Triangle based interpolation

Triangle based interpolation is introduced by an outline of two classical planar interpolation methods, viz. linear triangular facets and proximal polygons. These are shown to have opposite local bias. By applying cross products of triangles to obtain local gradients, a method designated slant-top proximal polygon interpolation is introduced that is intermediate between linear facets and polygonal interpolation in its local bias. This surface is not continuous, but, by extending and weighting the gradient planes, a C¹ surface can be obtained. The gradients also allow a roughness index to be calculated for each data point in the set. This index is used to control the shape of a blending function that provides a weighted combination of the gradient planes and linear interpolation. This results in a curvilinear, C¹,interpolation of the data set that is bounded by the linear interpolation and the weighted gradient planes and is tangent to the slant-top interpolation at the data points. These procedures may be applied to data with two, three, or four independent variables.     

Rock media mathematical models processing

This paper reports on mathematical models of rock media processing and on their use in designing open pit coal mines. Spatial mathematical model of rock media was processed on a 25 km² model site, incorporating 918 borehole logs. The model is capable of providing information concerning the geological structure of every point of the investigated area by plotting geological cross-sections along given lines or by plotting contour lines of the surface or the base for thickness of chosen lithological strata. The computation of one point of a grid involves the following steps: Borehole logs are numericaly coded. The geological structure at an arbitrarily chosen pointP is computed as follows. All borehole logs inside the circle (P; R) are used to compute theZ-coordinate of the ground atP by some interpolation formula chosen from those contained in the program system. Next, we check what stratum occurs topmost at boreholes inside the circle and which is most probable as the top stratumC ₁ atP. TheZ-coordinate of theC ₁ stratum surface atP is computed. Then what strata occur underC ₁ stratum and which of them is the most probable stratumC ₂ is determined. The process of computation is repeated until a sequence of strataC _i atP andZ _i coordinates of their surfaces is ascertained. The interpolation formulas included in the system are proper linear combination of PAF (polynomial approximations formulas, linear or quadratic and weighted) and WAF (weighted average formulas). Among the various interpolation formulas, some proved more useful for tectonic fault lines, others for ordinary sedimentary surfaces.     

Spatial Variability of Stable Isotope Ratios in Oysters (Crassostrea gigas) and Primary Producers Along an Estuarine Gradient (Bay of Brest, France)

This study aimed at characterizing the diet of the oyster Crassostrea gigas along an estuarine gradient in the Bay of Brest (France), through stable isotope (δ¹³C and δ¹⁵N) measurements in primary producers and wild oysters. The contribution of different potential food sources to the diet of C. gigas was estimated at high spatial resolution (over a gradient of 40 km with samplings every 2 km) to identify ecological transition zones and highlighted the dominance of resuspended biofilm in oysters diet. Although the different primary producers did not display any obvious pattern along the estuarine gradient, the stable isotope signatures of C. gigas differed among estuarine, inner Bay, and open sea sites. In particular, a striking ¹⁵N depletion pattern was found along the gradient which allowed to identify seven homogeneous groups. Moreover, some unexpected values found at two stations within the estuary revealed localized anthropogenic disturbances. Overall, our results suggest that suspension feeders might be better indicators of ecosystem functioning than primary producers and reflect the different ecological processes occurring along estuarine gradients, including localized anthropogenic inputs. We suggest that the usefulness of suspension feeders as indicators of ecosystem functional typology lies in the dominance of benthic material in their diet, which results in locally occurring processes being reflected in oysters’ stable isotope ratios.     

