China Sea Coastal Water Research Articles

Effect of dissolved organic nitrogen on the bloom of Prorocentrum donghaiense and Karenia spp. in the East China Sea coastal waters

Effect of dissolved organic nitrogen on the bloom of Prorocentrum donghaiense and Karenia spp. in the East China Sea coastal waters

Effect of dissolved organic nutrients on the bloom of Prorocentrum donghaiense in the East China Sea coastal waters

Prorocentrum donghaiense blooms occur annually in the East China Sea coastal waters, degrading ecosystem functions and impeding economic development. Dissolved organic nitrogen and phosphorus (DON and DOP) are the main components in the marine nutrient pools and are closely related to harmful algal blooms. From April to June 2019, a survey was conducted along the East China Sea coast (Sansha and Lianjiang counties) to investigate the relationship between dissolved organic nutrients and P. donghaiense bloom. Our findings showed that dinoflagellates dominated the phytoplankton community, and dissolved organic nutrients were the major factors influencing community structure during the P. donghaiense bloom. Redundancy analysis indicated that P. donghaiense abundance was primarily affected by DON in the Sansha area while it was primarily affected by DON and DOP in the Lianjiang area. Correlation analysis also confirmed a strong positive correlation between dissolved organic nutrients and P. donghaiense abundance both in the Sansha and Lianjiang coastal areas (p < 0.001). Furthermore, a culture experiment was carried out during the bloom to further investigate the effect of dissolved organic nutrients on the phytoplankton community structure. After 10 days of culture, dinoflagellates' relative abundance decreased from 97.1% to 28.2% in the inorganic treatment, whereas dinoflagellates continued to dominate the phytoplankton community in the organic treatment (76.9%). As a result, we propose that dissolved organic nutrients are responsible for the P. donghaiense bloom outbreak and promote the phytoplankton community shift from diatoms to dinoflagellates.

Assessing Safety of Market-Sold Fresh Fish: Tracking Fish Origins and Toxic Chemical Origins.

Increasing global and domestic food trade and required logistics create uncertainties in food safety inspection due to uncertainties in food origins and extensive trade activities. Modern blockchain techniques have been developed to inform consumers of food origins but do not provide food safety information in many cases. A novel food safety tracking and modeling framework for quantifying toxic chemical levels in the food and the food origins was developed. By integrating chemicals' multimedia environment exchange, food web, and source tracking systems, the framework was implemented to identify short-chain chlorinated paraffin (SCCP) contamination of fresh hairtail fish sold by a Walmart supermarket in Xi'an, northwestern China, and sourced in Eastern China Sea coastal waters. The framework was shown to successfully predict SCCP level with a mean of 17.8 ng g-1 in Walmart-sold hairtails, which was comparable to lab-analyzed 21.9 ng g-1 in Walmart-sold hairtails. The framework provides an alternative and cost-effective approach for safe food inspection compared to traditional food safety inspection techniques. These encouraging results suggest that the approach and rationale reported here could add additional information to the food origin tracking system to enhance transparency and consumers' confidence in the traded food they consumed.

Chlorinated organic contaminants in fish from the South China Sea: Assessing risk to Indo-Pacific humpback dolphin

