Photochemical production of the hydroxyl radical in Antarctic waters

Photochemical production rates and steady-state concentrations of the highly reactive OH radical were determined in Antarctic seawater in the Weddell-Scotia Confluence during the austral spring of 1993 and along the Antarctic Peninsula during the austral summer of 1994. OH radical photoproduction rates were 30±2 nM/day and 46±2 nM/day in surface open oceanic and coastal waters, respectively. Corresponding steady-state concentrations were 2.6×10⁻¹⁹ and 4.3×10⁻¹⁹ M which are similar to those found in tropical latitudes. In-situ irradiation experiments (drifter deployments) at different depths in the upper water column indicated that multiple sources for the OH radical existed at three Antarctic stations. Ultrafiltration studies and model calculations based on wavelength-dependent OH radical quantum yields indicated that the main sources were photochemical reactions of low molecular weight dissolved organic matter (DOM), nitrate, and nitrite. Production of the OH radical from nitrate photolysis was almost exclusively UV-B dependent, while OH radical production from nitrite photolysis was mainly UV-A dependent. OH production from DOM photolysis was both UV-A and UV-B dependent. In the upper few meters at open oceanic sites, nitrate and DOM were the dominant OH radical sources, while deeper in the water column DOM and nitrite were important because of the greater importance of UV-A with depth. During non-ozone hole conditions, nitrate contributed about 33%, while DOM plus nitrite contributed about 67% of the predicted OH radical production in open oceanic surface waters. During an ozone hole (151 Dobson units), the corresponding percentages changed to about 40 and 60% for nitrate and DOM due to the higher UV-B irradiance. Model calculations predict that during an ozone hole (151 Dobson units), OH radical production in surface waters will be enhanced by at least 20%, mostly from nitrate photolysis and to a lesser extent from DOM photochemical reactions. This study indicates that ozone hole events significantly increase OH radical production, as well as the photolysis of DOM, in Antarctic waters, and that rates can be as high or higher than those at lower latitudes, especially if differences in temperature and solar irradiance are taken into account.     

Photochemical production of molecular hydrogen in lake water and coastal seawater

Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L^− 1h^− 1) and lower in seawater (range: 19–45 pmol L^− 1 h ^− 1). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H₂ production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.     

天然水体中微量过氧化氢的测定方法

天然环境中的H2O2与水体中的光化学反应、氧化还原反应有密切关系,是影响化学物质（金属离子、腐殖质等）在水环境中的迁移、转化、归宿及生态效应的重要因素,也是酸雨形成的主要原因之一。地表天然水中的H2O2主要来自表层水中可溶解有机物（DOM）的光化学反应,     

The annual production of biogenic silica in the Antarctic Ocean

The total annual production of biogenic silica (BSi) of the Antarctic Ocean is estimated at about 50 tera (T = 10¹²) mol Si. This flux is calculated using available direct measurements of integrated silicic acid uptake rates, indirect estimates from field distribution of orthosilicic acid in austral winter compared with that in austral summer and/or after conversion of ^l4C primary production using appropriate Si/C mole ratios measured for the four Antarctic subsystems: the Polar Front Zone, the Permanently Open Ocean Zone, the Seasonal Ice Zone, and the continental shelves and coastal zones. We show that most of the total production of BSi occurs in the surface layers of the Permanently Open Ocean Zone and in the Seasonal Ice Zone, the contribution of the coastal areas being less relevant. Our results fit well with the previously described distributions of the net accumulation rates of opal in Antarctic abyssal and coastal sediments. The mean ratio of net opal accumulation at the sea-bed to the net production of BSi in the surface layer of the Antarctic Ocean is about 15%.     

Photochemical production of ammonium and transformation of dissolved organic matter in the Baltic Sea

The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH₄⁺ L^− 1 d^− 1. Estimated areal daily production rates ranged between 37 and 237 μmol NH₄⁺ m^− 2 d^− 1, which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.     

