Climate-Ice Sheet Simulations of Neoproterozoic Glaciation Before and After Collapse to Snowball Earth

2013 ◽  
pp. 91-105 ◽  
Author(s):  
David Pollard ◽  
James F. Kasting
Keyword(s):  
Ice Sheet ◽  
Snowball Earth ◽  
Before And After ◽  
Neoproterozoic Glaciation

Stratigraphic record of Neoproterozoic ice sheet collapse: the Kapp Lyell diamictite sequence, SW Spitsbergen, Svalbard

2009 ◽  
Vol 147 (3) ◽  
pp. 380-390 ◽  
Author(s):  
M. G. BJØRNERUD
Keyword(s):  
Ice Sheet ◽  
Snowball Earth ◽  
Submarine Landslides ◽  
Low Oxygen ◽  
Deep Basin ◽  
Stratigraphic Framework ◽  
Major Stage ◽  
Oxygen Conditions ◽  
Neoproterozoic Glaciation ◽  
Graphitic Material

AbstractThe diamictites of the Neoproterozoic Kapp Lyell Sequence in northern Wedel Jarlsberg Land, southwest Spitsbergen, have long been recognized as ancient glacial deposits, but their place within the global stratigraphic framework of ‘snowball Earth’ has remained unclear, owing to the complexity of superimposed Caledonian deformation and to the relatively inaccessible terrain in which they occur. Recently deglaciated exposures of the rocks now provide a more complete picture of the changing environment in which the diamictites were deposited, and new understanding of regional correlations help constrain their place in the global chronostratigraphy of the Cryogenian Period. The 2500 m thick Kapp Lyell Sequence consists of three distinct types of glaciomarine diamictite. The succession begins with about 1000 m of finely laminated diamictite containing abundant lonestones. The millimetre- to centimetre-scale laminae, apparent suspension deposits, consist of sand- to silt-sized particles of quartz and dolomite alternating with thin films of graphitic phyllite. The laminated unit gives way abruptly to 500–1000 m of unsorted, unlayered diamictite that alternates and interfingers with graded beds of conglomerate to sandstone. These apparent turbidite deposits become increasingly prevalent toward the top of the exposed section. Regional lithostratigraphic relationships suggest that the Kapp Lyell sequence corresponds to the second major stage of Neoproterozoic glaciation at c. 635 Ma. The graphitic material in the laminated unit yields δ13C values in the range of −20 to −22 ‰, pointing to a biogenic origin and an active marine biosphere at the time of deposition. The preservation of organic carbon and unusually large ratios of highly reactive Fe to total Fe suggest that low oxygen conditions prevailed in the deep basin that received these sediments. The transition from laminated, to unsorted, to graded diamictites may represent change from (1) a stable ice margin that released rare icebergs into a deep, quiet basin to (2) a collapsing ice sheet that unleashed flotillas of icebergs and large volumes of sediment to (3) submarine landslides that triggered turbidity flows from the rapidly deposited, gravitationally unstable sediments. The Kapp Lyell diamictite sequence appears to chronicle the demise of a large ice mass in this part of the Neoproterozoic world.

Neoproterozoic ‘snowball Earth’ simulations with a coupled climate/ice-sheet model

Nature ◽  
2000 ◽  
Vol 405 (6785) ◽  
pp. 425-429 ◽  
Author(s):  
William T. Hyde ◽  
Thomas J. Crowley ◽  
Steven K. Baum ◽  
W. Richard Peltier
Keyword(s):  
Ice Sheet ◽  
Snowball Earth

Ocean dynamics and climate during a Neoproterozoic snowball Earth and its aftermath as simulated in a coupled Earth system model

2020 ◽  
Author(s):  
Lennart Ramme ◽  
Jochem Marotzke
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Cold Climate ◽  
Ocean Dynamics ◽  
Snowball Earth ◽  
Ice Melt ◽  
Ocean Surface Currents ◽  
Before And After

