Response of the Pacific Sector of the Southern Ocean to Wind Stress Variability From 1995 to 2017

Abstract

Drifter, satellite, expendable bathythermograph (XBT), and Argo float data are used to study the response of the Pacific Sector of the Southern Ocean (PSSO) to the wind stress field in the period 1995-2017, in terms of eddy field, water mass transport, and heat fluxes at large and regional scales. Increasing wind stress over the PSSO in those two decades led to a growth of the Eddy Kinetic Energy (EKE) in the region of the Antarctic Circumpolar Current (ACC). Increases of the EKE occur with delays of 1-4 years with respect to peaks in the zonal component of the wind stress. The persistent ACC meander located south of New Zealand (between 150°E and 180°W and 50°S to 66°S) responds to the interannual wind variations earlier than the entire ACC branch in the PSSO. In the same area, an estimate of the ACC transport based on in situ data shows interannual variability but no significant decadal trend over the study period. The effects of the EKE variability on the meridional eddy heat fluxes are significant on interannual scales. The strengthening of the EKE field leads to a local increase in the poleward meridional eddy heat fluxes in the PSSO, especially in the ACC band. The weakening of the EKE field defines an area of equatorward meridional eddy heat fluxes in the middle of the PSSO (south of 40°S, between 130°W and 160°W) and prevalent poleward fluxes in the further western and eastern regions.

Topographic Modulation of the Wind Stress Impact on Eddy Activity in the Southern Ocean

“…We first consider the relationship between EKE and wind stress. We find the change in EKE generally lags by 0–46 months changes in the wind stress (Figures 2b–2d), which is consistent with previous studies (e.g., Patara et al., 2016; and Menna et al., 2020). It is worth noting that the correlations and lags between EKE and wind stress are slightly sensitive to the wind product and window length chosen to define the mean (i.e., using 3, 4, 6, and 12 months of running averages as presented in Figure S1 of Supporting Information and Table ).…”

“…For example, Hogg et al (2015) found that the two fields are well correlated with each other in the Indian and Pacific sectors of the Southern Ocean using satellite altimeter records and suggested that the long-term change of EKE is primarily controlled by local wind stress. Menna et al (2020) also found a high correlation between EKE and wind stress in the Pacific sector. Based on numerical Abstract Previous studies proposed that the increase in the eddy kinetic energy (EKE) in the Southern Ocean in recent decades is primarily caused by the strengthening of circumpolar surface westerlies.…”

“…Menna et al. (2020) also found a high correlation between EKE and wind stress in the Pacific sector. Based on numerical simulations, Patara et al.…”

“…The ACC is one of the most eddy‐rich regions in the global ocean (e.g., Fu et al., 2010), and these eddies play a crucial role in the adjustment of the Southern Ocean circulation to changes in surface wind forcing (e.g., Hallberg & Gnanadesikan, 2006; Marshall et al., 2017; Rintoul, 2018). Both observation analyses and numerical simulations have indicated that the eddy kinetic energy (EKE) in the Southern Ocean has significantly increased over the past few decades in regions confined to topographic features (e.g., Hogg et al., 2015; Martínez‐Moreno et al., 2019, 2021; Patara et al., 2016), which could lead to a local increase in the poleward meridional eddy heat transport (e.g., Abernathey & Cessi, 2014; Menna et al., 2020), and contribute to the warming of the Southern Ocean (Hogg et al., 2008). The changes in EKE are usually considered to be associated with a local increase of winds (e.g., Hogg et al., 2015), but they can also be a consequence of an increase in the instability of the mean flow (e.g., Barthel et al., 2017).…”

Connectivity Analysis Applied to Mesoscale Eddies in the Western Mediterranean Basin

“…Mesoscale eddies are detected everywhere in the ocean [15,16] and dominate the kinetic energy [17,18]. They can influence the global ocean circulation at all the scales, the mixing processes as well as the transport of water masses, heat, salt, and substances at great distance from the formation area.…”