PubMed · 15649350
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Nigel Williams. 2005-01-11. Fishing for context.. https://doi.org/10.1016/j.cub.2004.12.005
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Estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late Quaternary climate. We radiocarbon-dated marine shells and terrestrial plant remains deposited in two bays on Norway's west coast between 11,000 and 14,000 years ago, a time of large and abrupt climatic changes that included the Younger Dryas (YD) cold episode. The radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early YD, stabilized for 900 years, and dropped by 300 years within a century across the YD-Holocene transition.
Colonial diazotrophic cyanobacteria of the genus Trichodesmium are thought to play a significant role in the input of new nitrogen to upper layers of the tropical and subtropical oceanic ecosystems that cover nearly half of Earth's surface. Here we describe results of a transatlantic survey in which a noninvasive underwater digital microscope (the video plankton recorder), was towed across the North Atlantic at 6 meters per second while undulating between the surface and 130 meters. Colony abundance had a basin-scale trend, a clear association with anticyclonic eddies, and was not affected by hurricane-forced mixing. Subsurface abundance was higher than previously reported, which has important implications for the global ocean nitrogen cycle.
Results are presented for a study of manmade and natural radionuclides in north east Atlantic continental shelf and slope sediments to the west of Scotland. The data are interpreted in the context of sediment mixing and accumulation processes and are used to establish the westward extent of contamination of the sediment system. Offshore shelf and slope sediments were found to have post-glacial sedimentation rates of the order of 1 cm ky(-1) but nearshore sediments had much higher accumulation rates of the order of 0.1 cm y(-1). Surface mixed layer depths of up to 6 cm were observed and non-local mixing affected most of the slope sediments, resulting in advective transport of surface sediment to depths of up to 10 cm. Biodiffusion coefficients for offshore shelf and slope sediments were dominantly in the range 10(-8) to 10(-9) cm2 s(-1). The study confirmed that seawater contaminated with Sellafield waste radionuclides is dominantly entrained to the east of 7 degrees W and, consistent with this, higher levels of Sellafield derived radionuclides were confined to nearshore sediments, with lower levels to the west of 7 degrees W. 238Pu/(239,240)Pu data indicated that Sellafield contributed 75-91% of the total plutonium in coastal sediment but only about 4-8% of the total in slope sediments. By analogy, it can be concluded that a similar situation will apply to other contaminants in seawater entering the north east Atlantic via the North Channel.