<p>The Neoproterozoic glaciations, referred to as snowball Earth periods, describe the most extreme transition from a very cold climate to a state of strong greenhouse effect. Atmospheric CO<sub>2</sub> concentrations are rising during the snowball, due to the shutdown of oceanic and terrestrial carbon sinks, until a tipping point is reached and a rapid deglaciation sets in. Subsequently, a warm and completely ice-free climate under very high CO<sub>2</sub> concentrations develops. We show first results of simulations using a coupled atmosphere-ocean general circulation model covering the initiation, as well as the melting of the Marinoan snowball Earth (645 – 635 My ago) and the greenhouse climate in its aftermath. CO<sub>2</sub> concentrations are decreased to initiate a global glaciation and then increased again in order to melt the snowball Earth. As soon as a certain CO<sub>2</sub> threshold is reached, sea-ice melts rapidly, reaching a completely ice-free ocean after only one hundred years, in our model without land glaciers. The ocean becomes strongly stratified, because at the surface the freshwater from the sea-ice melt is warming up quickly, whereas the deeper ocean remains cold and salty. Ocean surface currents return to their pre-snowball behavior soon after the melt, but destratification is slow. The largest mixed layer depths of up to 500 m are reached in the mid latitudes of the winter hemisphere. We compare the climate before and after the snowball state and estimate the time needed for destratification.</p>

scholarly journals Response of the carbon cycle to the different orbital configurations of the last 9 interglacials

2016 ◽  
Author(s):  
Nathaelle Bouttes ◽  
Didier Swingedouw ◽  
Didier Roche ◽  
Maria Sanchez-Goni ◽  
Xavier Crosta
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Atmospheric Co2 ◽  
Oceanic Circulation ◽  
Co2 Concentrations ◽  
Before And After ◽  
Ocean Carbon ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Atmospheric CO2 levels during interglacials prior to the Mid Bruhnes Event (MBE, ~ 430 ka BP) have lower values of around 40 ppm than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to differences in external forcing before and after the MBE, might have increased the ocean carbon storage and thus explained the lower CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings and atmospheric CO2 concentrations over the nine last interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few ppm. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 is slightly smaller in these pre-MBE simulated interglacials including ice sheet variations, but the magnitude is still far too small. These results suggest a possible mis-representation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, that could explain the lower atmospheric CO2 concentrations during pre-MBE interglacials.

scholarly journals A geochemical modelling study of the evolution of the chemical composition of seawater linked to a global glaciation: implications for life sustainability

2007 ◽  
Vol 4 (3) ◽  
pp. 1839-1876
Author(s):  
G. Le Hir ◽  
Y. Goddéris ◽  
Y. Donnadieu ◽  
G. Ramstein
Keyword(s):  
Snowball Earth ◽  
Large Shift ◽  
Apparent Paradox ◽  
Seawater Ph ◽  
Oceanic Surface ◽  
Cap Carbonates ◽  
Before And After ◽  
Global Cycles ◽  
Global Glaciation ◽  
Modelling Study

Abstract. The Snowball Earth theory initially proposed by Kirschvink (Kirschvink, 1992) to explain the Neoproterozoic glacial episodes, suggested that the Earth was fully ice-covered at 720 My (Sturtian episode) and 640 My (Marinoan episode). This succession of extreme climatic crises induced a stress which is considered as a strong selective pressure on the evolution of life (Hoffman et al., 1998). However recent biological records (Corsetti, 2006) do not support this theory as little change is observed in the diversity of microfossils outcrops before and after the Marinoan glacial interval. In this contribution we address this apparent paradox. Using a numerical model of carbon-alkalinity global cycles, we quantify several environmental stresses caused by a global glaciation. We suggest that during global glaciations, the ocean becomes acidic (pH~6), and unsaturated with respect to carbonate minerals. Moreover the quick transition from ice-house to greenhouse conditions implies an abrupt and large shift of the oceanic surface temperature which causes an extended hypoxia. The intense continental weathering, in the aftermath of the glaciation, deeply affects the seawater composition inducing rapid changes in terms of pH and alkalinity. We also propose a new timing for post glacial perturbations and for the cap carbonates deposition, ~2 Myr instead of 200 kyr as suggested in a previous modelling study. In terms of Precambrian life sustainability, seawater pH modifications appear drastic all along the glaciation, but we show that the buffering action of the oceanic crust dissolution processes avoids a total collapse of biological productivity. In opposite short-lived and large post-glacial perturbations are more critical and may have played a role of environmental filter suggested in the classic snowball Earth theory. Only a permissive life (prokaryotes or simple eukaryotes) may explain the relative continuity in microfossils diversity observed before, during and after Neoproterozoic glaciation events.

