共查询到20条相似文献，搜索用时 15 毫秒
1.
Summer algal blooms in a coastal ecosystem: the role of atmospheric deposition versus entrainment fluxes 总被引：2，自引：1，他引：2
Jacob Carstensen Lise Marie Frohn Charlotte Bay Hasager Bo G. Gustafsson 《Estuarine, Coastal and Shelf Science》2005,62(4):595-608
The nitrogen inputs from atmospheric deposition and bottom water entrainment to the surface layer were modelled in the summer period (May–September) over a 11-year period (1989–1999) and compared to investigate the significance of these fluxes for generating blooms in the Kattegat. In the summer periods the average atmospheric deposition was 2.81 mg N m−2 d−1 compared to average entrainment fluxes of 5.42 mg N m−2 d−1, 1.21 mg N m−2 d−1 and 1.15 mg N m−2 d−1 for the northern, central and southern part of the Kattegat, respectively. Atmospheric nitrogen deposition alone could not sustain biomass increases associated with observed blooms and entrainment fluxes dominated the high nitrogen inputs to the surface layer. The potential for a bloom through growth was typically obtained after several days of high nitrogen inputs from entrainment in the frontal area of the northern Kattegat and to some extent from atmospheric deposition. The modelled nitrogen input in this area could account directly for 30% of the observed blooms in the Northern sub-basin, and through advective transport 24% and 19% of the observed blooms in the central and southern Kattegat. The direct nitrogen inputs through atmospheric deposition and entrainment to the central and southern sub-basins were small and could not be linked to any bloom observation. 相似文献
2.
Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean 总被引：3，自引：0，他引：3
Graldine Sarthou Alex R. Baker Jurjen Kramer Patrick Laan Agathe Laës Simon Ussher Eric P. Achterberg Hein J.W. de Baar Klaas R. Timmermans Stphane Blain 《Marine Chemistry》2007,104(3-4):186-202
Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters. 相似文献
3.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(10-11):1339-1352
Atmospheric iron and underway sea-surface dissolved (<0.2 μm) iron (DFe) concentrations were investigated along a north–south transect in the eastern Atlantic Ocean (27°N/16°W–19°S/5°E). Fe concentrations in aerosols and dry deposition fluxes of soluble Fe were at least two orders of magnitude higher in the Saharan dust plume than at the equator or at the extreme south of the transect. A weaker source of atmospheric Fe was also observed in the South Atlantic, possibly originating in southern Africa via the north-easterly outflow of the Angolan plume. Estimations of total atmospheric deposition fluxes (dry plus wet) of soluble Fe suggested that wet deposition dominated in the intertropical convergence zone, due to the very high amount of precipitation and to the fact that a substantial part of Fe was delivered in dissolved form. On the other hand, dry deposition dominated in the other regions of the transect (73–97%), where rainfall rates were much lower. Underway sea-surface DFe concentrations ranged 0.02–1.1 nM. Such low values (0.02 nM) are reported for the first time in the Atlantic Ocean and may be (co)-limiting for primary production. A significant correlation (Spearman's rho=0.862, p<0.01) was observed between mean DFe concentrations and total atmospheric deposition fluxes, confirming the importance of atmospheric deposition on the iron cycle in the Atlantic. Residence time of DFe in the surface waters relative to atmospheric inputs were estimated in the northern part of our study area (17±8 to 28±16 d). These values confirmed the rapid removal of Fe from the surface waters, possibly by colloidal aggregation. 相似文献
4.
