The Atlantic Ocean at the Last Glacial Maximum: 1. Objective Mapping of the GLAMAP Sea-Surface Conditions

Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard&#8211;Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance. &#160;

Download Full-text

Reconstruction of sea-surface temperature, salinity, and sea-ice cover in the northern North Atlantic during the last glacial maximum based on dinocyst assemblages

Canadian Journal of Earth Sciences ◽

10.1139/e99-091 ◽

2000 ◽

Vol 37 (5) ◽

pp. 725-750 ◽

Cited By ~ 101

Author(s):

Anne de Vernal ◽

Claude Hillaire-Marcel ◽

Jean-Louis Turon ◽

Jens Matthiessen

Keyword(s):

Sea Ice ◽

Surface Temperature ◽

Last Glacial Maximum ◽

North Atlantic ◽

Ice Cover ◽

Glacial Maximum ◽

Sea Surface ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Past sea-surface conditions over the northern North Atlantic during the last glacial maximum were examined from the study of 61 deep-sea cores. The last glacial maximum time slice studied here corresponds to an interval between Heinrich layers H2 and H1, and spanning about 20-16 ka on a 14C time scale. Transfer functions based on dinocyst assemblages were used to reconstruct sea-surface temperature, salinity, and sea-ice cover. The results illustrate extensive sea-ice cover along the eastern Canadian margins and sea-ice spreading, only during winter, over most of the northern North Atlantic. On the whole, much colder winter prevailed, despite relatively mild conditions in August (10-15°C at most offshore sites), thus suggesting a larger seasonal contrast of temperatures than today. Lower salinity than at present is reconstructed, especially along the eastern Canadian and Scandinavian margins, likely because of meltwater supply from the surrounding ice sheets. These reconstructions contrast with those established by CLIMAP on the basis of planktonic foraminifera. These differences are discussed with reference to the stratigraphical frame of the last glacial maximum, which was not the coldest phase of the last glacial stage. The respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses, which was apparently much more stratified than at present in the northern North Atlantic, thus preventing deep-water formation.

Download Full-text

The Atlantic Ocean at the Last Glacial Maximum: 2. Reconstructing the Current Systems with a Global Ocean Model

The South Atlantic in the Late Quaternary ◽

10.1007/978-3-642-18917-3_24 ◽

2003 ◽

pp. 549-583 ◽

Cited By ~ 2

Author(s):

A. Paul ◽

C. Schäfer-Neth

Keyword(s):

Atlantic Ocean ◽

Last Glacial Maximum ◽

Ocean Model ◽

Glacial Maximum ◽

Global Ocean ◽

Last Glacial ◽

Current Systems ◽

The Last Glacial Maximum ◽

The Last Glacial

Download Full-text

Moisture control on high-altitude cooling during the Last Glacial Maximum

10.5194/egusphere-egu21-12809 ◽

2021 ◽

Author(s):

Guillaume Leduc ◽

Etienne Longrain ◽

Pierre-Henri Blard ◽

Julien Charreau

Keyword(s):

High Altitude ◽

Last Glacial Maximum ◽

High Elevation ◽

Glacial Maximum ◽

Sea Surface ◽

Lapse Rate ◽

Central Pacific ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Reconstructing the spatial and temporal variabilities of the vertical atmospheric temperature gradient (lapse rate, LR) is key to predict the evolution of glaciers in a changing climate. Variations in this parameter may amplify or mitigate the future warming at high elevation, implying contrasted impacts on the stability of glaciers. Several regional studies suggested that the tropical LR was steeper than today during the last glacial maximum (LGM) (Loomis et al., 2017; Blard et al., &#160;2007), while another study concluded that the LGM lapse rate was similar than today (Tripati et al., 2014).Here we combine published LGM sea surface temperatures (SSTs) data and LGM moraines dated by cosmogenic nuclides to reconstruct the lapse rate along the American Cordillera. To do so, we combined paleo-Equilibrium Line Altitudes (ELAs) of glaciers with independent precipitation proxies to derive high latitude atmospheric temperatures. The whole dataset includes 34 paleo-glaciated sites along a North-South transect in the American Cordillera, ranging in latitude from 40&#176;N to 36&#176;S. Our reconstruction indicates that the lapse rate (LR) was steeper than today in the tropical American Cordillera (20&#176;N &#8211; 11&#176;S). The average &#916;LR (LGM &#8211; Modern) for this Tropical Andes region (20&#176;N &#8211; 11&#176;S) is ~-1.5 &#176;C.km-1 (20 sites). At higher latitude, in both hemispheres (Central Andes, 15&#176;S &#8211; 35&#176;S (8 sites); Sierra Nevada and San Bernardino mountains (40&#176;N &#8211; 34&#176;N) (6 sites), the LR was constant during the LGM.&#160;&#160;Our results show that a drier climate during the LGM is systematically associated with a steeper LR. Modification of LR during LGM was already observed from other tropical regions, in Hawaii-Central Pacific (Blard et al 2007), and in Eastern Africa (Loomis et al., 2017). Similarly, in these regions, precipitation did not increase during the LGM. With this multi-site exhaustive synthesis, we make a case that drier Tropical LGM conditions induce a steeper LR. This corresponds to an amplification of cooling at high altitude during the LGM. These results highlight the necessity to consider LR variations in modelling future climate. In a warmer and wetter Earth, temperature increase may be amplified at high elevation, due to smoother LR. If valid, this mechanism implies that tropical glaciers are more vulnerable than predicted by current climate modelling.&#160;ReferencesBlard, P.-H., Lav&#233;, J., Pik, R., Wagnon, P., & Bourl&#232;s, D. (2007). Persistence of full glacial conditions in the central Pacific until 15,000 years ago. Nature, 449(7162), 591.Loomis, S. E., Russell, J. M., Verschuren, D., Morrill, C., De Cort, G., Damst&#233;, J. S. S., &#8230; & Kelly, M. A. (2017). The tropical lapse rate steepened during the Last Glacial Maximum. Science advances, 3(1), e1600815.Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L., & Beaufort, L. (2014). Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing. Nature Geoscience, 7(3), 205.

