Chen, Tian-Yu, Rempfer, Johannes, Frank, Martin , Stumpf, Roland and Molina-Kescher, Mario (2013) Upper ocean vertical supply: A neglected primary factor controlling the distribution of neodymium concentrations of open ocean surface waters?. Journal of Geophysical Research: Oceans, 118 . pp. 3887-3894. DOI 10.1002/jgrc.20288.

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Abstract

Neodymium (Nd) isotopes are an important geochemical tool to trace the present and
past water mass mixing as well as continental inputs. The distribution of Nd concentrations
in open ocean surface waters (0–100 m) is generally assumed to be controlled by lateral
mixing of Nd from coastal surface currents and by removal through reversible particle
scavenging. However, using 228Ra activity as an indicator of coastal water mass influence,
surface water Nd concentration data available on key oceanic transects as a whole do not
support the above scenario. From a global compilation of available data, we find that more
stratified regions are generally associated with low surface Nd concentrations. This implies
that upper ocean vertical supply may be an as yet neglected primary factor in determining
the basin-scale variations of surface water Nd concentrations. Similar to the mechanism of
nutrients supply, it is likely that stratification inhibits vertical supply of Nd from the
subsurface thermocline waters and thus the magnitude of Nd flux to the surface layer.
Consistently, the estimated required input flux of Nd to the surface layer to maintain the
observed concentrations could be nearly two orders of magnitudes larger than riverine/dust
flux, and also larger than the model-based estimation on shelf-derived coastal flux. In
addition, preliminary results from modeling experiments reveal that the input from shallow
boundary sources, riverine input, and release from dust are actually not the primary factors
controlling Nd concentrations most notably in the Pacific and Southern Ocean surface
waters.

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