A continuous phase gradient in a “monocrystalline” pyrrhotite

X-ray diffraction and microprobe analyses of pseudomonocrystalline fragments of pyrrhotite from Bodenmais, Bavaria, revealed continuous gradients in composition and phase distribution. The gradients extend from the well-developed (0001) cleavage surfaces 15–30 μm into the bulk of the crystals. The phase gradient is made up two low-temperature pyrrhotites with monoclinic (4C) and hexagonal (5C) symmetry. The fraction of monoclinic pyrrhotite, expressed on the basis of recorded X-ray intensities, I, decreases exponentially according to I _(mon)/[I _(hex)+I _(mon)] = EXP (aX+b) where a is a constant ranging from ?0.04 to ?0.25, X is the depth from the (0001) cleavage surface in μm, and b is a constant determined by the intensity ratios obtained from the untreated cleavage surfaces. The phase gradient developed during retrograde reactions from a continuous composition gradient. This primary gradient was caused by the extraction of iron from a disordered, high-temperature hexagonal pyrrhotite during oxidation of the cleavage surfaces at temperatures above 254° C (upper stability limit of 4C pyrrhotite), probably above 308° C. The length of the c axis of the monoclinic superstructure slightly increases with the increase in iron and decrease in vacancy content of the bulk. This expansion is probably due to a minor compositional variation of the monoclinic phase controlled by the availability of vacancies during the transition to low-temperature phases.     

A finite element formulation of gradient-based plasticity for porous media with C1 interpolation of internal variables

In this paper a new finite element formulation for numerical analysis of diffused and localized failure behavior of saturated and partially saturated gradient poroplastic materials is proposed. The new finite element includes interpolation functions of first order (C₁) for the internal variables field while classical C₀ interpolation functions for the kinematic fields and pore pressure. This finite element formulation is compatible with a thermodynamically consistent gradient poroplastic theory previously proposed by the authors. In this material theory the internal variables are the only ones of non-local character. To verify the numerical efficiency of the proposed finite element formulation, the non-local gradient poroplastic constitutive theory is combined with the modified Cam Clay model for partially saturated continua. Thereby, the volumetric strain of the solid skeleton and the plastic porosity are the internal variables of the constitutive theory. The numerical results in this paper demonstrate the capabilities of the proposed finite element formulation to capture diffuse and localized failure modes of boundary value problems of porous media, depending on the acting confining pressure and on the material saturation degree.     

Controls on alkenone unsaturation ratios along the salinity gradient between the open ocean and the Baltic Sea

Alkenone unsaturation ratios of sedimentary lipids are used as a geochemical proxy for sea surface temperatures, and interest is growing in their potential as indicators of different water masses and possibly of salinity. We analyzed the abundance of unsaturated C₃₇ to C₃₈ ketones in lipid extracts of 57 surface sediment (0-1 cm) samples along a salinity gradient from 8 to 33 psu in the transition from the Skagerrak to the Baltic Sea (NW Europe). In addition to surface sediments, we analyzed alkenones in suspended particulate matter at 13 stations—over a gradient in salinity from 25 to 33 psu—during a bloom of the coccolithophore Emiliania huxleyi. Alkenones were detected in all samples (suspended matter and sediment) with variable contributions of the tetra-unsaturated C₃₇ alkenone compound (%C_37:4; range from 2 to 10% of total C₃₇ alkenone content). Comparing the alkenone unsaturation index (U₃₇^K′) and %C_37:4 data to climatological sea surface temperature and sea surface salinity data sets revealed that SST estimated from U₃₇^K′ of saline end members (samples from the Skagerrak) is in the general range of modern SST during bloom periods of haptophytes. At salinities below ∼30 psu %C_37:4 increases to above 5% and the unsaturation ratios cease to be related to climatological annual or seasonal sea surface temperatures. On the other hand, the %C_37:4 appears to be inversely and significantly correlated to salinity: Highest C_37:4 proportions in the inner Baltic Sea are caused by an unidentified organism, but in the transition area at salinities down to 10 psu, the producer apparently is E. huxleyi. The suspended matter data together with those from the water column support the hypothesis of changing biosynthesis of alkenones under salt stress by the coccolithophore E. huxleyi, but constrain the maximum of %C_37:4 attributable to salt stress to 10% of all C₃₇ alkenones.     

