DOCSLIB.ORG

The Indonesian Throughflow and Its Impact on Biogeochemistry in The

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Indonesian Throughflow and Its Impact on Biogeochemistry in The ASEAN Journal on Science & Technology for Development Vol 37, No 1, 2020, 29–35 DOI 10.29037/ajstd.596 REVIEW The Indonesian Throughflow and its Impact on Biogeochemistry in the Indonesian Seas Edwards Taufiqurrahman1,*, A’an J. Wahyudi1, and Yukio Masumoto2,3 1Research Center for Oceanography, Indonesian Institute of Sciences. Pasir Putih 1, Ancol Timur, Jakarta 14430, Indonesia 2Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 3Application Laboratory, Japan Agency for Marine-Earth Science and Technology, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan *Corresponding author: [email protected] KEYWORDS ABSTRACT It has been widely known that the Indonesian Throughflow (ITF) is an important inter-ocean Indonesian Seas connection with unique and complex oceanographic and geographic conditions, as well as a strong Indonesian Throughflow relation to both regional and global ocean currents and climate systems. Many studies on character- Marine biogeochemistry istics, mechanisms, and impacts of the ITF have been conducted, mainly focusing on the ITF pathways, Nutrient flux transport, water mass mixing processes, and their variability in connection with monsoons and climate systems. In this paper, we summarize some of the critical aspects related to ocean conditions within the Indonesian Seas and the Indonesian Throughflow, with the main focus on studies of marine biogeo- chemistry in a region affected by the ITF. Although the biogeochemical cycle is one of the key research topics that are needed to advance our ocean understanding, studies on marine biogeochemistry within the Indonesian Seas are quite limited due to less observed data compared to the physical parameters. Further studies on biogeochemistry and efforts to conduct in situ and remotely sensed observations in this region are strongly required. Here, we propose several biogeochemical observations correlated to the ITF. © The Author(s) 2020. This article is distributed under a Creative Commons Attribution-ShareAlike 4.0 International license. 1. INTRODUCTION relatively salty characteristics of the Pacific water tend to vanish due to strong vertical tidal mixing (Koch-Larrouy The Indonesian Seas have a complex oceanographic pro- et al. 2007), and/or sill-induced turbulent mixing (Van Ben- file as they are part of the Pacific and Indian Oceans, as nekom 1988). The mixing is believed to affect the carbon, well as the Pacific and Indian Ocean boundary. This unique oxygen, and nutrient (nitrate, phosphates) concentrations region is affected by intricate geological and geographical in the eastern Indonesian Seas and subsequently in the In- conditions, such as straddling on the equator and consists dian Ocean (Talley and Sprintall 2005; Ayers et al. 2014). of many smaller seas and straits divided by a large number The Indonesian Throughflow is the only ocean- of islands with various sizes (Wyrtki 1961). The water in the connector pathway in the equator (Sprintall et al. 2014), and Indonesian Seas mainly originate from the Pacific Ocean it has an important purpose in the transport of mass and from two directions: water that comes directly from the heat from the Pacific into the Indian Ocean (Feng et al. Pacific Ocean through the passages in the northeastern re- 2018). Numerical model experiments confirmed that, when gions filling the eastern Indonesian seas, and warmer wa- ITF is intentionally closed, the tropical Pacific tends to have ter from the South China Sea filling the Karimata Strait and warmer sea surface temperatures and larger upper ocean Java Sea (Wyrtki 1961). These waters eventually flow out heat content, while cooler sea surface temperatures (SST) mostly through the southern passages, making up contin- occur in the southern part of the Indian Ocean (Hirst et al. uous flows with swift currents and a large transport from 1993; Godfrey 1996). Moreover, closing the ITF can affect the Pacific to the Indian Ocean known as the Indonesian regions far from the Indonesian Seas, such as reducing Throughflow (ITF) (Figure 1). The ITF coming out of the In- the strength of the Indian Ocean’s South Equatorial Cur- donesian Seas flows westward across the Indian Ocean to rent and the Agulhas Current, enhancing the Pacific East eastern Africa, the majority of which then turns southward Australian Current, inducing a warmer eastern equatorial as the Agulhas current. The ITF also flows southward di- Pacific, and even enhancing El Niño Southern Oscillation rectly along the western coast of Australia as the Leeuwin (ENSO) variability (Song et al. 2007). The ITF, therefore, af- current (Talley and Sprintall 2005; Mayer et al. 2010; Sprint- fects the global ocean circulation known as the Global Con- all et al. 2014; Feng et al. 2018). veyor Belt (Koch-Larrouy et al. 2008), as well. As the ITF flows within the Indonesian