Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi: I. Formation, settling velocities and physical properties of aggregates

To investigate the role of ballasting by biogenic minerals in the export of organic matter in the ocean, a laboratory experiment was conducted comparing aggregate formation and settling velocity of non-calcifying and calcifying strains of the coccolithophore Emiliania huxleyi. Experiments were conducted by making aggregates using a roller table and following aggregate properties during incubation for a period of 40 days. Size, shape, and settling velocities of aggregates were described by image analysis of video pictures recorded during the roller tank incubation. Our results show that biogenic calcite has a strong effect on the formation rate and abundance of aggregates and on aggregate properties such as size, excess density, porosity, and settling velocity. Aggregates of calcifying cells (AGG_CAL) formed faster, were smaller and had higher settling velocities, excess densities, and mass than those of non-calcifying cells (AGG_NCAL). AGG_CAL showed no loss during the duration of the experiment, whereas AGG_NCAL decreased in size after 1 month of incubation. Potential mechanisms that can explain the different patterns in aggregate formation are discussed. Comparison of settling velocities of AGG_CAL and AGG_NCAL with aggregates formed by diatoms furthermore indicated that the ballast effect of calcite is greater than that of opal. Together these results help to better understand why calcite is of major importance for organic matter fluxes to the deep ocean.     

Iron availability and the release of iron-complexing ligands by Emiliania huxleyi

The ubiquitous algal species, Emiliania huxleyi, was incubated in sea water supplemented only with nitrate and phosphate (N and P) without chelating agents to control metal speciation. Growth was slow in a “low-iron” culture containing 1.3 nM iron and was found to be iron-limited, growth-accelerating when a 1-nM iron addition was made. The growth rate in a “high-iron” culture (5.4 nM iron) was greater, reaching 0.4 div day⁻¹ but this culture too was found to have become iron-limited when a 9-nM iron addition was made on day 17 of the incubation. Both cultures were found to release iron-complexing ligands in excess of the iron concentration, 6 nM in the low-iron culture, and 10 nM in the high-iron culture. More ligands were produced after the iron addition taking the ligand concentration to 11 nM in the low-iron culture. The data show that the ligands are released in response to the iron addition, when at least some of the iron had already been taken up. This type of release is contrary to the concept of a siderophore, which is supposed to be released in periods of lack of iron; however the increase in the ligand concentration is similar to that released by the natural community in response to the iron addition in the IRON-EX II experiment [Rue, E.L., Bruland, K.W., 1997. The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experiment. Limnol. Oceanogr. 42, 901–910]. The enhanced growth in the cultures when more iron was added indicated that the organically complexed iron present in the cultures was not immediately available to the organisms (or at least not at sufficiently high rate), and that the organisms responded to freshly added, inorganic, iron.     

依据减数分裂相关基因数量判别赫氏球石藻(Emiliania huxleyi)繁殖方式研究

繁殖方式是生物重要生物学特征之一。了解生物繁殖方式对遗传和育种研究具有重要意义。赫氏球石藻(Emiliania huxleyi)呈世界性分布,在生态系统中扮演重要角色,但其繁殖方式未知。本研究用分子系统学方法确定有基因组序列且行有性生殖的真核生物的减数分裂相关基因数量,建立了"减数分裂相关基因≥19个,其中减数分裂特异基因≥5个"的有性生殖判别标准;发现赫氏球石藻具有25个减数分裂相关基因,包括6个减数分裂特异基因。依据建立的标准判定赫氏球石藻行有性生殖。研究结果将有助于赫氏球石藻生活史和遗传学研究。     

The hydrography and biology of a bloom of the coccolithophorid Emiliania huxleyi in the northern North Sea

In June/July 1994 a study was made of a small bloom of the coccolithophorid Emiliania huxleyi in an area of the North Sea to the east of the Shetland Islands. Observations on the hydrography of the study area indicated the bloom was associated with Atlantic water and was confined to an area in which a stable shallow mixed layer had formed. There was no evidence to suggest association of horizontal physical structure with the bloom development. High cell densities of >1– cells dm⁻³, together with low concentrations of PIC (<50 μg dm⁻³) and detached liths (2– liths cm⁻³) indicated that the bloom was studied at an early stage of development. Biochemical and physiological observations indicated active growth was taking place. The results presented are discussed in comparison with previous studies carried out in both oceanic and shelf seas.     

