Climate during the last glacial maximum in the Wasatch and southern Uinta Mountains inferred from glacier modeling

Recent improvements in understanding glacial extents and chronologies in the Wasatch and Uinta Mountains and other mountain ranges in the western U.S. call for a more detailed approach to using glacier reconstructions to infer paleoclimates than commonly applied AAR-ELA-ÄT methods. A coupled 2-D mass balance and ice-flow numerical modeling approach developed by [Plummer, M.A., Phillips, F.M., 2003. A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. Quaternary Science Reviews 22, 1389–1406] allows exploration of the combined effects of temperature, precipitation, shortwave radiation and many secondary parameters on past ice extents in alpine settings. We apply this approach to the Little Cottonwood Canyon in the Wasatch Mountains and the Lake Fork and Yellowstone Canyons in the south-central Uinta Mountains. Results of modeling experiments indicate that the Little Cottonwood glacier required more precipitation during the local Last Glacial Maximum (LGM) than glaciers in the Uinta Mountains, assuming lapse rates were similar to modern. Model results suggest that if temperatures in the Wasatch Mountains and Uinta Mountains were  6 °C to 7 °C colder than modern, corresponding precipitation changes were  3 to 2× modern in Little Cottonwood Canyon and  2 to 1× modern in Lake Fork and Yellowstone Canyons. Greater amounts of precipitation in the Little Cottonwood Canyon likely reflect moisture derived from the surface of Lake Bonneville, and the lake may have also affected the mass balance of glaciers in the Uinta Mountains.     

Low-amplitude, synsedimentary folding of a deltaic complex: Roda Sandstone (lower Eocene), South-Pyrenean Foreland Basin

The South‐Pyrenean Foreland Basin is a sedimentary trough developed during Palaeogene times in response Pyrenean orogenesis. The structural development of the chain progressively involved the foreland basin deposits resulting in synsedimentary thrusting and growth of folds through the basin. The lower Eocene Roda Sandstone was deposited in a shallow‐marine environment whose topography (bathymetry) was modified by a series of growing gentle folds. This synsedimentary folding is evidenced in the field (i) thickening of sedimentary units above synclinal structures and thinning over anticlines; (ii) carbonate platform deposits growing on top of anticlines; (iii) the areal distribution of benthic foraminifera in transgressive facies assemblages determined by an irregular, fold‐influenced palaeobathymetry; (iv) variation of sandstone palaeocurrents related to the presence of a sedimentary trough formed by the synsedimentary growth of a syncline. In addition, synsedimentary folding has been evidenced from seismic data. In the Roda Sandstone example, the growth of gentle folds occurred in an area with high sedimentation rates (～0.21 ± 0.06 mm y^?1). Due to the high sedimentation rates, exceeding the folds uplift rate (～0.10 ± 0.01 mm y^?1), there are no noticeable unconformities in the growth strata at outcrop scale. However, the effects on the sedimentation are very significant, because the sediments were deposited close to sea level, and thus were very sensitive to fauna and facies distribution.     

A Multi-Observatory Inter-Comparison of Line-of-Sight Synoptic Solar Magnetograms

The observed photospheric magnetic field is a crucial parameter for understanding a range of fundamental solar and heliospheric phenomena. Synoptic maps, in particular, which are derived from the observed line-of-sight photospheric magnetic field and built up over a period of 27 days, are the main driver for global numerical models of the solar corona and inner heliosphere. Yet, in spite of 60 years of measurements, quantitative estimates remain elusive. In this study, we compare maps from seven solar observatories (Stanford/WSO, NSO/KPVT, NSO/SOLIS, NSO/GONG, SOHO/MDI, UCLA/MWO, and SDO /HMI) to identify consistencies and differences among them. We find that while there is a general qualitative consensus, there are also some significant differences. We compute conversion factors that relate measurements made by one observatory to another using both synoptic map pixel-by-pixel and histogram-equating techniques, and we also estimate the correlation between datasets. For example, Wilcox Solar Observatory (WSO) synoptic maps must be multiplied by a factor of 3?–?4 to match Mount Wilson Observatory (MWO) estimates. Additionally, we find no evidence that the MWO saturation correction factor should be applied to WSO data, as has been done in previous studies. Finally, we explore the relationship between these datasets over more than a solar cycle, demonstrating that, with a few notable exceptions, the conversion factors remain relatively constant. While our study was able to quantitatively describe the relationship between the datasets, it did not uncover any obvious “ground truth.” We offer several suggestions for how this may be addressed in the future.     

