Modified passive capillary samplers for collecting samples of snowmelt infiltration for stable isotope analysis in remote,seasonally inaccessible watersheds 1: laboratory evaluation

Snowmelt is the most significant source of runoff generation and recharge in many of the mountainous watersheds worldwide and this is especially true in the southwestern United States. Yet, the isotopic and geochemical composition of the soil–meltwater endmember remains poorly constrained. Using the isotopic compositions of snow and snowmelt runoff samples taken from the landscape surface as proxies for soil–meltwater endmembers is problematic since they are typically not representative of the actual composition of soil meltwater. Furthermore, the applicability of current methodologies to collect the isotopic composition of meltwater is limited because of the remote and often seasonally inaccessible nature of the terrain where snowpacks develop. Therefore, a robust methodology requiring little maintenance or monitoring is desirable. A lab experiment was conducted to determine the suitability of using a modified passive capillary sampler (M‐PCAPS) design to collect snowmelt infiltration for isotopic analysis. Passive capillary samplers are constructed from fiberglass wicks that can be installed in the soil to sample vadose‐zone waters under a wide range of matric potentials and require little maintenance. Results from this lab experiment indicate that the wicking process associated with M‐PCAPS does not fractionate water but certain precautions are necessary to prevent exchange between the wick and the atmosphere. In this experiment, M‐PCAPS effectively tracked the changing isotopic composition of a soil reservoir undergoing evaporation. Therefore, M‐PCAPS provide a robust methodology to sample the isotopic composition of snowmelt infiltration in remote watersheds and similar applications. Copyright © 2009 John Wiley & Sons, Ltd.     

A method to reduce the spin-up time of ocean models

The spin-up timescale in large-scale ocean models, i.e., the time it takes to reach an equilibrium state, is determined by the slow processes in the deep ocean and is usually in the order of a few thousand years. As these equilibrium states are taken as initial states for many calculations, much computer time is spent in the spin-up phase of ocean model computations. In this note, we propose a new approach which can lead to a very large reduction in spin-up time for quite a broad class of existing ocean models. Our approach is based on so-called Jacobian–Free Newton–Krylov methods which combine Newton’s method for solving non-linear systems with Krylov subspace methods for solving large systems of linear equations. As there is no need to construct the Jacobian matrices explicitly the method can in principle be applied to existing explicit time-stepping codes. To illustrate the method we apply it to a 3D planetary geostrophic ocean model with prognostic equations only for temperature and salinity. We compare the new method to the ‘ordinary’ spin-up run for several model resolutions and find a considerable reduction of spin-up time.     

The fate of suspended sediment and particulate organic carbon in transit through the channels of a river catchment

Particulate organic matter (POM) transiting through rivers could be lost to overbank storage, stored in‐channel, added to by erosion or autochthonous production, or turned over to release greenhouse gases to the atmosphere (either while in the water column or while stored in the channel). In the UK, a net loss of POM across catchments has been recorded, and the aim here was to investigate the balances of processes acting on the POM. This study considered records of suspended sediment and POM flux in comparison to stream flow, velocity, stream power, and residence time for the River Trent (English Midlands, 8,231 km²). We show that for the lower two thirds (106 km) of the River Trent, 2% is lost to overbank storage; 10% is lost to the atmosphere in the water column; and 31% is turned over while in temporary storage. Permanent in‐channel storage is negligible, and for the lower course of the river, material stored in‐channel will have a residence time of the order of hundreds of days between the last flood hydrograph of one winter and the first winter storm of the next winter (usually in the same calendar year). When considered at the scale of the UK, 1% POM in transit would be lost to overbank sedimentation; 5% turned over in the water column, and 14% turned over while in temporary storage. In the upper third of the study river channel, there is insufficient stream power to transport sediment and so in‐channel storage or in‐channel turnover over to the atmosphere dominate. The in‐channel processes of the River Trent do not conform to that expected for river channels as the headwaters are not eroding or transporting sediment. Therefore, the source of sediment must be lower down the channel network.     

A multi-envelope vertical coordinate system for numerical ocean modelling

A multi-envelope generalised coordinate system for numerical ocean modelling is introduced. In this system, computational levels are curved and adjusted to multiple ‘virtual bottoms’ (aka envelopes) rather than following geopotential levels or the actual bathymetry. This allows defining computational levels which are optimised to best represent different physical processes in different sub-domains of the model. In particular, we show how it can be used to improve the representation of tracer advection in the ocean interior. The new vertical system is compared with a widely used z-partial step scheme. The modelling skill of the models is assessed by comparison with the analytical solutions or results produced by a model with a very high-resolution z-level grid. Three idealised process-oriented numerical experiments are carried out. Experiments show that numerical errors produced by the new scheme are much smaller than those produced by the standard z-partial step scheme at a comparable vertical resolution. In particular, the new scheme shows superiority in simulating the formation of a cold intermediate layer in the ocean interior and in representing dense water cascading down a steep topography.     

