Short-term variability of dissolved rare earth elements and neodymium isotopes in the entire water column of the Panama Basin

Dr. Patricia Grasse1, Ed Hathorne2, Katharina Pahnke3, Philipp Böning4 and Martin Frank2, (1)GEOMAR Helmholtz Centre for Ocean Research Kiel, German Centre for Integrative Biodiversity Research (iDiv), Kiel, Germany, (2)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (3)University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), Germany, (4)University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), Oldenburg, Germany
Abstract:
The distribution of dissolved rare earth elements (REEs) and neodymium isotopes (εNd) in the open ocean traces water mass mixing and provides information on lithogenic inputs to the source regions of the water masses. However, the processes influencing the REE budget at the ocean margins, in particular source and sink mechanisms, are not yet well quantified. In this study the first dissolved REE concentrations and Nd isotope compositions of seawater from the Panama Basin.

The measured REE concentrations peak at the surface indicating high lithogenic input, which is supported by shale-normalized REE patterns in surface waters and highly radiogenic εNd signatures ranging between +1.4 and +4.3, the latter value constituting the most radiogenic value measured for seawater to date. In contrast, intermediate and deep water REE concentrations are low compared to other Pacific Basins and suggest enhanced removal via scavenging. The εNd signatures of intermediate and deep waters are less radiogenic than surface waters ranging between −1.4 and +1.3 but significantly more radiogenic than source water masses in the Eastern Equatorial Pacific. The εNd signatures consequently do not reflect mixing of intermediate and deep water masses entering the Panama Basin but can only be explained by lithogenic inputs originating from source rocks with highly radiogenic Nd isotope signatures such as the Central American Volcanic Arc (εNd +3 to +10). Our data demonstrate significant surface input via continental particles, which are partially dissolved in the water column and thereby release REEs and particularly radiogenic Nd isotope signatures to the subsurface ocean. Data obtained from a re-occupied station in the southern Panama Basin for the first time shows that these processes can partially reset water mass Nd isotope and REE signatures of the entire water column proximal to continental sources on time scales of a few years.

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