A chironomid-based reconstruction of late glacial summer temperatures in the southern Carpathians (Romania)

Late glacial and early Holocene summer temperatures were reconstructed based on fossil chironomid assemblages at Lake Brazi (Retezat Mountains) with a joint Norwegian–Swiss transfer function, providing an important addition to the late glacial quantitative climate reconstructions from Europe. The pattern of the late glacial temperature changes in Lake Brazi show both similarities and some differences from the NGRIP δ¹⁸O record and other European chironomid-based reconstructions. Our reconstruction indicates that at Lake Brazi (1740 m a.s.l.) summer air temperature increased by ~ 2.8°C at the Oldest Dryas/Bølling transition (GS-2/GI-1) and reached 8.1–8.7°C during the late glacial interstade. The onset of the Younger Dryas (GS-1) was characterized by a weak (< 1°C) decrease in chironomid-inferred temperatures. Similarly, at the GS-1/Holocene transition no major changes in summer temperature were recorded. In the early Holocene, summer temperature increased in two steps and reached ~ 12.0–13.3°C during the Preboreal. Two short-term cold events were detected during the early Holocene between 11,480–11,390 and 10,350–10,190 cal yr BP. The first cooling coincides with the Preboreal oscillation and shows a weak (0.7°C) temperature decrease, while the second is characterized by 1°C cooling. Both cold events coincide with cooling events in the Greenland ice core records and other European temperature reconstructions.     

Discriminating between pore‐filling load and bed‐structure load: a new porosity‐based method,exemplified for the river Rhine

Sediments contained in the river bed do not necessarily contribute to morphological change. The finest part of the sediment mixture often fills the pores between the larger grains and can be removed without causing a drop in bed level. The discrimination between pore‐filling load and bed‐structure load, therefore, is of practical importance for morphological predictions. In this study, a new method is proposed to estimate the cut‐off grain size that forms the boundary between pore‐filling load and bed‐structure load. The method evaluates the pore structure of the river bed geometrically. Only detailed grain‐size distributions of the river bed are required as input to the method. A preliminary validation shows that the calculated porosity and cut‐off size values agree well with experimental data. Application of the new cut‐off size method to the river Rhine demonstrates that the estimated cut‐off size decreases in a downstream direction from about 2 to 0·05 mm, covariant with the downstream fining of bed sediments. Grain size fractions that are pore‐filling load in the upstream part of the river thus gradually become bed‐structure load in the downstream part. The estimated (mass) percentage of pore‐filling load in the river bed ranges from 0% in areas with a unimodal river bed, to about 22% in reaches with a bimodal sand‐gravel bed. The estimated bed porosity varies between 0·15 and 0·35, which is considerably less than the often‐used standard value of 0·40. The predicted cut‐off size between pore‐filling load and bed‐structure load (D_c,p) is fundamentally different from the cut‐off size between wash‐load and bed‐material load (D_c,w), irrespective of the method used to determine D_c,p or D_c,w. D_c,w values are in the order of 10^?1 mm and mainly dependent on the flow characteristics, whereas D_c,p values are generally much larger (about 10⁰ mm in gravel‐bed rivers) and dependent on the bed composition. Knowledge of D_c,w is important for the prediction of the total sediment transport in a river (including suspended fines that do not interact with the bed), whereas knowledge of D_c,p helps to improve morphological predictions, especially if spatial variations in D_c,p are taken into account. An alternative to using a spatially variable value of D_c,p in morphological models is to use a spatially variable bed porosity, which can also be predicted with the new method. In addition to the morphological benefits, the new method also has sedimentological applications. The possibility to determine quickly whether a sediment mixture is clast‐supported or matrix‐supported may help to better understand downstream fining trends, sediment entrainment thresholds and variations in hydraulic conductivity.     

