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1.
Monthly collections of phytoplankton were supported by physical–chemical data and measures of chlorophyll a concentrations in the search for particular environmental factors that could explain the constant presence of desmids in a Mexican tropical lake, a characteristic not common among the phytoplanktic communities of Mexican lakes. Samplings were taken from the water column in the deepest part of the lake (40 m) and intensified in the metalimnetic zone, whose establishment was monitored by observations of temperature and oxygen profiles. The general behavior of Lake Zirahuén was typical of warm monomictic tropical lakes at high elevation: a short mixing phase during the hemispheric winter. The depth of ZMIX and Zeu revealed a well-illuminated epilimnion, suggesting that phytoplankton communities are not likely to be light-limited. The oligotrophic nature of the lake is indicated by discrete concentrations of inorganic nutrients, PTOT in the interval of 0.01–0.03 mg l−1 and chlorophyll a between 0.23 and 3.98 μg l−1. These characteristics together with a low concentration of calcium, define a lacustrine environment different from other Mexican lakes, and one that could be suitable for desmids communities.  相似文献   

2.
Although comparative analyses between dimictic and polymictic lakes have noted the key role of mixing regime in governing water quality, limnologists have historically focused on dimictic lakes, leaving polymictic lakes relatively understudied. In this study, we investigated whether the effects of agricultural development on water quality differed between dimictic and polymictic lakes in a naturally nutrient-rich region of Alberta, Canada. Through a spatial limnological analysis of 36 sites, we found that the relationship between surface water total phosphorus concentration and the percent of agriculture (% Agr) in the catchments differed between dimictic and polymictic lakes, where the proportion of variance explained was much more pronounced in the dimictic (79% explained) than in the polymictic systems (7% explained). Paleolimnological analyses of subfossil chironomids in surface sediment samples (0–1 cm) from 18 of the 36 study lakes, and in sediment core profiles from the dimictic and polymictic basins of a eutrophic lake, showed that water quality differed between mixis groups. We found that the surface sediment chironomid assemblages differed significantly between polymictic and dimictic lakes. Detailed analyses of the sediment cores demonstrated that the two basin types differed in their responses to land-use change through time, as only the dimictic basin showed a parallel increase in anoxia with increasing agricultural development. We suggest that in naturally-fertile landscapes, external nutrient loading exerts a more notable effect on dimictic lakes, whereas internal nutrient loading is more important in polymictic systems.  相似文献   

3.
Previous studies have used sondes to measure diel changes in dissolved oxygen and thereby estimate gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP). Most of these studies estimate rates for the surface layer and require knowing the depth of the mixed layer (Zmix), which is usually determined from discrete daily or weekly temperature profiles. However, Zmix is dynamic, as the thermal structure of lakes may change at scales of minutes rather than days or weeks. We studied two thermally stratified lakes that exhibited intermittent microstratification in the mixed layer. We combined sonde-based estimates of metabolism with high-frequency measurements of stratification using thermistor chains to determine how the short-term dynamics of stratification affect metabolic rates. We calculated estimates of metabolism using time series of Zmix measured at seasonal, weekly, daily, and 5-min intervals. Areal rates of GPP and R were up to 24 and 29% less, respectively, using the 5-min measurements of Zmix rather than weekly Zmix, while NEP was not significantly different. These reduced areal rates are mostly the consequence of the reduction in the depth of the mixed layer. Microstratification occurred frequently in both lakes and affected volumetric rates in one lake where R was significantly lower, NEP was significantly higher, and GPP was marginally lower compared to days without microstratification. Hence, microstratification not only affects the depth of the mixed layer, but also alters the processes that influence photosynthesis and respiration. Future studies should consider microstratification and possibly employ multiple sondes with thermistor chains that enable integrating metabolic rates to a specific depth, rather than assuming a stable upper mixed layer as the basis for calculations.  相似文献   

4.
Down-core variation in planktonic foraminifera (PF) at Site 1143 (ODP 184) has disclosed the evolution of upper water-column structure over the last 12 Ma in the southern South China Sea. In the early Late Miocene (∽10.6–7.8 Ma), there existed a lower percentage of total deep-dwelling species, reflecting a water thermocline deeper than that in the Middle Miocene, which resulted from the closure of Indonesian seaway and relevant intensification of the equatorial warm current. After the increase in deep-dwelling PF and the rising of thermocline during the late Late Miocene (7.6–6.4 Ma), the total deep-dwelling species decreased gradually from late Late Miocene (6.4 Ma) to the Pliocene, implying the deepening of water thermocline. The evolution of thermocline depth in the southern South China Sea reflected by the PF at Site 1143 might be a good indicator of the change of west Pacific “warm pool”.  相似文献   