Pressure solution at grain-to-grain contacts

Whereas much petrographic evidence for pressure solution, in sedimentary rocks has been accumulated since Sorby's work, its thermodynamic justification has never been clearly established, and has been challenged by some authors. Difficulties disappear when it is recognized that in the most general case migration of chemical components proceeds down chemical-potential gradients rather than down concentration gradients. Along a grain contact a chemical-potential gradient is produced by variations in contact pressure and by local variations in Helmholtz energy of the solid. For example, in a sand made up of even-sized spherical grains buried 500 m, the ratio of the diameter (D) of the grains to that of a spherical elastic contact circle (a) is D/a ～- 26. The chemical potential at the center of such an elastic contact is ～- 14kcal mol^?1 higher than in surrounding pore water saturated with respect to quartz. For comparison, at a temperature of 30°C, saturation with respect to amorphous silica rather than quartz raises the chemical potential by only 1.6 kcal mol^?1. If the diameter of the contact circle has enlarged to e.g. a = D/5, the chemical potential at its center is still 0.5 kcal mol ^?1 greater than that of free quartz under hydrostatic pressure. The corresponding potential gradients are the driving force of pressure solution. The concept of pressure solution thus does not contradict any thermodynamic principle; in particular, it does not require that the chemical component of the solid have a smaller partial volume in solution than in the solid state. Petrographic and experimental evidence can therefore be accepted without reservation.     

Method to characterize aquitards above leaky aquifers with water supply wells

Leaky aquifers provide protected drinking water since the aquifer is overlain by an aquitard, and this study develops a method to estimate hydraulic properties of the latter deposit. Steady pumping, supply well shutdowns, and slug tests generate data in adjacent monitoring well clusters that characterize the aquitard. An existing steady model estimates a site-averaged value of the aquitard permeability k if its thickness is known, and this site-averaged estimate may be compared with local k estimates from conventional and extended slug tests. A shutdown attenuation model estimates a local value of the consolidation coefficient C _V, which combines with the local k value to specify the compressibility α of the aquitard. The method is illustrated for the Fowl Meadow Aquifer, a stratified drift deposit used as a drinking water supply in eastern Massachusetts (USA), with an overlying silt aquitard of 10 m thickness. Steady data and theory suggest a site-averaged k of 2.3?×?10^–17?m² for the aquitard, while the shutdown attenuation model generates local C _V values that vary from 10^–5 to 10^–3?m²/s. The slug tests yield a local k variation (10^–17–10^–13?m²) that brackets the site-averaged value, and an α range of 10^–9–10^–7?Pa^–1.     

Matheronian geostatistics—Quo vadis?

Components of geostatistical estimation, developed as a method for ore deposit assessment, are discussed in detail. The assumption that spatial observations can be treated as a stochastic process is judged to be an inappropriate model for natural data. Problems of semivariogram formulation are reviewed, and this method is considered to be inadequate for estimating the function being sought. Characteristics of bivariate interpolation are summarized, highlighting kriging limitations as an interpolation method. Limitations are similar to those of inverse distance weighted observations interpolation. Attention is drawn to the local bias of kriging and misplaced claims that it is an “optimal” interpolation method. The so-called “estimation variance,” interpreted as providing confidence limits for estimation of mining blocks, is shown to be meaningless as an index of local variation. The claim that geostatistics constitutes a “new science” is examined in detail. Such novelties as exist in the method are shown to transgress accepted principles of scientific inference. Stochastic modeling in general is discussed, and purposes of the approach emphasized. For the purpose of detailed quantitative assessment it can provide only prediction qualified by hypothesis at best. Such an approach should play no part in ore deposit assessment where the need is for local detailed inventories; these can only be achieved properly through local deterministic methods, where prediction is purely deductive.     

An Alternative Measure of the Reliability of Ordinary Kriging Estimates

This paper presents an interpolation variance as an alternative to the measure of the reliability of ordinary kriging estimates. Contrary to the traditional kriging variance, the interpolation variance is data-values dependent, variogram dependent, and a measure of local accuracy. Natural phenomena are not homogeneous; therefore, local variability as expressed through data values must be recognized for a correct assessment of uncertainty. The interpolation variance is simply the weighted average of the squared differences between data values and the retained estimate. Ordinary kriging or simple kriging variances are the expected values of interpolation variances; therefore, these traditional homoscedastic estimation variances cannot properly measure local data dispersion. More precisely, the interpolation variance is an estimate of the local conditional variance, when the ordinary kriging weights are interpreted as conditional probabilities associated to the n neighboring data. This interpretation is valid if, and only if, all ordinary kriging weights are positive or constrained to be such. Extensive tests illustrate that the interpolation variance is a useful alternative to the traditional kriging variance.     