Site-dependent models of earthquake ground motion

Random vibration analyses of structural systems subjected to seismic loading are dependent upon the characterization of earthquake ground motion as a stochastic process. The response of structural systems to earthquakes is dependent strongly on the local geological conditions, which should be incorporated into seismological models of ground motion. In the study presented herein, three previously developed ground-motion models are adapted to incorporate site-dependent characteristics. Records obtained from two recording stations in California are used as a basis for the ground-motion models. Single-degree-of-freedom (SDOF) oscillators are subjected to ensembles of accelerograms generated from these models, and both elastic and inelastic response are considered. Response statistics are compared to those generated by the analysis of structural response to ensembles of recorded motion from the two sites. The important features of the ground motion for effective reproduction of response statistics are identified, and observations are made on the sensitivity of specific response parameters to site-dependent characteristics of the ground motion.     

Geochemical and mineralogical evidence for Sahara and Sahel dust additions to Quaternary soils on Lanzarote,eastern Canary Islands,Spain

Africa is the most important source of dust in the world today, and dust storms are frequent on the nearby Canary Islands. Previous workers have inferred that the Sahara is the most important source of dust to Canary Islands soils, with little contribution from the Sahel region. Soils overlying a late Quaternary basalt flow on Lanzarote, Canary Islands, contain, in addition to volcanic minerals, quartz and mica, exotic to the island’s bedrock. Kaolinite in the soils also likely has an exotic origin. Trace‐element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and African dust. Major‐element geochemistry, clay mineralogy and interpretation of satellite imagery suggest that dust additions to the Canary Islands come not only from the Sahara Desert, but also from the Sahel region.     

Sea breeze development under an offshore synoptic wind in the South-Western Cape and implications for the Stellenbosch wine-producing area

Summary Sea breezes were investigated during the maturation period of wine grapes in the South-Western Cape under particular synoptic wind conditions (onshore for Table Bay and offshore for False Bay). Observations from an automatic weather station network located in the Stellenbosch wine-producing area as well as the Regional Atmospheric Modelling System (RAMS, non-hydrostatic, parallel, version 4.3) were used. Results showed that two sea breezes developed, one from Table Bay late in the morning, and the other from False Bay later in the afternoon. The coastal low strengthened and deflected the sea breeze from Table Bay towards the south and south-east of the study area, while the offshore large-scale circulation hindered the development of the sea breeze in the opposite direction over False Bay and delayed its movement towards land. The decrease in temperature resulting from the onset of the sea breeze from the Atlantic early in the afternoon could be significant for viticulture, reducing the duration and intensity of high temperature stress on grapevine functioning at the coolest locations.     

Is tidal forcing critical to trigger large Sumatra earthquakes?

Complexity in the earthquake mechanism is manifested in different forms such as fractal distribution, clustering of seismicity, etc., and characterized as critical phenomenon. Occurrences of earthquakes generally represent the state of metastable equilibrium. The Andaman–Sumatra subduction zone is one of the most seismically active corridors (possibly in metastable state) in the world. Recently, the region faced three major earthquakes of magnitude more than 8.5 (M ~ 9.1 on December 26, 2004; M ~ 8.6 on March 28, 2005; M ~ 8.6 on April 11, 2012). Researchers have suggested multiple causes of earthquake generation in this region including the one with possible correlation of tidal stresses with earthquake occurrences. The latter issue, however, has been hotly debated in view of the fact that a small stress generated due to tidal forcing cannot cause such a bigger magnitude earthquake. We study here the impact of tidal forcing on critically generated earthquake phenomena. We examined the statistical behavior of recurrence time interval of earthquakes using the available data for period of about 40 years from 1973 to 2013. We constrain the simple empirical toy model using the concept of catastrophe theory to evaluate the impact of small tidal forcing on the critical state of earthquakes occurrences. In addition to the major role of Helmholtz free energy during the plate motion, our analysis suggests that the stability and critical behavior of the earthquake in Sumatra region could be associated with tidal forcing, however, only for triggering of some of the “Catastrophic–Chaotic” earthquake phenomenon.     

Medieval Warming, Little Ice Age, and European impact on the environment during the last millennium in the lower Hudson Valley, New York, USA

Establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts. We present a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency from a tidal marsh in the Hudson River Estuary. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from 800–1300 A.D., paralleling paleorecords southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. The presence of the Little Ice Age ensues with increases in Picea and Tsuga, coupled with increasing organic percentages due to cooler, moister conditions. European impact is manifested by a decline in arboreal pollen due to land clearance, increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), and an increase in inorganic particles to the watershed.