Global-scale validation of model-based load deformation of the Earth's crust from continental watermass and atmospheric pressure variations using GPS

Temporal mass variations in the continental hydrosphere and in the atmosphere lead to changes in the gravitational potential field that are associated with load-induced deformation of the Earth’s crust. Therefore, models that compute continental water storage and atmospheric pressure can be validated by measured load deformation time series. In this study, water mass variations as computed by the WaterGAP Global Hydrology Model (WGHM) and surface pressure as provided by the reanalysis product of the National Centers for Environmental Prediction describe the hydrological and atmospheric pressure loading, respectively. GPS observations from 14 years at 208 stations world-wide were reprocessed to estimate admittance factors for the associated load deformation time series in order to determine how well the model-based deformation fits to real data. We found that such site-specific scaling factors can be identified separately for water mass and air pressure loading. Regarding water storage variation as computed by WGHM, weighted global mean admittances are 0.74 ± 0.09, 0.66 ± 0.10, 0.90 ± 0.06 for the north, east and vertical component, respectively. For the dominant vertical component, there is a rather good fit to the observed displacements, and, averaged over all sites, WGHM is found to slightly overestimate temporal variations of water storage. For Europe and North America, with a dense GPS network, site-specific admittances show a good spatial coherence. Regarding regional over- or underestimation of WGHM water storage variations, they agree well with GRACE gravity field data. Globally averaged admittance estimates of pre-computed atmospheric loading displacements provided by the Goddard Geodetic VLBI Group were determined to be 0.88 ± 0.04, 0.97 ± 0.08, 1.13 ± 0.01 for the north, east and vertical, respectively. Here, a relatively large discrepancy for the dominant vertical component indicates an underestimation of corresponding loading predictions.     

Global surface mass from a new combination of GRACE,modelled OBP and reprocessed GPS data

Weekly surface loading variations are estimated from a joint least squares inversion of load-induced GPS site displacements, GRACE gravimetry and simulated ocean bottom pressure (OBP) from the finite element sea-ice ocean model (FESOM).In this study, we directly use normal equations derived from reprocessed GPS observations, where station and satellite positions are estimated simultaneously. The OBP weight of the model in the inversion is based on a new error model, obtained from 2 FESOM runs forced with different atmospheric data sets.Our findings indicate that the geocenter motion derived from the inversion is smooth, with non-seasonal RMS values of 1.4, 0.9 and 1.9 mm for the X, Y and Z directions, respectively. The absolute magnitude of the seasonal geocenter motion varies annually between 2 and 4.5 mm. Important hydrological regions such as the Amazon, Australia, South-East Asia and Europe are mostly affected by the geocenter motion, with magnitudes of up to 2 cm, when expressed in equivalent water height.The chosen solar radiation pressure model, used in the GPS processing, has only a marginal effect on the joint inversion results. Using the empirical CODE model slightly increases the annual amplitude of the Z component of the geocenter by 0.8 mm. However, in case of a GPS-only inversion, notable larger differences are found for the annual amplitude and phase estimates when applying the older physical ROCK models. Regardless of the used radiation pressure model the GPS network still exhibits maximum radial expansions in the order of 3 mm (0.45 ppb in terms of scale), which are most likely caused by remaining GPS technique errors.In an additional experiment, we have used the joint inversion solution as a background loading model in the GPS normal equations. The reduced time series, compared to those without a priori loading model, show a consistent decrease in RMS. In terms of the annual height component, 151 of the 189 stations show a reduction of at least 10% in seasonal amplitude.On the ocean floor, we find a positive overall correlation (0.51) of the inversion solution with time series from globally distributed independent bottom pressure recorders.Even after removing a seasonal fit we still find a correlation of 0.45. Furthermore, the geocenter motion has a significant effect on ocean bottom pressure as neglecting it causes the correlation to drop to 0.42.     

