Meeting Abstracts

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New Lagrangian Experiments Proposed for the Gulf of Mexico and Subpolar North Atlantic

Amy Bower
Woods Hole Oceanographic Institution
(Abstract received 05/17/2012 for session A)
ABSTRACT

Two proposed Lagrangian experiments will be described. The first is “Vertical Structure and Temporal Variability of Particle Dispersion in the Gulf of Mexico (GoM)”. Its primary objective is to improve the predictability of surface and subsurface pollutant trajectories and dilution in the GoM. We plan to conduct 12 “re-enactments” of the spill using near-surface drifters and acoustically tracked subsurface RAFOS floats. Groups of 3-5 instruments will be simultaneously released monthly for one year near the Deepwater Horizon (DWH) spill site at three levels, 0, 300 and 1100 m depth, to study the differences in dispersion statistics as a function of depth and time. Over 100 float-years of data will result from these releases. On four of the deployment cruises (cruises # 3, 6, 9, and12), the standard monthly re-enactments will be enhanced by mass drifter releases and subsequent recoveries of 50 more surface drifters that will be launched on a regular grid in an approximately 5-10 km domain centered at the DWH site, and then recovered several days later. These mass releases will allow mapping of the dynamical structures governing stirring, transport and dilution processes in the GoM, and will provide a better statistical context for the dispersion estimates resulting from the monthly re-enactments. This component will provide the equivalent of more than 200 drifter-deployments with unprecedented resolution of near-surface current- and wave-induced dispersion. What sets the proposed study apart from other GoM float and drifter releases is that it is focused on how the dispersion of a pollutant introduced at several depths at one location varies over a year, under different flow conditions.

The second proposed float study is part of an international effort to set up an observing system for the overturning circulation in the subpolar North Atlantic for a 10-year period, starting in 2014. The primary objective of the Lagrangian component of OSNAP is to map out the pathways of the Nordic Seas overflows in the subpolar region. Previous work at the Labrador Sea Water level has indicated that there are interior, as well as boundary, pathways for the spread of upper North Atlantic Deep Water, but less is known about the pathways of the deeper, denser overflow waters. To complement the deployment of moored arrays, gliders and ARGO floats along a section stretching from Labrador to Greenland to Ireland, about 50 RAFOS floats will be released sequentially at each of two locations: one northeast of the southern tip of Greenland in the Irminger Basin, and one over the eastern flank of the Reykjanes Ridge in the Iceland Basin. Each group will reveal the pathways connecting the three sub-basins of the subpolar region and are critical to the interpretation of variability in volume, heat and freshwater fluxes across the OSNAP line.