Physical processes contributing to the water mass transformation of the Indonesian Throughflow
- 372 Downloads
The properties of the waters that move from the Pacific to the Indian Ocean via passages in the Indonesian archipelago are observed to vary with along-flow-path distance. We study an ocean model of the Indonesian Seas with reference to the observed water property distributions and diagnose the mechanisms and magnitude of the water mass transformations using a thermodynamical methodology. This model includes a key parameterization of mixing due to baroclinic tidal dissipation and simulates realistic water property distributions in all of the seas within the archipelago. A combination of air–sea forcing and mixing is found to significantly change the character of the Indonesian Throughflow (ITF). Around 6 Sv (approximately 1/3 the model net ITF transport) of the flow leaves the Indonesian Seas with reduced density. Mixing transforms both the intermediate depth waters (transforming 4.3 Sv to lighter density) and the surface waters (made denser despite the buoyancy input by air–sea exchange, net transformation = 2 Sv). The intermediate transformation to lighter waters suggests that the Indonesian transformation contributes significantly to the upwelling of cold water in the global conveyor belt. The mixing induced by the wind is not driving the transformation. In contrast, the baroclinic tides have a major role in this transformation. In particular, they are the only source of energy acting on the thermocline and are responsible for creating the homostad thermocline water, a characteristic of the Indonesian outflow water. Furthermore, they cool the sea surface temperature by between 0.6 and 1.5°C, and thus allow the ocean to absorb more heat from the atmosphere. The additional heat imprints its characteristics into the thermocline. The Indonesian Seas cannot only be seen as a region of water mass transformation (in the sense of only transforming water masses in its interior) but also as a region of water mass formation (as it modifies the heat flux and induced more buoyancy flux). This analysis is complemented with a series of companion numerical experiments using different representations of the mixing and advection schemes. All the different schemes diagnose a lack of significant lateral mixing in the transformation.
KeywordsIndonesian Throughflow Water mass transformation Neutral density framework Thermodynamic Tidal mixing processes
This work is part of the DRAKKAR project and is supported by MERCATOR-ocean (projects 100043 and 061396) and by the Marine Environment and Security for the European Area project (MERSEA, SIP3 CI 2003 502885). The ocean model integrations have been performed at the Institut de Développement et des Ressources en Informatique Scientifique (IDRIS, project 51140 and 1396).
- Gordon AL (2005) Oceanography of the Indonesian seas and their throughflow. Oceanography (Wash DC) 18:14–27Google Scholar
- Koch-Larrouy A, Madec G, Blanke B, Molcard R (2008) Quantification of the water paths and exchanges in the Indonesian archipelago. Ocean Dynamics (in press)Google Scholar
- Levitus S, Boyer TP, Conkright ME, O’Brien T, Antonov J, Stephens C, Stathoplos L, Johnson D, Gelfeld R (1998) NOAA Atlas NESDIS 18, WORLD OCEAN DATABASE (1998) Vol. 1: Introduction. U.S. Government Printing Office, Washington D.C., p 346Google Scholar
- Lyard F, et Le Provost C (2002) Energy budget of the tidal hydrodynamic model fes99. Appears in C. Le Provosts’ talk: “Ocean tides after a decade of high precision satellite altimetry”, SWT Jason 1, Arles, 2003Google Scholar
- Madec G (2008) NEMO = the OPA9 ocean engine. Note du Pole de Modélisation. Institut Pierre-Simon Laplace., 1:100 pp. http://www.lodyc.jussieu.fr/nemo/
- Madec G, Delecluse P, Imbard M (1998) Opa8.1 ocean general circulation model reference manual. Note IPSL, 11:Paris VI, FranceGoogle Scholar
- Purba M, Atmadipoera A (1992) On the study of dynamic topography in the southern Java–Sumba waters, paper presented at Third Ocean Research Institute–Indonesian Institute of Sciences (LIPI) Seminar on Marine Sciences, Oceanography for Fisheries, Tokyo, August 19–21Google Scholar
- van Aken HM (2007) Annual report NIOZ http://www.nioz.nl/public/annual_report/2007/van%20aken.pdf
- Wajsowicz RC, Schneider EK (2001) The Indonesian Throughflow’s effect on global climate determined from the COLA Coupled Climate System. J Climate 14:3,029–3,042Google Scholar
- Wijffels SE, Meyers G, Godfrey JS (2008) A twenty year average of the Indonesian Throughflow: regional currents and the interbasin exchange. J Phys Oceanogr, doi: 10.1175/JPO2008/3987.1
- Wyrtki K (1961) Physical oceanography of the southeast Asian Waters, NAGA Rep. 2, Scripps Institution of OceanographyGoogle Scholar