Seas, its wa- All these aspects of the ITF have attracted the attention ter mass properties change significantly. The warm and of a large number of scientists. To understand the variabil- A journal of the ASEAN Committee on Science and Technology PRINT ISSN 0217-5460 ONLINE ISSN 2224-9028 www.ajstd.org 2. THE INDONESIAN THROUGHFLOW PATHWAY Trade winds over the tropical oceans drive the surface wa- ter in the ocean from east to west, raising the sea level on the western side and lowering it on the eastern side. Con- sequently, the sea level difference and pressure gradient between the Pacific and Indian Oceans appears, with lower sea level and pressure in the eastern Indian Ocean com- pared with the western Pacific Ocean (Wyrtki 1961, 1987). It was hypothesized that this pressure gradient drives the ITF in the Indonesian Seas that connects the two oceans and influences the transport volume. Yet a recent model suggested the ITF is actually an extension of the Pacific’s tropical current systems, including the Western Boundary Current (Mayer et al. 2010). There are three ITF inflow gateways, bringing in differ- ent types of water mass into the Indonesian Seas (Figure FIGURE 1. The Indonesian Throughflow consists of several currents, all bringing the Pacific Ocean waters to the Indian Ocean. The main input is 1). The first gateway is for the North Pacific Subtropical through the Makassar Strait, Halmahera Sea, and Maluku sea. Input flow Water and North Pacific Intermediate Water, which origi- from the South China Sea is also confirmed, flowing through the Sulu Sea nate from the North Equatorial Current system of the Pa- and Java Sea. The ITF then flows out to the Indian Ocean from the Lombok Strait, or from the Ombai Strait and Timor Passage after the waters mix cific Ocean that forms the Mindanao Current. These wa- in the Banda Sea. ters flow into the Sulawesi Sea and then continue to the Makassar Strait (Mayer et al. 2010). The Makassar Strait can only pass surface-to-upper thermocline water because of ity of a global climate system, for example, one should look the shallow Dewakang sill (Talley and Sprintall 2005), but into regional changes in the ITF area. Therefore, observa- about 80% of the ITF transport actually flows through this tion of long term changes in the water mass characteristics strait (Gordon et al. 2010). South of the Makassar Strait near and transport of the ITF is crucial to understanding and pre- the Dewakang sill, the flow bifurcates into two parts; one dicting the climate system, including the regional system part flows into the Lombok Strait and the other into the over Indonesia (Sprintall et al. 2019). Banda Sea (Talley and Sprintall 2005; Koch-Larrouy et al. Several research expeditions have been conducted to 2007; Mayer et al. 2010). Outflow via the Lombok Strait en- observe the ITF, with the main idea of observing the ITF ters the Indian Ocean, and the water mass of this outflow is variability to understand its causes and impacts. One of the known as the Indonesia Throughflow Water (ITW), charac- significant and successful studies is the International Nu- terized by low salinity upper thermocline water (Talley and santara Stratification and Transport (INSTANT) program, Sprintall 2005). which took place in 2004–2006. It was a multinational The second inflow gate is the Halmahera Sea for the research expedition that aimed to investigate the prop- South Pacific Subthermocline Water, and the third gate is erties of the ITF in its main in-and-out flow passages the Maluku Sea for the upper thermocline South Pacific (Sprintall et al. 2004; Gordon 2005). There are also other Subtropical Water (Mayer et al. 2010). The water pass- expeditions conducted by international or Indonesian re- ing through these two gates originates from those in the searchers, such as the “Ekspedisi Widya Nusantara” (EWIN) southern Pacific Ocean, which are known as South Pacific programs (Horhoruw et al. 2015; Yuan et al. 2018). In addi- Subthermocline Water and South Pacific Subtropical Wa- tion to these direct observational studies, numerical mod- ter. These waters flow into the Banda Sea, into which the eling (e.g. Schiller et al. 1998; Sasaki et al. 2018) and proxy- throughflow water from the first gateway also flows. The based (e.g. satellite data, tide gauges, corals) research (Gor- Banda Sea, therefore, can be considered a “mixing place” of don 2005; Iskandar 2005; Potemra 2005; Mayer et al. 2010; the water masses in the three pathways of the ITF inflow. Murty et al. 2018) have also been conducted. Furthermore, From the Banda sea, the flow goes through the Timor there was also the Infrastructure Development of Space and Ombai Straits out to the Indian Ocean. Sills in the Om- Oceanography (INDESO) project developed for the Govern- bai and Timor Straits are deep enough to allow the outflow ment of Indonesia in an attempt to build an accurate mon- to occupy the water column from the surface to the lower itoring and forecasting ocean system by using the physical thermocline.