5.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(11):1859-1870
Atmospheric dry deposition of nitrogen (N) and dinitrogen (N2) fixation rates were assessed in 2004 at the time-series DYFAMED station (northwestern Mediterranean, 43°25′N, 7°52′E). The atmospheric input was monitored over the whole year. Dinitrogen fixation was measured during different seasonal trophic states (from mesotrophy to oligotrophy) sampled during nine cruises. The bioavailability of atmospherically deposited nutrients was estimated by apparent solubility after 96 h. The solubility of dry atmospheric N deposition was highly variable (from ∼18% to more than 96% of total N). New N supplied to surface waters by the dry atmospheric deposition was mainly nitrate (NO3−) (∼57% of total N, compared to ∼6% released as ammonium (NH4+)). The mean bioavailable dry flux of total N was estimated to be ∼112 μmol m−2 d−1 over the whole year. The NO3− contribution (70 μmol NO3− m−2 d−1) was much higher than the NH4+ contribution (1.2 μmol NH4+ m−2 d−1). The N:P ratios in the bioavailable fraction of atmospheric inputs (122.5–1340) were always much higher than the Redfield N:P ratio (16). Insoluble N in atmospheric dry deposition (referred to as “organic” and believed to be strongly related to anthropogenic emissions) was ∼40 μmol m−2 d−1. N2 fixation rates ranged from 2 to 7.5 nmol L−1 d−1. The highest values were found in August, during the oligotrophic period (7.5 nmol L−1 at 10 m depth), and in April, during the productive period (4 nmol L−1 d−1 at 10 m depth). Daily integrated values of N2 fixation ranged from 22 to 100 μmol N m−2 d−1, with a maximum of 245 μmol N m−2 d−1 in August. No relationship was found between the availability of phosphorus or iron and the observed temporal variability of N2 fixation rates. The atmospheric dry deposition and N2 fixation represented 0.5–6% and 1–20% of the total biological nitrogen demand, respectively. Their contribution to new production was more significant: 1–28% and 2–55% for atmospheric dry deposition and N2 fixation, respectively. The dry atmospheric input was particularly significant in conditions of water column stratification (16–28% of new production), while N2 fixation reached its highest values in June (46% of new production) and in August (55%). 相似文献
6.
I~IOWDuceetal.(1980)calculatedthattheair-seaexchangeprocesscouldsupply80%--90%ofthediforedironinputtothephotcrzoneoftheSargassoAsfromairand16%--76%tothecentralNorthPacific.CuisessentialtotheTnarineorganisms,butexcessiveCuistoxictOtheOrganisms.CdandPh... 相似文献
7.
Measurements of nitrate and ammonium in precipitation and associated with aerosols were conducted at Rutgers University Marine Field Station in Tuckerton, New Jersey from March 2004 to March 2005 to characterize atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary. The arithmetic means of nitrate and ammonium concentrations for precipitation samples were 2.3mgL(-1) and 0.42mgL(-1), respectively. Nitrate and ammonium concentrations in aerosol samples averaged 3.7microgm(-3) and 1.6microgm(-3), respectively. Wet deposition rates appeared to vary with season; the highest rate of inorganic nitrogen deposition (nitrate+ammonium) occurred in the spring with an average value of 1.33kg-Nha(-2)month(-1). On an annual basis, the total (wet and dry) direct atmospheric deposition fluxes into the Mullica River-Great Bay Estuary were 7.08kg-Nha(-2)year(-1) for nitrate and 4.44kg-Nha(-2)year(-1) for ammonium. The total atmospheric inorganic nitrogen directly deposited to the Mullica River-Great Bay Estuary was estimated to be 4.79x10(4)kg-Nyear(-1), and the total atmospheric inorganic nitrogen deposited to the Mullica River watershed was estimated to be 1.69x10(6)kg-Nyear(-1). Only a fraction of the nitrogen deposited on the watershed will actually reach the estuary; most of the nitrogen will be retained in the watershed due to utilization and denitrification during transport. The amount of N reaching the Mullica River-Great Bay Estuary indirectly is estimated to be 5.07x10(4)kg-Nyear(-1), approximately 97% is retained within the watershed. This atmospheric nitrogen deposition may stimulate phytoplankton productivity in the Mullica River-Great Bay ecosystem. 相似文献
8.
