Hydrographic and Biological Survey of a Surface‐Intensified Anticyclonic Eddy in the Caribbean Sea

C G Van Der Boog,M F Leopold,K Schulz,M F De Jong,J D Pietrzak,S C V Geelhoed,M Scheidat,C A Katsman,H A Dijkstra

doi:10.1029/2018jc014877

Abstract

AbstractIn the Caribbean Sea, mesoscale anticyclonic ocean eddies impact the local ecosystem by mixing of low salinity river outflow with the nutrient‐rich waters upwelling along the Venezuelan and Colombian coast. To gain insight into the physics and the ecological impact of these anticyclones, we performed a combined hydrographic and biological survey of one Caribbean anticyclone in February 2018. We found that the anticyclone had a radius of 90 km and was surface intensified with the strongest velocities (0.72 m/s) in the upper 150 m of the water column. Below, isopycnal displacements were found down to 700 dbar. The core of the anticyclone entrained waters from the Orinoco River plume and contained slightly elevated chlorophyll concentrations compared to the surroundings. At the edge of the anticyclone we observed higher densities of flying fish but not higher densities of predators like seabirds and cetaceans. Below the surface, a strong temperature inversion (0.98 °C) was present within a barrier layer. In addition, we found thermohaline staircases that originated from double diffusion processes within Tropical Atlantic Central Water.

Highlights

In the Caribbean Sea, two major nutrient sources are available: the wind-driven upwelling along the Venezuelan and Colombian coast and the plumes of the Amazon and Orinoco River that are advected into the basin (Bidigare et al, 1993; Gilbes & Armstrong, 2004; Molleri et al, 2010; Morell & Corredor, 2001; Rueda-Roa & Muller-Karger, 2013)
Barrier Layer and Temperature Inversion In the previous section, it was shown that the low salinity in the core of the anticyclone and the elevated productivity suggests that the anticyclone entrained waters from the Orinoco River plume
The anticyclone originated near Grenada Passage, which is similar to the anticyclone surveyed by Rudzin et al (2017)

Summary

Introduction

In the Caribbean Sea, two major nutrient sources are available: the wind-driven upwelling along the Venezuelan and Colombian coast and the plumes of the Amazon and Orinoco River that are advected into the basin (Bidigare et al, 1993; Gilbes & Armstrong, 2004; Molleri et al, 2010; Morell & Corredor, 2001; Rueda-Roa & Muller-Karger, 2013). Observations were based on surface drifter data (Centurioni & Niiler, 2003; Molinari et al, 1981; Richardson, 2005) and satellite altimetry (e.g., Alvera-Azcárate et al, 2009; Nystuen & Andrade, 1993) These studies provide valuable information about the size and surface properties of the anticyclones, they do not provide details on their vertical structure. These can be obtained from dedicated surveys of eddies in the Caribbean Sea (Corredor et al, 2004; Morell et al, 2006; Rudzin et al, 2017; Silander, 2005). An overview of the hydrographic properties, including a water mass analysis, is given in the Appendix

Materials and Methods

Upper Ocean Characteristics

Ecological Implication

Summary, Discussion, and Conclusions