Load more

Recommended publications
  • Seasonal Influence of Indonesian Throughflow in the Southwestern Indian Ocean
    Seasonal influence of Indonesian Throughflow in the southwestern Indian Ocean Lei Zhou and Raghu Murtugudde Earth System Science Interdisciplinary Center, College Park, Maryland Markus Jochum National Center for Atmospheric Research, Boulder, Colorado Lei Zhou Address: Computer & Space Sciences Bldg. 2330, University of Maryland, College Park, MD 20742 E-mail: [email protected] Phone: 301-405-7093 1 Abstract The influence of the Indonesian Throughflow (ITF) on the dynamics and the thermodynamics in the southwestern Indian Ocean (SWIO) is studied by analyzing a forced ocean model simulation for the Indo-Pacific region. The warm ITF waters reach the subsurface SWIO from August to early December, with a detectable influence on weakening the vertical stratification and reducing the stability of the water column. As a dynamical consequence, baroclinic instabilities and oceanic intraseasonal variabilities (OISVs) are enhanced. The temporal and spatial scales of the OISVs are determined by the ITF-modified stratification. Thermodynamically, the ITF waters influence the subtle balance between the stratification and mixing in the SWIO. As a result, from October to early December, an unusual warm entrainment occurs and the SSTs warm faster than just net surface heat flux driven warming. In late December and January, signature of the ITF is seen as a relatively slower warming of SSTs. A conceptual model for the processes by which the ITF impacts the SWIO is proposed. 2 1. Introduction Sea surface temperature (SST) variations in the southern Indian Ocean are generally modest. But they are significantly larger in the southwestern Indian Ocean (SWIO, Annamalai et al. 2003). In an analysis of observational data, Klein et al.
    [Show full text]
  • The Indonesian Throughflow: the Fifteen Thousand Rivers – David Pickell
    The Indonesian Throughflow: The Fifteen Thousand Rivers – David Pickell If Indonesia did not exist, the earth’s day would be significantly shorter than the approximately twenty-four hours to which we have become accustomed. This would have a dramatic impact on the clock industry, of course, and familiar phrases like “twenty-four/seven” would have to be modified. But Indonesia does exist, and its seventeen thousand islands, together with a complicated multitude of underwater trenches, basins, channels, ridges, shelfs, and sills, continue their daily work of diverting, trapping, and otherwise disrupting one of the most voluminous flows of water on earth, a task that consumes so much energy that it slows the very spinning of the globe. The flow that passes through Indonesia is called the Indonesian Throughflow (ITF), and was first noted by oceanographer Klaus Wyrtki in 1957. Its source is the Philippine Sea and the West Caroline Basin, where the incessant blowing of the Trade Winds, and the currents they generate, have entrapped water from the great expanse of the Pacific. In the Pacific Ocean northeast of the Indonesian archipelago, the sea level is twenty centimeters above average; in the Indian Ocean south of Indonesia, because of similar forces acting in an opposite direction, the sea level is ten centimeters below average. This thirty centimeter differential—an American foot—sets in motion a massive movement of water. The volume of this flow is so great that familiar units like cubic meters and gallons quickly become unwieldy, so oceanographers have invented a unit they call the “Sverdrup,” named after Norwegian scientist Harald Sverdrup of the Scripps Institution of Oceanography.
