Climate Change Research

A recent Nature-Geosciences study:
Accelerating uplift in the North Atlantic region as an indicator of ice loss

Vertical motions of the rocky margins of Greenland and Antarctica respond to mass changes of their respective ice sheets. However, thesemotions can be obscured by episodes of glacial advance or retreat that occurred hundreds of thousands of years ago, which trigger a delayed response due to the viscous flow in the underlying mantle. Here we present high-precision global positioning system (GPS) data that describe the vertical motion of the rocky margins of Greenland, Iceland and Svalbard. We focus on vertical accelerations rather than velocities to avoid the confounding effects of past events. Our data show an acceleration of uplift over the past decade that represents an essentially instantaneous, elastic response to the recent accelerated melting of ice throughout the North Atlantic region. Our comparison of the GPS data to models for glacial isostatic adjustment suggests that some parts of western coastal Greenland were experiencing acceleratedmelting of coastal ice by the late 1990s. Using a simple elastic model, we estimate that western Greenland’s ice loss is accelerating at an average rate of 8.7+-3.5 Gt/yr/yr, whereas the rate for southeastern Greenland—based on limited data—falls at 12.5+-5.5 Gt/yr/yr.

Figure 1. Location of GPS sites used in this study. The red circles indicate sites with acceleration 0:5mm/yr/yr or greater; the yellow circles indicate acceleration less than this value.

Figure 2. Representative GPS time series for the North Atlantic region, showing site name and acceleration. The red (upper) time series (Greenland, Iceland) show positive acceleration and the blue (lower) time series (Fennoscandia, Canada) show no significant acceleration; for example, VISO shows uplift at an essentially constant rate

Figure 3. Histogram of vertical acceleration for GPS sites. a, Areas with significant land ice (Greenland, Iceland, Svalbard) with a mean and standard deviation of 0.87 and 0.46 mm/yr/yr. b, Adjacent North Atlantic areas with only seasonal ice or snow (including northeast Canada and Fennoscandia) with a mean and standard deviation of 0.04 and 0.44 mm/yr/yr.

Figure 4, Rate of ice gain or loss (b) and rock uplift (a) in Greenland, versus time. b shows recent estimates for Greenland mass balance. The vertical lines indicate uncertainty; the horizontal lines indicate averaging time30. The blue circles are from altimetry, the red squares are from net accumulation/loss and the green triangles are from GRACE. The straight-line (constant acceleration) fit through the mass balance data for 1996–2008 has a slope 21.8 GT/yr/yr. The black line is a constant-acceleration GRACE model. a shows GPS vertical motion, using a constant-acceleration model and the shaded areas indicate uncertainty (Supplementary Information). Positive values indicate accelerating uplift. The dashed lines indicate corresponding GIA estimates.

More details at Jiang et al. (2010)