Snowball Earth: Skating On Thin Ice? There is
Description: Snowball Earth: Skating On Thin Ice? There is evidence of at least two intervals of widespread glaciation during the late Neoproterozoic (600-800 Myr ago), which are commonly referred to as Snowball Earth episodes. The global nature of
Related Topics
Download Presentation
"Snowball Earth: Skating On Thin Ice? There is" is the property of its rightful owner. Permission is granted to download and print the materials on this website for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Presentation Transcript
slide1. Snowball Earth: Skating On Thin Ice? There is evidence of at least two intervals of widespread glaciation during the late Neoproterozoic (600-800 Myr ago), which are commonly referred to as “Snowball Earth” episodes. The global nature of these events is indicated by the fact that glacial deposits are found at low paleolatitudes during this time. Models of a global glacial event have produced a variety of solutions at low latitudes: thick ice, thin ice, slushball, and open ocean. The latter two models are similar, except that the slushball model has its ice-line at higher latitudes. To be viable, a model has to be able to account for the survival of life through the glaciations and also explain the existence of cap carbonates and other glacial debris deposited at low latitudes.. What is it, though, that causes some models to produce thin ice near the equator and others to have open water there? We examine this question using a zonally symmetric energy balance climate model (EBM) with flowing sea glaciers and the GENESIS Global Climate Model (GCM) to determine what parameter ranges produce each type of solution. Abstract Snowball Earth Solutions Energy Balance Model (EBM)
Coupled energy-balance climate/sea-glacier model originally described by Pollard and Kasting (2005). The model is zonally symmetric, seasonal, and applied to an all-ocean planet on a 1˚ latitudinal grid using a time step of 5 days. A single-layer atmosphere is used, and additional explicit layers are used for snow, ice, and upper ocean, all of which exchange heat and water vertically with the atmosphere. The EBM solves for both atmospheric and oceanic horizontal transport, and includes a hydrologic cycle.
GENESIS Global Climate Model (GENESIS GCM)
We used the GENESIS GCM version 3 described in Alder et al. (2011). The GCM consists of an atmospheric general circulation model coupled to multilayer surface models of vegetation, soil, ice, and snow. Sea-surface temperatures and sea ice are computed using a 50-m slab oceanic mixed layer, and a dynamic-thermodynamic sea-ice model. For our purposes, we ran the model as an aqua planet and started from an ice-free state. Models GCM Calculations: We did four runs of the GCM so far for 4 different values of CO2: 1000 ppm, 1700 ppm, 2500 ppm, and 10000 ppm. Parameters in the GCM were changed to match up with the run setup used in Abbot et al. (2011). Results cont. Conclusions and Future Work The purpose of this project was to find out what causes some models to produce thin ice near the equator and others, open water. For our EBM calculations, we had to turn off the sea glacier flow and the penetrative solar radiation into the ice in order to produce open water at the equator. Even then our band was much narrower than that found by Abbot et al. (2011). For our GCM calculations, we turned off the ocean heat transport, a simple penetrative radiation scheme, and modified the albedos. Our 1700 and 2500 ppm of CO2 runs yielded higher surface temperatures and open water at and around the equator. In our Figure 9 the positioning of our solutions seems to suggest that our curve will take on quite a different shape from Abbot et al. (2011). Obviously more runs are needed to fill out our curve, and that will be a part of the future of this project. In addition, we plan to incorporate a physically realistic treatment of penetrative solar radiation in ice in the GCM to see what impact that has on the solutions. References Abbot, DS, Voigt, A, and Koll, D (2011) The Jormungand global climate state and implications for Neoproterozoic glaciations. J. Geophys. Res., 116, D18103. Alder, JR, Hostetler, SW, Pollard, D, and Schmittner, A (2011) Evaluation of a present-day climate simulation with a new coupled atmosphere-ocean model GENMOM. Geosci. Model Dev., 3, 4, 69-83.