Distribution of Diatoms Along Environmental Gradients in the Charlotte Harbor,Florida (USA), Estuary and Its Watershed: Implications for Bioassessment of Salinity and Nutrient Concentrations

The relative abundance of diatom species in different habitats can be used as a tool to infer prior environmental conditions and evaluate management decisions that influence habitat quality. Diatom distribution patterns were examined to characterize relationships between assemblage composition and environmental gradients in a subtropical estuarine watershed. We identified environmental correlates of diatom distribution patterns across the Charlotte Harbor, Florida, watershed; evaluated differences among three major river drainages; and determined how accurately local environmental conditions can be predicted using inference models based on diatom assemblages. Sampling locations ranged from freshwater to marine (0.1–37.2 ppt salinity) and spanned broad nutrient concentration gradients. Salinity was the predominant driver of difference among diatom assemblages across the watershed, but other environmental variables had stronger correlations with assemblages within the subregions of the three rivers and harbor. Eighteen indicator taxa were significantly affiliated with subregions. Relationships between diatom taxon distributions and salinity, distance from the harbor, total phosphorus (TP), and total nitrogen (TN) were evaluated to determine the utility of diatom assemblages to predict environmental values using a weighted averaging-regression approach. Diatom-based inferences of these variables were strong (salinity R ²?=?0.96; distance R ²?=?0.93; TN R ²?=?0.83; TP R ²?=?0.83). Diatom assemblages provide reliable estimates of environmental parameters on different spatial scales across the watershed. Because many coastal diatom taxa are ubiquitous, the diatom training sets provided here should enable diatom-based environmental reconstructions in subtropical estuaries that are being rapidly altered by land and water use changes and sea level rise.     

Long-chain alkenone distributions and temperature dependence in lacustrine surface sediments from China

Long-chain alkenones (LCK) of lacustrine surface sediments were analyzed in 37 lakes from China. The results obtained were complemented by published data from 13 other Chinese lakes. These lakes are located across large temperature and precipitation gradients, therefore allowing for an assessment of the distribution pattern of LCK and their temperature dependency. Different distribution patterns of LCK (C₃₇ predominant pattern and C₃₈ predominant pattern) were detected in the surface sediment samples. The ratio of C_37:4 methyl ketone to the sum of C₃₇ alkenones observed in the different lakes is highly variable (5%-96%, with mean value of 55%), and more than that seen in marine systems. The finding that some of the ocean LCK precursor algae (Gephyrocapsa oceanica, Coccolithus pelagicus) were also present in the limnic systems suggested that both systems might have similar biosynthetic sources. Empirical relationships between the alkenone unsaturation index U₃₇^k′ and different temperature sets (mean annual air temperature, mean annual air temperature in different seasons, and lake surface water temperature of July) were tested. The best correlation between U₃₇^k′ and temperature was obtained using mean annual air temperature. A general linear regression of U₃₇^k′ and MAAT can be expressed as U₃₇^k′ = 0.0328 × T + 0.126 (n = 38, r² = 0.83). Although questions such as species-uncertainty and other unknown factors for U₃₇^k′ temperature dependence still remain, the equation might be representative of the average contribution of LCK to sediments for these data over a wide range of surface temperatures, water chemistry and different alkenones-producer algal populations. The general relationship of U₃₇^k′ and mean annual air temperature is consistent with that in marine systems. It supports the suggestion that the biosynthetic pathway of alkenones and the mechanism of their temperature signal may be similar in both marine and limnic systems. LCK might be used as an important paleotemperature proxy in limnic environment.     

Carbon isotopic changes in benthic foraminifera from the western South Atlantic: Reconstruction of glacial abyssal circulation patterns