A re-appraisal of the total biomass and annual production of Antarctic krill

Despite much research on Euphausia superba, estimates of their total biomass and production are still very uncertain. Recently, circumpolar krill databases, combined with growth models and revisions in acoustics have made it possible to refine previous estimates. Net-based databases of density and length frequency (KRILLBASE) yield a summer distributional range of ～19×10⁶ km² and a mean total abundance of 8×10¹⁴ post-larvae with biomass of 379 million tonnes (Mt). These values are based on a standardised net sampling method but they average over the period 1926–2004, during which krill abundance has fluctuated. To estimate krill biomass at the end of last century we combined the KRILLBASE map of relative krill density around Antarctica with an acoustics-derived biomass estimate of 37.3 Mt derived for the Scotia Sea area in 2000 by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Thus the CCAMLR 2000 survey area contains 28% of the total stock, with total biomass of ～133 Mt in January–February 2000. Gross postlarval production is estimated conservatively at 342–536 Mt yr^?1, based on three independent methods. These are high values, within the upper range of recent estimates, but consistent with the concept of high energy throughput for a species of this size. The similarity between the three production estimates reflects a broad agreement between the three growth models used, plus the fact that, for a given population size, production is relatively insensitive to the size distribution of krill at the start of the growth season. These production values lie within the envelope of what can be supported from the Southern Ocean primary production system and what is required to support an estimated predator consumption of 128–470 Mt yr^?1. Given the range of recent acoustics estimates, plus the need for precautionary management of the developing krill fishery, our net-based data provide an alternative estimate of total krill biomass.     

Photochemical production of low-molecular-weight carbonyl compounds in seawater and surface microlayer and their air-sea exchange

Coastal and oceanic surface microlayer samples were collected using a stainless steel screen, along with subsurface bulk seawater, and were analyzed for low-molecular-weight (LMW) carbonyl compounds, including formaldehyde, acetaldehyde, propanal, glyoxal, methylglyoxal, glyoxylic acid and pyruvic acid. The enrichment factor in surface microlayer compared to corresponding subsurface seawater ranged from 1.2 to 21. A time-series measurement at a coastal site showed strong diurnal variations in concentrations of the LMW carbonyl compounds in the surface microlayer and in the enrichment factor, with maxima in the early afternoon and minima in the early morning. Exposure of samples to sunlight resulted in the higher yields of these compounds in the surface microlayer than in the bulk seawater, by a factor of 1.1–25, suggesting that the higher photoproduction rate of LMW carbonyl compounds in the surface microlayer accounts for the majority of the observed enrichment in these samples. Potential sinks include biological uptake and mixing. Air-sea exchange may be a source for soluble compounds and a sink for less soluble compounds. The enrichment of the LMW carbonyl in surface microlayer may alter their net air-sea exchange direction e.g., from the ocean as a potential sink to a source for atmospheric acetaldehyde and acetone. The residence times of the LMW carbonyl compounds in the microlayer were estimated to be on the order of tens of seconds to minutes using a modified two-layer model. However, to maintain the observed microlayer enrichment factor, the residence time should be on the order of ˜ 1 hour. This prolonged residence time may be due to organic enrichment in the surface microlayer (‘organic film’) which inhibited molecular transfer of carbonyl compounds into and out of the microlayer. The deviated behavior from model prediction may also be due to changes in the apparent partition coefficients of these species as a result of thier physical and chemical interactions with organic matrix in the surface microlayer.     

Requirement of endogenous iron for cytotoxicity caused by hydrogen peroxide in Euglena gracilis

It is widely thought that redox-active metals in cells such as iron or copper catalyze the reduction of hydrogen peroxide to toxic hydroxyl radicals or their equivalent. However, this has not been directly demonstrated in vivo. To probe this requirement, the freshwater microorganism Euglena gracilis was used. Its intracellular iron content can be modulated by the concentration of iron in the defined growth medium without effect on the proliferation rate of the cells. E. gracilis contains two large storage pools of cytosolic iron which can be monitored to assess cellular iron status. The toxicity of H₂O₂ in E. gracilis was inversely related to the amount of iron in the extracellular medium. At high levels of external iron, the metal carried out the Fenton reaction with H₂O₂ outside the cell, producing hydroxyl radicals as detected by electron-spin resonance spin-trapping experiments. This reaction reduced the amount of H₂O₂ that could diffuse into cells to cause toxicity. When cells with different intracellular iron content were placed in iron-deficient media, the the toxicity of H₂O₂, measured by inhibition of proliferation, was directly related to the concentration of internal iron. Using cells deficient in iron, this oxidant did not inhibit proliferation at low concentration but was somewhat effective at higher concentrations. Although the iron chelating agents, 1,10-phenanthroline and desferrioxamine, also depressed cytosolic iron, they were cytotoxic to E. gracilis and so could not be used unambiguously to examine the role of intracellular iron in the toxic effects of hydrogen peroxide.     

