Submesoscale physical‐biogeochemical coupling across the Ligurian current (northwestern Mediterranean) using a bio‐optical glider

Abstract

A bio-optical autonomous underwater gliding vehicle, equipped with a conductivity, temperature, depth (CTD) sensor, an oxygen sensor, backscatter meters, chromophoric dissolved organic matter (CDOM) and chlorophyll fluorometers, and upwelling and downwelling radiometers was developed to characterize the biogeochemical response to physical forcing at the submesoscale (1-10 km). Winter data obtained in the northwestern Mediterranean basin in a 50-km transect that crossed the permanent, along-coast Ligurian Current show tight physical-biogeochemical coupling across the Ligurian Current, not observed using other sampling strategies. At the scale of the transect, the various biogeochemical parameters displayed independent behaviors, while at the submesoscale, there was a coherent covariance of these variables, especially in the frontal zone. Nearisopycnal tongues of elevated fluorescence and oxygen concentration were recorded down to a depth of 180 m and are the likely signature of a converging horizontal and downwelled water flow. Local anomalies in a horizontal section well below the mixed-layer depth are likely representative of downwelled waters from the euphotic layer. Intrusions of elevated CDOM concentrations together with signatures of smaller particles are the likely features of a local divergence and upwelled waters from subjacent aphotic layers. These are particularly apparent in the form of local anomalies in a horizontal section within the mixed layer. Similar tongues were observed in data from subsequent glider deployments. Such biogeochemical signatures enable the identification of upward and downward physical motions not observed by other technologies, reinforcing the need for coupled high-resolution physical-biogeochemical studies, not only for investigating biogeochemical processes themselves but also for resolving physical processes at these scales.

Guidelines Towards an Integrated Ocean Observation System for Ecosystems and Biogeochemical Cycles

“…Körtzinger et al 2004;Boss et al, 2008;Bishop and Wood, 2009) or gliders (e.g. Davis et al, 2008;Perry et al, 2008;Niewiadomska et al, 2008) which allow new observational scales in ocean biogeochemistry to be tackled. In parallel, certain marine mammals have now been equipped with biogeochemical sensors allowing sustained data acquisition to be initiated in areas where data scarcity is generally the rule (e.g.…”

“…O2, Chla, optically resolved POC (Davis et al, 2008;Niewiadomska et al, 2008;Perry et al, 2008) and soon, very likely, NO 3 (Johnson, unpublished). Acoustic backscattering measurements have also been used to provide bulk information on zooplankton biomass (Davis et al, 2008).…”

Gliders as a Component of Future Observing Systems

“…, Gary Meyers (2) , Chari Pattiaratchi (3) , Ralf Bachmayer (4) , Dan Hayes (5) , Sylvie Pouliquen (6) , Loic Petit de la Villeon (6) , Thierry Carval (6) , Alexandre Ganachaud (7) , Lionel Gourdeau (7) , Laurent Mortier (8) , Hervé Claustre (9) , Vincent Taillandier (9) , Pascale Lherminier (10) , Thierry Terre (10) , Martin Visbeck (11) , Johannes Karstensen (11) , Gerd Krahmann (11) , Alberto Alvarez (12) , Michel Rixen (12) , Pierre-Marie Poulain (13) , Svein Osterhus (14) , Joaquin Tintore (15) , Simon Ruiz (15) , Bartolomeo Garau (15) , David Smeed (16) , Gwyn Griffiths (16) , Lucas Merckelbach (16) , Toby Sherwin (17) , Claudia Schmid (18) , John A. Barth (19) , Oscar Schofield ( (23) SIO …”

A New Glider-Compatible Optical Sensor for Dissolved Organic Matter Measurements: Test Case from the NW Mediterranean Sea

“…In our data, spring contourplots (Figure 7) may suggest some similar downwelling at the front edge. What resembles a downwelling patch is located approximately at the same position (∼25-40 km), but less pronounced in terms of depth, compared to the study of Niewiadomska et al (2008) (see S A and O 2 inversions in the 50-150 m depth range, and the deepening of Chl-a, Trp-like, Phe-like and BB700 data).…”

“…The first glider measurements of physical-biogeochemical interactions across this frontal zone was presented by Niewiadomska et al (2008) during the winter time, i.e., when NC velocities are higher and the mesoscale activity at its maximum. Their study was carried out along the first half of the transect presented here and highlighted the importance of biogeochemical tracers for understanding submesoscale frontal dynamics.…”