High-resolution variability of dissolved and suspended organic matter in the Cape Verde Frontal Zone

Abstract

Distributions of dissolved (DOM) and suspended (POM) organic matter, and their chromophoric (CDOM) and fluorescent (FDOM) fractions, are investigated at high resolution (< 10 km) in the Cape Verde Frontal Zone (CVFZ) during fall 2017. In the epipelagic layer (< 200 m), meso- and submesoscale structures (meanders, eddies) captured by the high resolution sampling dictate the tight coupling between physical and biogeochemical parameters at the front. Remarkably, fluorescent humic-like substances show relatively high fluorescence intensities between 50 and 150 m, apparently not related to local mineralization processes. We hypothesize that it is due to the input of Sahara dust, which transports highly re-worked DOM with distinctive optical properties. In the mesopelagic layer (200-1500 m), our results suggest that DOM and POM mineralization occurs mainly during the transit of the water masses from the formation sites to the CVFZ. Therefore, most of the local mineralization seems to be due to fast-sinking POM produced in situ or imported from the Mauritanian upwelling. These local mineralization processes lead to the production of refractory CDOM, an empirical evidence of the microbial carbon pump mechanism. DOM released from these fast-sinking POM is the likely reason behind the observed columns of relatively high DOC surrounded by areas of lower concentration. DOM and POM dynamics in the CVFZ has turned out to be very complex, in parallel to the complexity of meso- and submesoscale structures present in the area. On top of this high resolution variability, the input of Sahara dust or the release of DOM from sinking particles have been hypothesized to explain the observed distributions.

Dissolved Organic Matter Fluorescence as a Tracer of Upwelling and Microbial Activities in Two Cyclonic Eddies in the Eastern Tropical North Atlantic

“…Therefore, Saharan dust might have attenuated UV exposure during cruise M156, limiting the photodegradation of humic‐like FDOM (Herman et al., 1999; Smyth, 2011). Moreover, Saharan dust can also be a source of humic‐like FDOM, especially of FDOM peak M (C398) (Campanero et al., 2022; Sánchez‐Pérez et al., 2016) and iron contained in dust and associated with humic substances might also attenuate photodegradation in surface waters (Y. H. Xiao et al., 2013).…”

Solid phase extraction of ocean dissolved organic matter with PPL cartridges: efficiency and selectivity

“…The CBGF transports large amounts of coastal dissolved (DOM) and suspended organic matter (POM) originated in the Mauritanian coast to the adjacent oligotrophic open ocean (Gabric et al, 1993;Ohde et al, 2015). In surface and central waters, the distribution of DOM and POM is dictated by the position of the CVF and associated meanders and eddies (A ́lvarez- Salgado and Arıśtegui, 2015;Campanero et al, 2022;Valiente et al, 2022). In intermediate and deep waters, POM and DOM distribute according to water mass mixing and large-scale remineralization of these materials from the water mass formation areas to the CVFZ (Campanero et al, 2022;Valiente et al, 2022).…”

“…In surface and central waters, the distribution of DOM and POM is dictated by the position of the CVF and associated meanders and eddies (A ́lvarez- Salgado and Arıśtegui, 2015;Campanero et al, 2022;Valiente et al, 2022). In intermediate and deep waters, POM and DOM distribute according to water mass mixing and large-scale remineralization of these materials from the water mass formation areas to the CVFZ (Campanero et al, 2022;Valiente et al, 2022). The organic matter that is mineralized in the intermediate and deep layers of the CVFZ is primarily sinking POM, which is less susceptible to lateral transport in the surface layer, so it sinks fast into the deeper layer (Fischer et al, 2009;A ́lvarez-Salgado and Arıśtegui, 2015;Campanero et al, 2022;Valiente et al, 2022).…”

The role of submesoscale filaments in restratification of the surface mixed layer and dissolved oxygen variability in large Lake Geneva: field evidence complemented by Lagrangian particle-tracking

“…Due to the vertical motion associated with submesoscale processes, momentum and tracers such as heat, mass, oxygen, pollutants and carbon can be exchanged between the surface and the deep pycnocline (Smith et al, 2016;Erickson and Thompson, 2018;Su et al, 2018;Archer et al, 2020;Freilich and Mahadevan, 2021). Existing observational evidence and numerical studies indicate that submesoscale processes such as fronts and filaments can play an important role in ocean productivity, biogeochemical fluxes and biodiversity patterns (Mahadevan, 2016;Pascual et al, 2017;Lehahn et al, 2018;Hernańdez-Hernańdez et al, 2020;Fadeev et al, 2021;Kaiser et al, 2021;Campanero et al, 2022;Xiu et al, 2022). Based on an idealized modeling study, Levy and Martin (2013) demonstrated that the primary production associated with mesoscale currents can be underestimated by a third if submesoscale processes are not included.…”