A computationally and cognitively plausible model of supervised and unsupervised learning

Author version made available in accordance with the publisher's policy. "The final publication is available at link.springer.com”The issue of chance correction has been discussed for many decades in the context of statistics, psychology and machine learning, with multiple measures being shown to have desirable properties, including various definitions of Kappa or Correlation, and the psychologically validated ΔP measures. In this paper, we discuss the relationships between these measures, showing that they form part of a single family of measures, and that using an appropriate measure can positively impact learning

Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA

A composite 11.82 m-long (9876e-67 cal yr BP) sediment record from Yellowstone Lake, Wyoming was analyzed using a robust set of biological and geochemical proxies to investigate the paleoenvironmental evolution of the lake and its catchment in response to long-term climate forcing. Oxygen isotopes from diatom frustules were analyzed to reconstruct Holocene climate changes, and pollen, charcoal, diatom assemblages, and biogenic silica provided information on terrestrial and limnological responses. The long-term trends recorded in the terrestrial and limnic ecosystems over the last 9800 years reflect the influence of changes in the amplification of the seasonal cycle of insolation on regional climate. The early Holocene (9880e6700 cal yr BP) summer insolation maximum and strengthening of the northeastern Pacific subtropical high-pressure system created warm dry conditions and decreasing summer insolation in the middle (6700e3000 cal yr BP) and late (3000e-67 cal yr BP) Holocene resulted in progressively cooler, wetter conditions. Submillenial climate variation is also apparent, with a wetter/cooler interval between 7000 and 6800 cal yr BP and warmer and/or drier conditions from 4500 to 3000 cal yr BP and at ca. 1100 cal yr BP. These data show that the Yellowstone Lake basin had a climate history typical of a summer-dry region, which helps to better define the spatial variability of Holocene climate in the Greater Yellowstone Ecosystem

Geochemistry and mineralogy of a silica chimney from an inactive seafloor hydrothermal field (East Pacific Rise, 18°S)

International audienceAn inactive vent field comprised of dead chimneys was discovered on the ultrafast East Pacific Rise (EPR) at 18 degrees S during the research campaign NAUDUR with the R/V Le Nadir in December 1993. One of these chimneys was sampled, studied and found to be largely composed of silica-mineralized bacterial-like filaments. The filaments are inferred to be the result of microbial activity leading to silica (+/- Fe-oxyhydroxide) precipitation. The chimney grew from the most external layer (precipitated 226 +/- 4 yr. B.P.) towards the central chimney conduit. Hydrothermal activity ceased 154 +/- 13 yr. B.P. and the chimney conduit was completely sealed. Mixing between an end-member hydrothermal fluid and seawater explains the Sr-Nd isotopic composition of the chimney. Seawater was the major source of Sr to the chimney, whereas the dominant Nd source was the local mid-ocean ridge basalt (MORB) leached by the hydrothermal fluids. The mixing scenarios point to a dynamic hydrothermal system with fluctuating fluid compositions. The proportion of seawater within the venting fluid responsible for the precipitation of the silica chimney layers varied between 94 and 85%. Pb-isotope data indicates that all of the Pb in the chimney was derived from the underlying MORB. The precipitation temperatures of the chimney layers varied between 55 and 71 degrees C, and were a function of the seawater/end-member hydrothermal fluid mixing ratio. delta Si-30 correlates with the temperature of precipitation implying that temperature is one of the major controls of the Si-isotope composition of the chimney. Concentrations of elements across the chimney wall were a function of this mixing ratio and the composition of the end-member hydrothermal fluid. The inward growth of the chimney wall and accompanying decrease in wall permeability resulted in an inward decrease in the seawater/hydrothermal fluid mixing ratio, which in turn exerted a control on the concentrations of the elements supplied mainly by the hydrothermal fluids. The silica chimney is significantly enriched in U, likely a result of bacterial concentration of U from the seawater-dominated vent fluid. The chimney is poor in rare earth elements (REE). It inherited its REE distribution patterns from the parent end-member hydrothermal fluids. The dilution of the hydrothermal fluid with over 85% seawater could not obliterate the particular REE features (positive Eu anomaly) of the hydrothermal fluids

