Acta Oceanologica Sinica

With moorings equipped with Acoustic Doppler Current Profilers (ADCP) in the northern South China Sea (SCS) in 2008 and 2009, we observed three near-inertial oscillation (NIO) events coded 2008a, 2009a and 2009b induced by passages of typhoons or tropical storms. This study compares characteristics of the three NIO events. Event 2008a was the strongest one among the three, and had the longest sustaining period (15 d), while events 2009a and 2009b sustained for only 4 and 8 d, respectively. The three events were distinguished by vertical energy distribution and phase propagation. As for the frequency shift of the NIO, event 2008a had a peak frequency lower than the local Coriolis frequency (red-shift), while events 2009a and 2009b showed blue-shift. The behavior of individual NIO event is jointly decided by the typhoon disturbance and the background ocean condition. Especially the background flow plays an important role by effects of advection and modulation. The results in this study provide observational evidence of variational NIO response to background flow field. As indicated by the distribution of vorticity and effective Coriolis frequency derived from numerical modeling, the large amplitude and elongated sustaining period of event 2008a were attributed to the waveguide effect of the background shear flow. This effect redistributed the NIO energy after the typhoon passage, absorbed incident waves and trapped energy in the area of the negative vorticity. While the background flow during events 2009a and 2009b did not have such effects due to the near-zero vorticity in the mooring area.

Deep-water channel systems are important petroleum reservoirs, and many have been discovered worldwide. Understanding deep-water channel sedimentary elements and evolution is helpful for deep-sea petroleum exploration and development. Based on high-resolution 3D seismic data, the Miocene channel system in the deep-water Taranaki Basin, New Zealand, was analyzed by using seismic interpretation techniques such as interlayer attribute extraction and strata slicing. The channel system was divided into five composite channels (CC-I to CC-V) according to four secondary level channel boundaries, and sedimentary elements such as channels, slump deposits, inner levees, mass transport deposits, and hemipelagic drape deposits were identified in the channel system. The morphological characteristics of several composite channels exhibited stark variances, and the overall morphology of the composite channels changed from relatively straight to highly sinuous to relatively straight. The evolution of the composite channels involved a gradual and repeated process of erosion and filling, and the composite channels could be divided into three evolutionary stages: initial erosion-filling, later erosion-filling (multistage), and channel abandonment. The middle Miocene channel system may have formed as a consequence of combined regional tectonic activity and global climatic change, and its intricate morphological alterations may have been influenced by the channel’s ability to self-regulate and gravity flow properties. When studying the sedimentary evolution of a large-scale deep-water channel system in the Taranaki Basin during the Oligocene-Miocene, which transitioned from a passive margin to plate convergence, it can be understood how tectonic activity affected the channel and can also provide a theoretical reference for the evolution of the deep-water channels in areas with similar tectonic conversion environments around the world.

The geochemical signatures of fifty-four rock samples and three supplementary drill stem test (DST) oils from the Yacheng-Sanya formations in the central Qiongdongnan Basin (CQB) were analysed. Reconstruction of the early Oligocene—early Miocene (36–16 Ma) palaeovegetation and source analyses of organic matter (OM) were conducted using aliphatic biomarkers in ancient sediments and DST oils. Both the interpreted aquatic and terrigenous OM contributed to the CQB source rocks (SRs) but had varying relative proportions. The four distribution patterns derived from n-alkanes, terpanes, and steranes are representative of four OM composition models of the Yacheng-Sanya SRs, including model A, model B, model C, and model D, which were classified based on the increasing contribution from terrigenous OM relative to aquatic OM. Some terrigenous higher plant-derived biomarkers, including oleanane, des-A-oleanane, C29ααα 20R sterane, bicadinanes, the C19/(C19 + C23) tricyclic terpane ratio, and other n-alkane-derived ratios suggest that angiosperms had increased proportions in the palaeoflora from early Oligocene to early Miocene, and the bloom of terrigenous higher plants was observed during deposition of upper Lingshui Formation to lower Sanya Formation. These findings are consistent with the incremental total organic carbon and free hydrocarbons + potential hydrocarbons (S1 + S2) in the lower Lingshui-lower Sanya strata with a significant enrichment of OM in the E3l1-N1s2 shales. The maturity- and environment-sensitive aliphatic parameters of the CQB SRs and DST oils suggest that all the samples have predominantly reached their early oil-generation windows but have not exceeded the peak oil windows, except for some immature Sanya Formation shales. In addition, most of the OM in the analysed samples was characterised by mixed OM contributions under anoxic to sub-anoxic conditions. Furthermore, terrestrial-dominant SRs were interpreted to have developed mainly in the Lingshui-Sanya formations and were deposited in sub-oxic to oxic environments, compared to the anoxic to sub-anoxic conditions of the Yacheng Formation.

