–3 kyr later than the onset of rising global CO2 and prior to rising temperatures observed in the North Atlantic region at the Heinrich Stadial 1–Bølling transition. However, deglaciation in the Sawatch Range approximately aligns with the timing of Great Basin pluvial lake lowering. Recent data–modeling comparison efforts highlight the influence of the large North American ice sheets on climate in the western United States, and we hypothesize that recession of the North American ice sheets may have influenced the timing and rate of deglaciation in the Sawatch Range. While we cannot definitively argue for exclusively North Atlantic forcing or North American ice sheet forcing, our data demonstrate the importance of regional forcing mechanisms for past climate records.

scholarly journals Climate response to freshwater perturbations in Northern or Southern Hemispheres at the last glacial inception, the last glacial maximum and the present-day

2010 ◽  
Vol 6 (3) ◽  
pp. 1077-1110
Author(s):  
G. Philippon-Berthier ◽  
G. Ramstein ◽  
S. Charbit ◽  
C. Ritz
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Freshwater Inputs ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Freshwater inputs in North Atlantic due to huge surge of icebergs coming from ice sheets might be responsible for drastic regional and global abrupt climatic transitions. To quantify the sensitivity of climate system to these freshwater inputs, we use a model of intermediate complexity coupled to ice-sheet models for both Northern and Southern Hemispheres. We mimic the Dansgaard-Oeschger and Heinrich Events by forcing the model with appropriate freshwater perturbations. The originality of this study is to investigate with such a global model, the response of the coupled system to freshwater discharges for three different climate contexts, the Last Glacial Maximum (LGM), the Last Glacial Inception (LGI) and the present-day (PD) climates. We first show that in all climate contexts, the North Atlantic circulation is more sensitive to freshwater flux when ice sheets are present. Secondly, the "seesaw" mechanism occurs mostly for the North Atlantic freshwater perturbation whereas it remains very weak for the Southern Ocean freshwater release. Moreover, this seesaw is generally enhanced when ice sheets are interactive. The most striking result is that the freshwater perturbation amplifies the inception of the North American ice sheet at LGI the sea-level drop associated is significantly increased and in a much better agreement with data.

scholarly journals Extratropical cyclones over the North Atlantic and western Europe during the Last Glacial Maximum and implications for proxy interpretation

2020 ◽  
Vol 16 (2) ◽  
pp. 611-626 ◽  
Author(s):  
Joaquim G. Pinto ◽  
Patrick Ludwig
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Western Europe ◽  
Dust Storms ◽  
Glacial Maximum ◽  
Extratropical Cyclones ◽  
Last Glacial ◽  
The North ◽  
Dominant Feature ◽  
The North Atlantic

Abstract. Extratropical cyclones are a dominant feature of the midlatitudes, as their passage is associated with strong winds, precipitation and temperature changes. The statistics and characteristics of extratropical cyclones over the North Atlantic region exhibit some fundamental differences between pre-industrial (PI) and Last Glacial Maximum (LGM) climate conditions. Here, the statistics are analysed based on results of a tracking algorithm applied to global PI and LGM climate simulations. During the LGM, both the number and the intensity of detected cyclones were higher compared to PI. In particular, increased cyclone track activity is detected close to the Laurentide ice sheet and over central Europe. To determine changes in cyclone characteristics, the top 30 extreme storm events for PI and LGM have been simulated with a regional climate model and high resolution (12.5 km grid spacing) over the eastern North Atlantic and western Europe. Results show that LGM extreme cyclones were characterised by weaker precipitation, enhanced frontal temperature gradients and stronger wind speeds than PI analogues. These results are in line with the view of a colder and drier Europe, characterised by little vegetation and affected by frequent dust storms, leading to reallocation and build-up of thick loess deposits in Europe.

A weaker Atlantic Meridional Overturning Circulation at the Last Glacial Maximum led to a greater deep ocean carbon content

2020 ◽  
Author(s):  
Laurie Menviel ◽  
Paul Spence ◽  
Luke Skinner ◽  
Kazuyo Tachikawa ◽  
Tobias Friedrich ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Ocean Carbon ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>While paleoproxy records and modelling studies consistently suggest that North Atlantic  Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than during pre-industrial times, its strength is still subject to debate partly due to different signals across the North Atlantic. Here, using a series of LGM experiments performed with a carbon isotopes enabled Earth system model, we show that proxy records are consistent with a shallower and weaker NADW. A significant equatorward advance of sea-ice over the Labrador Sea and the Nordic Seas shifts the NADW convection sites to the south of the Norwegian Sea. While the deep western boundary current in the Northwest Atlantic weakens with NADW, a change in density gradients strengthens the deep southward flow in the Northeast Atlantic. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic despite its transport being reduced. This resultant globally weaker oceanic circulation leads to an increase in deep ocean carbon of ~500 GtC, thus significantly contributing to the lower LGM atmospheric CO<sub>2</sub> concentration.</p><p> </p>

