Quantifying iceberg evolution in a temperate fjord

Fjord-terminating glaciers contribute significantly to current sea level rise through surface and submarine melt and iceberg calving. Contact with relatively warmer ocean waters melts glacier termini, thus destabilizing them and enhancing iceberg calving. Icebergs floating inside fjords have the potential to lower submarine melt by cooling the incoming ocean water before it reaches the terminus, creating a feedback whereby an increase in iceberg concentration lowers the fjord water temperature, stabilizes the terminus, and reduces the flux of icebergs into the fjord. This feedback could potentially regulate glacier retreat. However, lack of knowledge about the distribution of size, location, and melt of icebergs inside fjords has previously prevented us from examining this phenomenon. In this study we examine the size and distribution of icebergs inside Columbia Fjord in Alaska using satellite imagery to determine their impact on fjord circulation. In addition, we create a simple iceberg evolution model which allows us to examine the loss of ice along the fjord. We discover that the majority of iceberg loss occurs 2-5km from the terminus. We examine the energy balance of the fjord to determine the significance that iceberg melt has on lowering incoming ocean water temperatures. We find that icebergs may provide a cooling effect that can stabilize the terminus of Columbia Glacier. While we have shown that icebergs can produce a stabilizing feedback for one terminating glacier, our methods could be applied to other temperate fjord-terminating glaciers where satellite imagery is available.