5.
Most studies of benthic macroinvertebrate communities are from shallow lakes or restricted to the littoral zone of deep, temperate lakes, with just a few dealing with the deep benthos. Furthermore, the deep benthic macroinvertebrate communities of tropical lakes are almost unknown. The present work describes the benthic macroinvertebrate communities of three tropical, warm monomictic lakes in “Lagunas de Montebello” National Park, Mexico, by describing the differences along the bathymetric profile, from the littoral down to the profound benthos. We studied the benthic macroinvertebrate communities in the two contrasting hydrodynamic periods of the warm monomictic lakes: a) stratification, when the hypolimnion becomes anoxic, and b) mixing, when the water column becomes oxygenated. We expected: 1) a reduction in the benthic macroinvertebrate taxonomic richness, density, and biomass from the littoral to the deep zone, 2) an impoverished benthic macroinvertebrate community while stratified (anoxia) compared to mixing (oxygenated), and 3) depletion in the taxonomic richness, density, and biomass of the profundal benthic macroinvertebrates in the tropical compared to temperate lakes. We found: 1) a decreasing trend in taxonomic richness (6 ± 2–3 ± 1 taxa), density (1868.7 ± 1069.7–349.1 ± 601.8 in. m−2) and biomass (277.8 ± 188.9–85.1 ± 95.6 mg C m−2) from the littoral to the deep zone; chironomids dominated the littoral zone, while oligochaetes dominated the deep zone. 2) Lower density and biomass but not taxonomic richness while stratified (4 ± 3 taxa; 586.2 ± 527.6 in. m−2; 81.6 ± 164.3 mg C m−2) compared to mixing (4 ± 3 taxa; 877.5 ± 1051.4 in. m−2; 190.1 ± 131.1 mg C m−2). 3) lower taxonomic richness and density but not biomass in tropical Montebello oligotrophic lakes (3 ± 3 taxa; 349.1 ± 601.8 in. m−2; 85.1 ± 195.6 mg C m−2) compared to temperate analogous (2–48 taxa; 492−83,189 8 in. m−2; 0.13−201.5 mg m−2). We conclude the early onset and long-lasting hypolimnetic anoxia restrict the benthic macroinvertebrate community radiation and diversification in tropical, oligotrophic, warm monomictic lakes.  相似文献   

6.
Brook Lemma   《Limnologica》2009,39(3):230-243
Bishoftu-Guda and Hora-Arsedi are two crater lakes found in close proximity with each other in a locality known as Bishoftu, 50 km south of Addis Ababa, capital city of Ethiopia. The main objective of this study was to measure some physico-chemical features and discuss their relations with the dial vertical migration (DVM) behavior of Paradiaptomus africanus, the dominant macrozooplankton in both lakes. By depth measurements of dissolved oxygen and temperature showed that there is persistent stratification in these lakes. Secchi depth was shallow and the water chemistry as shown from conductivity and chemical analysis were comparable between the two lakes. These data were compared with previous reports to bring out the overall limnological scenario of the two lakes. Then, the relations of these data to the DVM of P. africanus in both lakes were discussed. It was found out that DVM of P. africanus occurred in Lakes Bishoftu-Guda and Hora-Arsedi mostly within a range of about 3 m very likely for two reasons, namely avoidance of solar radiation and ultimately vertebrate visual predation. However, the depth of DVM of P. africanus was found to be very shallow probably due to high water turbidity that provided this calanoid sufficient refuge by daylight from both dangers, while at the same time P. africanus remained in warm and oxygen-rich waters. Temperature was not much of a factor affecting DVM as it remained above 19 °C at all depths. As this study was conducted over limited time frames, seasonal studies regarding changes in physico-chemical parameters, plankton, vertebrate predators and human interference were recommended so that the information so gathered could be used in the management of the study lakes.  相似文献   

7.
Vertical distributions of chlorophyll in deep, warm monomictic lakes   总被引：1，自引：0，他引：1  
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r 2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth of the euphotic zone (z eu) is consistently shallower than the depth of the surface mixed layer (z SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear to disrupt the annual cycle of maximum chlorophyll in winter.  相似文献   