Changes in Projected Spatial and Seasonal Groundwater Recharge in the Upper Colorado River Basin

The Colorado River is an important source of water in the western United States, supplying the needs of more than 38 million people in the United States and Mexico. Groundwater discharge to streams has been shown to be a critical component of streamflow in the Upper Colorado River Basin (UCRB), particularly during low‐flow periods. Understanding impacts on groundwater in the basin from projected climate change will assist water managers in the region in planning for potential changes in the river and groundwater system. A previous study on changes in basin‐wide groundwater recharge in the UCRB under projected climate change found substantial increases in temperature, moderate increases in precipitation, and mostly periods of stable or slight increases in simulated groundwater recharge through 2099. This study quantifies projected spatial and seasonal changes in groundwater recharge within the UCRB from recent historical (1950 to 2015) through future (2016 to 2099) time periods, using a distributed‐parameter groundwater recharge model with downscaled climate data from 97 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections. Simulation results indicate that projected increases in basin‐wide recharge of up to 15% are not distributed uniformly within the basin or throughout the year. Northernmost subregions within the UCRB are projected an increase in groundwater recharge, while recharge in other mainly southern subregions will decline. Seasonal changes in recharge also are projected within the UCRB, with decreases of 50% or more in summer months and increases of 50% or more in winter months for all subregions, and increases of 10% or more in spring months for many subregions.     

On the transport of bodies within and from the asteroid belt

Abstract— This paper explores two processes, sweeping secular resonance (Ward, 1981) and gas drag (Lecar and Franklin, 1997), at work during the dispersal of the solar nebula. we have two aims not previously considered for the two mechanisms: (1) to explain the likely depletion, by a factor of 1000 or so, of the rocky material in the inner belt (2.0 < a < 3.2 AU); (2) to introduce a means for providing—or contributing to—the dispersion in semimajor axis of the various asteroidal taxonomic classes. We suggest that large asteroids with birthplaces separated by an astronomical unit or more can be finally deposited, owing to drag, at the same semimajor axis. For example, we find that bodies with radii up to 100 km can be transferred by gas drag from the outer belt (a > 3.3 AU) well into the inner one, and that an object already in the inner belt as large or even larger than Vesta (r = 250 km)—thought to be the parent body of many meteorites—can be inwardly displaced by as much as an astronomical unit if the nebula dispersal times lie close to 10⁵ years. For such times, a large fraction of the inner belt's primordial mass can be ejected, with most of it passing into the inner solar system.     

Diatoms on Earth, Comets, Europa and in Interstellar Space

There exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains. We review the observational data and consider the known properties of diatoms and bacteria. It is suggested that these characteristics are consistent with the concept of acosmic microbiological system in which these or similar microorganisms might exist on comets, Europa and in interstellar space.     

Fidelity of ocean bottom seismic observations

The often poor quality of ocean bottom seismic data, particularly that observed on horizontal seismometers, is shown to be the result of instruments responding to motions in ways not intended. Instruments designed to obtain the particle motion of the ocean bottom are found to also respond to motions of the water. The shear discontinuity across the ocean floor boundary results in torques that cause package rotation, rather than rectilinear motion, in response to horizontal ground or water motion. The problems are exacerbated by bottom currents and soft sediments. The theory and data presented in this paper suggest that the only reliable way of obtaining high fidelity particle motion data from the ocean floor is to bury the sensors below the bottom in a package with density close to that of the sediment. Long period signals couple well to ocean bottom seismometers, but torques generated by bottom currents can cause noise at both long and short periods. The predicted effects are illustrated using parameters appropriate for the operational OBS developed for the U. S. Office of Naval Research. Examples of data from ocean bottom and buried sensors are also presented.     

THE NAKHLITES PART I: PETROGRAPHY AND MINERAL CHEMISTRY

The only two Nakhlite meteorites, Nakhla and Lafayette, are identical in mineral composition, consisting of augite (Wo₃₉En₃₈Fs₂₃), olivine (Fo_32–35), plagioclase (An₂₇), K-feldspar (Or₇₅Ab₂₂An₃), titaniferous magnetite with exsolved ilmenite, iddingsite (?), and minor amounts of fluor-chlorapatite, FeS, pyrite, chalcopyrite, and K-rich glass. The texture is suggestive of a cumulative origin.