    [Show full text]
  • Sea Surface Temperature Changes at the Indonesian Throughflow Region
    Send Orders of Reprints at [email protected] 2 The Open Oceanography Journal, 2015, 8, 2-8 Open Access Anomalies of the Sea Surface Temperature in the Indonesian Throughflow Regions: A Need for Further Investigation B.R. Manjunatha1,*, K. Muni Krishna2 and A. Aswini2 1Department of Marine Geology, Mangalore University, Mangalagangotri, India 2Department of Meteorology and Oceanography, Andhra University, Visakhapatnam, India Abstract: Indonesian throughflow (ITF) regions are important in terms of inter-oceanic exchange of heat as well as freshwater between the Pacific Ocean and the Indian Ocean. These regions also linking the North Pacific Ocean and North Atlantic through a global conveyor belt. However, information about the long-term variations of sea surface temperature (SST) across the ITF regions is rather limited. Here, we use long-term Hadley sea surface temperature and advance satellite-derived sea-surface winds to understand long-term changes in and around the ITF. The SST has been lower during the summer season (May–August) with a pronounced minimum in the eastern Indonesia region (INA) and then decreases towards the west due to the activity of southeasterly monsoon winds. The cooling is noticed in the beginning of May, intensifies during July and subsides during the later half of August. The Lambok Strait has been identified as the coolest region (<26°C) in the ITF. Though there has been a general agreement of warm and cool SSTs with El Niño and La Niña conditions respectively, and increasing trend since 1970s, however, there is no consensus among the major passages in the ITF, suggesting complex internal dynamic processes those need to be studied.
    [Show full text]
  • Zonal Current Characteristics in the Southeastern Tropical Indian
    https://doi.org/10.5194/os-2020-91 Preprint. Discussion started: 12 October 2020 c Author(s) 2020. CC BY 4.0 License. Zonal Current Characteristics in the Southeastern Tropical Indian Ocean (SETIO) Nining Sari Ningsih1, Sholihati Lathifa Sakina2, Raden Dwi Susanto3,2, Farrah Hanifah1 1Research Group of Oceanography, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Indonesia 5 2Department of Oceanography, Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Indonesia 3Department of Atmospheric & Oceanic Science, University of Maryland, USA Correspondence to: Nining Sari Ningsih ([email protected]) Abstract. Zonal current characteristics in the Southeastern Tropical Indian Ocean (SETIO) adjacent to the southern Sumatra- 10 Java coasts have been studied using 64 years (1950-2013) data derived from simulated results of a 1/8◦ global version of the HYbrid Coordinate Ocean Model (HYCOM). This study has revealed distinctive features of zonal currents in the South Java Current (SJC) region, the Indonesian Throughflow (ITF)/South Equatorial Current (SEC) region, and the transition zone between the SJC and ITF/SEC regions. Empirical orthogonal function (EOF) analysis is applied to investigate explained variance of the current data and give results for almost 95-98% of total variance. The first temporal mode of EOF is then 15 investigated by using ensemble empirical mode decomposition (EEMD) for distinguishing the signals. The EEMD analysis shows that zonal currents in the SETIO vary considerably from intraseasonal to interannual timescales. In the SJC region, the zonal currents are consecutively dominated by semiannual (0.140 power/year), intraseasonal (0.070 power/year), and annual (0.038 power/year) signals, while semiannual (0.135 power/year) and intraseasonal (0.033 power/year) signals with pronounced interannual variations (0.012 power/year) of current appear consecutively to be dominant modes of variability in 20 the transition zone between the SJC and ITF/SEC regions.
