Mass, nutrients and dissolved organic carbon (DOC) lateral transports off northwest Africa during fall 2002 and spring 2003

Abstract

Abstract. The circulation patterns and the impact of the lateral export of nutrients and organic matter off NW Africa are examined by applying an inverse model to two hydrographic datasets gathered in fall 2002 and spring 2003. These estimates show significant changes in the circulation patterns at central levels from fall to spring, particularly in the southern boundary of the domain related to zonal shifts of the Cape Verde Frontal Zone. Southward transports at the surface and central levels at 26∘ N are 5.6±1.9 Sv in fall and increase to 6.7±1.6 Sv in spring; westward transports at 26∘ W are 6.0±1.8 Sv in fall and weaken to 4.0±1.8 Sv in spring. At 21∘ N a remarkable temporal variability is obtained, with a northward mass transport of 4.4±1.5 Sv in fall and a southward transport of 5.2±1.6 Sv in spring. At intermediate levels important spatiotemporal differences are also observed, and it must be highlighted that a northward net mass transport of 2.0±1.9 Sv is obtained in fall at both the south and north transects. The variability in the circulation patterns is also reflected in lateral transports of inorganic nutrients (SiO2, NO3, PO4) and dissolved organic carbon (DOC). Hence, in fall the area acts as a sink of inorganic nutrients and a source of DOC, while in spring it reverses to a source of inorganic nutrients and a sink of DOC. A comparison between nutrient fluxes from both in situ observations and numerical modeling output is finally addressed.

Lateral transports of mass, inorganic nutrients and dissolved oxygen in the Cape Verde Frontal Zone in summer 2017

“…In this work, the dynamics related to the water masses and their O 2 and inorganic nutrient concentrations in the limit between the eastern NASG and the NATG during the summer are analyzed. The sampled water masses in the northern area of the CVB during July-August of 2017 match with those documented so far and their spatial distributions (Hernández-Guerra et al, 2005;Pastor et al, 2012;Peña-Izquierdo et al, 2012;Burgoa et al, 2020). Θ − S A diagrams from the cruise FLUXES-I exhibit a latitudinal change between SACW and NACW, from south to north, below the mixing layer and above 700 m (Pelegrí et al, 2017).…”

“…The differences of CT and S A observed between the water masses at the Θ − S A diagrams are verified in the sections of CT and S A , where the water masses can be defined and identified along the sections. At central levels, SACW was mainly sampled in the south-east corner with around 35.65 g kg −1 of S A at 300 m. In contrast, NACW was found in transects N and W with around 36.15 g kg −1 of S A at 300 m. On the other hand, CVFZ was located where isohaline of S A = 36.15 g kg −1 , equivalent to isohaline of 36 of S P , intersects the 150 m isobath (Zenk et al, 1991;Burgoa et al, 2020) (Fig. A4).…”

“…Dianeutral transfers between the layers were considered to be negligible as compared to other sources of lateral transports, so they were not included in the inverse model. Furthermore, the inverse model provides information only from the box boundaries and cannot be used to provide any details of dianeutral fluxes spatial distribution within the box (Burgoa et al, 2020).…”

“…In recent years, several authors have addressed the distribution of O 2 and inorganic nutrients and also their link to the physical processes taking into account the water mass distributions and transports in this margin of the North Atlantic Ocean (Pelegrí et al, 2006;Machín et al, 2006;Pastor et al, 2008;Álvarez and Álvarez-Salgado, 2009;Peña-Izquierdo et al, 2012;Pastor et al, 2013;Peña-Izquierdo et al, 2015;Hosegood et al, 2017;Burgoa et al, 2020). These physical processes range from the regional scale, usually associated to advective processes, to mesoscale and smaller scales, usually associated to mixing processes (Pastor et al, 2008).…”

Variability in Water-Column Respiration and Its Dependence on Organic Carbon Sources in the Canary Current Upwelling Region

“…Moreover, surface chlorophyll a (Chla) was higher in the spring than in the fall, particularly in open ocean waters (Figures 1a,b). A detailed description on the hydrography, circulation and mass transport in the region of study during the two cruises is described in Burgoa et al (2020).…”