The extreme melt across the Greenland ice sheet in 2012

Abstract

The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors – including the Oceansat‐2 scatterometer, the Moderate‐resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder – are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

“…The 2012 melt season anomaly was driven partly by extreme, shortlived melt episodes (i.e. Nghiem et al, 2012;Bennartz et al, 2013;Tedesco et al, 2013), which as discussed may result in more ice content. Increases in modeled melt rates at higher sites are even more pronounced than at J1, with rates at J4 increasing from less than 100 kg m −2 over the period from 1958 to 1999, to a rate of 305 and 580 kg m −2 in 2010 and 2012 respectively (Fig.…”

“…As a consequence, the area of the ice sheet covered by percolation facies has grown, and the amount of surface melt and subsequently refrozen meltwater retained in the firn has increased (Tedesco et al, 2008;Fettweis et al, 2011;Harper et al, 2012van Angelen et al, 2014). Extreme warming events such as in July 2012 (Nghiem et al, 2012;Bennartz et al, 2013) have further intensified melt, but it is unknown whether increasing meltwater production and subsequent percolation and refreezing at high elevations has shifted the equilibrium line higher and affected the buffering and transport of meltwater over the interior of the ice sheet. Furthermore, these processes and their high spatial and temporal variability have implications for altimetry-derived mass balance estimates.…”

Greenland meltwater storage in firn limited by near-surface ice formation

“…Here, we employ in-situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over melt water storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012 5,6 , revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (above ~1900 m a.s.l.…”

Mapping the bathymetry of supraglacial lakes and streams on the Greenland ice sheet using field measurements and high-resolution satellite images

“…Recent accelerated melting of the Greenland ice sheet (GrIS) , including a record melt season in 2012 (Nghiem et al, 2012;Bennartz et al, 2013), underscores the need to improve our understanding of the ice sheet's hydrology and thus constrain estimates of the current and future contributions of the GrIS to sea level rise. These estimates are subject to a number of significant uncertainties, many related to the role of meltwater on the surface of the ice sheet.…”

“…Remote sensing is a valuable tool for monitoring the GrIS, with a variety of instruments used to detect and characterize melt (e.g., Nghiem et al, 2012;Tedesco et al, 2013, and references therein). Analysis of satellite images, for example, has provided long-term, synoptic information on patterns of meltwater storage and drainage, establishing the importance of supraglacial lakes as temporary reservoirs (e.g., Liang et al, 2012).…”