Protoraphis Simonsen, a newly recorded marine epizoic diatom genus for China Abstract Epizoic diatoms on marine copepods are common in nature and may have a special ecological relationship with their hosts. However, this special ecological group is not well known, and it has only rarely been studied in the China seas. To address this knowledge gap, the species diversity and classification of epizoic diatoms on planktonic copepods were studied with samples collected from the East China Sea. In the present study, a marine araphid diatom genus Protoraphis and its type species, Pr. hustedtiana, were observed and identified by light and electron microscopy, thus representing the first record of this genus and its type species in China. This genus is characterized by a median sternum strongly bent to opposite sides and terminate in two transapical grooves at the valve ends. Protoraphis hustedtiana was found to be epizoic on the posterior body appendages and segments of the marine calanoid copepod Candacia bradyi. An internal view shows a complex, ear-shaped process that is close to the apical slit field. The ecological habitats and geographical distributions of Protoraphis were also discussed, and, together with complementary morphological studies, our results have increased the number of records for marine epizoic diatoms to three genera with three species in China, including Pseudohimantidium and Pseudofalcula.

Connectivity of fish assemblages along the mangrove-seagrass-coral reef continuum in Wenchang, China Abstract Understanding the connectivity of fish among different typical habitats is important for conducting ecosystem-based management, particularly when designing marine protected areas (MPA) or setting MPA networks. To clarify of connectivity among mangrove, seagrass beds, and coral reef habitats in Wenchang, Hainan Province, China, the fish community structure was studied in wet and dry seasons of 2018. Gill nets were placed across the three habitat types, and the number of species, individuals, and body size of individual fish were recorded. In total, 3 815 individuals belonging to 154 species of 57 families were collected. The highest number of individuals and species was documented in mangroves (117 species, 2 623 individuals), followed by coral reefs (61 species, 438 individuals) and seagrass beds (46 species, 754 individuals). The similarity tests revealed highly significant differences among the three habitats. Approximately 23.4% species used two habitats and 11.0% species used three habitats. A significant difference (p<0.05) in habitat use among eight species (Mugil cephalus, Gerres oblongus, Siganus fuscescens, Terapon jarbua, Sillago maculata, Upeneus tragula, Lutjanus russellii, and Monacanthus chinensis) was detected, with a clear ontogenetic shift in habitat use from mangrove or seagrass beds to coral reefs. The similarity indices suggested that fish assemblages can be divided into three large groups namely coral, seagrass, and mangrove habitat types. This study demonstrated that connectivity exists between mangrove-seagrass-coral reef continuum in Wenchang area; therefore, we recommend that fish connectivity should be considered when designing MPAs or MPA network where possible.

Bedrock samples from the Chukchi Borderland, Arctic Ocean—First Chinese dredge in the polar regions

China-France Oceanography Satellite (CFOSAT) simultaneously observes the typhoon-induced wind and wave fields

Upwelling off the west coast of Hainan Island: sensitivity to wave-mixing Abstract The coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system is employed to investigate the role of wave-mixing playing in the upwelling off the west coast of Hainan Island (WHU). Waves, tides and sea surface temperature (SST) are reproduced reasonably well by the model when validated by observations. Model results suggest the WHU is tidally driven. Further investigations indicate that inclusion of wave-mixing promotes the intensity of the WHU, making the simulated SST become more consistent with remote-sensed ones. Dynamically, wave-mixing facilitates the “outcrop” of more upwelled cold water, triggering stronger WHU and leading to a three-dimensional dynamical adjustment. From the perspective of time, wave-mixing contributes to establishing an earlier tidal mixing front strong enough to generate WHU and that is, WHU may occur earlier when taking wave-mixing into consideration.

Sea level anomalies in the northwestern Pacific during 2011 associated with La Niña and negative Indian Ocean Dipole Abstract The sea level anomalies (SLAs) pattern in the northwestern Pacific delineated significant differences between La Niña events occurring with and without negative Indian Ocean Dipole (IOD) events. During the pure La Niña events, positive the sea surface level anomalies (SLAs) appear in the northwestern Pacific, but SLAs are weakened and negative SLAs appear in the northwestern Pacific under the contribution of the negative IOD events in 2010/2011. The negative IOD events can trigger significant westerly wind anomalies in the western tropical Pacific, which lead to the breakdown of the pronounced positive SLAs in the northwestern Pacific. Meanwhile, negative SLAs excited by the positive wind stress curl near the dateline propagated westward in the form of Rossby waves until it approached the western Pacific boundary in mid-2011, which maintained and enhanced the negative phase of SLAs in the northwestern Pacific and eventually, it could significantly influence the bifurcation and transport of the North Equatorial Current (NEC).

