Greenland Ice Sheet (GrIS) mass loss has accelerated since the turn of the twenty‐first century. Several recent episodes of rapid GrIS ablation coincided with intense moisture transport over Greenland by atmospheric rivers (ARs), suggesting that these events influence the evolution of GrIS surface mass balance (SMB). ARs likely provide melt energy through several physical mechanisms, and conversely, may increase SMB through enhanced snow accumulation. In this study, we compile a long‐term (1980–2016) record of moisture transport events using a conventional AR identification algorithm as well as a self‐organizing map classification applied to MERRA‐2 data. We then analyze AR effects on the GrIS using melt data from passive microwave satellite observations and regional climate model output. Results show that anomalously strong moisture transport by ARs clearly contributed to increased GrIS mass loss in recent years. AR activity over Greenland was above normal throughout the 2000s and early 2010s, and recent melting seasons with above‐average GrIS melt feature positive moisture transport anomalies over Greenland. Analysis of individual AR impacts shows a pronounced increase in GrIS surface melt after strong AR events. AR effects on SMB are more complex, as strong summer ARs cause sharp SMB losses in the ablation zone that exceed moderate SMB gains induced by ARs in the accumulation zone during summer and in all areas during other seasons. Our results demonstrate the influence of the strongest ARs in controlling GrIS SMB, and we conclude that projections of future GrIS SMB should accurately capture these rare ephemeral events.
This study reports the occurrence of intense atmospheric rivers (ARs) during the two large Weddell Polynya events in November 1973 and September 2017 and investigates their role in the opening events via their enhancement of sea ice melt. Few days before the polynya openings, persistent ARs maintained a sustained positive total energy flux at the surface, resulting in sea ice thinning and a decline in sea ice concentration in the Maud Rise region. The ARs were associated with anomalously high amounts of total precipitable water and cloud liquid water content exceeding 3 SDs above the climatological mean. The above-normal integrated water vapor transport (IVT above the 99th climatological percentile), as well as opaque cloud bands, warmed the surface (+10°C in skin and air temperature) via substantial increases (+250 W m−2) in downward longwave radiation and advection of warm air masses, resulting in sea ice melt and inhibited nighttime refreezing.
The Greenland Ice Sheet (GrIS) has been losing mass in recent decades, with an acceleration in mass loss since 2000. In this study, we apply a self‐organizing map classification to integrated vapor transport data from the ERA‐Interim reanalysis to determine if these GrIS mass loss trends are linked to increases in moisture transport to Greenland. We find that “moist” days (i.e., days featuring anomalously intense water vapor transport to Greenland) were significantly more common during 2000–2015 compared to 1979–1994. Furthermore, the two most intense GrIS melt seasons during the last 36 years were either preceded by a record percentage of moist winter days (2010) or occurred during a summer with a record frequency of moist days (2012). We hypothesize that moisture transport events alter the GrIS energy budget by increasing downwelling longwave radiation and turbulent fluxes of sensible and latent energy.
In July 2012, the surface of the Greenland Ice Sheet (GrIS) melted to an extent unprecedented over the last 100 years; we questioned the potential for such an extreme melt event to impact marine phytoplankton offshore. We hypothesized that stratification from meltwater could reduce light limitation for phytoplankton, and used a suite of numerical models to quantify the impact for 2003–2012. Because much of the 2012 meltwater discharged from southern Greenland, our study focused on the southwestern and southeastern coasts of Greenland, and the Labrador Sea. A 1‐D phytoplankton model used output from a Regional Ocean Modeling System (ROMS) coupled with a Regional Climate Model and a hydrological model of meltwater from runoff sources on the ice sheet, peripheral glaciers, and tundra. ROMS was run with and without meltwater to test the sensitivity of phytoplankton photosynthetic rates to the meltwater input. With meltwater, the pycnocline was shallower during late summer and early fall and thus light limitation on photosynthesis was reduced. Averaged over all years, added meltwater had the potential to increase gross primary production by 3–12% in the summer (July–August), and 13–60% in the fall (September–October). This meltwater effect was amplified when light was more limiting, and thus was greatest in the fall, under cloudier conditions, with higher self‐shading, and with more light‐sensitive phytoplankton groups. As the GrIS melt is projected to increase, late summer primary production in this region has the potential to increase as well, which could constitute an important biosphere response to high‐latitude climate change.
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