The Indonesian throughflow, its variability and centennial change

Geoscience Letters, Jan 2018

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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The Indonesian throughflow, its variability and centennial change

Feng et al. Geosci. Lett. The Indonesian throughflow, its variability and centennial change Ming Feng 0 2 Ningning Zhang 1 Qinyan Liu 3 Susan Wijffels 0 2 0 CSIRO Oceans and Atmosphere, Indian Ocean Marine Research Centre , Crawley, WA , Australia 1 School of Marine Sciences, Nanjing University of Information Science and Technology , Nanjing , China 2 Centre for Southern Hemisphere Oceans Research, CSIRO Oceans and Atmosphere , Hobart, TAS , Australia 3 South China Sea Institute of Oceanology, Chinese Academy of Sciences , Guangzhou , China 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. Indonesian throughflow; ENSO; Indian Ocean dipole; Decadal variations; Climate change; Island rule; Overturning circulation Introduction The ITF provides a low-latitude pathway for warm, fresh waters from the Pacific to enter the Indian Ocean through the Indonesian seas (Gordon 2005) . The ITF transport is an important regulator of the meridional overturning of the Indian and Pacific Oceans, and possibly the global thermohaline circulation (Gordon 1986; Sloyan and Rintoul 2001) . Wyrtki (1961) produced quantitative description of the seasonally varying flow patterns in the warm seas surrounding Indonesia, providing the first estimate of the strength of the Indonesian throughflow (ITF). Since then, there have been great efforts to estimate the ITF transport using observations (Godfrey and Golding 1981; Fieux et  al. 1994, 1996; Meyers et  al. 1995) . The most comprehensive observations of all the major Indonesian channels were during the International Nusantara Stratification and Transport Program (INSTANT (Gordon et al. 2010; Sprintall et al. 2004, 2009) , when simultaneous measurements were conducted in the major inflow and outflow passages from the end of 2003 to early 2007), and the ITF transport was estimated to be around 15Sv (1Sv  =  106  m3  s−1) during the 3-year period (Fig. 1). Although the ITF is regarded as an important component of the Indo-Pacific and global overturning circulation, its transport and variability have been estimated using wind-driven circulation theory. There is still lack of general understanding on how the deep overturning circulation contributes to the ITF transport. In this study, we review the variability and dynamic drivers of the ITF in literatures, and emphasize on a potential connection between the overturning and wind-driven circulations in the contribution to the ITF. We introduce the roles of the ITF in ocean circulation and climate in the Indo-Pacific Ocean; and the sources of the ITF water (and their fate) in the Indian Ocean; after reviewing the interannual variations of the ITF volume transport, we then discuss the centennial trend of the ITF under the influence of the global warming. The role of the ITF on ocean circulatio (...truncated)


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Ming Feng, Ningning Zhang, Qinyan Liu, Susan Wijffels. The Indonesian throughflow, its variability and centennial change, Geoscience Letters, 2018, pp. 3, Volume 5, Issue 1, DOI: 10.1186/s40562-018-0102-2