2016 Vol. 35, No. 12

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2016, 35(12): 0-0.
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Succession of causative species during spring blooms in the East China Sea: coupled biophysical numerical modeling
SUN Ke, QIU Zhongfeng, HE Yijun, FAN Wei, WEI Zexun
2016, 35(12): 1-11. doi: 10.1007/s13131-016-0964-0
Abstract:
In the East China Sea (ECS), the succession of causative species responsible for blooms is a recurrent phenomenon during the spring, which changes from diatoms to dinoflagellates. Observations from space and in situ cruises captured this pattern of succession during spring of 2005. In this study, we coupled two biological models, which were developed previously for Skeletonema costatum and Prorocentrum donghaiense, into a circulation model tailored for the ECS. The coupled biophysical model was used to hindcast the blooms and to test the hypothesis proposed in earlier studies that phosphate (PO43-) is the first-order decider of the succession. The coupled model successfully reproduced the hydrodynamics (as described in a companion paper by Sun et al., the spatiotemporal distribution of the chlorophyll a (Chl a) concentration, and the species succession reasonably well. By analyzing the effects of different factors on the surface Chl a distribution, we confirmed that the offshore boundaries of the blooms were confined by PO43-. In addition, we suggest that surface wind fields may modulate the horizontal distribution of blooms. Thus, during the dispersal of blooms, surface winds coupled with PO43- may control the succession of blooms in the ECS. The proposed coupled model provides a benchmark to facilitate future improvements by including more size classes for organisms, multiple nutrient schemes, and additional processes.
SST diurnal warming in the China seas and northwestern Pacific Ocean using MTSAT satellite observations
TU Qianguang, PAN Delu, HAO Zengzhou, YAN Yunwei
2016, 35(12): 12-18. doi: 10.1007/s13131-016-0968-9
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Hourly sea surface temperature (SST) observations from the geostationary satellite are increasingly used in studies of the diurnal warming of the surface oceans. The aim of this study is to derive the spatial and temporal distribution of diurnal warming in the China seas and northwestern Pacific Ocean from Multi-functional Transport Satellite (MTSAT) SST. The MTSAT SST is validated against drifting buoy measurements firstly. It shows mean biases is about -0.2℃ and standard deviation is about 0.6℃ comparable to other satellite SST accuracy. The results show that the tropics, mid-latitudes controlled by subtropical high and marginal seas are frequently affected by large diurnal warming. The Kuroshio and its extension regions are smaller compared with the surrounding regions. A clear seasonal signal, peaking at spring and summer can be seen from the long time series of diurnal warming in the domain in average. It may due to large insolation and low wind speed in spring and summer, while the winter being the opposite. Surface wind speed modulates the amplitude of the diurnal cycle by influencing the surface heat flux and by determining the momentum flux. For the shallow marginal seas, such as the East China Sea, turbidity would be another important factor promoting diurnal warming. It suggests the need for the diurnal variation to be considered in SST measurement, air-sea flux estimation and multiple sensors SST blending.
Object-based image analysis for mapping geomorphic zones of coral reefs in the Xisha Islands, China
XU Jingping, ZHAO Jianhua, LI Fang, WANG Lin, SONG Derui, WEN Shiyong, WANG Fei, GAO Ning
2016, 35(12): 19-27. doi: 10.1007/s13131-016-0921-y
Abstract:
Mapping regional spatial patterns of coral reef geomorphology provides the primary information to understand the constructive processes in the reef ecosystem. However, this work is challenged by the pixel-based image classification method for its comparatively low accuracy. In this paper, an object-based image analysis (OBIA) method was presented to map intra-reef geomorphology of coral reefs in the Xisha Islands, China using Landsat 8 satellite imagery. Following the work of the Millennium Coral Reef Mapping Project, a regional reef class hierarchy with ten geomorphic classes was first defined. Then, incorporating the hierarchical concept and integrating the spectral and additional spatial information such as context, shape and contextual relationships, a large-scale geomorphic map was produced by OBIA with accuracies generally more than 80%. Although the robustness of OBIA has been validated in the applications of coral reef mapping from individual reefs to reef system in this paper, further work is still required to improve its transferability.