Martha A. Sutula Brian C. Perez Enrique Reyes Daniel L. Childers Steve Davis John W. Day Jr. David Rudnick Fred Sklar 《Estuarine, Coastal and Shelf Science》2003,57(5-6):757-781
Physical and biological processes controlling spatial and temporal variations in material concentration and exchange between the Southern Everglades wetlands and Florida Bay were studied for 2.5 years in three of the five major creek systems draining the watershed. Daily total nitrogen (TN), and total phosphorus (TP) fluxes were measured for 2 years in Taylor River, and ten 10-day intensive studies were conducted in this creek to estimate the seasonal flux of dissolved inorganic nitrogen (N), phosphorus (P), total organic carbon (TOC), and suspended matter. Four 10-day studies were conducted simultaneously in Taylor, McCormick, and Trout Creeks to study the spatial variation in concentration and flux. The annual fluxes of TOC, TN, and TP from the Southern Everglades were estimated from regression equations. The Southern Everglades watershed, a 460-km2 area that includes Taylor Slough and the area south of the C-111 canal, exported 7.1 g C m−2, 0.46 g N m−2, and 0.007 g P m−2, annually. Everglades P flux is three to four orders of magnitude lower than published flux estimates from wetlands influenced by terrigenous sedimentary inputs. These low P flux values reflect both the inherently low P content of Everglades surface water and the efficiency of Everglades carbonate sediments and biota in conserving and recycling this limiting nutrient. The seasonal variation of freshwater input to the watershed was responsible for major temporal variations in N, P, and C export to Florida Bay; approximately 99% of the export occurred during the rainy season. Wind-driven forcing was most important during the later stages of the dry season when low freshwater head coincided with southerly winds, resulting in a net import of water and materials into the wetlands. We also observed an east to west decrease in TN:TP ratio from 212:1 to 127:1. Major spatial gradients in N:P ratios and nutrient concentration and flux among the creek were consistent with the westward decrease in surface water runoff from the P-limited Everglades and increased advection of relatively P-rich Gulf of Mexico (GOM) waters into Florida Bay. Comparison of measured nutrient flux from Everglades surface water inputs from this study with published estimates of other sources of nutrients to Florida Bay (i.e. atmospheric deposition, anthropogenic inputs from the Florida Keys, advection from the GOM) show that Everglades runoff represents only 2% of N inputs and 0.5% of P input to Florida Bay. 相似文献
9.
台湾海峡大气微量金属的化学特征及其入海通量 总被引：1，自引：1，他引：0
2006～2007年，利用大容量气溶胶采样器在台湾海峡采集79个大气气溶胶样品．采用ICP—MS分析法测定了样品中Pb、Cu、Cd、V、Zn、Fe和Al等金属元素的含量．分析结果显示，台湾海峡大气微量金属含量呈现出明显的季节变化，对大部分元素而言，含量最低值出现在夏季，而最高值出现在冬季，气溶胶中微量金属的含量变化与海峡的气象条件等因素有关．通过富集因子、相关性分析和因子分析，对微量金属的来源进行了判别．台湾海峡大气微量金属的来源特征为：Cu、Pb、Cd、V主要来自污染源，而Al、Fe、Zn则主要来自地壳源．比较和分析了台湾海峡海域微量金属的大气与河流输入，Cu和Zn的大气输入低于九龙江和闽江的输入，而Pb、Cd的大气输入则超过了这2条河流的输入． 相似文献
10.
I. A. Gorchakova I. I. Mokhov P. P. Anikin A. S. Emilenko 《Izvestiya Atmospheric and Oceanic Physics》2018,54(2):154-161
The aerosol longwave radiative forcing of the atmosphere and heating rate of the near-surface aerosol layer are estimated for the extreme smoke conditions in the Moscow region in summer 2010. Thermal radiation fluxes in the atmosphere are determined using the integral transmission function and semiempirical aerosol model developed on the basis of standard aerosol models and measurements at the Zvenigorod Scientific Station, Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences. The aerosol radiative forcing reached 33 W/m2 at the lower atmospheric boundary and ranged between–1.0 and 1.0 W/m2 at the upper atmospheric boundary. The heating rate of the 10-m atmospheric layer near surface was up to 0.2 K/h during the maximum smoke conditions on August 7–9. The sensitivity of the aerosol longwave radiative forcing to the changes in the aerosol absorption coefficient and aerosol optical thickness are estimated. 相似文献
11.
