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.

Causes and consequences of variability in the timing of spring phytoplankton blooms

Abstract: Established conceptual models of the initiation and progression of spring phytoplankton blooms are reconsidered in light of recent observations We use biological simulation modelling as a tool for the analysis of spring plankton blooms in shallow, coastal waters in temperate latitudes of the North Atlantic The model shows that interannual variability in the timing of bloom initiation arises from year-to-year differences in incident irradiation, as determined by weather (cloudiness) This variability in timing results in some years when the spring bloom occurs in cold water temperatures near 0°C Model results suggest that due to low temperature inhibition of heterotrophic consumption, more fresh organic material is delivered to the benthos in these cold-water blooms than when the bloom occurs in waters only 3°C warmer Thus we suggest that variable bloom timing can be important to the trophodynamic fate of bloom products We suggest that variability in timing of spring phytoplankton blooms in offshore and open ocean waters is also related to weather, through controls on the light field and wind mixing Our analyses of wind-driven vertical mixing demonstrate such blooms can begin following the winter period of deep convection, and prior to the vernal development of stratification, provided that wind speed is below a certain, predictable threshold, which we estimate In such cases, there may be several spring bloom pulses, each interrupted by self-shading light limitation or vertical mixing events Eventually the seasonal thermocline develops and nutrient exhaustion curtails bloom production This means that the spring phytoplankton bloom in offshore and open ocean areas may be significantly more productive, result in more export production, and be more important to the carbon cycle, than has been previously assumed Furthermore, these features of temperate marine planktonic ecosystems are not only sensitive to annual variations in weather, but also any trends that might result from greenhouse warming or other factors that affect the climate system

A comparison of four methods for determining planktonic community production1

Abstract: Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the 14C method, the O2 and CO, light-dark bottle methods, and the I80 method. 0, production in the experimental enclosures (volume - 1.3 x lo4 liters) was also measured directly. Photosynthetic and respiratory quotients were close to 1 .O. Gross production values determined by 0, light-dark experiments, CO2 light-dark experiments, and I80 were similar. 14C production ranged from 60 to 100% of gross production measured in CO, light-dark experiments, indicating that 14C uptake is not precisely fixed with respect to other measures of community metabolism. There was no evidence that 14C or any other method underestimated the rate of primary production in vitro by more than 40%. Productivities in vitro ranged from 35 to 100% of those in the mesocosm at similar light intensities. In samples from one of the ecosystems, the rate of respiration in the light (calculated from I80 data) was an order of magnitude greater than the rate in the dark. This difference may be ascribed to either photorespiration or light enhancement of mitochondrial respiration.

Causation issues in structural equation modeling research

Abstract: As the use of structural equation modeling (SEM) has increased, confusion has grown concerning the correct use of and the conclusions that can be legitimately drawn from these methodologies. It appears that much of the controversy surrounding SEM is related to the degree of certainty with which causal statements can be drawn from these procedures. SEM is discussed in relation to the conditions necessary for providing causal evidence. Both the weaknesses and the strengths of SEM are examined. Although structural modeling cannot ensure that necessary causal conditions have been met, it is argued that SEM methods may offer the potential for tentative causal inferences to be drawn when used with carefully specified and controlled designs. Keeping in mind that no statistical methodology can in and of itself determine causality, specific guidelines are suggested to help researchers approach a potential for providing causal evidence with SEM procedures.

Analysis of organic carbon in marine sediments1

Abstract: A method is presented for measuring organic carbon in both carbonate-rich and carbonate-poor marine sediments. Samples are sonicated with phosphoric acid to remove carbonates. The spent acid supernatant is analyzed for dissolved organic carbon, the solid residue for total carbon; their sum yields the organic carbon content of the sample. The technique is free from carbonate interferences, involves no losses due to acid solubilization, and has excellent precision (better than ±0.02% Corg) and accuracy (better than ±2%).