Effects of virus infection on expression of cell cycle regulatory proteins in the unicellular marine algae Emiliania huxleyi

The authors have investigated the biochemical events by which marine algal virus infection induces cell cycle arrest. The key G₂/M-phase regulatory proteins are analyzed by immunobloting in unicellular Emiliania huxleyi, suggesting that virus induced cell cycle arrest is related with virus''s effect on cyclins and cyclin dependent kinases. E. huxleyi virus (EhV) represses Cdc2/cyclinB complex activity by inhibiting the activity of Cdc2 kinase in a phosphorylation-related manner, blocking host cells G₂/M checkpoint. Dephosphorylated/inactive Cdc25C combined with up-regulation of Wee1 expression at early infect period appears to be important mechanisms by which EhV represses Cdc2/cyclinB complex activity that is required for entry into M phase. This study has allowed us to confirm that algal virus infection leads to selective activation or inhibition of certain cell-cycle factors, which may play a significant role in establishing a more efficient environment for viral gene expression and DNA replication.     

Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δN, δ and δ

Sinking particles were analyzed for their nitrogen isotopic ratio δ¹⁵N) of total particulate nitrogen (PN), stable carbon isotopic ratio (δ¹³C) and radioactive isotopic ratio (δ¹⁴C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ¹⁵N and δ¹³C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ¹⁵N and δ¹³C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ¹⁴C of sinking POC. After this correction, common downward decreasing trends in δ¹⁵N and δ¹³C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ¹⁵N and δ¹³C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of ¹⁵N- and ¹³C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.     

Phytoplankton growth, microzooplankton herbivory and community structure in the southeast Bering Sea: insight into the formation and temporal persistence of an Emiliania huxleyi bloom

Using the seawater dilution technique, we measured phytoplankton growth and microzooplankton grazing rates within and outside of the 1999 Bering Sea coccolithophorid bloom. We found that reduced microzooplankton grazing mortality is a key component in the formation and temporal persistence of the Emiliania huxleyi bloom that continues to proliferate in the southeast Bering Sea. Total chlorophyll a (Chl a) at the study sites ranged from 0.40 to 4.45 μg C l⁻¹. Highest phytoplankton biomass was found within the bloom, which was a mixed assemblage of diatoms and E. huxleyi. Here, 75% of the Chl a came from cells >10 μm and was attributed primarily to the high abundance of the diatom Nitzschia spp. Nutrient-enhanced total phytoplankton growth rates averaged 0.53 d⁻¹ across all experimental stations. Average growth rates for >10 μm and <10 μm cells were nearly equal, while microzooplankton grazing varied among stations and size fractions. Grazing on phytoplankton cells >10 μm ranged from 0.19 to 1.14 d⁻¹. Grazing on cells <10 μm ranged from 0.02 to 1.07 d⁻¹, and was significantly higher at non-bloom (avg. 0.71 d⁻¹) than at bloom (avg. 0.14 d⁻¹) stations. Averaged across all stations, grazing by microzooplankton accounted for 110% and 81% of phytoplankton growth for >10 and <10 μm cells, respectively. These findings contradict the paradigm that microzooplankton are constrained to diets of nanophytoplankton and strongly suggests that their grazing capability extends beyond boundaries assumed by size-based models. Dinoflagellates and oligotrich ciliates dominated the microzooplankton community. Estimates of abundance and biomass for microzooplankton >10 μm were higher than previously reported for the region, ranging from 22,000 to 227,430 cells l⁻¹ and 18 to 164 μg C l⁻¹. Highest abundance and biomass occurred in the bloom and corresponded with increased abundance of the large ciliate Laboea, and the heterotrophic dinoflagellates Protoperidinium and Gyrodinium spp. Despite low grazing rates on phytoplankton <10 μm within the bloom, the abundance and biomass of small microzooplankton (<20 μm) capable of grazing E. huxleyi was relatively high at bloom stations. This body of evidence, coupled with observed high grazing rates on large phytoplankton cells, suggests the phytoplankton community composition was strongly regulated by herbivorous activity of microzooplankton. Because grazing behavior deviated from size-based model predictions and was not proportional to microzooplankton biomass, alternate mechanisms that dictate levels of grazing activity were in effect in the southeastern Bering Sea. We hypothesize that these mechanisms included morphological or chemical signaling between phytoplankton and micrograzers, which led to selective grazing pressure.     

