2017 Vol. 36, No. 3

2017, Vol. 36, No. 3 Content
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An oceanic eddy statistical comparison using multiple observational data in the Kuroshio Extension region
JI Jinlin, DONG Changming, ZHANG Biao, LIU Yu
2017, 36(3): 1-7. doi: 10.1007/s13131-016-0882-1
Eddy characteristics derived from different data resources are compared:sea surface temperature (SST), sea surface height anomaly (SSHA) and surface drifter trajectories. The comparison suggests that the eddy statistical characteristics are different using different variables to delineate eddies, but they show the similar trend. Based on the comparison, abnormal eddies with warm (cold) cores but counter-clockwise (clockwise) rotation are found in the Kuroshio Extension region.
Derivation of the thermal characteristics of mesoscale eddies
CHEN Xuan, PAN Jing, ZHENG Chongwei, ZHANG Xi, HE Ming
2017, 36(3): 8-13. doi: 10.1007/s13131-017-1036-9
This study aims at explaining the relationship between thermodynamic characteristics and direction of rotation of mesoscale eddies (MEs). The geometric characteristics of the MEs are under the following assumptions:the structure of the MEs is symmetrical, and changes of oceanic physical variables are close to linear features in the radial direction in the ME regions. Based on these assumptions, by using primitive equations without friction under a cylindrical coordinate system, the thermodynamic characteristics of the MEs are derived, showing that the conventional relationship of warm anticyclonic eddies with high sea surface height (SSH) and cold cyclonic eddies with low SSH is not consistent with the SSH and sea surface temperature (SST) observations of eddies. The results show that the symmetrical form is an ideal approximation for the geometric characteristics of MEs. In consideration of the above assumptions, there are advantages for derivation of the characteristics of the MEs under a cylindrical coordinate.
Cool water brought by upwelling in the Sanya Bay benefits corals in the background of global warming
YANG Dingtian
2017, 36(3): 14-19. doi: 10.1007/s13131-017-1037-8
It has been reported that global warming has negative effects on coral ecosystems in the past 50 years and the effects vary in different ocean environment. In order to make clear the coral reef status in the background of global warming along the south coast of Hainan Island of China, satellite and in situ data are used to retrieve the information of the coral reef status and surrounding environmental factors. The results show that cool water induced by upwelling along the south coast of Hainan Island is found in the area every summer month, especially in the relatively strong El Niño years (2002-2003 and 2005). From the NOAA satellite data, degree heating week (DHW) index does not exceed 3 in Sanya Bay even in the relatively strong El Niño years. By comparison of a coral reef growth rate in the Sanya Bay with respect to El Niño events from 1957 to 2000, coral's growth rate is relatively greater during 1972, 1991-1994 and 1998 El Niño event. By analyzing the environmental factors, it is found that the cool water induced by upwelling may be the main reason for protecting corals from global warming effects.
An evaluation of input/dissipation terms in WAVEWATCH III using in situ and satellite significant wave height data in the South China Sea
WANG Jichao, ZHANG Jie, YANG Jungang, BAO Wendi, WU Guoli, REN Qifeng
2017, 36(3): 20-25. doi: 10.1007/s13131-017-1038-7
A WAVEWATCH III version 3.14 (WW3) wave model is used to evaluate input/dissipation source term packages WAM3, WAM4 and TC96 considering the effect of atmospheric instability. The comparisons of a significant wave height acquired from the model with different packages have been performed based on wave observation radar and HY-2 altimetry significant wave height data through five experiments in the South China Sea domain spanning latitudes of 0°-35°N and longitudes of 100°-135°E. The sensitivity of the wind speed correction parameter in the TC96 package also has been analyzed. From the results, the model is unable to dissipate the wave energy efficiently during a swell propagation with either source packages. It is found that TC96 formulation with the "effective wind speed" strategy performs better than WAM3 and WAM4 formulations. The wind speed correction parameter in the TC96 source package is very sensitive and needs to be calibrated and selected before the WW3 model can be applied to a specific region.
The temporal and spatial variations in the Pacific wind and wave fields for the period 2002-2011
XU Yao, BI Fan, SONG Jinbao, HE Hailun
2017, 36(3): 26-36. doi: 10.1007/s13131-017-1039-6
The temporal and spatial variations in the wind and wave fields in the Pacific Ocean between 2002 and 2011 are analyzed using a third-generation wave model (WAVEWATCH III). The model performance for a significant wave height is validated using in situ buoy data. The results show that the wave model effectively hindcasts the significant wave height in the Pacific Ocean, but the errors are relatively large in the mid- and low-latitude regions. The spatial distributions and temporal variations in a wind speed and the significant wave height in the Pacific Ocean are then considered after dividing the Pacific Ocean into five regions, which show meridional differences and seasonal cycles. Regional mean values are used to give yearly average time series for each separate zone. The high latitude region in the Southern Hemisphere had a stronger significant wave height trend in the model results than regions at other latitudes. The sources and sinks of wave energy are then investigated. Their regional mean values are used to quantify variations in surface waves. Finally, the spectral analyses of the daily mean wind speeds and the significant wave heights are obtained. The significant wave height and the wind speed spectra are found to be connected in some ways but also show certain differences.
