The Response of Tidewater Glacier Termini Positions in Hornsund (Svalbard) to Climate Forcing, 1992-2020

Many Arctic marine-ter minating glaciers have undergone rapid retreats in recent decades. Seasonal and year-to-year variations in terminus position act on all tidewater glaciers, but the key controls on those changes vary from region to region. Here, we examined seasonal and decadal changes in termini positions of seven tidewater glaciers in the inner part of Hornsund, the southernmost fjord of Spitsbergen (Svalbard Archipelago), based on a variety of data from 1992 to 2020. Combining satellite imagery, basic meteorological data (air temperature, positive degree day index (PDD), liquid precipitation), sea surface temperature (SST), mean temperature in the glacier forefield bays, fast sea ice cover, and bathymetry near the glacier front, we examined the influence of potential controlling parameters on interannual and seasonal variability of the glacier termini. We found regional synchrony between terminus advance/retreat and climate variables. At a regional scale, annual fluctuation changes are related to PDD and SST, while summer fluctuations are linked to PDD, although individual glaciers are shown to have differing sensitivities to potential climate drivers. We also found that the retreat period in Hornsund generally lasts from June to October-December. Onset of the retreat is related to sea and air temperature, and in some cases follows the disappearance of the ice cover. These results indicate that the expected increase in meltwater runoff in Svalbard, the input of relatively warm Atlantic water to the fjord, and the increasing trend of longer summer and warmer winter periods will have implications for glacier velocity and frontal ablation.Plain Language Summary In recent decades, marine-terminating glaciers in the Arctic have undergone rapid retreats. In addition to long-term changes in front position, those glaciers also experience seasonal advance and retreat. However, the key controls on those changes vary from region to region. Here, we used satellite images to investigate decadal and seasonal fluctuations of seven tidewater glaciers in Hornsund, the southernmost fjord of the Svalbard Archipelago. We compared glacier fluctuations with meteorological and oceanographic data to examine potential controls on variability of the glacier termini. Our results show a general synchronous pattern of glacier fluctuations with local climate variables. Front position changes are related to temperature-based index and sea surface temperature when analyzed regionally, although individual glaciers have differing sensitivities to potential climate drivers. We also found that the retreat period lasts from June to October-December in Hornsund. Glaciers start to retreat when sea and air temperatures are significantly high, and in some cases follow the disappearance of the ice cover. Our results indicate that the expected increase in air temperature, the amount of meltwater, input of warm water to the fjord, and longer summer and warmer winter periods will affect glacier velocity, calving, and terminus position of the glaciers in the future.