Global distribution and climatological features of the 5–6-day planetary waves seen in the SABER/TIMED temperatures (2002–2007)

The paper is focused on the global spatial structure, seasonal and interannual variability of the ～5-day Rossby (W1) and ～6-day Kelvin (E1) waves derived from the SABER/TIMED temperature measurements for 6 full years (January 2002–December 2007). The latitude structure of the ～5-day W1 wave is related to the gravest symmetric wave number 1 Rossby wave. The vertical structure of the ～5-day Rossby wave amplitude consists of double-peaked maxima centred at ～80–90 km and ～105–110 km. This wave has a vertically propagating phase structure from the stratosphere up to 120 km altitude with a mean vertical wavelength of ～50–60 km. The ～6-day E1 wave is an equatorially trapped wave symmetric about the equator and located between 20°N and 20°S. Its seasonal behaviour indicates some equinoctial and June solstice amplifications, while the vertical phase structure indicates that this is a vertically propagating wave between 20–100 km altitudes with a mean vertical wavelength of ～25 km.     

Micrometeorological measurements in Nigeria during the total solar eclipse of 29 March, 2006

The total solar eclipse of 29 March, 2006 which was visible at Ibadan (7.55°N, 4.56°E), south-western Nigeria was utilized to document atmospheric surface-layer effects of the eclipse for the first time in Nigeria. The meteorological parameters measured are global radiation, net radiation, wind speed (at different heights), atmospheric pressure and soil temperature (5, 10 and 30 cm), moisture and heat flux and rainfall. The results revealed remarkable dynamic atmospheric effects. The observations showed that the incoming solar radiation, net radiation and air temperature were significantly affected.There was an upsurge of wind speed just before the first contact of the eclipse followed by a very sharp decrease in wind speed due to the cooling and stabilization of the atmospheric boundary layer. The atmospheric pressure lags the eclipse maximum by 1 h 30 min, while the soil temperature at 5 and 10 cm remain constant during the maximum phase of the eclipse.     

Ancient Os isotope signatures from the Ontong Java Plateau lithosphere: Tracing lithospheric accretion history

In order to better understand the nature and formation of oceanic lithosphere beneath the Early Cretaceous Ontong Java Plateau, Re–Os isotopes have been analysed in a suite of peridotite xenoliths from Malaita, Solomon Islands. Geological, thermobarometric and petrological evidence from previous studies reveal that the xenoliths represent virtually the entire thickness of the southern part of subplateau lithospheric mantle (< 120 km). This study demonstrates that vertical Os isotopic variations correlate with compositional variations in a stratified lithosphere. The shallowest plateau lithosphere (< 85 km) is dominated by fertile lherzolites showing a restricted range of ¹⁸⁷Os/¹⁸⁸Os (0.1222 to 0.1288), consistent with an origin from ~ 160 Ma Pacific lithosphere. In contrast, the basal section of subplateau lithospheric mantle (~ 95–120 km) is enriched in refractory harzburgites with highly unradiogenic ¹⁸⁷Os/¹⁸⁸Os ratios ranging from 0.1152 to 0.1196, which yield Proterozoic model ages of 0.9–1.7 Ga. Although the whole range of Os isotope compositions of Malaita peridotites is within the variations seen in modern abyssal peridotites, the contrasting isotopic compositions of shallow and deep plateau lithosphere suggest their derivation from different mantle reservoirs. We propose that the subplateau lithosphere forms a genetically unrelated two-layered structure, comprising shallower, typical oceanic lithosphere underpinned by deeper impinged material, which included a component of recycled Proterozoic lithosphere. The impingement of residual but chemically heterogeneous mantle, mechanically coupled to the recently formed, thin lithosphere, may have a bearing on the anomalous initial uplift and late subsidence history of the seismically anomalous plateau root.     

