The Indonesian Throughflow plays an important role in the global ocean circulation and climate. Existing studies of the Indonesian Throughflow have focused on the Makassar Strait and the exit straits, where the upper thermocline currents carry North Pacific waters to the Indian Ocean. Here we show, using mooring observations, that a previous unknown intermediate western boundary current (with the core at ~1000 m depth) exists in the Maluku Sea, which transports intermediate waters (primarily the Antarctic Intermediate Water) from the Pacific into the Seram-Banda Seas through the Lifamatola Passage above the bottom overflow. Our results suggest the importance of the western boundary current in global ocean intermediate circulation and overturn. We anticipate that our study is the beginning of more extensive investigations of the intermediate circulation of the Indo-Pacific ocean in global overturn, which shall improve our understanding of ocean heat and CO2 storages significantly.
The ocean currents in the Halmahera Sea are studied using a subsurface mooring deployed in the Jailolo Strait from November 2015 to October 2017. The subtidal currents of the mooring measurements are characterized by a two-layer system, with the current variability below about 200 m in opposite phases to that in the upper layer. The mean along-strait velocity (ASV) is toward the Indonesian seas in the whole water column, producing an estimated mean transport of 2.44 ± 0.42 Sv (1 Sv ≡ 106 m3 s−1). The errors of the transport calculation based on the single mooring measurements are estimated to be less than 15% using simulations of high-resolution ocean models. A weak current is observed to flow northward during 2017 at the bottom of the strait. The ASV variability is found to be dominated by an annual cycle both in the upper and lower layers. The total transport, however, is dominated by semiannual variability because of the cancelation of the annual transports in the upper and lower layers. The variability of the transport is suggested to be driven by the pressure difference between the Pacific Ocean and the Indonesian seas, as evidenced by the agreement between the satellite pressure gradient and the two-layer transports. The transport of the Jailolo Strait during the 2015/16 super El Niño is found to be nearly the same as that during the 2016 La Niña, suggesting that the interannual variability of the transport is much smaller than the seasonal cycle.
The characteristics, distribution, and accumulation of detrital sediment on the surface sediment in the Senunu Sea are used as a preliminary study to identify the detrital and sedimentation processes’ origin. This study aims to present the characters and composition of detrital sediment on Senunu seabed. It illustrates the influence of land sediment sources on sediment compositions settled on the bottom of the surrounding seas. Specific review on the sediment character in this region was done to identify surface sediment layers carrying tailings materials from ore mining on land and differentiate them from natural sediment. 53 sediment core from the Senunu bottom were collected and analyzed for their detrital characteristics using a binocular microscope. In general, sediment composition in Senunu seabed was terrigenous sediment with dominant material quartz, andesite, and tuffaceous breccia. Based on the detrital analysis, sediment lithology of natural seabed sediment and sediment containing tailing material is distinguished by color, layer contact, grain packing, grain shape, biota association, and specific mineral content quartz, mica, and magnetite. Surface sediment containing tailing material had more quartz mineral, had more similar grain size and crystal shape, fresher mineral condition, clearer color, and looser grain relation than seabed sediment that did not contain tailings material.. Based on the different characters and distribution patterns, sediment carrying tailings in the Senunu seabed. Based on the other characters and distribution patterns, sediments carrying tailings in the Senunu seabed on average were 2-167 centimeter thick at the surface with accumulated tailing 1-50% of total sediment at the sea bottom. Furthermore, the distribution of these tailing deposits is influenced mainly by morphodynamic, hydrodynamic conditions and the process of redeposition.
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