Samuel T. Kodama

Changes in Pleistocene Antarctic temperatures often coincide with variations in Northern Hemisphere summer insolation. While models invoking global CO₂ changes and shifts in oceanic and atmospheric circulation explain the temperature coherence between the poles, the role of Southern Hemisphere insolation in local Antarctic temperatures remain unclear. Here we present a temporal and geochemical record of Antarctic surface melting recorded by evaporitic carbonate formation from eight sites spanning the Amundsen Sea to the Ross Sea and 365m - 2000m in elevation. Isotopic data indicate water sourced from surface melt that weathers local rock and saturates carbonate through evaporation. U–Th dates restrict carbonate formation to three of the five most recent periods of high Southern Hemisphere summer insolation. These observations calibrate the effective albedo of darkened surfaces near nunataks and identify a Southern Hemisphere summer insolation threshold at which surface melt can occur under polar conditions.

Changes in Pleistocene Antarctic temperatures often coincide with variations in Northern Hemisphere summer insolation. While models invoking global CO₂ changes and shifts in oceanic and atmospheric circulation explain the temperature coherence between the poles, the role of Southern Hemisphere insolation in local Antarctic temperatures remain unclear. Here we present a temporal and geochemical record of Antarctic surface melting recorded by evaporitic carbonate formation from eight sites spanning the Amundsen Sea to the Ross Sea and 365m - 2000m in elevation. Isotopic data indicate water sourced from surface melt that weathers local rock and saturates carbonate through evaporation. U–Th dates restrict carbonate formation to three of the five most recent periods of high Southern Hemisphere summer insolation. These observations calibrate the effective albedo of darkened surfaces near nunataks and identify a Southern Hemisphere summer insolation threshold at which surface melt can occur under polar conditions.

We generate three new empirically-based deglacial ice sheet histories (ice sheet thickness reconstructions) of the North American Ice Sheet Complex (ICE-NADI-1, ICE-NADI-1_min, and ICE-NADI-1_max) from 25 ka to 1 ka in 500-year intervals using a simple, steady-state numerical ice sheet model. To build the ice sheet histories, we adopt the North America Deglaciation Isochrones (NADI-1; Dalton et al., 2023). Our new ICE-NADI-1 ice sheet thickness reconstruction contains a peak North American sea-level equivalent (SLE) ice volume of 64 m of at the Last Glacial Maximum, 25 % smaller than the North American ice volume contained within ICE-7G (Roy & Peltier, 2017). North American ice saddle merging contributes 13 m SLE to global sea-level fall leading into the Last Glacial Maximum. Across Meltwater Pulse 1a (14.5–14 ka), our ICE-NADI-1 ice sheet thickness reconstruction contributes 6.3 m SLE, and the peak ice loss rate (13 mm SLE/year) is less than half the rate of ice loss in ICE-7G. Glacial isostatic adjustment simulations show that our new ICE-NADI-1 ice sheet thickness reconstruction fits relative sea-level observations across North America as well or better than previous reconstructions. Predicted present-day vertical land motion with ICE-NADI-1 differs from previous predictions by up to 9 mm per year. Because NADI-1 ice margins capture geologic uncertainty in ice margin, we are able to quantitatively assess the sensitivity of glacial isostatic adjustment predictions (relative sea level, paleotopography, and present-day vertical land motion) to ice geometry, which previously has not been possible. We find this uncertainty comparable in magnitude to that associated with unknowns in Earth structure. Ultimately, our ice sheet thickness reconstructions illustrate how 2-D ice margins inform the history of ice volume evolution, granting new insight into North American Ice Sheet Complex dynamics and the associated changes in global sea level, relative sea level, and vertical land motion.

Changes in Pleistocene Antarctic temperatures often coincide with variations in Northern Hemisphere summer insolation. While models invoking global CO₂ changes and shifts in oceanic and atmospheric circulation explain the temperature coherence between the poles, the role of Southern Hemisphere insolation in local Antarctic temperatures remain unclear. Here we present a temporal and geochemical record of Antarctic surface melting recorded by evaporitic carbonate formation from eight sites spanning the Amundsen Sea to the Ross Sea and 365m - 2000m in elevation. Isotopic data indicate water sourced from surface melt that weathers local rock and saturates carbonate through evaporation. U–Th dates restrict carbonate formation to three of the five most recent periods of high Southern Hemisphere summer insolation. These observations calibrate the effective albedo of darkened surfaces near nunataks and identify a Southern Hemisphere summer insolation threshold at which surface melt can occur under polar conditions.