Cenozoic changes in atmospheric lead recorded in central Pacific ferromanganese crusts

The possible sources of pre-anthropogenic Pb contributed to the world's oceans have been the focus of considerable study. The role of eolian dust versus riverine inputs has been of particular interest. With better calibration of isotopic records from central Pacific ferromanganese crusts using Os isotope stratigraphy it now appears that deep water Pb isotopic compositions were effectively homogeneous over a distance of 5000 km for the past 80 Myr. The composition shifted slightly from high ²⁰⁶Pb/²⁰⁴Pb ratios in the range of 18.87 ± 0.02 before 65 Ma to lower values of 18.62 ± 0.02 by 45 Ma and then gradually increased again very slightly to the present day ratio of 18.67 ± 0.02. The regional homogeneity provides evidence of a dominant well-mixed atmospheric source the most likely candidate for which is volcanic aerosols contributed either directly or as soluble condensates on eolian dust. The slight shift in Pb isotope composition of deep waters in the central Pacific between 65 and 45 Ma may be the result of a regional- or perhaps global-scale change in the sources of volcanic exhalations and volcanic activity caused by an increase in the importance of melting and assimilation of older continental crustal components over the Cenozoic.     

Applying local Green's functions to study the influence of the crustal structure on hydrological loading displacements

The influence of the elastic Earth properties on seasonal or shorter periodic surface deformations due to atmospheric surface pressure and terrestrial water storage variations is usually modeled by applying a local half-space model or an one dimensional spherical Earth model like PREM from which a unique set of elastic load Love numbers, or alternatively, elastic Green's functions are derived. The first model is valid only if load and observer almost coincide, the second model considers only the response of an average Earth structure. However, for surface loads with horizontal scales less than 2500 km², as for instance, for strong localized hydrological signals associated with heavy precipitation events and river floods, the Earth elastic response becomes very sensitive to inhomogeneities in the Earth crustal structure.We derive a set of local Green's functions defined globally on a 1° × 1° grid for the 3-layer crustal structure TEA12. Local Green's functions show standard deviations of ±12% in the vertical and ±21% in the horizontal directions for distances in the range from 0.1° to 0.5°. By means of Green's function scatter plots, we analyze the dependence of the load response to various crustal rocks and layer thicknesses. The application of local Green's functions instead of a mean global Green's function introduces a variability of 0.5–1.0 mm into the hydrological loading displacements, both in vertical and in horizontal directions. Maximum changes due to the local crustal structures are from −25% to +26% in the vertical and −91% to +55% in the horizontal displacements. In addition, the horizontal displacement can change its direction significantly. The lateral deviations in surface deformation due to local crustal elastic properties are found to be much larger than the differences between various commonly used one-dimensional Earth models.     

Empirical relationship between leaf wax n-alkane δD and altitude in the Wuyi,Shennongjia and Tianshan Mountains,China: Implications for paleoaltimetry

Estimating past elevation not only provides evidence for vertical movements of the Earth's lithosphere, but also increases our understanding of interactions between tectonics, relief and climate in geological history. Development of biomarker hydrogen isotope-based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance. Here we present leaf wax-derived n-alkane δD (δD_wax) values along three soil altitudinal transects, at different latitudes, in the Wuyi, Shennongjia and Tianshan Mountains in China, to investigate δD_wax gradients and the apparent fractionation between leaf wax and precipitation (ε_wax-p).We find that soil δD_wax track altitudinal variations of precipitation δD along the three transects that span variable environment conditions and vertical vegetation spectra. An empirical δD_wax-altitude relation is therefore established in which the average δD_wax lapse rate of ? 2.27 ± 0.38‰/100 m is suitable for predicting relative paleoelevation change (relative uplift). The application of this empirical gradient is restricted to phases in the mountain uplift stage when the atmospheric circulation had not distinctly changed and to when the climate was not arid. An empirical δD_wax–latitude–altitude formula is also calculated: δD_wax = 3.483LAT ? 0.0227ALT ? 261.5, which gives the preliminary spatial distribution pattern of δD_wax in modern China.Mean value of ε_wax-p in the extreme humid Wuyi Mountains is quite negative (? 154‰), compared to the humid Shennongjia (? 129‰) and the arid (but with abundant summer precipitation) Tianshan Mountains (? 130‰), which suggests aridity or water availability in the growing season is the primary factor controlling soil/sediment ε_wax-p. Along the Tianshan transects, values of ε_wax-p are speculated to be constant with altitude; while along the Wuyi and Shennongjia transects, ε_wax-p are also constant at the low-mid altitudes, but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation δD or the vegetation shift to grass/conifer.Additionally, a reversal of altitude effect in the vertical variation of δD_wax was found in the alpine zone of the Tianshan Mountains, which might be caused by atmospheric circulation change with altitude. This implies that the paleo-circulation pattern and its changes should also be evaluated when stable isotope-based paleoaltimetry is applied.     

