Abstract
Submesoscale interleaving layers are caused by lateral intrusions of dissimilar water masses in frontal zones, which are significant processes in shaping physical, biogeochemical, and ecological parameters in the ocean. Possible interleaving layers were sometimes observed by ship-based conductivity-temperature-depth (CTD) surveys with coarse spacing between adjacent stations in the Kuroshio region east of Taiwan but have never been examined dynamically. Here we show the characteristics of interleaving layers observed by a Seaglider with two repeated hydrographic surveys along a triangle track east of Taiwan from December 2016 to March 2017. Salinity profiles indicate that prominent interleaving layers appeared in the intermediate layer (approximately 500–800 m) with vertical and horizontal length scales of O(50) m and O(10–100) km, respectively, during our observations. A dipole eddy pair and a relatively large anticyclonic eddy impinged on the Kuroshio during the first and second surveys, respectively, which brought certain impacts on the interleaving motion as the eddy potentially altered the density slope across the Kuroshio. The associated instability analysis and the Turner angle suggest that the double diffusive instability is the primary driving mechanism for the development of interleaving layers.
Highlights
Submesoscale processes in the ocean have been widely studied for advancing our understanding of their dynamics in transferring energy from large- to small-scale oceanic motions and for parameterizing their effects in large-scale ocean circulation models[1,2,3]
Each interleaving layer in these frontal zones has its own characteristic, but the formation mechanism essentially starts from finite disturbances in the front of two dissimilar water masses, which trigger lateral www.nature.com/scientificreports intrusions from one to the other water
The hydrographic samplings along the transect N1 captured the influence of the anticyclonic eddy (A1 in Fig. 1) of the eddy pair
Summary
Submesoscale processes in the ocean have been widely studied for advancing our understanding of their dynamics in transferring energy from large- to small-scale oceanic motions and for parameterizing their effects in large-scale ocean circulation models[1,2,3]. As the Kuroshio flows poleward along the east coast of Taiwan, the frequent impingement of mesoscale eddies can cause O(50–100) km zonal shifts in the Kuroshio’s maximum velocity axis with a synoptic time variation in its velocity structure and O(10) Sv (1 Sv = 106 m3 s−1) variation in the mean volume transport (~20 Sv) This variability potentially converts energy from mesoscale to submesoscale processes, which creates density slope tilting and water mass exchange in the www.nature.com/scientificreports/. The spacing of adjacent CTD stations[6] (~20 km) is too coarse to resolve the horizontal coherence of the interleaving layers and associated dynamics The existence of this submesoscale structure indicates potential water mass exchange between South China Sea Water, Kuroshio Water or North Pacific Water in the Kuroshio. The first and second surveys, were completed from 15 December 2016 to 14 January 2017 and from 14 January 2017 to 5 March 2017, respectively (Methods)
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