Atmospherically-promoted photosynthetic activity in a well-mixed ecosystem: Significance of wet deposition events of nitrogen compounds 总被引：1，自引：0，他引：1
C. Boulart P. Flament V. Gentilhomme K. Deboudt C. Migon F. Lizon M. Schapira A. Lefebvre 《Estuarine, Coastal and Shelf Science》2006,69(3-4):449
Wet atmospheric deposition of dissolved N, P and Si species is studied in well-mixed coastal ecosystem to evaluate its potential to stimulate photosynthetic activities in nutrient-depleted conditions. Our results show that, during spring, seawater is greatly depleted in major nutrients: Dissolved Inorganic Nitrogen (DIN), Dissolved Inorganic Phosphorus (DIP) and Silicic acid (Si), in parallel with an increase of phytoplanktonic biomass. In spring (March–May) and summer (June–September), wet atmospheric deposition is the predominant source (>60%, relative to riverine contribution) for nitrates and ammonium inputs to this N-limited coastal ecosystem. During winter (October–February), riverine inputs of DIN predominate (>80%) and are annually the most important source of DIP (>90%). This situation allows us to calculate the possibility for a significant contribution to primary production in May 2003, from atmospheric deposition (total input for DIN ≈300 kg km−2 month−1). Based on usual Redfield ratios and assuming that all of the atmospheric-derived N (AD-N) in rainwater is bioavailable for phytoplankton growth, we can estimate new production due to AD-N of 950 mg C m−2 month−1, during this period of depletion in the water column. During the same episode (May 2003), photosynthetic activity rate, considered as gross primary production, was estimated to approximately 30 300 mg C m−2 month−1. Calculation indicates that new photosynthetic activity due to wet atmospheric inputs of nitrogen could be up to 3%. 相似文献
12.
黄河下游营养盐浓度、入海通量月变化及“人造洪峰”的影响 总被引：9，自引：3，他引：6
于2009年至2011年在黄河下游采集溶解及颗粒态营养盐样品,分析了黄河下游各形态营养盐的浓度变化及营养盐入海通量,结果表明各形态氮的浓度多呈丰水期低、枯水期高,溶解无机氮是溶解态氮的主要存在形式;受黄河高悬浮颗粒物含量的影响,磷以颗粒态占绝对优势,而溶解态磷以溶解无机磷为主要存在形态;生物硅的含量平均约占硅酸盐与生物硅之和的20％,硅的浓度丰水期高于枯水期.颗粒态磷与生物硅的含量与悬浮颗粒物含量呈正相关.营养盐的组成具有高氮磷比、高硅磷比、低硅氮比的特点.近年来黄河下游溶解无机氮浓度显著升高而溶解无机磷变化不大,硅酸盐的浓度有所下降.黄河下游水沙通量、营养盐入海通量有明显的季节变化,丰水期占全年总入海通量的42％～84％.调水调沙期间,各营养盐的浓度和组成均有明显变化,氮的浓度、DIN/PO4-P下降,磷与硅的浓度、SiO3-Si/DIN、SiO3-Si/PO4-P升高,颗粒态营养盐的比例明显增加.短期内大量水沙及营养盐入海通量对黄河口及渤海生态系统产生重要影响. 相似文献
13.
近海生态系统的人为营养盐输入及其控制对策浅析 总被引：1，自引：1，他引：0
人为活动每年新增大量的活性氮、磷，导致全球氮、磷循环失衡，新增活性氮、磷主要来源于合成氮肥的生产和施用、畜肥的施用、具固氮能力的农作物如豆科植物等的大规模种植，以及化石燃料燃烧产生的氮氧化物等，而农作物生产与畜禽养殖是改变全球氮、磷循环的主要原因。随着生活污水排放量和化肥施用量的激增，大量氮、磷进入近海，导致营养盐污染和富营养化，这已成为全球性的海洋生态环境问题，通过河流径流和大气沉降进入近海生态环境中的新增氮和磷一半以上与人为活动有关。本文以波罗的海和东海为例，分析了发达国家和发展中国家近海的富营养化问题，研究表明从源头缓解富营养化的对策应同时聚焦氮与磷负荷的削减，具体措施包括降低农业生产活动中化肥的土壤渗漏、合理施肥、种植多年生植物和种植休耕季覆被作物等。 相似文献
14.
