Characteristics And Mechanism Of The Interannual Variability Of The Karimata Strait Throughflow

The Karimata Strait（KS）throughflow between the South China Sea（SCS）and Java Sea plays an essential role in heat and freshwater budget in the SCS and dual roles in strengthening/reducing the primary Indonesian throughflow（ITF）in the Makassar Strait.A sustained long-term monitoring of the ITF is logistically challenging and expensive;therefore,proxies are needed.Here,we use a combination of in situ measurement of the KS throughflow and satellite-derived sea surface height（SSH）and sea surface wind（SSW）to determine the interannual and decadal modulations in seasonal amplitude of the KS throughflow associated with El Ni（?）o-Southern Oscillation（ENSO）,Indian Ocean dipole（IOD）,Pacific Decadal Oscillation（PDO）.Linear regression,correlation,harmonic,power spectrum analyses and ensemble empirical mode decomposition are used.The results manifest that there are significant interannual to decadal modulations in the seasonal amplitude of the KS throughflow.The modulations of the seasonal amplitude in the volume and heat transports range 1.36～1.92 Sv(1 Sv=10⁶m³s^-1)and 126.41～173.36 TW(1 TW=10¹²W),respectively,with a significant cycle of～9years.From 1994 to 2020,the seasonal amplitude of volume transport through the KS shows an increasing trend of 37.75±15.69 m Sv decade^-1(1 m Sv=10³m³s^-1).The seasonal amplitude of the heat transport also increases,at a rate of 4.78±1.52 TW decade^-1.The seasonal amplitude in the freshwater transport varies between 8.28 and111.58 Sv,with a significant decreasing trend of-17.86±3.68 m Sv decade^-1.The KS volume transport is positively correlated with PDO and ENSO indices（r=0.69 and r=0.58）,with a lag of 12 and 10 months,respectively.The results of composite analysis suggest that the interannual variability of the KS transport is related to the interannual anomalies of the SSH gradient and the local SSW fields in boreal winter.The relationships between the KS transport and the other straits of the SCS throughflow are also discussed.HYCOM reanalysis data shows that the KS transport is negatively correlated with the surface transport in the Luzon Strait（r=-0.40）,and is positively correlated with the volume transport in middle layer and deep layer,but has no significant correlation with the Mindoro strait,the Balabac strait and the western boundary current.The seasonal amplitude of the volume transports of the SCS throughflow have significant interannual to decadal modulations.All of them are correlated with ENSO index on the interannual scale except for the western boundary current and the KS.The seasonal amplitudes of the transports of the main straits in the SCS throughflow have a long-term increasing trend,while the seasonal amplitude of the transport in the Mindoro Strait has a long-term decreasing trend.