Evolution of freshwater plumes and salinity fronts in the northern Bay of Bengal

[1] The evolution of freshwater plumes and the associated salinity fronts in the northern Bay of Bengal ( henceforth the bay) is studied using rotated empirical orthogonal function (REOF) analysis and extended associate pattern analysis (EAPA). The results show that sea surface salinity distribution is featured by eastern-bay and western-bay plumes in the northern bay during different seasons. The western-bay plume begins in early July, peaks in late August, and then turns into a bay-shaped plume with the two plumes in either side of the bay, which peaks in late October. The southward extension of the western-bay plume can be explained by the southwestward geostrophic flow associated with the cyclonic gyre in the northern bay, which counters the northeastward Ekman drift driven by wind stress. The offshore expansion of the western-bay plume is induced by the offshore Ekman drift which also produces a salinity front near the east coast of India. The bay-shaped plume appears when the cyclonic gyre shifts westward and a weak anticyclonic gyre occupies the northeastern bay. As the season advances, the western part of the bay-shaped plume decays while the eastern part persists until the following June, which is believed to be associated with the anticyclonic gyre in the northern bay. The evolution of the plumes except the eastern part of the bay-shaped plume in fall can be partly explained by the seasonal variation of mass transport associated with the Sverdrup balance. The fact that the western-bay (eastern-bay) plume appears when surface freshwater flux in the northeastern bay increases ( decreases) dramatically suggests that the plumes are not produced directly by surface freshwater flux. River discharge seems to be the freshwater source for the plumes and has little to do with the evolution of the plumes.

Distribution patterns of chlorophyll a in spring and autumn in association with hydrological features in the southern Yellow Sea and northern East China Sea

Two field studies were conducted to measure pigments in the Southern Yellow Sea (SYS) and the northern East China Sea (NECS) in April (spring) and September (autumn) to evaluate the distribution pattern of phytoplankton stock (Chl a concentration) and the impact of hydrological features such as water mass, mixing and tidal front on these patterns. The results indicated that the Chl a concentration was 2.43 +/- 2.64 (Mean +/- SD) mg m(-3) in April (range, 0.35 to 17.02 mg m(-3)) and 1.75 +/- 3.10 mg m(-3) in September (from 0.07 to 36.54 mg m(-3)) in 2003. Additionally, four areas with higher Chl a concentrations were observed in the surface water in April, while two were observed in September, and these areas were located within or near the point at which different water masses converged (temperature front area). The distribution pattern of Chl a was generally consistent between onshore and offshore stations at different depths in April and September. Specifically, higher Chl a concentrations were observed along the coastal line in September, which consisted of a mixing area and a tidal front area, although the distributional pattern of Chl a concentrations varied along transects in April. The maximum Chl a concentration at each station was observed in the surface and subsurface layer (0-10 m) for onshore stations and the thermocline layer (10-30 m) for offshore stations in September, while the greatest concentrations were generally observed in surface and subsurface water (0-10 m) in April. The formation of the Chl a distributional pattern in the SYS and NECS and its relationship with possible influencing factors is also discussed. Although physical forces had a close relationship with Chl a distribution, more data are required to clearly and comprehensively elucidate the spatial pattern dynamics of Chl a in the SYS and NECS.

INVOLVEMENT OF CA(2+) SIGNALING PATHWAY DURING OOCYTE MATURATION OF THE NORTHERN QUAHOG MERCENARIA MERCENARIA

In many molluses, it has been found that Ca2+ signaling pathway is involved in the resumption of meiotic maturation in oocytes. To better understand the possible role of Ca2+ signaling pathway in regulating meiotic maturation in oocytes of the northern quahog Mercenaria mercenaria, free extracellular Ca2+, A23187 (calcium ionophore), verapamil (calcium channel blocker), and trifluoperazin (calmodulin antagonist) were used to incubate oocytes or serotonin-induced oocytes by pharmacological methods. Results show that extracellular Ca2+ (50 similar to 200 mM) and A23187 (1 similar to 10 mu M) can stimulate the meiotic maturation. In addition, verapamil (1 similar to 100 mu M) and trifluoperazin (10 similar to 1,000 mu M) could inhibit serotonin-induced oocyte maturation. Therefore, Ca2+ is essential for the reinitiation of meiotic maturation in oocytes of the northern quahog. Moreover, an increase i [Ca2+]i can promote meiotic maturation.

