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1.
Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m−2 and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation.  相似文献   

2.
We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3–7°S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent second-order ridge-segments near 4°02′S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4°48′S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an  18 km2 area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005−06 at the East Pacific Rise, 9°50′N and reference to global seismic catalogues reveals that a swarm of large (M 4.6−5.6) seismic events was centred on the 5°S segment over a  24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5°S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at  3000 m depth and 407 °C: the hottest vent-fluids yet reported from anywhere along the global ridge crest.  相似文献   

3.
A sodium resonance lidar at 589 nm has been operated in São José dos Campos, Brazil (23°S, 46°W) since 1972 mainly for studies related to the origin, chemistry and dynamics of the mesospheric sodium layer. Beginning in 1993, the improved laser capability has also enabled the processing of the Rayleigh signal from which the temperatures from 35 to 65 km are retrieved on a nightly mean basis. We used these nightly profiles to determine the monthly temperature profiles from 1993 to 2006. The mean temperature characteristics for each year and for the whole period are obtained. Seasonal thermal amplitude is small (6 K peak to peak at 40 and 60 km). Compared with the MSISE-90 model, a large difference is noted, with temperature lower than the model below the stratopause and higher above. Also the seasonal variation has a large difference with better agreement occurring around local winter, but with temperatures higher by 8–10 K at the equinoxes. The semiannual component is dominant over the annual at all altitudes. Linear trends with decreasing temperature of 1.09, 2.29 and 1.42 K/decade are observed at 40, 50 and 60 km, respectively.  相似文献   

4.
The aim of this paper is to report some periodicities observed in the ionospheric parameter foF2 measured at Tucuman (26.9°S; 65.4°W), station placed near the southern crest of the equatorial anomaly. For that, monthly medians of foF2 at several hours of LT for the period 1958–1987 are used. The data are run with Fast Fourier Transform (FFT). Data gaps (4–5 months) are filled by means of linear interpolation. Several periodicities are present. Besides the solar cycle dominant dependence (11 years), semi-annual, annual, five years and quasi-biennial periodicities are also observed. A marked quasi-biennial periodicity is observed at daytime and nighttime hours being their greater amplitude at local noon and midnight. Different mechanisms or combined effects possibly cause them. It is suggested that the solar activity by means of extreme ultraviolet radiation (EUV), which present a quasi-biennial oscillation (QBO) and it is responsible for the ionization, could be the dominant mechanism for the diurnal quasi-biennial periodicity of foF2. At night, since the photoionization by extreme ultraviolet radiation is not significant and the F2 layer is lower than during daytime (100 km) other mechanism may be operative for the quasi-biennial periodicity observed. Possibly the stratospheric QBO contributes to the modulation of the observed behaviour in foF2 at night. This result is preliminary because it needs to be extended to other stations so as to extract definite conclusions. Moreover, we cannot dismiss the possibility of a combined effect of both these mechanisms mainly at daytime and/or QBO influence of geomagnetic parameters.  相似文献   

5.
Horizontal winds in the mesosphere and lower thermosphere over the Antarctic have been measured by a meteor radar at Rothera (67.5°S, 68.0°W) and MF radar at Davis (68.6°S, 78.0°E). Data from Rothera recorded over a 20-month interval in 2005–2006 and data from Davis recorded over the 13-year interval 1994–2006 are examined to investigate the monthly mean behaviour of the lunar semidiurnal tide. Both data sets show a clear signal of the 12.42-h lunar semidiurnal (M2) tide. The amplitude reaches values as large as 8 m s−1. The vertical wavelengths of the tide vary seasonally from 10 to 65 km. Comparisons of the phase of the tide measured over the two sites reveals that it does not purely consist of a migrating wavenumber 2 mode. This suggests that other, non-migrating, modes are likely to be present.  相似文献   

