Sources, fate, and pathways of Leeuwin Current water in the Indian Ocean and Great Australian Bight: A Lagrangian study in an eddy‐resolving ocean model

Abstract

The Leeuwin Current is the dominant circulation feature in the eastern Indian Ocean, transporting tropical and subtropical water southward. While it is known that the Leeuwin Current draws its water from a multitude of sources, existing Indian Ocean circulation schematics have never quantified the fluxes of tropical and subtropical source water flowing into the Leeuwin Current. This paper uses virtual Lagrangian particles to quantify the transport of these sources along the Leeuwin Current's mean pathway. Here the pathways and exchange of Leeuwin Current source waters across six coastally bound sectors on the south‐west Australian coast are analyzed. This constitutes the first quantitative assessment of Leeuwin Current pathways within an offline, 50 year integration time, eddy‐resolving global ocean model simulation. Along the Leeuwin Current's pathway, we find a mean poleward transport of 3.7 Sv in which the tropical sources account for 60–78% of the transport. While the net transport is small, we see large transports flowing in and out of all the offshore boundaries of the Leeuwin Current sectors. Along the Leeuwin Current's pathway, we find that water from the Indonesian Throughflow contributes 50–66% of the seasonal signal. By applying conditions on the routes particles take entering the Leeuwin Current, we find particles are more likely to travel offshore north of 30°S, while south of 30°S, particles are more likely to continue downstream. We find a 0.2 Sv pathway of water from the Leeuwin Current's source regions, flowing through the entire Leeuwin Current pathway into the Great Australian Bight.

Estimates of Surface and Subsurface Boundary Current Transport Around Australia

“…In a recent study, Ridgway and Godfrey () suggested that the monsoon wind setup sea levels on the Gulf of Carpentaria (GC) controlled the seasonality of the LC. In ozROMS, HLC accounted for ∼70% of the seasonal variance of LC, SAC and ZC in agreement with Yit Sen Bull and van Sebille (). A small secondary maximum in transport occurred in January (summer) for HLC, LC, and SAC.…”

“…Magnitudes of the transport, temporal, and spatial variability of the major surface boundary currents (e.g., LC, SAC, EAC, and FC) are generally known but details of inflows into these surface current systems and the transport and variability of the subsurface current systems are largely uncertain. It is known that both the LC and EAC strengthen as they flow southward along the western and eastern shelf slopes of Australia with inflows from the subtropical branches of SICC and SEC, respectively (Domingues et al, ; Ridgway et al, ), however a recent study by Yit Sen Bull and van Sebille () suggested that tropical sources account for between 60 and 78% of the LC transport.…”

Plastic Pollution Patterns in Offshore, Nearshore and Estuarine Waters: A Case Study from Perth, Western Australia

“…Transport of international plastic pollutants to the area is facilitated through entrainment of Indian Ocean surface waters and the ITF, which extends into the Holloway and then Leeuwin Current, capable of transporting water down the coast from Asia (Meyers et al, 1995;Pattiaratchi and Woo, 2009). ITF waters are hereby modeled to make up the highest proportion of water transported in the LC (Yit Sen Bull and van Sebille, 2016). Importantly, the three countries with the highest estimated influx of mismanaged plastic waste to the ocean-namely China, Indonesia and the Philippines-are directly connected to Western Australia by these surface currents (Jambeck et al, 2015).…”

“…The LC is driven by an alongshore geopotential gradient created by warm, nutrient-poor Pacific Ocean waters spilling into the Indian Ocean with the Indonesian Through-flow (ITF) (Pearce and Phillips, 1988;Fieux et al, 2005). While most of the ITF contributes to the westward flowing Indian Ocean Equatorial current, some of it flows into the Holloway current along the North West shelf of Australia and extends further south where it contributes to the LC (Pearce and Phillips, 1988;Yit Sen Bull and van Sebille, 2016). Seasonal variability of the LC creates strongest transport during the austral winter months, as opposing winds weaken (Godfrey and Ridgway, 1985;Feng et al, 2003).…”

On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

“…Feng et al (2003) studied the seasonal cycle of the LC at 328S; they found that the LC meridional transport attained a maximum during JuneJuly (5 Sv) and that its annual mean over the entire record was 3.4 Sv. More recently, Yit Sen Bull and van Sebille (2016) used Lagrangian virtual floats in their eddy-revolving ocean general circulation model (OGCM) to find annual-mean LC transport values similar to Feng et al's (2003).…”