Benthic remineralization and burial of biogenic SiO2, CaCO3, organic carbon, and detrital material in the Southern Ocean along a transect at 170° West

We investigated the composition, recycling, and mass accumulation rates of sediments along a transect in the Southern Ocean located from 66°S to 57°S at 170°W. This transect also corresponds to the location of a sediment trap mooring line. The sediments at the seven sites studied range from largely terrigenous material to nearly pure (>90%) biogenic silica. CaCO₃ is a minor but persistent component at most sites. Mass accumulation rates have been determined on the basis of excess ²³⁰Th in the sediments, i.e., ²³⁰Th-normalized accumulation rates. The influence of redistribution of sediments on the sea floor has been estimated from ¹⁴C analyses. The recycling of material delivered to the sediments has been characterized on the basis of pore water studies that make extensive use of both in situ sampling and shipboard extractions. The influence of the highly variable rates of input of particulate matter that characterize much of the Southern Ocean upon pore water gradients and fluxes across the sediment water interface has been considered.We find only poor correspondence between BSiO₂ burial fraction (=burial/particulate flux), a quantifiable measure of preservation efficiency, and BSiO₂ particulate rain along the transect. However, preservation does appear to be closely linked to a combination of sedimentation rate and particulate rain.The burial fraction of BSiO₂ is small relative to benthic rain (5–19%). Despite the small fraction buried, burial flux normalized to (sedimentation rate)^1/2 appears to provide a very consistent means of predicting benthic particulate rain over a large range of rain rates, including data from a number of different studies and environments. At sites with BSiO₂ rain 250 mmol m⁻² yr⁻¹ the average difference between predicted and observed rain is 25–30%. Such rain rates occur in many marine areas, particularly the Southern Ocean, with the result that this relationship potentially provides a means of estimating BSiO₂ benthic rain over prolonged periods in the past on the basis of readily measured sediment parameters.At the southern-most deep ocean station, the particulate flux was characterized by an extremely high C_org/CaCO₃ ratio (>10), but this high ratio does not appear to have a substantial influence on CaCO₃ burial. CaCO₃ is preserved in the sediments at this site despite a particulate flux with a 10-fold excess of C_org above that required for complete dissolution in the sediments. The unexpectedly high preservation of CaCO₃ is due largely to the very steep C_org oxidation rate profile at this site. As a result, a large fraction of the organic matter oxidized in the sediments does so in close proximity to the sediment–water interface where most of the metabolic CO₂ is neutralized by CO₃²⁻ from the overlying water, rather than by the dissolution of sedimentary CaCO₃.Diagenetic modeling indicates that at several of the stations, the remineralization fluxes of carbonate species across the sediment–water interface may not have been at steady state as a result of the highly pulsed nature of particulate rain in this environment. We estimate that at the time of our sampling it is possible that near-interface fluxes could have been a factor of 1.6–2 times the annual average.At every site on the transect, the burial fluxes of detrital material are substantially greater than the detrital particulate rain measured in the sediment traps, by as much as a factor of 40. Detrital burial is bimodal, being greatest at the southern and northern extremes of the transect. We postulate that the excess of burial over particulate rain in the south reflects the contribution of ice rafted debris at these high latitudes. Increases in the supply at the northern stations must have a different source. We believe that the excess at these stations is material eroded from the sea floor to the west, possibly on the Campbell Plateau, and advected by currents to the northern portion of the transect at depths below the shallow traps.     