Simulations of dissolved oxygen concentration in CMIP5 Earth system models
BAO Ying, LI Yangchun
2016, 35(12): 28-37. doi: 10.1007/s13131-016-0959-x
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The climatologies of dissolved oxygen concentration in the ocean simulated by nine Earth system models (ESMs) from the historical emission driven experiment of CMIP5 (Phase 5 of the Climate Model Inter-comparison Project) are quantitatively evaluated by comparing the simulated oxygen to the WOA09 observation based on common statistical metrics. At the sea surface, distribution of dissolved oxygen is well simulated by all nine ESMs due to well-simulated sea surface temperature (SST), with both globally-averaged error and root mean square error (RMSE) close to zero, and both correlation coefficients and normalized standard deviation close to 1. However, the model performance differs from each other at the intermediate depth and deep ocean where important water masses exist. At the depth of 500 to 1 000 m where the oxygen minimum zones (OMZs) exist, all ESMs show a maximum of globally-averaged error and RMSE, and a minimum of the spatial correlation coefficient. In the ocean interior, the reason for model biases is complicated, and both the meridional overturning circulation (MOC) and the particulate organic carbon flux contribute to the biases of dissolved oxygen distribution. Analysis results show the physical bias contributes more. Simulation bias of important water masses such as North Atlantic Deep Water (NADW), Antarctic Bottom Water (AABW) and North Pacific Intermediate Water (NPIW) indicated by distributions of MOCs greatly affects the distributions of oxygen in north Atlantic, Southern Ocean and north Pacific, respectively. Although the model simulations of oxygen differ greatly from each other in the ocean interior, the multi-model mean shows a better agreement with the observation.
Long duplication of 18S ribosomal DNA in Cynoglossus lineolatus (Pleuronectiformes: Cynoglossidae): novel molecular evidence for unequal crossing over model
GONG Li, SHI Wei, YANG Min, SI Lizhen, KONG Xiaoyu
2016, 35(12): 38-50. doi: 10.1007/s13131-016-0957-z
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Although 18S rDNA sequence is extremely conservative, the polymorphism still has been found in few species. In the present study, three types (Type A, B and C) of 18S rDNA sequence coexisted in Cynoglossus lineolatus genome, suggesting a non-concerted evolution process, rather than a strictly concerted evolution fashion. Based on the differences of sequence variation, GC content, secondary structure and minimum free energy, Types A and B were speculated as the potential pseudogenes. Additionally, a fascinating finding was a 189-bp duplication of 18S rDNA in Type A sequence. To our knowledge, this is the first report on such a long duplication in teleostean ribosomal DNA. Compared with several theories accounting for the formation of tandem repeats, the unequal crossing over model was thought to be the most likely mechanism to generate the 189-bp duplication of 18S rDNA. These results not only provide a novel molecular evidence for the unequal crossing over model, but also benefit for the further study on 18S rDNA in fishes.
Habitat suitability of Scapharca subcrenata (Lischke) in the shallow water of the Xiaoheishan Island
ZHOU Jian, SONG Jingjing, BAI Qianling, LIU Chengyue, ZHANG Zhipeng, TANG Haitian
2016, 35(12): 51-57. doi: 10.1007/s13131-016-0958-y
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The habitat suitability index (HSI) model was used to identify potential sites for sustainable restoration of ark shell, Scapharca subcrenata (Lischke), in the shallow water of Xiaoheishan Island, using a geographic information system framework. The seven input variables of the HSI model were sediment composition, water temperature, salinity, dissolved oxygen, water depth, pH, and ammonia. A non-linear suitability function for each variable factor was used to transform the value into a normalized quality index ranging from 0 (non-suitability) to 1 (best suitability). In present study, the analysis of habitat suitability was conducted for four seasons respectively. The majority of the study area has a high HSI value (>0.6) year round, which implies a strong suitability for restoration, with the optimal habitat located on the eastern side of the island. Correspondence analysis indicated that water temperature was the main factor causing seasonal variation, while sediment composition and water depth were the two major reasons for the differences in sites. The results of this work could provide support for restoration decision making through identification of potential sites for sustainable establishment of S. subcrenata.