Assimilating OSTIA SST into regional modeling systems for the Yellow Sea using ensemble methods
JI Xuanliang, KWON Kyung Man, CHOI Byoung-Ju, LIU Guimei, PARK Kwang-Soon, WANG Hui, BYUN Do-Seong, LI Yun, JI Qiyan, ZHU Xueming
2017, 36(3): 37-51. doi: 10.1007/s13131-017-0978-2
The effects of sea surface temperature (SST) data assimilation in two regional ocean modeling systems were examined for the Yellow Sea (YS). The SST data from the Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) were assimilated. The National Marine Environmental Forecasting Center (NMEFC) modeling system uses the ensemble optimal interpolation method for ocean data assimilation and the Kunsan National University (KNU) modeling system uses the ensemble Kalman filter. Without data assimilation, the NMEFC modeling system was better in simulating the subsurface temperature while the KNU modeling system was better in simulating SST. The disparity between both modeling systems might be related to differences in calculating the surface heat flux, horizontal grid spacing, and atmospheric forcing data. The data assimilation reduced the root mean square error (RMSE) of the SST from 1.78℃ (1.46℃) to 1.30℃ (1.21℃) for the NMEFC (KNU) modeling system when the simulated temperature was compared to Optimum Interpolation Sea Surface Temperature (OISST) SST dataset. A comparison with the buoy SST data indicated a 41% (31%) decrease in the SST error for the NMEFC (KNU) modeling system by the data assimilation. In both data assimilative systems, the RMSE of the temperature was less than 1.5℃ in the upper 20 m and approximately 3.1℃ in the lower layer in October. In contrast, it was less than 1.0℃ throughout the water column in February. This study suggests that assimilations of the observed temperature profiles are necessary in order to correct the lower layer temperature during the stratified season and an ocean modeling system with small grid spacing and optimal data assimilation method is preferable to ensure accurate predictions of the coastal ocean in the YS.
Comparison of TMI and AMSR-E sea surface temperatures with Argo near-surface temperatures over the global oceans
CHEN Xingrong, LIU Zenghong, SUN Chaohui, WANG Haiyan
2017, 36(3): 52-59. doi: 10.1007/s13131-017-1040-0
Satellite-derived sea surface temperatures (SSTs) from the tropical rainfall measuring mission (TRMM) microwave imager (TMI) and the advanced microwave scanning radiometer for the earth observing system (AMSR-E) were compared with non-pumped near-surface temperatures (NSTs) obtained from Argo profiling floats over the global oceans. Factors that might cause temperature differences were examined, including wind speed, columnar water vapor, liquid cloud water, and geographic location. The results show that both TMI and AMSR-E SSTs are highly correlated with the Argo NSTs; however, at low wind speeds, they are on average warmer than the Argo NSTs. The TMI performs slightly better than the AMSR-E at low wind speeds, whereas the TMI SST retrievals might be poorly calibrated at high wind speeds. The temperature differences indicate a warm bias of the TMI/AMSR-E when columnar water vapor is low, which can indicate that neither TMI nor AMSR-E SSTs are well calibrated at high latitudes. The SST in the Kuroshio Extension region has higher variability than in the Kuroshio region. The variability of the temperature difference between the satellite-retrieved SSTs and the Argo NSTs is lower in the Kuroshio Extension during spring. At low wind speeds, neither TMI nor AMSR-E SSTs are well calibrated, although the TMI performs better than the AMSR-E.