Hyde, WT, Crowley, TJ, Baum, SK, and Peltier, WR (2000) Neoproterozoic“Snowball Earth” simulations with a coupled climate/ice-sheet model. Nature, 405(6785), 425-429. Kirschvink, J (1992) Late Proterozoic low-latitude global glaciation: The snowball Earth, in The Proterozoic Biosphere: A Multidisciplinary Study, edited by J Schopf and C Klein, pp. 51-52, Cambridge Univ. Press, New York. McKay, C (2000) Thickness of tropical ice and photosynthesis on a snowball Earth, Geophys. Res. Lett., 27(14), 2153-2156. Pollard, D and Kasting, JF (2005) Snowball Earth: A thin-ice solution with flowing sea glaciers, J. Geophys. Res., 110, C07010, doi:10.1029/2004JC002525. Pollard, D and Kasting, JF (2006) Reply to comment by Stephen G. Warren and Richard E. Brandt on “Snowball Earth: A thin-ice solution with flowing sea glaciers,” J. Geophys. Res., 111, C09017, doi:10.1029/2006JC003488. Acknowledgments and Contact This project is supported by NASA Exobiology grant 424-07.
For questions or comments, please contact April L Roberson at alr335@psu.edu. “Hard Snowball” model (Kirshvink, 1990):
Kilometer-thick ice everywhere. Accounts for cap carbonates. Not viable because kilometers of ice prevent the penetration of light necessary for the photosynthetic biota below.
“Thin-ice” model (McKay, 2000) (Pollard and Kasting, 2005, 2006) : The “thin-ice” model has been discussed previously and can account for continuation of photosynthetic life and glacial deposits at low paleolatitudes. McKay predicts the ice at the equator would be less than 10 m thick, whereas Pollard and Kasting found it to be around 2m in their model.
“Slushball Earth” model (Hyde et al., 2000):
Tropics remain ice-free, thus allowing for the survival of photosynthetic life. Climate state is metastable and, hence, improbable. Not viable as it does not allow the formation of cap carbonates.
“Jormungand” or “open-ocean” model (Abbot et al., 2011):
The recently proposed “open-ocean” or “Jormungand” model can also explain the continuation of photosynthetic life and the existence of cap carbonates at low paleolatitudes. This solution features a band of open water (+/- 10˚) about the equator surrounded by ice poleward from there.
The two solutions we are looking at in this project are the “Thin-ice” model proposed by Pollard and Kasting (2005) and the “Jormungand” model proposed by Abbot et al. (2011). These are the two prevailing solutions that can explain the survival of photosynthetic life and the formation/location of cap carbonates and other glacial debris. These two solutions are very similar in appearance as well, except instead of open water from +/- 10˚, Pollard and Kasting get thin ice of 2 m from roughly +/- 13˚ of the equator.
In the following models we seek to recreate a “Jormungand” state from the same models used by Pollard and Kasting (2005, 2006) that showed thin-ice at the equator. 1Geosciences, Penn State University, University Park, PA, United States, 2Earth and Environmental Systems Institute, Penn State University, University Park, PA, United States April L Roberson1, April M Stout1, Dave Pollard2, James F Kasting1 Results EBM Calculations: We ran the EBM to equilibrium in several different tests (shown below) to attempt to obtain open water at the equator. All of these runs are without sea glacier flow. Fig 1: Plot of Surface temperature, Surface albedo, and ice thickness vs. Latitude. No Ocean heat transport yields thin-ice at the equator. Fig 2: Same plot as Fig 1, but with Penetrative solar radiation into the ice turned off. This yields an open water solution. Fig 3: Same plot as Fig 1, but with no ocean heat transport and penetrative solar radiation into the ice turned off. This yields very thin ice at the equator. Fig 4: Same plot as Fig 1, but with albedos used in Abbot et al. (2011) for their EBM. This yields thin ice at the equator. Fig 5: Same as Fig 4, but with no penetrative solar radiation. This yields thin ice at the equator. Fig 6: Same as Fig 4, but with no penetrative solar radiation and no ocean heat transport. This yields thin ice at the equator. Fig 7: Plot of Global temperature vs. GCM year. Run for 4 different CO2 values to equilibrium. Fig 8: Plot of Ice fraction vs. GCM year. Run for 4 different CO2 values to equilibrium. Fig 9: Our 4 runs with CO2 values (1000, 1700, 2500, and 10000 ppm) superimposed on Figure 1 from Abbot et al. (2011). Based on the positioning of our solutions it appears that we will have a different curve than Abbot et al. (2011). Fig 11: Plot of temperature vs. latitude (ocean only) for our run ‘b’ (1700 ppm of CO2). The temperature gets above freezing at and around the equator. Fig 12: Plot of ice fraction vs. latitude (ocean only) for our run ‘b’ (1700 ppm of CO2). The ice fraction goes to zero from about +/- 25˚ of the equator. Fig 13: Plot of temperature vs. latitude (ocean only) for our run ‘c’ (2500 ppm of CO2). The temperature gets above freezing from about +/- 60˚ of the equator (similar to modern day). Fig 14: Plot of ice fraction vs. latitude (ocean only) for our run ‘c’ (2500 ppm of CO2). The ice fraction goes to zero from about +/- 55-60˚ of the equator (similar to modern day). Fig 10: Global map of ice fraction from March and September for our ‘c’ run (2500 ppm of CO2).<br>
Coupled energy-balance climate/sea-glacier model originally described by Pollard and Kasting (2005). The model is zonally symmetric, seasonal, and applied to an all-ocean planet on a 1˚ latitudinal grid using a time step of 5 days. A single-layer atmosphere is used, and additional explicit layers are used for snow, ice, and upper ocean, all of which exchange heat and water vertically with the atmosphere. The EBM solves for both atmospheric and oceanic horizontal transport, and includes a hydrologic cycle.
