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Twila Moon

Affiliate Scientist



Department Affiliation

Polar Science Center


2000-present and while at APL-UW

Use of glacial fronts by narwhals (Monodon monoceros) in West Greenland

Laidre, K.L., T. Moon, D.D.W. Hauser, R. McGovern, M.P. Heide-Jørgensen, R. Dietz, and B. Hudson, "Use of glacial fronts by narwhals (Monodon monoceros) in West Greenland," Proc. R. Soc. Biol. Lett., 12, doi:10.1098/rsbl.2016.0457, 2016.

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26 Oct 2016

Glacial fronts are important summer habitat for narwhals (Monodon monoceros); however, no studies have quantified which glacial properties attract whales. We investigated the importance of glacial habitats using telemetry data from n = 15 whales tagged in September of 1993, 1994, 2006 and 2007 in Melville Bay, West Greenland. For 41 marine-terminating glaciers, we estimated (i) narwhal presence/absence, (ii) number of 24 h periods spent at glaciers and (iii) the fraction of narwhals that visited each glacier (at 5, 7 and 10 km) in autumn. We also compiled data on glacier width, ice thickness, ice velocity, front advance/retreat, area and extent of iceberg discharge, bathymetry, subglacial freshwater run-off and sediment flux. Narwhal use of glacial habitats expanded in the 2000s probably due to reduced summer fast ice and later autumn freeze-up. Using a generalized multivariate framework, glacier ice front thickness (vertical height in the water column) was a significant covariate in all models. A negative relationship with glacier velocity was included in several models and glacier front width was a significant predictor in the 2000s. Results suggest narwhals prefer glaciers with potential for higher ambient freshwater melt over glaciers with silt-laden discharge. This may represent a preference for summer freshwater habitat, similar to other Arctic monodontids.

The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords

Carroll, D., and 11 others, including B. Hudson and T. Moon, "The impact of glacier geometry on meltwater plume structure and submarine melt in Greenland fjords," Geophys. Res. Lett., 43, 9739-9748, doi:10.1002/2016GL070170, 2016.

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28 Sep 2016

Meltwater from the Greenland Ice Sheet often drains subglacially into fjords, driving upwelling plumes at glacier termini. Ocean models and observations of submarine termini suggest that plumes enhance melt and undercutting, leading to calving and potential glacier destabilization. Here we systematically evaluate how simulated plume structure and submarine melt during summer months depends on realistic ranges of subglacial discharge, glacier depth, and ocean stratification from 12 Greenland fjords. Our results show that grounding line depth is a strong control on plume-induced submarine melt: deep glaciers produce warm, salty subsurface plumes that undercut termini, and shallow glaciers produce cold, fresh surface-trapped plumes that can overcut termini. Due to sustained upwelling velocities, plumes in cold, shallow fjords can induce equivalent depth-averaged melt rates compared to warm, deep fjords. These results detail a direct ocean-ice feedback that can affect the Greenland Ice Sheet.

Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland

Moon, T., I, Joughin, and B. Smith, "Seasonal to multiyear variability of glacier surface velocity, terminus position, and sea ice/ice melange in northwest Greenland," J. Geophys. Res., 120, 818-833, doi:10.1002/2015JF003494, 2015.

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13 May 2015

Glacier ice discharge, which depends on ice velocity and terminus fluctuations, is a primary component of Greenland Ice Sheet mass loss. Some research suggests that ice melange influences terminus calving, in turn affecting glacier velocity. The details and broad spatiotemporal consistency of these relationships, however, is undetermined. Focusing on 16 northwestern Greenland glaciers during 2009 through summer 2014, we examined seasonal surface velocity changes, glacier terminus position, and sea ice and ice melange conditions. For a longer-term analysis, we also produced extended records of four glaciers from 1999 to 2014. There is a strong correspondence between seasonal near-terminus sea ice/melange conditions and terminus change, with rigid ice melange conditions associated with advance and open water associated with retreat. Extended sea ice-free periods and reduced rigid melange are also linked with anomalously large terminus retreat. In all but one case, sustained multiyear retreat of greater than 1 km during both the 15-year and 6-year records was accompanied by interannual velocity increases. Seasonal velocity patterns, however, correspond more strongly with runoff changes than terminus behavior. Projections of continued warming and longer sea ice-free periods around Greenland indicate that notable retreat over wide areas may continue. This sustained retreat likely will contribute to multiyear speedup. Longer melt seasons and earlier breakup of melange may also alter the timing of seasonal ice flow variability.

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Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland

Joughin, I., I. Howat, R.B. Alley, G. Ekstrom, M. Fahnestock, T. Moon, M. Nettles, M. Truffer, and V.C. Tsai, "Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland," J. Geophys. Res., 113, doi:10.1029/2007JF000837, 2008.

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26 Jan 2008

We used satellite images to examine the calving behavior of Helheim and Kangerdlugssuaq Glaciers, Greenland, from 2001 to 2006, a period in which they retreated and sped up. These data show that many large iceberg-calving episodes coincided with teleseismically detected glacial earthquakes, suggesting that calving-related processes are the source of the seismicity. For each of several events for which we have observations, the ice front calved back to a large, pre-existing rift. These rifts form where the ice has thinned to near flotation as the ice front retreats down the back side of a bathymetric high, which agrees well with earlier theoretical predictions. In addition to the recent retreat in a period of higher temperatures, analysis of several images shows that Helheim retreated in the 20th Century during a warmer period and then re-advanced during a subsequent cooler period. This apparent sensitivity to warming suggests that higher temperatures may promote an initial retreat off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into deeper water. The cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in Greenland can advance rapidly. Greenland's larger reservoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center