Temporal and spatial variability of the carbon cycle in the east of China's seas: a three-dimensional physical-biogeochemical modeling study
JI Xuanliang, LIU Guimei, GAO Shan, WANG Hui, ZHANG Miaoyin
2017, 36(3): 60-71. doi: 10.1007/s13131-017-0977-3
In the east of China's seas, there is a wide range of the continental shelf. The nutrient cycle and the carbon cycle in the east of China's seas exhibit a strong variability on seasonal to decadal time scales. On the basis of a regional ocean modeling system (ROMS), a three dimensional physical-biogeochemical model including the carbon cycle with the resolution (1/12)°×(1/12)° is established to investigate the physical variations, ecosystem responses and carbon cycle consequences in the east of China's seas. The ROMS-Nutrient Phytoplankton Zooplankton Detritus (NPZD) model is driven by daily air-sea fluxes (wind stress, long wave radiation, short wave radiation, sensible heat and latent heat, freshwater fluxes) that derived from the National Centers for Environmental Prediction (NCEP) reanalysis2 from 1982 to 2005. The coupled model is capable of reproducing the observed seasonal variation characteristics over the same period in the East China Sea. The integrated air-sea CO2 flux over the entire east of China's seas reveals a strong seasonal cycle, functioning as a source of CO2 to the atmosphere from June to October, while serving as a sink of CO2 to the atmosphere in the other months. The 24 a mean value of air-sea CO2 flux over the entire east of China's seas is about 1.06 mol/(m2·a), which is equivalent to a regional total of 3.22 Mt/a, indicating that in the east of China's seas there is a sink of CO2 to the atmosphere. The partial pressure of carbon dioxide in sea water in the east of China's seas has an increasing rate of 1.15 μatm/a (1μtm/a=0.101 325 Pa), but pH in sea water has an opposite tendency, which decreases with a rate of 0.001 3 a-1 from 1982 to 2005. Biological activity is a dominant factor that controls the pCO2air in the east of China's seas, and followed by a temperature. The inverse relationship between the interannual variability of air-sea CO2 flux averaged from the domain area and Niño3 SST Index indicates that the carbon cycle in the east of China's seas has a high correlation with El Niño-Southern Oscillation (ENSO).
Marine Chemistry
Sources and conservative mixing of uranium in the Taiwan Strait
CEN Rongrong, LIU Yanna, XING Na, CHEN Min, CHENG Hua, CAI Yihua
2017, 36(3): 72-81. doi: 10.1007/s13131-017-0985-3
Seawater samples are collected in the spring of 2013 from the Taiwan Strait for the analysis of uranium (U) concentrations and isotopic compositions using MC-ICP-MS, and the geochemical behavior patterns of U in the Taiwan Strait are then investigated. Average concentrations of individual U isotopes are (3.23±0.14) μg/kg for 238U, (2.34±0.09)×10-2 μg/kg for 235U and (2.05±0.07)×10-4 μg/kg for 234U. Correspondingly, the U isotopic compositions are 155±18 for δ234U and 138±2 for 238U:235U. The U concentrations and isotopic ratios in the Taiwan Strait are similar to those of open ocean seawater, suggesting the dominance of the open ocean input to the strait's U pool. However, river input, as suggested by the slightly lower salinity than that of the open ocean, also affected the U concentrations and isotopic compositions in the strait. From a compilation of U concentrations in the Taiwan Strait and adjacent areas, including the Jiulong Estuary and Zhujiang Estuary, the Xiamen Bay and the northern South China Sea, a strong and significant relationship between U concentration and salinity[U:S; U=(0.093 4±0.002 4)S+(0.092 0±0.061 5)] is revealed, suggesting conservative mixing of U in the Taiwan Strait. To better understand the U geochemistry in the Taiwan Strait, a multiple endmembers mixing model is applied to estimate the contributions of potential sources. The open ocean seawater contributed 69%-95% of U in the Taiwan Strait, with river water approximately 2%, and dust deposition only around 0.13%. Therefore, the model results supported the open ocean input source and the conservative mixing behavior of U derived from the observation of U concentrations and isotopic ratios and U:S ratios. The sediment interstitial water may be an important source of U to the Taiwan Strait with a possible contribution of 3%-29%, consistent with previous investigations based on radium isotopes. However, further investigations are warranted to examine the U concentration in the sediment interstitial water and its input to the overlying seawater in the Taiwan Strait.
Marine Geology
Major and trace element geochemistry of the mid-Bay of Bengal surface sediments: implications for provenance
LI Jingrui, LIU Shengfa, FENG Xiuli, SUN Xingquan, SHI Xuefa
2017, 36(3): 82-90. doi: 10.1007/s13131-017-1041-z
The major and trace elements in 110 surface sediment samples collected from the middle of the Bay of Bengal (mid-Bay of Bengal) are analyzed to investigate provenance. Si levels are highest, followed by Al, and the distributions of these two elements are identical. The average CIA* (chemical index of alteration) value is 72.07, indicating that the degree of weathering of the sediments in the study area is intermediate between those of sediments of the Himalayan and Indian rivers. Factor analyses and discrimination function analyses imply that the two main provenances are the Himalayan and the Indian continent. The inverse model calculation of the Ti-normalized element ratios of the Bay of Bengal sediments indicate an estimated average contribution of 83.5% and 16.5% from the Himalayan and peninsular Indian rivers to the study area, respectively. The Himalayan source contributes more sediment to the eastern part of the study area, whereas the western part receives more sediment from the Indian Peninsula than did the eastern part. The primary mechanisms for deposition of sediments in the study area are the transport of Himalayan matter by turbidity currents and river-diluted water and the transport of Indian matter to the study area by a surface circulation in the Bay of Bengal, particularly the East India Coastal Current.
