Relating ocean temperatures to frontal ablation rates at Svalbard tidewater glaciers: Insights from glacier proximal datasets

Abstract

Fjord-terminating glaciers in Svalbard lose mass through submarine melt and calving (collectively: frontal ablation), and surface melt. With the recently observed Atlantification of water masses in the Barents Sea, warmer waters enter these fjords and may reach glacier fronts, where their role in accelerating frontal ablation remains insufficiently understood. Here, the impact of ocean temperatures on frontal ablation at two glaciers is assessed using time series of water temperature at depth, analysed alongside meteorological and glaciological variables. Ocean temperatures at depth are harvested at distances of 1 km from the calving fronts of the glaciers Kronebreen and Tunabreen, western Svalbard, from 2016 to 2017. We find ocean temperature at depth to control c. 50% of frontal ablation, making it the most important factor. However, its absolute importance is considerably less than found by a 2013–2014 study, where temperatures were sampled much further away from the glaciers. In light of evidence that accelerating levels of global mass loss from marine terminating glaciers are being driven by frontal ablation, our findings illustrate the importance of sampling calving front proximal water masses.

Contribution of calving to frontal ablation quantified from seismic and hydroacoustic observations calibrated with lidar volume measurements

“…Similar values were found recently at other tidewater glaciers (Minowa et al, 2019;Walter et al, 2019). This implies and confirms recent studies that water temperature is the main driver of frontal ablation through underwater melting and thermal undercutting, which in consequence controls subaerial calving (Bartholomaus et al, 2013;Luckman et al, 2015;Vallot et al, 2018;How et al, 2019;Mercenier et al, 2019). Using the cross-sectional submarine area (0.23 and 0.29 km 2 in 2009 and 2014, respectively), our residual frontal melting component of Kronebreen of 0.4-0.8 km 3 a −1 (Fig.…”

“…For visual inspection, we extract the corresponding images within 1 min around each calving event detected in the seismic record to generate an animated image sequence. Fewer than 5 % of all events visible in the time-lapse images represent submarine calving, similar to observations at other glaciers in Svalbard (How et al, 2019). In addition, an autonomous calving event detector is implemented to compare the time series of seismicity and directly observed calving (see Fig.…”

“…For the time period of our experiment between 24 August and 2 September, the approach of Köhler et al (2016) yields an ice loss of about 18×10 6 m 3 . Since about two-thirds of the grounded vertical terminus area of Kronebreen is submarine (Lindbäck et al, 2018) and assuming that submarine ice loss occurs mainly through melting as suggested by our visual calving observations at Kronebreen and How et al (2019), the corresponding dynamic ice loss would be 6 × 10 6 m 3 , which is just slightly above the values estimated from the KRBN and KRBS records in this study; i.e., the contribution of calving to frontal ablation would be 18 %-30 % (Table 1). For the entire year of 2016, the approach of Köhler et al (2016) yields an ice loss of about 640 ± 80 × 10 6 m 3 .…”

“…Frontal ablation at marine-terminating glaciers comprises ice loss through subaerial and submarine melting and iceberg calving. Submarine melting strongly promotes calving through thermal undercutting (Bartholomaus et al, 2013;Luckman et al, 2015;Vallot et al, 2018;How et al, 2019). To monitor and better understand the dynamic ice loss contribution, field records of calving can be obtained visually through human observation and time-lapse imagery (e.g., O'Neel et al, 2003;Chapuis et al, 2010;How et al, 2019), as well as through terrestrial remote sensing such as groundbased radar (Chapuis et al, 2010;Walter et al, 2019) and lidar surveys (Pętlicki and Kinnard, 2016).…”

“…Submarine melting strongly promotes calving through thermal undercutting (Bartholomaus et al, 2013;Luckman et al, 2015;Vallot et al, 2018;How et al, 2019). To monitor and better understand the dynamic ice loss contribution, field records of calving can be obtained visually through human observation and time-lapse imagery (e.g., O'Neel et al, 2003;Chapuis et al, 2010;How et al, 2019), as well as through terrestrial remote sensing such as groundbased radar (Chapuis et al, 2010;Walter et al, 2019) and lidar surveys (Pętlicki and Kinnard, 2016). Calving events are also successfully detected from passive indirect techniques such as seismic (Ekström et al, 2003;Amundson et al, 2008;O'Neel et al, 2010;Walter et al, 2012;Bartholomaus et al, Published by Copernicus Publications on behalf of the European Geosciences Union.…”