Sinking Rate and Community Structures of Autumn Phytoplankton Responses to Mesoscale Physical Processes in the Western South China Sea

To examine the influence of mesoscale eddy on the natural phytoplankton community and its sinking rate changes, a comprehensive investigation cruise was carried out in the western South China Sea in autumn 2016. A total of 108 phytoplankton species were found, which belong to 54 phytoplankton genera; most of them were dominated by Dinophyta (54 genera), followed by Bacillariophyta (50 genera), Cyanophyta (3 genera), and Chrysophyta (1 genus). Bacillariophyta and Dinophyta were the main phytoplankton communities in the investigated sea area. The sinking rate of phytoplankton ranged from 0.12 to 3.17 m day–1, determined by the SETCOL method. The highest phytoplankton sinking rate was found in the 200-m water layer, followed by the DCM layer. No significant correlation was found between phytoplankton sinking rates and most of the environmental parameters during this cruise. At a similar time, we have carried out the estimation of carbon flux in the investigated sea area by using the sinking rate of phytoplankton, which showed that the carbon flux ranged from 2.41 × 10–6 to 0.006 mg C m–2 day–1; in addition, the maximum was at the 200-m layer. Phytoplankton community and sinking rate were significantly affected by the mesoscale eddy processes. The cold eddy could affect the community distribution of diatom and dinoflagellate, and the upwelling mainly affects the community of dinoflagellate. Both of them could contribute to a higher sedimentation rate of phytoplankton in the surface and DCM layers. Warm eddy could reduce the abundance of phytoplankton in the surface layer; simultaneously, the sinking rate of phytoplankton in the shallow water layer above 100 m is also reduced. These results can fill in the knowledge gap of mesoscale eddy processes in the study of phytoplankton community change and sinking rate; furthermore, it can provide insights into phytoplankton carbon and its implementation in further carbon sink.

The Development and Field Applications of Ultra-Deepwater Structural Conductor Jetting in Western South China Sea

Lingshui X-1 block is located in ultra-deepwater region in western South China Sea. Drilling in this area are encountering many technical problems, such as low temperature, poor lithology in shallow formation, low fracture pressure gradient, gas hydrate and shallow geological hazards, which bring great technical challenges to subsea wellhead stability (Yang et al., 2013). In order to ensure wellhead stability and improve top-hole operation efficiency, jetting technology was used for spud-in. First of all, carrying capacity curve of structural conductor was obtained from mechanics analysis of shallow seabed soil in Lingshui X-1 block. Secondly, structural conductor size selection and load analysis were carried out to determine safe setting depth of structural conductor in Lingshui X-1 block. Finally, bit stick-out, bit size selection, Weight on Bit (WOB) and pump rate were optimized on the basis of comprehensive analysis of ultra-deepwater under top-hole jetting technology and BHA characteristics. Well LSX-1-1 was taken as an example to illustrate field operation for top-hole jetting. This successful case of top-hole jetting technology in Lingshui X-1 block of western South China Sea could provide technical guidance for future drilling activity in similar ultra-deepwater wells.

Summer Phytoplankton Blooms Induced by Upwelling in the Western South China Sea

During summer, phytoplankton blooms occur frequently off the southeast Vietnam coast in the western South China Sea (WSCS). Using multi-source remote sensing data, such as sea surface temperature (SST), sea surface wind (SSW), aerosol optical thickness (AOT), sea level anomalies (SLA), and chlorophyll-a (Chl-a) data from 1998 to 2020 and in situ observations of analyzed data, we report the patterns of spatial variation of summer phytoplankton blooms in this region. The partial correlation and multiple stepwise linear regression analyses reveal that Ekman transport (ET) and Ekman pumping velocity (EPV) exert a greater impact on the summer phytoplankton blooms than the other environmental factors, suggesting that the phytoplankton blooms in the region may be mainly triggered by the enhanced nutrients by wind-induced upwelling and vertical mixing. AOT only weakly correlates with Chl-a concentration in the region, probably these prominent abundant nutrients in the region come from upwelling and convective-overturn. A northeastward jet causes the distribution of high Chl-a in the WSCS to be plume-shaped. A new finding in this study is that the northward current in this area may cause the northward deviation of phytoplankton blooms from the areas of upwelling.

Macrobenthos diversity along the Exclusive Economic Zone of East Coast Peninsular Malaysia

Aim: To examine the standing stock of macrobenthos along a depth gradient at regional scales in the Sunda Shelf of Malaysian Economic Exclusive Zone (EEZ). Methodology: Macrobenthos was sampled with a Smith–McIntyre grab at 19 stations on the continental shelf of the South-western South China Sea (east coast of Peninsular Malaysia) within the EEZ and was carried out onboard MV SEAFDEC II in May/June 2016. Results: The faunal composition, abundance, and diversity of species, together with environmental parameters were studied. A total of 10,232 individuals comprising 105 families were identified. The dominant macrobenthic group was Mollusca (55.25%), followed by Annelida (26.80%) and Arthropoda (15.36%), while the Echinodermata and Miscellaneous group recorded 1.13% and 1.43% respectively. Based on Bray-Curtis species similarities, five different sample groups (SGs) were distinguished, which were located in different zones and gradients of EEZ. Interpretation: Variations in the macrobenthic community is significantly associated with depth, temperature, and salinity. Further research should be conducted on other factors that contribute to the diversity of macrobenthos along the east coast of Peninsular Malaysia’s EEZ.

A checklist of spiders from Yongxing Island, South China Sea, with taxonomic notes on four species of goblin spiders

Yongxing Island (about 1.85 km2) is the largest island of the Xisha Islands. It is located in the Western South China Sea and belongs to the tropical ocean monsoon climate zone. Yongxing Island is quite rich in biological resources, for example, plants and birds which have been well documented. However, there are limited reports on spider resources in Yongxing Island. A preliminary checklist of spiders of the Yongxing Island is provided, based on a short-term study undertaken in January 2008. A total of 23 species, belonging to 21 genera and 11 families, were recorded from the area, which forms baseline information of spiders of the Yongxing Island. Amongst these, Oonopidae, Pholcidae, Araneidae and Salticidae were found to have more species in the area. Brignolia parumpunctata (Simon, 1893), Opopaea apicalis (Simon, 1893), Opopaea deserticola Simon, 1891 and Xyphinus baehrae Kranz-Baltensperger, 2014 were firstly reported from China, for which we provide taxonomic description in this paper.

Phytoplankton Community in the Western South China Sea in Winter and Summer

Phytoplankton are known as important harbingers of climate change in aquatic ecosystems. Here, the influence of the oceanographic settings on the phytoplankton community structure in the western South China Sea (SCS) was investigated during two seasons, i.e., the winter (December 2006) and summer (August–September, 2007). The phytoplankton community was mainly composed of diatoms (192 taxa), dinoflagellates (109 taxa), and cyanobacteria (4 taxa). The chain-forming diatoms and cyanobacteria Trichodesmium were the dominants throughout the study period. The phytoplankton community structure displayed distinct variation between two seasons, shifting from a diatom-dominated regime in winter to a cyanobacteria-dominated system in summer. The increased abundance of overall phytoplankton and cyanobacteria in the water column during the summer signifies the impact of nutrient advection due to upwelling and enriched eddy activity. That the symbiotic cyanobacteria–diatom (Rhizosolenia–Richelia) association was abundant during the winter signifies the influence of cool temperature. On the contrary, Trichodesmium dominance during the summer implies its tolerance to increased temperature. Overall, the two seasonal variations within the local phytoplankton community in the western SCS could simulate their community shift over the forthcoming climatic conditions.