Home  >  Query result

N2 fixation rate and diazotroph community structure in the western tropical North Pacific Ocean (WTNP)
Run Zhang, Dongsheng Zhang, Min Chen, Zhibing Jiang, Chunsheng Wang, Minfang Zheng, Yusheng Qiu, Jie Huang
In the present study, we report N2 fixation rate (15N isotope tracer assay) and the diazotroph community structure (using the molecular method) in the western tropical North Pacific Ocean (WTNP) (13–20°N, 120–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods. Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current (Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation. In surface waters, volumetric N2 fixation rate (calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged (1.2±0.5) nmol/(L·d), with <0 μm size fraction contributed predominantly (88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N2 fixation rate over the upper 200 m ranged between 150 μmol/(m2·d) and 480 μmol/(m2·d) (average (225±105) μmol/(m2·d). N2 fixation can account for 6.2%±3.7% of the depth-integrated primary production, suggesting that N2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations.
key words: western tropical North Pacific Ocean (WTNP), N2 fixation, 15N isotope tracer assay, unicellular diazotroph
Nitrogen uptake regime regulated by ice melting during austral summer in the Prydz Bay, Antarctica
Run Zhang, Qiang Ma, Min Chen, Minfang Zheng, Jianping Cao, Yusheng Qiu
doi: 10.1007/s13131-019-1434-2
Using a combination of stable isotope (15N) and radionuclide (226Ra) analyses, we examine possible controls on the interactions between melting ice and the uptake of nitrogen in the Prydz Bay during the 2006 austral summer. We find that specific rates of uptake for nitrate and ammonium correlate positively to their concentrations, thus suggesting a substrate effect. In the study area, we observe that regions along open, oceanic water have high f-ratios (nitrate uptake/nitrate+ammonium uptake), while areas near the Amery Ice Shelf have significantly low f-ratios. Further analysis reveals a negative correlation between the f-ratio and the melt water fraction, thus implying that the melting of ice plays an essential role in regulating pelagic N dynamics in the Southern Ocean (SO). Stratification, produced by melting ice, should profoundly affect the efficiency of the SO’s biological pump and consequently affect the concentration of CO2 in the atmosphere. Results presented in this study add information to an already significant base of understanding of the controls on pelagic C and N dynamics in the SO. This provides unique insights for either interpreting past changes in geologic records or for predicting future climate change trends.
key words: nitrogen uptake regime, ice melting, Prydz Bay, Antarctica
The difference analysis of physical-mechanical properties of sediments in the central South Yellow Sea and Zhe-Min coastal area in China
Yuanqin XU, Ping LI, Peiying LI, Jun DU, Lejun LIU, Wei GAO, Jie LIU
doi: 10.1007/s13131-017-1000-8
The difference analysis of physical-mechanical properties of muddy sediments is made in the central South Yellow Sea and the Zhe-Min (Zhejiang Province to Fujian Province of China) coastal area. The results show that sediments in the two regions are both dominated by mud. There are perfect negative power function correlations between the water content and the density, the compression coefficient and the compression modulus; a good positive power function correlation between the liquid limit and the plastic limit, a perfect positive linear correlation between the water content and the void ratio, and a perfect polynomial function correlation between the miniature vane shear strength and the pocket penetration resistance. In general, compared with sediments in the Zhe-Min coastal area, sediments in the central South Yellow Sea possess high water content, high void ratio, low density, high plasticity, high compressibility, low shear strength. The causes of the differences between physical-mechanical properties of sediments are analyzed from the topographic features, material sources, hydrodynamic conditions, deposition rate, and material composition. Compared with the Zhe-Min coastal area, the central South Yellow Sea is far from the Mainland and low-lying; has poor hydrodynamic condition; the materials diffused to the area are less and dominated by fine clay, have the high content of smectite and organic matters. These factors lead to sediments of the central South Yellow Sea has the higher water content, the higher plasticity, the lower density, and the lower strength than sediments in the Zhe-Min coastal area.
key words: sediment, Zhe-Min coastal area, central South Yellow Sea, physical-mechanical properties, difference analysis
Fast acclimation of phytoplankton assemblies to acute salinity stress in the Jiulong River Estuary
Gang Li
doi: 10.1007/s13131-019-1389-3
Mixing of freshwater and seawater creates the well-known salinity gradients along the estuaries. In order to investigate how phytoplankton respond to the acute salinity changes, we exposed natural phytoplankton assemblies from the Jiulong River Estuary to differential saline field water while continuously monitoring their photosynthetic performances under both indoor- and outdoor-growth conditions. When the natural cell assemblies from salinity 30 field water were exposed to series low saline field water (salinity 25, 17, 13 and 7.5), the effective Photosystem II quantum yield (ΔF/Fm′) decreased sharply, e.g., to one-fifth of its initials after 5 min exposure to salinity 7.5 field water, and then increased fast during the following 40 min and almost completely recovered after 320 min. During such an exposure process, non-photochemical quenching (NPQ) sharply increased from 0 to 0.85 within 5 min, and then decreased to nearly 0 within the following 70 min. When these cells re-acclimated to salinity 7.5 field water were exposed to series high saline field water (salinity 13, 17, 25 and 30), a similar response pattern was observed, with the decreased ΔF/Fm′ accompanied with increased NPQ, and followed by the recovery-induced increase in ΔF/Fm′ and decrease in NPQ. A similar response pattern as ΔF/Fm′ to the acute osmotic stress was also observed in the photosynthetic carbon fixation capacity according to radiocarbon (14C) incorporation. Our results indicate that estuarine phytoplankton assemblies could rapidly recover from the acute osmotic stress, implying a potential cause for their frequent blooms in coastal-estuarine waters where despite drastically varying salinity, available nutrients are abundant due to the land-derived runoffs or mixing-caused relaxations from sediments.
