Institutional Repository of South China Sea Institute of Oceanology, CAS
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Community structure of coralline algae and its relationship with environment in Sanya reefs, China
No full textCoralline algae are an important functional group in coral reef ecosystems. Despite the importance of coralline algae, little is known about their abundance and community structure, especially within Sanya reefs. It was fundamental to study coralline algae species abundance and distribution, and evaluate the effects of environmental factors on the species composition and abundance in Sanya reefs. A total of 24 species in 10 genera were identified based on 11 sampling stations, with the family Corallinaceae being dominant within the study area. The 7 dominant species, which constituted 62.4% of the overall collection, were Amphiroa ephedraea (16.8%), Mesophyllum simulans (11.1%), Porolithon onkodes (9.8%), Neogoniolithon fosliei (7.5%), Mesophyllum mesomorphum (6.6%), Pneophyllum conicum (6.6%) and Hydrolithon boergesenii (4.0%). There was significant spatial variability in the species composition and abundance of coralline algae (ANOSIM: R = 0.356, P = 0.013). The correlation analysis between biotic and abiotic variables indicated that the turbidity had a negative effect and salinity had a positive correlation on the pattern of coralline algae assemblages (global = 0.486, BIOENV analysis). The living cover of coralline algae was greater in deep water than in shallow water at the same sites. This suggests that physical disturbance, either natural or anthropogenic, is more important in regulating the coralline algae community structure in Sanya reefs
Influence on phytoplankton of different developmental stages of mesoscale eddies off eastern Australia
No full textThe influence of oceanic mesoscale eddies on their internal phytoplankton levels varies at different developmental stages. Based on 12 years of satellite ocean color observations, we investigated the variability of phytoplankton inside 4564 anticyclonic eddies and 3675 cyclonic eddies off eastern Australia in different development stages using the method of composited average analysis. The results indicated that the lowest level of chlorophyll was observed in the forth (decay) development stage for anticyclonic eddies, which was associated with the warmest SST, largest eddies amplitude, rotation speeds, angular velocities and surface water convergence. It is indicated that downwelling induced by anticyclonic eddies dominates the chlorophyll variations. Because the convergence induced by the ageostrophic velocity components occurred throughout the eddy's development stage, relaxation of the density perturbations (upwelling) associated with eddy decay was not observed in this study. Chlorophyll concentration near the center of cyclonic eddies decreased from the first to the middle stage, and then increased to the largest levels at the last stage. Although vertical motions induced by the ageostrophic velocity components varied from divergence to convergence during the development of an eddy, a higher eddy-ambient water exchange occurred and dominated the increases in total divergence and chlorophyll concentration in the last stage
Strengthened Indonesian Throughflow Drives Decadal Warming in the Southern Indian Ocean
No full textRemarkable warming of the Southern Indian Ocean during the recent two decades is assessed using a heat budget analysis based on the Estimating the Circulation and Climate of the Ocean version 4 release 3 model results. The annual mean temperature averaged in the upper-700m Southern Indian Ocean during 1998-2015 has experienced significant warming at a rate of 1.03x10(-2)degrees C/year. A heat budget analysis indicates that the increase is mostly driven by decreased cooling from net air-sea heat flux and increased warming from heat advection. Increased Indonesian Throughflow advection is the largest contributor to warming the upper 700m of the Southern Indian Ocean, while the reduction of surface turbulent heat flux is of secondary importance. These results expand our understanding of the decadal heat balance in the Indian Ocean and of Indo-Pacific decadal climate variability. Plain Language Summary This study identified the important role of the strengthened Indonesian Throughflow volume and heat transports during the global surface warming hiatus period in warming up the Southern Indian Ocean in the past two decades. Roles of other processes, such as air-sea heat fluxes, cross-equatorial cells, and the Agulhas Current, have also been quantified using the model. It appears that the heat transport anomaly is the dominant factor that drives the Southern Indian Ocean warming. Quantifying the decadal ocean heat balance is important to understand the redistribution of the anthropogenic heat uptake in the oceans. The results are useful in assessing coupled model performance in simulating climate change impacts on the global oceans. The study may have broad implications in the climate change research field, as well as the study of broad-scale oceanography, ocean circulation, and the Indonesian Throughflow
Detecting the transport barriers in the Pearl River estuary, Southern China with the aid of Lagrangian coherent structures
