Understanding the mass loss of the Novaya Zemlya ice cap and its drivers
Summary
The main contributor to present-day sea level rise is the melt of glaciers and ice caps. Changes in ice mass are particularly marked in the Arctic, where the warming is almost twice as fast as the global average. The mass loss of the ice cap on Novaya Zemlya is less studied than other parts of the Arctic, and its exact mass loss rates and drivers remain uncertain. Novaya Zemlya is not easily accessible for scientists, making remote sensing an indispensable method to study these changes. This thesis presents the ice mass loss of the Novaya Zemlya ice cap derived with the use of the CryoSat-2 radar altimeter for the period 2010-2018. Moreover, it aims to disentangle the drivers of this mass loss by studying the correlation with air temperature, ocean temperature, glacier retreat rates, glacier velocity and large-scale climatic variability. Furthermore, this thesis presents a new method to retrieve the elevation change rates from the CryoSat-2 measurements by using an external DEM.
The retrieved elevation change rates are highly negative on the lower elevations -- with extreme thinning rates of up to 3 m/yr -- and slightly negative or in balance on the higher parts of the ice cap. A mean mass loss rate of -10.4±2.0 Gt/yr was found for the entire ice cap. The mass loss was significantly higher on the glaciers on the Barents Sea coast than on the glaciers on the Kara Sea coast, likely caused by a faster warming of the Barents Sea region. The mass loss over the ice cap was highly correlated with the summer mean temperatures on the ice cap, indicating that at least part of the mass loss is likely driven by surface melt. Moreover, the marine-terminating glaciers show a faster frontal thinning than the land-terminating glaciers. This indicates a role of ice dynamics in the mass loss, which was further supported by a correlation between mass loss from marine-terminating glaciers and ocean temperature in the surface layer. The warming ocean waters cause an increase in basal melt, enhancing the calving rate and causing dynamic thinning.
The results of the newly developed DEM method for estimating elevation change rates from CryoSat-2 measurements were in agreement with the results from the modified plane-fitting method, but provide a higher spatial coverage. This is a promising result for further development of this new method.