Institutional Repository of South China Sea Institute of Oceanology, CAS
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Comparison of Satellite-Derived Phytoplankton Size Classes Using In-Situ Measurements in the South China Sea
No full textOcean colour remote sensing is used as a tool to detect phytoplankton size classes (PSCs). In this study, the Medium Resolution Imaging Spectrometer (MERIS), Moderate Resolution Imaging Spectroradiometer (MODIS), and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) phytoplankton size classes (PSCs) products were compared with in-situ High Performance Liquid Chromatography (HPLC) data for the South China Sea (SCS), collected from August 2006 to September 2011. Four algorithms were evaluated to determine their ability to detect three phytoplankton size classes. Chlorophyll-a (Chl-a) and absorption spectra of phytoplankton (aph(A)) were also measured to help understand PSC's algorithm performance. Results show that the three abundance-based approaches performed better than the inherent optical property (IOP)-based approach in the SCS. The size detection of microplankton and picoplankton was generally better than that of nanoplankton. A three-component model was recommended to produce maps of surface PSCs in the SCS. For the IOP-based approach, satellite retrievals of inherent optical properties and the PSCs algorithm both have impacts on inversion accuracy. However, for abundance-based approaches, the selection of the PSCs algorithm seems to be more critical, owing to low uncertainty in satellite Chl-a input dat
Salinification in the South China Sea Since Late 2012: A Reversal of the Freshening Since the 1990s
No full textSalinification has occurred in the South China Sea from late 2012 to the present, as shown by satellite Aquarius/Soil Moisture Active Passive data and Argo float data. This salinification follows a 20year freshening trend that started in 1993. The salinification signal is strongest near the surface and extends downward under the seasonal thermocline to a depth of 150m. The salinification occurs when the phase of the Pacific Decadal Oscillation switches from negative to positive. Diagnosis of the salinity budget suggests that an increasing net surface freshwater loss and the horizontal salt advection through the Luzon Strait driven by the South China Sea throughflow contributed to this ongoing salinification. In particular, a decrease in precipitation and enhanced Luzon Strait transport dominated the current intense salinification. Of particular interest is whether this salinification will continue until it reaches the previous maximum recorded in 1992. Plain Language Summary A significant salinification is taking place in the South China Sea starting from late 2012 to the present, as seen in satellite and Argo float data. The temperature, in contrast, exhibits no significant change. The salinification is mainly associated with switches in the Pacific Decadal Oscillation from negative to positive phase from late 2012 to the present. A decrease in precipitation and enhanced Luzon Strait transport dominated the current intense salinification. After a freshening period that lasted 20years, we are particularly interested in whether the salinification will continue in the future
The 30-50-Day Intraseasonal Oscillation of SST and Precipitation in the South Tropical Indian Ocean
No full textThe Sea Surface Temperature (SST) in the South Tropical Indian Ocean (STIO) displays significant intraseasonal oscillation (ISO) in two regions. A striking 30-50-day ISO found over the east of thermocline ridge (Region A, 80-90 degrees E, 6-12 degrees S), as identified by the Empirical Mode Decomposition (EMD) method, is distinguished from the SST signature over the thermocline ridge (Region B, 52.5-65 degrees E, 6-13 degrees S). The 30-50-day ISO of SST in the Region A is active in March-May (MAM) and suppressed in September-November (SON). Meanwhile, a 30-50-day ISO of precipitation correlates with the SST over the Region A. SST leads precipitation by 10 days, implying a pronounced ocean-atmosphere interaction at the intraseasonal timescale, especially the oceanic feedback to the atmosphere during Madden-Julian Oscillation (MJO) events. Analysis on mechanism of the ISO manifests heat fluxes are critical to the development of the intraseasonal SST variability. The local thermocline in Region A, as the shallowest in MAM and the thickest in SON, is likely to modulate the strength of ISO and contribute to its sustainability. It suggests that thermocline plays a more important role in Region A than in Region B, leading to the difference between the two regions
Potential deposition of biogenic silica source sediment in the Paleo-Yangtze Grand Underwater Delta estimated with satellite remote sensing
