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Circulation, biogeochemistry and carbon cycling in ocean margins
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Carbonate chemistry along the main routes of the Indonesian throughflow
P-M1-02-S
Faisal Hamzah* , State key laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, China
Institute for Marine Research and Observation, Ministry of Marine Affairs and Fisheries, Bali, Indonesia
Minhan Dai, State key laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University, Xiamen, China
Zexun Wei, First Institute of Oceanography, State Oceanic Administration, Qingdao, China
Hanif Budi Prayitno, Research Center for Oceanography, Indonesian Institute of Sciences, Jakarta, Indonesia
Presenter Email: faisalhamzah@kkp.go.id |
| The Indonesian Seas (IS) and their throughflow, referred as Indonesian Throughflow (ITF) are well known to play an important role in the global thermohaline circulation. Much less known is the marine chemistry of the IS. Here, we present a large dataset of the carbonate system parameters collected during cruises to the main routes of the ITF in the transition monsoon season in October 2015 and November 2017. Our study area spanned southern Philippine Sea, the Sulawesi Sea, the Makassar Strait and Lombok Strait. Along the routes, two water masses namely North Pacific subtropical water (NPSW; T = 18-25 oC, S = 34.6-34.8 and
s0= 24) and North Pacific intermediate water (NPIW; T = 7-11 oC, S = 34.3-34.5 and s0= 26.5) were revealed in the upper thermocline waters. In the southern Philippine Sea high total alkalinity (TAlk; 2300 μmol kg-1) and pH (8.10) in the upper 50 m water column were observed due to the influence of Mindanao Eddy where lower values of dissolved inorganic carbon (DIC; 1920 μmol kg-1) than expected were found, reflective of freshwater injection from Maluku Sea by the northeastward flow. Such freshwater discharge with salinity ~33.9 from Sulu Sea remained visible in the upper layer 20 m northern Makassar Strait featuring lower DIC, TAlk, and higher pH ranging respectively 1914-1987 μmol kg-1, 2225-2277 μmol kg-1 and 8.05-8.10. Along the Makassar Strait (before Dewakang sill), the NPSW appeared at ~ 100 m isodepth characterized by DIC of 2072 μmol kg-1, TAlk of 2291 μmol kg-1, and pH of 7.92. Meanwhile the NPIW was also found along the ~ 300 m isodepth with slightly higher DIC (~ 2206 μmol kg-1) and TAlk (~ 2299 μmol kg-1), but lower pH (7.85). Moreover, in the southern Makassar Strait, the NPSW features high DIC (2100 μmol kg-1) but slightly lower TAlk (2283 μmol kg-1) and pH (7.85), which is distinct from the NPIW. We calculated that the ITF associated carbon flux was 194.8±194 Tg C y-1 along the main routes of Mindanao-Sulawesi passage. The net flux to the Indian Ocean from the Makassar Strait was 202±69 Tg C y-1, among which ~40 Tg C y-1 was via the Lombok Strait. This study demonstrated that the carbonate chemistry along the main routes of the ITF were primarily shaped by the combination of water mass mixing and freshwater discharge played a significantly important role. |
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