Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 116 (2015): 29-41, doi:10.1016/j.dsr2.2014.07.007.
Description:
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.
Description:
Funding for ship time, sampling operations, and hydrographic 552 data was provided by the U. S.
National Science Foundation to the US GEOTRACES North Atlantic Transect Management team
of W. Jenkins (OCE-0926423), E. Boyle (OCE-0926204), and G. Cutter (OCE-0926092).
Radionuclide studies were supported by NSF (OCE-0927064 to L-DEO, OCE-0926860 to WHOI,
OCE-0927757 to URI, and OCE-0927754 to UMN). LFR was also supported by Marie Curie
Reintegration Grant and the European Research Council.
Keywords:
GEOTRACES
;
North Atlantic Ocean
;
Thorium
;
Protactinium
;
Scavenging
;
Ventilation
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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