External nutrient sources,internal nutrient pools,and phytoplankton production in Chesapeake Bay

External nutrient loadings, internal nutrient pools, and phytoplankton production were examined for three major subsystems of the Chesapeake Bay Estuary—the upper Mainstem, the Patuxent Estuary, and the 01 Potomac Estuary—during 1985–1989. The atomic nitrogen to phosphorus ratios (TN:TP) of total loads to the 01 Mainstem, Patuxent, and the Potomac were 51, 29 and 35, respectively. Most of these loads entered at the head of the estuaries from riverine sources and major wastewater treatment plants. Approximately 7–16% for the nitrogen load entered the head of each estuary as particulate matter in contrast to 48–69% for phosphorus. This difference is hypothesized to favor a greater loss of phosphorus than nitrogen through sedimentation and burial. This process could be important in driving estuarine nitrogen to phosphorus ratios above those of inputs. Water column TN: TP ratios in the tidal fresh, oligohaline, and mesohaline salinity zones of each estuary ranged from 56 to 82 in the Mainstem, 27 to 48 in the Patuxent, and 72 to 126 in the Potomac. A major storm event in the Potomac watershed was shown to greatly increase the particulate fraction of nitrogen and phosphorus and lower the TN:TP in the river-borne loads. The load during the month that contained this storm (November 1985) accounted for 11% of the nitrogen and 31% of the phosphorus that was delivered to the estuary by the Potomac River during the entire 60-month period examined here. Within the Mainstem estuary, salinity dilution plots revealed strong net sources of ammonium and phosphate in the oligohaline to upper mesohaline region, indicating that these areas were sites of considerable internal recycling of nutrients to surface waters. The sedimentation of particulate nutrient loads in the upper reaches of the estuary is probably a major source of these recycled nutrients. A net sink of nitrate was indicated during summer. A combination of inputs and these internal recycling processes caused dissolved inorganic N to P ratios to approach 16:1 in the mesohaline zone of the Mainstem during late summer; this ratio was much higher at other times and in the lower salinity zones. Phytoplankton biomass in the mesohaline Mainstem reached a peak in spring and was relatively constant throughout the other seasons. Productivity was highest in spring and summer, accounting for approximately 33% and 44%, respectively, of the total annual productivity in this region. In the Patuxent and Potomac, the TN:TP ratios of external loads documented here are 2–4 times higher than those observed over the previous two decades. These changes are attributed to point-source phosphorus controls and the likelihood that nitrogen-rich nonpoint source inputs, including contributions from the atmosphere, have increased. These higher N:P ratios relative to Redfield proportions (16:1) now suggest a greater overall potential for phosphorus-limitation rather than nitrogen-limitation of phytoplankton in the areas studied.     

Short-Period Waves That Heat the Corona Detected at the 1999 Eclipse

As a part of a study of the cause of solar coronal heating, we searched for high-frequency (1 Hz) intensity oscillations in coronal loops in the [Fexiv] coronal green line. We summarize results from observations made at the 11 August 1999 total solar eclipse from Râmnicu-Vâlcea, Romania, through clear skies. We discuss the image reduction and analysis through two simultaneous series of coronal CCD images digitized at 10 Hz for a total time of about 140 s. One series of images was taken through a 3.6 Å filter isolating the 5303 Å[Fexiv] coronal green line and the other through a 100 Å filter in the nearby K-corona continuum. Previous observations, described in Pasachoff et al. (2000), showed no evidence for oscillations in the [Fexiv] green line at a level greater than 2% of coronal intensity. We describe several improvements made over the 1998 eclipse that led to increased image clarity and sensitivity. The corona was brighter in 1999 with the solar maximum, further improving the data. We use Fourier analysis to search in the [Fexiv] channel for intensity oscillations in loops at the base of the corona. Such oscillations in the 1-Hz range are predicted as a result of density fluctuations from the resonant absorption of MHD waves. The dissipation of a significant amount of mechanical energy from the photosphere into the corona through this mechanism could provide sufficient energy to heat the corona. A Monte Carlo model of the data suggests the presence of enhanced power, particularly in the 0.75–1.0 Hz range, and we conclude that MHD waves remain a viable method for coronal heating.     