6.
Groundwater samples were collected along a flow path in a shallow, fractured tuffaceous aquifer from the Oasis Valley–Beatty Wash region of southern Nevada, USA, and analyzed for a number of oxyanion-forming trace elements including arsenic (As), antimony (Sb), selenium (Se), molybdenum (Mo), and tungsten (W). In addition, ancillary geochemical parameters, including pH, major solute compositions, dissolved silica, dissolved oxygen, and iron and manganese concentrations were quantified in the groundwaters. Arsenic concentrations range from 70 nmol/kg up to 316 nmol/kg in groundwaters of the Oasis Valley–Beatty Wash flow system, and generally exhibit increasing concentrations with flow down-gradient along the flow path. Antimony, W, and to a lesser extent, Mo, exhibit similar increasing concentration trends with flow down-gradient in the aquifer, albeit, at lower concentrations levels (e.g., mean ± SD for Sb, W, and Mo are 2.3 ± 0.9 nmol/kg, 7.4 ± 3.7 nmol/kg, and 101 ± 19 nmol/kg, respectively). Selenium concentration, which range between 4 and 11 nmol/kg, generally decrease in groundwaters with flow down-gradients in the Oasis Valley–Beatty Wash groundwater flow systems. Inverse modeling of groundwater chemistry evolution from the lower reaches of the Oasis Valley flow path using PHREEQC indicate that the groundwater composition is consistent with mixing of nearly equal proportions of groundwater from upper reaches of Oasis Valley and Beatty Wash groundwater, along with dissolution of volcanic glass, potassium feldspar, and gypsum, followed by calcite precipitation, and formation of secondary zeolites (analcime), clay minerals (Ca-montmorillonite), and cristobalite. The geochemical modeling indicates that the concentrations of As and the other oxyanion-forming trace elements are controlled by dissolution of volcanic glass, water–rock interaction with mineralized zones within the aquifer (i.e., sulfide oxidation), desorption from aquifer surface sites, and mixing of Oasis Valley and Beatty Wash groundwaters.  相似文献   

7.
We have used the thermodynamic model of the climate to estimate the effect of variations in the oceanic cloud cover on the surface temperature of the Earth in the North Hemisphere (NH) during the period 1984–1990. We assume that the variations in the cloud cover are proportional to the variation of the cosmic ray flux measured during the same period. The results indicate that the effect in the temperature is slightly noticeable when we consider the surface hemispheric temperature on July 1987, finding an average temperature anomaly between −0.06°C and −0.14°C, along a latitudinal band between 20° and 40°. The surface temperature averaged globally in the NH presents a decrease of 0.01°C in average, which is almost the same for continents and oceans. However, these values are not significant when compared to the overall variability of the time series with and without forcing.  相似文献   

8.
Internal gravity waves (IGWs) over Kharkiv (49°30′N, 36°51′E) have been studied by using an automatic goniometer of a meteor radar (AG MR), with its antenna directed to the East. The AG MR carries out Doppler measurements of the radial drift velocity and the position of the reflecting area of meteor trails. In order to obtain information about IGW parameters, an algorithm was used that processes the AG MR wind data by dividing the measured volume into several sub-volumes, and by carrying out wavelet analysis of wind variations in these areas. Results of 1 year (1987) of AG MR data show a good qualitative correspondence with literature results. There is an increase of IGW activity during the change of the zonal background wind in spring and autumn. It was found that the mean IGW horizontal phase velocity and predominating horizontal propagation direction change with season. However, the mean period (1.5 h), the dominant amplitude (30 m/s) and the vertical phase velocity do not strongly vary in the course of the year. The mean vertical and horizontal wavelengths were found to be 40 and 250 km, respectively.  相似文献   

9.
We take a fresh look at the topography, structure and seismicity of the Ganges–Brahmaputra Delta (GBD)–Burma Arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential. The GBD, the world's largest delta, has been built from sediments eroded from the Himalayan collision. These sediments prograded the continental margin of the Indian subcontinent by  400 km, forming a huge sediment pile that is now entering the Burma Arc subduction zone. Subduction of oceanic lithosphere with > 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land. The prism starts at an apex south of the GBD shelf edge at  18°N and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit. The front of the prism is blind, buried by the GBD sediments. Thus, the deformation front extends 100 km west of the surface fold belt beneath the Comilla Tract, which is uplifted by 3–4 m relative to the delta. This accretionary prism has the lowest surface slope of any active subduction zone. The gradient of the prism is only  0.1°, rising to  0.5° in the forearc region to the east. This low slope is consistent with the high level of overpressure found in the subsurface, and indicates a very weak detachment. Since its onset, the collision of the GBD and Burma Arc has expanded westward at  2 cm/yr, and propagated southwards at  5 cm/yr. Seismic hazard in the GBD is largely unknown. Intermediate-size earthquakes are associated with surface ruptures and fold growth in the external part of the prism. However, the possibility of large subduction ruptures has not been accounted for, and may be higher than generally believed. Although sediment-clogged systems are thought to not be able to sustain the stresses and strain-weakening behavior required for great earthquakes, some of the largest known earthquakes have occurred in heavily-sedimented subduction zones. A large earthquake in 1762 ruptured  250 km of the southern part of the GBD, suggesting large earthquakes are possible there. A large, but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism, and is the only known candidate for a rupture of the plate boundary along the subaerial part of the GBD–Burma Arc collision zone.  相似文献   