Onshore-offshore variations of copepod community in northern South China Sea

Copepod communities in onshore and offshore waters show a gradient from primarily near shore to primarily oceanic species. Understanding the transition between these communities is fundamental to determining the range of coastal influence. Copepod communities in the northern South China Sea (nSCS) were studied based on samples collected by vertically towing a net in 10 February-6 March (winter) and 26 August-6 September (summer) of 2004. Calanoida species richness, total copepod abundance, Shannon-Weaver diversity index, and onshore-offshore occurrence of dominant species showed obvious change from onshore to offshore waters. Although the offshore stations had lower abundance than the shelf stations, they had more species and larger diversity index. Abundance of some species (groups) with dominance index > 5% (Calanus sinicus, Euchaeta spp., Temora spp., Paracalanus parvus, and Subeucalanus subtenuis) declined from onshore to offshore waters. Warm water species (Pleuromamma abdominalis, P. gracilis, and P. robusta) occurred in offshore waters in both cruises. Station (q-type) cluster analysis in winter and summer separated copepod community into onshore and offshore communities at similar to 40% level of similarity. The two communities were divided at the position of similar to 100-m isobath. In summer, C. sinicus occurred in the upwelling area east of Hainan Island, indicating the presence of an oversummering stock of this species.

Sources and transport of dissolved and particulate organic carbon in the Mississippi River estuary and adjacent coastal waters of the northern Gulf of Mexico

Dissolved organic carbon (DOC), stable carbon isotopic (delta(13)C) compositions of DOC and particulate organic carbon (POC), and elemental C/N ratios of POC were measured for samples collected from the lower Mississippi and Atchafalaya rivers and adjacent coastal waters in the northern Gulf of Mexico during the low flow season in June 2000 and high flow season in April 2001. These isotopic and C/N results combined with DOC measurements were used to assess the sources and transport of terrestrial organic matter from the Mississippi and Atchafalaya rivers to the coastal region in the northern Gulf of Mexico. delta(13)C values of both POC (-23.8parts per thousand to -26.8parts per thousand) and DOC (-25.0parts per thousand to -29.0parts per thousand) carried by the two rivers were more depleted than the values measured for the samples collected in the offshore waters. Strong seasonal variations in delta(13)C distributions were observed for both POC and DOC in the surface waters of the region. Fresh water discharge and horizontal mixing played important roles in the distribution and transport of terrestrial POC and DOC offshore. Our results indicate that both POC and DOC exhibited non-conservative behavior during the mixing especially in the mid-salinity range. Based on a simple two end-member mixing model, the comparison of the measured DOC-delta(13)C with the calculated conservative isotopic mixing curve indicated that there was a significant in situ production of marine-derived DOC in the mid- to high-salinity waters consistent with our in situ chlorophyll-a measurements. Our DOC-delta(13)C data suggest that a removal of terrestrial DOC mainly occurred in the high-salinity (>25) waters during the mixing. Our study indicates that the mid- to high- (10-30) salinity range was the most dynamic zone for organic carbon transport and cycling in the Mississippi River estuary. Variability in isotopic and elemental compositions along with variability in DOC and POC concentrations suggest that autochthonous production, bacterial utilization, and photo-oxidation could all play important roles in regulating and removing terrestrial DOC in the northern Gulf of Mexico and further study of these individual processes is warranted. (C) 2004 Elsevier B.V. All rights reserved.

Density-dependent effects on seston dynamics and rates of filtering and biodeposition of the suspension-cultured scallop Chlamys farreri in a eutrophic bay (northern China): An experimental study in semi-in situ flow-through systems

