WHOI PO

Speaker: Cora Hersh

Title: The long lives of subducted spice and vorticity anomalies in the subtropical oceans

Abstract: Subtropical cells, which exist in nearly all ocean basins, connect subducting subtropical waters to upwelling sites along the equator. This tight link between the subtropics and the tropics, on a scale of 5-15 years, is well-established in a time-averaged sense by modeling and observations. Recently, evidence has emerged of spice and potential vorticity anomaly persistence along mean flow pathways on isopycnals. We provide the first global view of subtropical water mass anomaly propagation, using both an observational dataset (Argo) and the Estimating the Circulation and Climate of the Ocean (ECCO) state estimate Version 4 Release 4. In this global synthesis that complements the existing body of largely regional studies, we find long-lived interannual water mass anomalies that translate along mean advective pathways in all ventilated subtropical gyres. They are detectable over multiple years and several thousand kilometers. Some anomalies are persistent enough to reach both the western boundary and equatorial current systems before being entirely eroded, and thus could form ocean “tunnels” to impact remote climate variability. The success of ECCO in capturing these phenomena is encouragement to further explore their upstream sources and downstream impacts within this framework.

 Speaker: Sean Chen

Title: A model study of deep cyclones under the meandering Gulf Stream

Abstract: Deep cyclones are mesoscale low-pressure features that extend vertically throughout the water column within the meander troughs of the Gulf Stream. They are analogous to extratropical cyclones that form within the meanders of the jet stream in the atmosphere. Although deep cyclones were repeatedly documented under the Gulf Stream meanders near 68ºW during the Synoptic Ocean Prediction (SYNOP) field campaign in the 1980-90s, few detailed studies have investigated the spatial distributions of these features along the Gulf Stream and the mechanisms of their formations. These phenomena have also been hypothesized to contribute to sediment resuspension and dispersals in the deep ocean by inducing strong episodic abyssal flows known as benthic storms. In this study, we use a realistic ocean model to explore the development of deep cyclones under the Gulf Stream meanders in both Hatteras and Sohm abyssal plains, investigate the key mechanisms leading to their formations, and seek to characterize the dispersal of Lagrangian particles released at abyssal depths within a deep cyclone.