key words: PSII quantum yield, carbon fixation, salinity gradients, phytoplankton assemblies, Jiulong River Estuary
Substitution of His260 residue alters the thermostability of Pseudoalteromonas carrageenovora arylsulfatase
Yanbing Zhu, Xiaoqian Yin, Han Liu, Hebin Li, Yanhong Chen, Lijun Li, Anfeng Xiao, Hui Ni
doi: 10.1007/s13131-019-1356-z
This study aimed to improve the thermostability of arylsulfatase from Pseudoalteromonas carrageenovora. A library of P. carrageenovora arylsulfatase mutants was constructed by introducing random mutagenesis using error-prone PCR. After screening, two mutants of H260L and D84A/H260L showed enhanced thermal stability than the wild-type predecessor (WT). Site-directed mutagenesis demonstrated that only amino acid residue at Position 260 plays an important role in the thermostability of P. carrageenovora arylsulfatase. Thermal inactivation analysis showed that the half-life (t1/2) values at 55°C for H260L, H260I, H260Q, H260F and H260R were 40.6, 48.4, 30.9, 29.1 and 34.5 min, respectively, while that of WT was 9.1 min. Structure modeling demonstrated that the additional hydrogen bonds and/or optimization of surface charge-charge interactions could be responsible for the increased thermostability imparted by H260L, H260I, H260Q, H260F and H260R.
key words: arylsulfatase, Pseudoalteromonas carrageenovora, directed evolution, error-prone PCR, thermostability
Morphological studies of six free-living spirotrichean ciliates (Protozoa: Ciliophora) with three new records from the coastal South China Sea
Xumiao CHEN, Kuidong XU
doi: 10.1007/s13131-018-1304-3
The living morphology and infraciliature of six spirotrichous ciliates collected from the coastal South China Sea were investigated using live observation and protargol impregnation. These are Euplotes woodruffi Gaw, 1939, Hemigastrostyla enigmatica (Dragesco and Dragesco-Kernéis, 1986) Song and Wilbert, 1997, Neourostylopsis flavicana (Wang et al., 2011) Chen et al., 2013, Protogastrostyla pulchra (Perejaslawzewa, 1886) Gong et al., 2007, Pseudoamphisiella alveolata (Kahl, 1932) Song and Warren, 2000, and Pseudokahliella marina (Foissner et al., 1982) Berger et al., 1985. Among these, Protogastrostyla pulchra, Pseudoamphisiella alveolata and Pseudokahliella marina are reported from the South China Sea for the first time, which manifest obvious differences apart from other Chinese populations. As new contribution, the detailed description of isolates from mangrove habitat of E. woodruffi andH. enigmatica, and aquaculture pond isolate of N. flavicana, are present.
key words: South China Sea, new record, ciliates, Spirotrichea, taxonomy
The September 16, 2015 Mw 8.3 Illapel, Chile Earthquake: characteristics of tsunami wave from near-field to far-field
Zhiyuan REN, Ye YUAN, Peitao WANG, Tingting FAN, Juncheng WANG, Jingming HOU
doi: 10.1007/s13131-017-1005-3
On September 16, 2015, an earthquake with magnitude ofMw 8.3 occurred 46 km offshore from Illapel, Chile, generating a 4.4-m local tsunami measured at Coquimbo. In this study, the characteristics of tsunami are presented by a combination of analysis of observations and numerical simulation based on sources of USGS and NOAA. The records of 16 DART buoys in deep water, ten tidal gauges along coasts of near-field, and ten coastal gauges in the far-field are studied by applying Fourier analyses. The numerical simulation based on nonlinear shallow water equations and nested grids is carried out to provide overall tsunami propagation scenarios, and the results match well with the observations in deep water and but not well in coasts closed to the epicenter. Due to the short distance to the epicenter and the shelf resonance of southern Peru and Chile, the maximum amplitude ranged from 0.1 m to 2 m, except for Coquimbo. In deep water, the maximum amplitude of buoys decayed from 9.8 cm to 0.8 cm, suggesting a centimeter-scale Pacific-wide tsunami, while the governing period was 13–17 min and 32 min. Whereas in the far-field coastal region, the tsunami wave amplified to be around 0.2 m to 0.8 m, mostly as a result of run-up effect and resonance from coast reflection. Although the tsunami was relatively moderate in deep water, it still produced non-negligible tsunami hazards in local region and the coasts of far-field.