Indo-Pacific humpback (Sousa chinensis) dolphins are primarily exposed to chlorinated organic contaminants through the consumption of contaminated fish. We assessed the potential risk of chlorinated organic contaminants to Indo-Pacific humpback dolphins by determining the concentration of 21 organochlorine pesticides (OCPs) and 28 polychlorinated biphenyls (PCBs) in 14 fish species collected from the South China Sea coastal waters. The results of the study showed that bioaccumulation of OCPs and PCBs was influenced by sampling location, fish species, and fish niche. The average ∑DDT (Dichlorodiphenyltrichloroethane) concentration was 3 times higher in benthopelagic fish (488 ng/g) compared to pelagic-neritic fish (155 ng/g) from Jiangmen, whereas an opposite pattern of the lower DDTs concentration in benthopelagic and demersal fish compared to pelagic fish from Zhuhai (p < 0.05). Furthermore, the molecular diagnostic ratios using DDT and its metabolites (DDT/(DDD + DDE) were less than one, suggesting the DDT contamination at Zhuhai and Jiangmen may due to the historical agricultural usage of the lands. The reference dose-based (RfD) risk quotient (RQ) suggested that DDTs are potential risk in Qinzhou, which is in accordance with the high DDTs concentration found in fishes captured in Qinzhou. The RfD risk quotient of PCBs is at potential risk for all sites (RQ > 100), except Xiamen and Qinzhou. A highest average ∑DDT concentration was observed Qinzhou. This study showed that fish consumption might pose a health risk to Indo-Pacific humpback dolphins. However, further studies are required to determine the contribution of fish niche to the overall risk.

Paleoceanographic evolution of the Japan Sea over the last 460 kyr – A coccolithophore perspective

Abstract Changes in the intensity of the influx of the Tsushima Warm Current (TWC) in the south-central part of the Japan Sea (JS), or East Sea in Korean, were reconstructed for the last 460 kyr at IODP Site U1427 using the composition and abundance of the coccolithophore assemblage. In addition, the recent distribution of coccolithophore taxa in the JS and the East China Sea was assessed using electron microscopy. Coccolithophore assemblages, dominated by Emiliania huxleyi and Gephyrocapsa species, and coccolith abundance reveal a strong relationship between sea level and ocean variability over the last five glacial/interglacial cycles, in good agreement with planktic foraminiferal data. Three different circulation modes based on calcareous nannofossil and foraminifera TWC indicators were proposed for the JS. Coccolith production was low and TWC indicators (i.e., Gephyrocapsa oceanica, Calcidiscus leptoporus s.l., and Helicosphaera carteri) absent due to the isolation of the JS during glacials in response to global sea level falls (Mode 1). In contrast, coccolith abundance and TWC indicators reach a maximum due to the most intense TWC flow through the Tsushima Strait during interglacials (Mode 3). Intermediate conditions (Mode 2) are characterized by moderate/high coccolith numbers, presence of TWC coccolith indicators, and rare TWC planktic foraminifera indicators. This mode resulted in intermittent variations in the contribution of the TWC and East China Sea coastal water due to relatively low sea level stands (ca. −90 m to −20 m). Coccoliths dominated the carbonate sequence prior to MIS 8 and were major contributors to the total carbonate of the sediment at Site U1427, suggesting high coccolithophore productivity and a bloom-type environment during MIS 11 and 9. These changes in the carbonate chemistry caused by glacio-eustacy in the JS at the northwest margin of the Pacific Ocean should be considered in future paleoceanographic and paleoclimate models.

East Asian Monsoon History and Paleoceanography of the Japan Sea Over the Last 460,000 Years

AbstractThe Japan Sea is directly influenced by the Asian monsoon, a system that transports moisture and heat across southeast Asia during the boreal summer, and is a major driver of the Earth's ocean‐atmospheric circulation. Foraminiferal and facies analyses of a 460‐kyr record from Integrated Ocean Drilling Program Expedition 346 Site U1427 in the Japan Sea reveal a record of nutrient flux and oxygenation that varied due to sea level and East Asian monsoon intensity. The East Asian summer monsoon (EASM) was most intense during marine isotope stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c when the Tsushima Warm Current flowed into an unrestricted well‐mixed normal salinity Japan Sea, whereas East Asian winter monsoon (EAWM) conditions dominated MIS 2, MIS 4, MIS 6, and MIS 8 when sea level minima restricted the Japan Sea resulting in low‐salinity and oxygen conditions in the absence of Tsushima flow. Reduced oxygen stratified, low‐salinity, and higher productivity oceanic conditions characterize Terminations TV, TIII, TII, and TI when East China Sea coastal waters breached the Tsushima Strait. Chinese loess, cave, and Lake Biwa (Japan) and U1427 proxy records suggest EASM intensification during low to high insolation transitions, whereas the strongest EAWM prevailed during lowest insolation periods or high to low insolation transitions. Ice sheet/CO2 forcing leads to the strongest EAWM events in glacials and enhanced EASM in interglacials. Mismatches between proxy patterns suggest that latitudinal and land/sea thermal contrasts played a role in East Asian monsoon variability, suggesting that a complex interplay between ice sheet dynamics, insolation, and thermal gradients controls monsoonal intensity.