The impact of rain to observed signal from Chinese Gaofen-3 synthetic aperture radar in typhoons Abstract Gaofen-3 (GF-3), a Chinese civil synthetic aperture radar (SAR) at C-band, has operated since August 2016. Remarkably, several typhoons have been captured by GF-3 around the China Seas over its last two-year mission. In this study, six images acquired in Global Observation (GLO) and Wide ScanSAR (WSC) modes at vertical-vertical (VV) polarization channel are discussed. This work focuses on investigating the observation of rainfall using GF-3 SAR. These images were collocated with winds from the European Centre for Medium-Range Weather Forecasts (ECMWF), significant wave height simulated from the WAVEWATCH-III (WW3) model, sea surface currents from climate forecast system version 2 (CFSv2) of the National Centers for Environmental Prediction (NCEP) and rain rate data from the Tropical Rainfall Measuring Mission (TRMM) satellite. Sea surface roughness, was compared with the normalized radar cross section (NRCS) from SAR observations, and indicated a 0.8 correlation (COR). We analyzed the dependences of the difference between model-simulated NRCS and SAR-measured NRCS on the TRMM rain rate and WW3-simulated significant wave height. It was found that the effects of rain on SAR damps the radar signal at incidence angles ranging from 15° to 30°, while it enhances the radar signal at incidence angles ranging from 30° to 45° and incidence angles smaller than 10°. This behavior is consistent with previous studies and an algorithm for rain rate retrieval is anticipated for GF-3 SAR.

A numerical study on salinity stratification at the Oujiang River Estuary, China Abstract The Oujiang River Estuary (ORE) is a macrotidal estuary with drastic variation of river discharge and large tidal range. Numerical simulations based on the unstructured grid, Finite-Volume, primitive equation Community Ocean Model (FVCOM) are conducted to investigate the intratidal and intertidal variations of salinity with an extremely upstream river boundary and large computational domain. The dynamic equation of potential energy anomaly is adopted to evaluate the stratification and mixing processes from model results. Meanwhile, the stability of estuarine stratification on different timescales and its spatial variation are studied using estuarine Richardson number and stratification parameter. The critical values of tidal range and river discharge that determine the stratification state are obtained. The critical values exhibit distinct spatial difference. The north branch of the ORE exhibits well-mixed conditions when the tidal range exceeds 3.8, 4.0 and 4.6 m at upper inlet, middle segment and the river mouth, respectively. When river discharge is below 280 m3/s or exceeds 510 m3/s, the upper part of the north branch is well-mixed sustainably. Near the river mouth, river discharge of 280 m3/s is a rough critical value that separates well-mixed and stratified states. It is also concluded that periodic stratification exists in the North Channel. The lower estuary appears to be partially stratified at early ebb or early flood tide, and well-mixed in other tidal stages. The stratification only develops during early ebb in the upper segment. The enhancement of stratification is mainly caused by longitudinal advection and lateral velocity shear, while turbulent mixing and longitudinal tidal strain are the main factors of stratification attenuation.

Acoustic sound speed profile inversion based on orthogonal matching pursuit Abstract The estimation of ocean sound speed profiles (SSPs) requires the inversion of an acoustic field using limited observations. Such inverse problems are underdetermined, and require regularization to ensure physically realistic solutions. The empirical orthonormal function (EOF) is capable of a very large compression of the data set. In this paper, the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion, and the pressure is expanded in a sparse domain using EOFs. Since the parameters of the inverse model are sparse, compressive sensing (CS) can help solve such underdetermined problems accurately, efficiently, and with enhanced resolution. Here, the orthogonal matching pursuit (OMP) is used to estimate range-independent acoustic SSPs using the simulated acoustic field. The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment. By shortening the duration of the training set, the temporal correlation between EOF and test sets is enhanced, and the accuracy of sound velocity inversion is improved. The SSP estimation error versus depth is calculated, and the 99% confidence interval of error is within ±0.6 m/s. The 82% of mean absolute error (MAE) is less than 1 m/s. It is shown that SSPs can be well estimated using OMP.

Bimodality and growth of the spectra of typhoon-generated waves in northern South China Sea Abstract Buoy-based observations of wave spectra during the passage of three typhoons in the northern South China Sea are examined. Though most spectra of mature typhoon-generated waves are unimodal, double-peaked spectra account for a significant proportion during the growing and decaying stages. This is due either to the superposition of swells on local wind waves or to the mechanism of nonlinear interaction between different wave components. The growth rate of energy density is an effective way to predict spectrum variation. The dominant wave direction depends on the location of the typhoon center to the site, but the direction spread shows no regularity in distant regions. In this study, a new six-parameter spectral formula is proposed to represent double-peaked spectra and is shown to provide a better fit than previous models. The theoretical relationship between shape parameter and spectral width is still applicable to each peak. The characteristics of the variations of spectral parameters are analyzed. It is demonstrated that the spectral parameters are not only related to the typhoon intensity and typhoon track, but also have strong intercorrelations. Moreover, the growth relation between significant wave height and significant wave period is obtained to fit the typhoon-generated waves.