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Reconstructing and Understanding How Past Warming Affected Sea Level, Ice Sheets, and Permafrost.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Reconstructing and Understanding How Past Warming Affected Sea Level, Ice Sheets, and Permafrost./
Author:	Creel, Roger Cameron.
Description:	1 online resource (231 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-06, Section: B.
Contained By:	Dissertations Abstracts International85-06B.
Subject:	Geophysics. -
Online resource:	click for full text (PQDT)
ISBN:	9798380909761

Reconstructing and Understanding How Past Warming Affected Sea Level, Ice Sheets, and Permafrost.
Creel, Roger Cameron.

Reconstructing and Understanding How Past Warming Affected Sea Level, Ice Sheets, and Permafrost. - 1 online resource (231 pages)

Source: Dissertations Abstracts International, Volume: 85-06, Section: B.

Thesis (Ph.D.)--Columbia University, 2024.

Includes bibliographical references

Natural climate variability over the past hundreds of thousands of years provides a unique window into the drivers and processes that connect different parts of our climate system. This thesis investigates interactions between Earth's mantle, its oceans, and ice sheets over the Quaternary. The dominant process that connects these spheres is glacial isostatic adjustment (GIA), which is the deformation of Earth's mantle (and consequently its surface, gravity field, and sea level) in response to changes in ice and ocean mass loading. This dissertation focuses on time periods during which surface temperatures were warming or warmer than today to understand how these warm intervals affected ice sheets, permafrost, and sea level. I put my results in the context of current and future warming to improve predictions of future change and compare natural to anthropogenic variability.The thesis opens with an investigation of relative (i.e., local) sea level around Norway over the last 16 thousand years (ka). Postglacial Norwegian sea level, though dominated by postglacial rebound and associated sea-level fall, is punctuated by two periods of sea-level rise. The causes of these episodes, named the 'Tapes' and 'Younger Dryas' transgressions, remain debated despite more than a century of study. I produce the first standardized and quality-controlled compilation of Norwegian sea-level data, then employ an ensemble of empirical Bayesian hierarchical statistical models to estimate relative sea level along the Norwegian coastline. The resulting model enables an examination of the relative contributions of isostatic rebound and global mean sea-level (GMSL) rise to the Tapes transgression, and lays the foundation for future applications such as inversion of sea-level data for Fennoscandian ice-sheet volume and the comparison of modern rates of Norwegian sea-level rise to pre-industrial rates.Chapter Two aims to better understand sea-level and Antarctic ice-sheet variability during the Holocene, which is the last time global temperatures may have exceeded early industrial (1850 CE) values. Both the Greenland and Antarctic ice sheets likely retreated inland of their present-day extents during the Holocene, yet previous GMSL reconstructions suggest that Holocene GMSL never surpassed early industrial levels. I use relative sea-level observations, GIA predictions, and new estimates of postglacial thermosteric sea-level and mountain glacier evolution to show that the available evidence is consistent with GMSL that exceeded early industrial levels in the mid-Holocene (8-4 ka) and an Antarctic Ice Sheet that was smaller than present at some time in the last 6000 years. I also demonstrate that Antarctic ice retreat lags Antarctic temperature by 250 years, which highlights the vulnerability of the future Antarctic ice sheet to 20th and 21st century warming. Comparing our reconstruction to projections for the future indicates that GMSL rise in the next 125 years will very likely (\uD835\uDC43>0.9) be faster than at any time in the last 5000 years, and that by 2080 GMSL will more likely than not be the highest of any time in the past 115,000 years.In Chapter Three, I explore the effect of GIA on subsea permafrost. Subsea permafrost forms when sea-level rise submerges terrestrial permafrost. Subsea permafrost underlies ∼1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for GIA, which leads to deviations of local sea level from the global mean. I incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces estimates of present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects and deformation related to Northern Hemisphere ice sheets. Additionally, I extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change's sixth assessment report. I find that subsea permafrost is preserved under a low-emissions scenario but mostly disappears under a high-emissions scenario.In the final chapter, I turn to the Last Interglacial (LIG, 129-116 ka), a time interval considered a partial analogue for future warming due to its elevated temperatures. Observations of oscillations in LIG local sea level, combined with an assumption that the Laurentide Ice Sheet collapsed prior to the LIG, have been used to infer Antarctic and Greenland ice-sheet melt histories as well as oscillations in LIG global mean sea level. However, evidence of a Laurentide Ice Sheet outburst flood at ∼125 ka suggests that Laurentide Ice Sheet remnants may have persisted longer into the LIG than typically thought. Here we explore the effect on LIG sea level of a Laurentide collapse that occurred during rather than prior to the LIG and a West Antarctic Ice Sheet that collapsed in the early LIG. We find that due to GIA, this asynchronous ice-sheet evolution produces a global pattern of sea-level oscillations that is similar to field observations. We demonstrate that the oscillation pattern can be produced by the combination of ongoing GIA from the penultimate deglaciation with the fingerprint of West Antarctic collapse. By showing that LIG Laurentide persistence would lead to an RSL oscillation that accords with field evidence, we highlight the need for LIG climate simulations to consider Laurentide ice-sheet dynamics and for more constraints on the LIG history of the Laurentide Ice Sheet.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798380909761Subjects--Topical Terms:

