Drought recorded by Ba/Ca in coastal benthic foraminifera

Inda Brinkmann, Christine Barras, Tom Jilbert, Tomas Næraa, K. Mareike Paul, Magali Schweizer, Helena L. Filipsson

Research output: Contribution to journalArticlepeer-review


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 of 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 data set measured from living (CTG-labeled) 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 a proxy for past riverine discharge and to identify periods of drought.

Original languageEnglish
Pages (from-to)2523-2535
Number of pages13
Issue number9
Publication statusPublished - 2022 May 16

Bibliographical note

Funding Information:
This research has been supported by the Vetenskapsrådet (grant no. 2017-04190), the Kungliga Fysiografiska Sällskapet i Lund (grant no. -), the Academy of Finland (grant nos. 317684 and 319956), and the Crafoordska Stiftelsen (grant no. -).

Acknowledgements. The authors thank the captain and crew of the RV Oscar von Sydow and RV Skagerak for technical assistance. We thank Sami Jokinen and Hanna Nilsson for their help during the cruises. We acknowledge the staff of the Kristineberg Marine Research Station for their support during the field campaigns. Further, the hydrographic data used in this project are from SMHI’s database, including SHARK. The SHARK data collection is organized by the Swedish environmental monitoring program and funded by the Swedish Agency for Marine and Water Management (SwAM). Finally, we thank the editor and the two anonymous referees for their feedback.

Publisher Copyright:
© 2022 Inda Brinkmann et al.

Subject classification (UKÄ)

  • Climate Research
  • Geochemistry
  • Oceanography, Hydrology, Water Resources
  • Other Earth and Related Environmental Sciences


  • foraminifera, drought, climate, 2018, fjords


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