What is glacier mass balance?
Mass balance is the amount of snow and ice lost or gained on a glacier over a given period. It is reported as a single value representing the change averaged over the entire glacier surface.
Field data are obtained during two visits to a glacier, in spring and in autumn. These data are used to derive the winter balance and the summer balance. These are added to yield the net balance, the annual state of the glacier’s health, as measured between two consecutive autumns.
NPI mass balance program
NPI measures mass balance on four area glaciers (Fig. A): Austre Brøggerbreen, with measurements from 1967; Midtre Lovénbreen, (since 1968); Kongsvegen (since 1987); and the glacier system Kronebreen/Holtedahlfonna (since 2003).
The smaller low-lying glaciers Austre Brøggerbreen (C) and Midtre Lovénbreen (D) almost always have negative net balances, since their accumulation areas are not at a high enough altitude to retain winter snow through the summer melt season. Net balances are more positive on Kongsvegen (E) and Kronebreen-Holtedahlfonna (F) since their accumulation areas are both higher and larger than the smaller glaciers. When calving is included, however, Kronebreen-Holtedahlfonna’s net balance is roughly as negative as the smaller glaciers.
Summer balance for all the glaciers is more variable than winter accumulation. In general, summer temperature has the most impact on the net balance.
Mass balance 2021/22
Net mass balance for 2021/22 was strongly negative for all the glaciers, more negative than the average for the period 2005-2022 (Fig. B), but not as negative as the record year 2019/20, despite the record warm summer temperature recorded at Ny-Ålesund.
However, we did our fieldwork at the end of August; measurements made some weeks later by colleagues working on the nearby glacier Austre Lovénbreen indicate a further loss of about 30-40 cm water equivalent. We expect that once we remeasure the mass balance stakes next spring, to account for the further autumn melt, we will find that the net balance for 2022 was as negative as 2020, possibly even more so.
The summed net balance (Fig. G), which is equivalent to the glacier volume change, adjusted by the mean glacier density, shows the long-term negative trend of all of the monitored glaciers, as well as the increasingly negative trend over the past decade.
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