686174
Geophysics.
Subjects--Index Terms:

Future projectionIndex Terms--Genre/Form:

554714
Electronic books.

Reconstructing and Understanding How Past Warming Affected Sea Level, Ice Sheets, and Permafrost.
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520 $a Natural climate variability over the past hundreds of thousands of years provides a unique window into the drivers and processes that connect different parts of our climate system. This thesis investigates interactions between Earth's mantle, its oceans, and ice sheets over the Quaternary. The dominant process that connects these spheres is glacial isostatic adjustment (GIA), which is the deformation of Earth's mantle (and consequently its surface, gravity field, and sea level) in response to changes in ice and ocean mass loading. This dissertation focuses on time periods during which surface temperatures were warming or warmer than today to understand how these warm intervals affected ice sheets, permafrost, and sea level. I put my results in the context of current and future warming to improve predictions of future change and compare natural to anthropogenic variability.The thesis opens with an investigation of relative (i.e., local) sea level around Norway over the last 16 thousand years (ka). Postglacial Norwegian sea level, though dominated by postglacial rebound and associated sea-level fall, is punctuated by two periods of sea-level rise. The causes of these episodes, named the 'Tapes' and 'Younger Dryas' transgressions, remain debated despite more than a century of study. I produce the first standardized and quality-controlled compilation of Norwegian sea-level data, then employ an ensemble of empirical Bayesian hierarchical statistical models to estimate relative sea level along the Norwegian coastline. The resulting model enables an examination of the relative contributions of isostatic rebound and global mean sea-level (GMSL) rise to the Tapes transgression, and lays the foundation for future applications such as inversion of sea-level data for Fennoscandian ice-sheet volume and the comparison of modern rates of Norwegian sea-level rise to pre-industrial rates.Chapter Two aims to better understand sea-level and Antarctic ice-sheet variability during the Holocene, which is the last time global temperatures may have exceeded early industrial (1850 CE) values. Both the Greenland and Antarctic ice sheets likely retreated inland of their present-day extents during the Holocene, yet previous GMSL reconstructions suggest that Holocene GMSL never surpassed early industrial levels. I use relative sea-level observations, GIA predictions, and new estimates of postglacial thermosteric sea-level and mountain glacier evolution to show that the available evidence is consistent with GMSL that exceeded early industrial levels in the mid-Holocene (8-4 ka) and an Antarctic Ice Sheet that was smaller than present at some time in the last 6000 years. I also demonstrate that Antarctic ice retreat lags Antarctic temperature by 250 years, which highlights the vulnerability of the future Antarctic ice sheet to 20th and 21st century warming. Comparing our reconstruction to projections for the future indicates that GMSL rise in the next 125 years will very likely (\uD835\uDC43>0.9) be faster than at any time in the last 5000 years, and that by 2080 GMSL will more likely than not be the highest of any time in the past 115,000 years.In Chapter Three, I explore the effect of GIA on subsea permafrost. Subsea permafrost forms when sea-level rise submerges terrestrial permafrost. Subsea permafrost underlies ∼1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for GIA, which leads to deviations of local sea level from the global mean. I incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces estimates of present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects and deformation related to Northern Hemisphere ice sheets. Additionally, I extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change's sixth assessment report. I find that subsea permafrost is preserved under a low-emissions scenario but mostly disappears under a high-emissions scenario.In the final chapter, I turn to the Last Interglacial (LIG, 129-116 ka), a time interval considered a partial analogue for future warming due to its elevated temperatures. Observations of oscillations in LIG local sea level, combined with an assumption that the Laurentide Ice Sheet collapsed prior to the LIG, have been used to infer Antarctic and Greenland ice-sheet melt histories as well as oscillations in LIG global mean sea level. However, evidence of a Laurentide Ice Sheet outburst flood at ∼125 ka suggests that Laurentide Ice Sheet remnants may have persisted longer into the LIG than typically thought. Here we explore the effect on LIG sea level of a Laurentide collapse that occurred during rather than prior to the LIG and a West Antarctic Ice Sheet that collapsed in the early LIG. We find that due to GIA, this asynchronous ice-sheet evolution produces a global pattern of sea-level oscillations that is similar to field observations. We demonstrate that the oscillation pattern can be produced by the combination of ongoing GIA from the penultimate deglaciation with the fingerprint of West Antarctic collapse. By showing that LIG Laurentide persistence would lead to an RSL oscillation that accords with field evidence, we highlight the need for LIG climate simulations to consider Laurentide ice-sheet dynamics and for more constraints on the LIG history of the Laurentide Ice Sheet.
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