Atlantic surface water inflow to the Nordic seas during the Pleistocene–Holocene transition (mid–late Younger Dryas and Pre‐Boreal periods, 12 450–10 000 a BP)

The inflow of Atlantic Water to the Nordic seas from mid–late Younger Dryas to earliest Holocene (12 450–10 000 a BP) is reconstructed on the basis of a high‐resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice‐rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid–late Younger Dryas and Pre‐Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east–west temperature gradient across the Faroe–Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near‐continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessing global Sentinel-2 coverage dynamics and data availability for operational Earth observation (EO) applications using the EO-Compass

ABSTRACT

Sentinel-2 scenes are increasingly being used in operational Earth observation (EO) applications at regional, continental and global scales, in near-real time applications, and with multi-temporal approaches. On a broader scale, they are therefore one of the most important facilitators of the Digital Earth. However, the data quality and availability are not spatially and temporally homogeneous due to effects related to cloudiness, the position on the Earth or the acquisition plan. The spatio-temporal inhomogeneity of the underlying data may therefore affect any big remote sensing analysis and is important to consider. This study presents an assessment of the metadata for all accessible Sentinel-2 Level-1C scenes acquired in 2017, enabling the spatio-temporal coverage and availability to be quantified, including scene availability and cloudiness. Spatial exploratory analysis of the global, multi-temporal metadata also reveals that higher acquisition frequencies do not necessarily yield more cloud-free scenes and exposes metadata quality issues, e.g. systematically incorrect cloud cover estimation in high, non-vegetated altitudes. The continuously updated datasets and analysis results are accessible as a Web application called EO-Compass. It contributes to a better understanding and selection of Sentinel-2 scenes, and improves the planning and interpretation of remote sensing analyses.     

A study of the atmospheric circulation between equator and 60oN during the winter and summer seasons

Summary The mean zonal and meridional wind components and the mean mass circulation in different latitudes are discussed in relation to previous studies. Divergence and vertical motion are calculated for various latitude belts. There is evidence for a strong tropical Hadley cell with a temperate latitude indirect circulation during the winter season. During summer, the northern Hadley cell is weaker and displaced poleward; a circulation in the opposite sense appears in equatorial latitudes.The regional patterns of divergence and vertical motion appear related particularly to the position of the subtropical high pressure cells. Subsidence and lower-layer divergence are characteristic of the eastern flanks of the subtropical anticyclones, while the opposite pattern prevails on its western flanks. These longitudinal contrasts appear particularly pronounced during the summer season. The three-dimensional flow pattern in the tropics is illustrated by selected trajectories for the winter and summer seasons.     

Role of melt during deformation in the deep crust

Deformation in the deep crust is strongly influenced by the presence of melt. Injected melt (or magma) weakens the crust because strain will tend to localize where melt is present. The amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate. For plutons that intrude into rocks which are near the solidus temperature of the melt, crystallization times can be quite long (> 1Myr).
Partial melting of deep crustal rocks can lead to melt-enhanced embrittlement. This occurs because the volume change for most melting reactions is positive. Therefore, when the rate of melt production outpaces the rate at which melt can leave the system, the melt pressure increases. Eventually, the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture.
Conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the Central Gneiss belt (Canada); this suggests that melt-enhanced embrittlement occurred in these rocks. An expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived. Assuming that migmatite has a small tensile strength, differential stresses are ≤ 20 MPa in migmatitic rocks at the time melt-enhanced embrittlement occurs. The occurrence of melt-enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting. Furthermore, repeated episodes of melt-enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains.     

Changing predictability of Indian monsoon rainfall anomalies?

The predictability of Indian summer monsoon rainfall from pre-season circulation indices is explored from observations during 1939–91. The predictand is the all-India average of June–September precipitation NIR, and the precursors examined are the latitude position of the 500 mb ridge along 75°E in April (L), the pressure tendency April minus January at Darwin (DPT), March-April-May temperature at six stations in west central India (T6), the sea surface temperature (SST) anomaly in the northeastern Arabian Sea in May (ASM), SST anomaly in the Arabian Sea in January (ANJ), northern hemisphere temperature anomaly in January–February (NHT), and Eurasian snow cover in January (SNOW). Monsoon rainfall tends to be enhanced with a more northerly ridge position, small Darwin pressure tendency, warmer pre-season conditions, and reduced winter snow cover. However, relationships have varied considerably over the past half-century, with the strongest associations during 1950–80, and a drastic weakening in the 1980s. Four prediction models were constructed based on stepwise multiple regression, using as predictors combinations of L, DPT, T6, ASM, and NHT, with 1939–68 as “dependent” dataset, or training period, and 1969–91 as “independent” dataset or verification period. For the 1969–80 portion of the verification period calculated and observed NIR values agreed closely, with the models explaining 74–79% of the variance. By contrast, after 1980 predictions deteriorated drastically, with the explained variance for the 1969–89 time span dropping to 25–31%. The monsoon rainfall of 1990 and 1991 turned out to be again highly predictable from models based on stepwise multiple regression and linear discriminant analysis and using as input L + DPT or L + DPT + NHT, and with this encouragement an experimental real-time forecast was issued of the 1992 monsoon rainfall. These results underline the need for investigations into decadal-scale changes in the general circulation setting and raise concern for the continued success of seasonal forecasting.     

Correlations and sequence stratigraphic model for Messinian carbonate platforms of the western and central Mediterranean

Distance correlations of Late Tortonian–Messinian littoral carbonate complexes are proposed from the study of eight platforms in the western and central Mediterranean. Correlations are based on the identification of two major biological sedimentary cycles and of two index surfaces. Surface A is a maximum flooding surface during cycle 1 at around 6.7 Ma. Surface B is a regional marine planation surface at around 5.95 Ma, at the base of cycle 2 (Terminal Carbonate Complex). A general sedimentary model is proposed for the 7–5.6-Ma time-span. The boundary between cycles 1 and 2 is coincident with the onset of the Messinian Salinity Crisis, and appears to be related to major environmental–paleo-oceanographic changes in the Mediterranean, rather than to a major sea-level drop or to climatic change.     

Screening and ranking of sedimentary basins for sequestration of CO<Subscript>2</Subscript> in geological media in response to climate change

Sedimentary basins are suitable to different degrees for CO ₂ geological sequestration as a result of various intrinsic and extrinsic characteristics, of which the geothermal regime is one of the most important. Warm basins are less favorable for CO ₂ sequestration than cold basins because of reduced capacity in terms of CO ₂ mass, and because of higher CO ₂ buoyancy, which drives the upward CO ₂ migration. A set of 15 criteria, with several classes each, has been developed for the assessment and ranking of sedimentary basins in terms of their suitability for CO ₂ sequestration. Using a parametric normalization procedure, a basin's individual scores are summed to a total score using weights that express the relative importance of different criteria. The total score is ranked to determine the most suitable basin or region thereof for the geological sequestration of CO ₂. The method is extremely flexible in that it allows changes in the functions that express the importance of various classes for any given criterion, and in the weights that express the relative importance of various criteria. Examples of application are given for Canada's case and for the Alberta basin in Canada.     

Couplex Benchmark Computations Obtained with the Software Toolbox UG

This paper describes the numerical results for the COUPLEX benchmark obtained with the simulation software UG using vertex centered finite volume and higher order discontinuous Galerkin schemes. Multigrid solvers on unstructured grids, local mesh refinement and parallel computation are employed to yield very accurate solutions. Since the full range of results required in the benchmarks is too large to be displayed in this paper we focus on the comparison of discretization schemes, assessment of numerical errors and the presentation of parallel computations.