Intrusions of excess nitrate in the Kuroshio subsurface layer

Vertical profiles of nutrient concentration were investigated in the southeastern East China Sea and the Kuroshio (30°N–31°N, 128°E–130°E) in June 2013, in order to understand the effects of less-saline water intrusions on nutrient composition. The ratio of nitrate to phosphate is commonly <16; however, values >16 were observed in the northern edge of the Kuroshio at a depth of 50–100m at the beginning of June, associated with a less-saline water intrusion with a density (σt) of 23.5–24.8. This less-saline water was not present at the end of June. A positive excess nitrate concentration was found in water with a salinity of <34.17, revealing a significant negative correlation between salinity and excess nitrate concentrations. This less-saline excess-nitrate water originated from winter mixing of the East China Sea coastal waters, which were affected by the Changjiang River according to a back-trajectory analysis, and was transported to the east by the Kuroshio >500km away from the source. The excess-nitrate water existed below the euphotic layer, and it prevented the utilization of nutrients by the phytoplankton during the transportation. The intrusion of this less-saline water increased the nitrate to phosphate ratio and supplied excess nitrate to the Kuroshio subsurface layer.

Distribution of nanoflagellates in five water masses of the East China Sea in autumn and winter

The variations of abundance, biomass and trophic structure of nanoflagellates (NF) among five typical water masses in the East China Sea were investigated in autumn (November 19–December 23, 2006) and winter (February 22–March 11, 2007). It was found that water mass had a significant impact on the distribution of NF. Either in autumn or in winter, the highest abundance and biomass of NF were recorded in the East China Sea Shelf Mixing Water (ECSSMW), and the lowest in the Kuroshio Subsurface Water (KSSW). While in the East China Sea Coastal Water (ECSCW), the abundance and biomass of both heterotrophic nanoflagellates (HNF) and pigmented phototrophic nanoflagellates (PNF) were only slightly higher than that in Taiwan Strait Water (TSW) and Kuroshio Surface Water (KSW). In respect to the seasonal variation, the abundance and biomass of NF in TSW declined in winter, while in other 4 water masses, they showed an increasing trend from autumn to winter, mainly due to the decrease (in TSW) or increase (in ECSCW, ECSSMW, KSW and KSSW) of HNF. The distribution pattern of abundance- or biomass-based PNF/HNF ratio was found to be correlated to the nutrient level of the water mass. Results of Pearson correlation analysis and principle component analysis indicated that PNF was mainly constrained by nutrient supply, and HNF was controlled by food availability in the East China Sea.

Reconstruction of environmental changes using a multi‐proxy approach in the Ulleung Basin (Sea of Japan) over the last 48 ka

