What is meant by an "ice sheet fingerprint"?

Ice sheet fingerprints are called so because they create unique, location-specific patterns of sea level change around the world, much like a fingerprint uniquely identifies an individual. The fingerprints arise because of changes that happen to the gravitation, rotation and deformation of Earth when ice melts.

When ice sheets in Greenland, Antarctica, or other ice-covered regions melt, they lose a significant amount of mass. This loss of mass reduces the gravitational pull that the ice sheet exerts on the surrounding ocean water. As a result, water that was previously "pulled" towards the ice sheet starts to redistribute away from the melting region. This causes sea levels to fall near the ice sheet and rise in more distant locations. The gravitational effect is a primary driver of the distinct fingerprint pattern, creating lower sea levels close to the source of melting and higher levels farther away. These fingerprints create a complex pattern of sea level changes that vary significantly across different coastal regions.

The redistribution of water mass due to ice melt also impacts the Earth's rotation. As water moves from higher latitudes (closer to the poles) to lower latitudes (closer to the equator), it can alter the distribution of the Earth's mass. This redistribution affects the Earth's rotational inertia, causing subtle changes in its rotation. These rotational changes further influence sea level patterns globally, contributing to the unique fingerprint effect.

Finally, the melting ice can cause a change in the shape or deformation of Earth. Near where ice is melting, the land rises from what is known as isostatic rebound. As the weight of the ice on top of the land literally melts away, the land underneath the ice often rises. This rebound in land height is still impacting some areas from the ice that covered them over 20,000 years ago during the Last Glacial Maximum. Today, this same process is being observed due to climate change as the ice sheets and mountain glaciers melt away. This is causing the land to rise in those areas and can actually lead to lower sea levels than the global value in places nearest to the ice sheets. This is not common globally, but is a factor in places like Alaska. In other places, ice sheet melting is causing the land to sink. Since Earth is sphere, the weight of the ice sheets can cause the land below it to compress or sink, whereas other nearby areas bulge out. This is similar to what happens when someone sits on a yoga ball. The area below the weight sinks while other parts of the ball bulge out. As the ice melts and the weight lifts, this causes the land where the ice was to rise, but it also causes the nearby areas that were bulged out to sink back down. This is why sea levels are rising faster in places like the Northeastern U.S. than in other parts of the country.

Each melting ice sheet contributes to a global pattern of sea level changes, with its distinct fingerprint superimposed on the effects of other melting sources. For example, the melting of the Greenland ice sheet primarily impacts the North Atlantic, leading to lower sea levels near Greenland and higher levels along the eastern coast of North America and Europe. Conversely, the melting of the Antarctic ice sheet significantly affects the Southern Hemisphere, particularly in regions like Australia and South America.