Roger Cameron Creel

Understanding the behavior of Earth's ice sheets during the Holocene (~11.7 thousand years ago to present) helps us place climate warming due to human activities in the context of natural climate variability. Mounting field evidence from the Antarctic and Greenland ice sheets indicates that both ice sheets retreated past their present extents over the last 10,000 years, then readvanced to the present. By contrast, standard global ice sheet reconstructions model global mean sea level as reaching present-levels between 3 and 6 thousand years ago and remaining there until the pre-industrial. Using an ensemble of glacial isostatic adjustment models and a large collection of relative sea level (RSL) data, I show that global mean sea level (GMSL) likely exceeded present levels during the mid-Holocene. I also find that regardless of emissions scenario, GMSL by 2100 will be higher than at any time in more than 100,000 years.

Versions of this project were presented at American Geophysical Union 2021, European Geophysical Union 2022, World Climate Research Program Sea Level meeting 2022, SCAR-INSTANT (Instabilities in Antarctica) meeting 2023, and WAIS (West Antarctic Ice Sheet) meeting 2023. The manuscript is available as an EarthArXiV preprint here, and is currently in revision at Nature Communications.

Subsea permafrost, which is perennially cryotic sediment lying below sea level, forms when rising seas flood terrestrial permafrost on the Arctic continental shelf. Understanding subsea permafrost is important because it contains vast amounts of carbon, which, if released, could enter the atmosphere as greenhouse gasses. RSL variations control subsea permafrost stability, yet no existing subsea permafrost model includes glacial isostatic adjustment (GIA). I address this deficit by adding GIA into a model of pan-Arctic subsea permafrost for the last 400,000 years. This model enables me and my colleagues to estimate present-day subsea permafrost extent, then extend the simulation ~1000 years into the future to quantify how much subsea permafrost will thaw with high emissions.

A talk based on this project was presented at the 2022 PALSEA Annual meeting, a 2022 NASA-GISS Sea Level seminar, and a 2023 PalaeoPERCS seminar. The manuscript is available as an EarthArXiV preprint here and was just (Jan 3) accepted at Nature Communications.

Global mean sea level (GMSL) during the last interglacial (LIG, 130 – 115 thousand years ago) period was higher than present, likely because more sunlight hit Earth’s high latitudes. Estimates of LIG sea-level require measuring the elevation and age of sediments or organisms that formed near sea level. Those measurements must be corrected for the gravitational, rotational, and deformational effects of water loading of the solid Earth, together termed glacial isostatic adjustment (GIA). Uncertainty about Earth’s rheology and past ice history undermine this GIA correction, and, by extension, estimates of LIG relative and global mean sea level. We address this challenge by comparing LIG sea-level data from the Lucayan archipelago and stratigraphic information gathered during fieldwork to a large ensemble of GIA predictions within a Bayesian statistical framework. Our posterior LIG GMSL curves are lower than many previous estimates, suggesting that the West Antarctic Ice Sheet may be less vulnerable to future collapse. We also explore whether oscillations in LIG sea level can clarify fundamental questions about the stability of ice sheets during the LIG. For instance, how long did the Laurentide ice sheet persist and how completely did the West Antarctic Ice Sheet collapse during the LIG?

This work is published in Proceedings of the National Academy of Sciences in 2021, Science Advances and Quaternary Science Reviews in 2023, and is under revision at Geology magazine.

RSL patterns near ice sheets can open a valuable window into the interplay of ice sheet melt and local solid earth effects. Norway is singular for having detailed sea level records extending nearly 20,000 years into the past. We collect and quality-control 1000 RSL observations from the Norwegian coastline, then use an ensemble of Bayesian statistical models to assess spatiotemporal patterns of Norwegian RSL change.

One paper related to this work was published in Quaternary Science Reviews in 2022 and another was just (Jan 20) accepted at Journal of Quaternary Science.

Interest in the mathematical foundations of Bayesian modeling led me to collaborate on two papers with Professor William Menke at Columbia. Our first paper explores Gaussian process regression, a powerful Bayesian modeling technique and staple of machine learning, through the lens of geophysical inverse theory. Our second explains what makes differential data attractive, when they should not be used, and the situations to which they are well suited.

The papers together have important practical applications and are ripe for interdisciplinary application. For example, we can pinpoint where more observations of ancient—or modern—sea level would most improve existing models. Our tool helps researchers planning expensive field work prioritize locations from which additional data would most benefit communities in making sea-level mitigation decisions.

These works were published in Bulletin of the Seismological Society of America in 2021 and in Surveys in Geophysics in 2022.

The Ordovician-Silurian glaciation (450 – 380 million years ago) marked the first ice sheet collapse of the Phanerozoic era. Understanding how ice sheets could have survived in a world with atmospheric CO2 concentrations twenty times present levels requires analysis of that period’s sedimentary rocks. I applied petrographic, chemostratigraphic, and trace-elemental analysis to Ordovician-Silurian carbonates to determine that they recorded contemporaneous climate signals despite significant post-depositional alteration. I also contributed to a study that used clumped isotope measurements of calcitic and phosphatic marine fossils to measure Ordovician tropical sea surface temperatures and seawater oxygen isotope ratios.

This work was published in Geochimica et Cosmochimica Acta in 2018, Palaeogeography, Palaeoclimatology, Palaeoecology in 2016, and Geology in 2015.