Ocean expansion and land-based ice melting are contributing to rising sea levels as a result of climate change. How frequently glaciers calve is one of many variables that will affect sea level rise in the near future. Large icebergs that break off from tidewater glaciers or glaciers that end in the ocean and float into coastal fjords are what causes them to occur. The glaciers are moving across the land faster, dumping more ice into the ocean, which causes the sea level to rise more quickly.
The largest single glacier contributing to sea level rise in Greenland, Helheim Glacier, was studied using GPS measurements by a research team from Columbia University, Oxford University, and the Oxford University Mathematical Institute. A almost perfect natural experiment, the GPS captured high-temporal-resolution observations of the glacier’s flow response to lake outflow.The results showed that the Helheim Glacier behaves very differently from the inland ice sheet, which moves swiftly and downward during lake drainage events. Helheim Glacier, in contrast, displayed a comparatively small ‘pulse’ of movement, during which the glacier briefly accelerated before slowing down again, with no net increase in movement.Using a numerical model of the subglacial drainage system, the researchers concluded that this observation was most likely caused by the Helheim glacier having an efficient system of channels and caverns along its bed. As a result, the fluids that are draining from the glacier bed can be quickly removed without increasing the overall net movement. The researchers were concerned that glaciers without an efficient drainage system, where the surface melt is currently minimal but may develop in the future due to climate change, may experience a different consequence even though this appears to be good news for sea level rise implications (such as in Antarctica).They carried out a mathematical model based on the conditions of colder, Antarctic tidewater glaciers. According to the findings, lake drainages would cause a net increase in glacier movement under these conditions. This was principally brought on by the delayed evacuation of flood waters throughout the course of the winter via the less efficient subglacial drainage system. However, there haven’t yet been any in-situ observations of Antarctic tidewater glacier responses to lake drainage.
The study casts doubt on several established techniques for inferring glacial drainage patterns from glacier velocities observed in satellite imagery (which are currently used in sea level rise models).
Lead author Associate Professor Laura Stevens explained, “What we’ve seen here at Helheim is that you can have a big input of meltwater into the drainage system during a lake drainage event, but that melt input doesn’t result in an appreciable change in glacier speed when you average over the week of the drainage event” (Department of Earth Sciences, Oxford University).
Lake drainage events, such as the one seen in the Helheim GPS data, are often disregarded because the best temporal precision of currently known satellite-derived glacier speeds is just about one week.
These tidewater glaciers are difficult, continued Associate Professor Stevens. We need to learn a lot more about how meltwater drainage works and affects tidewater glacier rates before we can confidently forecast how tidewater glaciers will respond to future atmospheric and oceanic warming.