AbstractBased on elemental geochemical data, we reconstructed the sediment provenance, surface productivity and bottom water redox conditions for the last 48 ka in the Ulleung Basin (Sea of Japan) and inferred the factors controlling them. Al2O3/TiO2 ratio and chemical index of alteration (CIA) suggest that sediment provenance changed during the glacial period (48–18 ka) compared to the deglacial (ca. 18–11 ka) and Holocene. Mass accumulation rates of total organic carbon (TOC), CaCO3, phosphorus, cadmium and excess barium reveal low paleoproductivity during low sea stand. During 18–11 ka, productivity increased due to increasing inflow of nutrient‐rich water masses – the Oyashio and the East China Sea coastal water – in tandem with the rising sea level. Maximum productivity occurred during Younger Dryas and Pre‐boreal periods when sea level was at ∼ −60 m and then gradually decreased as the Tsushima Warm Current inflow kicked off at ca. 9.3 ka, consistent with other paleoredox proxies, which reveal the presence of anoxic bottom water during ca. 12–9 ka. With the changes in paleoredox proxies and their ratios (TOC, Mo, U, Mn, C/S ratio and Uauthigenic and Mo contents), we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation‐induced productivity changes. The global climate and sea‐level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection, subsequently driving the oxygenation of bottom water in the Ulleung Basin. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Spatial-temporal variability of total and size-fractionated phytoplankton biomass in the Yangtze River Estuary and adjacent East China Sea coastal waters, China

The spatial and seasonal dynamics of total and size-fractionated phytoplankton biomass (chlorophyll- a) as well as physical and chemical factors in the Yangtze River Estuary and adjacent East China Sea coastal waters were investigated from April 2002 to February 2003. Average surface total and water column integrated chlorophyll a biomass showed a clear seasonal variation in response to the Yangtze River discharge, with the highest in summer (∼4 mg m−3 and &amp;gt;60 mg m−2), intermediate in spring and autumn (∼1 mg m−3 and 26–28 mg m−2), and the lowest in winter (0.5 mg m−3 and &amp;lt;20 mg m−2). Summer maximum chlorophyll a concentrations (&amp;gt;10 mg m−3) occurred at intermediate salinities (∼20–30) region beyond the front zone between 112.5°E and 123°E with sufficient nutrients replenishment for phytoplankton growth. Generally, spatial distribution of size-fractionated phytoplankton showed that phytoplankton biomass was dominated by the large size fraction (&amp;gt;20 μm) in the turbid eutrophic estuarine and near-shore waters, while the small-sized phytoplankton (&amp;lt;5 μm) were dominant in the offshore stations. Phosphate was the main limiting nutrient of phytoplankton biomass in river diluted water and most near-shore stations, while dissolved inorganic nitrogen became the potential limiting nutrient in some offshore stations, except for summer when phosphate limited almost all in the whole investigation region. Controlling the inputs of phosphate loading from the Yangtze River is one of the most effective strategies for reducing the increasing eutrophication and occurrences of harmful algal blooms in Yangtze River Estuary and adjacent East China Sea coastal waters.

Orbital- and millennial-scale paleoceanographic changes in the north-eastern Japan Basin, East Sea/Japan Sea during the late Quaternary

Two gravity sediment cores (GH99-1239 and GH99-1246) obtained from the north-eastern Japan Basin in the East Sea/Japan Sea were analyzed for the orbital- and millennial-scale paleoceanographic changes. Chronostrati- graphically, core GH99-1239 represents a continuous sedimentary record since 32 ka, based on correlation of distinct lithological markers (i.e. dark layer or TL layer) with those in core GH98-1232 collected nearby. For core GH99-1246, the age model is constructed through correlation of lightness (L � ) values and tephra (Aso-4 and Toya) layers with those in the well-dated Oki Ridge core (MD01-2407), indicating about 134 ka of sedimentation since the latest Marine Isotope Stage (MIS) 6. New geochemical data from both cores corroborate orbital-scale paleoceanographic variation, such that surface-water productivity, represented by biogenic opal and total organic carbon (TOC) contents, increased during MIS 1 and MIS 5; CaCO3 contents do not show such distinct glacial-interglacial cycles, but were influenced by dissolution and preservation rather than foraminiferal production. During the glacial periods when sea ice was prevalent, surface- water productivity was low, and bottom-water conditions became anoxic, as indicated by high total sulfur (TS) contents and high Mo concentrations. The geochemical data further document millennial-scale paleoceanographic variability, corresponding to a series of thin TL layers in response to Dansgaard-Oeschger cycles but irrespective of the glacial or interglacial periods. In particular, thin TL layers formed during MIS 3 are characterized by less TOC (about 1%) and TS (about 0.4%) contents and lower Mo (about 5 p.p.m.) concentration, whereas those during MIS 4 and MIS 5 exhibit more TOC (up to 4%) and TS (up to 5%) contents and higher Mo (up to 120 p.p.m.) concentration. Such a discrepancy is attributed to different degree of surface-water productivity and of bottom-water oxygenation, which is closely related to the sea level position and extent of ventilation. Flux of the East China Sea Coastal Water controlled by millennial-scale paleoclimatic events is the most critical factor in deciding the properties of TL layers in the north-eastern Japan Basin. Our results strongly confirm that TL layers in the Japan Basin also validate the unique feature of basin-wide paleoceano- graphic signals in the East Sea/Japan Sea. Copyright # 2011 John Wiley & Sons, Ltd.

