Biogeochemical Argo: The Test Case of the NAOS Mediterranean Array

Abstract

The necessity of wide, global-scale observing systems for marine biogeochemistry emerged dramatically in the last decade. A global network based on Biogeochemical (BGC) Argo floats is considered to be one of the most promising approaches for reaching this goal. As a first step, pilot studies were encouraged to test the feasibility of a global BGC-Argo array, to consolidate the methods and practices under development, and to set up the array's characteristics. A pilot study in The Mediterranean Seadeemed a suitable candidate for a test case because it combines a relatively large diversity of oceanic BGC conditions in a reduced open-ocean basin-was consequently approved as a part of the "Novel Argo ocean Observing System" (NAOS) project, a French national initiative to promote, consolidate, and develop the Argo network. We present here a first assessment of the NAOS Mediterranean array, in view of scientific choices on observing-system strategy, on implementation and statistics on network performances, and on data-quality control.

A Regional Neural Network Approach to Estimate Water-Column Nutrient Concentrations and Carbonate System Variables in the Mediterranean Sea: CANYON-MED

“…The variables required are limited to systematically measured variables such as temperature, pressure, and salinity as well as high-quality O 2 measurements as inputs which are also widely measured (Bittig and Körtzinger, 2015). Thus, with the increased densification of high-quality O 2 measurements from BGC-Argo floats, as well as ocean gliders and moorings in the Mediterranean Sea (Testor et al, 2019;Tintoré et al, 2019;D'Ortenzio et al, 2020), CANYON-MED has a strong potential to support the development of new applications for marine biogeochemistry.…”

Profiling float observation of thermohaline staircases in the western Mediterranean Sea and impact on nutrient fluxes

“…Notably, the DW properties were modified during this period as an effect of the eastern Mediterranean transient (Gasparini et al, 2005): the observed injection of heat and salt in the deep Tyrrhenian Sea would have favored the deepest layers merging. Moreover, Durante et al (2019) documented an upward lift of the vertical structure by several hundred meters after 2010, and the presence of smaller steps below the deepest thick step, which is likely due to the ingression of a new denser water mass from the large production of anomalous DW in the Liguro-Provençal basin during the winters of 2005 and 2006. In the Algerian Basin, the present vertical structure is similar to those structures observed in 1994 (Krahmann, 1997): the vertical structure extended between 500 and 1300 dbar, with seven layers ranging between 28 and 67 m in average thickness.…”

“…Another CTD dataset has been collected by profiling floats, autonomous platforms that drift in the interior ocean and evenly surface for positioning and data transmission. The profiling floats considered in this study belonged to the Mediterranean Biogeochemical (BGC) Argo array (D'Ortenzio et al, 2020). The sampling strategy of this array is better suited for observations of thermohaline staircases than is the MedArgo array (Poulain et al, 2007) because the BGC-Argo profiles are deeper, 1000 dbar instead of 700 dbar, and remain longer within the deployment basin thanks to a parking depth of 1000 dbar, instead of 350 dbar for the MedArgo array.…”

“…During the cruise PEACETIME, repeated casts were carried out at a station located in the central Tyrrhenian Sea, a well-characterized deep area where intense thermohaline staircases are confined (Molcard and Tait, 1977;Zodiatis and Gasparini, 1996;Falco et al, 2016;Durante et al, 2019). The profiles from the surface to the bottom were collected every day during 4 d, showing well-ordered thermohaline staircases (Fig.…”

“…In order to untangle the two processes, an accurate measurement of thermohaline changes requires temporal continuity of layers, which is the most challenging aspect for observations. Indeed, because thermohaline staircases occur far from the coastal zones and develop at depth, data acquisition is often limited to high-resolution but shortterm records (e.g., Buffett et al, 2017) or coarse temporal resolution but long-term records (e.g., Falco et al, 2016;Durante et al, 2019). Moreover, most of the existing studies have not considered the role of thermohaline staircases in nutrient distribution, because pertinent observations of biogeochemical parameters were hard to obtain in the water column at relevant temporal and spatial scales.…”