Thunderstorm-associated responses in the vertical motion of the mid-latitude F-region ionosphere

Mid-latitude Digisonde Doppler velocities, auroral electrojet (AE) indices and cloud-to-ground (CG) lightning strokes during August 2003–2004 were used to study the perturbations in the F-region vertical drift associated with terrestrial thunderstorms. A superposed epoch analysis (SEA) showed that the F-region vertical drifts V_z had a net descent of ～0.6 m s^?1 peaking ～3 h after lightning. Stronger downward perturbations of up to ～0.9 m s^?1 were observed in the afternoon on the day prior to lightning days. The perturbations were less significant on the day after and insignificant during the remaining intervals up to 144 h on either side of the lightning. The stronger responses on the day before are consistent with causality because the lightning times were merely proxies for the physical mechanisms involved. The actual causes are unclear, but we discuss the possible roles of lightning-induced ionisation enhancements, intense electric fields penetrating upward from electrified clouds, and atmospheric gravity waves (AGWs) radiated from thunderstorms or from the accompanying tropospheric fronts. There is no doubt that the behaviour of the mid-latitude F-region is controlled by the thermospheric winds and the solar wind-magnetosphere electrical generators, but our results suggest that electrified clouds also account for a significant, albeit relatively small component of the ionospheric variability.     

Crustal structure of the Reykjanes Ridge near 62°N,on the basis of seismic refraction and gravity data

Explosion deep seismic sounding data sections of high quality had been obtained with RV Meteor in the Reykjanes Iceland Seismic Project (RRISP77 [Angenheister, G., Gebrande, H., Miller, H., Goldflam, P., Weigel, W., Jacoby, W.R., Pálmason, G., Björnsson, S., Einarsson, P., Pavlenkova, N.I., Zverev, S., Litvinenko, I.V., Loncarecic, B., Solomon, S., 1980. Reykjanes Ridge Iceland Seismic Experiment (RRISP 77). J. Geophys. 47, 228–238]) which close an information gap near 62°N. Preliminary results were presented by Weigel [Weigel, W., 1980. Aufbau des Reykjanes Rückens nach refraktionsseismischen Messungen. In: Weigel, W. (Ed.), Reykjanes Rücken, Island, Norwegischer Kontinentalrand. Abschlusskolloquium, Hamburg zur Meteor-Expedition, vol. 45. DFG, Bonn, pp. 53–61], and here we report on the data and results of interpretation. Clear refracted phases to 90 km distance permit crustal and uppermost mantle structure to be modelled by ray tracing. The apparent P-wave velocities are around 4.5, 6–6.5, 7–7.6 and 8.2–8.7 km/s, but no wide-angle reflections have been clearly seen. Accompanying sparker reflection data reveal thin sediment ponds in the axial zone and up to 400 m thick sediments at 10 Ma crustal age. Ray tracing reveals the following model below the sediments: (1) a distinct, 1–2 km thick upper crust (layer 2A) with Vp increasing with age (to 10 Ma) from <3.4 to 4.9 km/s and with a vertical gradient of 0.1–0.2 km/s/km, (2) a lower crust or layer 3 beginning at depths of 2 (axis) to 4 km (10 Ma age) below sea level with 6.1–6.8 km/s and similar vertical gradients as above, (3) the lower crust bottoms at 5.2–9.5 km depth below sea level (0–10 Ma) with a marked discontinuity, underneath which (4) Vp rises from about 7.5–7.8 km/s (0–10 Ma) with a positive vertical gradient of, again, 0.1–0.2 km/s/km such that 8 km/s would be reached at 12 km and deeper near the axis. Our preferred interpretation is that the mantle begins at the distinct discontinuity (“Moho”), but a deeper “Moho” of Vp ≈ 8 km/s cannot be excluded. From Iceland southward to 60°N several experiments show a decrease of crustal thickness from 14 to 8 km. Velocity trends with age across the ridge reflect cooling and filling of cracks, and thickness trends probably suggest volcanic productivity variations as previously suggested.Gravity inversion concentrates on a profile across the ridge with the above seismic a priori information; with 0.2–0.5 km depth uncertainty it leads to a good fit (±2.5 mGal where seismic data exist). Best fitting densities are (in kg/m³) for sediments, 2180; upper crust, 2450–2570; lower crust, 2850–2940; mantle lithosphere, 3215–3240 with a deficit for an asthenospheric wedge of no more than −100 kg/m³. The morphological ridges and troughs superimposed on the SE ridge flank are partly correlated, partly anti-correlated with the Bouguer anomaly and suggest that variable crustal density variations accompany the morphology variations.     