The Erection Technology of Pile Foundation Construction Platform for the Sanmenkou Cross-Harbor Bridge

The south gate bridge of the Sanmenkou cross-harbor bridge at Xiangshan County lied in the East China Sea coastal waters. The foudation for the bridge pier in the water used bored piles, the greatest depth up to 42m. This article described the Program selection, design and construction methods about the construction trestle and platform when the piles foundation were built in the water.

Depositional environment in the southern Ulleung Basin, East Sea (Sea of Japan), during the last 48 000 years

The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin, the East Sea (Sea of Japan). The data include sediment color (L*), X-ray radiographs, grain size distribution and AMS14C date. Four kinds of sediments (homogeneous, laminated, crudely laminated and hybrid sediments) are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation. Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon (EAM). The relative contributions of the East China Sea Coastal Water (ECSCW) and the Tsushima Warm Current (TWC) were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP. During the interstadial, the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia, and then more strongly low-salinity, nutrient-enriched water was introduced into the East Sea. The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition. During the lowest stand of sea level in the last glacial maximum (LGM), the isolated East Sea dominated by stratified water masses and the euxinic depositional environment formed. The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high. During the late Younger Dryas (YD) period, the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM. The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.

Early Pleistocene evolution of the Japan Sea Intermediate Water

AbstractThe Early Pleistocene fossil record of the Japan Sea reveals that the planktonic foraminifer Globorotalia inflata succeeded in expanding its range from the East China Sea to the Japan Sea during interglacial stages of the Early Pleistocene; however, the species is only found in surface sediment samples from the southwestern‐most part of the sea. Based on the ecology of G. inflata and the water mass structure of the Japan Sea, it appears that its geographical distribution is mainly controlled by the low temperature of the intermediate water, which is caused by the cool‐water mass of Japan Sea Proper Water. The temporal and spatial patterns of G. inflata occurrence indicate that the intermediate water at 200 m depth during interglacial stages between 1.46 and 1.3 Ma was warmest during the Quaternary. This warm intermediate water probably resulted from the influence of the low‐salinity nature of the Tsushima Current due to the large inflow of East China Sea Coastal Water. After 1.3 Ma, the intermediate water at 200 m depth became cooler in a step‐wise manner. This cooling can be explained by an intensification of thermohaline circulation in the Japan Sea associated with strengthening of the East Asian winter monsoon and an increase in salinity due to enlargement of the southern strait. Copyright © 2009 John Wiley &amp; Sons, Ltd.

