Comparison of Ba/Ca and as freshwater proxies: A multi-species core-top study on planktonic foraminifera from the vicinity of the Orinoco River mouth

Bahr, André, Schönfeld, Joachim, Hoffmann, Julia, Voigt, Silke, Aurahs, Ralf, Kucera, Michal, Flögel, Sascha, Jentzen, Anna and Gerdes, Axel (2013) Comparison of Ba/Ca and as freshwater proxies: A multi-species core-top study on planktonic foraminifera from the vicinity of the Orinoco River mouth Earth and Planetary Science Letters, 383 . pp. 45-57. DOI 10.1016/j.epsl.2013.09.036.

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Past river run-off is an important measure for the continental hydrological cycle and the assessment of freshwater input into the ocean. However, paleosalinity reconstructions applying different proxies in parallel often show offsets between the respective methods. Here, we compare the established foraminiferal Ba/Ca and View the MathML source salinity proxies for their capability to record the highly seasonal Orinoco freshwater plume in the eastern Caribbean. For this purpose we obtained a data set comprising Ba/Ca and View the MathML source determined on multiple species of planktonic foraminifera from core tops distributed around the Orinoco River mouth.

Our findings indicate that interpretations based on either proxy could lead to different conclusions. In particular, Ba/Ca and View the MathML source diverge in their spatial distribution due to different governing factors. Apparently, the Orinoco freshwater plume is best tracked by Ba/Ca ratios of G. ruber (pink and sensu lato morphotypes), while View the MathML source based on the same species is more related to the local precipitation-evaporation balance overprinting the riverine freshwater contribution. Other shallow dwelling species (G. sacculifer, O. universa) show a muted response to the freshwater discharge, most likely due to their ecological and habitat preferences. Extremely high Ba/Ca ratios recorded by G. ruber are attributed to Ba2+-desorption from suspended matter derived from the Orinoco.

Samples taken most proximal to the freshwater source do not show pronounced Ba/Ca or View the MathML source anomalies. Here, the suspension loaded freshwater lid developing during maximum discharge suppresses foraminiferal populations. Both proxies are therefore biased towards dry season conditions at these sites, when surface salinity is only minimally reduced.

Document Type: Article
Additional Information: WOS:000328593500006
Keywords: foraminiferal Ba/Ca; View the MathML source of seawater; Ba desorption; Orinoco; Globigerinoides ruber
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
DOI etc.: 10.1016/j.epsl.2013.09.036
ISSN: 0012-821X
Projects: Future Ocean
Date Deposited: 22 Oct 2013 12:52
Last Modified: 06 Mar 2017 13:37

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