    [Show full text]
  • The Indonesian Seas and Their Role in the Coupled Ocean–Climate System Janet Sprintall1*, Arnold L
    PROGRESS ARTICLE PUBLISHED ONLINE: 22 JUNE 2014 | DOI: 10.1038/NGEO2188 The Indonesian seas and their role in the coupled ocean–climate system Janet Sprintall1*, Arnold L. Gordon2, Ariane Koch-Larrouy3, Tong Lee4, James T. Potemra5, Kandaga Pujiana6,7 and Susan E. Wijffels8 The Indonesian seas represent the only pathway that connects different ocean basins in the tropics, and therefore play a pivotal role in the coupled ocean and climate system. Here, water flows from the Pacific to the Indian Ocean through a series of narrow straits. The throughflow is characterized by strong velocities at water depths of about 100 m, with more minor contributions from surface flow than previously thought. A synthesis of observational data and model simulations indicates that the tem- perature, salinity and velocity depth profiles of the Indonesian throughflow are determined by intense vertical mixing within the Indonesian seas. This mixing results in the net upwelling of thermocline water in the Indonesian seas, which in turn lowers sea surface temperatures in this region by about 0.5 °C, with implications for precipitation and air–sea heat flux. Moreover, the depth and velocity of the core of the Indonesian throughflow has varied with the El Niño/Southern Oscillation and Indian Ocean Dipole on interannual to decadal timescales. Specifically, the throughflow slows and shoals during El Niño events. Changes in the Indonesian throughflow alter surface and subsurface heat content and sea level in the Indian Ocean between 10 and 15° S. We conclude that inter-ocean exchange through the Indonesian seas serves as a feedback modulating the regional precipitation and wind patterns.
    [Show full text]
  • Discovering the Indonesian Throughflow
    or collective redistirbution of any portion article of any by of this or collective redistirbution Th THE INDONESIAN SEAS articleis has been in published Discovering Oceanography the 18, Number journal of Th 4, a quarterly , Volume Indonesian permitted only w is photocopy machine, reposting, means or other Throughflow BY KLAUS WYRTKI In the summer of 1954, I accepted a po- maps of surface salinity for the region. distributions, and water-mass analysis, sition as an oceanographer at the Marine Surface salinity offered much insight one could obtain a better understanding 2005 by Th e Oceanography Copyright Society. Science Institute in Djakarta, Indone- into the advection of water in this area, of the circulation than would be possible sia. When I arrived in November 1954, which has such a pronounced annual from each component alone. I found out that all the Dutch scientists reversal of the circulation. As a starting point, I constructed had left—I was the only scientist and Because the Samudera offered only monthly maps of the surface circula- the director of the institute. I had a fi ne, limited possibilities for research, I soon tion based on ship-drift observations. of Th approval the ith almost new research vessel, the 200-ton decided to concentrate on analyzing ex- These charts led me to wonder where all Samudera. It had only six Nansen bottles, isting data. My goal was to give a compre- the water goes that fl ows east in the Java one bathythermograph, and two winches hensive description of the circulation and Sea during the northwest monsoon, and gran e Oceanography is Society.
    [Show full text]
  • Indonesian Throughflow Transport Variability
    or collective redistirbution of any portion article of any by of this or collective redistirbution Th THE INDONESIAN SEAS articleis has been in published Oceanography INDONESIAN THROUGHFLOW 18, Number journal of Th 4, a quarterly , Volume TRANSPORT VARIABILITY ESTIMATED permitted only w is photocopy machine, reposting, means or other FROM Satellite 2005 by Th e Oceanography Copyright Society. AltimetryBY JAMES T. POTEMRA ith the approval of Th approval the ith gran e Oceanography is Society. All rights reserved. Permission or Th e Oceanography [email protected] Society. Send to: all correspondence Figure 1. Th e Pacifi c to Indian Ocean exchange, known as the Indonesian throughfl ow (ITF), has been sampled with a repeat expendable bathythermograph (XBT) hydrographic section from Australia to Indonesia (IX-1, red stars). Sea-level estimates from the TOPEX/Poseidon (T/P) satel- lite (ground tracks given with the black lines) are used to estimate ITF transport. Th e major straits through which the ITF passes are indicated on the map. ted to copy this article Repu for use copy this and research. to in teaching ted e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. blication, systemmatic reproduction, reproduction, systemmatic blication, 98 Oceanography Vol. 18, No. 4, Dec. 2005 The relatively intense boundary cur- ment of sea level that may be used to prise the Indonesian seas (Figure 1). rents of the western equatorial Pacifi c, index ITF fl ow. Velocities through some of the narrow as well as the western Pacifi c warm pool, Wyrtki (1987) was the fi rst to suggest straits, Lombok Strait for example, can have long been recognized as key com- that ITF transport could be estimated be quite extreme, reaching more than 1 ponents in the global climate system.
