Causes and Consequences of Diachronous V-Shaped Ridges in the North Atlantic Ocean

In the North Atlantic Ocean, the geometry of diachronous V-shaped features that straddle the Reykjanes Ridge is often attributed to thermal pulses which advect away from the center of the Iceland plume. Recently, two alternative hypotheses have been proposed: rift propagation and buoyant mantle upwelling. Here, we evaluate these different proposals using basin-wide geophysical and geochemical observations. The centerpiece of our analysis is a pair of seismic reflection profiles oriented parallel to flowlines that span the North Atlantic Ocean. V-shaped ridges and troughs are mapped on both Neogene and Paleogene oceanic crust, enabling a detailed chronology of activity to be established for the last 50 million years. Estimates of the cumulative horizontal displacement across normal faults help to discriminate between brittle and magmatic modes of plate separation, suggesting that crustal architecture is sensitive to the changing planform of the plume. Water-loaded residual depth measurements are used to estimate crustal thickness and to infer mantle potential temperature which varies by 25◦C on timescales of 3–8 Ma. This variation is consistent with the range of temperatures inferred from geochemical modeling of dredged basaltic rocks along the ridge axis itself, from changes in Neogene deep-water circulation, and from the regional record of episodic Cenozoic magmatism. We conclude that radial propagation of transient thermal anomalies within an asthenospheric channel that is 150 50 km thick best accounts for the available geophysical and geochemical observations

Separating Forced from Chaotic Climate Variability over the Past Millennium

Reconstructions of past climate show notable temperature variability over the past millennium, with relatively warm conditions during the Medieval Climate Anomaly (MCA) and a relatively cold Little Ice Age (LIA). Multimodel simulations of the past millennium are used together with a wide range of reconstructions of Northern Hemispheric mean annual temperature to separate climate variability from 850 to 1950 CE into components attributable to external forcing and internal climate variability. External forcing is found to contribute significantly to long-term temperature variations irrespective of the proxy reconstruction, particularly from 1400 onward. Over the MCA alone, however, the effect of forcing is only detectable in about half of the reconstructions considered, and the response to forcing in the models cannot explain the warm conditions around 1000 CE seen in some reconstructions. The residual from the detection analysis is used to estimate internal variability independent from climate modeling, and it is found that the recent observed 50- and 100-yr hemispheric temperature trends are substantially larger than any of the internally generated trends even using the large residuals over the MCA. Variations in solar output and explosive volcanism are found to be the main drivers of climate change from 1400 to 1900, but for the first time a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800 is also detected. The proxy reconstructions tend to show a smaller forced response than is simulated by the models. This discrepancy is shown, at least partly, to be likely associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations

Sonography of a Carotid Body Tumor: A Case Report

A carotid body tumor is typically a benign mass and can have a low malignant potential. It can grow in between, attach to, or surround the internal carotid artery and external carotid artery in the neck. If this mass grows too big, it can compress the two arteries, causing problems in getting blood flow to the brain. The purpose for this sonography examination was to evaluate a patient with the following symptoms: dizziness, facial nerve injury, and sensorineural hearing loss. The carotid body tumor is a highly vascular tumor. This sonography examination provides a good opportunity to teach the importance of the use of color Doppler and proper documentation of this pathology that is often incorrectly documented with improper settings. This case reviews a 69-year-old Caucasian male with a carotid body tumor. The sonographic features, prevalence, common symptoms, prognosis, and treatments of the carotid body tumor are reviewed. </jats:p

Mountain Chickadee

This chapter studies the mountain chickadees of the Sierra Nevada. Using sophisticated acoustic analyses, observant biologists have learned that the songs of mountain chickadees at higher elevations are different—in the timing and frequency of their notes—from the songs of their kin dwelling lower down. Such distinctions may signal to prospective mates their fitness for the rigors of high country living. In addition, the high elevation mountain chickadee's hippocampus—a region of the brain associated with spatial memory—is larger and more neuron-dense than that of its lowland relative, giving them a superior ability to find cached stores of seed—a life-saving skill at high elevations where conditions are harshest. The chickadee is just like the improbable life that moves in us when things are at their worst. If we listen, we can attend to an interior world that holds and concentrates all the beauties of the natural world.</p

