Search

Sedimentation of fine-grained deposits on coastal zones and continental shelves are important because of the association with chemical pollutants, and the implication to the impact on biological processes, the stratigraphic correlations, and changes in sedimentary environments. The Yellow Sea continental shelf receives large quantities of sediment from the Huanghe (Yellow) River. Unfortunately, little attention has been yet paid to the sedimentation on the shallow shelf and its features, and the vertical sediment flux in the area is poorly understood. In this study, nine cores were collected in northern Yellow Sea by theR/V Science 1 in September, 1998 and 1999 to examine the sedimentation rate, sediment flux and the provenance with210Pb analysis. The210Pb activity profiles showed that the vertical sediment flux ranged from 0.06 to 1.18 g/cm2·a in the region. In central part of the area, there was a patch of fine-grained mud, with the flux below 0.33 g/cm2·a. Most profiles were featured in two-segment model. Differences in the profiles reflected spatial and temporal variations in hydrodynamic and sedimentary processes. In order to determine the provenance and sedimentary setting in the area, the geochemistry of Ca, Fe, Sr, Cu, Ti and Rb in 11 surficial sediment samples were studied, which showed that in the central northern Yellow Sea, the mud deposit was from multi-source but mainly from the Huanghe River.

It has been widely recognized that low silicate content in seawater is a major limiting factor to phytoplankton primary production in Jiaozhou Bay. However the reason of Si-limitation remains poorly understood. In the present study we measured the biogenic silicate content and discussed the accumulation of silicate in Jiaozhou Bay sediment. The results show that the biogenic silica content in the sediment of the Jiaozhou Bay is obviously much higher than those in the Yellow Sea and the Bohai Sea. The Bsi:TN ratios and BSi:16P ratios in the sediment are>1 and the OC:BSi ratio in sediment is lower than these of Redfield ratio (106∶16), indicating that the decomposition rate of OC is much higher than that for BSi in similar conditions. Therefore, the majority of the biogenic silicate was buried and thus did not participate in silicate recycling. Silicate accumulation in sediment may explain why Si limits the phytoplankton growth in the Jiaozhou Bay. Comparing the flux of biogenic silicate from sediments with primary production rate, it can be concluded that only 15.5% of biogenic silicate is hydrolyzed during the journey from surface to bottom in seawater, thus approximate 84.5% of biogenic silicate could reach the bottom. The silicate releasing rate from the sediment to seawater is considerably lower than that of sedimentation of biogenic silicate, indicating silicate accumulation in sediment too. In a word, the silicate accumulation in sediment is the key reason of silicate limiting to phytoplankton growth in Jiaozhou Bay.

Forty-eight surface sediments of the southern Yellow Sea are separated into three grain-size fractions. Four forms of extractable nitrogen (nitrogen in ion-exchangeable form (Nie), nitrogen in weak-acid extractable form (Nwa), nitrogen in strong-alkali extractable form (Nsa) and nitrogen in strong-oxidant form (Nso)) are obtained by the sequential extraction. The results show that the contents and the distributions of the extractable nitrogen in the southern Yellow Sea surface sediments are closely related to sediment grain size. The distributions of Nie, Nso and total nitrogen (TN) present positive correlations with fine particles content, while Nwa and Nsa does not have such correlation. The net contents of all the forms of nitrogen increase with sediment grain size finer.

High-precision isotope composition determinations using multicollector, magnetic-sector inductively coupled plasma mass spectrometry (MC-ICPMS) have recently revealed that some transition metal isotopes such as those of Mo, Fe, Cu, Zn etc. can be used as biogeochemical tracers in global change research. The Mo isotope system may be useful in paleoredox investigations indicating that δ97/95Mo in seawater may co-vary with changes in the relative proportions of anoxic and oxic sedimentation in the ocean, and that this variation may be recorded in δ97/95Mo of anoxic sediments. The Mo continental flux into the oceans and the global Mo isotope budget can be estimated from δ97/95Mo values. The Fe isotope composition in seawater is an important issue because Fe plays a controlling role in biological productivity in the oceans and its abundance in seawater may have substantial effect on climate changes. Iron isotope fractionations could result from bio- and abio-processes and have about 0.1% variation (δ56/54Fe), so Fe isotopes considered alone cannot be used to distinguish the products of abiotic and biotic Fe processing in geological records. Cu and Zn isotopes are also used as biogeochemical tracers, but the researches are relatively less. This review mainly focuses on the methods for preparation, purification and determination, of new isotope tracer samples, and on isotope applications in marine environmental changes.

