Moored Observations of Transport and Variability of Halmahera Sea Currents

发布时间:2020-02-15 文章来源:

Recently, the Journal of Physical Oceanography of the American Meteorological Society, which is one of the most reputable academic journals in the physical oceanography research of the world, has online published an important research paper, entitled with “Moored Observations of Transport and Variability of Halmahera Sea Currents” (Li et al. 2020).  This latest research achievement was jointly made by Chinese scientists: Dr Yuan Dongliang’s research group, with First author: Dr Li Xiang and Corresponding author: Dr Yuan Dongliang, and Indoensian Scientists supported by the Research Center for Oceanography, Indonesian Institute of Sciences (RCO/LIPI) using the R/V Baruna Jaya VIII,  aiming at revealing the vertical structure and seasonal-to-interannual variability of the currents and transport of the Halmahera Sea based on a subsurface mooring. 


The Great Ocean Conveyer Belt (GOCB) is the route of the general thermocline circulation of the global oceans, which is known to play an important role in climate change of the earth and mass and heat balance of the oceans.  Based on measurements in the Makassar Strait of the Indonesian seas, showing that the majority of the Indonesian Throughflow (ITF) comes from the North Pacific Ocean, it has been suggested that the cold deep South Ocean waters flow northward through the deep South Pacific Ocean and upwells in the North Pacific to the surface to supply the mass transport of the ITF.  Due to the existence of zero wind curl lines in the South Pacific and below the Inter-Tropical Convergence Zone immediately north of the Equator, the wind-driven circulation in the South Pacific is suggested to be a closed gyre, playing a trivial role in the GOCB.  In Li et al. (2020) study, the time series measurements of ocean currents in the Jailolo Strait of the Halmahera Sea have been successfully conducted for the first time in history, showing that significant South Pacific tropical waters join the ITF to enter the Indian Ocean, which must come from upwelling in the South Pacific.  Thus, the importance of the Halmahera Sea mooring measurements is that it reveals, for the first time in history, that the South Pacific Ocean also plays an important role in the GOCB.  A new branch of the ITF is uncovered.  The old drawing of the GOCB shall be revised and new understandings of the global ocean thermocline circulation have thus been achieved.


Focusing on the two consecutive years of moored observation in the Jailolo Strait from November 2015 to October 2017, the transport of the Halmahera Sea was directly measured for the first time history, indicating that the 2-year mean transport of the Jailolo Strait is estimated to be -2.44 Sv ± 0.42 Sv to the Indonesian seas based on the mooring data. The largest uncertainty may exist in the horizontal extrapolation, which, however, is supported by the SADCP measurements and high-resolution ocean model simulations.

Figure 1. Volume transports of the Jailolo Strait in upper and lower layers

At the same time, the analysis also covers the mean along strait velocity, which is shown to flow towards the Indonesian Seas throughout the water column except at the bottom, where a northward flow during 2017 is observed. The variability of the sub-tidal currents is found to be characterized by a two-layer system with dominant annual cycles. In the upper 200 m, the currents are northward to the Pacific Ocean during December through April, but stronger and southward for the rest of the year. Below 200 m, the currents are also dominated by an annual cycle but with an opposite phase.

Figure 2. 120-day low passed and mean along strait velocity (ASV) of the 2-year mooring measurements in the Jailolo Strait of the Halmahera Sea

The results in this paper also indicate that the pressure difference between the far equatorial western Pacific Ocean and the Indonesian Seas drives the variability of the transports through the Jailolo Strait, which is diagnosed by the satellite sea surface height (SSH) and ocean bottom pressure (OBP) data. Especially, the seasonal variability of the transports in both upper and lower layers is dominated by the annual cycle of SSH in the Indonesian Seas.  


Besides, the interannual transport in the Jailolo Strait during the 2015-2016 super El Ni?o is found to be much smaller than the seasonal cycle based on the mooring observations, suggesting that most of El Ni?o signal did not propagate into the Indonesian seas through the Halmahera Sea. The observation challenges the existing studies suggesting a major inter-basin wave guide from the western Pacific Ocean through the Halmahera Sea to the west coasts of the New Guinea and the Australia continent and to the eastern Indian Ocean.

Figure 3. Schematic of the upper-ocean circulation of the Indonesian Seas


This study is strongly supported by the mooring data from the ocean observation system deployed in Indonesian Sea, which is prestigious for its largest mooring observation array currently. Moreover, NSFC (41421005, 41720104008, 91858204, and 41876025) also provides sufficient funding support to this study.


Li, X., Yuan, D., Wang, Z., Li, Y. et al. (2020). Moored observations of transport and variability of Halmahera Sea currents. Journal of Physical Oceanography, 50(2), DOI:  


Yuan, D., Li, X. et al. (2018). Observed Transport Variations in the Maluku Channel of the Indonesian Seas Associated with Western Boundary Current Changes, J. Phys. Oceanogr., 48(8), 1803-1813.