A Multiplatform Experiment to Unravel Meso- and Submesoscale Processes in an Intense Front (AlborEx)

Ananda Pascual,John T Allen,Amala Mahadevan,Baptiste Mourre,Antonio Olita,Pierre-Marie Poulain,Benjamin Casas,Antonio Tovar-Sanchez,Joaquín Tintoré,Mariona Claret,Arthur Capet,Evan Mason,Simon Ruiz,Charles Troupin

doi:10.3389/fmars.2017.00039

Abstract

The challenges associated with meso- and submesoscale variability (between 1-100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions associated with mesoscale and submesoscale features in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior.

Highlights

Meso- and submesoscale features play a major role in the redistribution of properties such as heat, salt, and biogeochemical tracers, with a significant impact on the ocean’s primary productivity
Sea surface temperature (SST) images, sea surface altimetry and ocean color were closely screened and used to determine the positions of the two CTD surveys to be conducted during the experiment
The circulation patterns depicted by surface altimetry in March 2014 (Figure 2) represent the typical circulation of the Alboran Sea with the presence of both the Western and Eastern Alboran Gyres (e.g., Renault et al, 2012)

Summary

Introduction

Meso- and submesoscale features play a major role in the redistribution of properties such as heat, salt, and biogeochemical tracers, with a significant impact on the ocean’s primary productivity. The dynamics associated with these features result in enhanced vertical velocities that may locally generate mixing or enforce stratification on time scales that range from a few days to several months and from a few km to 100 km (Mahadevan, 2016; McWilliams, 2016). Modeling studies of frontal regions suggest that vertical exchange is enhanced at density fronts (Lévy et al, 2001; Lapeyre and Klein, 2006; Mahadevan and Tandon, 2006; Capet et al, 2008; Omand et al, 2015). To account for the net impact of these mechanisms we need to observe and quantify them in-situ, and integrate them with satellite imagery and model simulations obtained using combinations of one- or two-way nesting (Penven et al, 2006; Mason et al, 2010) or adaptive resolution models

Methods

Results

Conclusion