230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes

Christopher T. Hayes*, Robert F. Anderson, Martin Q. Fleisher, Kuo Fang Huang, Laura F. Robinson, Yanbin Lu, Hai Cheng, R. Lawrence Edwards, S. Bradley Moran

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

61 Citations (Scopus)

Abstract

The long-lived uranium decay products 230Th and 231Pa are widely used as quantitative tracers of adsorption to sinking particles (scavenging) in the ocean by exploiting the principles of radioactive disequilibria. Because of their preservation in the Pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column, the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean. This includes the vertical flux of particulate matter to the seafloor, the lateral flux of insoluble elements to continental margins (boundary scavenging), and the southward flux of water out of the deep North Atlantic. In a section of unprecedented vertical and zonal resolution, the distributions of 230Th and 231Pa across the North Atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux. Enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the Mid-Atlantic Ridge. Boundary scavenging is clearly expressed in the water column along a transect between Mauritania and Cape Verde which is used to quantify a bias in sediment fluxes calculated using 230Th-normalization and to demonstrate enhanced 231Pa removal from the deep North Atlantic by this mechanism. The influence of deep ocean ventilation that leads to the southward export of 231Pa is apparent. The 231Pa/230Th ratio, however, predominantly reflects spatial variability in scavenging intensity, complicating its applicability as a proxy for the Atlantic meridional overturning circulation.

Original languageEnglish
Pages (from-to)29-41
Number of pages13
JournalDeep Sea Research Part II: Topical Studies in Oceanography
Volume116
Early online date25 Jun 2014
DOIs
Publication statusPublished - 1 Jun 2015

Keywords

  • GEOTRACES
  • North Atlantic Ocean
  • Protactinium
  • Scavenging
  • Thorium
  • Ventilation

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