An Assessment of Metals (Pb and Cu) Contamination in Bottom Sediment from South China Sea Coastal Waters, Malaysia

Problem statement: The accumulation of metal contaminants in sediments can pose serious environmental problems to the surrounding areas. Tr ace metal contamination in sediment could affect the water quality and the bio-assimilation and bioa ccumulation of metals in aquatic organisms, resulting in potential long-term implications on hu man health and ecosystem. Approach: About 154 bottom sediment samples were collected using Smith McIntyre in a transect pattern from South China Sea East Coast coastal water (Terengganu, Pahang and Johor coastal area). The study focused on the levels of Pb and Cu in order to assess the extent o f environment pollution and to discuss the origin o f these contaminants in the sediment. Results: Results showed that the average concentration of P b and Cu was 33.70 µg g -1 dry weights and 22.40 µg g -1 dry weights, respectively. Pb and Cu have relative ly lower Enrichment Factors (EF) value and geo-accumulation (I geo ) indices in study area and these analysis validated that elevated heavy metals conce ntration in most sample are not due to artificial contamination. Conclusion: Overall, geochemistry of the samples showed the ef fect of both natural and anthropogenic inputs to the catchment, however, natural processes were more dominant than anthropogenic inputs in concentrating metals. Resul ts obtained would help to develop strategies for pollution control and sediment remediation of coast al waters in the South China Sea.

Alkaline phosphatase activity of phytoplankton in East China Sea coastal waters with frequent harmful algal bloom occurrences

Alkaline phosphatase activity (APA) was measured during 3 cruises in spring 2002, 2003 and 2005 using bulk and single-cell assays in coastal waters in the East China Sea which experience frequent harmful algal bloom occurrences. The bulk APA ranged from below the detection limit to 73.53 nmol l(-1) h(-1), with mean values of 15.73 +/- 14.12, 23.77 +/- 15.20 and 11.48 +/- 12.44 nmol l(-1) h(-1) for 2002, 2003 and 2005, respectively. The cell-bound fraction (mainly phytoplankton) was the major contributor to APA, with averages of 74 and 80% during 2003 and 2005, respectively. During the spring of 2005, most of the dominant dinoflagellates had high percentages of enzyme-labeled fluorescence (ELF)-labeled cells, while only a few diatoms and chrysophytes were labeled with ELF. Among the dinoflagellates, Protoperidinium spp. and Karenia mikimotoi had the highest percentages of ELF-labeled cells (84 and 82 %, respectively), whereas Gonyaulax spp. and Dinophysis spp. had the lowest percentages of labeled species (17 and 21 %, respectively). An alkaline phosphatase (AP) kinetic experiment was performed during 2005, with a turnover time of 10 h and a maximum potential velocity of 206.1 nmol l(-1) h(-1). The present results showed that severe phosphorus (P) stress occurred during springs in the study area, in particular when Prorocentrum donghaiense bloomed during 2003. AP played an important role in hydrolyzing soluble nonreactive phosphorus. The dominant dinoflagellates, which suffered more severe P stress compared to the diatoms, were the major AP producers during the spring of 2005, and differences in physiological P status existed among different dinoflagellate species.

Orbital-scale stratigraphy and high-resolution analysis of biogenic components and deep-water oxygenation conditions in the Japan Sea during the last 640 kyr

