Increased Terrestrial to Ocean Sediment and Carbon Fluxes in the Northern Chesapeake Bay Associated With Twentieth Century Land Alteration

We calculated Chesapeake Bay (CB) sediment and carbon fluxes before and after major anthropogenic land clearance using robust monitoring, modeling and sedimentary data. Four distinct fluxes in the estuarine system were considered including (1) the flux of eroded material from the watershed to streams, (2) the flux of suspended sediment at river fall lines, (3) the burial flux in tributary sediments, and (4) the burial flux in main CB sediments. The sedimentary maximum in Ambrosia (ragweed) pollen marked peak land clearance (~1900 a.d.). Rivers feeding CB had a total organic carbon (TOC)/total suspended solids of 0.24?±?0.12, and we used this observation to calculate TOC fluxes from sediment fluxes. Sediment and carbon fluxes increased by 138–269% across all four regions after land clearance. Our results demonstrate that sediment delivery to CB is subject to significant lags and that excess post-land clearance sediment loads have not reached the ocean. Post-land clearance increases in erosional flux from watersheds, and burial in estuaries are important processes that must be considered to calculate accurate global sediment and carbon budgets.     

Antarctic tourism and environmental concerns

Increasing numbers of tourists are visiting the Antarctic. Totals from the past three seasons (1989–1990, 1990–1991, 1991–1992) were 2581, 4842, and 6495 respectively (Enzenbacher, 1992). Some environmental issues arising from Antarctic tourist activity include: wildlife tolerance, waste disposal, passenger education, tour operator management practices, personnel experience, frequency of visits and ship design. Current guidelines provide a practical approach to tourism, but do not address all issues arising from tourist activity. Antarctic Treaty Parties agreed to examine the question of a comprehensive regulation of tourist activities in the Antarctic Treaty Area and policies are under review. Some issues may prove difficult to resolve. Compliance with existing guidelines is to be encouraged, at least until more is known about the environmental effects of tourism. A management plan for tourism is needed along with more research on how tourism is conducted and the effects visits have on Antarctica's marine and terrestrial ecosystems. Cooperation between Treaty Parties and tour operators is important for the development of appropriate tourism regulations.     

A geostatistically based inverse model for three-dimensional variably saturated flow

We present a geostatistically based inverse model for characterizing heterogeneity in parameters of unsaturated hydraulic conductivity for three-dimensional flow. Pressure and moisture content are related to perturbations in hydraulic parameters through cross-covariances, which are calculated to first-order. Sensitivities needed for covariance calculations are derived using the adjoint state sensitivity method. Approximations of the conditional mean parameter fields are then obtained from the cokriging estimator. Correlation between parameters and pressure – moisture content perturbations is seen to be strongly dependent on mean pressure or moisture content. High correlation between parameters and pressure data was obtained under saturated or near saturated flow conditions, providing accurate estimation of saturated hydraulic conductivity, while moisture content measurements provided accurate estimation of the pore size distribution parameter under unsaturated flow conditions.     

Effect of suspension and sedimentation on the amount of microbial colonization of salt marsh microdetritus

The relative density of bacterial colonization of small (5 to 40 μ diameter) suspended and sedimented detritus particles in salt marsh creeks was studied using an europium chelate-fluorescent brightener stain coupled with epifluorescent microscopy. Particles were obtained from four substations at each of three sites in salt marshes bordering the York River, Virginia. Coverage of detrital particles by bacteria was uniformly low, averaging 1.54%±1.83% of the particle surface area. Suspended particles larger than 10 μ diameter had lower bacterial densities than did sedimented particles in the same size ranges. It is speculated that microbial growth may be enhanced on sedimented particles both through lack of motion and access to greater nutrient concentrations.     

Mineralogy,chemistry and crystallization sequence of clay minerals in altered tholeiitic basalts from the Peru Trench

Petrographic examination of amygdules and veins associated with moderately altered pillow basalts dredged from the Peru Trench has revealed that a consistent pattern of mineral crystallization has occurred. This sequence is: (1) green, weakly pleochroic clay (R.I. > 1.56); (2) dark yellowish brown, non-pleochroic clay (R.I. > 1.56); (3) light yellowish brown to colorless, fibrous, weakly pleochroic clay (R.I. < 1.56); and (4) calcite or celadonite. Chemical and X-ray diffraction analyses suggest that all clay mineral amygdule and vein fillings are dominated by intimate mixtures of an Fe-rich saponite and nontronite with very small admixtures of serpentine and illite. It is argued that sequential mineral fillings of fractures and vesicles may provide significant information about the chemistry of circulating interstitial fluids. For the pillow basalts studied the first-formed clays were enriched in nontronite, thereby suggesting Fe-rich fluids. These in turn were followed by saponite-rich clays and calcite. The change from Fe-and Mg-rich fluids to dominantly Ca-rich fluids is thought to correspond to a change from mafic mineral alteration to plagioclase alteration in the pillow basalts. An increase in the Fe³⁺/Fe²⁺ ratio of clays toward the centers of vesicles may indicate a change toward a more oxidizing environment of alteration.     

Formation of an eroded lava channel within an Elysium Planitia impact crater: Distinguishing between a mechanical and thermal origin

A lava channel identified on the wall of an Elysium Planitia impact crater is investigated to identify the dominant erosion mechanism, mechanical vs. thermal, acting during channel formation. Observations of channel morphology are used to supplement analytical models of lava channel formation in order to calculate the duration of channel formation, the velocity of the lava flowing through the channel, and the erosion rate in each erosion regime considered. Results demonstrate that the channel observed in the Elysium Planitia impact crater formed primarily due to mechanical erosion. In a more general sense, results of this study suggest that lava channels can form primarily due to thermal erosion in the presence of more gradual slopes and more consolidated substrates whereas lava channels can form primarily due to mechanical erosion in the presence of more energetic flows on steeper slopes and more poorly consolidated substrates. Therefore, both erosion regimes must be considered when analyzing origins of eroded lava channels that cut through strata of different strengths.     

ENSO,the IOD and the intraseasonal prediction of heat extremes across Australia using POAMA-2

The simulation and prediction of extreme heat over Australia on intraseasonal timescales in association with the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is assessed using the Bureau of Meteorology’s Predictive Ocean Atmosphere Model for Australia (POAMA). The analysis is based on hindcasts over 1981–2010 and focuses on weeks 2 and 3 of the forecasts, i.e. beyond a typical weather forecast. POAMA simulates the observed increased probabilities of extreme heat during El Niño events, focussed over south eastern and southern Australia in SON and over northern Australia in DJF, and the decreased probabilities of extreme heat during La Niña events, although the magnitude of these relationships is smaller than observed. POAMA also captures the signal of increased probabilities of extreme heat during positive phases of the IOD across southern Australia in SON and over Western Australia in JJA, but again underestimates the strength of the relationship. Shortcomings in the simulation of extreme heat in association with ENSO and the IOD over southern Australia may be linked to deficiencies in the teleconnection with Indian Ocean SSTs. Forecast skill for intraseasonal episodes of extreme heat is assessed using the Symmetric Extremal Dependence Index. Skill is highest over northern Australia in MAM and JJA and over south-eastern and eastern Australia in JJA and SON, whereas skill is generally poor over south-west Western Australia. Results show there are windows of forecast opportunity related to the state of ENSO and the IOD, where the skill in predicting extreme temperatures over certain regions is increased.