No full textBiogenic silica sediment constitutes one of the critical sources of particle income in the oceans. In this paper, satellite remote sensing of primary production, sinking flux, and molar ratio of Si/C were utilized to elucidate potential biogenic silica sediment in the Paleo-Yangtze Grand Underwater Delta. Primary production retrieval showed that daily primary production in the Paleo-Yangtze Grand Delta was 3.3-10.8Mtd(-1), with 5.8Mtd(-1) on average. Sinking flux, retrieved with in situ observations and satellite remote sensing, was within the range of 109-657mgCm(-2)d(-1), or about 23% of total primary production, on average. A molar ratio of Si/C of 0.11-0.45 interval was used in the area, for the Paleo-Yangtze Grand Delta was similar to coastal water and affected by many factors. Considering that phytoplankton in the Paleo-Yangtze Grand Underwater Delta is mainly diatom (80% on average), about 0.21-0.88 billion tons of biogenic silica source sediment is produced in the area annually. With the reduction of land source sediment occurring in recent years in the area, biogenic silica sediment may be one of the dominant sediment sources for maintaining the future stability of the Paleo-Yangtze Grand Underwater Delta
Modern pollen distribution in the northeastern Indian Ocean and its significance
No full textIn order to provide a reference for reconstructing the paleoclimate of the northeastern Indian Ocean, 36 airborne pollen samples were analyzed using methods for airborne pollen, and 26 surface water samples were analyzed using a lab method for surface water. We found that little pollen is airborne over the Indian Ocean in spring, but airborne pollen types and concentrations can help to deduce paleomonsoon strength and direction. The conclusions included the following: (1) Pollen in the sediment was transported mainly via ocean currents instead of the early summer or spring wind. (2) Airborne pollen types and concentrations are proportional to the wind speed and inversely proportional to the pollen distance transported and depend on whether the wind is from the land or from the sea. If the wind is from the land, the pollen concentration is proportional to the angle between the wind direction and the coastline. (3) The pollen concentration in the sample collected from a water depth of 30-45 m is higher than in the samples collected from a depth of 5 m. The pollen concentration and salinity are higher in the equatorial area than in the Northern Hemisphere
Rare earth elements and yttrium in ferromanganese deposits from the South China Sea: distribution, composition and resource considerations
No full textFerromanganese nodules and crusts contain relatively high concentration of rare earth elements (REE) and yttrium (REY), with a growing interest in exploitation as an alternative to land-based REY resources. On the basis of comprehensive geochemical approach, the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed. The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity. Total REY contents range from 69.1x10(-6) to 2 919.4x10(-6), with an average value of 1 459.5x10(-6). Especially, the enrichment rate of Ce content is high, accounting for almost 60% of the total REY. This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts. Moreover, the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin. Finally, Light REE (LREE) and heavy REE (HREE) oxides of the ferromanganese deposits in the study area can be classified into four grades: non-enriched type, weakly enriched type, enriched type, and extremely enriched type. According to the classification criteria of rare earth resources, the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals
Zircon U-Pb age, geochemistry and Sr-Nd-Hf isotopes of the Baolige granite complex in the Great Hingan Range, NE China
No full textThe Solonker zone is widely accepted as the suture between the North China Craton and the Siberia-Mongolia continental plate. The Baolige granite complex is located to the north side of the Solonker Suture and is mainly composed of monzogranite and granite. Zircon U-Pb ages, geochemistry, and Sr-Nd-Hf isotopic data of the Baolige granites were presented to constrain their petrogenesis and tectonic settings. Two monzogranite samples from Baolige yielded weighted mean zircon Pb-206/U-238 ages of 310.7 +/- 2.1Ma (mean square of weighted deviates (MSWD)=1.3) and 307.4 +/- 1.6Ma (MSWD=0.77), whereas the granite intruded into the monzogranite yielded an age of 296.2 +/- 2.0Ma (MSWD=1.2). Both the Baolige monzogranite and granite contain high contents of SiO2, K2O, and Al2O3, low contents of TiO2, MgO, and CaO, and are peraluminous high-K calc-alkaline. These rocks are characterized by enrichments of K, Rb, U, Pb, Th, and light rare earth elements and depletions of Nb, Ta, Ti, and heavy rare earth elements and contain slightly negative or no Eu anomalies, similar to typical