On the cross-shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007

Azis Ismail, Mochamad Furqon and Ribbe, Joachim (2019) On the cross-shelf exchange driven by frontal eddies along a western boundary current during austral winter 2007. Estuarine, Coastal and Shelf Science, 227:106314. pp. 1-13. ISSN 0272-7714


Abstract

Western boundary currents are characterized by high mesoscale eddy activity including that of cyclonic frontal eddies (CFEs). These form frequently adjacent to the shelf-break, export coastal water and affect biological productivity. Here, we study the physical properties of eddies identified within the intensification zone of the East Australian Current (EAC) through the analysis of remotely sensed data, the application of an ocean circulation model and the evaluation of Lagrangian simulations during austral winter 2007. We examine the spatial and temporal evolution of identified eddies, investigate their formation mechanism, and quantify the contribution made to cross-shelf exchanges. The mesoscale eddies are tracked from generation to decay using an eddy detection and tracking method. In this case study, we identify two CFEs referred to as C1 and C2 with lifetimes of 11 and 38 days and radii of 45 and 70 km, respectively, and one anticyclonic eddy (ACE) with a lifetime of 62 days and a radius of 60 km. Both CFEs interact with the ACE leading to quasi-stationary dipole-eddies located in the vicinity of the shelf. This is the first time dipole-eddies are reported for the intensification zone of the EAC. The location of CFEs characterised by negative sea surface height anomaly (SSHA) and clockwise rotation coincides with remotely-sensed sea surface temperature (SST) and chlorophyll-a (Chl-a) anomalies. CFEs C1 and C2 appear to contribute in different ways to the cross-shelf transport along the shelf-break. CFE C1 drives a stronger onshore transport, while CFE C2 appears to enhance the offshore transport. The estimated daily cross-shelf export of shelf water associated with CFE C2 is estimated with about 1.23 Sv (~106 km3 day-1). It renews the regional shelf water in about 7 days. The lifetime of CFE C2 is about 38 days, thus the eddy had the potential to flush the shelf at least five times. The transient CFEs were found for the first time to intensify the cross-shelf exchange that is due to the wind-driven cyclonic circulation of the Fraser Gyre. This seasonally occurring gyre dominates the local shelf during austral autumn and winter. The results from this study demonstrate the importance of CFEs in exporting cooler and Chl-a enriched shelf water into the warmer and oligotrophic waters of the southward-flowing EAC.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences (1 Jul 2013 - 5 Sep 2019)
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences (1 Jul 2013 - 5 Sep 2019)
Date Deposited: 23 Sep 2019 03:07
Last Modified: 02 Jun 2021 03:19
Uncontrolled Keywords: cyclonic frontal eddies, dipole-eddies, cross-shelf transport, East Australian Current, sea surface height anomaly
Fields of Research (2008): 04 Earth Sciences > 0405 Oceanography > 040503 Physical Oceanography
Fields of Research (2020): 37 EARTH SCIENCES > 3708 Oceanography > 370803 Physical oceanography
Socio-Economic Objectives (2008): D Environment > 96 Environment > 9611 Physical and Chemical Conditions of Water > 961102 Physical and Chemical Conditions of Water in Coastal and Estuarine Environments
Identification Number or DOI: https://doi.org/10.1016/j.ecss.2019.106314
URI: http://eprints.usq.edu.au/id/eprint/36868

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