过氧化氢对锯缘青蟹N-乙酰-β-D-氨基葡萄糖苷酶的抑制动力学

研究过氧化氢对锯缘青蟹N-乙酰-β-D-氨基葡萄糖苷酶活力的影响及抑制动力学．其结果表明，过氧化氢对该酶有显著的抑制作用，随着过氧化氢浓度的增高，酶活力呈指数下降，测出可使酶活力下降50％的过氧化氢浓度（抑制半衰期，IC50）为115mmol／dm^3．低浓度过氧化氢对该酶的抑制过程显示为可逆效应．采用底物反应动力学方法研究过氧化氢对该酶的抑制作用动力学并建立动力学模型，测定游离酶（E）和酶．底物络合物（ES）的微观抑制速度常数k＋0和k＋0，并加以比较．实验结果（k＋0〉k＋0）表明底物对酶被过氧化氢的抑制作用有一定保护作用．过氧化氢可能是通过氧化酶活性中心功能基团而导致酶活性的丧失．     

Primary production export flux in Marguerite Bay (Antarctic Peninsula): Linking upper water-column production to sediment trap flux

A study was carried out to assess primary production and associated export flux in the coastal waters of the western Antarctic Peninsula at an oceanographic time-series site. New, i.e., exportable, primary production in the upper water-column was estimated in two ways; by nutrient deficit measurements, and by primary production rate measurements using separate ¹⁴C-labelled radioisotope and ¹⁵N-labelled stable isotope uptake incubations. The resulting average annual exportable primary production estimates at the time-series site from nutrient deficit and primary production rates were 13 and 16 mol C m⁻², respectively. Regenerated primary production was measured using ¹⁵N-labelled ammonium and urea uptake, and was low throughout the sampling period.The exportable primary production measurements were compared with sediment trap flux measurements from 2 locations; the time-series site and at a site 40 km away in deeper water. Results showed ∼1% of the upper mixed layer exportable primary production was exported to traps at 200 m depth at the time-series site (total water column depth 520 m). The maximum particle flux rate to sediment traps at the deeper offshore site (total water column depth 820 m) was lower than the flux at the coastal time-series site. Flux of particulate organic carbon was similar throughout the spring–summer high flux period for both sites. Remineralisation of particulate organic matter predominantly occurred in the upper water-column (<200 m depth), with minimal remineralisation below 200 m, at both sites. This highly productive region on the Western Antarctic Peninsula is therefore best characterised as ‘high recycling, low export’.     

5000 aBP南部大洋南大西洋区南极表层水温急剧下降和浮冰扩张

我们根据南部大洋大西洋区南纬 53°活塞岩心分析结果重建南大西洋全新世南极表层水变化史。此岩心沉积速率较高 (全新世平均值为50 cm/ 1 0 3a) ,且位于亚南极的南大西洋 ,适用于古气候研究。钻位位于现代极地前缘带( PFZ)以南约 3°,冬季海冰边界以北约 2°。利用硅藻转换函数、硅藻内有机质的碳和氮同位素、粗粒沉积物 ( >1 50 μm～ 2 mm)中放射虫、有孔虫和浮冰碎屑相对丰度 ,对硅藻和有孔虫的氧同位素、二月表层海水和海冰盖层温度进行了测定 ,提供了 50 0 0 a BP表层水特征急剧变化的证据。1 0 0 0 0～ 550 0 a BP粗粒沉积物 ( >1…     

Photochemical oxidation of dimethylsulfide in seawater

Dimethylsulfide(DMS) is generally thought to be lost from the surface oceans by evasion into the atmosphere as well as consumption by microbe.However,photochemical process might be important in the removal of DMS in the oceanic photic zone.A kinetic investigation into the photochemical oxidation of DMS in seawater was performed.The photo-oxidation rates of DMS were influenced by various factors including the medium,dissolved oxygen,photosensitizers,and heavy metal ions.The photo-oxidation rates of DMS were higher in seawater than in distilled water,presumably due to the effect of salinity existing in seawater.Three usual photosensitizers(humic acid,fulvic acid and anthroquinone),especially in the presence of oxygen,were able to enhance the photo-oxidation rate of DMS,with the fastest rate observed with anthroquinone.Photo-oxidation of DMS followed first order reaction kinetics with the rate constant ranging from 2.5×10-5 to 34.3×10-5 s-1.Quantitative analysis showed that approximately 32% of the photochemically removed DMS was converted to dimethylsulfoxide.One of the important findings was that the presence of Hg2 could markedly accelerate the photo-oxidation rate of DMS in seawater.The mechanism of mercuric catalysis for DMS photolysis was suggested according to the way of CTTM(charge transfer to metal) of DMS-Hg2 complex.     