Modelling phytoplankton succession on the Bering Sea shelf: role of climate influences and trophic interactions in generating Emiliania huxleyi blooms 1997–2000

Several years of continuous physical and biological anomalies have been affecting the Bering Sea shelf ecosystem starting from 1997. Such anomalies reached their peak in a striking visual phenomenon: the first appearance in the area of bright waters caused by massive blooms of the coccolithophore Emiliania huxleyi (E. huxleyi). This study is intended to provide an insight into the mechanisms of phytoplankton succession in the south-eastern part of the shelf during such years and addresses the causes of E. huxleyi success by means of a 2-layer ecosystem model, field data and satellite-derived information. A number of potential hypotheses are delineated based on observations conducted in the area and on previous knowledge of E. huxleyi general ecology. Some of these hypotheses are then considered as causative factors and explored with the model. The unusual climatic conditions of 1997 resulted most notably in a particularly shallow mixed layer depth and high sea surface temperature (about 4 °C above climatological mean). Despite the fact that the model could not reproduce for E. huxleyi a clear non-bloom to bloom transition (pre- vs. post-1997), several tests suggest that this species was favoured by the shallow mixed layer depth in conjunction with a lack of photoinhibition. A top-down control by microzooplankton selectively grazing phytoplankton other than E. huxleyi appears to be responsible for the long persistence of the blooms. Interestingly, observations reveal that the high N:P ratio hypothesis, regarded as crucial in the formation of blooms of this species in previous studies, does not hold on the Bering Sea shelf.     

Dry bulk density and CaCO3 relationships in upper Quaternary sediments of the eastern equatorial Pacific

Results from 1110 paired CaCO₃ and bulk density measurements from cores raised from the eastern equatorial Pacific permit formulation of well constrained CaCO₃-DBD relationships for that region. The cores lie along a N-S transect at 110°W from 10°N to 3°S underneath the different currents of the equatorial current system and along an E-W transect from 110° to 90°W, at approximately 3°S. Two distinct, crescent-shaped dry bulk density-CaCO₃ relationships are observed. For equal CaCO₃ percentages, sediments from those sites at 110°W, which are situated in the high productivity zone, have lower dry bulk density. Cores raised from closer to shore have relatively greater DBD.     

Carbonate chemistry and projected future changes in pH and CaCO3 saturation state of the South China Sea

To study the dissolved carbonate system in the South China Sea (SCS) and to understand the water mass exchange between the SCS and the West Philippine Sea (WPS), pH, total alkalinity and total CO₂ were measured aboard the R/V Ocean Researcher 1. Because of the sill that separates these two seas in the Luzon Strait with a maximum depth of 2200 m, the SCS Deep Water has characteristics similar to those of water at about 2200 m in the WPS. The minimum pH and the maxima of normalized alkalinity and total CO₂ commonly found in the open oceans at mid-depth also prevail in the WPS but are, however, very weak in the SCS. Rivers and inflows from Kuroshio Surface and Deep Waters through the Luzon Strait as well as those through the Mindoro Strait transport carbon to the SCS year-round. Meanwhile, the outflowing Taiwan Strait water as well as the SCS Surface and Intermediate Waters of the Luzon Strait transports carbon out of the SCS year-round. The Sunda Shelf is also a channel for carbon transport into the SCS in the wet season and out of the SCS in the dry season.fCO₂ data and mass balance calculations indicate that the SCS is a weak CO₂ source in the wet season but an even weaker CO₂ sink in the dry season. With these facts taken together, the SCS is likely a very weak CO₂ source. Anthropogenic CO₂ penetrates to about 1500 m in depth in the SCS, and the entire SCS contains 0.60 ± 0.15 × 10¹⁵ g of excess carbon. Typical profiles of pH as well as the degree of saturation of each of calcite and aragonite in 1850 and 1997 are presented, and those for 2050 AD are projected. The maximum decrease in pH is estimated to be 0.16 pH units in the surface layer when the amount of CO₂ is doubled. It is anticipated that aragonite in the upper continental slope will likely start to dissolve, thereby neutralizing excess CO₂ by around 2050 AD. This paper is unique in that it presents the results of the first attempt ever to estimate the past, present and future physico-chemical properties of the world's largest marginal sea.     

