Deciphering some unique paleotemperature indicators in halite-bearing saline lake deposits from Death Valley, California, USA

Saline lake deposits are arguably the best source of mid- to low-latitude terrestrial paleoclimate data. Alternating clastic sediments and evaporites of different chemical composition have long been recognized as sensitive records of changes in inflow and aridity related to a variety of climate parameters. Several sources of paleotemperature information from a halite-bearing saline lake deposit are described here – pseudomorphs of a cold-temperature evaporite mineral, homogenization temperatures of fluid inclusions in halite, and stable-isotope compositions of fluid inclusions in halite. Examples of these paleoclimate data come from analysis of the lower half of a 185-m core drilled in Pleistocene saline lake deposits at Death Valley, California. Daily and seasonal temperature variations in saline lake waters create conditions for the appearance and disappearance of temperature-dependent mineral phases. In the Death Valley core, hexagonal-shaped halite crystals, probable pseudomorphs of the cold-temperature hydrous mineral, hydrohalite (NaCl2H₂O), provide evidence of brine temperatures below about 0 °C. Homogenization temperatures of fluid inclusions in primary halite offer an actual (not proxy) record of surface-brine temperatures. Samples with primary fluid-inclusion textures are carefully selected and handled, and data are collected from single-phase aqueous-brine inclusions chilled to nucleate vapor bubbles. Temperature variations are observable at scales of individual halite crystals (hours to days), single halite beds (weeks to months or years), and multiples of beds to entire facies (hundreds to tens of thousands of years). A ¹⁸O/D stable isotope record from the minute quantities of brines in fluid inclusions in halite is accessible using a method recently developed at the University of Calgary. The stable isotope record from the Death Valley core, a complex response to climate variables including temperature, humidity, storm patterns or seasons, and inflow sources, compliments and expands the interpretation emerging from the stratigraphy and homogenization temperatures.     

Development of a regional ocean model for New Zealand

A regional ocean model with a horizontal resolution of 1/6° encompassing the New Zealand Exclusive Economic Zone is described. The regional model successfully downscaled solutions from a high resolution, global, coupled model HadCEM. Transport estimates from the global and regional models were compared with observations, and both models supported largely consistent, climatological mean solutions. The regional model used monthly mean forcing at the surface. Nevertheless, the regional model eddy kinetic energy (EKE) spatial patterns compared favourably with long‐term mean satellite altimetric estimates, although the modelled background EKE amplitudes were much lower than observed. A series of permanent eddies associated with the western boundary current system around the top of the North Island of New Zealand were reproduced, and an eddy adjacent to Norfolk Ridge was identified in both the global and regional models. The western boundary current system around the North Island of New Zealand and the associated eddies were the most sensitive components of the model solutions, being influenced by initial conditions, wind forcing, and the model domain size.     

Variations in storm response along a microtidal transgressive barrier-island arc

Storm response along the transgressive Chandeleur barrier-island arc southeast of the Mississippi delta plain is variable because of local differences in sediment supply, shoreline orientation and barrier morphology. A study of the morphological impact of Hurricane Frederic (1979) affirmed that tropical storms are the primary agents causing erosion and migration of this barrier arc.Frederic's greatest impact was in the duneless southern Chandeleurs, where sheet-flow overwash caused flattening of the barrier profile, destruction of a strip of marsh 50–100 m wide, and shoreline retreat of approximately 30 m. In contrast, overwash in the northern Chandeleurs was confined between dunes in channels established by previous storms. This channelized overwash breached the northern Chandeleur barriers in nineteen places. As Frederic passed, return flow through these channels transported overwashed sediment back to the nearshore zone. These ebb deposits were a source for longshore drift sediments, which quickly sealed storm channels, reestablishing a coherent northern Chandeleur barrier arc.These storm response patterns may help explain long-term changes in barrier morphology. During an 84-yr period (1885–1969) the southern Chandeleurs decreased 41 % in area, with an average retreat rate of 9.1 m yr^?1, compared to a 15% increase in area and an average shoreline retreat rate of 7.2 m yr^?1 for the northern Chandeleurs.     

Petrographic and geochemical characterization of seep carbonate from Bush Hill (GC 185) gas vent and hydrate site of the Gulf of Mexico