Fresh Ammonia Ice Clouds in Jupiter: I. Spectroscopic Identification, Spatial Distribution, and Dynamical Implications

We report the first spectroscopic detection of discrete ammonia ice clouds in the atmosphere of Jupiter, as discovered utilizing the Galileo Near-Infrared Mapping Spectrometer (NIMS). Spectrally identifiable ammonia clouds (SIACs) cover less than 1% of the globe, as measured in complete global imagery obtained in September 1996 during Galileo's second orbit. More than half of the most spectrally prominent SIACs reside within a small latitudinal band, extending from 2° to 7° N latitude, just south of the 5-μm hot spots. The most prominent of these are spatially correlated with nearby 5-μm-bright hot spots lying 1.5°-3.0° of latitude to the north: they reside over a small range of relative longitudes on the eastward side of hot spots, about 37% of the longitudinal distance to the next hot spot to the east. This strong correlation between the positions of hot spots and the most prominent equatorial SIACs suggests that they are linked by a common planetary wave. Good agreement is demonstrated between regions of condensation predicted by the Rossby wave model of A. J. Friedson and G. S. Orton (1999, Bull. Am. Astron. Assoc31, 1155-1156) and the observed longitudinal positions of fresh ammonia clouds relative to 5-μm hot spots. Consistency is also demonstrated between (1) the lifetime of particles as determined by the wave phase speed and cloud width and (2) the sedimentation time for 10-μm radius particles consistent with previously reported ammonia particle size by T. Y. Brooke et al. (1998, Icarus136, 1-13). A young age (<two days) for most SIAC cloud particles is indicated. To the south, the most prominent SIACs are located to the northwest of the Great Red Spot, in a region where a westward flow of jovian air, diverted approximately 10° of latitude northward by the Great Red Spot, encounters a large eastward flow. SIACs have been observed repeatedly by NIMS at this location during Galileo's first four years in Jupiter orbit. It is speculated that due to the three-dimensional interactions of these flows, relatively large amounts of ammonia gas are steadily transported from the sub-cloud troposphere (below the ∼600-mbar level) to the high troposphere, nearly continuously forming fresh ammonia ice clouds to the northwest of the Great Red Spot.     

The Enso-Fire Dynamic in Insular Southeast Asia

We examined the spatiotemporal patterns of fire in insular Southeast Asia from July 1996 to December 2001 using a set of consistent, nighttime fire observations provided by the Along Track Scanning Radiometer (ATSR) sensor. Monthly ATSR fire counts were analyzed relative to georeferenced climatic and land-cover data from a variety of sources. We found that fires were strongly correlated with Southern Oscillation Index (SOI) (r = ?0.75) and Niño 3.4 index (r = 0.72) in forested land-cover types within the equatorial belt (5.5^°S–5.5^°N). Cross-correlation analysis revealed that detrended SOI was modestly correlated (r = 0.42) with detrended monthly fire count with a positive lag of four months. However, our analysis also revealed that fire counts reached their maximum 6 months before the absolute maximum of SOI. Annual sums of SOI (∑_SOI) and fire counts revealed linearity for ∑_SOI≤ 0. Overall, the results suggest that ENSO indices may have limited predictive utility at a monthly time scale, but that temporal aggregation and additional fire observations may enhance our capacity to forecast fires in different cover types based on ENSO data.     

Electron tunneling properties of outer-membrane decaheme cytochromes from Shewanella oneidensis

We have characterized the outer-membrane decaheme cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 at the single-molecule level using scanning tunneling microscopy (STM) and tunneling spectroscopy (TS). These cytochrome proteins are of great interest because they are thought to mediate bacterial electron transfer reactions in anoxic waters that control the reductive dissolution of oxide minerals. In our study, to characterize the electron transfer properties of these proteins on a model surface, the purified cytochromes were chemically immobilized as molecular monolayers on Au(111) substrates via a recombinant tetra-cysteine sequence as verified by X-ray photoelectron spectroscopy. Atomic force microscopy images confirm the monolayer films were ∼5-8 nm thick which is consistent with the apparent lateral dimensions of individual cytochrome molecules obtained with STM. Current-voltage TS of single cytochrome molecules revealed that OmcA and MtrC have different abilities to mediate tunneling current despite having otherwise very similar molecular and biochemical properties. These observations suggest that, based on their electron tunneling properties, the two cytochromes could have specific roles during bacterial metal reduction. Additionally, this study establishes single-molecule STM/TS as an effective means for revealing insights into biogeochemical redox processes in the environment.     