8.
The trophic importance of bacterioplankton as a source of carbon and sulfur nutrition for consumers in meromictic lakes was tested using stable carbon (delta 13C) and sulfur (delta 34S) isotopic measurements. Studies in three lakes near Syracuse, New York, showed that most consumers ultimately derive their C and S nutrition from a mixture of terrestrial detritus, phytoplankton, and littoral vegetation, rather than from bacterioplankton. Food webs in these meromictic lakes are thus similar to those in other lakes that lack dense populations of bacterioplankton.  相似文献   

9.
Variations of polythionates (sulfane disulfonates) and sulfate in the Yugama crater lake, Japan, have been monitored for more than 25 years. Just before the 1982 eruption at the crater lake, polythionate ions decreased to zero from the normal level of about 2000 ppm and sulfate ions increased from 2500 to 5000 ppm. During the 1982 eruption polythionate and sulfate ions varied inversely in concentration and the variations exactly coincided with the frequency of volcanic earthquakes and subsequent explosions. These observations are interpreted in terms of aqueous reactions of fumarolic SO2-H2S gases, resulting in precipitation of alunite. The behavior of polythionate and sulfate ions strongly suggests that they are useful indicator for prediction of impending volcanic hazards from active crater lakes.  相似文献   

10.
湖泊热力结构不仅影响湖泊内部生态环境,而且与区域气象和气候系统相互影响,但目前对湖泊垂直温度的观测研究仍非常匮乏.本研究基于青藏高原拉昂错连续的湖温和气象观测,分析了小时尺度和日尺度热力分层规律和混合层深度的变化特征.结果表明:拉昂错为冷多次完全混合型湖泊;湖表温度8月达到最大值,湖面敞水区和沿岸的湖表温度季节震荡相同,但存在一定的空间差异;与空气温度相比,湖表温度变幅小,降温更慢,峰值滞后约1个月.同时发现,拉昂错混合层深度变化较为规律,辐射和风速是影响湖泊混合层深度的主要外界因子.探明真实的高原湖泊分层规律,有利于提高湖泊模拟能力,为优化湖泊参数化方案提供参考.  相似文献   

11.
In many coastal plain estuaries light attenuation by suspended sediments confines the photic zone to a small fraction of the water column, such that light limitation is a major control on phytoplankon production and turnover rate. For a variety of estuarine systems (e.g. San Francisco Bay, Puget Sound, Delaware Bay, Hudson River plume), photic-zone productivity can be estimated as a function of phytoplankton biomass times mean irradiance of the photic zone. Net water column productivity also varies with light availability, and in San Francisco Bay net productivity is zero (estimated respiratory loss of phytoplankton balances photosynthesis) when the ratio of photic depth (Zp) to mixed depth (Zm) is less than about 0.2. Thus whenever Zp: Zm < 0.2, the water column is a sink for phytoplankton production.Much of the spatial and temporal variability of phytoplankton biomass or productivity in estuaries is explained by variations in the ratio of photic depth to mixed depth. For example, phytoplankton blooms often coincide with stratification events that reduce the depth of the surface mixed layer (increase Zp: Zm). Shallow estuarine embayments (high Zp: Zm) are often characterized by high phytoplankton biomass relative to adjacent channels (low Zp: Zm). Many estuaries have longitudinal gradients in productivity that mirror the distribution of suspended sediments: productivity is low near the riverine source of sediments (low Zp: Zm) and increases toward the estuary mouth where turbidity decreases. Some of these generalizations are qualitative in nature, and detailed understanding of the interaction between turbidity and estuarine phytoplankton dynamics requires improved understanding of vertical mixing rates and phytoplankton respiration.  相似文献   

12.
Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (3He/4He)fumarole to (3He/4He)air between 5 and 6 correlated with variations of several chemical species. High 3He/4He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the 3He/4He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.  相似文献   

