Abstract
As one of the Indonesian Throughflow (ITF) outflow passages, the Sumba Strait is a meeting point for the Pacific and the Indian Ocean water mass. In order to study the long-term variability of ITF flowing via Sumba Strait, this research uses observational data from the Ekspedisi WIdya Nusantara (EWIN) research cruise conducted in August 2016 to validate the altimetric geostrophic surface current by referencing the shear velocity. Stating the referenced level to 700 m, geostrophic transport is calculated using the Monthly Isopycnal/Mixed-Layer Ocean Climatology (MIMOC) data. Over the period of 1993-2016, the results demonstrate a dominant seasonal pattern for the geostrophic variability. While the total geostrophic transport shows a main westward direction towards the Indian Ocean, the Sumba Strait provides only a small portion (less than 0.1 Sv) for westward ITF geostrophic current. Intraseasonally, the maximum transport occurs during the southeast monsoon. The reversal of South Java Current (SJC), which flows with the eastward direction heading to the Savu Sea, is observed as the intrusion for westward ITF in almost every monsoon season. Despite having an unclear year to year cycle, climate mode of the Indian Ocean may have more influence on the surface geostrophic variability at the Sumba Strait. On the other hand, ocean-atmosphere coupling in the Pacific Ocean has a role in regulating geostrophic transport variation within the Sumba Strait. Using a statistical approach, the findings emphasize that the throughflow may well be impacted as well as feedback on both ENSO and IOD since there is robustness in those variables.
Highlights
It has been well-known that Indonesian seas are the only pathway for the Pacific and Indian Ocean interconnection in the equatorial zone (Broecker, 1997; Koch-Larrouy et al, 2007; Sprintall and Revelard, 2014)
The primary data comes from the Ekspedisi Widya Nusantara (EWIN 2016) annual research cruise, which was conducted by Research Center for Oceanography- Indonesian Institute of Sciences (LIPI) using Research Vessel (R/V) Baruna Jaya VIII
It marks the promising place for the meeting point between the Pacific water mass which is transported as Indonesian Throughflow (ITF) from the inflow gates of northern Indonesian region and Indian Ocean water mass associated with the South Java Current (SJC)
Summary
It has been well-known that Indonesian seas are the only pathway for the Pacific and Indian Ocean interconnection in the equatorial zone (Broecker, 1997; Koch-Larrouy et al, 2007; Sprintall and Revelard, 2014) These flows, which has been named as the Indonesian Throughflow (ITF) (Wyrtki, 1987), bring the Pacific warm water into the Indian Ocean through the internal Indonesian Seas (Wijffels et al, 1992; Ganachaud et al, 2000) giving the influence for global ocean thermohaline, heat budget (Gordon, 1986) and being a significant part in Australasian regional climate (Hautala et al, 2001). The information on ITF variability within the Sumba Strait is less than the other outflow passages (Hautala et al, 2001)
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