Authigenic carbonates are common at cold seep sites as a result of microbial oxidation of hydrocarbons. Seep carbonate samples were collected from the surface of the Bush Hill (Green Canyon Block 185, Gulf of Mexico), a mound containing gas hydrate. The carbonates consisted of oily, porous limestone slabs and blocks containing bioclasts and matrix. Analysis by X-ray diffraction shows that aragonite is the dominant mineral (89–99 wt% with an average of 94 wt%) in the matrix of seep carbonate. This cement occurs in microcrystalline, microspar, and sparite forms. The moderate ¹³C depletion of the seep carbonate (the most depleted one has δ¹³C value of −29.4‰, and 26 of 38 subsamples have δ¹³C values >−20.0‰) indicates that the non-methane hydrocarbons was incorporated during seep carbonate precipitation. Relative enrichment of ¹⁸O may be related to localized destabilization of gas hydrate or derived from ¹⁸O-enriched pore water originated from smectite–illite transition in the deep sediments. The total content of rare earth elements (REE) of the 5% HNO₃-treated solution of the carbonates is from 0.40 ppm to 30.9 ppm. The shale-normalized REE patterns show varied Ce anomalies from significantly negative, slightly negative, and no to positive Ce anomalies. Variable content of trace elements, total REE, and Ce anomalies in different samples and even in the different carbonate mineral forms (microcrystalline, microspar and sparite) of the same sample suggest that the formation condition of the Bush Hill seep carbonate is variable and complex, which is possibly controlled by the rate of fluid flux.     

Archaeol as a methanogen biomarker in ombrotrophic bogs

In order to develop new tools in the reconstruction of microbiological processes in ancient continental settings, we determined the concentration of archaeol and sn-2-hydroxyarchaeol in four Holocene ombrotrophic peatlands, spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal water table, archaeol and sn-2-hydroxyarchaeol concentration markedly increased at all four sites, again consistent with an anaerobic source, but differed strongly among sites. The differences apparently reflect a combination of vegetation - ericaceous and graminoid plants as opposed to Sphagnum spp. and other mosses lacking root systems - and temperature influence on methanogenesis. In particular, low ether lipid concentrations in Finland probably reflect the lack of vascular vegetation possessing well-developed root systems, together with low mean annual temperature. Similarly low concentrations of archaeol and sn-2-hydroxyarchaeol in a German bog likely result from winter temperatures below 0 °C and a relatively shorter growing season. The occurrence of sn-2-hydroxyarchaeol is limited to a narrow and shallow depth range, indicating that it is poorly preserved, but archaeol persists throughout the cores. Decoupling the concentration of archaeol and the more labile sn-2-hydroxyarchaeol below ca. 50 cm suggests that the former records fossil biomass rather than living biomass. If so, then downcore variation in archaeol concentration likely reflects past changes in methane cycling, and archaeol, pending further developmental research, could serve as a new tool for reconstruction of past peatland biogeochemistry.     

The XIV Global Warming International Conference ＆ Expo （GWXIV）——Global extreme events

The focus of this year‘s conference is Global Extreme Events, characterized as large-scale climatic effects that have been increasing in magnitude and frequency. Prof. Sinyan Shen, Chairman of the GW International Program Committee, has been leading the world on Global Extreme Events and Emergency Response. In the long term climate change will cause the Earth to transit to another equilibrium state through many oscillations in climatic pattern. Global warming causes extreme events and bad weather in the near term. The immediate     

Topographically‐independent ice flow in northwestern British Columbia: implications for Cordilleran Ice Sheet reconstruction

Studies in southern British Columbia have shown that Cordilleran Ice Sheet flow was controlled by topograph, even in full glacial time. New ice‐flow evidence from the Nass River region, northern British Columbia, however, indicates that ice was thicker there and that the continental ice‐sheet phase of glaciation was reached. Inspection of high elevation sites has revealed a suite of ice‐flow indicators (mainly striae) undetected by earlier work. These suggest that at the Last Glacial Maximum (Fraser Glaciation), ice flowed southwestward across the Nass River region from an ice divide that probably was located in the Skeena Mountain area. Comparisons with adjacent work allow this divide to be mapped over a wide area. The results suggest that maximum ice thicknesses in the northern part of the Cordilleran Ice Sheet were larger than reported previously. The location of storm tracks in full glacial time may have played an important role in the production of an ice sheet that was thicker in northern British Columbia than it was in the southern half of the province. During deglaciation, ice thinned and gradually became confined to fiords and valleys, resulting in numerous and variable ice‐flow directions at that time. Topographic control was thus exerted on ice flow only after the glacial maximum was reached, despite the significant amount of relief in this region. Copyright © 2002 John Wiley & Sons, Ltd.     

Climatic Change and Desert Vegetation Distribution: Assessing Thirty Years of Change in Southern Nevada's Mojave Desert

A major theme in physical geography and biogeography is understanding how vegetation changes across geographic gradients during climate change. We assess shifts in distributions of fifteen Mojave Desert plant species based on a 2008 resurvey of 103 vegetation transects that were established in 1979. We model changes in species distributions using Maximum Entropy (Maxent) with environmental and climate variables to predict probability of species’ occurrences. Climate during the ten-year period preceding the 2008 vegetation survey was 1.5°C warmer and 3 cm per year of precipitation drier than the ten years preceding 1979. Species inhabiting the highest elevations and strongly correlated with precipitation displayed areal reductions from 1979 through 2008.