13.
Eruptions through crater lakes or shallow seawater, referred to here as subaqueous eruptions, present hazards from hydromagmatic explosions, such as base surges, lahars, and tsunamis, which may not exist at volcanoes on dry land. We have systematically compiled information from eruptions through surface water in order to understand the circumstances under which these hazards occur and what disastrous effects they have caused in the past. Subaqueous eruptions represent only 8% of all recorded eruptions but have produced about 20% of all fatalities associated with volcanic activity in historical time. Excluding eruptions that have resulted in about a hundred deaths or less, lahars have killed people in the largest number of historical subaqueous eruptions (8), followed by pyroclastic flows (excluding base surges; 5) tsunamis (4), and base surges (2). Subaqueous eruptions have produced lahars primarily on high (>1000 m), steep-sided volcanoes containing small (<1 km diameter) crater lakes. Tsunamis and other water waves have caused death or destroyed man-made structures only at submarine volcanoes and at Lake Taal in the Philippines. In spite of evidence that magma–water mixing makes eruptions more explosive, such explosions and their associated base surges have caused fewer deaths, and have been implicated in fewer eruptions involving large numbers of fatalities than lahars and tsunamis. The latter hazards are more deadly because they travel much farther from a volcano and inundate coastal areas and stream valleys that tend to be densely settled.  相似文献   

14.
Temperature profiles in summer (February/March 1990) were measured in 24 lakes along a latitudinal transect from central Chile (32° S) to Patagonia (47° S), and on Easter Island (27° S). The lakes of the temperature zone, between 47° S and 38° S, are warm monomictic with surface and deep-water temperatures ranging from 12 °C to 21 °C and from 5.5 °C to 10 °C respectively. The heat content per unit area in midsummer was found to vary with lake area. The local stability of stratification (N 2) varied by more than two orders of magnitude, declining with increasing latitude, altitude, and depth. The lakes can be classified according to morphometric and temperature characteristics, mixing depth, stability of stratification and glacial turbidity. Lago General Carrera (463 m) was found to be almost as deep as Lago Nahuel Huapi (464 m), which is considered to be the deepest lake in South America.  相似文献   

15.
Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake.  相似文献   

16.
In this study, data from MODIS land surface temperature product level 3 (MOD11A2) were used to investigate the spatiotemporal variation of Eurasian lakes water surface temperature (LSWT) from 2001 to 2015, and to examine the most influencing factors of that variation. The temperature of most lakes in the dry climate zone and in the equatorial climatic zone varied from 17 to 31°C and from 23 to 27°C, respectively. LSWTs in the warm temperate and cold climatic zones were in the range of 20 to 27°C and −0.6 and 17°C, respectively. The average day time LSWT in the polar climate zone was −0.71°C in the summer. Lakes in high latitude and in the Tibetan Plateau displayed low LSWT, ranging from −11 to 26°C during the night time. Large spatial variations of diurnal temperature difference (DTD) were observed in lakes across Eurasia. However, variations in DTDs were small in lakes located in high latitude and in tropical rainforest regions. The shallow lakes showed a rapid response of LSWT to solar and atmospheric forcing, while in the large and deep lakes, that response was sluggish. Results of this study demonstrated the applicability of remote sensing and MODIS LST products to capture the spatial–temporal variability of LSWT across continental scales, in particular for the vast wilderness areas and protected environment in high latitude regions of the world. The approach can be used in future studies examining processes and factors controlling large scale variability of LSWT.  相似文献   

17.
Lake Albano, located 20 km to the SE of Rome, is hosted within the most recent crater of the quiescent Alban Hills volcanic complex that produced hydromagmatic eruptions in Holocene times. Stratigraphic, archaeological and historical evidence indicates that the lake level underwent important variations in the Bronze Age. Before the IV century B.C. several lahars were generated by water overflows from the lake and in the IV century B.C. Romans excavated a drainage tunnel. The lake is located above a buried carbonate horst that contains a pressurized medium-enthalpy geothermal reservoir from which fluids escape to the surface to produce many important gas manifestations of mostly CO2. Previous studies recognized the presence of gas emissions also from the crater bottom. In 1997 the possibility of a Nyos-type event triggered by a lake rollover was considered very low, because the CO2 water concentration at depth was found to be far from saturation. However, considering the high population density nearby, the Italian Civil Protection Department recommended that periodical monitoring be carried out. To this scope we initiated in 2001 a systematic geochemical study of the lake. Thirteen vertical profiles have been repeatedly carried out in 2001–2006, especially in the deepest part of the lake (167 m in 2006), measuring T, pH, dissolved O2 and electrical conductivity. Water samples were collected from various depths and chemically and isotopically analysed. Two similar profiles have been measured also in the nearby Nemi crater lake. Results indicate that in the 4.5 years of monitoring the pressure of gas dissolved in the Lake Albano deep waters remained much lower than the hydrostatic pressure. A CO2 soil survey carried out on the borders of the two lakes, indicates the presence of some zones of anomalous degassing of likely magmatic origin. A water overturn or a heavy mixing of deep and shallow waters likely occurred in winter 2003–2004, when cold rainfall cooled the surface water below 8.5 °C. Such overturns cause only a limited gas exsolution from the lake when the deep water is brought to a few meters depth but can explain the observed decrease with time of dissolved CO2 at depth and related water pH increase. A gas hazard could occur in the case of a sudden injection through the lake bottom of a huge quantity of CO2-rich fluids, which might be caused by earthquake induced fracturing of the rock pile beneath the lake. A limnic gas eruption might also occur should CO2 concentration build up within the lake for a long time.  相似文献   