Chloroplast DNA Microsatellites Reveal Contrasting Phylogeographic Structure in Mahogany (Swietenia macrophylla King, Meliaceae) from Amazonia and Central America

Big-leaf mahogany (Swietenia macrophylla) is one of the most valuable and overharvested timber trees of tropical America. A description of the organization of genetic variation across its broad range would be useful for management of genetic diversity and for understanding its demographic history. Here we report on a phylogeographic analysis of mahogany based on six polymorphic cpDNA simple sequence repeat loci (cpSSRs) genotyped in 16 populations distributed across the Brazilian Amazon and Mesoamerica (N = 245 individuals). Of the 31 cpDNA haplotypes identified, 15 occurred in Amazonia and 16 in Mesoamerica with no single haplotype shared between the two regions. The populations from Central America showed moderate differentiation (FST = 0.36) while within population genetic diversity was generally high (mean Nei's HE = 0.639). In contrast, the Amazonian populations were strongly differentiated (FST = 0.95) and contained low haplotype diversity (mean HE = 0.176), with the exception of the highly diverse Marajoara population from the Eastern Amazon (HE = 0.925). SAMOVA identified a single Mesoamerican phylogroup and four Amazonian phylogroups, indicating stronger phylogeographic structure within Amazonia. The results demonstrate high levels of cpDNA variation and differentiation of regional S. macrophylla populations, and provide the first evidence of a major phylogeographic break between Mesoamerican and South American mahogany populations

Obsidian

This chapter examines how the obsidian craters just east of the Sierra Nevada mountain range erupted in the last few millennia, some in recent centuries. Obsidian, because it lacks the constraints imposed by an internal molecular order, can in fact be flaked into tools with edges that are many times sharper than a razor blade. In the Sierra Nevada, the authors found flakes of obsidian, shards left by indigenous hunters who worked the black volcanic glass into arrowpoints, their edges sharpened to translucence, to hunt the animals that would sustain their loved ones. Throughout their millennia of continuous presence in the Mono Basin, they would have witnessed volcanic eruptions give birth to the region's pale hills. The chapter then looks at the deep resemblance between the making of a mountain and the making of a mind.</p

Western Tanager

This chapter discusses the western tanager, which is a seasonal migrant to the Sierra. Upon arrival, the birds claim their territory, announcing their presence with burry, robin-like songs called out from branches in the Sierra's conifer forests. The tanagers come to the Sierra to take sustenance from the bursts of abundant insect life and berries that arrive in late summer—and from this sustenance nurture their young. However, danger lurks everywhere for the nestlings—from the predations of Steller's jays and nutcrackers; from owls and snakes and even bears; and too from female cowbirds. Learning about the western tanager, we see the resemblance between us. We have, like the tanager, our own way of singing, of nesting, of caring for our young.</p

Paintbrush

This chapter assesses the genus of flowering plants known as Castilleja, the paintbrushes. Species of Castilleja occur throughout the Sierra, from the oak savannas of the lowland foothills to the fragrant conifer forests of the mid-elevations to the sky gardens of the alpine fellfields, blossoming in flames of vermillion and violet and cream and silvery mauve. It is not the flowers' petals that give paintbrushes their colorful fireworks but rather their bracts—specialized leaves that grow underneath the petals. Meanwhile, the job of a paintbrush's roots is not so much to independently mine the soil for what they need, but to find their way through subterranean blackness toward the roots of other plants. In this sense, the root of the paintbrush might be described more accurately as a haustorium, derived from the Latin haustor—one who drinks, one who takes in nourishment.</p