No full textKnowledge of horizontal transport pathways is important for the protection of the marine ecosystem in coastal areas. In this paper, we develop a 3D model to simulate hydrodynamics and particle transport in the Pearl River Estuary (PRE), Southern China, to study the barriers to transport in the PRE. Specifically, we use the flow velocity produced by the model to locate Lagrangian coherent structures (LCSs) hidden in ocean surface currents. Our findings show that a remarkable LCS begins upstream near the Humen inlet, extends to the Wanshan Islands via Neilingding Island, and can act as a transport barrier in the estuary. This LCS appeared 1-2 h after high tide and was persistent for 6-7 h during every ebb tide. Particles released on the west side of the LCS moved downstream, exited the estuary by Daxi Channel, and seldom spread to the east side, especially the Hong Kong Sea area. An analysis of several scenarios suggested that the formation of this LCS was due to topography restrictions and tidal forces. (C) 2018 Elsevier Ltd. All rights reserved
Interannual Variability of Eddy Kinetic Energy in the Subtropical Southeast Indian Ocean Associated With the El Nino-Southern Oscillation
No full textInterannual variability of eddy kinetic energy (EKE) in the subtropical southeast Indian Ocean (SEIO) is investigated using satellite observations in three regions in the 20 degrees S-35 degrees S latitude band: R1 (108 degrees E-115 degrees E), R2 (100 degrees E-108 degrees E), and R3 (60 degrees E-100 degrees E). The El Nino-Southern Oscillation (ENSO) plays an important role in modulating the interannual variability of EKE in the SEIO. EKE in the three regions shows negative correlations with the Nino3.4, lagging Nino3.4 by 2, 14, and 22 months, respectively. In R1, the ENSO modulates the interannual variability of EKE through influencing baroclinic instability of meridional velocity shear between the upper poleward Leeuwin Current (LC) and the underlying equatorward Leeuwin Undercurrent (LUC). During La Nina (El Nino) year, both the poleward LC and equatorward LUC strengthened (weakened) due to the high (low) sea level anomaly (SLA) propagating from the Pacific Ocean as Rossby wave under geostrophic equilibrium, and baroclinic instability of vertical shear enhanced (slackened), further induced the strong (weak) EKE in the eastern boundary. In R2, the ENSO modulates the interannual variability of EKE through influencing baroclinic instability of zonal velocity shear between the central and southern branches of the upper eastward South Indian Countercurrent (SICC) and the lower extending westward South Equatorial Current (SEC). In R3, both the ENSO and the Southern Annual Mode modulate the interannual variability of EKE through influencing baroclinic instability of zonal velocity shear between the SICC and SEC. The interannual variability of EKE in the interior SEIO could be influenced by westward propagation of EKE originated from eastern boundary
Impacts of Insufficient Observations on the Monitoring of Short- and Long-Term Suspended Solids Variations in Highly Dynamic Waters, and Implications for an Optimal Observation Strategy
No full textCoastal water regions represent some of the most fragile ecosystems, exposed to both climate change and human activities. While remote sensing provides unprecedented amounts of data for water quality monitoring on regional to global scales, the performance of satellite observations is frequently impeded by revisiting intervals and unfavorable conditions, such as cloud coverage and sun glint. Therefore, it is crucial to evaluate the impacts of varied sampling strategies (time and frequency) and insufficient observations on the monitoring of short-term and long-term tendencies of water quality parameters, such as suspended solids (SS), in highly dynamic coastal waters. Taking advantage of the first high-frequency in situ SS dataset (at 30 min sampling intervals from 2007 to 2008), collected in Deep Bay, China, this paper presents a quantitative analysis of the influences of sampling strategies on the monitoring of SS, in terms of sampling frequency and time of day. Dramatic variations of SS were observed, with standard deviation coefficients of 48.9% and 54.1%, at two fixed stations; in addition, significant uncertainties were revealed, with the average absolute percent difference of approximately 13%, related to sampling frequency and time, using nonlinear optimization and random simulation methods. For a sampling frequency of less than two observations per day, the relative error of SS was higher than 50%, and stabilized at approximately 10%, when at least four or five samplings were conducted per day. The optimal recommended sampling times for SS were at around 9:00, 12:00, 14:00, and 16:00 in Deep Bay. The pseudo MODIS SS dataset was obtained from high-frequency in situ SS measurements at 10:30 and 14:00, masked by the temporal gap distribution of MODIS coverage to avoid uncertainties propagated from atmospheric correction and SS models. Noteworthy uncertainties of daily observations from the Terra/Aqua MODIS were found, with mean relative errors of 19.2% and 17.8%, respectively, whereas at the monthly level, the mean relative error of Terra/Aqua MODIS observations was approximately 10.7% (standard deviation of 8.4%). Sensitivity analysis between MODIS coverage and SS relative errors indicated that temporal coverage (the percentage of valid MODIS observations for a month) of more than 70% is required to obtain high-precision SS measurements at a 5% error level. Furthermore, approximately 20% of relative errors were found with the coverage of 30%, which was the average coverage of satellite observations over global coastal waters. These results highlight the need for high-frequency measurements of geostationary satellites like GOCI and multi-source ocean color sensors to capture the dynamic process of coastal waters in both the short and long term
Modulation of Tropical Cyclogenesis Location and Frequency over the Indo-Western North Pacific by the Intraseasonal Indo-Western Pacific Convection Oscillation during the Boreal Extended Summer
