Characteristics and temporal variations of near-bottom currents near the Dongsha Island in the northern South China Sea
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摘要
Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation.
Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation.
Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation.
引文
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Beardsley R C,Duda T F,Lynch J F,et al.2004.Barotropic tide in the Northeast South China Sea.IEEE Journal of Oceanic Engineering,29(4):1075-1086
Cao Anzhou,Guo Zheng,Lv Xianqing,et al.2017.Coherent and incoherent features,seasonal behaviors and spatial variations of internal tides in the northern South China Sea.Journal of Marine Systems,172:75-83
Chen Hui,Xie Xinong,Zhang Wenyan,et al.2016.Deep-water sedimentary systems and their relationship with bottom currents at the intersection of Xisha Trough and Northwest Sub-Basin,South China Sea.Marine Geology,378:101-113
Duda T F,Lynch J F,Irish J D,et al.2004.Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea.IEEE Journal of Oceanic Engineering,29(4):1105-1130
Egbert G D,Erofeeva S Y.2002.Efficient inverse modeling of Barotropic ocean tides.Journal of Atmospheric and Oceanic Technology,19(2):183-204
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Gonella J.1972.A rotary-component method for analysing meteorological and oceanographic vector time series.Deep Sea Research and Oceanographic Abstracts,19(12):833-846
Guo Pu,Fang Wendong,Liu Changjian,et al.2012.Seasonal characteristics of internal tides on the continental shelf in the northern South China Sea.Journal of Geophysical Research:Oceans117(C4):C04023
Hu Jianyu,Kawamura H,Hong H,et al.2000.A review on the currents in the South China Sea:seasonal circulation,South China Sea warm current and Kuroshio Intrusion.Journal of Oceanography,56(6):607-624
Klymak J M,Alford M H,Pinkel R,et al.2011.The breaking and scattering of the internal tide on a continental slope.Journal of Physical Oceanography,41(5):926-945
Lan Jian,Wang Yu,Cui Fengjuan,et al.2015.Seasonal variation in the South China Sea deep circulation.Journal of Geophysical Research:Oceans,120(3):1682-1690
Lan Jian,Zhang Ningning,Wang Yu.2013.On the dynamics of the South China Sea deep circulation.Journal of Geophysical Research:Oceans,118(3):1206-1210
Lee I H,Wang Yuhuai,Yang Y,et al.2012.Temporal variability of internal tides in the northeast South China Sea.Journal of Geophysical Research:Oceans,117(C2):C02013
Lei Shao,Li Xuejie,Geng Jianhua,et al.2007.Deep water bottom current deposition in the northern South China Sea.Science in China Series D:Earth Sciences,50(7):1060-1066
Li Li,Qu Tangdong.2006.Thermohaline circulation in the deep South China Sea basin inferred from oxygen distributions.Journal of Geophysical Research:Oceans,111(C5):C05017
Lien R C,Tang T Y,Chang M H,et al.2005.Energy of nonlinear internal waves in the South China Sea.Geophysical Research Letters,32(5):L05615
Ma B B,Lien R C,Ko D S.2013.The variability of internal tides in the Northern South China Sea.Journal of Oceanography,69(5):619-630
Pawlowicz R,Beardsley B,Lentz S.2002.Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE.Computers&Geosciences,28(8):929-937
Shu Yeqiang,Wang Qiang,Zu Tingting.2018.Progress on shelf and slope circulation in the northern South China Sea.Science China Earth Sciences,61(5):560-571
Su Jilan.2004.Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary.Continental Shelf Research,24(16):1745-1760
Torrence C,Compo G P.1998.A practical guide to wavelet analysis Bulletin of the American Meteorological Society,79(1):61-78
Wang Guihua,Xie Shangping,Qu Tangdong,et al.2011.Deep South China Sea circulation.Geophysical Research Letters,38(5):L05601
Xu Zhenhua,Yin Baoshu,Hou Yijun,et al.2013.Variability of internal tides and near-inertial waves on the continental slope of the northwestern South China Sea.Journal of Geophysical Research:Oceans,118(1):197-211
Zhang Yanwei,Liu Zhifei,Zhao Yulong,et al.2014.Mesoscale eddies transport deep-sea sediments.Scientific Reports,4:5937
Zhang Zhiwei,Zhao Wei,Tian Jiwei,et al.2013.A mesoscale eddy pair southwest of Taiwan and its influence on deep circulation Journal of Geophysical Research:Oceans,118(12):6479-6494
Zhao Zhongxiang,Klemas V,Zheng Quanan,et al.2004.Remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern South China Sea.Geophysical Research Letters,31(6):L06302
Zheng Quanan,Susanto R D,Ho C R,et al.2007.Statistical and dynamical analyses of generation mechanisms of solitary internal waves in the northern South China Sea.Journal of Geophysical Research:Oceans,112(C3):C03021
