National Aeronautics and Space Administration

Sea Level Rise Seminar
Speaker: Mainak Mondal (NYU)
Title: Effects of Ambient Currents and Tides on Melting at the Grounding Line of Thwaites Glacier

This is an on-line, virtual presentation only. Please consult with event host Patrick Alexander for connection details.

Abstract:
The stability of Thwaites Glacier's grounding line is central to projections of West Antarctic Ice Sheet retreat and global sea-level rise. While warm water intrusions are a known driver of melting, the role of along-shelf ambient currents and tidal forcing remains underexplored. Using a high-resolution, idealized MITgcm model, we investigate how ambient flow, tides, and subglacial discharge modulate circulation and melting near the grounding line.


We find that even weak ambient currents disrupt classical buoyancy-driven circulation by introducing Ekman layers and geostrophic flows that redistribute heat and freshwater. A positive along-shelf flow drives Ekman transport toward the grounding line, causing accumulation of cold, stratified water and the formation of a stable freshwater lens. Reversing the flow disrupts this lens and alters the melt pattern. The addition of subglacial discharge weakens the lens further, modifying vertical mixing and the delivery of heat to the ice-ocean interface. Tidal forcing generates multiple freshwater lenses and enhances vertical mixing via residual circulation, strongly influencing temporal and spatial variability in melt rates.

These findings underscore the importance of including realistic three-dimensional ocean dynamics -- especially tides, subglacial discharge, and shore-parallel flows—in models of grounding-zone melting. By linking stratified Ekman transport, tidal mixing, and freshwater lens dynamics, this study provides new insights into the sensitivity of grounding-line melt to small-scale ocean processes and helps improve projections of Antarctic ice-sheet retreat.

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GISS Lunch Seminar
Speaker: Daniele Visioni (Cornell Univ)
Title: Climate Intervention with Stratospheric Aerosols: steps towards a more robust assessment

This is a hybrid presentation, presented both in-person and on-line. Please consult with event host Joseph Kelly for connection details if you wish to virtually attend.

Abstract:
Past explosive volcanic eruptions have shown that large SO2 injections in the stratosphere have a temporary cooling effect on our planet temperatures. This has led some to consider whether artificial injections of sulfate (Stratospheric Aerosols Intervention, SAI) could temporarily ameliorate some of the effects of climate change, as a supplement to emission reduction. Numerous climate models have analyzed the potential impacts of SAI: based on current international multi-model comparisons as part of the Geoengineering Model Intercomparison Project (GeoMIP), and large ensembles of simulations we produced with the Community Earth System Model, I will describe broad areas of agreement but also highlight large inter-model differences and shortcomings from the simulation of the aerosol cloud downstream to regional climate changes, as well as discuss the problems and some potential solutions with fully mapping the potential space of different SAI applications.

Building on this, I will share some personal insights about areas where future research should be headed, as the topic of Climate Intervention gains relevance internationally, especially drawing on recent discussions held at the Sixth Session of the United Nation Environmental Agency held in February 2024 and through the World Climate Research Programme Lighthouse Activity on Climate Intervention Research. It is clear that the basis for any potential future agreement around this topic can't just include improved modeling tools and better observational capabilities, but also a wide range of collaborations across disciplines both in the natural and social realms and a strong commitment to international cooperation.

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Special Seminar
Speaker: Clare Singer (Univ. Colorado)
Title: Earth's energy imbalance: Why is it changing? What does it mean?

This is a hybrid presentation, presented both in-person and on-line. Please consult with event host Joseph Kelly for connection details if you wish to virtually attend.

Abstract:
Earth's energy imbalance (EEI) measures the net radiant energy at the top of the atmosphere, or the net radiant heating of the Earth system. EEI has been increasing since the start of the CERES record. This itself is unsurprising, but the rate of increase is much faster than expected. A workshop was recently convened by MPI–Meteorology at Ringberg to define and answer some of the questions posed by the CERES observational record. I will give a summary of these discussions and some preliminary conclusions from the workshop.

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GISS Lunch Seminar
Speaker: Jakob Snöink (Univ. Bremen)
Title: Sea ice stripes and more on CO2-rich aquaplanets with ROCKE-3D

This is a hybrid presentation, presented both in-person and on-line. Please consult with event host Joseph Kelly for connection details if you wish to virtually attend.

Abstract:
The outer edge of the habitable zone (HZ) around M-dwarfs can host planets with atmospheres rich in CO2 (or other greenhouse gases), a prerequisite for liquid surface water to be present. This study investigates the climate state of such CO2-rich atmospheres on synchronously rotating Proxima Centauri b-like aquaplanets.

We use the NASA GISS ROCKE-3D version 2 General Circulation Model (GCM). ROCKE-3D has been validated against other terrestrial exoplanetary GCMs in the THAI project, and is one of the few exoplanetary GCMs that includes a dynamic ocean component. This dynamic ocean allows for a physically-based calculation of the ocean heat transport, which is especially important in the outer HZ. We performed simulations for 3 configurations with 1 bar atmospheres ranging between 40% CO2 - 60% N2 to 99% CO2 - 1% N2. The importance of ocean heat transport in these configurations is demonstrated through surface energy budget considerations. We bridge classical Earth climate features and (exo-) planetary climate theory, while drawing parallels between both fields.

Our results reveal two main features:

Two persistent bands of sea ice stripes encompass the entire planetary nightside across all CO2 mixing ratios tested. These ice stripes modulate lower atmospheric climate and circulation which is separated from the upper atmosphere by a temperature inversion. An emphasis lies on their modulation of the hydrological cycle, both near the surface, through energy fluxes, and aloft, through cloud formation.

At the substellar region (global dayside) a "trident" pattern, which may be described as an extension to the commonly observed surface "lobster" pattern, emerges. Its spatial distribution is modulated by the sea ice stripes through "drying" and "blocking" effects sensitive to the partial pressure of CO2. We provide explanations of connections and influences between the two patterns.

These features are visible and different from N2-dominated aquaplanets in top-of-atmosphere radiative fluxes and may thereby be used to constrain surface features and planetary climate in future observations of CO2-rich aquaplanets.

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