10.
Panarea, characterized by gas unrest in 2002–2003, is the volcanic island with the least constrained structure in the eastern-central Aeolian Arc (Italy). Based on structural measurements, we define here its deformation pattern relative to the Arc. The main deformations are subvertical extension fractures (63% of data), normal faults (25%) and dikes (12%). The mean orientation of the extension fractures and faults is N38°E, with a mean opening direction of N135° ± 8°, implying extension with a moderate component of dextral shear. These data, matched with those available for Stromboli volcano (pure opening) and Vulcano, Lipari and Salina volcanoes (predominant dextral motions) along the eastern-central Arc, suggest a progressive westward rotation of the extension direction and an increase in the dextral shear. The dextral shear turns into compression in the western arc. The recent unrest at Panarea, coeval to that of nearby Stromboli, may also be explained by the structural context, as both volcanoes lie along the portion of the Arc subject to extension.  相似文献   

11.
Active oceanic ridges are part of the global system of diverging plate boundaries encircling the Earth. They represent weak zones of the lithosphere. They are isostatically equilibrated. The system as a whole is considered to be well adapted to the present field of plate driving forces. The search for regularities in the pattern of active oceanic ridges may, therefore, provide valuable information as to the large-scale characteristics of structures and processes in the Earth’s mantle. Two large belts of active oceanic ridges are envisaged: (1) The semi-circular belt bordering the Pacific plate which extends from South of Tasmania to Northwest of Vancouver Island over a length of 20,000 km. It appears to encircle a center P1 in the central Pacific region. (2) The circum-African belt bordering the African plate which extends from the Azores to the Gulf of Aden over a length of 24,000 km. It appears to encircle a center A1 in central Africa. The attempt is made to determine the position of these centers. Extent and position of the ridge systems are described by 34 fixed points. Points R01–R20 mark the circum-African ridge system, points R21-R34 the Pacific ridge system. A least-squares adjustment is used to determine the optimum position of the centers P1 and A1. Center P1 of the Pacific ridge system is located at 169.8°W/2.6°S. Center A1 of the circum-African ridge system is located at 11.6°E/2.4°N. The location error of the centers is less than 2.8°. In view of the great extent of the ridge systems, and considering the fact that the location of P1 and A1 is based on independent data sets, the nearly antipodal and equatorial position of the centers is remarkable. The newly defined centers P1 and A1 are located close to the Pacific pole P, at 170°W/0°N, and the African pole A, at 10°E/0°N. Within the limits of error the center P1 coincides with pole P, the center A1 with pole A. Originally, these poles were introduced in order to describe a fundamental hemispherical symmetry which is apparent in the evolution of the Earth’s lithosphere during the last 180 Ma. The new results confirm the unique position of poles P and A in the global tectonic framework.  相似文献   

12.
Using 3 years of high-quality temperature measurements (2002–2004) recorded from Maui, HI (20.8°N), we have investigated the characteristics of mesospheric seasonal oscillations at low-latitudes. Measurements of the near-infrared OH (6,2) and O2 (0,1) nightglow emission layers (centered at 87 and 94 km) independently reveal a distinct semi-annual oscillation (SAO) and annual oscillation (AO) with amplitudes of 3.8 and 2.0 K, respectively. An observed asymmetry in the seasonal variation of the nocturnal mean, previously reported by Taylor et al. [2005. Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes. Advances in Space Research 35, doi:10.1016/j.asr.2005.05.111] from this site is shown to be due to a superposed AO of amplitude 50% of the SAO signature. Detailed investigations of the local-time variation of the SAO amplitude and phase combined with TIME-GCM simulations of the seasonal variation of the diurnal tide strongly suggest a large local-time dependence of the amplitude (but not phase) of the observed SAO. These data indicate that the true mean temperature SAO amplitude could be as high as 7 K at this latitude.  相似文献   