No full textThe influence of the intraseasonal Indo-western Pacific convection oscillation (IPCO) on tropical cyclone (TC) genesis location and frequency over the Indo-western North Pacific (WNP) during the boreal extended summer (May-October) is explored. Observational analysis shows that the impacts of the intraseasonal IPCO on TCs over the Indo-WNP include an evident "phase lock of TC genesis location'' and distinct differences in TC frequency. In the WNP, in the positive intraseasonal IPCO phase, the atmosphere gains heat through the release of latent heat in cumulus convective condensation, and the anomalous cyclonic circulation weakens the western Pacific subtropical high (WPSH) and enhances TC genesis, thereby tending to produce many more TCs. Moreover, the diminished WPSH and the westward shift of the centers of anomalous cyclonic circulations lock TC genesis locations to the west WNP and lower latitudes (around 5 degrees-20 degrees N), especially in the South China Sea. The almost opposite situation occurs in a negative phase. In the north Indian Ocean, the total TC genesis frequencies in the two intraseasonal IPCO phases are approximate. However, in the positive intraseasonal IPCO phase, the environmental conditions to the north of 13 degrees N are similar to those in the WNP except without the WPSH control, whereas south of 13 degrees N the situation is reversed, leading to a northward shift of the TC genesis location (around 13 degrees-20 degrees N). The negative phase reflects an opposite situation
A three-dimensional modeling study on eddy-mean flow interaction between a Gaussian-type anticyclonic eddy and Kuroshio
No full textThe Princeton ocean model is employed to study the energy balance of a fast-moving anticyclonic eddy (AE) during eddy-mean flow interaction. The AE is initialized with an axisymmetric Gaussian-type temperature profile and is placed to the east of the Philippine Islands. An energy analysis suggests that the advection term, pressure work and friction term play dominant roles in the initial eddy decay. During the strong interaction stage, barotropic instability (BTI) becomes the main force for the eddy kinetic energy (EKE) production, with the largest positive BTI in the interaction zone, which means that the eddy always obtains kinetic energy from the Kuroshio during this stage. Most of the EKE dissipation, the large conversion from the eddy available potential energy to the EKE and that from the mean kinetic energy to the EKE all occur at the upper layer during the strong interaction stage. When the AE interacts with the mean flow on the eastern side of the Kuroshio, whether the AE gains kinetic energy from the Kuroshio or loses kinetic energy to the Kuroshio is mainly determined by its shape in the interaction zone
Wind and wave dataset for Matara, Sri Lanka
No full textWe present a continuous in situ hydro-meteorology observational dataset from a set of instruments first deployed in December 2012 in the south of Sri Lanka, facing toward the north Indian Ocean. In these waters, simultaneous records of wind and wave data are sparse due to difficulties in deploying measurement instruments, although the area hosts one of the busiest shipping lanes in the world. This study describes the survey, deployment, and measurements of wind and waves, with the aim of offering future users of the dataset the most comprehensive and as much information as possible. This dataset advances our understanding of the nearshore hydrodynamic processes and wave climate, including sea waves and swells, in the north Indian Ocean. Moreover, it is a valuable resource for ocean model parameterization and validation. The archived dataset (Table 1) is examined in detail, including wave data at two locations with water depths of 20 and 10 m comprising synchronous time series of wind, ocean astronomical tide, air pressure, etc. In addition, we use these wave observations to evaluate the ERA-Interim reanalysis product. Based on Buoy 2 data, the swells are the main component of waves year-round, although monsoons can markedly alter the proportion between swell and wind sea. The dataset (Luo et al., 2017) is publicly available from Science Data Bank (https://doi.org/10.11922/sciencedb.447)
Offshore Fault Geometrics in the Pearl River Estuary, Southeastern China: Evidence from Seismic Reflection Data
No full textThe Pearl River Estuary (PRE) is located at the onshore-offshore transition zone between South China and South China Sea Basin, and it is of great significant value in discussing tectonic relationships between South China block and South China Sea block and seismic activities along the offshore active faults in PRE. However, the researches on geometric characteristics of offshore faults in this area are extremely lacking. To investigate the offshore fault distribution and their geometric features in the PRE in greater detail, we acquired thirteen seismic reflection profiles in 2015. Combining the analysis of the seismic reflection and free-air gravity anomaly data, this paper revealed the location, continuity, and geometry of the littoral fault zone and other offshore faults in PRE. The littoral fault zone is composed of the major Dangan Islands fault and several parallel, high-angle, normal faults, which mainly trend northeast to northeast-to-east and dip to the southeast with large displacements. The fault zone is divided into three different segments by the northwest-trending faults. Moreover, the basement depth around Dangan Islands is very shallow, while it suddenly increases along the islands westward and southward. These has resulted in the islands and neighboring areas becoming the places where the stress accumulates easily. The seismogenic pattern of this area is closely related to the comprehensive effect of intersecting faults together with the low velocity layer