天然水体中的胶体粒子

介绍了天然水特别是海水中胶体粒子的基本特性和最新研究成果 ,如胶体粒子的大小、组成、粒径分布情况、逗留时间、对痕量金属的吸附、一些相关的分析分离方法以及在生态环境中的可能作用等 ,并对今后的有关研究方向作出预测。     

Nutrient distributions and new production in polar regions: parallels and contrasts between the Arctic and Antarctic

Polar regions are poorly understood components of global biogeochemical cycles. This paper discusses the influences of nitrate and ammonium concentrations on nitrate uptake (and hence new production), particularly with regard to data collected within marginal ice zones in the Arctic and Antarctic. Subsurface ammonium maxima in waters over 150 m are frequently encountered in the Arctic and occasionally in the Antarctic. Such maxima result from the heterotrophic remineralization of organic matter, and because stratified environments occur more frequently in the Arctic, significant concentrations of ammonium accumulate as a result of lower diffusive losses. Causal agents (bacteria vs. Zooplankton) may also be different in the Arctic from those in the Antarctic. Elevated ammonium concentrations significantly reduce nitrate uptake, and it is suggested that this nutrient interaction may play a significant role in controlling new production, particularly in open water regions. The new production of the Southern Ocean is estimated, and it is suggested that the production and flux from the surface layer is significant relative to the world's oceans.     

海水中无机物的光化学反应

综述了近几十年来国内外关于海水中无机物的光化学反应的研究状况。首先,阐述了海洋光化学在海洋科学中的重要性,历年来的发展状况以及海水的光化学与其它相关领域之间的相互影响作用。其次,本文分别从阴离子的光化学反应,阳离子的光化学反应和过氧化氢的光化学反应三个方面对海水中无机物的光化学反应进行了论述,详细介绍了铁、锰、铜、汞、过氧化氢、硝酸盐和碘化物随反应介质、温度、酸碱度、有机物浓度和光照等外界因素的不同而发生的光化学反应的变化。另外,讨论了上述物质发生光化学反应的主控因素及其在反应过程中对周围环境的影响作用,并对部分物质的反应机理作了介绍。最后,本文指出了这一研究领域存在的问题和不足,并提出今后的研究建议。     

Calcium in the Antarctic Ocean

Calcium in sea water was determined of the samples taken from the Antarctic and Indian Oceans. Surface water commonly contains less calcium relative to chlorinity than does deep water. The tendency, however, is very faint in the Antarctic Ocean. In the surface waters, the Ca/Cl ratio is lower in the tropical and subtropical waters and the ratio well correlates with phosphate. The Ca/P ratio is calculated as 37 in atomic ratio. These may indicate that calcium is uptaken by organisms to make skeletal parts from surface water which is supersaturated with respect to calcite or aragonite. On the other hand, no definite correlationship between calcium and phosphate is found in subsurface water. This fact suggests that the regeneration process of calcium from organic debris is different from that of phosphate. The increase-rate of calcium in the abyssal water is estimated to be 0.18g at./(1 yr), which is due to the dissolution of calcium carbonate. The rate is about a half of total carbonate increase in the water.     

Dissolved Organic Matter in Oceanic Waters

The amount of information on oceanic dissolved organic matter (DOM) has increased dramatically in the last decade thanks to the advances in chemical characterization. This information has supported the development of some novel and important ideas for DOM dynamics in the ocean. Consequently, we have a better understanding of the importance of DOM in oceanic biogeochemical cycles. Here we review studies published mainly during 1995–2001, synthesize them and discuss unsolved problems and future challenges. The measurement, distribution and turnover of dissolved organic carbon (DOC) are presented as the bulk dynamics of the oceanic DOM. The size spectrum, elemental composition, and chemical compositions at molecular and functional group levels are described. The mechanisms proposed for the survival of biomolecules in DOM are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.