A method for simultaneous determination of particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP) in seawater was improved. After using cellulose acetate membrane to filter the seawater samples and washing the membrane with 1mol/L hydrochloric acid, PIP was extracted into hydrochloric acid phase and POP was left on the membrane. POP was oxygenated at 120°C, 0.12MPa with potassium persulphate. Phosphomolybdate blue spectrophotometry was used in the determination. The proper volume of seawater sample for simultaneously determining PIP and POP was 100–150ml, containing PIP≥0.27μg, POP≥0.69μg. Relative Standard Deviation (RSD) of the determination of PIP and POP was 5.8% and 4.3% respectively. This method was used to determine POP and PIP in the surface water of Huiquan Bay, Qingdao, China. PIP content there averaged at 69.0μg/L and POP at 3.3 μg/L. PIP is the main form (>93%) of particulate phosphorus (PP). Maximum PIP coincided with flood tide, indicating that PIP mainly originated from disturbance of surface sediments. At the offshore area, maximum of PIP appeared at flood tide and minimum of PIP appeared at ebb-tide. The maximum of POP presented at about 10:00am, which suggests that POP is closely related to biological metabolism. The control factor of POP in seawater was concluded to be biological metabolization.

The forms of phosphorus and silicon in the natural grain sizes surface sediments of the southern Bohai Sea were studied. In sediments, the organic matter bound form of phosphorus was the main form of transferable phosphorus and ranged from 0.37 μmol/g to 1.57 μmol/g, accounting for 10.7% of the total phosphorus, others were the carbonate bound form, iron-manganese oxide bound form and ion-exchange able form; the transferable form of phosphorus accounted for 19.2% of the total phosphorus. Silicon’s carbonate bound form was predominant over others among its transferable forms, and content ranged from 1.55 μmol/g to 8.94 μmol/g, accounting for 0.05% of the total silicon; the total amount of transferable silicon forms accounted for only 0.12% of the total silicon. Therefore, 19.2% of the total phosphorus and 0.12% of the total silicon contained in the surface sediments of the southern Bohai Sea could participate in the biogeochemical cycling.

Based on the author's previously obtained results on P and Si forms in southern Bohai Sea surface sediments, this study mainly foucusing on the controlling factors, existence forms, and biogeochemical processes of P and Si showed that the transferable forms of phosphorus in sediments were mainly controlled by the mineralization of organic matters and the reduction of high-valence iron; whereas the transferable forms of silicon were possibly controlled by the dissolution and precipitation as well as biochemical processes of living organisms.

A new convenient sulfide electrochemical sensor for marine environmental in-situ monitoring and real time survey was developed. The new sensor based on a solid Ag2S membrane electrode has outstanding chemical sensitivity and stability. It responds to the activity of sulfide ions according to a Nernstian slope of −31mV/decade. The sensor can be used to determine the total concentration of sulfides (C T) by calibrating the pH value of the solution to a standard pH. The practical measurement range for total sulfide concentration is 0.1–10 mg/L in seawater. The sensor has a very low potential drift (

Based on a new idea for research on cycling of marine biogenic elements, this study showed that only the leachable form phosphorus in natural grain sizes marine sediments constitutes the transferable phosphorous in the sediments. The transferable phosphorus content in the natural grain sizes surface sediments in the Huanghe River estuary adjacent waters ranges from 58.5–69.8 μg/g, accounting for only 9.1%–11.0% of the total phosphorus content, whereas the leachable form (“transferable”) phosphorus content in the sediment after it was totally ground into powder was found to be 454.8–529.2 μg/g, accounting for 73.4%–89.1% of the total phosphorus. Analysis of the correlation between the biomass of benthos and the leachable form (“transferable”) phosphorus showed that most of the leachable form (“transferable”) phosphorus in the totally ground sediment did not participate in the marine biogeochemical cycling. Furthermore, a synchronous survey on benthos showed that the biomass of meio-and macro-benthos exhibited good positive correlation with the leachable form of phosphorus in the natural grain sizes sediment, but poorer correlation with the leachable form (“transferable”) phosphorus in the totally ground sediment, indicating that transferable phosphorus in marine sediment is the leachable form of phosphorus in the natural grain sizes sediments, and is not the previously known leachable form (“transferable”) phosphorus obtained from the totally ground sediment.

This study on the sectional and vertical distribution of dissolved oxygen (DO) and the O2 fluxes across the sea-air interface in East China Sea (ESC) waters shows that the waters were in steady state and that the difference of DO was great in upper and bottom waters in Apr. 1994; but that seawater mixing was strong and the difference of DO was small in upper and bottom waters in Oct. 1994. The above conclusions were specially obvious in continental shelf waters under 100 m. The DO maximum in subsurface layer waters appeared only at several stations and in general the DO in the waters decreased with depth. The horizontal distributions of O2 fluxes across the sea-air interface appeared in stripes in Leg 9404 when most regions covered were supersaturated with O2 seawater to air flux was large, and that on section No. 1 was 1.594 L/m2·d. The horizontal distribution of O2 fluxes across the sea-air interface appeared lumpy in Leg 9410, when most regions covered were unsaturated with O2·O2 was dissolved from air to seawater, and the fluxes were 0.819 L/m2·d on section No. 1 in Leg 9310, 0.219 L/m2·d in Leg 9410. The main reasons for DO change in surface layer seawater were the mixture of upper and bottom layer water, and the exchange of O2 across the sea-air interface. The variation of DO by biological activity was only 20% of total change of DO.