Florian Schütte

Mesoscale Eddies in the Northwestern Pacific Ocean: Three‐Dimensional Eddy Structures and Heat/Salt Transports

The region encompassing the Kuroshio Extension (KE) in the Northwestern Pacific Ocean (25°N–45°N and 130°E–180°E) is one of the most eddy-energetic regions of the global ocean. The three-dimensional structures and transports of mesoscale eddies in this region are comprehensively investigated by combined use of satellite data and Argo profiles. With the allocation of Argo profiles inside detected eddies, the spatial variations of structures of eddy temperature and salinity anomalies are analyzed. The results show that eddies predominantly have subsurface (near-surface) intensified temperature and salinity anomalies south (north) of the KE jet, which is related to different background stratifications between these regions. A new method based on eddy trajectories and the inferred three-dimensional eddy structures is proposed to estimate heat and salt transports by eddy movements in a Lagrangian framework. Spatial distributions of eddy transports are presented over the vicinity of the KE for the first time. The magnitude of eddy-induced meridional heat (freshwater volume) transport is on the order of 0.01 PW (103 m3/s). The eddy heat transport divergence results in an oceanic heat loss south and heat gain north of the KE, thereby reinforcing and counteracting the oceanic heat loss from air-sea fluxes south and north of the KE jet, respectively. It also suggests a poleward heat transport across the KE jet due to eddy propagation.

Subsurface Fine‐Scale Patterns in an Anticyclonic Eddy Off Cap‐Vert Peninsula Observed From Glider Measurements

Glider measurements acquired along four transects between Cap-Vert Peninsula and theCape Verde archipelago in the eastern tropical North Atlantic during March–April 2014 were used to investigate fine-scale stirring in an anticyclonic eddy. The anticyclone was formed near 12°N off the continental shelf and propagated northwest toward the Cape Verde islands. At depth, between 100 and–400 m, the isolated anticyclone core contained relatively oxygenated, low-salinity South Atlantic CentralWater, while the surrounding water masses were saltier and poorly oxygenated. The dynamical and thermohaline subsurface environment favored the generation offine-scale horizontal and vertical temperature and salinity structures in and around the core of the anticyclone. These features exhibited horizontal scales of O(10–30 km) relatively small with respect to the eddy radius of O(150 km). The vertical scales of O(5–100 m) were associated to density-compensated gradient. Spectra of salinity and oxygen along isopycnals revealed a slope of around k-2in the 10- to 100-km horizontal scale range.Further analyses suggest that the fine-scale structures are likely related to tracer stirring processes. Such mesoscale anticyclonic eddies and the embedded fine-scale tracers in and around them could play a major role in the transport of South Atlantic Central Water masses and ventilation of the North Atlantic Oxygen Minimum Zone.

A new eddy detection method with object segmentation strategies for satellite altimetry

This paper introduces a new eddy detection method based on object segmentation strategies. It incorporates the advantages of the Okubo-Weiss (OW) method, and improves the algorithm robustness by using three different segmentation methods. First, by intersecting the OW mask with the positive and negative SLA masks, two separate initial eddy candidate segment masks for anticyclonic and cyclonic eddies are produced. Then the number of extrema inside the individual segments is calculated. If the number is two/greater than two, a histogram threshold/watershed method is applied to further divide the segments into subsegments. If the number is one, the segment is tested by predefined eddy criteria. If the criteria are not fulfilled, the eddy boundary is repeatedly shrunk by one pixel inward until the segment meets all the criteria. In this case it is saved as an eddy. A segment is discarded if the number of extrema is zero. The eddy detection results of this method, of the OW method and of a geometric eddy detection method are displayed and analyzed statistically. The seasonal cycle of eddy number from the three eddy detection methods is discussed in comparison to the EKE.