Extensive ice thickness surveys by NASA's Operation IceBridge enable over a decade of ice discharge measurements at high precision for the majority of Greenland's marine-terminating outlet glaciers, prompting a reassessment of the temporal and spatial distribution of glacier change. Annual measurements for 178 outlet glaciers reveal that, despite widespread acceleration, only 15 glaciers accounted for 77% of the 739 ± 29 Gt of ice lost due to acceleration since 2000 and four accounted for~50%. Among the top sources of loss are several glaciers that have received little scientific attention. The relative contribution of ice discharge to total loss decreased from 58% before 2005 to 32% between 2009 and 2012. As such, 84% of the increase in mass loss after 2009 was due to increased surface runoff. These observations support recent model projections that surface mass balance, rather than ice dynamics, will dominate the ice sheet's contribution to 21st century sea level rise.
The Greenland Ice Sheet is losing mass at accelerated rates in the 21st century, making it the largest single contributor to rising sea levels. Faster flow of outlet glaciers has substantially contributed to this loss, with the cause of speedup, and potential for future change, uncertain. Here we combine more than three decades of remotely sensed observational products of outlet glacier velocity, elevation, and front position changes over the full ice sheet. We compare decadal variability in discharge and calving front position and find that increased glacier discharge was due almost entirely to the retreat of glacier fronts, rather than inland ice sheet processes, with a remarkably consistent speedup of 4-5% per km of retreat across the ice sheet. We show that widespread retreat between 2000 and 2005 resulted in a stepincrease in discharge and a switch to a new dynamic state of sustained mass loss that would persist even under a decline in surface melt.
Abstract. Rapid changes in thickness and velocity have been
observed at many marine-terminating glaciers in Greenland, impacting the
volume of ice they export, or discharge, from the ice sheet. While annual
estimates of ice-sheet-wide discharge have been previously derived,
higher-resolution records are required to fully constrain the temporal
response of these glaciers to various climatic and mechanical drivers that
vary in sub-annual scales. Here we sample outlet glaciers wider than 1 km
(N=230) to derive the first continuous, ice-sheet-wide record of total ice
sheet discharge for the 2000–2016 period, resolving a seasonal variability
of 6 %. The amplitude of seasonality varies spatially across the ice
sheet from 5 % in the southeastern region to 9 % in the northwest
region. We analyze seasonal to annual variability in the discharge time
series with respect to both modeled meltwater runoff, obtained from
RACMO2.3p2, and glacier front position changes over the same period. We find
that year-to-year changes in total ice sheet discharge are related to annual
front changes (r2=0.59, p=10-4) and that the annual
magnitude of discharge is closely related to cumulative front position
changes (r2=0.79), which show a net retreat of >400 km,
or an average retreat of >2 km, at each surveyed glacier. Neither
maximum seasonal runoff or annual runoff totals are correlated to annual
discharge, which suggests that larger annual quantities of runoff do not
relate to increased annual discharge. Discharge and runoff, however, follow
similar patterns of seasonal variability with near-coincident periods of
acceleration and seasonal maxima. These results suggest that changes in
glacier front position drive secular trends in discharge, whereas the impact
of runoff is likely limited to the summer months when observed seasonal
variations are substantially controlled by the timing of meltwater input.
A novel energy capturing technique for wasted parasitic magnetic noise based upon a magneto-mechano-electric (MME) generator, consisting of piezoelectric single crystal fibers and Ni metal plate in the form of cantilever structure.
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