Cool Indonesian throughflow as a consequence of restricted surface layer flow

Abstract

Approximately 10 million m3 x s(-1) of water flow from the Pacific Ocean into the Indian Ocean through the Indonesian seas. Within the Makassar Strait, the primary pathway of the flow, the Indonesian throughflow is far cooler than estimated earlier, as pointed out recently on the basis of ocean current and temperature measurements. Here we analyse ocean current and stratification data along with satellite-derived wind measurements, and find that during the boreal winter monsoon, the wind drives buoyant, low-salinity Java Sea surface water into the southern Makassar Strait, creating a northward pressure gradient in the surface layer of the strait. This surface layer 'freshwater plug' inhibits the warm surface water from the Pacific Ocean from flowing southward into the Indian Ocean, leading to a cooler Indian Ocean sea surface, which in turn may weaken the Asian monsoon. The summer wind reversal eliminates the obstructing pressure gradient, by transferring more-saline Banda Sea surface water into the southern Makassar Strait. The coupling of the southeast Asian freshwater budget to the Pacific and Indian Ocean surface temperatures by the proposed mechanism may represent an important negative feedback within the climate system.

INSTANT: A new international array to measure the Indonesian Throughflow

“…These fresh waters from the south act to decrease and, at times, reverse the southward flow within the Makassar Strait surface layer [Gordon et al, 2003]. CTDs taken in the deep overflow across the Lifamatola Passage show that the 1940-m Lifamatola sill allows the deep water from the Pacific Ocean to enter the Banda Sea, where it must upwell through mixing with the overlying thermocline waters, thus creating a heat sink.…”

Temporally integrated estimate of the Indonesian throughflow using tritium

“…[11] For calculating the integrals in equation (1), we examined three different cases, assuming (1) a constant [Fieux et al, 1994]), or (3) a velocity profile with a triangular shape and a maximum transport at 200 m as determined by Gordon et al [2003b] from current measurements. The various methods lead to throughflow values which are identical to within 6% percent, so we conveniently use the constant flow approximation where the integrals can be expressed simply as Q in  I in (1989-t)/H and Q out  I out (1989)/H (where Q in and Q out are the mean flow integrated over the depth H and I in , I out are the tritium water column inventories).…”

Geodetic Observations of the Ocean Surface Topography, Geoid, Currents, and Changes in Ocean Mass and Volume

“…Another scientific application is to estimate strait and inter-ocean transport using the combined altimetry sea surface height and GRACE ocean bottom pressure data [48] and [53]. These applications are of fundamental interest to address research problems in oceanography [18] and climate change [19] and [21]. The improvement and the constraints of the GIA processes resulting from the Last Glacial Maximum and to a lesser extent, the Little Ice Age, have significant impact on accurate estimates of oceanic mass variation.…”

“…, Jens Schröter (3) , Victor Zlotnicki (4) , Peter Bender (5) , Alexander Braun (6) , Anny Cazenave (7) , Don Chamber (8) , Jianbin Duan (1) , William Emery (9) , Georgia Fotopoulos (6) , Viktor Gouretski (10) , Richard Gross (4) , Thomas Gruber (11) , Junyi Guo (1) , Guoqi Han (12) , Chris Hughes (13) , Masayoshi Ishii (14) , Steven Jayne (15) , Johnny Johannessen (16) , Per Knudsen (17) , Chung-Yen Kuo (18) , Eric Leuliette (19) , Sydney Levitus (20) , Nikolai Maximenko (21) , Laury Miller (19) , James Morison (22) , Harunur Rashid (23) , John Ries (24) , Markus Rothache (25) , Reiner Rummel (11) , Kazuo Shibuya (26) , Michael Sideris (27) , Y. Tony Song (4) , Detlef Stammer (28) , Maik Thomas (29) , Josh Willis (4) , Philip Woodworth ( The tools of geodesy have the potential to transform the Ocean Observing System. Geodetic observations are unique in the way that these methods produce accurate, quantitative, and integrated observations of gravity, ocean circulation, sea surface height, ocean bottom pressure, and mass exchanges among the ocean, cryosphere, and land.…”