13.
Twentieth century environmental lead chronologies for the western North Atlantic, Pacific, and Indian Oceans have been reconstructed from annually-banded scleractinian corals. Measurements of lattice-bound Pb in sequential coral bands reveal temporal changes in surface water Pb concentrations and Pb isotopic distributions. Perturbations are observable in all specimens studied, attesting to global augmentation of environmental Pb by industrialization.In the western North Atlantic, Pb perturbations have occurred in direct response to the American industrial revolution and the subsequent introduction and phasing-out of alkyl Pb additives in gasoline. Surface ocean conditions near Bermuda may be reliably reconstructed from the coral data via a lead distribution coefficient of 2.3 for the species,Diploria strigosa. Based on210Pb measurements, a similar distribution coefficient may be characteristic of corals in general. Surface Pb concentrations in the pre-industrial Sargasso Sea were about 15–20 pM. Concentrations rose to near 90 pM by 1923 as a result of metals manufacture and fossil fuel combustion. Beginning in the late 1940's, increased utilization of leaded gasoline eventually led to a peak concentration of 240 pM in 1971, representing an approximate 15-fold increase over background. Surface ocean concentrations are presently declining rapidly (128 pM in 1984) as a result of curtailed alkyl Pb usage. Lead isotopic shifts parallel the concentration record indicating that characteristic industrial and alkyl Pb source signatures have not changed appreciably in time. Industrial releases recorded in the Florida Keys reflect a weaker source and evidence of recirculated Pb (5–6 years old) from the North Atlantic subtropical gyre. An inferred background concentration of 38 pM suggests influence of shelf and/or resuspended inputs of Pb to these coastal waters.In remote areas of the South Pacific and Indian Oceans, industrial signals are fainter and the corals studied much younger than their Atlantic counterparts. Contemporary Pb concentrations implied by coral measurements (assumingKD = 2.3) are 40–50 pM for surface waters near Tutuila and Galapagos in the South Pacific, and 25–29 pM near Mauritius in the Indian Ocean. A single coral band from Fiji (1920 ± 5yr) implies a pre-industrial surface water concentration of 16–19 pM Pb for the South Pacific. In view of reported surface water measurements and the North Atlantic coral data, the Pacific coral extrapolations may be slightly high. This could be a result of small variations inKD among different coral genera, or incorporation of diagenetic Pb by corals sampled in coastal environments.  相似文献   

14.
Nearly 900 nocturnal temperature profiles (85–105 km) from the Colorado State University Na lidar at Fort Collins, CO (40.59N, 105.14W) from 1990 to 2007. After the removal of an episodic warming attributable to Mt. Pinatubo eruption, the time series is analyzed as the sum of the climatological mean, annual and semiannual oscillation, solar cycle effect and trends along with possible annual/semiannual modulation of the latter two. The direct seasonal variation is consistent with the concept of the two-level mesopause. The trends in summer and winter are comparable 90–96 km at −0.15±0.1 K/year. The summer trend turns positive above 96 km. The winter trend is negative with minimum of −0.3 K/year at 100 km but positive at 104 km. The negative trend values are a factor of five smaller than an earlier analysis of the early part of this data due to removal of an episodic event.  相似文献   