Uptake of carbon and sulfur during seafloor serpentinization and the effects of subduction metamorphism in Ligurian peridotites

reserved7siThe concentrations and isotope compositions of carbon and sulfur in Ligurian serpentinites having different metamorphic histories were analyzed in order to investigate the behavior of sulfur and carbon during seafloor serpentinization and during subduction metamorphism. Serpentinites associated with gabbros and with seafloor hydrothermal sulfide deposits in northern Apennine ophiolites that exhibit only slight effects of low-grade metamorphism have high sulfur contents (190–1440 ppm total sulfur) and δ34STotal S values of up to 9.8‰ through interaction with hydrothermal fluids in high-temperature ultramafic-hosted hydrothermal systems on the seafloor. Fluid circulation was driven by mafic intrusions and the hydrothermal fluids contained a mixture of basaltic and seawater-derived sulfur. The serpentinites contain 250–480 ppm total carbon having δ13CTotal C values of − 9.4 to − 6.0‰, reflecting mixtures of seawater carbonate (~ 0‰) and reduced (organic) carbon having δ13C ≈ − 25‰ and derived from multiple sources. Entrainment of cold seawater into the subsurface beneath seafloor hydrothermal sulfide deposits maintained locally low temperatures and enabled microbial reduction of seawater sulfate. Combined with previous work documenting low-temperature serpentinization on the seafloor away from such gabbro-driven high-temperature hydrothermal activity, these results provide an integrated view of serpentinization processes in tectonically extended oceanic basement exposed in oceanic core complexes. High-P–T antigorite serpentinites in the Voltri massif (Ligurian Alps) have sulfur and carbon contents and isotope compositions similar to those of the Apennine ophiolites, indicating that the protoliths underwent similar hydrothermal processes on the seafloor. Recrystallization of chrysotile and lizardite to antigorite and minor partial dehydration to olivine during subduction metamorphism result in no significant changes in the contents or isotope compositions of sulfur or carbon in the serpentinites. We estimate that the uptake of carbon and sulfur by serpentinites in oceanic basement is comparable to or greater than that per unit volume of mafic oceanic crust. The high P–T stability of serpentine can, however, make serpentinites important for transport of carbon and sulfur to greater depths in subduction zones.mixedJ.C. Alt ; W.C. Shanks III; L. Crispini; L. Gaggero; E.M. Schwarzenbach; G.L. Früh-Green; S.M. BernasconiJ. C., Alt; W. C., Shanks III; Crispini, Laura; Gaggero, Laura; E. M., Schwarzenbach; G. L., Früh Green; S. M., Bernascon

Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA

A composite 11.82 m-long (9876–-67 cal yr BP) sediment record from Yellowstone Lake, Wyoming was analyzed using a robust set of biological and geochemical proxies to investigate the paleoenvironmental evolution of the lake and its catchment in response to long-term climate forcing. Oxygen isotopes from diatom frustules were analyzed to reconstruct Holocene climate changes, and pollen, charcoal, diatom assemblages, and biogenic silica provided information on terrestrial and limnological responses. The long-term trends recorded in the terrestrial and limnic ecosystems over the last 9800 years reflect the influence of changes in the amplification of the seasonal cycle of insolation on regional climate. The early Holocene (9880–6700 cal yr BP) summer insolation maximum and strengthening of the northeastern Pacific subtropical high-pressure system created warm dry conditions and decreasing summer insolation in the middle (6700–3000 cal yr BP) and late (3000–-67 cal yr BP) Holocene resulted in progressively cooler, wetter conditions. Submillenial climate variation is also apparent, with a wetter/cooler interval between 7000 and 6800 cal yr BP and warmer and/or drier conditions from 4500 to 3000 cal yr BP and at ca. 1100 cal yr BP. These data show that the Yellowstone Lake basin had a climate history typical of a summer-dry region, which helps to better define the spatial variability of Holocene climate in the Greater Yellowstone Ecosystem