Eighteen short cores were analyzed for major and trace metals (Al, Fe, Ca, Mg, Mn, Si, K, Ti, Pb, Zn, Cu, Ni, Cr), 210Pb, 137Cs, and other sediment characteristics, so as to describe the chronology of pollution and calculate metal concentration factors and fluxes. Substantial evidence was found that trace metal profiles are influenced by anthropogenic sources and by changes in sediment composition. Only Zn presents concentrations (up to 13.1 μmol g−) and concentration factors (1.3 to 13.2) that can be attributed to heavy contamination. Pb, Cu and Ni, in this order, are less significant. The areal distribution of concentrations and inventories reflects the importance of direct sources, in particular the industrial area of Porto Marghera and the Dese river. The inventories of excess metals, above pre-industrial levels, were determined for each core and the three different parts of the study area, the amounts of Zn accumulated in sediments are 11.0 Mmol, 5.1 Mmol and 0.37 Mmol in the Campalto, S. Erasmo, and Palude di Cona areas, respectively. Ruxes were also calculated and compared with those suggested for the atmospheric delivery by Cochran et al. [(1995)b. Atmospheric fluxes of heavy metal contaminants to the Venice Lagoon, Rapp. Comm. Int. Mer Médit., 34, 136.], the atmospheric contribution is predominant or significant in many cases, especially at sites far from the major local inputs. Concentrations and fluxes show a significant increase in the anthropogenic metal supply starting from the second decade of this century, with maximum inputs in the period between the (1930)s and the (1970)s. At some stations a decrease in heavy metal contamination of surficial sediments was found and this could be ascribed to a reduced input of pollutants in recent years. 相似文献
15.
An integrated mass balance and modelling approach for analysis of estuarine nutrient fluxes is demonstrated in the Swan River Estuary, a microtidal system with strong hydrological dependence on seasonal river inflows. Mass balance components included estimation of gauged and ungauged inputs to the estuary and losses to the ocean (outflow and tidal exchange). Modelling components included estimation of atmospheric (N fixation, denitrification) and sediment–water column nutrient exchanges. Gross and net denitrification derived using two independent methods were significantly correlated (r2 = 0.49, p < 0.01) with net rates averaging 40% of gross. Annual nitrogen (N) and phosphorus (P) loads from major tributaries were linearly correlated with annual freshwater discharge and were 3-fold higher in wet years than in dry years. Urban drains and groundwater contributed, on average, 26% of N inputs and 19% of P inputs, with higher relative contributions in years of low river discharge. Overall, ungauged inputs accounted for almost 35% of total nitrogen loads. For N, elevated loading in wet years was accompanied by large increases in outflow (7x) and tidal flushing (2x) losses and resulted in overall lower retention efficiency (31%) relative to dry years (70%). For P, tidal flushing losses were similar in wet and dry years, while outflow losses (4-fold higher) were comparable in magnitude to increases in loading. As a result, P retention within the estuary was not substantially affected by inter-annual variation in water and P loading (ca. 50% in all years). Sediment nutrient stores increased in most years (remineralisation efficiency ca. 50%), but sediment nutrient releases were significant and in some circumstances were a net source of nutrients to the water column. 相似文献
16.
The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO42−, NO3−) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean. 相似文献
17.
Mitsuo Uematsu 《Journal of Oceanography》1987,43(6):395-401
I am deeply honored to have been selected as a recipient of the 1987 Okada Prize by the Oceanographical Society of Japan. The present paper reviews my work and recent studies of other investigators concerning mineral aerosol (dust) particles in the marine atmosphere over the Pacific Ocean. I would like to emphasize the importance of atmospheric deposition of continental substances to the ocean environment. From consecutive measurements of atmospheric dust concentrations and total deposition fluxes at 13 island stations in the Pacific Ocean, a strong seasonal transfort pattern of dust particles was found at most of the stations. High atmospheric dust concentrations occurred during the spring in both hemispheres. There was a latitudinal gradient in both the atmospheric dust concentration and flux, with the highest values observed at midlatitudes. When combined with observations of dust storms in Asia and isentropic trajectory analysis, it was clear that the dust over the central North Pacific was transported by the upper westerly winds from the arid desert regions in central and eastern Asia. Transport times were 1–2 weeks, and in some cases, atmospheric transport paths of over 10,000 km were observed. Infrequent short-term dust events contributed most of annual atmospheric dust flux to the open ocean. These sporadic inputs are major sources for both suspended mineral matter in the water column and the non-biogenic component of deep-sea sediments in the Pacific Ocean. The impact of atmospheric dust fluxes on chemical and biological processes in the water column remains to be determined. 相似文献
18.