The evolution characteristics of main waterways and their control mechanism in the radial sand ridges of the southern Yellow Sea
CHEN Kefeng, ZHENG Jinhai, ZHANG Chi, WANG Nairui, ZHOU Chunyan
2017, 36(3): 91-98. doi: 10.1007/s13131-017-1042-y
The comparison of the underwater topographic data in recent four decades shows that main waterways of the radial sand ridges area in the southern Yellow Sea tend to gradually migrate southward (scour depth and southward extension of the main channels in Xiyang, southward approach of Lanshayang Waterway and Xiaomiaohong Waterway on South Flank). Although there are various hypotheses about the cause and mechanism of the overall southward migration of the radial sand ridges, no universal and reliable understanding has been obtained so far. The mechanism of this process becomes a challenging problem which serves a key issue in the morphodynamics of the radial sand ridges and the harbor construction in this area. On the basis of the shoreline positions and underwater terrains at different development stages of the Huanghe Delta coast in northern Jiangsu Province, China since the northward return of the Huanghe River and flowed into the Bohai Sea, combined with the tidal wave numerical simulation study, the characteristics and hydrodynamic changes of the tidal wave system in the southern Yellow Sea at different evolution stages are investigated. It is shown that due to the shoreline retreat and the erosion of underwater delta, tidal current velocity is enhanced, and the enhanced area gradually migrates southward. It is revealed that this southward migration of a large-scale regional hydrodynamic axis is possibly a dominant mechanism leading to the overall southward migration of the radial sand ridges.
The influence of earthquakes on Zhubi Reef in the Nansha Islands of the South China Sea
GUO Lei, ZHAN Wenhuan, ZHANG Fan, ZHANG Jinchang, YAO Yantao, LI Jian, FENG Yingci, CHEN Mei, CHENG Gong
2017, 36(3): 99-108. doi: 10.1007/s13131-017-1008-0
It is exceedingly important to estimate the stability of coral reefs. In recent years, growing construction projects have been carried out on the reef flat in the South China Sea. As a special marine geotechnical medium, it is made of the reef debris underwent overwhelmingly long geological age. Reefs grow thickly on the carbonate platform after the Late Oligocene and have five to six main sedimentary facies. It can be used as a recorder to measure the occurrence time of recent earthquake. A model of reef body is presented to study the influence of earthquakes according to the geological structure characteristic of reefs in the Nansha Islands. Furthermore, GeoStudio is used to simulate stress and deformation situations within it under various earthquake intensities. A safety factor is calculated by the limit equilibrium method, and the possible scenarios of earthquake-induced landslides and sliding scale are defined with a Newmark sliding block method, as well as stress distribution and deformation behaviors. Therefore, the numerical results suggest that the connections between the coral reef and the earthquake are as follows:(1) the reef body has a good stability under self-gravity state; (2) after the earthquake, it may cause slope's instability and bring out slumping when the safety factor is smaller than 1 (FS<1); (3) the safety factor decreases with the increasing earthquake intensity, and fluctuates around a particular value after a while; and (4) as a new developed part of the reef, the smaller shallow landslide will be easily subject to collapse caused by the earthquake. It is concluded that it is feasible to provide a reference for evaluating the stability of coral reef using a geotechnical engineering simulation method. This can help the engineering constructions in the South China Sea.
Ocean Engineering
A seasonal grade division of the global offshore wind energy resource
ZHENG Chongwei, LI Chongyin, GAO Chengzhi, LIU Mingyang
2017, 36(3): 109-114. doi: 10.1007/s13131-017-1043-x
Under the background of energy crisis, the development of renewable energy will significantly alleviate the energy and environmental crisis. On the basis of the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-interim) wind data, the annual and seasonal grade divisions of the global offshore wind energy are investigated. The results show that the annual mean offshore wind energy has great potential. The wind energy over the westerly oceans of the Northern and Southern Hemispheres is graded as Class 7 (the highest), whereas that over most of the mid-low latitude oceans are higher than Class 4. The wind energy over the Arctic Ocean (Class 4) is more optimistic than the traditional evaluations. Seasonally, the westerly oceans of the Northern Hemisphere with a Class 7 wind energy are found to be largest in January, followed by April and October, and smallest in July. The area of the Class 7 wind energy over the westerly oceans of the Southern Hemisphere are found to be largest in July and slightly smaller in the other months. In July, the wind energy over the Arabian Sea and the Bay of Bengal is graded as Class 7, which is obviously richer than that in other months. It is shown that in this data set in April and October, the majority of the northern Indian Ocean are regions of indigent wind energy resource.
News and Views
Chinese seventh Arctic scientific expedition
LIU Na, KONG Bin, LIN Lina, HE Yan, LIU Yanguang, LIN Longshan, ZHANG Tao, CHEN Jianfang
2017, 36(3): 115-116. doi: 10.1007/s13131-017-1044-9