Preprints
https://doi.org/10.5194/bg-2021-310
https://doi.org/10.5194/bg-2021-310

  25 Nov 2021

25 Nov 2021

Review status: this preprint is currently under review for the journal BG.

Drought recorded by Ba/Ca in coastal benthic foraminifera

Inda Brinkmann1, Christine Barras2, Tom Jilbert3, Tomas Naeraa1, K. Mareike Paul3, Magali Schweizer2, and Helena L. Filipsson1 Inda Brinkmann et al.
  • 1Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
  • 2LPG UMR CNRS 6112, University of Angers, University of Nantes, 2 bd Lavoisier 49045, Angers Cedex 01, France
  • 3Aquatic Biogeochemistry Research Unit, Ecosystems and Environment Research Program, Faculty of Biological and Environmental Sciences, University of Helsinki, Viikinkaari 1, 00790 Helsinki, Finland

Abstract. Increasing occurrences of extreme weather events, such as the 2018 drought over northern Europe, are a concerning issue under global climate change. High resolution archives of natural hydroclimate proxies, such as rapidly accumulating sediments containing biogenic carbonates, offer the potential to investigate the frequency and mechanisms of such events in the past. Droughts alter the barium (Ba) concentration of near-continent seawater through the reduction in Ba input from terrestrial runoff, which in turn may be recorded as changes in the chemical composition (Ba/Ca) of foraminiferal calcium carbonates accumulating in sediments. However, so far the use Ba/Ca as a discharge indicator has been restricted to planktonic foraminifera, despite the high relative abundance of benthic species in coastal, shallow-water sites. Moreover, benthic foraminiferal Ba/Ca has mainly been used in open ocean records as a proxy for paleo-productivity. Here we report on a new geochemical dataset measured from living (CTG-labelled) benthic foraminiferal species to investigate the capability of benthic Ba/Ca to record changes in river runoff over a gradient of contrasting hydroclimatic conditions. Individual foraminifera (Bulimina marginata, Nonionellina labradorica) were analyzed by laser-ablation ICP-MS over a seasonal and spatial gradient within Gullmar Fjord, Swedish west coast during 2018–2019. The results are compared to an extensive meteorological and hydrological data set, as well as sediment and pore-water geochemistry. Benthic foraminiferal Ba/Ca correlates significantly to riverine runoff, however, the signals contain both spatial trends with distance to Ba-source, and species-specific influences such as micro-habitat preferences. We deduce that shallow-infaunal foraminifera are especially suitable as proxy for terrestrial Ba input and discuss the potential influence of water-column and pore-water Ba cycling. While distance to Ba-source, water depth, pore-water geochemistry, and species-specific effects need to be considered in interpreting the data, our results demonstrate confidence in the use of Ba/Ca of benthic foraminifera from near-continent records as proxy for past riverine discharge and to identify periods of drought.

Inda Brinkmann et al.

Status: open (until 06 Jan 2022)

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Inda Brinkmann et al.

Inda Brinkmann et al.

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Short summary
The concentration of the trace metal barium (Ba) in coastal seawater is a function of continental input, such as by riverine discharge. Our geochemical records of the severely hot and dry year 2018, and following wet year 2019, reveal that prolonged drought imprints with exceptionally low Ba concentrations in benthic foraminiferal calcium carbonates of coastal sediments. This highlights the potential of benthic Ba/Ca to trace past climate extremes and variability in coastal marine records.
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