Search results for "oceanic"
showing 10 items of 642 documents
Emergence of blueschists on Earth linked to secular changes in oceanic crust composition
2015
The oldest blueschists—metamorphic rocks formed during subduction—are of Neoproterozoic age1, and 0.7–0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago2. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa−1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface3. Here we show that the absence of blueschists in the ancient geological rec…
Imation of land surface emissivity differences in the split-window channels of AVHRR
1994
Abstract A method for estimating the difference between the channel emissivities in NOAA-AVHRR Channels 4 and 5 is proposed and applied to a data set from the HAPEX-MOBILHY experiment. The method is based on the separation between the atmospheric and emissivity effects in the brightness temperature difference measured with AVHRR Channels 4 and 5. Atmospheric profiles coincident to the satellite overpass and a radiative transfer model are required to estimate the atmospheric correction for brightness temperatures. With this procedure, the emissivity difference Δe is obtained at the satellite spatial and spectral resolution, which has a great interest for correcting thermal images with the sp…
Large eddy simulation model for wind-driven sea circulation in coastal areas
2013
Abstract. In the present paper a state-of-the-art large eddy simulation model (LES-COAST), suited for the analysis of water circulation and mixing in closed or semi-closed areas, is presented and applied to the study of the hydrodynamic characteristics of the Muggia bay, the industrial harbor of the city of Trieste, Italy. The model solves the non-hydrostatic, unsteady Navier–Stokes equations, under the Boussinesq approximation for temperature and salinity buoyancy effects, using a novel, two-eddy viscosity Smagorinsky model for the closure of the subgrid-scale momentum fluxes. The model employs: a simple and effective technique to take into account wind-stress inhomogeneity related to the …
Global Estimation of Soil Moisture Persistence with L and C-Band Microwave Sensors
2018
© 2018 IEEE Measurements of soil moisture are needed for a better global understanding of the land surface-climate feedbacks at both the local and the global scale. Satellite sensors operating in the low frequency microwave spectrum (from 1 to 10 GHz) have proven to be suitable for soil moisture retrievals. These sensors now cover nearly 4 decades thus allowing for global multi-mission climate data records. In this paper, we assess the possibility of using L-band (SMOS) and C-band (AMSR2, ASCAT) remotely sensed soil moisture time series for the global estimation of soil moisture persistence. A multi-output Gaussian process regression model is applied to ensure spatio-temporal coverage of th…
A statistical subgrid-scale algorithm for precipitation formation in stratiform clouds in the ECHAM5 single column model
2011
Abstract. Cloud properties are usually assumed to be homogeneous within the cloudy part of the grid-box, i.e. subgrid-scale inhomogeneities in cloud cover and/or microphysical properties are often neglected. However, precipitation formation is initiated by large particles. Thus mean values are not representative and could lead to a delayed onset of precipitation. For a more physical description of the subgrid-scale structure of clouds we introduce a new statistical sub-column algorithm to study the impact of cloud inhomogeneities on stratiform precipitation. Each model column is divided into N independent sub-columns with sub-boxes in each layer, which are completely clear or cloudy. The cl…
An overview of the geochemical characteristics of oceanic carbonatites: New insights from Fuerteventura carbonatites (Canary islands)
2021
The occurrence of carbonatites in oceanic settings is very rare if compared with their continental counterpart, having been reported only in Cape Verde and Canary Islands. This paper provides an overview of the main geochemical characteristics of oceanic carbonatites, around which many debates still exist regarding their petrogenesis. We present new data on trace elements in minerals and whole-rock, together with the first noble gases isotopic study (He, Ne, Ar) in apatite, calcite, and clinopyroxene from Fuerteventura carbonatites (Canary Islands). Trace elements show a similar trend as Cape Verde carbonatites, almost tracing the same patterns on multi-element and REE abundance diagrams. 3…
Carbon-isotope record and palaeoenvironmental changes during the early Toarcian oceanic anoxic event in shallow-marine carbonates of the Adriatic Car…
2013
AbstractGeochemical (δ13C, δ18O and Mn) compositions of Lower Jurassic shallow-water carbonates cropping out in Croatia were analyzed to elucidate the impact of the early Toarcian oceanic anoxic event (T-OAE) on the Adriatic Carbonate Platform (AdCP). The bulk-rock carbon-isotope records through the studied sections (Velebit-A, Velebit-B and Gornje Jelenje) are characterized by two significant excursions: (i) an initial positive trend interrupted by a pronounced negative shift (c. 2.5‰) that is followed by (ii) an increasing trend of positive values (up to 4.5‰). A comparison with δ13C trends obtained from well-calibrated sections from other localities in Europe shows that the overall chara…
Recycled crustal carbon in the depleted mantle source of El Hierro volcano, Canary Islands
2021
The Canary Islands, in the eastern Atlantic, are among the most enigmatic Oceanic Island provinces on Earth, as the mantle source feeding its volcanism exhibits wide spatial heterogeneity and a multiplicity of sources. Multi-isotope whole-rock studies have long revealed the presence of a recycled oceanic crust/lithosphere component in the mantle source. However, noble gas systematics have been more challenging to interpret, and the available carbon isotope data is limited and cannot support/dismiss this interpretation. Here, we present the very first isotopic characterisation of CO2 and noble gases (He-Ne-Ar) in fluid inclusions (FI) in minerals hosted in mantle xenoliths from El Hierro, th…
A global Canopy Water Content product from AVHRR/Metop
2020
Abstract Spatially and temporally explicit canopy water content (CWC) data are important for monitoring vegetation status, and constitute essential information for studying ecosystem-climate interactions. Despite many efforts there is currently no operational CWC product available to users. In the context of the Satellite Application Facility for Land Surface Analysis (LSA-SAF), we have developed an algorithm to produce a global dataset of CWC based on data from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board Meteorological–Operational (MetOp) satellites forming the EUMETSAT Polar System (EPS). CWC reflects the water conditions at the leaf level and information related …
Estimation of vegetation loss coefficients and canopy penetration depths from SMAP radiometer and IceSAT lidar data
2017
In this study the framework of the τ — ω model is used to derive vegetation loss coefficients and canopy penetration depths from SMAP multi-temporal retrievals of vegetation optical depth, single scattering albedo and ICESat lidar vegetation heights. The vegetation loss coefficients serve as a global indicator of how strong absorption and scattering processes attenuate L-band microwave radiation. By inverting the vegetation loss coefficients, penetration depths into the canopy can be obtained, which are displayed for the global forest reservoirs. A simple penetration index is formed combining vegetation heights and penetration depth estimates. The distribution and level of this index reveal…