Volume and mass changes of the Greenland ice sheet inferred from ICESat and GRACE

This study examines the recent evolution of the Greenland ice sheet and its six major drainage basins. Based on laser altimetry data acquired by the Ice, Cloud and Land Elevation Satellite (ICESat), covering the period September–November 2003 to February–March 2008, ice surface height changes and their temporal variations were inferred. Our refined repeat track analysis is solely based on ICESat data and is independent of external elevation models, since it accounts for both ice height changes and the local topography. From the high resolution ice height change pattern we infer an overall mean surface height trend of −0.12 ± 0.006 m yr⁻¹. Furthermore, the largest changes could be identified at coastal margins of the ice sheet, exhibiting rates of more than −2 m yr⁻¹. The total ice volume change of the entire ice sheet amounts to −205.4 ± 10.6 km³ yr⁻¹. In addition, we assessed mass changes from 78 monthly Gravity Recovery and Climate Experiment (GRACE) solutions. The Release-04 gravity field solutions of GeoForschungsZentrum Potsdam cover the period between August 2002 and June 2009. We applied an adjusted regional integration approach in order to minimize the leakage effects. Attention was paid to an optimized filtering which reduces error effects from different sources. The overall error assessment accounts for GRACE errors as well as for errors due to imperfect model reductions. In particular, errors caused by uncertainties in the glacial isostatic adjustment models could be identified as the largest source of errors. Finally, we determined both seasonal and long-term mass change rates. The latter amounts to an overall ice mass change of −191.2 ± 20.9 Gt yr⁻¹ corresponding to 0.53 ± 0.06 mm yr⁻¹ equivalent eustatic sea level rise. From the combination of the volume and mass change estimates we determined a mean density of the lost mass to be 930 ± 11 kg m⁻³. This value supports our applied density assumption 900 ± 30 kg m⁻³ which was used to perform the volume–mass-conversion of our ICESat results. Hence, mass change estimates from two independent observation techniques were inferred and are generally in good agreement.     

Sea level rise in the north-western part of the Arabian Gulf

Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10.     

Evidence for global circuit current flow through water droplet layers

Foggy air and clear air have appreciably different electrical conductivities. The conductivity gradient at horizontal droplet boundaries causes droplet charging, as a result of vertical current flow in the global atmospheric electrical circuit. The charging is poorly known, as both the current flow through atmospheric water droplet layers and the air conductivity are poorly characterised experimentally. Surface measurements during three days of continuous fog using new instrument techniques show that a shallow (of order 100 m deep) fog layer still permits the vertical conduction current to pass. Further, the conductivity in the fog is estimated to be approximately 20% lower than in clear air. Assuming a fog transition thickness of one metre, this implies a vertical conductivity gradient of order 10 fS m^?2 at the boundary. The actual vertical conductivity gradient at a cloud boundary would probably be greater, due to the presence of larger droplets in clouds compared to fog, and cleaner, more conductive clear air aloft.     

