Several Antarctic Peninsula (AP) ice shelves have lost significant fractions of their volume over the past decades, coincident with rapid regional climate change. Wilkins Ice Shelf (WIS), on the ...western side of the AP, is the most recent, experiencing a sequence of large calving events in 2008 and 2009. We analyze the mass balance for WIS for the period 1992−2008 and find that the averaged rate of ice‐shelf thinning was ∼0.8 m a−1, driven by a mean basal melt rate of 〈wb〉 = 1.3 ± 0.4 m a−1. Interannual variability was large, associated with changes in both surface mass accumulation and 〈wb〉. Basal melt rate declined significantly around 2000 from 1.8 ± 0.4 m a−1 for 1992–2000 to ∼0.75 ± 0.55 m a−1for 2001–2008; the latter value corresponding to approximately steady‐state ice‐shelf mass. Observations of ocean temperatureT obtained during 2007–2009 by instrumented seals reveal a cold, deep halo of Winter Water (WW; T ≈ −1.6°C) surrounding WIS. The base of the WW in the halo is ∼170 m, approximately the mean ice draft for WIS. We hypothesize that the transition in 〈wb〉 in 2000 was caused by a small perturbation (∼10–20 m) in the relative depths of the ice base and the bottom of the WW layer in the halo. We conclude that basal melting of thin ice shelves like WIS is very sensitive to upper‐ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker West Antarctic ice shelves such as George VI and Pine Island Glacier.
Key Points
Quantify mass balance of Wilkins Ice Shelf, Antarctica
Use instrumented seals to map temperature of water causing basal melt
Highlight ice shelf sensitivity to local, small scale processes
The effect of light on survival of entomopathogens is well described and efforts are underway to develop formulations that may protect an entomopathogen from damage by sunlight. The availability of ...solar simulators allows for year-round testing of solar protectants. A commercial formulation of Bacillus thuringiensis Berliner and an unformulated baculovirus isolated from Anagrapha falcifera (Kirby) were exposed to various amounts of light from a solar simulator or the sun to determine the relative effect of each source on loss of insecticidal activity. Rate of pathogen degradation was essentially the same for both light sources when original activity remaining was regressed against total energy (as measured by joules/m2). The amount of time required to reduce activity was different, however, because of a difference in total energies produced by the solar simulator and natural sunlight. Virus was approximately two times more sensitive to light than bacteria. To obtain 50% reduction of virus activity, exposure to 1.8 × 107 joules was required, whereas 3.2 × 107 joules was necessary to achieve a similar loss of activity for B. thuringiensis. The importance of reporting energy levels from various solar simulators is discussed.
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