Water is a primary driver of the physical, geochemical and biological evolution of the Earth. The near-surface hydrosphere (exosphere) includes the atmosphere, cryosphere (glacial and polar ice), the biosphere, surface water, groundwater, and the oceans. The amounts of water in these various reservoirs of the hydrologic cycle have likely varied significantly over the past 700 Ma, with the cryosphere and continental biosphere reservoirs likely showing the most dramatic variations relative to the modern. For example, 700 Ma, during snowball-Earth conditions, the planet may have been almost entirely enveloped in ice, whereas throughout much of the Phanerozoic, greenhouse conditions predominately prevailed and the Earth had a much smaller cryosphere. Similarly, before about 444 Ma and the proliferation of land plants, the continental biosphere reservoir would have effectively non-existent. However, today, plants play a critical role in storage and transfer of water within the hydrologic cycle. Because the amount of water in the exosphere is thought to have remained relatively constant during the past 700 Ma, variations in the amounts of water held by the in the various exogenic reservoirs exert concomitant effects on other reservoirs in the exosphere.
We present a conceptual and numerical model that examines variations in the amount of water in the various reservoirs of the near-surface hydrologic cycle (exosphere) during the past 700 Ma and quantify variations in the rates of exchange of water between these reservoirs in deep time. Variations in the sizes of major reservoirs are primarily controlled by changes in global average temperature, and the movement of water between the atmosphere, surface water, and ocean reservoirs varies in concert with the waxing and waning of the cryosphere.
We find that variations in the sizes of major reservoirs are primarily controlled by changes in global average temperature, and the flux of water between the atmosphere, surface water, and ocean reservoirs varies in concert with the waxing and waning of the cryosphere, with some fluxes decreasing to 0.0 kg/yr during snowball-Earth conditions. We find that the amount of water precipitated from the atmosphere to the cryosphere increases from greenhouse conditions to -10.5°C and decreases from -10.5°C to snowball-earth conditions, highlighting "tipping-point" behavior due to changes in temperature and cryosphere surface area. The amount of surface runoff to the oceans varies in proportion to the amount of water removed from the surface water reservoir and transferred into the continental biosphere. Variations in the movement of water between near-surface reservoirs that are driven by the waxing and waning of the cryosphere and emergence and growth of plant life thus have significant implications for the transfer of weathering products to the oceans and could contribute to short-term (<1 Ma) variations in seawater composition and isotopic signatures. / Ph. D. / Water drives the evolution of the planet, and the distribution of water throughout Earth’s atmosphere and surface has varied during the geologic past. The amounts of water in the atmosphere, polar ice, the biosphere, surface water, groundwater, and the oceans have changed during the past 700 million years, and the polar ice and biosphere reservoirs have undergone the most significant changes during that time. For example, at extremely cold conditions the planet may have been covered in ice, and during warmer conditions the planet may have been covered in little to no ice. Similarly, before 444 million years ago, the biosphere on Earth’s continental surface was almost non-existent. The evolution of land plants after 444 Ma resulted in an increase in the amount of water in the biosphere. Changes in the amounts of water in one reservoir of water over time will have effects on the other reservoirs of water in the water cycle.
We produce a numerical model that examines changes in the sizes of water cycle reservoirs and the movement of water between those reservoirs during the past 700 million years. Variations in reservoir sizes are primarily controlled by changes in global average temperature, and the movement of water between the atmosphere, surface water, and ocean reservoirs varies with changes in the amount of polar ice on Earth. We find that total annual precipitation to polar ice increases from greenhouse temperatures to - 10.5°C and decreases from -10.5°C to cold snowball-earth temperatures due to changes in both temperature and the surface area of polar ice. The amount of surface runoff to the oceans varies in proportion to the amount of water removed from the surface water reservoir and transferred into the continental biosphere. Variations in the movement of water between reservoirs that are driven by the waxing and waning of polar ice and the growth of plant life have significant implications for the movement of dissolved material to the oceans and could contribute to short-term (<1 Ma) variations in seawater chemistry.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82865 |
| Date | 20 April 2018 |
| Creators | Angel, Adam M. |
| Contributors | Geosciences, Bodnar, Robert J., Gill, Benjamin C., Wilson, Alicia M., Lowell, Robert P. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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