Cold tolerance of subtropical Porites lutea from the northern South China Sea
CHEN Tianran, LI Shu, SHI Qi, CHEN Tegu
2016, 35(12): 58-64. doi: 10.1007/s13131-016-0940-8
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Marginal scleractinian corals growing at their latitudinal limits should be quite sensitive to variations in winter sea surface temperatures (SSTs). An extreme cold event occurring in early 2008 offered a unique opportunity to examine the effect of cold-water anomalies on Porites lutea corals and their physiological tolerance and acclimation in the subtropical northern South China Sea (NSCS). Besides in-situ observation, a subsequent aquarium-based experiment was designed for reproducing the chilling process and a 50-year-long Sr/Ca ratio profile from two P. lutea skeletal slabs was analyzed for reconstructed the historical annual minimum SSTs which ceased Porites calcification. The 2008 low-temperature anomaly caused the minimum daily mean SSTs dropped below 13℃ in the Daya Bay. The stress symptoms displayed by local P. lutea colonies included polyp retraction, reduced coloration and pale, but none showed tissue sloughing. The ability of P. lutea to survive implied its tolerance of extreme low temperatures. Here we suggest a model on the tolerance of high-latitude Porites under low-temperature stresses, which is when SSTs drop below 18℃, Porites corals contract their tentacles (losing heterotrophic capability), then cease calcification (reducing energy consumption), and meanwhile maintain relatively high levels of zooxanthellae density (sustaining host's life via photosynthetic capacity of symbiotic zooxanthellae). This study revealed remarkable acclimatization of P. lutea corals to low temperature extremes. This acclimatization is beneficial for Porites corals in the NSCS to expand their living ranges towards the higher-latitude areas and have the potential to be the incipient reef former.
A comparative study of spatial interpolation methods for determining fishery resources density in the Yellow Sea
CHEN Yunlong, SHAN Xiujuan, JIN Xianshi, YANG Tao, DAI Fangqun, YANG Dingtian
2016, 35(12): 65-72. doi: 10.1007/s13131-016-0966-y
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Spatial interpolation is a common tool used in the study of fishery ecology, especially for the construction of ecosystem models. To develop an appropriate interpolation method of determining fishery resources density in the Yellow Sea, we tested four frequently used methods, including inverse distance weighted interpolation (IDW), global polynomial interpolation (GPI), local polynomial interpolation (LPI) and ordinary kriging (OK). A cross-validation diagnostic was used to analyze the efficacy of interpolation, and a visual examination was conducted to evaluate the spatial performance of the different methods. The results showed that the original data were not normally distributed. A log transformation was then used to make the data fit a normal distribution. During four survey periods, an exponential model was shown to be the best semivariogram model in August and October 2014, while data from January and May 2015 exhibited the pure nugget effect. Using a paired-samples t test, no significant differences (P>0.05) between predicted and observed data were found in all four of the interpolation methods during the four survey periods. Results of the cross-validation diagnostic demonstrated that OK performed the best in August 2014, while IDW performed better during the other three survey periods. The GPI and LPI methods had relatively poor interpolation results compared to IDW and OK. With respect to the spatial distribution, OK was balanced and was not as disconnected as IDW nor as overly smooth as GPI and LPI, although OK still produced a few "bull's-eye" patterns in some areas. However, the degree of autocorrelation sometimes limits the application of OK. Thus, OK is highly recommended if data are spatially autocorrelated. With respect to feasibility and accuracy, we recommend IDW to be used as a routine interpolation method. IDW is more accurate than GPI and LPI and has a combination of desirable properties, such as easy accessibility and rapid processing.
Genome-wide transcriptional response of the Arctic bacterium Pseudoalteromonas sp. A2 to oxidative stress induced by hydrogen peroxide
LIN Xuezheng, WANG Zhen, LI Yang, LI Jiang
2016, 35(12): 73-80. doi: 10.1007/s13131-016-0892-z
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Oxidative stress is one of the major challenges faced by Arctic marine bacteria due to the high oxygen concentration of seawater, low temperatures and UV radiations. Transcriptome sequencing was performed to obtain the key functional genes involved in the adaptation to oxidative stress induced by hydrogen peroxide in the Arctic bacterium Pseudoalteromonas sp. A2. Exposure to 1 mmol/L H2O2 resulted in large alterations of the transcriptome profile, including significant up-regulation of 109 genes and significant down-regulation of 174 genes. COG functional classification revealed that among the significantly regulated genes with known function categories, more genes belonging to posttranslational modification, protein turnover and chaperones were significantly up-regulated, and more genes affiliated with chaperones and amino acid transport and metabolism were significantly down-regulated. It was notable that the expressions of eighteen genes affiliated with flagella and four genes affiliated with heat shock proteins were significantly up-regulated. Meanwhile, the expression of nine genes belonging to cytochrome and cytochrome oxidase, and five genes belonging to TonB-dependent receptor, were significantly down-regulated. Among the eighteen genes with antioxidant activity categorized by GO analysis, the expression of one gene was significantly up-regulated; however, the expressions of two genes were significantly down-regulated. Briefly, RNA-Seq indicated that, except for the classical anti-oxidative genes and stress proteins, genes affiliated with flagella and function unknown played important roles in coping with oxidative stress in Pseudoalteromonas sp. A2. This overall survey of transcriptome and oxidative stress-relevant genes can contribute to understand the adaptive mechanism of Arctic bacteria.
