The Nature of Eddy Kinetic Energy in the Labrador Sea: Different Types of Mesoscale Eddies, Their Temporal Variability, and Impact on Deep Convection

Abstract

Oceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of eddy kinetic energy (EKE) and its temporal variability in the LS with the help of a 52-yr-long hindcast simulation of a 1/208 ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 608 and 628N, mainly affect preconditioning, and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper-ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are convective eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a middepth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air-sea heat fluxes. A third class of eddies in the LS are the boundary current eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification.

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

“…If an unfortunate choice becomes apparent and a run is already quite advanced, it is not always possible to correct this choice and start afresh (as, e.g., the HPC allocation to the associated project may have already been mostly used up). A potential alternative is the use of nested models that allow basin‐scale high resolution while maintaining a global embedment through a coarser base model (e.g., North and South Atlantic such as VIKING20X, Rieck et al, 2019). Furthermore, the volume of output to be stored on disk increases proportionally with resolution, and analysis of this output increasingly requires parallel computation.…”

“…In parallel to the increase in the availability of high‐quality AMOC estimates, there has been a massive increase in high‐performance computing (HPC) resources and in our ability to exploit them to simulate the natural world. The latest generation of ocean and coupled ocean‐atmosphere models is being run at resolutions sufficient to simulate the ocean circulation with a remarkable level of detail (e.g., Böning et al, ; Haarsma et al, ; Iovino et al, ; Marzocchi et al, ; Moat et al, ; Rieck et al, 2019; Sein et al, , ). Features such as ocean mesoscale eddies are now increasingly present in ocean and ocean‐atmosphere simulations.…”

Max Planck Institute Earth System Model (MPI-ESM1.2) for the High-Resolution Model Intercomparison Project (HighResMIP)

“…However, the convection centre in the Labrador Sea is confined to a more southeastern area with deeper mixed layers in ER pp . This is due to resolved eddies, in particular Irminger Rings, that flatten the isopycnals, thereby limiting the northward extent of the convection area (Rieck et al, 2019). The resolved eddy activity can be seen in the eddy kinetic energy field (Fig.…”

“…These eddies confine deeper mixed layers to the area with minimum EKE. However, a resolution of 0.1 • is still not sufficient to resolve so-called convective eddies, which emerge from baroclinic instabilities at the rim of the mixed patch due to strong buoyancy gradients and are thought to be the main process for rapid restratification in spring (Rieck et al, 2019).…”

“…Another modelling challenge is the mixed layer depth in the Subantarctic frontal zone equatorwards of the ACC (Rintoul and Trull, 2001). This is an important area for heat and CO 2 uptake and for the formation of the Subantarctic Mode Water.…”