3D view of fine-structure through combining glider with geoseismic water column data

(LPO, subcontractors Géosciences Marines (Ifremer) and DT/INSU-Toulon; LEGI)

Seismic reflection methods applied to the water column produce spectacular images of oceanic fine structure near dynamical features such as oceanic fronts and eddies (figure 1 Papenberg et al., 2010). These images show the structure of the ocean in a way that has never been possible before, enabling the continuous profiling of sections of over 100 km in length, from sea-surface to seabed, with a horizontal resolution of 10 m and a vertical resolution of up to 2m (Géli et al., 2009). This illustrates the ubiquituous character of layering near energetic dynamical features such as mesoscale eddies or internal frontal structures.

The proposed work is to take advantage of seismic cruises, that are regularly scheduled by the “Geosciences Marines” (GM) laboratory of Ifremer to acquire information about the solid subsurface, including those operated commercially for the hydrocarbon industry. Several such cruises will take place during the time-span of this proposal, in oceanic regions of known strong subsurface mesoscale eddy or frontal activity. New very high-resolution data acquisition, combining seismic sections and more data more directly set for physical oceanography (XBT, XCTD, gliders…), could thus be acquired at relatively small additional cost. This will shed new light on the three-dimensional characteristics of layering or intrusions: e.g. do they correspond to two-dimensional sheets or rather to filament-like features? What are the respective scaling laws of their vertical and lateral distribution? As stated by Henry Stommel, one of the leading figures in physical oceanography, “The chief source of ideas in Oceanography comes, I think, from new observations”: we anticipate that pushing further the limit of quantitative high-resolution exploration of the subsurface small scales will substantially improve our understanding of non-linear scale interactions in the ocean. Beyond the exploratory character of the proposed work, recent experimental progress in both seismic oceanography (special issue of GRL 7) and in underwater glider deployment (Testor et al. 2009), make it now possible to quantify the scaling laws of layering and thus energy fluxes (Ménesguen et al. 2009) and to identify more precisely their preferred location with respect to mesoscale dynamical features. We stress that targeted regions should correspond to the immediate vicinity of energetic mesoscale structures that are more likely to be “hot spots” of dissipation than generic open ocean areas.