Extratropical cyclone characteristics over the North Atlantic and Western Europe during the Last Glacial Maximum

2020 ◽  
Author(s):  
Joaquim G. Pinto ◽  
Patrick Ludwig
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Western Europe ◽  
Dust Storms ◽  
Glacial Maximum ◽  
Extratropical Cyclones ◽  
Last Glacial ◽  
The North ◽  
Dominant Feature ◽  
The North Atlantic

<p>Extratropical cyclones are a dominant feature of the mid-latitudes, as their passage is associated with strong winds, precipitation, and temperature changes. The statistics and characteristics of extratropical cyclones over the North Atlantic region exhibit some fundamental differences between Pre-Industrial (PI) and Last Glacial Maximum (LGM) climate conditions. Here, the statistics are analysed based on results of a tracking algorithm applied to global PI and LGM climate simulations. During the LGM, both the number and the intensity of detected cyclones was higher compared to PI. In particular, increased cyclone track activity is detected close to the Laurentide ice sheet and over central Europe. To determine changes in cyclone characteristics, the top 30 extreme storm events for PI and LGM have been simulated with a regional climate model and high resolution (12.5 km grid spacing) over the eastern North Atlantic and Western Europe. Results show that LGM extreme cyclones were characterised by weaker precipitation, enhanced frontal temperature gradients, and stronger wind speeds than PI analogues. These results are in line with the view of a colder and drier Europe, characterised by little vegetation and affected by frequent dust storms, leading to reallocation and build-up of thick loess deposits in Europe.</p>

Last-glacial-maximum North Atlantic deep water: on, off or somewhere in-between?

1995 ◽  
Vol 348 (1324) ◽  
pp. 243-253 ◽  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Deep Water ◽  
Younger Dryas ◽  
Glacial Maximum ◽  
Nutrient Concentrations ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Intermediate Waters

Various papers have been published during the past decade concerning Last Glacial Maximum (LGM) North Atlantic Deep Water (NADW) flow. Using somewhat different methods, they have produced somewhat contradictory results. This review considers both apparent and real conflicts concerning the data and their interpretation, and attempts to resolve them. Despite the earlier (contradictory) interpretations, currently there is a widespread belief that nutrient concentrations in deep cores from the North Atlantic increased during glacial times and that concentrations in the upper-deep and intermediate waters decreased at least slightly. It is also clear that further north in the basin (particularly at upper-deep and intermediate depths), nutrient concentrations were as low or perhaps even lower than those seen today. Data from the Caribbean Sea, ventilated by intermediate waters through an approximately 1800 m sill, indicate that lower nutrient levels were also found at intermediate depths in the North and Tropical Atlantic; this data is supported by continental margin data. The recontoured 8 13 C data of Duplessy et al. ( Paleoceanography 3, 343—360 (1988)) remain a valid expression of the broadscale LGM Atlantic nutrient distribution. Data from the South Atlantic has been the most contradictory to date, but recent 8 13 c evidence from a low-productivity South Atlantic site supports Cd data indicating a relative stability in the nutrient chemistry of waters that are presently influenced by low-nutrient NADW. Sedimentary 231 Pa/ 230 Th data appear to require the continued export of Atlantic-generated 231 Pa from the Atlantic into the Southern Ocean. Finally, radiocarbon evidence from paired planktonic/benthic foraminifera indicates that the ventilation time of the North Atlantic remained low and that the ventilation time of the entire ocean did not change much beyond the uncertainty of the 14 C data. Taken together, this evidence suggests that the NADW became ‘Glacial North Atlantic Deep/Intermediate Water’ (GNAIDW) during glacial times, with perhaps a greater flux through intermediate waters than currently combined with a lesser flux through deeper waters. Although one cannot say much with confidence about the total GNAIDW flux, the data are consistent with a persistent but perhaps somewhat diminished role for NADW in the global thermohaline circulation during glacial times. A review of recent evidence concerning the response of the deep North Atlantic during the Younger Dryas concludes that there is no inconsistency between the new evidence and the occurence of a Younger Dryas NADW event in the deep western North Atlantic.

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