18.
This paper focuses on the chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4 and CO2. The δ13C-CH4 and δD-CH4 values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH4 is mainly produced by microbial activity. The δ13C-CO2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2 source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2 values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2 and CH4 at different depths are mainly depending on (1) CO2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2–CH4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2 and CH4 concentrations. In the hypolimnion, where the δ13C-CO2 values progressively increase with depth and the δ13C-CH4 values show an opposite trend, biogenic CO2 production from CH4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2 values, and measured δ13CTDIC values are not consistent, indicating that CO2 and the main carbon-bearing ion species (HCO3 ?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO2 and CH4. This study demonstrates that the vertical patterns of the CO2/CH4 ratio and of δ13C-CO2 and δ13C-CH4 are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO2 input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.  相似文献   

19.
Water chemistry of crater lakes, maars and water reservoirs linked to some Mexican volcanoes within and outside the Mexican Volcanic Belt has been determined for several years and examined regarding environmental and volcanic factors. All the analyzed lakes are relatively small with a maximum depth of 65 m, and are located in regions with different climates, from semi-arid to very humid, with altitudes ranging from 100 to more than 4000 m a.s.l. Crater lakes in active volcanoes (El Chichón, Popocatépetl) have very low pH, moderate to high temperatures and major ion concentrations varying with the level of volcanic unrest. Lakes in sub-arid and temperate-arid regions (like maars in Puebla and Guanajuato states) show high alkalinity and pH, with bicarbonate/carbonate, chloride, sodium and magnesium as predominant ions. Lakes located in humid climates (Central Michoacán and Veracruz state) have low mineralization and near-neutral pH values. In general, conservative dissolved ions and conductivity appear to be mostly controlled by precipitation/evaporation and by the ionic concentration of groundwater inputs. Calcium, magnesium, sulfate concentrations and pH are strongly influenced by volcanic-rock or volcanic gas interactions with water. The influence of low-level volcanic activity on crater lakes may be obscured by water–rock interactions, and climatic factors. One of the aims of this paper is to define the relative influence of these factors searching for a reference frame to recognize the early volcanic precursors in volcano-related lakes.  相似文献   

20.
Gas emissions from Erebus volcano, Antarctica, were measured by open-path Fourier transform infrared spectroscopy to understand degassing of its magmatic system. Two degassing phonolite lava lakes were present in the summit crater during observation in December 2004. We report analyses of H2O, CO2, CO, SO2, HF, HCl and OCS, (in order of molar abundance) in the plumes. Variations in the proportions of these species strongly reflect the dynamics of degassing, and sourcing of gas from different depths in the magmatic network. The highest observed ratios of CO2 and H2O are consistent with gas extracted from the melt at a depth of up to ∼ 2 km below the lava lakes. Magma degassing above this depth contributes to a higher H2O/CO2 proportion in the airborne plume. The ratio therefore reflects the balance of deeper vs. shallower contributions of volatiles and, possibly, a combination of closed- and open-system degassing. We observe a strong contrast in HF content in emissions from the two lava lakes, which we attribute to differing levels of magma ascent and/or cooling and crystallization of the magma supply. Fluxes of all gas species were determined using independent SO2 flux determinations and measured gas ratios. In the case of CO2 and water, ∼ 1 and ∼ 0.4 m3 s− 1, respectively, of parental basanite magma are required to sustain the calculated output. The discrepancy between the two figures is readily explained by sequestration of part of the magma supply at depth such that it only partially degasses its complement of water.  相似文献   

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