Freshening anomalies in the Indonesian throughflow and impacts on the Leeuwin Current during 2010-2011

Ming Feng; Jessica Benthuysen; Ningning Zhang; Dirk Slawinski

doi:10.1002/2015gl065848

The reversal of the multi-decadal trends of the equatorial Pacific easterly winds, and the Indonesian Throughflow and Leeuwin Current transports

Geophysical Research Letters ◽

10.1029/2011gl047291 ◽

2011 ◽

Vol 38 (11) ◽

pp. n/a-n/a ◽

Cited By ~ 69

Author(s):

Ming Feng ◽

Claus Böning ◽

Arne Biastoch ◽

Erik Behrens ◽

Evan Weller ◽

...

Keyword(s):

Equatorial Pacific ◽

Indonesian Throughflow ◽

Leeuwin Current

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

Ocean Science Discussions ◽

10.5194/osd-12-2231-2015 ◽

2015 ◽

Vol 12 (5) ◽

pp. 2231-2256

Author(s):

E. Lambert ◽

D. Le Bars ◽

W. P. M. de Ruijter

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Circulation Model ◽

Coastal Current ◽

Indonesian Throughflow ◽

Boundary Current ◽

South Indian Ocean ◽

Leeuwin Current ◽

South Indian ◽

The Indian Ocean

Abstract. East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.

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“Teddies” and the Origin of the Leeuwin Current

Journal of Physical Oceanography ◽

10.1175/1520-0485-32.9.2571 ◽

2002 ◽

Vol 32 (9) ◽

pp. 2571-2588 ◽

Cited By ~ 23

Author(s):

Doron Nof ◽

Thierry Pichevin ◽

Janet Sprintall

Keyword(s):

Indian Ocean ◽

Mass Flux ◽

Nonlinear Process ◽

High Amplitude ◽

Detailed Examination ◽

Generation Process ◽

Indonesian Throughflow ◽

The West ◽

Leeuwin Current ◽

Eddy Generation

Abstract The outflow from the Indonesian seas empties approximately 5–7 Sv of surface warm (and low salinity) Indonesian Throughflow water into the southern Indian Ocean (at roughly 12°S). Using a nonlinear 1½-layer model with a simple geometry consisting of a point source (of anomalous water) situated along a meridional wall on a β plane, the spreading of these waters is examined. An analytical solution is constructed with the aid of the “slowly varying” approach, and process-oriented numerical simulations are performed. It is found that, immediately after emptying into the ocean, the outflow splits into two branches. One branch carries approximately 13% of the source mass flux and forms a chain of high amplitude anticyclonic eddies (lenses) immediately to the west of the source. These eddies drift westward and penetrate into the interior of the Indian Ocean. The second branch carries the remaining 87% of the mass flux via a coastal southward flowing current. Ultimately, this second branch separates from the coast and turns westward. (A detailed examination of this second branch separation is, nevertheless, beyond the scope of this study.) It is suggested that the eddies recently observed to the west of the Island of Timor are a result of the above eddy generation process, which is not related to the classical eddy generation process associated with instabilities (i.e., the breakdown of a known steady solution). It is also suggested that this new nonlinear process explains why some of the Indonesian Throughflow water forms the source of the southward flowing coastal Leeuwin Current.

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

Ocean Science ◽

10.5194/os-12-771-2016 ◽

2016 ◽

Vol 12 (3) ◽

pp. 771-780 ◽

Cited By ~ 9

Author(s):

Erwin Lambert ◽

Dewi Le Bars ◽

Wilhelmus P. M. de Ruijter

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Circulation System ◽

Coastal Current ◽

Indonesian Throughflow ◽

South Indian Ocean ◽

Leeuwin Current ◽

South Indian ◽

Basin Scale ◽

The Indian Ocean

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 wind-driven 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-ocean-scale 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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Plio-Pleistocene Perth Basin water temperatures and Leeuwin Current dynamics (Indian Ocean) derived from oxygen and clumped isotope paleothermometry

10.5194/cp-2021-151 ◽

2021 ◽

Author(s):

David De Vleeschouwer ◽

Marion Peral ◽

Marta Marchegiano ◽

Angelina Füllberg ◽

Niklas Meinicke ◽

...

Keyword(s):

Indian Ocean ◽

Heat Transport ◽

Southern Hemisphere ◽

Latitudinal Gradients ◽

Time Interval ◽

Climate Projections ◽

Indonesian Throughflow ◽

Tectonic Event ◽

Large Variability ◽

Leeuwin Current

Abstract. The Pliocene sedimentary record provides a window into Earth’s climate dynamics under warmer-than-present boundary conditions. However, the Pliocene cannot be considered a stable warm climate that constitutes a solid baseline for middle-road future climate projections. Indeed, the increasing availability of time-continuous sedimentary archives (e.g., marine sediment cores) reveals complex temporal and spatial patterns of Pliocene ocean and climate variability on astronomical timescales. The Perth Basin is particularly interesting in that respect because it remains unclear if and how the Leeuwin Current sustained the comparably wet Pliocene climate in West-Australia, as well as how it influenced Southern Hemisphere paleoclimate variability. To constrain Leeuwin Current dynamics in time and space, this project constructed a new orbitally-resolved planktonic foraminifera (Trilobatus sacculifer) stable isotope record (δ18O and clumped isotopes Δ47) for the Plio-Pleistocene (4–2 Ma) interval of International Ocean Discovery Program (IODP) Site U1459. It complements an existing TEX86 record from the same site and similar planktonic isotope records from the Northern Carnarvon Basin (ODP Site 763 and IODP Site U1463). The comparison of TEX86 and Δ47 paleothermometers reveals that TEX86 likely reflects sea surface temperatures (SST, 23.8–28.9 °C), whereas T. sacculifer Δ47 calcification temperatures probably echo the state of the lower mixed layer and upper thermocline at the studied Site U1459 (18.2–20.8 °C). The isotopic δ18O gradient along a 19° S–29° S latitudinal transect, between 3.9–2.2 Ma, displays large variability, ranging between 0.5 and 2.0 ‰, whereby a low latitudinal gradient is indicative of a strong Leeuwin Current and vice versa. These results challenge the interpretation that suggested a tectonic event in the Indonesian Throughflow as the cause for the rapid steepening of the isotopic gradient (0.9 to 1.5 ‰) around 3.7 Ma. The tectonic interpretation appears obsolete as it is now clear that the 3.7 Ma steepening of the isotopic gradient is intermittent, with flat latitudinal gradients (~0.5 ‰) restored in the latest Pliocene (2.9–2.6 Ma). Still, the new analysis affirms that a combination of astronomical forcing of wind patterns and eustatic sea level controlled Leeuwin Current intensity. A period of relatively weak Leeuwin Current between 3.7 and 3.1 Ma is advocated; a time interval also marked by cooler conditions throughout the Southern Hemisphere. In conclusion, the intensity of the Leeuwin Current and the latitudinal position of the subtropical front are rooted in the same forcing: Heat transport through the Indonesian Throughflow (ITF) valve propagated to the temperate zone through Indian Ocean poleward heat transport. The common ITF forcing explains the observed coherence of Southern Hemisphere ocean and climate records.

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