Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

• Published in: Nature Geoscience
• Main Authors: Sheen, KL, Garabato, ACN, Brearley, JA, Meredith, MP, Polzin, KL, Smeed, DA, Forryan, A, King, BA, Sallée, JB, St Laurent, L, Thurnherr, AM, Toole, JM, Waterman, SN, Watson, AJ
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2014
• Subjects: Physical oceanography; Drake Passage; Southern Ocean
• Online Access: http://hdl.handle.net/10871/25914; https://doi.org/10.1038/ngeo2200

Published Journal Article This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record. The Southern Ocean plays a pivotal role in the global ocean circulation and climate. There, the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere. The sensitivity of the upper cell to climatic changes in forcing is relatively well established. However, little is known about how the lower cell responds, and in particular whether small-scale mixing in the abyssal Southern Ocean, an important controlling process of the lower cell, is influenced by atmospheric forcing. Here, we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades. Observational estimates of mixing rates, obtained along a repeat hydrographic transect across Drake Passage, are shown to be dependent on local oceanic eddy energy, derived from moored current meter and altimetric measurements. As the intensity of the regional eddy field is regulated by the Southern Hemisphere westerly winds, our findings suggest that Southern Ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing. © 2014 Macmillan Publishers Limited. The DIMES experiment is supported by the Natural Environment Research Council (NERC) of the UK and the US National Science Foundation. K.L.S. is supported by NERC. We are grateful to J. Ledwell, A. Bogdanoff, P. Courtois, K. Decoteau, D. Evans and X. Liang for their help in data collection and acknowledge the valuable assistance and hard work of the crew and technicians on the RRS James Cook, the RRS James Clark Ross and the RV Thomas G. Thompson. We also thank A. Thompson who provided many helpful comments, and E. Murowinski, R. Lueck and F. Wolk from Rockland Scientific for their support in ...