University of Rhode Island

About: University of Rhode Island is a education organization based out in Kingston, Rhode Island, United States. It is known for research contribution in the topics: Population & Bay. The organization has 11464 authors who have published 22770 publications receiving 841066 citations. The organization is also known as: URI & Rhode Island College of Agriculture and the Mechanic Arts.

Denitrification and nitrous oxide production in a coastal marine ecosystem1

Abstract: Denitrification was measured directly as the flux of N, from sediment cores collected at various times of year at three stations in the Narragansett Bay, R.I., area. Rates of N, production ranged from about 10 to 115 pmol N*m-2*h-1, with lowest values at 2°C in winter and highest at 15°C in summer. Denitrification represents a major sink for fixed N in the bay; annually the N, production is equal to about 50% of the fixed inorganic N loading to the bay from rivers, land, and sewage. About 35% of the organic nitrogen mineralized in the sediments is removed from the ecosystem by denitrification. The percentage of organic nitrogen being mineralized in the sediments as N20 relative to N, or N03- + NO,- is higher in polluted sediments than in relatively unpolluted sediments, but in all cases is < 10%. Brandt (1899) suggested that denitrifying bacteria were important in controlling the supply of available nitrogen in the ocean and, therefore, plankton production. While it is now established that N is usually the nutrient most limiting to phytoplankton production in marine waters (Thomas 1969; Ryther and Dunstan 197 l), the mechanisms controlling its supply are still not well understood. If Brandt’s hypothesis is correct, the role of denitrification should be especially evident in estuaries and other coastal areas where a significant portion of the nutrient supply comes from mineralization of organic matter in the sediments (see Nixon 198 1). During denitrification, nitrate or nitrite, instead of 02, is used as the terminal electro%acceptor for the oxidation of organic matter, and gaseous nitrogen is produced (Payne 1973). The abundant supply of organic matter and the low oxygen concentrations in coastal sediments would present favorable conditions for denitrification. No direct measurements of N2 production from subtidal coastal sediments have been reported other than those of Seitzinger et al. (1980). There is, however, considerable circumstantial evidence that denitrifi

Organic carbon dynamics and preservation in deep-sea sediments

Abstract: Three methods of estimating the particulate organic carbon fluxes to the sediment-water interface of the deep Pacific Ocean agree to within the error of the measurements at MANOP sites M, H, and C. Sediment trap experiments, pore water results, and surface sediment organic carbon data suggest that a major fraction of the particulate organic carbon raining to abyssal depths at these locations is degraded within the surface sediments rather than at the sediment-water interface or in the nephloid layer. Organic carbon rain rates at the three sites are similar—within a factor of two; however, the preservation rate of organic carbon and the chemistry of sediment pore waters are very different. A model developed to describe the pore water oxygen and sedimentary carbon distributions indicates model developed to describe the pore water oxygen and sedimentary carbon distributions indicates that changes in the rate constant for organic matter degradation and the bioturbation rate may contribute significantly to the observed differences in character of both pore water and sediment chemistry at these locations. The implication with respect to interpreting the sedimentary record is that cycles of organic carbon and redox sensitive metals (i.e., manganese) are not simply related to particulate organic carbon flux or surface water primary productivity. The residence time of organic carbon with respect to degradation in the surface sediments is on the order of 15 to 150 y.

The Papua New Guinea tsunami of 17 July 1998: anatomy of a catastrophic event

Abstract: . The Papua New Guinea (PNG) tsunami of July 1998 was a seminal event because it demonstrated that relatively small and relatively deepwater Submarine Mass Failures (SMFs) can cause devastating local tsunamis that strike without warning. There is a comprehensive data set that proves this event was caused by a submarine slump. Yet, the source of the tsunami has remained controversial. This controversy is attributed to several causes. Before the PNG event, it was questionable as to whether SMFs could cause devastating tsunamis. As a result, only limited modelling of SMFs as tsunami sources had been undertaken, and these excluded slumps. The results of these models were that SMFs in general were not considered to be a potential source of catastrophic tsunamis. To effectively model a SMF requires fairly detailed geological data, and these too had been lacking. In addition, qualitative data, such as evidence from survivors, tended to be disregarded in assessing alternative tsunami sources. The use of marine geological data to identify areas of recent submarine failure was not widely applied. The disastrous loss of life caused by the PNG tsunami resulted in a major investigation into the area offshore of the devastated coastline, with five marine expeditions taking place. This was the first time that a focussed, large-scale, international programme of marine surveying had taken place so soon after a major tsunami. It was also the first time that such a comprehensive data set became the basis for tsunami simulations. The use of marine mapping subsequently led to a larger involvement of marine geologists in the study of tsunamis, expanding the knowledge base of those studying the threat from SMF hazards. This paper provides an overview of the PNG tsunami and its impact on tsunami science. It presents revised interpretations of the slump architecture based on new seabed relief images and, using these, the most comprehensive tsunami simulation of the PNG event to date. Simulation results explain the measured runups to a high degree. The PNG tsunami has made a major impact on tsunami science. It is one of the most studied SMF tsunamis, yet it remains the only one known of its type: a slump.

Photochemistry in biomass burning plumes and implications for tropospheric ozone over the tropical South Atlantic

Abstract: Photochemistry occuring in biomass burning plumes over the tropical south Atlantic is analyzed using data collected during the Transport and Atmospheric Chemistry Near the Equator-Atlantic aircraft expedition conducted during the tropical dry season in September 1992 and a photochemical point model. Enhancement ratios (ΔY/ΔX, where Δ indicates the enhancement of a compound in the plume above the local background mixing ratio, Y are individual hydrocarbons, CO, O3, N2O, HNO3, peroxyacetyl nitrate (PAN), CH2O, acetone, H2O2, CH3OOH, HCOOH, CH3COOH or aerosols and X is CO or CO2) are reported as a function of plume age inferred from the progression of Δnon-methane hydrocarbons/ΔCO enhancement ratios. Emission, formation, and loss of species in plumes can be diagnosed from progression of enhancement ratios from fresh to old plumes. O3 is produced in plumes over at least a 1 week period with mean ΔO3/ΔCO = 0.7 in old plumes. However, enhancement ratios in plumes can be influenced by changing background mixing ratios and by photochemical loss of CO. We estimate a downward correction of ∼20% in enhancement ratios in old plumes relative to ΔCO to correct for CO loss. In a case study of a large persistent biomass burning plume at 4-km we found elevated concentrations of PAN in the fresh plume. The degradation of PAN helped maintain NOx mixing ratios in the plume where, over the course of a week, PAN was converted to HNO3. Ozone production in the plume was limited by the availability of NOx, and because of the short lifetime of O3 at 4-km, net ozone production in the plume was negligible. Within the region, the majority of O3 production takes place in air above median CO concentration, indicating that most O3 production occurs in plumes. Scaling up from the mean observed ΔO3/ΔCO in old plumes, we estimate a minimum regional O3 production of 17×1010molecules O3 cm−2 s−1. This O3 production rate is sufficient to fully explain the observed enhancement in tropospheric O3 over the tropical South Atlantic during the dry season.