Description: High-resolution measurements of the air-ice-ocean system during an October 2015 event in the Beaufort Sea demonstrate how stored ocean heat can be released to temporarily reverse seasonal ice advance. Strong on-ice winds over a vast fetch caused mixing and release of heat from the upper ocean. This heat was sufficient to melt large areas of thin, newly formed pancake ice; an average of 10 MJ/m2 was lost from the upper ocean in the study area, resulting in ∼3-5 cm pancake sea ice melt. Heat and salt budgets create a consistent picture of the evolving air-ice-ocean system during this event, in both a fixed and ice-following (Lagrangian) reference frame. The heat lost from the upper ocean is large compared with prior observations of ocean heat flux under thick, multi-year Arctic sea ice. In contrast to prior studies, where almost all heat lost goes into ice melt, a significant portion of the ocean heat released in this event goes directly to the atmosphere, while the remainder (∼30-40%) goes into melting sea ice. The magnitude of ocean mixing during this event may have been enhanced by large surface waves, reaching nearly 5 m at the peak, which are becoming increasingly common in the autumn Arctic Ocean. The wave effects are explored by comparing the air-ice-ocean evolution observed at short and long fetches, and a common scaling for Langmuir turbulence. After the event, the ocean mixed layer was deeper and cooler, and autumn ice formation resumed.

Description: Purpose: To investigate brain-wide white matter structural changes associated with amyotrophic lateral sclerosis (ALS) using an automatic single seed point tractography-based segmentation method, probabilistic neighborhood tractography (PNT), which provides quantitative measures of both tract integrity and shape. Materials and Methods: Diffusion MRI data were acquired from 30 patients with ALS (ALS Functional Rating Scale-Revised score 〉 20) and 30 matched controls. PNT was used to segment 12 major projection, commissural and association fibers, and assess differences in how the shape of an individual subject's tract compares to that of a predefined reference tract, in addition to providing tract-average mean diffusivity (〈D〉) and fractional anisotropy (FA) data. Results: Across all 12 tracts, group-averaged 〈D〉 was larger, while group-averaged FA was equal to or smaller in value for patients than controls. These differences were significant for right cingulum 〈D〉, and left and right corticospinal tract (CST) 〈D〉 and FA ( P -values 6 × 10 −5 to 0.03). Tract shape modeling indicated that there were significantly greater topological differences from the reference tract in left and right CST, and right uncinate fasciculus ( P -values 0.02 to 0.04) for patients than controls. The rate of disease progression was significantly negatively correlated with bilateral CST FA ( P -values 0.01 to 0.02). Conclusion: ALS, although particularly affecting CST, is associated with subtle changes in white matter tract integrity and shape in several other major fibers within the brain. Correlations between CST integrity and disease progression rate suggest that quantitative tractography may provide useful biomarkers of disease evolution in ALS. J. Magn. Reson. Imaging 2013;. © 2013 Wiley Periodicals, Inc.