The evolution of the natural and pristine Mediterranean coastline Port aux Princes-Sidi Daoued (Gulf of Tunis, NE-Tunisia) is studied during the period of 1887–2010 on the basis of an ancient minute of bathymetry (1887) and aerial photographs treated by numerical photogrammetric methods. Morphological changes of the coastline shows a general retreat despite the absence of the various anthropogenic actions. Adding to the drift currents and the currents of high energy that are generated by the N-W dominant waves along steeply sub-marine funds, the erosion is mainly due to the sea level rise which increased since the beginning of the 2000s. The Port aux Princes-Sidi Daoued coastline works as a single littoral cell limited by Jbel Korbous to the SW and the fishing harbor of Sidi Daoued to the N-E.

This paper is focused on the seasonality change of Arctic sea ice extent (SIE) from 1979 to 2100 using newly available simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). A new approach to compare the simulation metric of Arctic SIE between observation and 31 CMIP5 models was established. The approach is based on four factors including the climatological average, linear trend of SIE, span of melting season and annual range of SIE. It is more objective and can be popularized to other comparison of models. Six good models (GFDL-CM3, CESM1-BGC, MPI-ESM-LR, ACCESS-1.0, HadGEM2-CC, and HadGEM2-AO in turn) are found which meet the criterion closely based on above approach. Based on ensemble mean of the six models, we found that the Arctic sea ice will continue declining in each season and firstly drop below 1 million km2 (defined as the ice-free state) in September 2065 under RCP4.5 scenario and in September 2053 under RCP8.5 scenario. We also study the seasonal cycle of the Arctic SIE and find out the duration of Arctic summer (melting season) will increase by about 100 days under RCP4.5 scenario and about 200 days under RCP8.5 scenario relative to current circumstance by the end of the 21st century. Asymmetry of the Arctic SIE seasonal cycle with later freezing in fall and early melting in spring, would be more apparent in the future when the Arctic climate approaches to “tipping point”, or when the ice-free Arctic Ocean appears. Annual range of SIE (seasonal melting ice extent) will increase almost linearly in the near future 30–40 years before the Arctic appears ice-free ocean, indicating the more ice melting in summer, the more ice freezing in winter, which may cause more extreme weather events in both winter and summer in the future years.

The coupling numerical model of wave interaction with porous medium is used to study wave-induced pore water pressure in high permeability seabed. In the model, the wave field solver is based on the two dimensional Reynolds-averaged Navier-Stokes (RANS) equations with a k-ɛ closure, and Forchheimer equations are adopted for flow within the porous media. By introducing a Velocity-Pressure Correction equation for the wave flow and porous flow, a highly efficient coupling between the two flows is implemented. The numerical tests are conducted to study the effects of seabed thickness, porosity, particle size and intrinsic permeability coefficient on regular wave and solitary wave-induced pore water pressure response. The results indicate that, as compared with regular wave-induced, solitary wave-induced pore water pressure has larger values and stronger action on seabed with different parameters. The results also clearly show the flow characteristics of pore water flow within seabed and water wave flow on seabed. The maximum pore water flow velocities within seabed under solitary wave action are higher than those under regular wave action.

A taxonomic study of Hyalinoecia species based on the materials deposited in the Marine Biological Museum of the Chinese Academy of Sciences (MBMCAS) yielded two species: Hyalinoecia tubicola (Müller, 1776) and H. papillata Imajima, 1999. Both species were collected from the sandy bottoms in the northern South China Sea. Hyalinoecia tubicola is widely distributed from the coast of Guangdong Province southwards to the Xisha Islands. Hyalinoecia papillata is reported for the first time in the South China Sea. It differs from H. tubicola in having a prolonged, tongue-like prechaetal lobe with papillae along the lateral margins in the first parapodium (vs. auricular prechaetal lobe with smooth margins). The morphological description and illustration of both species are given.

The Luzon Strait is the main impact pathway of the Kuroshio on the circulation in South China Sea (SCS). Based on the analysis of the 1997–2007 altimeter data and 2005–2006 output data from a high resolution global HYCOM model, the total Luzon Strait Transport (LST) has remarkable subseasonal oscillations with a typical period of 90 to 120 days, and an average value of 1.9 Sv into SCS. Further spectrum analysis shows that the temporal variability of the LST at different depth is remarkable different. In the upper layer (0–300 m), westward inflow has significant seasonal and subseasonal variability. In the bottom layer (below 1 200 m), eastward outflow exhibits remarkable seasonal variability, while subseasonal variability is also clear. In the intermediate layer, the westward inflow is slightly bigger than the eastward outflow, and both of them have obvious seasonal and subseasonal variability. Because the seasonal variation of westward inflow and eastward out-flow is opposite, the total transport of intermediate layer exhibits significant 50–150 days variation, without obvious seasonal signals. The westward Rossby waves with a period of 90 to 120 days in the Western Pacific have very clear correlationship with the Luzon Strait Transport, this indicates that the interaction between these westward Rossby waves and Kuroshio might be the possible mechanism of the subseasonal variation of the LST.