Living and working in urban working class communities

Much has been written on the apparent urban renaissance in UK cities and the new lifestyle arrangements, working time patterns, economic activities and the more general reordering of work and life that appears to accompany it. Certainly, recent decades have witnessed a range of economic, social and cultural changes in the lives of those living and working in cities and surrounding suburbs. Much of the attention in this work has focused on those groups for whom the changes have appeared most profound: the high-income earners returning to live in the city - the gentrifiers - or those who suffer multiple deprivations as a result of economic restructuring. Seemingly absent from many accounts of urban change are those places where, at first glance, the effects of change have been less pronounced: low-income, working class neighbourhoods where most people continue to get by, albeit in the context of a harsher, and less secure political economic context. In light of this apparent silence, this paper draws on interviews from Wythenshawe in South Manchester, to examine how low-income mothers cope, live and labour, in a rapidly changing city, as they perform paid work at the same time as ensuring the social reproduction of the household.     

Sea level,climate change and coastal evolution in Morar,northwest Scotland

Analyses of geomorphologically contrasting sites in Morar, NW Scotland, describe the forcing mechanisms of coastal change. Isolation basins (i.e. basins behind rock sills and now isolated from the sea following isostatic uplift) accumulated continuous marine and freshwater sediments from c.12 to 2 ka BP. Raised dune, marsh and wetland sites register breaching, migration and stability of dunes from c. 9 to 2 ka BP. High-resolution methods designed to address issues of macroscale and microscale sea-level changes and patterns of storminess include 1-mm sampling for pollen, dinocyst and diatom analyses, infra-red photography, X-ray photography and thin-section analysis. The data enhance the record of relative sea-level change for the area. Major phases of landward migration of the coast occurred during the period of low sea-level rise in the mid-Holocene as the rate of rise decreased from c. 3 to < 1 mm/year. Relative sea-level change controls the broad pattern of coastal evolution at each site; local site-specific factors contribute to short-term process change. There is no record of extreme events such as tsunami. Within a system of dynamic metastable equilibrium, the Holocene records show that site-specific factors determine the exact timing of system breakdown, e.g. dune breaching, superimposed on regional sea-level rise. The global average sea-level rise of 3 to 6 mm/yr by AD 2050 predicted by IPCC would only partly be offset in the Morar area by isostatic uplift of about 1 mm/yr. A change from relative sea-level fall to sea-level rise, in areas where the regional rate of uplift no longer offsets global processes, is a critical factor in the management of coastal resources.     

Resonant tidal disruption in galactic nuclei

It has recently been shown by Rauch 38 Tremaine that the rate of angular momentum relaxation in nearly Keplerian star clusters is greatly increased by a process termed 'resonant relaxation'; it was also argued, via a series of scaling arguments, that tidal disruption of stars in galactic nuclei containing massive black holes could be noticeably enhanced by this process. We describe here the results of numerical simulations of resonant tidal disruption which quantitatively test the predictions made by Rauch 38 Tremaine. The simulation method is based on an N -body routine incorporating cloning of stars near the loss cone and a semirelativistic symplectic integration scheme. Normalized disruption rates for resonant and non-resonant nuclei are derived at orbital energies both above and below the critical energy, and the corresponding angular momentum distribution functions are found. The black hole mass above which resonant tidal disruption is quenched by relativistic precession is determined. We also briefly describe the discovery of chaos in the Wisdom–Holman symplectic integrator applied to highly eccentric orbits and propose a modified integration scheme that remains robust under these conditions. We find that resonant disruption rates exceed their non-resonant counterparts by an amount consistent with the predictions; in particular, we estimate the net tidal disruption rate for a fully resonant cluster to be about twice that of its non-resonant counterpart. No significant enhancement in rates is observed outside the critical radius. Relativistic quenching of the effect is found to occur for hole masses M  >  M _Q  = (8 ± 3) × 10⁷  M . The numerical results combined with the observed properties of galactic nuclei indicate that for most galaxies the resonant enhancement to tidal disruption rates will be very small.     

Stress fields of the San Andreas and Queen Charlotte transform faults

Analytic solutions to the stress fields resulting from the San Andreas and Queen Charlotte transform faults may be found by applying conformal mappings to the generalized plane stress solution of stresses in a half-plane. The mean stress fields (one-half the trace of the stress tensor) found in this manner show a similarity to the deformation found in western Canada and the western United States. The results refute the hypothesis that Alaska acts as a continental buttress against deformation of the Canadian Cordillera. Moreover, these results imply that the differences in the tectonics of major transform boundaries are caused primarily by differences in lithospheric structure and differences in stress distribution along the plate boundaries.