The Southern Ocean is chronically under-sampled due to its remoteness, harsh environment and sea-ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data, however they often underestimate surface mixed layer depth (MLD), with consequences for water-column properties. In this study, a coupled circulation and sea-ice model was implemented for the region adjacent to the West Antarctic Peninsula (WAP), a climatically sensitive region which has exhibited decadal trends toward higher temperatures, a shorter sea-ice season and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air-ice drag coefficients and Langmuir-circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air-ice drag coefficient also increased the modeled MLD by similar amounts, and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for a bias towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the WAP during late summer and suggests that areas of intense summertime sea-ice melt can still show net annual freezing due to high sea-ice formation during the winter.

The Greenland Ice Sheet (GrIS) is experiencing significant mass loss and freshwater discharge at glacier fronts. The freshwater input from Greenland will impact the physical properties of adjacent coastal seas, including important regions of deep water formation and contribute to global sea level rise. However, the biogeochemical impact of increasing freshwater discharge from the GrIS is less well constrained. Here, we demonstrate the use of bio-optical sensors on ocean gliders to track biogeochemical properties of meltwaters off Southwest Greenland. Our results reveal that fresh, coastal waters, with an oxygen isotopic composition characteristic of glacial meltwater, are distinguished by a high optical backscatter and high levels of fluorescing dissolved organic matter (FDOM), representative of the overall coloured dissolved organic matter pool. Reconstructions of geostrophic velocities are used to show that these particle and FDOM-enriched coastal waters cross the strong boundary currents into the Labrador Sea. Meltwater input into the Labrador Sea is likely driven by mesoscale processes, such as eddy formation and local bathymetric steering, in addition to wind-driven Ekman transport. Ocean gliders housing bio-optical sensors can provide the high-resolution observations of both dissolved and particulate glacially-derived material that are needed to understand meltwater dispersal mechanisms and their sensitivity to future climatic change.