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The Passage of the Bomb Radiocarbon Pulse into the Pacific Ocean

Published online by Cambridge University Press:  18 July 2016

William J Jenkins ,
Kathryn L Elder ,
Ann P McNichol  and
Karl von Reden
William J Jenkins*
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometer Facility, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
Kathryn L Elder
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometer Facility, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
Ann P McNichol
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometer Facility, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
Karl von Reden
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometer Facility, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
*
Corresponding author. Email: [email protected]
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Abstract

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We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150°W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced 14C into the oceanic thermocline. The changes over the 14 yr between occupations are demonstrably large relative to any possible drift in our analytical standardization. The computed difference field based on the gridded data in the upper 1600 m of the section exhibits a significant decrease over time (approaching 40 to 50‰ in Δ14C) in the upper 200–300 m, consistent with the decadal post-bomb decline in atmospheric 14C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50–60‰ in Δ14C, a clear signature of the downstream evolution of the 14C transient in this water mass. We use this observation to estimate the transit time of AAIW from its “source region” in the southeast South Pacific and to compute the effective reservoir age of this water mass. The 2 sections show small but significant changes in the abyssal 14C distributions. Between 1991 and 2005, Δ14C has increased by 9‰ below 2000 m north of 55°S. This change is accompanied overall by a modest increase in salinity and dissolved oxygen, as well as a slight decrease in dissolved silica. Such changes are indicative of greater ventilation. Calculation of “phosphate star” also indicates that this may be due to a shift from the Southern Ocean toward North Atlantic Deep Water as the ventilation source of the abyssal South Pacific.

Type
Marine
Information
Radiocarbon , Volume 52 , Issue 3: 20th Int. Radiocarbon Conference Proceedings , 2010 , pp. 1182 - 1190
Copyright
Copyright © 2010 by the Arizona Board of Regents on behalf of the University of Arizona 

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