Expected temporal absolute gravity change across the Taiwanese Orogen,a modeling approach

The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several μGal yr⁻¹. By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 μGal yr⁻¹ with the thin-skinned tectonic and 0.3 μGal yr⁻¹ with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.     

Short-term changes in the aerosol characteristics at Kharagpur (22°19′N, 87°19′E) during winter

In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 10⁹ m^?3 and mass loading is ~265±70 μg m^?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence.     

Enhancement of OI 630.0 nm emission at mid-latitudes during an intense magnetic storm

All-sky camera (ASC), Global Positioning System (GPS), and ionosonde measurements were used to investigate the upper atmospheric variations at mid-latitude during the strong geomagnetic storm on October 29–31, 2003. An arc-shaped 630.0 nm emission was observed in the northern sky on all-sky images taken at Mt. Bohyun (36.2°N, 128.9°E, GMLAT=29°N) in Korea during 17:48–8:58 UT in the main phase of the geomagnetic storm on October 29. The NmF₂ and hmF₂ from the ionosonde show strong disturbances at that time. The vertical profiles of electron densities, calculated by the ionospheric tomographic method using ground-based GPS slant total electron contents measurements, show the largest value at ∼440 km height at 18:30 UT on October 29 when the enhancements of OI 630.0 nm emission were observed. The arc-shaped red emission observed during the main phase of the magnetic storm is likely a low-latitude red aurora due to its short duration of ∼1 h. The result implies that the plasmapause was at L=1.4–1.6 during the geomagnetic storm. The fact that the arc did not follow a constant L-value appears to suggest that neutral precipitation and a traveling ionospheric disturbance could also be the cause of the arc.     

Seasonal plankton variability in Chilean Patagonia fjords: Carbon flow through the pelagic food web of Aysen Fjord and plankton dynamics in the Moraleda Channel basin

Two research cruises (CIMAR 13 Fiordos) were conducted in the N–S oriented macrobasin of the Moraleda Channel (42–47°S), which includes the E–W oriented Puyuhuapi Channel and Aysen Fjord, during two contrasting productive seasons: austral winter (27 July–7 August 2007) and spring (2–12 November 2007). These campaigns set out to assess the spatio-temporal variability, defined by the local topography along Moraleda Channel, in the biological, physical, and chemical oceanographic characteristics of different microbasins and to quantify the carbon budget of the pelagic trophic webs of Aysen Fjord.Seasonal carbon fluxes and fjord-system functioning vary widely in our study area. In terms of spatial topography, two constriction sills (Meninea and Elefantes) define three microbasins along Moraleda Channel, herein the (1) north (Guafo-Meninea), (2) central (Meninea-Elefantes), and (3) south (Elefantes-San Rafael Lagoon) microbasins. In winter, nutrient concentrations were high (i.e. nitrate range: 21–14 μM) and primary production was low (153–310 mgC m^?2 d^?1), suggesting that reduced light radiation depressed the plankton dynamics throughout Moraleda Channel. In spring, primary production followed a conspicuous N–S gradient, which was the highest (5167 mgC m^?2 d^?1) in the north microbasin and the lowest (742 mgC m^?2 d^?1) in the south microbasin. The seasonal pattern of the semi-enclosed Puyuhuapi Channel and Aysen Fjord, however, revealed no significant differences in primary production (～800 mgC m^?2 d^?1), and vertical fluxes of particulate organic carbon were nearly twice as high in spring as in winter (266 vs. 168 mgC m^?2 d^?1).At the time-series station (St. 79), the lithogenic fraction dominated the total sedimented matter (seston). The role of euphausiids in the biological carbon pump of the Patagonian fjords was evident, given the predominance of zooplankton fecal material, mostly euphausiid fecal strings (46% of all fecal material), among the recognizable particles contributing to the particulate organic carbon flux.The topographic constriction sills partially modulated the exchange of oceanic waters (Subantarctic Surface Water) with freshwater river discharges along the Moraleda Channel. This exchange affects salinity and nutrient availability and, thus, the plankton structure. The north microbasin was dominated by a seasonal alternation of the classical (spring) and microbial (winter) food webs. However, in the south microbasin, productivity was low and the system was dominated year-round by large inputs of glacier-derived, silt-rich freshwater carrying predominantly small-sized diatoms (Skeletonema spp) and bacteria. When superimposed upon this scenario, highly variable (seasonal) solar radiation and photoperiods could exacerbate north–south differences along Moraleda Channel.     

