Abstract
Abstract. Upwelling systems play a key role in the global carbon and nitrogen cycles and are also of local relevance due to their high productivity and fish resources. To capture and understand the high spatial and temporal variability in physical and biogeochemical parameters found in these regions, novel measurement techniques have to be combined in an interdisciplinary manner. Here we use high-resolution glider-based physical–biogeochemical observations in combination with ship-based underwater vision profiler, sensor and bottle data to investigate the drivers of oxygen and nitrate variability across the shelf break off Mauritania in June 2014. Distinct oxygen and nitrate variability shows up in our glider data. High-oxygen and low-nitrate anomalies were clearly related to water mass variability and probably linked to ocean transport. Low-oxygen and high-nitrate patches co-occurred with enhanced turbidity signals close to the seabed, which suggests locally high microbial respiration rates of resuspended organic matter near the sea floor. This interpretation is supported by high particle abundance observed by the underwater vision profiler and enhanced particle-based respiration rate estimates close to the seabed. Discrete in situ measurements of dissolved organic carbon and amino acids suggest the formation of dissolved organic carbon due to particle dissolution near the seabed fueling additional microbial respiration. During June an increase in the oxygen concentration on the shelf break of about 15 µmol kg−1 was observed. These changes go along with meridional circulation changes but cannot be explained by typical water mass property changes. Thus our high-resolution interdisciplinary observations highlight the complex interplay of remote and local physical–biogeochemical drivers of oxygen and nitrate variability off Mauritania, which cannot be captured by classical shipboard observations alone.
Highlights
The Mauritanian upwelling region is located in the shadow zone of the eastern tropical North Atlantic (ETNA), an area characterized by sluggish mean circulation (Luyten et al, 1983)
We use high-resolution glider-based physical–biogeochemical observations in combination with ship-based underwater vision profiler, sensor and bottle data to investigate the drivers of oxygen and nitrate variability across the shelf break off Mauritania in June 2014
South Atlantic Central Water (SACW) plays an important role for the oxygen supply into the region at the depth range of the shallow oxygen minimum zone (OMZ), which has already been investigated in various studies (Peña-Izquierdo et al, 2012, 2015; Klenz et al, 2018)
Summary
The Mauritanian upwelling region is located in the shadow zone of the eastern tropical North Atlantic (ETNA), an area characterized by sluggish mean circulation (Luyten et al, 1983). The deep OMZ has a core depth of about 400 m and minimum oxygen concentrations around 40 μmol kg−1 (Karstensen et al, 2008; Brandt et al, 2015). In this paper the focus is on the shallow OMZ with a core depth of about 100 m and oxygen concentrations between 40 and 60 μmol kg−1 (Karstensen et al, 2008; Brandt et al, 2015; Klenz et al, 2018). Recent observational and modeling studies investigated the importance of low-oxygen submesoscale coherent vortices, called “dead zone eddies” (Karstensen et al, 2015), for the maintenance of the offshore shallow OMZ (Schütte et al, 2016; Frenger et al, 2018), detailed studies on the shallow OMZ are sparse, close to the Mauri-
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