Zheng Hongbo,Yan Pin.2012.Deep-water bottom current research in the Northern South China Sea.Marine Georesources&Geotechnology,30(2):122-129
Beardsley R C,Duda T F,Lynch J F,et al.2004.Barotropic tide in the Northeast South China Sea.IEEE Journal of Oceanic Engineering,29(4):1075-1086
Cao Anzhou,Guo Zheng,Lv Xianqing,et al.2017.Coherent and incoherent features,seasonal behaviors and spatial variations of internal tides in the northern South China Sea.Journal of Marine Systems,172:75-83
Chen Hui,Xie Xinong,Zhang Wenyan,et al.2016.Deep-water sedimentary systems and their relationship with bottom currents at the intersection of Xisha Trough and Northwest Sub-Basin,South China Sea.Marine Geology,378:101-113
Duda T F,Lynch J F,Irish J D,et al.2004.Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea.IEEE Journal of Oceanic Engineering,29(4):1105-1130
Egbert G D,Erofeeva S Y.2002.Efficient inverse modeling of Barotropic ocean tides.Journal of Atmospheric and Oceanic Technology,19(2):183-204
Garrett C,Kunze E.2007.Internal tide generation in the deep ocean Annual Review of Fluid Mechanics,39(1):57-87
Gonella J.1972.A rotary-component method for analysing meteorological and oceanographic vector time series.Deep Sea Research and Oceanographic Abstracts,19(12):833-846
Guo Pu,Fang Wendong,Liu Changjian,et al.2012.Seasonal characteristics of internal tides on the continental shelf in the northern South China Sea.Journal of Geophysical Research:Oceans117(C4):C04023
Hu Jianyu,Kawamura H,Hong H,et al.2000.A review on the currents in the South China Sea:seasonal circulation,South China Sea warm current and Kuroshio Intrusion.Journal of Oceanography,56(6):607-624
Klymak J M,Alford M H,Pinkel R,et al.2011.The breaking and scattering of the internal tide on a continental slope.Journal of Physical Oceanography,41(5):926-945
Lan Jian,Wang Yu,Cui Fengjuan,et al.2015.Seasonal variation in the South China Sea deep circulation.Journal of Geophysical Research:Oceans,120(3):1682-1690
Lan Jian,Zhang Ningning,Wang Yu.2013.On the dynamics of the South China Sea deep circulation.Journal of Geophysical Research:Oceans,118(3):1206-1210
Lee I H,Wang Yuhuai,Yang Y,et al.2012.Temporal variability of internal tides in the northeast South China Sea.Journal of Geophysical Research:Oceans,117(C2):C02013
Lei Shao,Li Xuejie,Geng Jianhua,et al.2007.Deep water bottom current deposition in the northern South China Sea.Science in China Series D:Earth Sciences,50(7):1060-1066
Li Li,Qu Tangdong.2006.Thermohaline circulation in the deep South China Sea basin inferred from oxygen distributions.Journal of Geophysical Research:Oceans,111(C5):C05017
Lien R C,Tang T Y,Chang M H,et al.2005.Energy of nonlinear internal waves in the South China Sea.Geophysical Research Letters,32(5):L05615
Ma B B,Lien R C,Ko D S.2013.The variability of internal tides in the Northern South China Sea.Journal of Oceanography,69(5):619-630
Pawlowicz R,Beardsley B,Lentz S.2002.Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE.Computers&Geosciences,28(8):929-937
Shu Yeqiang,Wang Qiang,Zu Tingting.2018.Progress on shelf and slope circulation in the northern South China Sea.Science China Earth Sciences,61(5):560-571
Su Jilan.2004.Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary.Continental Shelf Research,24(16):1745-1760
Torrence C,Compo G P.1998.A practical guide to wavelet analysis Bulletin of the American Meteorological Society,79(1):61-78
Wang Guihua,Xie Shangping,Qu Tangdong,et al.2011.Deep South China Sea circulation.Geophysical Research Letters,38(5):L05601
Xu Zhenhua,Yin Baoshu,Hou Yijun,et al.2013.Variability of internal tides and near-inertial waves on the continental slope of the northwestern South China Sea.Journal of Geophysical Research:Oceans,118(1):197-211
Zhang Yanwei,Liu Zhifei,Zhao Yulong,et al.2014.Mesoscale eddies transport deep-sea sediments.Scientific Reports,4:5937
Zhang Zhiwei,Zhao Wei,Tian Jiwei,et al.2013.A mesoscale eddy pair southwest of Taiwan and its influence on deep circulation Journal of Geophysical Research:Oceans,118(12):6479-6494
Zhao Zhongxiang,Klemas V,Zheng Quanan,et al.2004.Remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern South China Sea.Geophysical Research Letters,31(6):L06302
Zheng Quanan,Susanto R D,Ho C R,et al.2007.Statistical and dynamical analyses of generation mechanisms of solitary internal waves in the northern South China Sea.Journal of Geophysical Research:Oceans,112(C3):C03021
Zheng Hongbo,Yan Pin.2012.Deep-water bottom current research in the Northern South China Sea.Marine Georesources&Geotechnology,30(2):122-129