Effects of stocking density on seston dynamics and filtering and biodeposition by the suspension-cultured Zhikong scallop Chlamys farreri Jones et Preston in a eutrophic bay (Sishili Bay, northern China), were determined in a 3-month semi-field experiment with continuous flow-through seawater from the bay. Results showed that the presence of the scallops could strongly decrease seston and chlorophyll a concentrations in the water column. Moreover, in a limited water column, increasing scallop density could cause seston depletion due to scallop's filtering and biodeposition process, and impair scallop growth. Both filtration rate and biodeposition rate of C. farreri showed significant negative correlation with their density and positive relationship with seston concentration. Calculation predicts that the daily removal of suspended matter from water column by the scallops in Sishili Bay ecosystem can be as high as 45% of the total suspended matter; and the daily production of biodeposits by the scallops in early summer in farming zone may amount to 7.78 g m(-2), with daily C, N and P biodeposition rates of 3.06 x 10(-1), 3.86 x 10(-2) and 9.80 x 10(-3) g m(-2), respectively. The filtering and biodeposition by suspension-cultured scallops could substantially enhance the deposition of total suspended particulate material, suppress accumulation of particulate organic matter in water column, and increase the flux of C, N and P to benthos, strongly enhancing pelagic-benthic coupling. It was suggested that the filtering-biodeposition process by intensively suspension-cultured bivalve filter-feeders could exert strong top-down control on phytoplankton biomass and other suspended particulate material in coastal ecosystems. This study also indicated that commercially suspension-cultured bivalves may simultaneously and potentially aid in mitigating eutrophication pressures on coastal ecosystems subject to anthropogenic N and P loadings, serving as a eutrophic-environment bioremediator. The ecological services (e.g. filtering capacity, top-down control, and benthic-pelagic coupling) functioned by extractive bivalve aquaculture should be emphasized in coastal ecosystems. (c) 2005 Elsevier B.V. All rights reserved.

Some palaemonid shrimps (Crustacea : Decapoda) from northern South China Sea, with descripitions of two new species

Thirty-four palaemonid species from the northern area of South China Sea are reported in the present paper, including two new species, Paranchistus lini, new species, and Periclimenes chacei, new species, and eight other species are reported for the first time from South China Sea: Leander tenuicornis (Say, 1818), Leandrites stenopus Holthuis, 1950, Palaemon debilis Dana, 1852, Urocaridella antonbrurnii (Bruce, 1967), Kemponia platycheles (Holthuis, 1952), Paraclimenes franklini (Bruce, 1990b), Paranchistus spondylis Suzuki, 1971, Periclimenes hirsutus Bruce, 1971.

A new three-phase culture method for Manila clam, Ruditapes philippinarum, farming in northern China

Studies on reproduction, hatchery management, and culture of Manila clams Ruditapes philippinarum were carried out in an attempt to optimize their culture conditions and techniques. Results from these studies led to the development of a three-phase culture method for Manila clam farming in northern China. The key components of the new method were: 1) early spawning and over-wintering indoors (greenhouse); 2) optimized larval culture conditions and techniques; 3) juvenile rearing in shallow, fertilized nursery ponds; 4) optimized stocking size and density and substrate for mudflat grow out. Broodstock were maturated indoors for a month from early April to early May. Primarily because of higher water temperatures in the greenhouse the clams spawned more than one month earlier than in the natural environment. From May to July, juveniles were reared for 1-2 months indoors to a size of 2.0-3.0 mm in shell length before being moved to outdoor, pre-disinfected, nursery ponds. Juveniles were then reared in the nursery ponds for one month to about 1.0 cm before being transferred to the mudflat for grow out. Juvenile clams in nursery ponds grew considerably faster than in the natural environment probably because of higher temperatures and more abundant natural food. During grow out, the clams were reared for 4-7 months until they reached a market size (3.0-3.3 cm). Juveniles produced after August were over-wintered in the greenhouse in which the water temperature was about 3 degrees C higher than that of the outdoor environment. Juveniles grew at an average rate of > 20 mu m day(-1), while in the natural environment no growth was observed during winter because of low temperatures. Juveniles in the greenhouse grew to 2-3 mm by the following March before being moved into outdoor nursery ponds. The three-phase culture method not only shortened the production period from spawn to market size from 24-36 months to about 10-14 months, but also prolonged the spawning season from 2 to 7 months, resulting in increased production of seed and market-size clams. Compared with the traditional method, the new method could increase the yield of market-size clams by 10-11 times, and increase the profit per ha mudflat by as much as 124 times and the profit per kg market-size clams produced by 13 times. (c) 2006 Elsevier B.V. All rights reserved.

