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Globally averaged riverine silicon (Si) concentrations and isotope composition (δ30Si) may be affected by the expansion and retreat of large ice sheets during glacial-interglacial cycles. Here we provide evidence of this based on the δ30Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ30Si measured in running waters (-0.25 ± 0.12‰), significantly lower than nonglacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06-0.17‰ of the observed ocean δ30Si rise (0.5-1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ30Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump.

Both the incidence and severity of herpes zoster (HZ) or shingles increase markedly with increasing age in association with a decline in varicella zoster virus (VZV)-specific immunity. Considerable evidence shows that behavioral stressors, prevalent in older adults, correlate with impairments of cellular immunity. Moreover, the presence of depressive symptoms in older adults is associated with declines in VZV-responder cell frequency (VZV-RCF), an immunological marker of shingles risk. In this review, we discuss recent findings that administration of a relaxation response-based intervention, tai chi chih (TCC), results in improvements in health functioning and immunity to VZV in older adults as compared with a control group. TCC is a slow moving meditation consisting of 20 separate standardized movements which can be readily used in elderly and medically compromised individuals. TCC offers standardized training and practice schedules, lending an important advantage over prior relaxation response-based therapies. Focus on older adults at increased risk for HZ and assay of VZV-specific immunity have implications for understanding the impact of behavioral factors and a behavioral intervention on a clinically relevant end-point and on the response of the immune system to infectious pathogens.

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming (1) and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65-99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized (2). Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre (3), or those indicated for the Mediterranean sapropels (4). With increased C[O.sub.2] levels and warming currently driving increased stratification in the global ocean (5), this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean (6-8), rather than recent suggestions of a 15°C mean annual temperature at this time (9)., The Arctic is a critical yet under-sampled region for palaeoclimate studies. The recent Integrated Ocean Drilling Program Arctic Coring Expedition has provided Arctic records back to the late Palaeogene (56 [...]

The asynchronous relationship between millennial-scale temperature changes over Greenland and Antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the Atlantic Ocean. Here we present new records from the South Atlantic that show rapid changes during the last deglaciation that were instantaneous (within dating uncertainty) and of opposite sign to those observed in the North Atlantic. Our results demonstrate a direct link between the abrupt changes associated with variations in the Atlantic meridional overturning circulation and the more gradual adjustments characteristic of the Southern Ocean. These results emphasize the importance of the Southern Ocean for the development and transmission of millennial-scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide., The last glacial and deglacial periods were characterized by millennial-scale shifts in global climate. Records from Greenland ice cores (1) and North Atlantic sediments (2,3) suggest that high latitudes in [...]

Author(s): Richard Davies (corresponding author) [1]; Joseph Cartwright [2]; Jennifer Pike [2]; Charles Line [1] Dating the onset of deep-water flow between the Arctic and North Atlantic oceans is critical [...]

Preservation of laminations in hemipelagic and pelagic sediments is routinely attributed to reduced oxygen conditions that inhibited benthic activity. As such, the degree of preservation of laminae is used commonly as a paleo-oxygenation indicator. Recent evidence from deep-sea pelagic sediments in the eastern equatorial Pacific and North Atlantic, however, demonstrates that preservation of laminae may occur by rapid deposition of ungrazed Thalassiothrix longissima diatom mats that overwhelm the benthos in otherwise oxic bottom waters. Here, we report that similar diatom mat laminae are common in hemipelagic sediments of the Guaymas Basin in the Gulf of California, have aided preservation of the laminated sediment sequence and have also enhanced opal burial. Examples of diatom mats influencing sediment preservation are also described from the northern California Margin and from the Miocene Monterey Formation, southern California. Thus, even in classical settings of laminated sediment occurrence, caution needs to be taken in correlating degree of lamina preservation with paleo-oxygen levels. Such studies must be underpinned by detailed microfabric and micropaleontological analyses.

An electron-microscope investigation of a late Quaternary laminated diatomaceous sapropel in the deepest part of the moat of the Napoli mud volcano on the Mediterranean ridge has been linked with recent progress in the understanding of the ecology of mat-forming diatoms to create a model of the formation of organic-carbon-rich sapropels. It is clear that diatoms played a key role in sapropel formation. Evidence of high diatom production has often been interpreted as upwelling-related, but a study of the diatoms involved indicates an alternative explanation, with diatoms growing under conditions of sustained seasonal stratification.