Argo float profiles of temperature, salinity, and pressure are used to derive the mixed‐layer depth (MLD) in the Southern Ocean. MLD is determined from individual profiles using both potential density and potential temperature criteria, and a monthly climatology is derived from individual MLDs using an objective mapping method. Quantitative data are available in the auxiliary material. The spatial structures of MLDs are similar in each month, with deep mixed layers within and just north of the Antarctic Circumpolar Current (ACC) in the Pacific and Indian oceans. The deepest mixed layers are found from June to October and are located just north of the ACC where Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are formed. Examination of individual MLDs indicates that deep mixed layers (MLD ≥ 400 m) from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of SAMW. The surface salinity for these deep mixed layers associated with the SAMW formation are slightly fresher compared to historical estimates. Differences in air‐sea heat exchanges, wind stress, and wind stress curl in the Pacific and Indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes. Wind mixing and Ekman transport of cold water from the south may assist the SAMW formation in the Indian Ocean. In the eastern Pacific, the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling.
The mixed layer heat balance in the Southern Ocean is examined by combining remotely sensed measurements and in situ observations from 1 June 2002 to 31 May 2006, coinciding with the period during which Advanced Microwave Scanning Radiometer-Earth Observing System (EOS) (AMSR-E) sea surface temperature measurements are available. Temperature/salinity profiles from Argo floats are used to derive the mixed layer depth. All terms in the heat budget are estimated directly from available data. The domain-averaged terms of oceanic heat advection, entrainment, diffusion, and air-sea flux are largely consistent with the evolution of the mixed layer temperature. The mixed layer temperature undergoes a strong seasonal cycle, which is largely attributed to the air-sea heat fluxes. Entrainment plays a secondary role. Oceanic advection also experiences a seasonal cycle, although it is relatively weak. Most of the seasonal variations in the advection term come from the Ekman advection, in contrast with western boundary current regions where geostrophic advection controls the total advection. Substantial imbalances exist in the regional heat budgets, especially near the northern boundary of the Antarctic Circumpolar Current. The biggest contributor to the surface heat budget error is thought to be the air-sea heat fluxes, because only limited Southern Hemisphere data are available for the reanalysis products, and hence these fluxes have large uncertainties. In particular, the lack of in situ measurements during winter is of fundamental concern. Sensitivity tests suggest that a proper representation of the mixed layer depth is important to close the budget. Salinity influences the stratification in the Southern Ocean; temperature alone provides an imperfect estimate of mixed layer depth and, because of this, also an imperfect estimate of the temperature of water entrained into the mixed layer from below.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.