TY - JOUR

T1 - Barium isotopes in stromatolites through deep-time: A novel tracer for metal cycling in the photic zone

AU - Hohl, Simon V.

AU - Lin, Yi-Bo

AU - Wei, Hai-Zhen

AU - Wei, Guany-Yi

AU - Viehmann, Sebastian

N1 - We want to acknowledge the help of Yuxiang Jiang, Zhongya Hu, Yisheng Yi and members of the SPP 1833 "Building a Habitable Earth" for assistance in collecting stromatolite samples. We would further like to acknowledge funding by NSFC funding no. 42150610481 – The "Stromatolite Geochemical Archive". Finally, we thank Laurence Coogan for editorial handling and two anonymous reviewers’ valuable comments on earlier versions of this manuscript.

PY - 2024/4/15

Y1 - 2024/4/15

N2 - In the search for reliable archives to reconstruct Earth's paleo-surface ocean chemistry, stromatolites have gained much attention in the past decade. Stromatolitic carbonates, i.e., lithified microbial mats, form in shallow neritic environments and have the unique potential to record the ambient water chemistry of the photic zone. Their wide occurrence in shallow marine sedimentary successions from at least ca. 3.5 billion years ago until today highlight these bio-sedimentary archives as excellent recorders of elemental fluctuations in microbial habitats of the near-shore surface ocean, embayed basins, and lacustrine systems. In this study, we test the application of Ba concentrations and its isotopes in Paleoarchean to Holocene stromatolites as a potential deep-time proxy for biogeochemical element cycling in ancient microbial habitats of different depositional environments. Barium systematics in stromatolites reflect biogeochemical Ba cycling in local, aqueous (micro)environments of photic zones under variable oxygen and sulphate saturation conditions. We obtained significant differences in authigenic Ba concentrations and isotopic compositions between open ocean and restricted depositional settings: Microbial communities in restricted embayment or lacustrine environments show distinct negative δ 138Ba auth values inversely correlated with Ba concentrations due to Ba (re)cycling. In contrast, stromatolites from non-restricted, marine depositional settings have the potential to record ambient seawater Ba isotopic compositions with the heaviest obtained δ 138Ba sw = 0.45 ‰ in the Archean, 0.61 ‰ in the Proterozoic and 0.57 ‰ in the Phanerozoic at a precision of ±0.04 ‰ (2SD). Our study suggests that variabilities in δ 138Ba of stromatolitic carbonates can directly be linked to environmental restriction and associated biogeochemical Ba cycling, probably related to micro-barite formation on microbial biofilms, with subsequent recycling in restricted environments leading to lighter Ba isotopic values in the ambient waters and carbonates. However, stromatolites of open marine settings record local surface ocean δ 138Ba compositions and may be used as unique archives in future studies to investigate the evolution of primary productivity in the photic zone through deep-time.

AB - In the search for reliable archives to reconstruct Earth's paleo-surface ocean chemistry, stromatolites have gained much attention in the past decade. Stromatolitic carbonates, i.e., lithified microbial mats, form in shallow neritic environments and have the unique potential to record the ambient water chemistry of the photic zone. Their wide occurrence in shallow marine sedimentary successions from at least ca. 3.5 billion years ago until today highlight these bio-sedimentary archives as excellent recorders of elemental fluctuations in microbial habitats of the near-shore surface ocean, embayed basins, and lacustrine systems. In this study, we test the application of Ba concentrations and its isotopes in Paleoarchean to Holocene stromatolites as a potential deep-time proxy for biogeochemical element cycling in ancient microbial habitats of different depositional environments. Barium systematics in stromatolites reflect biogeochemical Ba cycling in local, aqueous (micro)environments of photic zones under variable oxygen and sulphate saturation conditions. We obtained significant differences in authigenic Ba concentrations and isotopic compositions between open ocean and restricted depositional settings: Microbial communities in restricted embayment or lacustrine environments show distinct negative δ 138Ba auth values inversely correlated with Ba concentrations due to Ba (re)cycling. In contrast, stromatolites from non-restricted, marine depositional settings have the potential to record ambient seawater Ba isotopic compositions with the heaviest obtained δ 138Ba sw = 0.45 ‰ in the Archean, 0.61 ‰ in the Proterozoic and 0.57 ‰ in the Phanerozoic at a precision of ±0.04 ‰ (2SD). Our study suggests that variabilities in δ 138Ba of stromatolitic carbonates can directly be linked to environmental restriction and associated biogeochemical Ba cycling, probably related to micro-barite formation on microbial biofilms, with subsequent recycling in restricted environments leading to lighter Ba isotopic values in the ambient waters and carbonates. However, stromatolites of open marine settings record local surface ocean δ 138Ba compositions and may be used as unique archives in future studies to investigate the evolution of primary productivity in the photic zone through deep-time.

KW - Ba isotopes

KW - Biogeochemical metal cycling

KW - Deep time microbial life

KW - Microbial carbonate

KW - Microbial habitats

KW - Stromatolites

UR - http://www.scopus.com/inward/record.url?scp=85187689502&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2024.118639

DO - 10.1016/j.epsl.2024.118639

M3 - Article

VL - 632

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

M1 - 118639

ER -