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The distribution and composition of hydrocarbons in sediments of the South Mid-Atlantic Ridge
Xin HUANG, Shuai CHEN, Xiaoyuan WANG, Shuwen ZHANG, Fajin CHEN, Xiaoqiang PU
doi: 10.1007/s13131-018-1160-1
Sediment samples obtained from the South Mid-Atlantic Ridge are analyzed by a gas chromatography-mass spectrometer (GC-MS) for the abundances and distributions of hydrocarbons. The hydrocarbons in the samples exhibit a bimodal distribution of n-alkanes and are rich in 3-methylalkanes, 8-methylalkanes and 2, 4, (n-1)-trimethylalkanes, which may be the result of metabolic activity of benthic microorganism. Terpanes, hopanes and steranes are all enriched in the samples, which also support the microbial origin of hydrocarbons in samples. Bitumen and hydrocarbons in the samples show a trend that the contents are the highest in the Samples 22V-TVG10 and 26V-TVG05 collected near hydrothermal areas, and the lowest in samples 22IV-TVG01, 22V-TVG11, and 22V-TVG14 collected far from the hydrothermal areas, which suggest the possible influence on the samples by hydrothermal activity.
key words: hydrocarbons, South Mid-Atlantic Ridge, sediment, hydrothermal activity
The cruise observation of turbulent mixing in the upwelling region east of Hainan Island in the summer of 2012
Mingming LI, Lingling XIE, Xiaolong ZONG, Shuwen ZHANG, Lei ZHOU, Junyi LI
doi: 10.1007/s13131-018-1260-y
The turbulent mixing in the upwelling region east of Hainan Island in the South China Sea is analyzed based on in situ microstructure observations made in July 2012. During the observation, strong upwelling appears in the coastal waters, which are 3°C cooler than the offshore waters and have a salinity 1.0 greater than that of the offshore waters. The magnitude of the dissipation rate of turbulent kinetic energy ε in the upwelling region is O (10–9 W/kg), which is comparable to the general oceanic dissipation. The inferred eddy diffusivity Kρ is O (10–6 m2/s), which is one order of magnitude lower than that in the open ocean. The values are elevated to KρO (10–4 m2/s) near the boundaries. Weak mixing in the upwelling region is consistent with weak instability as a result of moderate shears versus strong stratifications by the joint influence of surface heating and upwelling of cold water. The validity of two fine-scale structure mixing parameterization models are tested by comparison with the observed dissipation rates. The results indicate that the model developed by MacKinnon and Gregg in 2003 provides relatively better estimates with magnitudes close to the observations. Mixing parameterization models need to be further improved in the coastal upwelling region.
key words: coastal upwelling, mixing, turbulent kinetic energy dissipation rate, eddy diffusivity, South China Sea
Unusual coastal ocean cooling in the northern South China Sea by a katabatic cold jet associated with Typhoon Mujigea (2015)
Yuxin SHI, Lingling XIE, Quanan ZHENG, Shuwen ZHANG, Mingming LI, Junyi LI
doi: 10.1007/s13131-019-1440-4
This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea (SCS) in October 2015. We analyze the satellite sea surface temperature (SST) time series from October 3 to 18, 2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2°C on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7 d of the typhoon passage, and lasted for 5 d from October 10 to 15. The maximum SST cooling was –4°C and occurred after 12 d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau (YGP), Typhoon Mujigea (2015) met the westerly wind front on October 5. The low-pressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough, thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau (QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4 d later after the maximum air temperature drop of –9°C on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.
key words: Typhoon Mujigea (2015), second-round cooling, katabatic cold jet, South China Sea, westerly wind front
Upwelling off the west coast of Hainan Island: sensitivity to wave-mixing
Peng BAI, Jingling YANG, Shuwen ZHANG, Lingling XIE, Junshan WU
The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system is employed to investigate the role of wave-mixing playing in the upwelling off the west coast of Hainan Island (WHU). Waves, tides and sea surface temperature (SST) are reproduced reasonably well by the model when validated by observations. Model results suggest the WHU is tidally driven. Further investigations indicate that inclusion of wave-mixing promotes the intensity of the WHU, making the simulated SST become more consistent with remote-sensed ones. Dynamically, wave-mixing facilitates the " outcrop” of more upwelled cold water, triggering stronger WHU and leading to a three-dimensional dynamical adjustment. From the perspective of time, wave-mixing contributes to establishing an earlier tidal mixing front strong enough to generate WHU and that is, WHU may occur earlier when taking wave-mixing into consideration.
key words: upwelling, wave-mixing, tidal mixing front, COAWST, Hainan Island

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