AMAZOMIX cruise - Glider dataset

Glider data associated with the AMAZOMIX cruise. The Amazon shelf encompasses a variety of physical processes, such as fluvial inputs, coastal currents, mesoscale, filaments, tides, internal waves and upwelling, influencing nutrient concentrations, chlorophyll and suspended matter. They also affect energy, salt and heat balances; parameters that condition physical/biogeochemical interactions and ecosystem functioning, from bacteria to plankton to fish resources. In particular, internal tidal waves are very energetic in this region. They impact biogeochemical cycles via the vertical mixture induced by their dissipation or vertical movements induced by their propagation. They thus allow a significant input of nutriments into the euphotic layer enhancing primary production, as observed on the surface from watercolour data. Internal tidal waves could thus influence the biological pump and the carbon cycle. In addition, overall marine biodiversity of the region, from bacteria to fish is not well described. The connectivity of species in the tropical Atlantic is also still an open question. The Caribbean region is by far more bio-diverse than the Brazilian one. One of the hypotheses is that the Amazon plume, which can extend up to 3,000 km off the mouth, would constitute a barrier for some organisms. The Amazon Shelf is thus an ideal experimental laboratory to study the impact of physical processes on the structure and function of neritic and oceanic marine ecosystems.
In this context, the objective of the multidisciplinary AMAZOMIX survey was to study the impact of the Amazon River plume, internal tides and associated turbulent mixing, on marine ecosystem in contrasting regions off the Amazon shelf. For that purpose, the multidisciplinary AMAZOMIX project brings together physicists, biogeochemists, bioopticians and biologists. The sampling strategy consists in the simultaneous acquisition of a comprehensive set of environmental and biological compartments, including micro-organisms (bacteria, phyto and zooplankton) and higher trophic levels (micronekton, demersal and pelagic fish). AMAZOMIX is the first campaign to develop this multi-disciplinary approach off the Amazon shelf. In situ results will be analysed in interaction with digital tools and data, modelling (1/36°, with and without tides, 1/12° coupled) and satellite data analyses.
The glider was equipped with:
- a Seabird pumped CTD (temperature, pressure, conductivity),
- an Aanderaa optode (dissolved oxygen),
- and a WetLabs optical puck (chlorophyll-a fluorescence, CDOM, turbidity).
Sensors sampled every 5 seconds, corresponding to a vertical resolution of approximately 1 m. Between surfacings, the glider estimated its position using navigation sensors (compass), allowing computation of mean dive-averaged horizontal currents by comparing dead-reckoned positions with GPS fixes.
Data were processed using the GEOMAR Matlab Toolbox (Krahmann, 2023), which included correction for thermal lag following Garau et al. (2011). Temperature and salinity were converted to conservative temperature and absolute salinity using the Gibbs Seawater Python library (McDougall & Barker, 2011). Profiles were validated against reference CTD casts at the deployment site.