Stable carbon isotope distribution of particulate organic matter in the ocean: a model study

The stable carbon isotopic composition of particulate organic matter in the ocean, δ¹³C_POC, shows characteristic spatial variations with high values in low latitudes and low values in high latitudes. The lowest δ¹³C_POC values (−32‰ to −35‰) have been reported in the Southern Ocean, whereas in arctic and subarctic regions δ¹³C_POC values do not drop below −27‰. This interhemispheric asymmetry is still unexplained. Global gradients in δ¹³C_POC are much greater than in δ¹³C_DIC, suggesting that variations in isotopic fractionation during organic matter production are primarily responsible for the observed range in δ¹³C_POC. Understanding the factors that control isotope variability is a prerequisite when applying δ¹³C_POC to the study of marine carbon biogeochemistry. The present model study attempts to reproduce the δ¹³C_POC distribution pattern in the ocean. The three-dimensional (3D) Hamburg Model of the Oceanic Carbon Cycle version 3.1 (HAMOCC3.1) was combined with two different parametrizations of the biological fractionation of stable carbon isotopes. In the first parametrization, it is assumed that the isotopic fractionation between CO₂ in seawater and the organic material produced by algae, _P, is a function of the ambient CO₂ concentration. The two parameters of this function are derived from observations and are not based on an assumption of any specific mechanism. Thus, this parametrization is purely empirical. The second parametrization is based on fractionation models for microalgae. It is supported by several laboratory experiments. Here the fractionation, _P, depends on the CO₂ concentration in seawater and on the (instantaneous) growth rates, μ_i, of the phytoplankton. In the Atlantic Ocean, where most field data are available, both parametrizations reproduce the latitudinal variability of the mean δ¹³C_POC distribution. The interhemispheric asymmetry of δ¹³C_POC can mostly be attributed to the interhemispheric asymmetry of CO₂ concentration in the water. However, the strong seasonal variations of δ¹³C_POC as reported by several authors, can only be explained by a growth rate-dependent fractionation, which reflects variations in the cellular carbon demand.     

CO2加富培养对鼠尾藻克制赤潮异弯藻效果的影响

采用实验生态学的方法,研究了大型海藻鼠尾藻(Sargassum thunbergii)对赤潮微藻中肋骨条藻(Skeletonema costatum)的克生效应及其对 CO2加富的响应变化.结果表明,正常培养的鼠尾藻新鲜组织、干粉末和水溶性抽提液能够导致中肋骨条藻的细胞密度显著降低(P<0.05), CO2加富培养的鼠尾藻新鲜组织、干粉末和水溶性抽提液能够更加明显地抑制中肋骨条藻种群生长(P<0.01).实验结果证实鼠尾藻对中肋骨条藻具有克生效应,而 CO2加富培养引起了鼠尾藻对中肋骨条藻克生效应的变化,使其对中肋骨条藻生长的抑制作用显著加强.正常培养的鼠尾藻培养水过滤液能够显著抑制中肋骨条藻的生长(P<0.05),而 CO2加富培养的鼠尾藻培养水过滤液对中肋骨条藻的生长没有表现出明显的影响(P>0.05),因此推测 CO2加富培养可能改变了鼠尾藻对中肋骨条藻克生作用的方式,作用方式由分泌克生物质转变为细胞直接接触转递.     

