East Antarctica’s ice is melting from below as warm ocean water creeps into ice shelf cavities, and a major driver of that warming has been hidden from view. The problem is that scientists cannot explain roughly three-quarters of the ongoing ice melt in vulnerable East Antarctic regions. The missing piece may be a vast, cold water mass called Antarctic Bottom Water, which is shrinking as it freshens. As it thins, warmer water above it slumps toward the ice shelves. This project will combine decades of ocean measurements with high-resolution simulations to track whether that shrinkage—not just wind-driven currents—is the overlooked cause of warming. If the team succeeds, climate models will finally account for this two-way connection between the deep ocean and the shelf seas. That would allow far more accurate predictions of sea-level rise, giving coastal planners and infrastructure managers the information they need to prepare for how fast and how far the coastline will shift. Without this understanding, the possibility of rapid, unstoppable sea-level rise cannot be ruled out.
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East Antarctica, once considered a stable "sleeping giant" of sea-level rise, is beginning to stir. Even a small amount of melting - just 1% of its ice – would raise global sea-levels by half a meter, redrawing coastlines everywhere. Antarctica’s melting is driven from below, by the ocean, as warmer water moves into ice shelf cavities. This process, a major yet mostly unexplained contributor to sea-level rise, is caused by complex changes in ocean heat transport that remain poorly understood. In vulnerable East Antarctic regions, about 30% of the ongoing ice melt has been linked to wind-driven movement of warm ocean water. However, the remaining 70% is still unexplained. This gap persists due to a lack of detailed, simultaneous observations of ocean properties and velocities, along with models that cannot yet resolve critical features like ice shelf cavities at high enough resolution. As a result, the possibility of “rapid and unstoppable” sea-level rise cannot be ruled out as East Antarctic regions continue to lose ice. To address this gap, we will directly observe then simulate a hidden but major driver of warming ocean temperatures. We argue that changes in ocean structure—through shifts in the volume and position of key water masses—are an overlooked driver of warming. Changes in Antarctic Bottom Water (AABW)—which, despite being formed in only four Antarctic regions, fills the deepest 40% of the ocean—significantly impact the position of warm Circumpolar Deep Water (CDW) that overlies it. Due to freshening at its source regions, AABW is shrinking by hundreds of meters per decade. As a result, CDW slumps toward Antarctica bringing heat closer to the ice shelves. 2WayXChange will use a groundbreaking combination of observations and simulations to reveal the previously overlooked role of AABW shrinkage—and its potential disappearance—in driving warming ocean temperatures. Our team offers the tools and capability to deliver a new understanding of the Southern Ocean and a step-change in prediction capability for sea-level change. We will track how water masses have evolved in the region and their influence on ice melt, by combining 50 years of ocean measurements in new ways. Our 4D-Dataset will provide the first-ever observational time series of ocean conditions and circulation in East Antarctica. Using this new suite of observations, we will determine why ocean waters have changed near three East Antarctic regions particularly vulnerable to ice melt. We will use a novel analytical approach, that separates water mass movement from composition changes, to determine how much warming is due to AABW shrinkage versus wind-driven movement. Building on our brand-new observational insights, we will use ground-breaking simulations to predict how shrinking AABW affects shelf warming, ice loss, and global sea-level rise, both in the past (1950-2025) and future (2025-2100), distinguishing between ocean- and wind-driven causes of warming over 150 years. Global temperatures are already exceeding climate targets. They are projected to temporarily surpass 1.5°C above pre-industrial levels in the next five years, accelerating ice melt and intensifying the connection we seek to understand. We will tackle one of the most imminent challenges of our warming world - achieving a deeper understanding of ocean heat transport that enable more accurate predictions of sea-level rise. 2WayXChange is poised to push scientific frontiers, providing crucial new insights into Southern Ocean dynamics and its global impact.
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