Paleoceanographic conditions in the Japan Sea changed drastically during the Late Quaternary in association with orbital and suborbital cycles and glacio-eustatic sea level changes. However, few studies have examined long-term sediment records older than 160 ka because of the lack of long and continuous cores and the difficulty in constructing high-resolution age models. In this study, we first constructed an orbital-scale stratigraphy of the sediments covering the last 640 kyr by comparing the SPECMAP ∂ 18O curve and the ∂ 18O curve of planktonic foraminifera ( ∂ 18O pf) in the Japan Sea together with the combination zones of dominant planktonic foraminifera species. Then, we reconstructed temporal variations in biogenic silica (BioSil) and biogenic carbonate (BioCarb) contents calculated from high-resolution major element analysis data determined by an XRF microscanner. In order to evaluate the deep-water oxygenation conditions, we also defined excess S as the difference between the content of S in the sediments and that for normal marine sediments calculated from the organic carbon content (C org) estimated from lightness ( L ⁎) by assuming a total sulfur content (S total)/C org ratio of 0.36, and examined its variability. BioSil shows orbital-scale variation and is generally low except during interglacial maxima when global sea level was high enough to allow a strong influx of the Tsushima Warm Current. BioCarb shows orbital- and suborbital-scale variations and tends to be higher in dark layers deposited during glacial stages, whereas the relationship is reversed during interglacial stages. The low BioCarb in dark layers deposited during interglacial stages is probably due to dissolution of biogenic carbonate caused by the increase in surface productivity as a result of the strong influx of nutrient rich East China Sea Coastal Water and consequent increase in surface productivity and decomposition rate of organic matter in the intermediate water. Excess S tends to be higher in thicker dark layers deposited during glacial maxima when the sea level dropped below − 90 m compared to adjacent light layers, suggesting development of euxinic deep-water conditions during these periods. The results demonstrated the presence of orbital- and suborbital-scale variations in BioSil and BioCarb and their association with dark and light layers in the Japan Sea that reflect variations in the nature and strength of inflow through the Tsushima Strait controlled by both climatic and sea level changes, whereas higher excess S reflects the development of euxinic deep-water condition during glacial maxima in association with glacio-eustatic sea level drops below − 90 m during the last 640 kyr.

The composition and bioavailability of phosphorus transport through the Changjiang (Yangtze) River during the 1998 flood

Water and suspended sediment (SS) samples were collected from the Changjiang River at the Datong Hydrological Station (DHS), five times from May 1997 through January 1999 in order to evaluate transport, composition and bioavailability of phosphorus (P) during a 1998 flood. Transport of most of the phosphorus compositions was substantially higher during the 1998 flood than at other sampling dates. Phosphorus associated with suspended sediment (TPP) accounted for more than 85% of total phosphorus (TP) transport during periods of preflood and flood. The high transport of TPP during the flood was due to unusually high concentrations of TPP and sediment discharge. The potentially bioavailable phosphorus in SS (PBAP) accounted for about 10% of TPP. PBAP with dissolved inorganic phosphorus (DIP) consisted of 15–89% of TP. For all the sampling dates, the concentrations of potential bioavailable phosphorus (BAP) ranged from 0.035–0.08 mg L−1, significantly higher than the limiting concentration for eutrophication. Therefore, the increasing temporal trends of TP concentration and high bioavailability of TP appear to support more frequent algal blooms in receiving East China Sea coastal waters in recent years. Hence, the underestimate of TPP transport by large rivers may also underestimate the biogeochemical cycling of other associated nutrients, such as nitrogen and carbon.

Land‐ocean linkages over orbital and millennial timescales recorded in Late Quaternary sediments of the Japan Sea

Late Quaternary sediments of the Japan Sea are characterized by centimeter‐ to meter‐scale alternations of dark and light layers which are synchronous basinwide. High‐resolution analyses of the sediments from Ocean Drilling Program site 797 reveal that deposition of the meter‐scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio‐eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the Tsushima Strait. The centimeter‐ to decimeter‐scale alternations reflect millennial‐scale variations which are possibly associated with Dansgaard‐Oeschger (D‐O) cycles, with each dark layer appearing to correspond to an interstadial. This variability is attributed to the development of a humid climate in central to eastern Asia and the consequent increase in discharge from the Huanghe and Changjiang Rivers during interstadials. This caused expansion of the East China Sea coastal water (ECSCW), which penetrated more strongly into the Japan Sea. The increased influence of the lower‐salinity, nutrient‐enriched ECSCW reduced deep water ventilation and enhanced the surface productivity, leading to the development of anoxic bottom waters and deposition of the dark layers. Thus the centimeter‐ to decimeter‐scale alternations of the dark and light layers record wet and dry cycles in central to eastern Asia possibly associated with D‐O cycles.