Sources, pathways and sinks of particulate organic matter in Hudson Bay: Evidence from lignin distributions

Hudson Bay is a large, estuarine, shelf-like sea at the southern margin of the Arctic, where changes in seasonal ice cover and river discharge appear already to be underway. Here we present lignin data for dated sediments from eleven box cores and evaluate sources of terrigenous carbon, transport pathways, and whether terrigenous organic matter has been influenced by recent environmental change. Lignin yields (0.04 to 1.46 mg/100 mg organic carbon) decreased from the margin to the interior and from south to north, broadly reflecting the distribution of river inputs. Lignin compositional patterns indicated distinct regional sources with boreal forest (woody gymnosperm) vegetation an important source in the south, vs. tundra (non-woody angiosperm) in the north. Lignin patterns suggest redistribution of a fine-grained, mineral-associated fraction of the southern-derived terrigenous carbon to the northeast part of the Bay and ultimately into west Hudson Strait with the Bay's cyclonic coastal circulation. A small component of the carbon makes it to the central basins of Hudson Bay but most of the terrigenous organic material in that area appears to derive from resuspension of older, isostatically-rebounding coastal and inner shelf deposits. Most modern plant debris appears to be retained near river mouths due to hydrodynamic sorting, with the exception of the southwest inner shelf, where these materials extend > 30 km from shore. Temporal changes in the composition of terrigenous organic carbon recorded in most of the southern Hudson Bay cores perhaps reflect increases in erosion and cross-shelf transport from coastal deposits, possibly mediated by change in ice climate. In contrast, temporal changes in the northwest may relate to changes in the supply of modern plant debris under recent warmer conditions. On the western shelf, changes may relate to ice climate and the distribution of northern coastal water and/or changes in the delivery of materials by the Churchill River due to water diversion. Although the cores show evidence of change related to the ice climate, there is little evidence that ice itself transports terrigenous organic carbon within the system.     

Some chemical characteristics of the brines in Bannock and Tyro Basins: salinity, sulphur compounds, Ca, F, pH, At, PO4, SiO2, NH3

Results of the chemical investigation on the Bannock and Tyro Basins are reported.Both basins were found to be hypersaline ( 10 times higher than salinity of normal seawater) and anoxic. In all investigated basins a region of transition, a few meters thick, was identified at depths > 3327 dbar. It is characterized by a sharp gradient of salinity, and all concentrations of analysed species increase strongly except for dissolved oxygen and nitrate, which immediately drop to zero. This region appears as a sharp boundary that prevents mixing. As a result, in the presence of organic matter, an anoxic condition developed with the complete depletion of dissolved oxygen. At the same time, hydrogen sulphide and ammonium accumulated within the brine. Between the Bannock and the Tyro brines differences occur in the measured concentrations of H₂S, SO²⁻₄, Ca²⁺ and NH₃. There are some differences also within the Bannock area sub-basins.The Libeccio sub-basin, in the Bannock area, contains a double-layered brine: the upper layer is 140 dbar thick and the lower layer is 300 dbar thick. A second interface between upper and lower brines develops at a depth of 3500 dbar. Nearly all of the measured concentrations vs. depth show the double layer, with the exception of ammonium, the concentration of which remains nearly constant throughout the anoxic column. Profiles of the other species analyzed show remarkable differences on passing from the upper to the lower brine. Hydrogen sulphide, sulphate and fluoride concentrations appear constant and then increase at the second interface. The calcium concentration is also constant in the upper brine, but decreases at the second interface. Total alkalinity and phosphate concentrations show a maximum peak just below the first interface. However, after passing through the second interface all the chemical parameters exhibit an almost constant behaviour down to the bottom.Hypersaline conditions are attributed to the dissolution of Messinian evaporite, and anoxia is suggested to originate from the oxidation of organic matter present in sediments and from the absence of bottom water circulation in such a deep and enclosed environment.The chemical conditions can be summarized as follows: in the Libeccio Basin the values for the species analysed have the ranges: 39–321 psu for ‘salinity’, 8.2−6.5 for pH, 2.7–4.0 mM for total alkalinity, 0.2-0 mM for dissolved oxygen, 0–1669 μM for hydrogen sulphide, 0–198 μM for thiol, 31–99 mM for sulphate, 11–21 mM for calcium, 7–100 μM for fluoride, 0.2–3080 μM for ammonium, 5.8-0 μM for nitrite, 0.2–12 μM for phosphate and 8–130 μM for silicate.     