Spatial and temporal relationships between precipitation and ANPP of four types of grasslands in northern China

Precipitation is considered to be the primary resource limiting terrestrial biological activity in water-limited regions. Its overriding effect on the production of grassland is complex. In this paper, field data of 48 sites (including temperate meadow steppe,temperate steppe, temperate desert steppe and alpine meadow) were gathered from 31 published papers and monographs to analyze the relationship between above-ground net primary productivity (ANPP) and precipitation by the method of regression analysis. The results indicated that there was a great difference between spatial pattern and temporal pattern by which precipitation influenced grassland ANPP. Mean annual precipitation (MAP) was the main factor determining spatial distribution of grassland ANPP (r~2 = 0.61,P ＜ 0.01); while temporally, no significant relationship was found between the variance of AN PP and inter-annual precipitation for the four types of grassland. However, after dividing annual precipitation into monthly value and taking time lag effect into account, the study found significant relationships between ANPP and precipitation. For the temperate meadow steppe, the key variable determining inter-annual change of ANPP was last August-May precipitation (r~2= 0.47, P = 0.01); for the temperate steppe, the key variable was July precipitation (r~2 = 0.36, P = 0.02); for the temperate desert steppe, the key variable was April-June precipitation (r~2 = 0.51, P ＜0.01); for the alpine meadow, the key variable was last September-May precipitation (r~2 = 0.29, P ＜ 0.05). In comparison with analogous research, the study demonstrated that the key factor determining inter-annual changes of grassland ANPP was the cumulative precipitation in certain periods of that year or the previous year.

Phylogeography of Pinus tabulaeformis Carr. (Pinaceae), a dominant species of coniferous forest in northern China

How coniferous trees in northern China changed their distribution ranges in response to Quaternary climatic oscillations remains largely unknown. Here we report a study of the phylogeography of Pinus tabulaeformis, an endemic and dominant species of coniferous forest in northern China. We examined sequence variation of maternally inherited, seed-dispersed mitochondrial DNA (mtDNA) (nad5 intron 1 and nad4/3-4) and paternally inherited, pollen- and seed-dispersed chloroplast DNA (cpDNA) (rpl16 and trnS-trnG) within and among 30 natural populations across the entire range of the species. Six mitotypes and five chlorotypes were recovered among 291 trees surveyed. Population divergence was high for mtDNA variation (G(ST) = 0.738, N-ST = 0.771) indicating low levels of seed-based gene flow and significant phylogeographical structure (N-ST > G(ST), P < 0.05). The spatial distribution of mitotypes suggests that five distinct population groups exist in the species: one in the west comprising seven populations, a second with a north-central distribution comprising 15 populations, a third with a southern and easterly distribution comprising five populations, a fourth comprising one central and one western population, and a fifth comprising a single population located in the north-central part of the species' range. Each group apart from the fourth group is characterized by a distinct mitotype, with other mitotypes, if present, occurring at low frequency. It is suggested, therefore, that most members of each group apart from Group 4 are derived from ancestors that occupied different isolated refugia in a previous period of range fragmentation of the species, possibly at the time of the Last Glacial Maximum. Possible locations for these refugia are suggested. A comparison of mitotype diversity between northern and southern subgroups within the north-central group of populations (Group 2) showed much greater uniformity in the northern part of the range both within and between populations. This could indicate a northward migration of the species from a southern refugium in this region during the postglacial period, although alternative explanations cannot be ruled out. Two chlorotypes were distributed across the geographical range of the species, resulting in lower levels of among-population chlorotype variation. The geographical pattern of variation for all five chlorotypes provided some indication of the species surviving past glaciations in more than one refugium, although differentiation was much less marked, presumably due to the greater dispersal of cpDNA via pollen.

Diurnal and seasonal variations of UV radiation on the northern edge of the Qinghai-Tibetan Plateau

We monitored UVA, UVB, and solar radiation from August 2001 to 2003 on the northern Qinghai-Tibetan Plateau to characterize the diurnal and seasonal variations of UV radiation on the world's highest plateau. Daily UVB radiation and the ratio of UVB to total solar radiation increased significantly when the atmospheric ozone concentration decreased as estimated by the total ozone mapping spectrometer (TOMS), as well as when cloud coverage decreased. The UVB/UVA ratio also showed a significant increase when the TOMS ozone concentration decreased in the morning. The seasonal variation pattern of UVB, however, was closely correlated with solar elevation but was little affected by the seasonal pattern of the atmospheric ozone amount. Compared to observations from the central plateau, the magnitude of the UVB increase attributed to ozone depletion was smaller at the northern edge. The study suggests that the temporal variation of ground UV radiation is determined by both solar elevation and the ozone amount, but the spatial difference on the plateau is likely to be ascribed mainly to the spatial variation of the ozone amount. (c) 2007 Published by Elsevier B.V.