Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect

Abigail E. Noble, Yolanda Echegoyen-Sanz, Edward A. Boyle, Daniel C. Ohnemus, Phoebe J. Lam, Rick Kayser, Matt Reuer, Jingfeng Wu, William Smethie

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

This study presents dissolved Pb concentration and isotopic composition distributions from GEOTRACES GA03, the U.S. North Atlantic Transect. Pb in the ocean is primarily derived from anthropogenic sources and Pb fluxes into the North Atlantic Ocean have been steadily decreasing following the phase-out of alkyl leaded gasoline usage in North America and Europe between 1975 and 1995. A compilation of dissolved Pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermocline maxima, although elevated concentrations greater than 60pmol/kg are still observed in the center of the North Atlantic gyre where ventilation timescales are longer than at the western boundary. The evolution of stable Pb isotopes at these stations shows a shift from dominantly North American-like composition in surface waters in the early 1980s towards a more European-like composition in later years. The most recent shallow signatures at the Bermuda Atlantic Time Series station (BATS) show an even more recent trend returning to higher <sup>206</sup>Pb/<sup>207</sup>Pb ratios after the completed phase-out of leaded gasoline in Europe, presumably because recently deposited Pb is more strongly influenced by industrial and incineration Pb than by residual alkyl leaded gasoline utilization. In surface waters, trends toward a more prominent European influence are also found in the middle of the basin and toward the European coast, coincident with higher concentrations of surface dissolved Pb. Scavenging of anthropogenic Pb is observed within the TAG hydrothermal plume, and it is unclear if there is any significant contribution to deep water by basaltic Pb leached by hydrothermal fluids. In the upper water column, many stations along the transect show Pb concentration maxima at ~100m depth, coincident with a low <sup>206</sup>Pb/<sup>207</sup>Pb isotopic signature that is typical of European emission sources. Although Pb ores from the United States historically tend to carry <sup>206</sup>Pb/<sup>207</sup>Pb signatures >1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in <sup>206</sup>Pb/<sup>207</sup>Pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope <sup>206</sup>Pb/<sup>207</sup>Pb ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low <sup>206</sup>Pb/<sup>207</sup>Pb signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor.

Original languageEnglish (US)
Pages (from-to)208-225
Number of pages18
JournalDeep-Sea Research Part II: Topical Studies in Oceanography
Volume116
DOIs
StatePublished - Jun 1 2015

Fingerprint

transect
isotope
gyre
ventilation
deep water
hydrothermal plume
surface water
anthropogenic source
incineration
hydrothermal fluid
thermocline
bottom water
water mass
mobilization
surface layer
stable isotope
isotopic composition
seafloor
water column
time series

Keywords

  • Anthropogenic
  • GEOTRACES
  • Lead
  • Lead isotopes
  • North Atlantic Ocean
  • Pb
  • Trace elements

ASJC Scopus subject areas

  • Oceanography

Cite this

Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect. / Noble, Abigail E.; Echegoyen-Sanz, Yolanda; Boyle, Edward A.; Ohnemus, Daniel C.; Lam, Phoebe J.; Kayser, Rick; Reuer, Matt; Wu, Jingfeng; Smethie, William.

In: Deep-Sea Research Part II: Topical Studies in Oceanography, Vol. 116, 01.06.2015, p. 208-225.

Research output: Contribution to journalArticle

Noble, Abigail E. ; Echegoyen-Sanz, Yolanda ; Boyle, Edward A. ; Ohnemus, Daniel C. ; Lam, Phoebe J. ; Kayser, Rick ; Reuer, Matt ; Wu, Jingfeng ; Smethie, William. / Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect. In: Deep-Sea Research Part II: Topical Studies in Oceanography. 2015 ; Vol. 116. pp. 208-225.
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N2 - This study presents dissolved Pb concentration and isotopic composition distributions from GEOTRACES GA03, the U.S. North Atlantic Transect. Pb in the ocean is primarily derived from anthropogenic sources and Pb fluxes into the North Atlantic Ocean have been steadily decreasing following the phase-out of alkyl leaded gasoline usage in North America and Europe between 1975 and 1995. A compilation of dissolved Pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermocline maxima, although elevated concentrations greater than 60pmol/kg are still observed in the center of the North Atlantic gyre where ventilation timescales are longer than at the western boundary. The evolution of stable Pb isotopes at these stations shows a shift from dominantly North American-like composition in surface waters in the early 1980s towards a more European-like composition in later years. The most recent shallow signatures at the Bermuda Atlantic Time Series station (BATS) show an even more recent trend returning to higher 206Pb/207Pb ratios after the completed phase-out of leaded gasoline in Europe, presumably because recently deposited Pb is more strongly influenced by industrial and incineration Pb than by residual alkyl leaded gasoline utilization. In surface waters, trends toward a more prominent European influence are also found in the middle of the basin and toward the European coast, coincident with higher concentrations of surface dissolved Pb. Scavenging of anthropogenic Pb is observed within the TAG hydrothermal plume, and it is unclear if there is any significant contribution to deep water by basaltic Pb leached by hydrothermal fluids. In the upper water column, many stations along the transect show Pb concentration maxima at ~100m depth, coincident with a low 206Pb/207Pb isotopic signature that is typical of European emission sources. Although Pb ores from the United States historically tend to carry 206Pb/207Pb signatures >1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in 206Pb/207Pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope 206Pb/207Pb ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low 206Pb/207Pb signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor.

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