arc-related granitoids. The Ti-in-zircon thermometry yielded 650-759 degrees C for the monzogranite and 645-796 degrees C for the granite. The monzogranite shows positive zircon epsilon(Hf)(t) values (4.7-13.2) and whole-rock epsilon(Nd)(t) values (3.6-5.2), with T-DM2(Hf) ages of 1,324-557Ma and T-DM2(Nd) ages of 1,015-821Ma, and I-Sr of 0.70363-0.70386. The granite shows epsilon(Hf)(t) values of 15.6-20.9 and epsilon(Nd)(t) values of 4.0-5.1, with T-DM2(Nd) ages of 957-832Ma, and I-Sr of 0.70364-0.70406. Geochemical evidence indicates that the Baolige granite complex is highly fractionated I-type and was likely formed by partial melting of the Neoproterozoic juvenile crust in a continental arc setting. We concluded that the Paleo-Asian Ocean may have undergone north-dipping subduction beneath the Siberia-Mongolia continental plate during the Late Carboniferous, and the subduction may have continued to the Early Permian (ca. 296Ma)
Mid-late Holocene changes in sedimentary organic matter on the inner shelf of the East China Sea
No full textMarginal seas are important transitional zones for the delivery of terrestrial organic matter (TOM) from land to the open sea, and they play an important role in the carbon cycle. Tracing the source of sedimentary organic matter (SOM) deposited in marginal seas is fundamental to our understanding of the dispersal, degradation, migration, and conversion of organic matter. This paper presents high-resolution records of bulk organic matter and biomarker proxies from Core T08 that was recovered from the inner shelf of the East China Sea (ECS), and aims to identify the contributions of marine and terrestrial organic matter over the past 3725 yrs. Total organic carbon (TOC) values were low (0.50%) and showed no significant change between 3725 and 1800 yr BP (Period I), and increased continuously from 0.40% to 0.86% after 1800 yr BP (Period II: 1800-750 yr BP; Period III: 750 yr BP present). The TMBR' (ratio of terrestrial to marine biomarkers) and delta C-13(roc) (delta C-13 of TOC) values showed steady TOM contribution during Period I and higher TOM contribution driven by the increased Changjiang River (CR)-derived TOM under strong East Asian Summer Monsoon (EASM) and El Nino during Period II. During Period III, the increase in marine organic matter (MOM) contribution was indicated by the TMBR', and this was caused by enhanced marine productivity related to intensified vertical mixture that was driven by the strengthened East Asian Winter Monsoon (EAWM). delta(CTroc)-C-13 shows a contrary trend to the TMBR' during Period III, probably influenced by variations in the C-3 vegetation type during this period. Spectral analysis of the TMBR' series for the last 1200 yrs shows cycles with periods of 119, 75-85, and 54 yrs, confirming that climate-related events influenced the variation in SOM under the modulation of solar activity and solar irradiance at the centennial scale
Crustal structure revealed by a deep seismic sounding profile of Baijing-Gaoming-Jinwan in the Pearl River Delta
No full textThe Pearl River Estuary area, located in the middle part of the southern China coastal seismic belt, has long been considered a potential source of strong earthquakes above magnitude 7.0. To scientifically assess the potential strong earthquake risk in this area, a three-dimensional artificial seismic sounding experiment, consisting of a receiving array and seabed seismograph, was performed to reveal the deep crustal structure in this region. We used artificial ship-borne air-gun excitation shots as sources, and fixed and mobile stations as receivers to record seismic data from May to August 2015. This paper presents results along a line from the western side of the Pearl River Estuary to the western side of the Baijing-Gaoming-Jinwan profile. A two-dimensional velocity structure was constructed using seismic travel-time tomography. The inversion results show that the Moho depth is 27 km in the coastal area and 30 km in the northwest of the Pearl River Estuary area, indicating that the crust thins from land to sea. Two structural discontinuities and multiple low-velocity anomalies appear in the crustal section. Inside both discontinuity zones, a low-velocity layer, with a minimum velocity of 6.05 km s(-1), exists at a depth of about 15 km, and another, with a minimum velocity of 6.37 km s(-1), exists at a depth of about 21.5 km between the middle and lower crust. These low velocities suggest that the discontinuities may consist of partly molten material. Earthquakes with magnitudes higher than 5.0 occurred in the low-velocity layer along the profile. The deep Kaiping-Enping fault, rooted in the crust, may be one of the most important channels for deep material upwelling and is related to tectonic movement since the Cretaceous in the Pearl River Delta tectonic rift basin
