Upper ocean observations in eastern C aribbean S ea reveal barrier layer within a warm core eddy

Abstract

Three‐dimensional measurements of a large warm core eddy (WCE) and the Caribbean Current are acquired using oceanic profilers deployed during a NOAA research aircraft study in September 2014 in the eastern Caribbean Sea. Measurements of the near‐surface atmosphere are also collected to examine air‐sea processes over the eddy. These novel measurements showcase temperature and salinity for the eddy and background flow, upper ocean stratification, a residing barrier layer (BL), velocity structure, and water mass characteristics. The eddy's thermal structure is alike that of WCEs in the Gulf of Mexico (GoM) whereas surrounding waters have relatively deeper isotherms compared to its GoM counterparts. Analyses suggest that upper ocean stratification within the study region is due to a BL. These are the first observations of a BL inside a WCE to the best of our knowledge. Reduced shear comparisons suggest that the upper ocean, especially within the WCE, would be more resistant to tropical cyclone (TC) induced mixing than the GoM because of the BL. The eddy is suspected to originate from North Brazil Current rings, given its fresh anomalies relative to climatology and surrounding waters and its trajectory prior to sampling. Atmospheric measurements suggest the WCE is influencing the lower atmosphere along its boundaries. These observations signify that not only does this WCE have deep thermal structure and modulate the near‐surface atmosphere but it is unique because it has a BL. The findings and analyses suggest that a similar eddy could potentially influence air‐sea processes, such as those during TC passage.

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

“…The thickest layers were observed within the core and at the periphery of the anticyclone (BLT = 35±1 dbar). This is in line with observations of Rudzin et al (), who found thicker barrier layers inside than outside their surveyed anticyclone.…”

“…The anticyclone originated near Grenada Passage, which is similar to the anticyclone surveyed by Rudzin et al (). Based on the low salinity and elevated silicate concentrations in the core of the anticyclone, we suggest that the anticyclone entrained surface waters originating from the Orinoco River.…”

“…Ffield () showed that the salinity of NBC Rings depends on the position of the Amazon River plume. The salinity anomalies found in this study as well as in the study of Rudzin et al () therefore highlight the importance of the Amazon and Orinoco River plumes on the formation and properties of Caribbean anticyclones.…”

“…Although these differences seem large, the anticyclone observed by Silander () had a similar surface‐intensified flow structure. Also, the velocities of the anticyclone observed by Rudzin et al () have a surface‐intensified pattern, which reveals the possibility that all three anticyclones were shallow and the weak isopycnal displacement at depth was induced by the anticyclone above. Therefore, we think that most Caribbean anticyclones transport only water in the upper layer, while the passage of the shallow anticyclone induces a weak depression of the isopycnals at larger depths.…”

EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

“…Eddies such as the anticyclonic features associated with North Brazil Current Rings eventually carry freshwater, originating from the Amazon/Orinoco river, into the region. Linkages between the freshwater surplus by the rivers and intensification of storms and cyclones have been reported for the large scale (Reul et al 2014) and for the region east of the Antilles, in the Caribbean, for individual eddies (Rudzin et al 2017).…”