Nicklas G. Pisias

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The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean-atmosphere system. But it remains difficult to assess the likelihood of future changes in the thermohaline circulation, mainly owing to(More)
The emergence of low-frequency, high-amplitude, quasi-periodic ($100-kyr) glacial variability during the middle Pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system. This middle Pleistocene transition (MPT) began 1250 ka and was complete by 700 ka. Its onset was accompanied by(More)
Late Pleistocene changes in oceanic primary productivity along the equator in the Indian and Pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep-sea cores. We show that variations in equatorial productivity are primarily caused by glacial-interglacial variability and by precession-controlled changes in the(More)
The addition of a 10% talc internal standard to North Pacific sediments allows the relative abundances of clay minerals to be determined both accurately and precisely by X-ray powder diffractometry. Linear programming can be used to generate factors for converting talc-normalized peak areas to weight percentages; hence, absolute clay-mineral abundances can(More)
Introduction Deep-sea sedimentation is important to the geochemical cycles of many chemical species. For example, the widespread accumulation of siliceous and calcareous biogenic marine sediments plays an important part in the biogeochemical cycling of Si, Ca, and C (e.g., Burdige, 2006). Hydrothermal solutions and sediments from active spreading centers(More)
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