We generate three new empirically-based deglacial ice sheet histories (ice sheet thickness reconstructions) of the North American Ice Sheet Complex (ICE-NADI-1, ICE-NADI-1_min, and ICE-NADI-1_max) from 25 ka to 1 ka in 500-year intervals using a simple, steady-state numerical ice sheet model. To build the ice sheet histories, we adopt the North America Deglaciation Isochrones (NADI-1; Dalton et al., 2023). Our new ICE-NADI-1 ice sheet thickness reconstruction contains a peak North American sea-level equivalent (SLE) ice volume of 64 m of at the Last Glacial Maximum, 25 % smaller than the North American ice volume contained within ICE-7G (Roy & Peltier, 2017). North American ice saddle merging contributes 13 m SLE to global sea-level fall leading into the Last Glacial Maximum. Across Meltwater Pulse 1a (14.5–14 ka), our ICE-NADI-1 ice sheet thickness reconstruction contributes 6.3 m SLE, and the peak ice loss rate (13 mm SLE/year) is less than half the rate of ice loss in ICE-7G. Glacial isostatic adjustment simulations show that our new ICE-NADI-1 ice sheet thickness reconstruction fits relative sea-level observations across North America as well or better than previous reconstructions. Predicted present-day vertical land motion with ICE-NADI-1 differs from previous predictions by up to 9 mm per year. Because NADI-1 ice margins capture geologic uncertainty in ice margin, we are able to quantitatively assess the sensitivity of glacial isostatic adjustment predictions (relative sea level, paleotopography, and present-day vertical land motion) to ice geometry, which previously has not been possible. We find this uncertainty comparable in magnitude to that associated with unknowns in Earth structure. Ultimately, our ice sheet thickness reconstructions illustrate how 2-D ice margins inform the history of ice volume evolution, granting new insight into North American Ice Sheet Complex dynamics and the associated changes in global sea level, relative sea level, and vertical land motion.

We generate three new empirically-based deglacial ice sheet histories (ice sheet thickness reconstructions) of the North American Ice Sheet Complex (ICE-NADI-1, ICE-NADI-1_min, and ICE-NADI-1_max) from 25 ka to 1 ka in 500-year intervals using a simple, steady-state numerical ice sheet model. To build the ice sheet histories, we adopt the North America Deglaciation Isochrones (NADI-1; Dalton et al., 2023). Our new ICE-NADI-1 ice sheet thickness reconstruction contains a peak North American sea-level equivalent (SLE) ice volume of 64 m of at the Last Glacial Maximum, 25 % smaller than the North American ice volume contained within ICE-7G (Roy & Peltier, 2017). North American ice saddle merging contributes 13 m SLE to global sea-level fall leading into the Last Glacial Maximum. Across Meltwater Pulse 1a (14.5–14 ka), our ICE-NADI-1 ice sheet thickness reconstruction contributes 6.3 m SLE, and the peak ice loss rate (13 mm SLE/year) is less than half the rate of ice loss in ICE-7G. Glacial isostatic adjustment simulations show that our new ICE-NADI-1 ice sheet thickness reconstruction fits relative sea-level observations across North America as well or better than previous reconstructions. Predicted present-day vertical land motion with ICE-NADI-1 differs from previous predictions by up to 9 mm per year. Because NADI-1 ice margins capture geologic uncertainty in ice margin, we are able to quantitatively assess the sensitivity of glacial isostatic adjustment predictions (relative sea level, paleotopography, and present-day vertical land motion) to ice geometry, which previously has not been possible. We find this uncertainty comparable in magnitude to that associated with unknowns in Earth structure. Ultimately, our ice sheet thickness reconstructions illustrate how 2-D ice margins inform the history of ice volume evolution, granting new insight into North American Ice Sheet Complex dynamics and the associated changes in global sea level, relative sea level, and vertical land motion.

During the Mid‐Pleistocene Transition (∼1,250–750 ka) glacial cycle amplitude and duration increased, from smaller, ∼40 ka‐period middle Pleistocene ice sheets to larger, ∼100 ka‐period late Pleistocene ice sheets. This transition in glacial period and size has been attributed to some combination of long‐term, monotonic, carbon and climate system forcings and ice sheet feedbacks. The early Pleistocene glacial cycles (2,700‐2,000 ka), however, exhibit a ∼100 ka periodicity that coincides with low‐latitude advances of the Laurentide ice sheet further south than the Last Glacial Maximum, and a synthesis of global climate records reveals that the early Pleistocene glacial cycles imparted a larger impact on the climate system than the middle Pleistocene glacial cycles. The occurrence of large, ∼100 ka duration glacial cycles during the early and late Pleistocene necessitates a periodic forcing. We demonstrate that Earth's 2,400 ka eccentricity cycle, through its modulation of precession, controls the magnitude of ice sheet growth at obliquity minima and grows large ice sheets during the early and late Pleistocene. We then relate ice sheet size to glacial cycle duration by showing that terminations are more likely to occur when ice sheets exceed a size threshold and show that during the early and late Pleistocene variable precession conditions result in either: (a) limited growth, such that a termination cannot occur, extending glacial cycle duration, or (b) the largest growths of the Pleistocene. Therefore, we propose that the magnitude and period of Pleistocene ice ages are paced by long‐period changes in the eccentricity of Earth's orbit.

The glacial isostatic adjustment (GIA) and sea level modeling communities have historically lagged other fields in adhering to the FAIR principles of making model outputs findable, accessible, interoperable, and reusable – a delay that has slowed scientific discovery. While sharing model outputs has improved recently, usability of available outputs continues to be hindered by lack of standardization. Meanwhile, legacy model outputs can be lost as the technology storing them grows obsolete and their creators retire or leave academia.The GIAmachine initiative addresses this problem. GIAmachine aims to make accessible as many published GIA and sea level model outputs as are retrievable bycataloguing and standardizing published GIA and sea level model outputs; contacting authors of published-but-inaccessible models to encourage them to upload their outputs to DOI-minting repositories;partnering with the GHub science gateway to make a long-term home for these newly available outputs;building Jupyter notebooks on GHub that make these models interoperable and easy to use; and encouraging the GIA and sea level modeling communities to follow the FAIR principles. Our poster will introduce the GIAmachine online portal and outline outstanding challenges. We appreciate community input for designing a living resource that meets the specific needs of current and future scientists.