Contemporary ice sheet thinning drives subglacial groundwater exfiltration with potential feedbacks on glacier flow.

Observations indicate that groundwater-laden sedimentary aquifers are extensive beneath large portions of the Greenland and Antarctic ice sheets. A reduction in the mechanical loading of aquifers is known to lead to groundwater exfiltration, a discharge of groundwater from the aquifer. Here, we provide a simple expression predicting exfiltration rates under a thinning ice sheet. Using contemporary satellite altimetry observations, we predict that exfiltration rates may reach tens to hundreds of millimeters per year under the fastest thinning parts of the Antarctic Ice Sheet. In parts of West Antarctica, predicted rates of exfiltration would cause the total subglacial water discharge rate to be nearly double what is currently predicted from subglacial basal melting alone. Continued Antarctic Ice Sheet thinning into the future guarantees that the rate and potential importance of exfiltration will only continue to grow. Such an increase in warm, nutrient-laden subglacial water discharge would cause changes in ice sliding, melt of basal ice and marine biological communities.