GENESIS Global Climate Model (GENESIS GCM)
We used the GENESIS GCM version 3 described in Alder et al. (2011). The GCM consists of an atmospheric general circulation model coupled to multilayer surface models of vegetation, soil, ice, and snow. Sea-surface temperatures and sea ice are computed using a 50-m slab oceanic mixed layer, and a dynamic-thermodynamic sea-ice model. For our purposes, we ran the model as an aqua planet and started from an ice-free state. Models GCM Calculations: We did four runs of the GCM so far for 4 different values of CO2: 1000 ppm, 1700 ppm, 2500 ppm, and 10000 ppm. Parameters in the GCM were changed to match up with the run setup used in Abbot et al. (2011). Results cont. Conclusions and Future Work The purpose of this project was to find out what causes some models to produce thin ice near the equator and others, open water. For our EBM calculations, we had to turn off the sea glacier flow and the penetrative solar radiation into the ice in order to produce open water at the equator. Even then our band was much narrower than that found by Abbot et al. (2011). For our GCM calculations, we turned off the ocean heat transport, a simple penetrative radiation scheme, and modified the albedos. Our 1700 and 2500 ppm of CO2 runs yielded higher surface temperatures and open water at and around the equator. In our Figure 9 the positioning of our solutions seems to suggest that our curve will take on quite a different shape from Abbot et al. (2011). Obviously more runs are needed to fill out our curve, and that will be a part of the future of this project. In addition, we plan to incorporate a physically realistic treatment of penetrative solar radiation in ice in the GCM to see what impact that has on the solutions. References Abbot, DS, Voigt, A, and Koll, D (2011) The Jormungand global climate state and implications for Neoproterozoic glaciations. J. Geophys. Res., 116, D18103. Alder, JR, Hostetler, SW, Pollard, D, and Schmittner, A (2011) Evaluation of a present-day climate simulation with a new coupled atmosphere-ocean model GENMOM. Geosci. Model Dev., 3, 4, 69-83.
Hyde, WT, Crowley, TJ, Baum, SK, and Peltier, WR (2000) Neoproterozoic“Snowball Earth” simulations with a coupled climate/ice-sheet model. Nature, 405(6785), 425-429. Kirschvink, J (1992) Late Proterozoic low-latitude global glaciation: The snowball Earth, in The Proterozoic Biosphere: A Multidisciplinary Study, edited by J Schopf and C Klein, pp. 51-52, Cambridge Univ. Press, New York. McKay, C (2000) Thickness of tropical ice and photosynthesis on a snowball Earth, Geophys. Res. Lett., 27(14), 2153-2156. Pollard, D and Kasting, JF (2005) Snowball Earth: A thin-ice solution with flowing sea glaciers, J. Geophys. Res., 110, C07010, doi:10.1029/2004JC002525. Pollard, D and Kasting, JF (2006) Reply to comment by Stephen G. Warren and Richard E. Brandt on “Snowball Earth: A thin-ice solution with flowing sea glaciers,” J. Geophys. Res., 111, C09017, doi:10.1029/2006JC003488. Acknowledgments and Contact This project is supported by NASA Exobiology grant 424-07.