Latitudinal and interannual variations of the spring phytoplankton bloom peak in the East Asian marginal seas
CHEN Cheng, MAO Zhihua, HAN Guoqi, ZHU Qiankun, GONG Fang, WANG Tianyu
2016, 35(12): 81-88. doi: 10.1007/s13131-016-0867-0
Abstract:
Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas (17°-58°N, including the northern South China Sea (SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year (2003-2012) median timing of the annual Chlorophyll a concentration (Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of (21.20±2.86) km/d (decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period (the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.
Numerical investigation of solitary wave action on two rectangular boxes with a narrow gap
NING Dezhi, SU Xiaojie, ZHAO Ming
2016, 35(12): 89-99. doi: 10.1007/s13131-016-0967-x
Abstract:
Based on the time-domain higher-order boundary element method (HOBEM), a two-dimensional numerical wave flume is developed to investigate solitary wave interaction with two rectangular boxes with a narrow gap. In the numerical model, the fully nonlinear boundary conditions are satisfied on the free surface, the mixed Eulerian-Lagrangian method is adopted to track the transient water surface and the fourth-order Runga-Kutta method is used to predict the velocity potential and wave elevation on the free surface. The acceleration potential technique is used to compute the transient wave forces along the wetted object surface. A piston-type wavemaker is used to generate solitary waves. The proposed model is validated by comparing the simulated wave run-up and the wave loads with the published experimental and numerical results of the reflection of a solitary wave from a vertical wall. Then, numerical experiments are performed to study the effects of the narrow gap and the size of each box on the wave run-ups at the two sides of the two-box system and in the narrow gap between two boxes, and the wave loads on the two boxes. The interaction between double solitary waves with a time interval between them with a two-box system is also investigated.
Experimental study on the wave loads of twin-plate breakwater under oblique waves
GU Qian, HUANG Guoxing, ZHANG Ningchuan, LI Longxiang, SHAO Zhong'an
2016, 35(12): 100-109. doi: 10.1007/s13131-016-0925-7
Abstract:
In this study, systematic physical model tests were performed to investigate the wave forces on the twin-plate breakwater under irregular waves. Based on the experimental results, the effects of the relative plate width B/L, wave height Hs/D and incident angle θ0 on the wave forces were analyzed and discussed. The results showed s that:(1) The envelopes of the total wave pressure were generally symmetrical along the direction of plate width under the incident angles (θ0) being 0°, 15°, 30°, 45° and 60°. In particular, the envelopes of wave pressure at θ0=30° were larger than all other cases. (2) The synchronous pressure distribution of the breakwater under oblique wave action was more complicated comparing to the normal incident waves. (3) Based on data analysis, an empirical formula was obtained to estimate the total vertical force of the twin-plate breakwater. This empirical formula can be a good reference for the design basis of engineering applications under specified wave conditions.
Hurricane damage assessment for residential construction considering the non-stationarity in hurricane intensity and frequency
WANG Cao, LI Quanwang, PANG Long, ZOU Aming, ZHANG Long
2016, 35(12): 110-118. doi: 10.1007/s13131-016-0828-7
Abstract:
Natural hazards such as hurricanes may cause extensive economic losses and social disruption for civil structures and infrastructures in coastal areas, implying the importance of understanding the construction performance subjected to hurricanes and assessing the hurricane damages properly. The intensity and frequency of hurricanes have been reported to change with time due to the potential impact of climate change. In this paper, a probability-based model of hurricane damage assessment for coastal constructions is proposed taking into account the non-stationarity in hurricane intensity and frequency. The non-homogeneous Poisson process is employed to model the non-stationarity in hurricane occurrence while the non-stationarity in hurricane intensity is reflected by the time-variant statistical parameters (e.g., mean value and/or standard deviation), with which the mean value and variation of the cumulative hurricane damage are evaluated explicitly. The Miami-Dade County, Florida, USA, is chosen to illustrate the hurricane damage assessment method proposed in this paper. The role of non-stationarity in hurricane intensity and occurrence rate due to climate change in hurricane damage is investigated using some representative changing patterns of hurricane parameters.