Biogeography in Pa-231/Th-230 ratios and a balanced Pa-231 budget for the Pacific Ocean

Christopher T. Hayes*, Robert F. Anderson, Martin Q. Fleisher, Sascha Serno, Gisela Winckler, Rainer Gersonde

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The ratio of unsupported protactinium-231 to thorium-230 in marine sediments, (Pa/Th)(xs), is potentially sensitive to several processes of oceanographic and climatological interest: deep ocean circulation, marine biological productivity (as it relates to total particle flux) and particle composition (specifically, biogenic opal and authigenic Mn). In order to attribute variations in (Pa/Th)(xs) observed in sediment records to changes in specific processes through time, a better understanding of the chemical cycling of these elements in the modern ocean is necessary. To this end, a survey was undertaken of (Pa/Th)(xs) in surface sediments from the subarctic Pacific (SO202-INOPEX expedition) in combination with a Pacific-wide compilation of published data. Throughout the Pacific, (Pa/Th)(xs) is robustly correlated with the opal content of sediments. In the North and equatorial Pacific, simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of Pa in the eastern equatorial Pacific and subarctic Pacific. Deep ocean water mass ageing (>3.5 km) associated with the Pacific overturning appears to play a secondary role in determining the basin scale distribution of (Pa/Th)(xs). A basin-wide extrapolation of Pa removal is performed which suggests that the Pacific Pa budget is nearly in balance. We hypothesize that through time (Pa/Th)(xs) distributions in the Pacific could define the evolving boundaries of contrasting biogeographic provinces in the North Pacific, while the influence of hydrothermal scavenging of Pa potentially confounds this approach in the South Pacific. (C) 2014 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)307-318
Number of pages12
JournalEarth and Planetary Science Letters
Volume391
DOIs
Publication statusPublished - 1 Apr 2014

Keywords

  • thorium
  • protactinium
  • biogeographic provinces
  • boundary scavenging
  • INOPEX
  • MERIDIONAL OVERTURNING CIRCULATION
  • LAST GLACIAL MAXIMUM
  • SOUTHERN-OCEAN
  • NORTH PACIFIC
  • DEEP-WATER
  • PARTICLE COMPOSITION
  • ATLANTIC-OCEAN
  • THORIUM ISOTOPES
  • ORGANIC-CARBON
  • THERMOHALINE CIRCULATION

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