    [Show full text]
  • Spreading of the Indonesian Throughflow in the Indian Ocean*
    772 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 34 Spreading of the Indonesian Through¯ow in the Indian Ocean* QIAN SONG,ARNOLD L. GORDON, AND MARTIN VISBECK Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York (Manuscript received 27 March 2003, in ®nal form 19 August 2003) ABSTRACT The Indonesian Through¯ow (ITF) spreading pathways and time scales in the Indian Ocean are investigated using both observational data and two numerical tracer experiments, one being a three-dimensional Lagrangian trajectory experiment and the other a transit-time probability density function (PDF) tracer experiment, in an ocean general circulation model. The model climatology is in agreement with observations and other model results except that speeds of boundary currents are lower. Upon reaching the western boundary within the South Equatorial Current (SEC), the trajectories of the ITF tracers within the thermocline exhibit bifurcation. The Lagrangian trajectory experiment shows that at the western boundary about 38%65% thermocline ITF water ¯ows southward to join the Agulhas Current, consequently exiting the Indian Ocean, and the rest, about 62%65%, ¯ows northward to the north of SEC. In boreal summer, ITF water penetrates into the Northern Hemisphere within the Somali Current. The primary spreading pathway of the thermocline ITF water north of SEC is upwelling to the surface layer with subsequent advection southward within the surface Ekman layer toward the southern Indian Ocean subtropics. There it is subducted and advected northward in the upper thermocline to rejoin the SEC. Both the observations and the trajectory experiment suggest that the upwelling occurs mainly along the coast of Somalia during boreal summer and in the open ocean within a cyclonic gyre in the Tropics south of the equator throughout the year.
    [Show full text]
  • The Connection of the Indonesian Throughflow, South Indian Ocean
    Ocean Sci., 12, 771–780, 2016 www.ocean-sci.net/12/771/2016/ doi:10.5194/os-12-771-2016 © Author(s) 2016. CC Attribution 3.0 License. The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current Erwin Lambert, Dewi Le Bars, and Wilhelmus P. M. de Ruijter Institute of Marine and Atmospheric Sciences Utrecht, Utrecht University, Utrecht, the Netherlands Correspondence to: Erwin Lambert ([email protected]) Received: 18 August 2015 – Published in Ocean Sci. Discuss.: 25 September 2015 Revised: 15 April 2016 – Accepted: 5 May 2016 – Published: 2 June 2016 Abstract. East of Madagascar, the shallow “South Indian 1 Introduction Ocean Counter Current (SICC)” flows from west to east across the Indian Ocean against the direction of the wind- In the upper layer of the South Indian Ocean (SIO) three driven circulation. The SICC impinges on west Australia and unique anomalous currents have been identified: the Leeuwin enhances the sea level slope, strengthening the alongshore Current (LC; Cresswell and Golding, 1980), which flows coastal jet: the Leeuwin Current (LC), which flows poleward poleward along Australia; the South Indian Ocean Counter along Australia. An observed transport maximum of the LC Current (SICC; Palastanga et al., 2007), which flows from around 22◦ S can likely be attributed to this impingement of Madagascar to Australia in the upper ±300 m; and the In- the SICC. The LC is often described as a regional coastal donesian Throughflow (ITF; Godfrey and Golding, 1981), current that is forced by an offshore meridional density gra- which flows through the Indonesian passages from the tropi- dient or sea surface slope.
