Nbreen: all good things come to an end

With the removal of the IMAU automatic weather station, GPS units and mass balance stakes last April, the Nordenskiöldbreen project -or Nbreen for short- came to an end after 18 years.

The Nbreen project started in 2006 as a collaboration between IMAU and Uppsala University. It was part of GLACIODYN (Dynamic Response of Arctic Glaciers to Global Warming), a lead IPY (Fourth International Polar Year) project. Its main goal was to clarify the link between glacier dynamics and meltwater input. This link has been known for decades and suggests that glacier flow might accelerate in a warming climate with more melt. To measure this effect, GLACIODYN deployed accurate GPS units to measure glacier velocity on different glaciers in the Arctic.

On 'our' glacier Nordenskiöldbreen, in Svalbard, we installed 11 GPS units along the main flowline and one reference station on a nunatak (a mountain that protrudes through the ice). A sonic altimeter was also installed to continuously measure the local melt rates, and soon we decided to add a temperature sensor. A year later, in 2009, we decided a full weather station (AWS) was needed to measure the surface energy balance, which has been operational until it was removed last April.

The project was not without its problems: buried GPS units, moisture intrusions in the AWS electronics, crevasses preventing station visits, disappearing sea ice in the fjords necessitating detours and increasing  travel times, Covid-19 preventing fieldwork altogether, and safety concerns owing to the presence of polar bears... Some problems triggered creative solutions. A mountain-loving PhD student got the idea to attach RECCO reflectors to the GPS units, which are mainly intended for avalanche rescue, but turned out to be perfectly suited to trace back buried equipment. In the end, the moisture problems in the AWS were solved by simply replacing it with a new one.

In these 18 years, in which 10 different people from IMAU participated during 17 fieldwork visits, sometimes during harsh weather conditions, we have gathered a unique long-term data set. Nordenskiöldbreen is not a particularly fast flowing glacier, with mean velocities around 40 metres per year and peak velocities that reach 90 metres per year in early summer, yet our data confirmed that the peak velocity in early summer is linked to the onset of the melt season. Over the years we also observed additional velocity peaks in autumn, related to rainfall events, which are a clear sign of the rapidly warming climate in Svalbard. Despite this warming, the glacier wide mass balance shows no trend towards more melt, but this can also be hidden by the  large inter-annual variability.

All good things come to an end, and that also holds for this great project. But the data it produced will be a source of discovery for many years to come!

Carleen Tijm-Reijmer, Paul Smeets, Maurice van Tiggelen and Michiel van den Broeke