Cholinesterase activities in the Antarctic scallop Adamussium colbecki: Tissue expression and effect of ZnCl2 exposure

Biochemical characterization of cholinesterase activity (ChE) was carried out on the Antarctic scallop Adamussium colbecki collected in winter 2000 from Campo Icaro (Ross Sea, Antarctica) in order to increase its suitability as a sentinel organism for monitoring the Antarctic environment. The digestive gland, gills and adductor muscle were investigated for substrate specificity and inhibitors sensitivity using acetylthiocholine iodide (ASCh) and butyrylthiocholine iodide (BSCh) as substrates and tetra (monoisopropyl)pyrophosphor-tetramide (Iso-OMPA), 1,5-bis(4-allyldimethylammoniumphenyl)-penthan-3-one dibromide (BW284c51) and the insecticide chlorpyrifos as inhibitors. Effect of in vivo exposure to ZnCl₂ was also investigated. All the tissues expressed ChE activity (gill > adductor muscle > digestive gland) and low substrates specificity throughout the hydrolysis of both ASCh and BSCh substrates. Partial (25–29%) and total inhibition (100%) of ChE activity in gills was demonstrated following in vitro incubation with Iso-OMPA and BW284c51 (3 mM), respectively. Concentration-dependent inhibition was also evident with chlorpyrifos in the range 10⁻⁴–10⁻¹⁰ M (IC₅₀ 10⁻⁶) while in vivo exposure to ZnCl₂ did not seem to affect ChE activity in the scallop. The potential use of ChE in the A. colbecki as biomarker for monitoring water contamination in the marine Antarctic environment is discussed.     

桐花树胎生发育过程中内源性脱落酸、赤霉素和糖分含量的变化

种子胎生是红树植物典型的适应特征之一。本研究以胎生红树植物桐花树（Aegiceras corniculatum）花蕾、种子和胚轴为材料,研究了胎生发育过程中繁殖体内源性脱落酸（ABA）、赤霉素（GA₃）、可溶性糖和淀粉含量的动态变化。结果表明：ABA含量在胎生发育过程中呈现先降低后升高的显著变化,即在种子形成前的花蕾期最高\[（1.86±0.07） μg/g\],在种子期达到最低值\[（0.75±0.07） μg/g\],然后随种子萌发逐渐回升;GA₃含量则呈现相反的变化趋势,先升高后降低,即在种子期最高\[（12.60±0.05 ）μg/g\],然后随种子萌发逐渐降低\[（1.97±0.05） μg/g\];繁殖体可溶性糖含量随发育进程先升高后降低,在种子萌发早期达到最高值;淀粉含量始终呈现增加的趋势,并在种子萌发晚期达到最高值。在胎生过程中,桐花树繁殖器官的内源性ABA和GA₃含量以及可溶性糖和淀粉含量的动态变化表明,ABA和GA₃通过对糖代谢的综合调控作用可能是红树植物胎生的重要机制之一。     

Limited nutritional benefit to the seagrass Halophila ovalis, in culture, following sediment organic matter enrichment

Essential nutrients for seagrass growth may be derived from benthic decomposition of organic matter. To test this idea, cores of Halophila ovalis (seagrass-vegetated) and unvegetated sediment (control) were amended with either particulate organic matter (POM) or dissolved organic matter (DOM) to test whether a positive feed-back loop exists, where increased organic matter results in increased seagrass nutrients. POM was added in the form of seagrass wrack (0, 1, 5, 12 g core⁻¹) and DOM was added with sucrose diffusion tubes at the root zone (0, 0.8, 2.4, 5.2 g core⁻¹). Cores were incubated under saturating light conditions (12 h light/12 h dark) at 18 °C, for 4 weeks. Results suggest a complex balance between positive and negative effects of organic matter enrichment. Whilst leaf molar concentrations of N and P of H. ovalis increased (by 15 and 30% respectively), plant growth declined (up to 50% relative to control) for both DOM and POM enrichments. Phosphate was removed from sediment porewater following POM addition and most likely translocated to the leaves. Stressors other than nutrient limitation (e.g. biogeochemical constraints) reduce growth and affect the nutrient dynamics of the seagrass and should be the focus of future work.     