scholarly journals Winter drainage of surface lakes on the Greenland Ice Sheet from Sentinel-1 SAR Imagery

2020 ◽  
Author(s):  
Corinne Benedek ◽  
Ian Willis
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Shape From Shading ◽  
Surface Mass ◽  
Before And After ◽  
Radar Imagery ◽  
Optical Imagery ◽  
Satellite Radar ◽  
Sar Imagery ◽  
Lake Drainage

Abstract. Surface lakes on the Greenland Ice Sheet play a key role in its surface mass balance, hydrology, and biogeochemistry. They often drain rapidly in the summer via hydrofracture, which immediately delivers lake water to the ice sheet base over timescales of hours to days and then allows meltwater to reach the base for the rest of the summer. Rapid lake drainage, therefore, influences subglacial drainage evolution, water pressures, ice flow, biogeochemical activity, and ultimately the delivery of water, sediments and nutrients to the ocean. It is assumed that rapid lake drainage events are confined to the summer, as this is when all observations to date have been made. Here we develop a method to quantify backscatter changes in satellite radar imagery, which we use to document the drainage of six different lakes during three winters in fast flowing parts of the Greenland Ice Sheet. Analysis of optical imagery from before and after the three winters supports the radar-based evidence for winter lake drainage events and also provides estimates of lake drainage volumes, which range between 0.000046 and 0.0202 km3. For three of the events, optical imagery allows photoclinometry (shape from shading) calculations to be made showing mean vertical collapse of the lake surfaces ranging between 4.04 m and 7.25 m, and drainage volumes of 0.004 km3 to 0.049 km3. The findings show that background winter ice motion can trigger rapid lake drainage, which may have important implications for subglacial hydrology and biogeochemical processes.

Strong effects of tropical ice-sheet coverage and thickness on the hard snowball Earth bifurcation point

2016 ◽  
Vol 48 (11-12) ◽  
pp. 3459-3474 ◽  
Author(s):  
Yonggang Liu ◽  
W. Richard Peltier ◽  
Jun Yang ◽  
Guido Vettoretti ◽  
Yuwei Wang
Keyword(s):  
Bifurcation Point ◽  
Ice Sheet ◽  
Snowball Earth

scholarly journals Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation

2015 ◽  
Vol 8 (9) ◽  
pp. 704-707 ◽  
Author(s):  
Douglas I. Benn ◽  
Guillaume Le Hir ◽  
Huiming Bao ◽  
Yannick Donnadieu ◽  
Christophe Dumas ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Snowball Earth

Deformation Replication

1970 ◽  
Vol 28 ◽  
pp. 280-281
Author(s):  
J. Temple Black
Keyword(s):  
Cutting Speed ◽  
Machining Process ◽  
Depth Of Cut ◽  
Rake Face ◽  
Orthogonal Machining ◽  
Aluminum Chips ◽  
Before And After ◽  
Materials Used ◽  
Glass Knife ◽  
Very High

Tool materials used in ultramicrotomy are glass, developed by Latta and Hartmann (1) and diamond, introduced by Fernandez-Moran (2). While diamonds produce more good sections per knife edge than glass, they are expensive; require careful mounting and handling; and are time consuming to clean before and after usage, purchase from vendors (3-6 months waiting time), and regrind. Glass offers an easily accessible, inexpensive material ($0.04 per knife) with very high compressive strength (3) that can be employed in microtomy of metals (4) as well as biological materials. When the orthogonal machining process is being studied, glass offers additional advantages. Sections of metal or plastic can be dried down on the rake face, coated with Au-Pd, and examined directly in the SEM with no additional handling (5). Figure 1 shows aluminum chips microtomed with a 75° glass knife at a cutting speed of 1 mm/sec with a depth of cut of 1000 Å lying on the rake face of the knife.

Sign in / Sign up

Export Citation Format

Share Document