15.
The region located between the Carpathian–Balkan and Aegean arcs, the Moesian Platform and Bulgarian Rhodope, is generally assumed to have been stably attached to the East European craton during the Cenozoic evolution of these arcs. The kinematic evolution of this region is, however, poorly constrained by paleomagnetic analysis. In this paper we provide new paleomagnetic data (800 volcanic and sedimentary samples from 12 localities) showing no significant post-Eocene rotation of the Moesian platform and Rhodope with respect to Eurasia, therefore confirming the stability of this region. We compare this result to a provided review of paleomagnetic data from the South Carpathians (Tisza block) and the Aegean region. The Tisza block underwent 68.4 ± 16.7° of middle Miocene ( 15–10 Ma) clockwise rotation with respect to the Moesian Platform, in line with previous rotation estimates based on structural geology. The stability of the Moesian platform during middle Miocene eastward emplacement of the Tisza block into the Carpathian back-arc supports dextral shear along the Southern Carpathians recorded by 13–6 Ma clockwise strike-slip related rotations in foreland deposits. The new reference direction for the Moesian platform and Rhodope allows accurate quantification of the rotation difference with the west Aegean domain at 38.0 ± 7.2° occurring between 15 and 8 Ma. To accommodate this rotation, we propose that the pivot point of the west-Aegean rotation was located approximately in the middle of the rotating domain rather than at the northern tip as previously proposed. This new scenario predicts less extension southeast of the pivot point, in good agreement with estimates from Aegean structural geology. Northwest of the pivot point, the model requires contraction or extrusion that can be accommodated by the coeval motion of the Tisza Block around the northwestern edge of the Moesian platform.  相似文献   

16.
The present study reports long-term variabilities and trends in the middle atmospheric temperature (March 1998–2008) derived from Rayleigh backscattered signals received by the Nd:YAG lidar system at Gadanki (13.5°N, 79.2°E). The monthly mean temperature compositely averaged for the years 1998–2008 shows maximum temperature of 270 K in the months of March–April and September at altitudes between 45 and 55 km. The altitude profile of trend coefficients estimated from the 10 years of temperature observations using regression analysis shows that there exists cooling at the rate with 1σ uncertainty of 0.12±0.1 K/year in the lower stratospheric altitudes (35–42 km) and 0.2±0.08 K/year at altitudes near 55–60 km. The trend is nearly zero (no significant cooling or warming) at altitudes 40–55 km. The regression analysis reveals the significant ENSO response in the lower stratosphere (1 K/SOI) and also in mesosphere (0.6 K/SOI). The solar cycle response shows negative maxima of 1.5 K/100F10.7 units at altitudes 36 km, 41 km and 1 K/100F10.7 units at 57 km. The response is positive at mesospheric altitude near 67 km (1.3 K/100F10.7 units). The amplitudes and phases of semiannual, annual and quasi-biennial oscillations are estimated using least squares method. The semiannual oscillation shows larger amplitudes at altitudes near 35, 45, 62 and 74 km whereas the annual oscillation peaks at 70 km. The quasi-biennial oscillations show larger amplitudes below 35 km and above 70 km. The phase profiles of semiannual and annual oscillations show downward propagation.  相似文献   

17.
In solar cycles 22–23, all solar indices showed maxima near 1990 and 2000 and minima in 1996. The maximum to minimum variation was only 1–2% in the UV range 240–350 nm. Dobson ozone intensities did not show any clear relationship with solar cycle and ozone variations were less than 10%. The UV-B (295–325 nm) observed at ground by Brewer spectrophotometers at some locations had variations of 50–100% for 295–300 nm, and 20–50% for 305–325 nm. The maxima were in different years at different locations (even with separations of only 300 km), did not match with the solar cycle, and were far too large to be explained on the basis of ozone changes (1% decrease of ozone is expected to cause 2% increase of UV-B). Thus, if the data are not bad, the UV-B changes do not match with solar activity or ozone changes and must be mostly due to other local effects (clouds, etc.?). When data are averaged over wide geographical regions, UV-B variation ranges are smaller (10–20%, probably because localised, highly varying cloud effects get filtered out), and are roughly as expected from ozone variations.  相似文献   