T. Ramírez D. Corts J.M. Mercado M. Vargas-Yaez M. Sebastin E. Liger 《Estuarine, Coastal and Shelf Science》2005,65(4):347
The seasonal dynamics of inorganic nutrients and phytoplankton biomass (chlorophyll a), and its relation with hydrological features, was studied in the NW Alboran Sea during four cruises conducted in February, April, July and October 2002. In the upper layers, the seasonal pattern of nutrient concentrations and their molar ratios (N:Si:P) was greatly influenced by hydrological conditions. The higher nutrient concentrations were observed during the spring cruise (2.54 μM NO3−, 0.21 μM PO43− and 1.55 μM Si(OH)4, on average), coinciding with the increase of salinity due to upwelling induced by westerlies. The lowest nutrient concentrations were observed during summer (<0.54 μM NO3−, 0.13 μM PO43− and 0.75 μM Si(OH)4, on average), when the lower salinities were detected. Nutrient molar ratios (N:Si:P) followed the same seasonal pattern as nutrient distribution. During all the cruises, the ratio N:P in the top 20 m was lower than 16:1, indicating a NO3− deficiency relative to PO43−. The N:P ratio increased with depth, reaching values higher than 16:1 in the deeper layers (200–300 m). The N:Si ratio in the top 20 m was lower than 1:1, excepting during spring when N:Si ratios higher than 1:1 were observed in some stations due to the upwelling event. The N:Si ratio increased with depth, showing a maximum at 50–100 m (>1.5:1), which indicates a shift towards Si-deficiency in these layers. The Si:P ratio was much lower than 16:1 throughout the water column during the four cruises. In general, the spatial and seasonal variation of phytoplankton biomass showed a strong coupling with hydrological and chemical fields. The higher chlorophyll a concentrations at the depth of the chlorophyll maximum were found in April (2.57 mg m−3 on average), while the lowest phytoplankton biomass corresponded to the winter cruise (0.74 mg m−3 on average). The low nitrate concentrations together with the low N:P ratios found in the upper layers (top 20 m) during the winter, summer and autumn cruises suggest that N-limitation could occur in these layers during great part of the year. However, N-limitation during the spring cruise was temporally overcome by nutrient enrichment caused by an intense wind-driven upwelling event. 相似文献
19.
Relationship between atmospheric deposition fluxes and concentrations of Si and210Po in the surface air were examined through daily basis simultaneous observation at the coast of the Japan Sea. Both the Si and210Po, the atmospheric fluxes were highly variable from day to day. According to correlation analysis, there was no significant correlation between flux and atmospheric concentration of these terrigenous materials in the surface air. On the other hand, flux of Si and210Po significantly correlated to precipitation rate. These results indicate that the atmospheric flux of terrigenous material is not constantly proportional to atmospheric concentration in the surface air. This may be due to the deposition flux represents an integrated value throughout the air column of in-and below-cloud, while the air concentration represents only the environment of earth's surface. 相似文献
20.
海洋生物固氮作用研究进展 总被引：1，自引：0，他引：1
近年来,海洋生物固氮作用研究已成为海洋氮循环研究热点之一,因为它补充了海洋中的结合态氮,影响着海洋氮储库的收支平衡,进而调控海洋的初级生产力,并因此与海洋颗粒有机碳的迁出以及海洋对大气CO2的吸收密切相关.海洋生物固氮作用的研究主要是在近30a开展起来的,现有观点认为全球海洋生物固氮速率为100～200 Tg/a.15↑N2示踪法和乙炔还原法是最重要的生物固氮速率实测方法,而硝酸盐异常指数法、15↑N同位素收支平衡法、卫星遥测法等则是重要的间接估测方法.束毛藻曾被认为是全球海洋最重要的固氮生物,但近年来也发现了固氮生物在微微（pi-co）级和微（nano）级的分布,表明以往基于束毛藻的固氮速率可能是被低估的.海洋生物固氮作用营养盐限制的研究主要集中在铁和磷这2个元素的作用,但目前尚无定论.在中国边缘海生物固氮作用的研究还很匮乏,少数研究表明除黑潮区外,由束毛藻所支持的固氮速率并不高.就海洋固氮作用研究的未来发展,指出今后必须在更大时空尺度上开展海洋生物固氮作用研究,以弥补现有实测数据的不足,并获取固氮微生物种类组成的准确信息,在确定海洋生物固氮作用控制因素的同时,追踪新固定氮的流向,进而为海洋氮循环提供准确信息. 相似文献