Oxygen- and carbon-isotopic analyses have been performed on the benthic foraminifer Planulina wuellerstorfi in seven Late Quaternary cores from the Vema Channel-Rio Grande Rise region. The cores are distributed over the water-depth interval of 2340 to 3939 m, which includes the present transition from North Atlantic Deep Water (NADW) to Antarctic Bottom Water (AABW).The carbon-isotopic records in the cores vary as a function of water depth. The shallowest and deepest cores show no significant glacial-interglacial difference in δ¹³C. Four of the five cores presently located in the NADW have benthic foraminiferal δ¹³C that is lower during glacial isotopic stages. Based on bathymetric gradients in δ¹³C, we conclude that, like today, there were two water masses present in the Vema Channel during glacial intervals: a water mass enriched in ¹³C overlying another water mass depleted in ¹³C. The largest gradient of change of δ¹³C with depth, however, occurred at 2.7 km, ～ 1 km shallower than the present position of this gradient.On the basis of paleontologic and sedimentologic evidence, we consider it unlikely that the NADW:AABW transition shallowed to this level. Reduced carbon-isotopic gradients between the deep basins of the North Atlantic and Pacific Oceans during the last glaciation suggest that production of NADW was reduced. Lower production of NADW may have modified the local abyssal circulation pattern in the Vema Channel region.     

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C₃ forest browsers in the Amazon (mean δ¹³C = −13.4‰), to mixed C₃ grazers and/or browsers living either in C₃ grasslands, or mixed C₃ forested and grassland habitats in Honduras (mean δ¹³C = −9.3‰), Buenos Aires province, Argentina (δ¹³C = −8.7‰), and Bahia, Brazil (mean δ¹³C = −8.6‰), to predominantly C₄ grazers in northern Argentina (δ¹³C = −4.4‰), to specialized C₄ grazers in the Chaco of Bolivia (δ¹³C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C₃-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.     

n-Alkane parameters from a deep sea sediment transect off southwest Africa reflect continental vegetation and climate conditions

An isobathic transect of marine surface sediments from 1°N to 28°S off southwest Africa was used to further evaluate the potential of the chain length distribution and carbon stable isotope composition of higher plant n-alkanes as proxies for continental vegetation and climate conditions. We found a strong increase in the n-C_29–33 weighted mean average δ¹³C values from −33‰ near the equator to around −26‰ further south. Additionally, C_25–35 n-alkanes reveal a southward trend of increasing average chain length from 30.0 to 30.5. The data reflect the changing contribution of plants employing different photosynthetic pathways (C₃ and C₄) and/or being differently influenced by the environmental conditions of their habitat. The C₄ plant proportions calculated from the data (ca. 20% for rivers draining the rainforest, to ca. 70% at higher latitude) correspond to the C₄ plant abundance in continental catchment areas postulated by considering prevailing wind systems and river outflows. Furthermore, the C₄ plant contribution to the sediments correlates with the mean annual precipitation and aridity at selected continental locations in the postulated catchment areas, suggesting that the C₄ plant fraction in marine sediments can be used to assess these environmental parameters.     

Carbon, sulfur, and oxygen isotope evidence for a strong depth gradient and oceanic oxidation after the Ediacaran Hankalchough glaciation

In order to understand spatial variations of stable isotope geochemistry in the Quruqtagh basin (northwestern China) in the aftermath of an Ediacaran glaciation, we analyzed carbonate carbon isotopes (δ¹³C_carb), carbonate oxygen isotopes (δ¹⁸O_carb), carbonate associated sulfate sulfur (δ³⁴S_CAS) and oxygen isotopes (δ¹⁸O_CAS), and pyrite sulfur isotopes (δ³⁴S_py) of a cap dolostone atop the Ediacaran Hankalchough glacial diamictite at four sections. The four studied sections (YKG, MK, H and ZBS) represent an onshore-offshore transect in the Quruqtagh basin. Our data show a strong paleobathymetry-dependent isotopic gradient. From the onshore to offshore sections, δ¹³C_carb values decrease from −2‰ to −16‰ (VPDB), whereas δ¹⁸O_carb values increase from −4‰ to −1‰ (VPDB). Both δ³⁴S_CAS and δ³⁴S_py show stratigraphic variations in the two onshore sections (MK and YKG), but are more stable in the two offshore sections (H and ZBS). δ¹⁸O_CAS values of onshore samples are consistent with terrestrial oxidative weathering of pyrite. We propose that following the Hankalchough glaciation seawater in the Quruqtagh basin was characterized by a strong isotopic gradient. The isotopic data may be interpreted using a three-component mixing model that involves three reservoirs: deep-basin water, surface water, and terrestrial weathering input. In this model, the negative δ¹³C_carb values in the offshore sections are related to the upwelling of deep-basin water (where anaerobic oxidation of dissolved organic carbon resulted in ¹³C-depleted DIC), whereas sulfur isotope variations are strongly controlled by surface water sulfate and terrestrial weathering input derived from oxidative weathering of pyrite. The new data provide evidence for the oceanic oxidation following the Hankalchough glaciation.     