18.
The Cenozoic (mostly Neogene) volcanic activity in Syria is part of the extensive magmatism that took place in the Mashrek Region, Middle East, from upper Eocene to Holocene (40–0.0005 Ma). Samples in western Syria are mostly high TiO2 (TiO2 1.8–3.7 wt.%) alkaline mafic rocks (basanites, hawaiites and alkali basalts) plus rare transitional/tholeiitic basalts and basaltic andesites) with within-plate-like trace element signature.On the basis of incompatible trace element content, the volcanic activity in Syria has been divided into two stages: the first lasting from 25 to 5 Ma and the second from 5 to recent times. Indeed, the Syrian lavas show incompatible trace element content increasing with decreasing age from 25 to 5 Ma, followed by an abrupt decrease to low values roughly at the Miocene–Pliocene boundary. This temporal shift in composition is related to major tectonic re-organization occurred during upper Miocene.The proposed petrogenetic model invokes three steps: (a) passive upwelling of the shallow asthenosphere during the development of the Dead Sea transform fault system. Different degrees of partial melting were followed by variable extents of fractional crystallization and limited upper crustal contamination; (b) the Miocene–Pliocene boundary tectonic change enhanced passive decompression of the same sources and a consequent increase in degree of partial melting resulting in low incompatible trace element content of the relatively high-volume liquids; (c) after this phase, the incompatible trace element content in the basaltic magmas increased as consequence of fractional crystallization processes.Major and trace element content similarities with the rest of the circum-Mediterranean igneous rocks are consistent with a common relatively shallow origin for the Cenozoic anorogenic magmatism of the entire circum-Mediterranean area (the so-called Common Magmatic Reservoir). Because much of the igneous activity in the studied area is concentrated near the Dead Sea fault, the origin of Cenozoic magmatism in Syria (and in the rest of the circum-Mediterranean area) reflects a strong lithospheric control on the loci of partial melting. Mantle plumes from lower mantle and/or north-westward channelling of the Afar mantle plume is not needed to explain volcanic activity in Syria and the Mashrek area.  相似文献   

19.
In the subglacial eruption at Gjálp in October 1996 a 6 km long and 500 m high subglacial hyaloclastite ridge was formed while large volumes of ice were melted by extremely fast heat transfer from magma to ice. Repeated surveying of ice surface geometry, measurement of inflow of ice, and a full Stokes 2-D ice flow model have been combined to estimate the heat output from Gjálp for the period 1996–2005. The very high heat output of order 106 MW during the eruption was followed by rapid decline, dropping to  2500 MW by mid 1997. It remained similar until mid 1999 but declined to 700 MW in 1999–2001. Since 2001 heat output has been insignificant, probably of order 10 MW. The total heat carried with the 1.2 × 1012 kg of basaltic andesite erupted (0.45 km3 DRE) is estimated to have been 1.5 × 1018 J. About two thirds of the thermal energy released from the 0.7 km3 edifice in Gjálp occurred during the 13-day long eruption, 20% was released from end of eruption until mid 1997, a further 10% in 1997–2001, and from mid 2001 to present, only a small fraction remained. The post-eruption heat output history can be reconciled with the gradual release of 5 × 1017 J thermal energy remaining in the Gjálp ridge after the eruption, assuming single phase liquid convection in the cooling edifice. The average temperature of the edifice is found to have been approximately 240 °C at the end of the eruption, dropping to  110 °C after 9 months and reaching  40 °C in 2001. Although an initial period of several months of very high permeability is possible, the most probable value of the permeability from 1997 onwards is of order 10− 12 m2. This is consistent with consolidated/palagonitized hyaloclastite but incompatible with unconsolidated tephra. This may indicate that palagonitization had advanced sufficiently in the first 1–2 years to form a consolidated hyaloclastite ridge, resistant to erosion. No ice flow traversing the Gjálp ridge has been observed, suggesting that it has effectively been shielded from glacial erosion in its first 10 years of existence.  相似文献   

20.
Marine plastic pollution is ubiquitous throughout the world’s oceans, and has been found in high concentrations in oceanic gyres of both the northern and southern hemispheres. The number of studies demonstrating plastic debris at seabird colonies and plastic ingestion by adult seabirds has increased over the past few decades. Despite the recent discovery of a large aggregation of plastic debris in the South Pacific subtropical gyre, the incidence of plastics at seabird colonies in New Zealand is unknown. Between 2011 and 2012 we surveyed six offshore islands on the northeast coast of New Zealand’s North Island for burrow-nesting seabird colonies and the presence of plastic fragments. We found non-research related plastic fragments (0.031 pieces/m2) on one island only, Ohinau, within dense flesh-footed shearwater (Puffinus carneipes) colonies. On Ohinau, we found a linear relationship between burrow density and plastic density, with 3.5 times more breeding burrows in areas with plastic fragments found. From these data we conclude that plastic ingestion is a potentially a serious issue for flesh-footed shearwaters in New Zealand. Although these results do not rule out plastic ingestion by other species, they suggest the need for further research on the relationship between New Zealand’s pelagic seabirds and marine plastic pollution.  相似文献   

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