“Geophysical Research Letters” published a study from IMEDEA, IFISC and SOCIB which revisits previous estimates of mesoscale activity and eddydriven offshore transport using a new altimetric product
Feb. 11, 2015
The important contribution of mesoscale eddies to oceanic fluxes is well known. Traveling eddies trap water in
their cores and, hence, transport mass, physical properties and biogeochemical tracers along paths that do not
necessarily follow large-scale circulation patterns. Eddy-driven transport is therefore an essential regulator of
global climate and oceanic productivity.
Assessing eddy contributions to oceanic transport requires identification of individual eddies, followed by an
estimate of the volume of water trapped within them. Altimetry, i.e., satellite remote-sensing of sea surface
elevation, provides the information required to identify eddies and follow their trajectories. The article by Capet
et al. (2014) evaluates how the new revision of the satellite sea level anomaly maps released by AVISO in April
2014 affects the representation of mesoscale eddies in the Eastern Boundary Upwelling Systems (EBUS). Due to
a finer effective resolution, the new product enables the detection of more eddies (+37%) and also shows
changes in eddy characteristics, most notably a tendency for smaller eddy radii. Estimates of the eddy transport
differences from the revised and previous AVISO products yields the counterintuitive result that the new product
returns a lower westward eddy transport (-12%). Despite the higher number of eddies identified, this finding
arises from the quadratic impact of eddy radius on eddy volume estimation.
Mesoscale activity is an important factor controlling oceanic productivity, especially in EBUS which support a
large part of the world fisheries. While this study should help to understand the complex interplay between
mixing and biological activity, it also suggests the need for a reassessment of the mesoscale contribution to
oceanic transport in other regions of the world where the revised altimetry product also reveals higher levels of
mesoscale activity.
Figure: Global map of sea surface elevation. Red colors indicate positive
anomalies typical of anticyclonic eddies and blue colors indicate
negative anomalies caused by cyclonic eddies; colored lines represent their
trajectories. Gray shading highlights the four Eastern Boundary Upwelling
Systems for which eddy-induced offshore transport has been evaluated.
