sign in sign up
<<
Home , Makassar Strait, Sibutu Passage

South China Throughflow Impact on the

A. L. Gordon1 , B. Huber1, E. J. Metzger2, R. D. Susanto1, H. Hurlburt2, Rameyo Adi3

The transfer of western Pacific water into the Indian 100°E 105°E 110°E 115°E 120°E 125°E 130°E 135°E 140°E 145°E The SCS throughflow ( to Strait) is ENSO de- Ocean, the Indonesian Throughflow (ITF), influences ocean pendent via the Sibutu pathway, while the ~40 m Karimata path ap-

scale heat and freshwater inventories, and associated sea sur- 20°N Luzon Strait 20°N pears to be mostly forced by the local monsoon wind. During El Niño face temperature (SST) patterns. The ITF effects on SST pat- the SCS throughflow is high, blocking and hence reducing the sur- terns link the ocean to such climate phenomena as ENSO and face layer contribution into the ITF from the Mindanao Current; 15°N S China Sea 15°N the Asian monsoon. Western Tropical Pacific ITF Portals during La Niña, the SCS throughflow is low, permitting greater contri- bution of Mindanao current surface water into the ITF, altering its N. Pacific 10°N 10°N depth profile and associated volume and heat transport. A 1996-1998 and 2004-2011 observational time series of the

Mindanao [eddy] Makassar Strait throughflow, the primary pathway for Pacific Sibutu Psg Retroflection 5°N 5°N 235 m 1350 m inflow into the ITF, sheds light on the nature of the tropical Pacific Portals Sea Halmahera [eddy] Retroflection Ocean surface water contribution to the ITF. The depth profile of -7 2 S. Pacific 0° Halmahera 0° Luzon Strait Karimata Str Maluku Sea the Pacific water flowing into Makassar Strait exhibits thermocline Lifamatola Sea -8 Makassar Strait 1 cc: 0.499 40 m Passage 1 580 m cc: 0.238 intensification, inducing a cooler transport-weighted temperature 1940 m -9 0 1 12 than might otherwise be expected. 5°S Makassar Strait 5°S -10 -1 680 m -11 -2 1300-1500 m -12 -3 5 Sv 2.6 Lombok280 Strait m 10°S 7.5 ~ 0 10°S Timor Passage ~15 -13 -4 Sv 100°E 105°E 110°E 115°E 120°E 125°E 130°E 135°E 140°E 145°E 50 -14 -5

V (m/s) Schematic of the Indonesian Throughflow circulation. The primary source for the ITF is the western tropical Pacific -15 -6 0.2 at ~ 4oN, but additional inflow is derived from the South China Sea, drawn from Luzon Strait. 100 -16 -7 La Niña El Niño 0 Topographic sill depths are given in black italics. The ITF is depicted by the blue arrows. ITF transports in Sv (106 m3/s) are shown for each passage in green [from the INSTANT program, 2004-2006]. -17 -8 -2 -1 0 1 2 ï Makassar Strait Throughflow mooring site is indicated by the red circle. Makassar Strait carries 80-85% of the total -18 La Niña El Niño N4 150 ITF. -19 ï -2 -1 0 1 2 N4 Depth (m) ï The SCS surface water derives from the Pacific Ocean via 200 3 Monthly full water column transports from HYCOM Luzon Strait / Sibutu Passage and their potential ENSO relationships (N4 - Nino4 ï the Luzon Strait, which is diluted with excess freshwater, 2 cc: 0.95 index) - before entering into Makassar Strait, both from the south 250 ï 1 Top left: Makassar Strait shows a weak ENSO de- through and from the north by a pathway pendence, with reduced transport during El Niño. 0 through the Sulu Sea and Sibutu Passage. Top right: Luzon Strait displays a stronger relation- -1 ship to ENSO, with increased transport into the 300 1997 1998 2005 2006 2007 2008 2009 2010 2011 SCS during El Niño. -2 Bottom left: Luzon Strait transport is highly corre- -3 North-South flow in Labani Channel, Makassar Strait, from moored ADCP measurements during the Arlindo (1996-98), IN- +<&20*/%DïPRQWKO\WUDQVSRUWOD\HUVïïQRVHDVRQDOF\FOHïVPWKïï lated with Sibutu Passage transport. STANT (2004-07) and MITF (2007-present) programs. The mooring location is depicted by the red circle on the map. 5 Northward/Eastward 0LQGï6XO -4 Makassar Sibutu Passage Transport (Sv) The strong 1997/98 El Niño suppressed the throughflow. The velocity maximum shoaled, with increasing maximum speed, 4 Sibutu -5 through 2007. The peak in maximum speed occurred in 2008/2009.

