4 research outputs found
Joint analysis of coastal altimetry and high-frequency (HF)Â radar data: observability of seasonal and mesoscale ocean dynamics in the Bay of Biscay
Land-based coastal high-frequency (HF) radar systems provide operational measurements of
coastal surface currents (within 1â3 m depth) with high spatial
(300 mâ10 km) and temporal (ââ€â1 h) sampling resolutions, while the
near-continuous altimetry missions provide information, from 1993 until today,
on geostrophic currents in the global ocean with typical along-track and
temporal sampling resolutions of â>â7 km and â>â9Â days, respectively. During
the last years, the altimetry community has made a step forward in improving
these data in the coastal area, where the data present lower quality than in
the open ocean. The combination of HF radar and altimetry measurements arises
as a promising strategy to improve the continuous monitoring of the coastal
area (e.g. by expanding the measurements made by HF radars to adjacent areas
covered by the altimetry or by validating/confirming improvements brought by
specific coastal algorithms or new altimeter missions). A first step towards
this combination is the comparison of both data sets in overlapping areas.In this study, a HFÂ radar system and two Jason-2 satellite altimetry
products with different processing are compared over the period from
1 January 2009 to 24 July 2015. The results provide an evaluation of the
performance of different coastal altimetry data sets within the study area
and a better understanding of the ocean variability contained in the
HFÂ radar and altimetry data sets. Both observing systems detect the main
mesoscale processes within the study area (the Iberian Poleward Current and
mesoscale eddies), and the highest correlations between radar and altimetry
(up to 0.64) occur in the slope where the Iberian Poleward Current
represents a significant part of the variability in the circulation.
Besides, the use of an Ekman model, to add the wind-induced current
component to the altimetry-derived geostrophic currents, increases the
agreement between both data sets (increasing the correlation by around 10 %).</p
Coastal submesoscale processes and their effect on phytoplankton distribution in the southeastern Bay of Biscay
Submesoscale processes have a determinant role in the dynamics of oceans by transporting momentum, heat, mass, and particles. Furthermore, they can define niches where different phytoplankton species flourish and accumulate not only by nutrient provisioning but also by modifying the water column structure or active gathering through advection. In coastal areas, however, submesoscale oceanic processes act together with coastal ones, and their effect on phytoplankton distribution is not straightforward. The present study brings the relevance of hydrodynamic variables, such as vorticity, into consideration in the study of phytoplankton distribution, via the analysis of in situ and remote multidisciplinary data. In situ data were obtained during the ETOILE oceanographic cruise, which surveyed the Capbreton Canyon area in the southeastern part of the Bay of Biscay in early August 2017. The main objective of this cruise was to describe the link between the occurrence and distribution of phytoplankton spectral groups and mesoscale to submesoscale ocean processes. In situ discrete hydrographic measurements and multi-spectral chlorophyll a (chl a) fluorescence profiles were obtained in selected stations, while temperature, conductivity, and in vivo chl a fluorescence were also continuously recorded at the surface. On top of these data, remote sensing data available for this area, such as high-frequency radar and satellite data, were also processed and analysed. From the joint analysis of these observations, we discuss the relative importance and effects of several environmental factors on phytoplankton spectral group distribution above and below the pycnocline and at the deep chlorophyll maximum (DCM) by performing a set of generalized additive models (GAMs). Overall, salinity is the most important parameter modulating not only total chl a but also the contribution of the two dominant spectral groups of phytoplankton, brown and green algae groups. However, at the DCM, among the measured variables, vorticity is the main modulating environmental factor for phytoplankton distribution and explains 19.30â% of the variance. Since the observed distribution of chl a within the DCM cannot be statistically explained without the vorticity, this research sheds light on the impact of the dynamic variables in the distribution of spectral groups at high spatial resolution