Salinity dominance on the Indian Ocean Eastern Gyral current

Abstract. East of Madagascar, the shallow "South Indian Ocean Counter Current (SICC)" flows from west to east across the Indian Ocean against the direction of the winddriven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22 • S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical "super gyre" that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-oceanscale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.

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“…A similar structure has recently been identified and analysed from observations (e.g. Menezes et al, 2013).…”

Section: Resultsmentioning

confidence: 79%

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

2016

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“…In the Indian Ocean, a positive bias exists just after the ITF exit. It becomes negative near the Eastern Gyral Current (EGC) that flows eastward near 15 • S. In the upper ocean, a strong salinity front exists between the fresh water from the ITF in the SEC and the salty subtropical waters (Menezes et al, 2013). Note also that the ITW joins the SEC and spreads westward in the Indian Ocean by advection and diffusion (Gordon et al, 1997).…”

Section: Resultsmentioning

confidence: 99%

“…A recent paper of Menezes et al (2013) shows that root mean square (rms) difference between the Aquarius (7-day Level-3 product version 2.0) and Argo is about 0.28 PSU in the tropical eastern basin of the Indian ocean (5-20 • S; 90-140 • E), i.e. in a region where the fresh ITF is spread westward.…”

Section: Aquarius Datamentioning

confidence: 99%

Evaluation of an operational ocean model configuration at 1/12° spatial resolution for the Indonesian seas (NEMO2.3/INDO12) – Part 1: Ocean physics

et al. 2016

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Abstract. INDO12 is a 1/12 • regional version of the NEMO physical ocean model covering the whole Indonesian EEZ (Exclusive Economic Zone). It has been developed and is now running every week in the framework of the IN-DESO (Infrastructure Development of Space Oceanography) project implemented by the Indonesian Ministry of Marine Affairs and Fisheries.The initial hydrographic conditions as well as openboundary conditions are derived from the operational global ocean forecasting system at 1/4 • operated by Mercator Océan. Atmospheric forcing fields (3-hourly ECMWF (European Centre for Medium-Range Weather Forecast) analyses) are used to force the regional model. INDO12 is also forced by tidal currents and elevations, and by the inverse barometer effect. The turbulent mixing induced by internal tides is taken into account through a specific parameterisation. In this study we evaluate the model skill through comparisons with various data sets including outputs of the parent model, climatologies, in situ temperature and salinity measurements, and satellite data. The biogeochemical model results assessment is presented in a companion paper (Gutknecht et al., 2015).The simulated and altimeter-derived Eddy Kinetic Energy fields display similar patterns and confirm that tides are a dominant forcing in the area. The volume transport of the Indonesian throughflow (ITF) is in good agreement with the INSTANT estimates while the transport through Luzon Strait is, on average, westward but probably too weak. Compared to satellite data, surface salinity and temperature fields display marked biases in the South China Sea. Significant water mass transformation occurs along the main routes of the ITF and compares well with observations. Vertical mixing is able to modify the South and North Pacific subtropical water-salinity maximum as seen in T -S diagrams.In spite of a few weaknesses, INDO12 proves to be able to provide a very realistic simulation of the ocean circulation and water mass transformation through the Indonesian Archipelago. Work is ongoing to reduce or eliminate the remaining problems in the second INDO12 version.

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“…The Agulhas leakage transport may have important roles in modulating the strength of the Atlantic overturning circulation. Some of the ITF water recirculates in the Eastern Gyral Current before feeding the Leeuwin Current (Domingues et al 2007;Menezes et al 2013;Van Sebille et al 2014). The ITF transport is important for basin-scale heat and freshwater budget in both the Pacific and Indian Ocean (Vranes et al 2002).…”

Section: Sources and Pathways Of The Itf Watermentioning

confidence: 99%

The Indonesian throughflow, its variability and centennial change

et al. 2018

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The Indonesian Throughflow (ITF) is an important component of the upper cell of the global overturning circulation that provides a low-latitude pathway for warm, fresh waters from the Pacific to enter the Indian Ocean. Variability and changes of the ITF have significant impacts on Indo-Pacific oceanography and global climate. In this paper, the observed features of the ITF and its interannual to decadal variability are reviewed, and processes that influence the centennial change of the ITF under the influence of the global warming are discussed. The ITF flows across a region that comprises the intersection of two ocean waveguides-those of the equatorial Pacific and equatorial Indian Ocean. The ITF geostrophic transport is stronger during La Niñas and weaker during El Niños due to the influences through the Pacific waveguide. The Indian Ocean wind variability associated with the Indian Ocean Dipole (IOD) in many years offsets the Pacific ENSO influences on the ITF geostrophic transport during the developing and mature phases of El Niño and La Niña through the Indian Ocean waveguide, due to the co-varying IOD variability with ENSO. Decadal and multi-decadal changes of the geostrophic ITF transport have been revealed: there was a weakening change from the mid-1970s climate regime shift followed by a strengthening trend of about 1Sv every 10 year during 1984-2013. These decadal changes are mostly due to the ITF responses to decadal variations of the trade winds in the Pacific. Thus, Godfrey's Island Rule, as well as other ITF proxies, appears to be able to quantify decadal variations of the ITF. Climate models project a weakening trend of the ITF under the global warming. Both climate models and downscaled ocean model show that this ITF weakening is not directly associated with the changes of the trade winds in the Pacific into the future, and the reduction of deep upwelling in the Pacific basin is mainly responsible for the ITF weakening. There is a need to amend the Island Rule to take into account the contributions from the overturning circulation which the current ITF proxies fail to capture. The implication of a weakened ITF on the Indo-Pacific Ocean circulation still needs to be assessed.

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Salinity dominance on the Indian Ocean Eastern Gyral current

Cited by 40 publications

References 31 publications

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

Evaluation of an operational ocean model configuration at 1/12° spatial resolution for the Indonesian seas (NEMO2.3/INDO12) – Part 1: Ocean physics

The Indonesian throughflow, its variability and centennial change

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