Description: [1]  A significant portion of the world's glacier ice drains through tidewater outlets, though much remains unknown about the response to recent climate change of tidewater glaciers. We present a 64 year record of length change for 50 Alaska tidewater glaciers. We use USGS topographic maps to provide a base length for glaciers before 1970. Using all available cloud-free Landsat images, we manually digitize calving front outlines for each glacier between 1972 and 2012, resulting in a total of more than10,000 outlines. Tidewater glacier lengths vary seasonally; focusing on the 36 glaciers terminating in tidewater throughout the study period, we find a mean (± std. dev.) seasonal variation of 60 ± 85 m a − 1 . We use these oscillations to determine the significance of interannual changes in glacier length. All 36 glaciers underwent at least one period (≥ 1 year) of significant advance or retreat; 28 glaciers underwent at least one period of both significant advance and retreat.Over the entire period 1948-2012, 24 of these glaciers retreated a total (± uncertainty) of 107.95 ± 0.29 km, 11 advanced a total of 7.71 ± 0.20, and one (Chenega Glacier) did not change significantly. Retreats and advances are highlyvariable in time; several glaciers underwent rapid, short-term retreats of a few years duration. These retreats occurred after large changes in summer sea surface temperature anomalies; further study is needed to determine what triggered these retreats. No coherent regional behavior signal is apparent in the length record, although two subregions show a coherence similar to recent observations in Greenland.

Description: Our incomplete knowledge of the proportion of mass loss due to frontal ablation (the sum of ice loss through calving and submarine melt) from tidewater glaciers outside of the Greenland and Antarctic ice sheets has been cited as a major hindrance to accurate predictions of global sea level rise. We present a 28 year record (1985–2013) of frontal ablation for 27 Alaska tidewater glaciers (representing 96% of the total tidewater glacier area in the region), calculated from satellite-derived ice velocities and modeled estimates of glacier ice thickness. We account for cross-sectional ice thickness variation, long-term thickness changes, mass lost between an upstream flux gate and the terminus, and mass change due to changes in terminus position. The total mean rate of frontal ablation for these 27 glaciers over the period 1985–2013 is 15.11 ± 3.63 Gt a −1 . Two glaciers, Hubbard and Columbia, account for approximately 50% of these losses. The regional total ablation has decreased at a rate of 0.14 Gt a −1 over this time period, likely due to the slowing and thinning of many of the glaciers in the study area. Frontal ablation constitutes only ~ 4% of the total annual regional ablation, but roughly 20% of net mass loss. Comparing several commonly-used approximations in the calculation of frontal ablation we find that neglecting cross-sectional thickness variations severely underestimates frontal ablation.

Description: This work is part of the Glacier Mass Balance Intercomparison Exercise (GlaMBIE), which aims to collect and analyze regional assessments of glacier mass balance across the range of available methods. Here we present our assessment of glacier elevation change in the Svalbard region from spaceborne optical data using the geodetic method. We have developed an approach based on extrapolating elevation values over 10-year time intervals using the ASTER and SPOT-5 DEM time series available over the region. Our approach consists of using the time series of co-registered summer DEMs (from July to October) to derive the median elevation within fixed elevation bands (e.g. bins of 100 m), interpolate the median elevation data points over time using a RANSAC (RANdom SAmple Consensus) linear interpolation, and extrapolate the elevation information for each band that corresponds to the pre-defined period. We then derived the area-weighted mean to calculate elevation changes over each glacier based on RGI6.0.This approach is different from other multi-temporal approaches, which commonly assess the elevation evolution of individual pixels (or a window filter) and then aggregate the derived trends in a second step (e.g. Hugonnet et al. 2021). Therefore, we compared our results with already available methods for deriving elevation change estimates from the geodetic method by comparing regional assessment and individual glacier estimates. This work also aims to discuss the challenges related to spaceborne optical DEMs for calculating glacier elevation change, including issues and different approaches related to co-registration, noise filtering, and gap filling.