Vertical and horizontal distribution of magnetic susceptibility and metal contents in an industrial district of central Iran

This study was conducted to determine the vertical and horizontal distribution of selected metals and magnetic susceptibility (χlf) in an industrial site located in Isfahan province, central Iran. For this purpose, we used a grid sampling methodology and excavated 202 profiles. Soil samples were then collected from 0–30, 60–90, and 120–150 cm depths. The mass magnetic susceptibility (χ) of the soil samples was measured at both low and high frequencies (χlf and χhf) using the Bartington MS2 dual frequency sensor; and χfd was also calculated. Soil samples were also analyzed for iron (Fe), manganese (Mn), lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), chromium (Cr) and cobalt (Co) concentrations. The results showed that there were positive significant correlations among selected metals including Zn, Pb, Fe and Mn, which were mainly added through coal fly ash from an iron smelting factory at the studied site, while the concentration of Ni, Cr and Co was mainly controlled by the parent material of the soils. The trends in results at the site of study were similar in vertical and horizontal distribution for the industrial originated metals as judged by pollution load index (PLI) using χlf. The results of SEM/EDX also confirmed the presence of spheroid of magnetic particles in the surface soil samples taken in close proximity of the factory. Based on the results using the contamination factors (CF) determined for selected metals, the following order was observed: Pb > Zn > Mn > Fe > Cu > Ni ≥ Co > Cr. The results also suggested that magnetic methods could be used to estimate the metal contamination from anthropogenic sources in industrial soils.     

Uncertainty in seasonal snow reconstruction: Relative impacts of model forcing and image availability

There are many areas of uncertainty when solving the inverse problems of snow water equivalent (SWE) reconstruction. These include (i) the ability to infer the Final Date of the Seasonal Snow (FDSS) cover, particularly from remote sensing; (ii) errors in model forcing data (such as air temperature or radiation fluxes); and (iii) weaknesses in the snow model used for the reconstruction, associated with both the fidelity of the equations used to simulate snow processes (structural uncertainty) and the parameter values selected for use in the model equations. We investigate the trade-offs among these sources of uncertainty using 10,000 station-years worth of data from the western US SNOTEL network. Model structural and parameter uncertainty are eliminated by using a perfect model scenario i.e. comparing results to modelled control runs. The model was calibrated for each station-year to ensure that the model simulations reflect reality. Results indicate that for a temperature index model, a ±5 days error in FDSS gives a median −25%/+32% error in maximum SWE. A 1 °C air temperature bias produces a SWE error larger than a 5 days error in the FDSS for 50% of the 10,000 cases. Similarly, a 5 days error in FDSS could be accounted for by a net radiation error of 13 W m⁻² or less during the melt period, in 50% of cases. Mean absolute errors of 1 °C or more are typically reported in the literature for air temperature interpolations at high elevations. Observed solar radiation during the melt season can differ by 30 W m⁻² over relatively short distances, while estimates from reanalysis (NARR, ERA-Interim, MERRA, CFSRR) and GOES satellites typically span more than 40 W m⁻². Using data from both MODIS sensors (Terra & Aqua) at all snow covered points in the western US, a consecutive 5 days gap in imagery at time of FDSS is likely to occur only 5–10% of the time. This work shows that errors in model forcing data are at least as important, if not more, than image availability when reconstructing SWE.     

Late Miocene to present-day exhumation and uplift of the Internal Zone of the Rif chain: Insights from low temperature thermochronometry and basin analysis

Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (⁴⁰Ar/³⁹Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60–100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01–0.03 mm/y) in relation with a northeastward tilting of 0.2–0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.