key words: 2015 Illapel earthquake, tsunami observation, numerical modeling, far-field, near-field
Wave prediction in a port using a fully nonlinear Boussinesq wave model
Young-Kwang Choi, Seung-Nam Seo, Jin-Yong Choi, Fengyan Shi, Kwang-Soon Park
doi: 10.1007/s13131-019-1456-2
A wave forecasting system using FUNWAVE-TVD which is based on the fully nonlinear Boussinesq equations by Chen (2006) was developed to provide an accurate wave prediction in the Port of Busan, South Korea. This system is linked to the Korea Operational Oceanographic System (KOOS) developed by Park et al. (2015). The computational domain covers a region of 9.6 km×7.0 km with a grid size of 2 m in both directions, which is sufficient to resolve short waves and dominant sea states. The total number of grid points exceeds 16 millions, making the model computational expensive. To provide real-time forecasting, an interpolation method, which is based on pre-calculated results of FUNWAVE-TVD and SWAN forecasting results at the FUNWAVE-TVD offshore boundary, was used. A total of 45 cases were pre-calculated, which took 71 days on 924 computational cores of a Linux cluster system. Wind wave generation and propagation from the deep water were computed using the SWAN in KOOS. SWAN results provided a boundary condition for the FUNWAVE-TVD forecasting system. To verify the model, wave observations were conducted at three locations inside the port in a time period of more than 7 months. A model/model comparison between FUNWAVE-TVD and SWAN was also carried out. It is found that, FUNWAVE-TVD improves the forecasting results significantly compared to SWAN which underestimates wave heights in sheltered areas due to incorrect physical mechanism of wave diffraction, as well as large wave heights caused by wave reflections inside the port.
key words: real-time wave forecasting, FUNWAVE-TVD, SWAN, KOOS, wave observations, wave diffraction
Impacts of changing scale on Getis-Ord Gi* hotspots of CPUE: a case study of the neon flying squid (Ommastrephes bartramii) in the northwest Pacific Ocean
Yongjiu FENG, Xinjun CHEN, Feng GAO, Yang LIU
doi: 10.1007/s13131-018-1212-6
We examined the scale impacts on spatial hot and cold spots of CPUE for Ommastrephes bartramii in the northwest Pacific Ocean. The original fishery data were tessellated to 18 spatial scales from 5′×5′ to 90′×90′ with a scale interval of 5′ to identify the local clusters. The changes in location, boundaries, and statistics regarding the Getis-Ord Gi* hot and cold spots in response to the spatial scales were analyzed in detail. Several statistics including Min, mean, Max, SD, CV, skewness, kurtosis, first quartile (Q1), median, third quartile (Q3), area and centroid were calculated for spatial hot and cold spots. Scaling impacts were examined for the selected statistics using linear, logarithmic, exponential, power law and polynomial functions. Clear scaling relations were identified for Max, SD and kurtosis for both hot and cold spots. For the remaining statistics, either a difference of scale impacts was found between the two clusters, or no clear scaling relation was identified. Spatial scales coarser than 30′ are not recommended to identify the local spatial patterns of fisheries because the boundary and locations of hot and cold spots at a coarser scale are significantly different from those at the original scale.
key words: Ommastrephes bartramii, scale impacts, local clusters, Getis-Ord Gi*, spatial hotspots
An evaluation of new satellite-derived latent and sensible heat fluxes with moored buoy data, OAFlux and NCEP2 reanalysis products
Lei ZHANG, Hanqing SHI
doi: 10.1007/s13131-017-1108-x
New satellite-derived latent and sensible heat fluxes are performed by using WindSat wind speed, WindSat sea surface temperature, the European Centre for Medium-range Weather Forecasting (ECMWF) air humidity, and ECMWF air temperature from 2004 to 2014. The 55 moored buoys are used to validate them by using the 30 min and 25 km collocation window. Furthermore, the objectively analyzed air-sea heat fluxes (OAFlux) products and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 2 (NCEP2) products are also used for global comparisons. The mean biases of sensible and latent heat fluxes between WindSat flux results and buoy flux data are –0.39 and –8.09 W/m2, respectively. In addition, the root-mean-square (RMS) errors of the sensible and latent heat fluxes between them are 5.53 and 24.69 W/m2, respectively. The RMS errors of sensible and latent heat fluxes are observed to gradually increase with an increasing buoy wind speed. The difference shows different characteristics with an increasing sea surface temperature, air humidity, and air temperature. The zonal average latent fluxes have some high regions which are mainly located in the trade wind zones where strong winds carry dry air in January, and the maximum value centers are found in the eastern waters of Japan and on the US east coast. Overall, the seasonal variability is pronounced in the Indian Ocean, the Pacific Ocean, and the Atlantic Ocean. The three sensible and latent heat fluxes have similar latitudinal dependencies; however, some differences are found in some local regions.
key words: latent and sensible heat fluxes, WindSat, ECMWF reanalysis data, OAFlux

Year of publication

Related authors

Related hot words