Ten-year observation of the Gironde tributary fluvial system: fluxes of suspended matter, particulate organic carbon and cadmium

A program of long-term observation of suspended solids (TSS), particulate organic carbon (POC) and cadmium transported into the Gironde estuary (France) by its major tributaries has been carried out between 1990 and 1999. This decade included contrasting hydrologic cycles and appears representative of a much longer period (1959–1999). The Garonne and the Dordogne river systems are the main tributaries of the Gironde estuary and derive their waters from drainage basins with different geological, industrial and agricultural features. To better understand their respective contributions, they have been observed separately and compared. Water and TSS fluxes of the Garonne River show greater temporal variations and discharge is more related to the hydrology of the drainage basin (e.g. wet/dry years, local flood events etc.). As POC and particulate Cd concentrations in suspended matter are much less variable than turbidity, their fluxes are mainly controlled by the TSS transport. A major part of annual fluxes of TSS and associated pollutants may occur within few flood days (depending on various parameters, e.g. intensity, duration, season, etc.), and also the succession of dry and wet years has an important influence on annual fluxes. The presented data allow calculating fluvial inputs into the Gironde as the sum of fluxes transported by its major tributaries, the Garonne and the Dordogne river systems. Mean annual fluxes into the Gironde observed in 1990–1999 are about 34×10⁹ m³ year⁻¹ for river water, 3.24×10⁶ t year⁻¹ for suspended solids (TSS) and 9.88×10⁹ mol year⁻¹ for particulate organic carbon (POC). Generally, these fluxes are dominated by the contributions of the Garonne River. However, in dry years, the mean contribution of the Dordogne river system (including Dronne and Isle rivers) to the POC input into the estuary exceeded that of the Garonne. This reflects significant differences in vegetation and soil due to natural properties and land management of the basins. Mean Cd fluxes into the estuary are about 110×10³ mol year⁻¹ of which 19.6×10³ mol year⁻¹ are transported in the dissolved and 90.8×10³ mol year⁻¹ in the particulate phases, respectively. In 1991 (dry year), the net (dissolved) Cd flux towards the ocean exceeded the gross fluvial input of total Cd, suggesting the release of Cd from an important stock in the maximum turbidity zone (MTZ) or the fluid mud of the Gironde estuary.     

南大洋普里兹湾基于234Th/238U不平衡法的POC输出通量研究

中国第22次南极科学考察(2005年11月至2006年3月)期间,测定了南极普里兹湾海域5个站位的从表层至150 m水深的不同层位水样中溶解态和颗粒态234Th,238U的放射性比活度以及颗粒有机碳.利用234Th/238U在上层水体中的不平衡,计算了南极普里兹湾上层水体中234Th的平均停留时间和输出通量.结果显示,随着纬度的增加,上层水体中颗粒态和溶解态234Th的平均停留时间总体趋向减小,并在中纬度站位出现了最低值,分别为1~8和29~48 d,而颗粒态和溶解态234Th的输出通量则在中纬度站位出现了最大值,分别为21~38和26~39 dpm/(m3·d).运用箱型清除模式,利用两种不同的方法估算了各水柱中从真光层底部输出的POC通量,平均值分别达到104.7 mmol/(m2·d)(E法)和120.6 mmol/(m2·d)(B法),表明南极普里兹湾夏季存在很高的新生产力,它将会对该海域碳的生物泵过程产生重要作用.