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Observational estimates of turbulent mixing in the Southeast Indian Ocean


Cyriac, A and Phillips, HE and Bindoff, NL and Mao, H and Feng, M, Observational estimates of turbulent mixing in the Southeast Indian Ocean, Journal of Physical Oceanography, 51, (7) pp. 2103-2128. ISSN 0022-3670 (2021) [Refereed Article]


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Copyright 2021 American Meteorological Society. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0)

DOI: doi:10.1175/JPO-D-20-0036.1


This study investigates the spatiotemporal variability of turbulent mixing in the eastern south Indian Ocean using a collection of data from electromagnetic autonomous profiling explorer (EM-APEX) profiling floats, shipboard CTD, and microstructure profilers. The floats collected 1566 profiles of temperature, salinity, and horizontal velocity data down to 1200 m over a period of about four months. A finescale parameterization is applied to the float and CTD data to estimate turbulent mixing. Elevated mixing is observed in the upper ocean, over bottom topography, and in mesoscale eddies. Mixing is enhanced in the anticyclonic eddies due to trapped near-inertial waves within the eddy. We found that cyclonic eddies contribute to turbulent mixing in the depth range of 500–1000 m, which is associated with downward-propagating internal waves. The mean diapycnal diffusivity over 250–500-m depth is O(10−6) m2 s−1, and it increases to O(10−5) m2 s−1 in 500–1000 m in cyclonic eddies. The turbulent mixing in this region has implications for water-mass transformation and large-scale circulation. Higher diffusivity [O(10−5) m2 s−1] is observed in the Antarctic Intermediate Water (AAIW) layer in cyclonic eddies, whereas weak diffusivity is observed in the Subantarctic Mode Water (SAMW) layer [O(10−6) m2 s−1]. Counterintuitively, then, the SAMW water-mass properties are strongly affected in cyclonic eddies, whereas the AAIW layer is less affected. Comparatively high diffusivity at the location of the South Indian Countercurrent (SICC) jets suggests there are wave–mean flow interactions in addition to the wave–eddy interactions that warrant further investigation.

Item Details

Item Type:Refereed Article
Keywords:internal waves, mixing, ocean circulation
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical oceanography
Objective Division:Environmental Management
Objective Group:Marine systems and management
Objective Field:Oceanic processes (excl. in the Antarctic and Southern Ocean)
UTAS Author:Cyriac, A (Ms Ajitha Cyriac)
UTAS Author:Phillips, HE (Associate Professor Helen Phillips)
UTAS Author:Bindoff, NL (Professor Nathan Bindoff)
ID Code:146784
Year Published:2021
Web of Science® Times Cited:5
Deposited By:Oceans and Cryosphere
Deposited On:2021-09-27
Last Modified:2022-08-24
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