Publication Date:
2017-02-24
Description:
Mesoscale cyclonic eddies are known to be highly productive. Less well-known are the dynamics and productivity of smaller cyclonic eddies, known as frontal eddies , that form on the landward side of western boundary currents. In this study we investigate the physical and biogeochemical properties of two contrasting cyclonic eddies in the East Australian Current (EAC). The first (“Murphy”), a mesoscale cyclonic eddy that formed at ∼28°S with a diameter of ∼160 km and high surface chlorophyll- a concentrations, which lived ∼47 days. The second (“Freddy”), a smaller frontal eddy (∼35 km diameter) that formed from a shelf water billow ∼7 days prior to sampling at ∼31.5°S and was advected off the shelf along the EAC front (from ∼200m to 4000m of water). Both eddies were at least 1000m deep with a similar steric height anomaly. We introduce and employ ‘the method of closest approach' using shipboard ADCP velocities to estimate the eddy centers, which reveals significant tilting through the water column. We estimate rotation rates of 4-10 days and 1-9 days and Rossby numbers 0.25-0.1 and 0.6-0.1, from the surface to 600m for Murphy and Freddy respectively. High-resolution altimetry measurements from the SARAL/AltiKA satellite provide estimates of the ageostrophic component of rotation. Our results show that the frontal eddy is significantly more ageostrophic, energetic and productive than the mesoscale cyclone, despite its small size and short life (∼4 weeks). We suggest that frontal eddies have potential to contribute significantly to the net productivity of the Tasman Sea region. This article is protected by copyright. All rights reserved.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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