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Conservative mixing of alkaline groundwater plume with saline waters at Hamelin Pool recorded in Ba isotopic compositions of stromatolitic carbonates
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  • Simon V. Hohl,
  • Yibo Lin,
  • Sebastian Viehmann,
  • Ashley N. Martin,
  • Pierre Sans-Jofre
Simon V. Hohl
Tongji University

Corresponding Author:[email protected]

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Yibo Lin
Nanjing University
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Sebastian Viehmann
Leibniz Universitat Hannover Naturwissenschaftliche Fakultat
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Ashley N. Martin
Leibniz Universität Hannover
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Pierre Sans-Jofre
Sorbonne Université
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Abstract

Hamelin Pool, W.-Australia, is a natural laboratory to study stromatolite formation in a hypersaline lagoon. Stromatolitic aragonites sampled at supratidal, intertidal and subtidal environments show gradual increase in Ba isotopic compositions (d138Bacarb = -0.12-0.57‰) with decreasing Ba/Ca following conservative mixing between groundwater and seawater. We observe fingerprints of the groundwater end-member in a supratidal sample showing particular light d138Bacarb corresponding with elevated Mn/Sr and low d18Ocarb as indicator for discharge from the local Tamala Limestone aquifer. In contrast, stromatolitic carbonates formed in equilibrium with a saline end-member show heavy d138Bacarb. Lagoonal d138Bafluid ranges from 0.44-0.6‰ at increasing PSU (3.6-65.6). The calculated partition coefficient for Ba into stromatolites is lowest at the subtidal (logDBa=0.45) and highest at the groundwater discharge site (logDBa=0.86). Injection of groundwaters into Hamelin Pool likely contributes to enhanced aragonite precipitation at up to 0.32mm/yr, possibly catalysed by nucleation within or onto extra-polymeric substances of microbially diverse mats.
11 Nov 2024Submitted to ESS Open Archive
11 Nov 2024Published in ESS Open Archive