    [Show full text]
  • Centennial Changes in the Indonesian Throughflow
    Confidential manuscript submitted to Geophysical Research Letters 1 Centennial changes in the Indonesian Throughflow connected to 2 the Atlantic Meridional Overturning Circulation: the ocean’s 3 transient conveyor belt 1 1 4 Shantong Sun and Andrew F. Thompson 1 5 California Institute of Technology, Pasadena, California 6 Key Points: • 7 Basin-scale transient responses of the global ocean overturning circulation are ex- 8 plored with a hierarchy of models. • 9 Changes in AMOC strength can produce a response in ITF volume transport on 10 centennial timescales. • 11 ITF transport time series may assist in monitoring and interpreting long-term trends 12 in the AMOC. Corresponding author: Shantong Sun, [email protected] –1– Confidential manuscript submitted to Geophysical Research Letters 13 Abstract 14 Climate models consistently project a robust weakening of the Indonesian Throughflow 15 (ITF) and the Atlantic Meridional Overturning Circulation (AMOC) in response to green- 16 house gas forcing. Previous studies of ITF variability have largely focused on local pro- 17 cesses in the Indo-Pacific basin. Here, we propose that much of the centennial-scale ITF 18 weakening is dynamically linked to changes in the Atlantic basin, and communicated be- 19 tween basins via wave processes. In response to an AMOC slowdown, the Indian Ocean 20 develops a northward surface transport anomaly that converges mass and modifies sea sur- 21 face height in the Indian Ocean, which weakens the ITF. We illustrate these dynamic inter- 22 basin connections using a 1.5-layer reduced gravity model and then validate the responses 23 in a comprehensive general circulation model.
    [Show full text]
  • Mean Circulation of the Indonesian Throughflow
    MEAN CIRCULATION OF THE INDONESIAN THROUGHFLOW AND A MECHANISM OF ITS PARTITIONING BETWEEN OUTFLOW PASSAGES: A REGIONAL MODEL STUDY by Ana Paula Berger, B.A. B.Sc. Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy Department of Institute for Marine and Antartic Studies (IMAS) University of Tasmania August, 2019 I declare that this thesis contains no material which has been accepted for a degree or diploma by the University or any other institution, except by way of background information and duly acknowledged in the thesis, and that, to the best of my knowledge and belief, this thesis contains no material previously published or written by another person, except where due acknowledgement is made in the text of the thesis. Signed: Ana Paula Berger Date: 20/04/2020 This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968 Signed: Ana Paula Berger Date: 20/04/2020 ABSTRACT The Indonesian Throughflow (ITF) is the only low latitude connection of the global circulation and is an essential pathway for mass, heat and salt exchange between the Pacific and Indian Oceans. The ITF is a boundary current constrained by topography and is characterised by two source pathways, a western and an eastern. At the exit to the Indian Ocean, observations show the ITF partitions amongst the three major outflow straits. The westernmost, Lombok Strait, has the lowest transport even though it is expected to carry most of the flow given that the ITF is a boundary current and this strait is a direct continuation of the western pathway.
    [Show full text]
  • Fifty Years of the Indonesian Throughflow*
    6342 JOURNAL OF CLIMATE VOLUME 22 Fifty Years of the Indonesian Throughflow* DEBRA TILLINGER AND ARNOLD L. GORDON Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York (Manuscript received 12 December 2008, in final form 14 May 2009) ABSTRACT Simple Ocean Data Assimilation (SODA) reanalysis data are used to produce a 50-yr record of flow through the Makassar Strait, the primary conduit for the Indonesian Throughflow (ITF). Two time series are constructed for comparison to the flow through the Makassar Strait as observed during 1997–98 and 2004–06: SODA along-channel speed within the Makassar Strait and Pacific to Indian Ocean interocean pressure difference calculated on isopycnal layers from SODA hydrology. These derived time series are compared to the total ITF as well as to the vertical distribution and frequency bands of ITF variability. The pressure difference method displays higher skill in replicating the observed Makassar ITF time series at periods longer than 9 months, particularly within the thermocline layer (50–200 m), the location of maximum flow. This is attributed to the connection between the thermocline layer and large-scale wind forcing, which affects the hydrology of the ITF inflow and outflow regions. In contrast, the surface layer (0–50 m) is more strongly correlated with local wind flow, and it is better predicted by SODA along-channel velocity. The pressure difference time series is extended over the 50-yr period of SODA and displays a strong correlation with ENSO as well as a correlation at the decadal scale with the island rule. 1. Introduction through July 1998 as part of the Arus Lintas Indonen (ARLINDO) program (Susanto and Gordon 2005) and The Indonesian Throughflow (ITF), the transport of from January 2004 to December 2006 as part of the Pacific Ocean water to the Indian Ocean through the International Nusantara Stratification and Transport Indonesian seas, is the only low-latitude connection (INSTANT) program (Gordon et al.
    [Show full text]