A re-examination of the mechanism of whiting events: A new role for diatoms in Fayetteville Green Lake (New York, USA)

Whiting events-the episodic precipitation of fine-grained suspended calcium carbonates in the water column-have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been proposed to explain the onset of these precipitation events, no consensus has been reached thus far. Fayetteville Green Lake (New York, USA) is a meromictic lake that experiences annual whitings. Materials suspended in the water column collected through the whiting season were characterized using scanning electron microscopy and scanning transmission X-ray microscopy. Whitings in Fayetteville Green Lake are initiated in the spring within the top few meters of the water column, by precipitation of fine amorphous calcium carbonate (ACC) phases nucleating on microbial cells, as well as on abundant extracellular polymeric substances (EPS) frequently associated with centric diatoms. Whiting particles found in the summer consist of 5-7 μm calcite grains forming aggregates with diatoms and EPS. Simple calculations demonstrate that calcite particles continuously grow over several days, then sink quickly through the water column. In the late summer, partial calcium carbonate dissolution is observed deeper in the water column. Settling whiting particles, however, reach the bottom of the lake, where they form a major constituent of the sediment, along with diatom frustules. The role of diatoms and associated EPS acting as nucleation surfaces for calcium carbonates is described for the first time here as a potential mechanism participating in whitings at Fayetteville Green Lake. This mechanism may have been largely overlooked in other whiting events in modern and ancient environments.

Sulfur cycling at natural hydrocarbon and sulfur seeps in Santa Paula Creek, CA

Biogeochemical cycling of sulfur is relatively understudied in terrestrial environments compared to marine environments. However, the comparative ease of access, observation, and sampling of terrestrial settings can expand our understanding of organisms and processes important in the modern sulfur cycle. Furthermore, these sites may allow for the discovery of useful process analogs for ancient sulfur-metabolizing microbial communities at times in Earth's past when atmospheric O₂ concentrations were lower and sulfide was more prevalent in Earth surface environments. We identified a new site at Santa Paula Creek (SPC) in Ventura County, CA-a remarkable freshwater, gravel-bedded mountain stream charged with a range of oxidized and reduced sulfur species and heavy hydrocarbons from the emergence of subsurface fluids within the underlying sulfur- and organic-rich Miocene-age Monterey Formation. SPC hosts a suite of morphologically distinct microbial biofacies that form in association with the naturally occurring hydrocarbon seeps and sulfur springs. We characterized the geology, stream geochemistry, and microbial facies and diversity of the Santa Paula Creek ecosystem. Using geochemical analyses and 16S rRNA gene sequencing, we found that SPC supports a dynamic sulfur cycle that is largely driven by sulfide-oxidizing microbial taxa, with contributions from smaller populations of sulfate-reducing and sulfur-disproportionating taxa. This preliminary characterization of SPC revealed an intriguing site in which to study geological and geochemical controls on microbial community composition and to expand our understanding of sulfur cycling in terrestrial environments.

Objectivism in information utilization: theory and measurement

A self-report scale was constructed and validated that measures individual differences in objectivism--the tendency to base one's judgments and beliefs on empirical information and rational considerations. Validity data showed that, compared to people who score low on the Objectivism Scale, highly objective individuals enjoy thinking more, rely more on observable facts when making decisions, and place less emphasis on subjective and intuitive styles of decision making. Among graduate students in psychology, objectivism correlated positively with ratings of research-oriented careers, but negatively with ratings of mental health careers; also, highly objective students were more critical of nonobjective psychological assessment techniques and placed greater importance on research. Objectivism also predicted preferences for newspaper articles, college course selections, and the criteria respondents use when making decisions.

Tomograpy in radionuclide brain imaging and cisternography

A new radionuclide tomographic scanner produces 12 tomographic brain images instead of a single conventional brain scan. This scanner has important advantages over conventional radionuclide scanning. The size, shape, and extent of a lesion and its relationship to surrounding structures are better defined. Tomography often permits a firm diagnostic impression in studies that would be equivocal with the use of routine scanning. Tomography may also be used in conjunction with radionuclide cisternography to provide a clear visualization of the CSF pathways and ventricles and to distinguish overlying structures.

Radionuclide angiography: a sensitive diagnostic test for anterior circulation ischemia

Radionuclide angiography, using high resolution equipment, is a sensitive noninvasive, safe, and rapid diagnostic test for ischemia of the anterior circulation of the brain. The test permits recognition of focally increased or decreased circulation immediately following the onset of a neurologic deficit. The sensitivity of the test is improved by using multiple projections of the head. The distribution of the anterior cerebral artery is best seen in the anterior projection; the lateral projection is used to resolve the superior and inferior divisions of the middle cerebral artery or to identify multiple regions of ischemia. Both projections should be used routinely.

Carotid-cavernous fistula. Demonstration of asymptomatic vascular "steal"

Abnormal distribution of cerebral vascular flow was studied in a patient who had a traumatic carotid-cavernous sinus fistula. Serial studies were performed using a method for determining relative cerebral vascular flow:99mtechnetium-diethylenetriamine pentaacetic acid (99mTc-DTPA) was injected intravenously and flow data were processed by a digital computer. Serial studies documented the occurrence of a vascular "steal" during temporary carotid occlusion; postoperative studies showed disappearance of the steal and obliteration of thiling arterial structures and capillary filling in the brain, and in demonstrating alteration in the cerebral circulation.

Dynamic radionuclide scanning in the diagnosis of thrombosis of the superior sagittal sinus

Two cases of superior sagittal sinus thrombosis were diagnosed using a new technique of dynamic radionuclide brain-imaging. With the patient's head in the posterior oblique position, and 80-lens optical camera records the appearance of radionuclides in the superior sagittal sinus. This technique is quick and noninvasive, and serial studies are easily performed. Dural sinus thrombosis is difficult to diagnose on clinical findings alone. Dynamic canning should be used to screen high risk patients, such as those having pseudotumor syndrome or clotting disorders and elderly patients having pulmonary emboli or unexplained deterioration of mental status.

Neurologic diagnosis using the 80-lens optical camera

This article describes the clinical application of the 80-lens optical camera in the diagnosis of cerebral infarction, subdural hematoma, intracranial tumor, and hydrocephalus. The 80-lens camera is a simple noncomputerized addition to the Anger scintillation camera that permits an estimation of the cerebral blood flow. The study is noninvasive and quick, minimizing the effect of movement artifact and showing areas of either increased or decreased blood flow. Abnormal tumor vessels appear, and subdural hematomas show brain displacement away from the skull edge. Interpretation of blood flow pattern is not affected by scalp or skull trauma, eliminating a source of error incurred with static scans.

Radionuclide cisternography after head injury

Thirty-seven patients with severe head injury underwent radionuclide cisternography to detect early and late effects of trauma on cerebrospinal fluid (CSF) circulation. Thirty-one patients had subdural hematomas or hygromas and six had cerebral contusions without extracerebral masses. Cisternographic results were abnormal in 23 patients with subdural masses and normal in five who had only cerebral contusions. Of eight patients undergoing serial studies, one had persistent partial obstruction, five had partial resolution of abnormalities, and the two with progressive obstruction had their conditions improved by shunting. Angiography suggested transtentorial herniation in 11 patients with cisternal block, six of whom had clinical signs of herniation on the same side.