-6 The throughflow is weakest in boreal winter, strongest in boreal summer. 3 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 Luzon Strait Transport (Sv) 2

North-south monthly velocity anomaly MAK 1 in Labani Channel at 60 m from the 0.2 HYCOM El NiñoLa Niña 2004-2011 Makassar ADCP moored time series (blue) and from HYCOM 0 output (red). The seasonal signal has 0.1 El Niño Transport (Sv) Transport been removed, and the data smoothed ï The South China Sea hydrological budget and throughflow with a 7-month running mean. The gray dashed curve is a 3rd order poly- 0 ï have an impact on the larger scale SST patterns and climate nomial fit to the MAK data. La Niña

V anomaly (m/s) phenomena, by exerting a 'freshwater plug' inhibiting tropical Note the apparent regime change in ï ï El Niño 2007, roughly coinciding with a shift Pacific surface water participation in the ITF. from prolonged El Niño to a period of more frequent El Niño/La Niña transi- ï tions. ï Southward/Westward ï The HYCOM output in Makassar Strait 2004 2006 2008 2010 2003 2004 2005 2006 2007 2008 2009 2010 2011 The transfer of buoyant SCS surface agrees remarkably well with the obser- 2 water via Karimata Strait inhibits Prolonged El Niño Prolonged El Niño vations, so can we investigate the rela- Mindanao injection to ITF in the 0-40 m Luzon Strait Throughflow: tionships among the inflow sources 0 Above: Monthly transport anomaly (rel 2003-2010) of the upper 100 m through Makassar Strait, layer; the SCS surface layer transfer via and ITF using HYCOM-derived trans- Niño4 Sibutu Passage, and the Mindanao-Sulu Sea input from the Western Pacific. Values from large during El Niño; HYCOM; seasonal cycles were removed. Sibutu Passage inhibits Mindanao small during La Niña port anomalies. ï 1990 1995 2000 2005 2010 injection to ITF in the 0-100 m layer. Below: Monthly transport anomaly for the full water column, Makassar, Mindanao- Sulu Sea and Luzon Strait. Values from HYCOM; seasonal cycles removed. Mindanao Current

The profile changes with season and interannually, and likely Sibutu Passage inflow tracks Luzon Strait - both are in approximate anti-phase with the Makas- Hypothesis: “Turning off” Luzon Strait & sar Strait and Mindanao-Sulu transports. Sibutu Passage throughflow reduced the Flow through Sibutu allows full SCS surface longer time scales. The participation of surface ocean water in layer ~100 m to access the ITF. The South China Sea throughflow via Sibutu is large (negative anomaly) during El Niño and “freshwater plug” leading to the observed the ITF is clearly restricted, protecting the warmest of the tropical reduced (positive anomaly) during La Niña. 2007-2008 condition. An ENSO role is DRIVER: Luzon Strait Throughflow proposed. Pacific water from leakage into the . The restriction +<&20*/%DïPRQWKO\IXOOZDWHUFROXPQWUDQVSRUWïQRVHDVRQDOF\FOHïVPWKïï of the surface water component of the ITF is likely a conse- 8 SCS surface water via Karimata allows SCS surface layer 0LQGï6XO Makassar Karimata Strait 0-40 m access to ITF only in the 0-40 layer. quence of the injection of low salinity, buoyant surface water from Luzon DRIVER: local monsoon the South China Sea (SCS) into the Makassar Strait, which 6 blocks entry of Mindanao Current surface water into Makassar SCS surface Strait, diverting it into the North Equatorial Counter Current. 4 Jan-Mar Jul-Sep SCS Throughflow near zero water via 110°E 120°E 130°E 110°E 120°E 130°E Sibutu Passage SCS Freshwater Plug 20°N 20°N 2 0-100 m SCS throughflow near zero S 0 m Transport (Sv) Transport

10°N 10°N Mindanao surface water into ITF 34.5 0

34.0

33.5

33.0

0° 32.5 0° ï Acknowledgements 32.0

31.5 This research was funded in full or in part under the Cooperative Institute for Climate Applications Research (CICAR) award number NA08OAR4320754 from the National Oceanic SCS Throughflow larger and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily Mindanao westward transport increased reflect the views of the National Oceanic and Atmospheric Administration or the Department of Commerce.

10°S 10°S ï The INSTANT Makassar mooring program was supported by NSF grants 0219782 and 0725935 to A. Gordon. 2003 2004 2005 2006 2007 2008 2009 2010 2011 110°E 120°E 130°E 110°E 120°E 130°E SCS throughflow larger Affiliations 1. Lamont-Doherty Observatory of Columbia University, Palisades, NY 10964 Sea surface salinity seasonal averages from World Ocean Atlas 2009 (NODC) 2. Naval Research Lab, Code 7323, Stennis Space Center MS, 39529-5004 3. Balitbang-KP, Jakarta,