For questions or comments, please contact April L Roberson at alr335@psu.edu. “Hard Snowball” model (Kirshvink, 1990):
Kilometer-thick ice everywhere. Accounts for cap carbonates. Not viable because kilometers of ice prevent the penetration of light necessary for the photosynthetic biota below.
“Thin-ice” model (McKay, 2000) (Pollard and Kasting, 2005, 2006) : The “thin-ice” model has been discussed previously and can account for continuation of photosynthetic life and glacial deposits at low paleolatitudes. McKay predicts the ice at the equator would be less than 10 m thick, whereas Pollard and Kasting found it to be around 2m in their model.
“Slushball Earth” model (Hyde et al., 2000):
Tropics remain ice-free, thus allowing for the survival of photosynthetic life. Climate state is metastable and, hence, improbable. Not viable as it does not allow the formation of cap carbonates.
“Jormungand” or “open-ocean” model (Abbot et al., 2011):
The recently proposed “open-ocean” or “Jormungand” model can also explain the continuation of photosynthetic life and the existence of cap carbonates at low paleolatitudes. This solution features a band of open water (+/- 10˚) about the equator surrounded by ice poleward from there.
The two solutions we are looking at in this project are the “Thin-ice” model proposed by Pollard and Kasting (2005) and the “Jormungand” model proposed by Abbot et al. (2011). These are the two prevailing solutions that can explain the survival of photosynthetic life and the formation/location of cap carbonates and other glacial debris. These two solutions are very similar in appearance as well, except instead of open water from +/- 10˚, Pollard and Kasting get thin ice of 2 m from roughly +/- 13˚ of the equator.
In the following models we seek to recreate a “Jormungand” state from the same models used by Pollard and Kasting (2005, 2006) that showed thin-ice at the equator. 1Geosciences, Penn State University, University Park, PA, United States, 2Earth and Environmental Systems Institute, Penn State University, University Park, PA, United States April L Roberson1, April M Stout1, Dave Pollard2, James F Kasting1 Results EBM Calculations: We ran the EBM to equilibrium in several different tests (shown below) to attempt to obtain open water at the equator. All of these runs are without sea glacier flow. Fig 1: Plot of Surface temperature, Surface albedo, and ice thickness vs. Latitude. No Ocean heat transport yields thin-ice at the equator. Fig 2: Same plot as Fig 1, but with Penetrative solar radiation into the ice turned off. This yields an open water solution. Fig 3: Same plot as Fig 1, but with no ocean heat transport and penetrative solar radiation into the ice turned off. This yields very thin ice at the equator. Fig 4: Same plot as Fig 1, but with albedos used in Abbot et al. (2011) for their EBM. This yields thin ice at the equator. Fig 5: Same as Fig 4, but with no penetrative solar radiation. This yields thin ice at the equator. Fig 6: Same as Fig 4, but with no penetrative solar radiation and no ocean heat transport. This yields thin ice at the equator. Fig 7: Plot of Global temperature vs. GCM year. Run for 4 different CO2 values to equilibrium. Fig 8: Plot of Ice fraction vs. GCM year. Run for 4 different CO2 values to equilibrium. Fig 9: Our 4 runs with CO2 values (1000, 1700, 2500, and 10000 ppm) superimposed on Figure 1 from Abbot et al. (2011). Based on the positioning of our solutions it appears that we will have a different curve than Abbot et al. (2011). Fig 11: Plot of temperature vs. latitude (ocean only) for our run ‘b’ (1700 ppm of CO2). The temperature gets above freezing at and around the equator. Fig 12: Plot of ice fraction vs. latitude (ocean only) for our run ‘b’ (1700 ppm of CO2). The ice fraction goes to zero from about +/- 25˚ of the equator. Fig 13: Plot of temperature vs. latitude (ocean only) for our run ‘c’ (2500 ppm of CO2). The temperature gets above freezing from about +/- 60˚ of the equator (similar to modern day). Fig 14: Plot of ice fraction vs. latitude (ocean only) for our run ‘c’ (2500 ppm of CO2). The ice fraction goes to zero from about +/- 55-60˚ of the equator (similar to modern day). Fig 10: Global map of ice fraction from March and September for our ‘c’ run (2500 ppm of CO2).<br>