Marine radiocarbon reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic Coast of North America

Radiocarbon dates from known age, pre-bomb eastern oyster (Crassostrea virginica) shells provide local marine reservoir corrections (?R) for Chesapeake Bay and the Middle Atlantic coastal area of eastern North America. These data suggest subregional variability in ?R, ranging from 148 ± 46 ¹⁴C yr on the Potomac River to ? 109 ± 38 ¹⁴C yr at Swan Point, Maryland. The ?R weighted mean for the Chesapeake's Western Shore (129 ± 22 ¹⁴C yr) is substantially higher than the Eastern Shore (? 88 ± 23 ¹⁴C yr), with outer Atlantic Coast samples falling between these values (106 ± 46 and 2 ± 46 ¹⁴C yr). These differences may result from a combination of factors, including ¹⁴C-depleted freshwater that enters the bay from some if its drainages, ¹⁴C-depleted seawater that enters the bay at its mouth, and/or biological carbon recycling. We advocate using different subregional ?R corrections when calibrating ¹⁴C dates on aquatic specimens from the Chesapeake Bay and coastal Middle Atlantic region of North America.     

Ck-Reconstruction of Surfaces from Partial Data

In this paper, we study the problem of constructing a smooth approximant of a surface defined by the equation z = f(x ₁, x ₂), the data being a finite set of patches on this surface. This problem occurs, for example, after geophysical processing such as migration of time-maps or depth-maps. The usual algorithms to solve this problem are picking points on the patches to get Lagrange's data or trying to get local junctions on patches. But the first method does not use the continuous aspect of the data and the second one does not perform well to get a global regular approximant (C ¹ or more). As an approximant of f, a discrete smoothing spline belonging to a suitable piecewise polynomial space is proposed. The originality of the method consists in the fidelity criterion used to fit the data, which takes into account their particular aspect (surface's patches): the idea is to define a function that minimizes the volume located between the data patches and the function, and which is globally C ^k. We first demonstrate the new method on a theoretical aspect and numerical results on real data are given.     

Compound specific δD values of long chain n-alkanes derived from terrestrial higher plants are indicative of the δD of meteoric waters: Evidence from surface soils in eastern China

The stable carbon and hydrogen isotope composition of higher plant-derived long chain n-alkanes (δ¹³C_n-alkanes and δD_n-alkanes) from 45 surface soil samples (within well characterized vegetation zones) from eastern China (18°N–50°N) are reported. The weighted average δD_n-alkanes value for n-C₂₇, n-C₂₉ and n-C₃₁ in the samples and the annual average δD of meteoric water recorded at 12 weather stations proximal to the sampling sites show similar spatial variations. The δD of n-alkanes shows a gradual depletion in value with increasing latitude. The results demonstrate that, on a large spatial scale, the δD values of long chain n-alkanes derived from higher plants have the potential to record the δD of meteoric water, although many other factors can also influence the isotope values. There appears to be no apparent relationship between the δD of the n-alkanes extracted from the surface soil and the overlying vegetation type (i.e. forest/grassland or C₃/C₄ composition). Therefore, palaeoenvironmental studies utilizing δD_n-alkanes from higher plant-derived material in geological samples have the potential to provide additional information with regard to the past hydrological cycle.     

Carbon in olivine single crystals analyzed by the 12C(d,p)13C method and by photoelectron spectroscopy

Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60–180 wt.-ppm, were analyzed by means of the ¹²C(d. p)¹³C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar⁺ ion sputtering respectively, between 200–930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1–2 μm or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0–0.6, 0.6–1.2, and 1.2–1.8 μm. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D= 10^?13 exp(?7.8/RT) [m²· sec^?1; KJ · mole^?1] and from XPS data between 450–925 K: D = 10^?14 exp(-6/RT) [m² · sec^?1; KJ · mole^?1] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole^?1 respectively.