Download Full-text

Amplification of high-altitude temperature changes in the American Cordillera driven by precipitation during the Last Glacial Maximum

10.5194/egusphere-egu2020-19512 ◽

2020 ◽

Author(s):

Pierre-Henri Blard ◽

Etienne Legrain ◽

Julien Charreau

Keyword(s):

High Altitude ◽

Last Glacial Maximum ◽

High Elevation ◽

Glacial Maximum ◽

Sea Surface ◽

Lapse Rate ◽

Central Pacific ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Reconstructing the spatial and temporal variabilities of the vertical atmospheric temperature gradient (lapse rate, LR) is key to predict the evolution of glaciers in a changing climate. Variations in this parameter may indeed amplify or mitigate the future warming at high elevation, implying contrasted impacts on the stability of glaciers. Several regional studies suggested that the tropical LR was steeper than today during the last glacial maximum (LGM) (Loomis et al., 2017; Blard et al., 2007), while another study concluded that the LGM lapse rate was similar than today (Tripati et al., 2014).Here we combine published LGM sea surface temperatures (SSTs) data and LGM moraines dated by cosmogenic nuclides to reconstruct the lapse rate along the American Cordillera. To do so, we combined paleo-Equilibrium Line Altitudes (ELAs) of glaciers with independent precipitation proxies to derive high latitude atmospheric temperatures. The whole dataset includes 34 paleo-glaciated sites along a North-South transect in the American Cordillera, ranging in latitude from 40&#176;N to 36&#176;S. Our reconstruction indicates that the lapse rate (LR) was steeper than today in the tropical American Cordillera (20&#176;N &#8211; 11&#176;S). The average &#916;LR (LGM &#8211; Modern) for this Tropical Andes region (20&#176;N &#8211; 11&#176;S) is ~-2 &#176;C.km-1 (20 sites). At higher latitude, in both hemispheres, the LR was constant or decreased during the LGM. More precisely, this &#916;LR change in the Central Andes (15&#176;S &#8211; 35&#176;S) is between 0 and 1&#176;C.km-1 (8 sites), while it is ~1 &#176;C.km-1 in Sierra Nevada and San Bernardino mountains (40&#176;N &#8211; 34&#176;N) (6 sites).&#160;Our results show that a drier climate during the LGM is systematically associated with a steeper LR. Modification of LR during the LGM was already observed from other tropical regions, in Hawaii-Central Pacific (Blard et al 2007), and in Eastern Africa (Loomis et al., 2017). Similarly, in these regions, precipitation did not increase during the LGM. With this multi-site exhaustive synthesis, we make a case that drier Tropical LGM conditions induce a steeper LR. This corresponds to an amplification of cooling at high altitude during the LGM. These results highlight the necessity to consider LR variations in modelling future climate. In a warmer and wetter Earth, temperature increase may be amplified at high elevation, due to smoother LR. If true, this mechanism indicates that tropical glaciers are more threatened by climate change than predicted by current climate modelling.ReferencesBlard, P.-H., Lav&#233;, J., Pik, R., Wagnon, P., & Bourl&#232;s, D. (2007). Persistence of full glacial conditions in the central Pacific until 15,000 years ago. Nature, 449(7162), 591.Loomis, S. E., Russell, J. M., Verschuren, D., Morrill, C., De Cort, G., Damst&#233;, J. S. S., &#8230; & Kelly, M. A. (2017). The tropical lapse rate steepened during the Last Glacial Maximum. Science advances, 3(1), e1600815.Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L., & Beaufort, L. (2014). Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing. Nature Geoscience, 7(3), 205.

Download Full-text