Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements
Marine sedimentary archives are routinely used to reconstruct past environmental changes. In many cases, bioturbation and sedimentary mixing affect the proxy time-series and the age-depth relationship. While idealized models of bioturbation exist, they usually assume homogeneous mixing, thus that a...
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| Format: | Article |
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Frontiers Media S.A.
2022-05-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/feart.2022.871902/full |
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| author | Alexandra M. Zuhr Alexandra M. Zuhr Andrew M. Dolman Sze Ling Ho Jeroen Groeneveld Ludvig Löwemark Hendrik Grotheer Chih-Chieh Su Thomas Laepple Thomas Laepple |
| author_facet | Alexandra M. Zuhr Alexandra M. Zuhr Andrew M. Dolman Sze Ling Ho Jeroen Groeneveld Ludvig Löwemark Hendrik Grotheer Chih-Chieh Su Thomas Laepple Thomas Laepple |
| author_sort | Alexandra M. Zuhr |
| collection | DOAJ |
| description | Marine sedimentary archives are routinely used to reconstruct past environmental changes. In many cases, bioturbation and sedimentary mixing affect the proxy time-series and the age-depth relationship. While idealized models of bioturbation exist, they usually assume homogeneous mixing, thus that a single sample is representative for the sediment layer it is sampled from. However, it is largely unknown to which extent this assumption holds for sediments used for paleoclimate reconstructions. To shed light on 1) the age-depth relationship and its full uncertainty, 2) the magnitude of mixing processes affecting the downcore proxy variations, and 3) the representativity of the discrete sample for the sediment layer, we designed and performed a case study on South China Sea sediment material which was collected using a box corer and which covers the last glacial cycle. Using the radiocarbon content of foraminiferal tests as a tracer of time, we characterize the spatial age-heterogeneity of sediments in a three-dimensional setup. In total, 118 radiocarbon measurements were performed on defined small- and large-volume bulk samples ( ∼ 200 specimens each) to investigate the horizontal heterogeneity of the sediment. Additionally, replicated measurements on small numbers of specimens (10 × 5 specimens) were performed to assess the heterogeneity within a sample volume. Visual assessment of X-ray images and a quantitative assessment of the mixing strength show typical mixing from bioturbation corresponding to around 10 cm mixing depth. Notably, our 3D radiocarbon distribution reveals that the horizontal heterogeneity (up to 1,250 years), contributing to the age uncertainty, is several times larger than the typically assumed radiocarbon based age-model error (single errors up to 250 years). Furthermore, the assumption of a perfectly bioturbated layer with no mixing underneath is not met. Our analysis further demonstrates that the age-heterogeneity might be a function of sample size; smaller samples might contain single features from the incomplete mixing and are thus less representative than larger samples. We provide suggestions for future studies, optimal sampling strategies for quantitative paleoclimate reconstructions and realistic uncertainty in age models, as well as discuss possible implications for the interpretation of paleoclimate records. |
| first_indexed | 2024-12-12T10:03:52Z |
| format | Article |
| id | doaj.art-09d1e820fd8f424c86df20a0b9c58759 |
| institution | Directory Open Access Journal |
| issn | 2296-6463 |
| language | English |
| last_indexed | 2024-12-12T10:03:52Z |
| publishDate | 2022-05-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Earth Science |
| spelling | doaj.art-09d1e820fd8f424c86df20a0b9c587592022-12-22T00:27:56ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632022-05-011010.3389/feart.2022.871902871902Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon MeasurementsAlexandra M. Zuhr0Alexandra M. Zuhr1Andrew M. Dolman2Sze Ling Ho3Jeroen Groeneveld4Ludvig Löwemark5Hendrik Grotheer6Chih-Chieh Su7Thomas Laepple8Thomas Laepple9Research Unit Potsdam, Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Potsdam, GermanyInstitute of Geosciences, University of Potsdam, Potsdam, GermanyResearch Unit Potsdam, Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Potsdam, GermanyInstitute of Oceanography, National Taiwan University, Taipei, TaiwanInstitute for Geology, University of Hamburg, Hamburg, GermanyDepartment of Geosciences, National Taiwan University, Taipei, TaiwanResearch Unit Bremerhaven, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, GermanyInstitute of Oceanography, National Taiwan University, Taipei, TaiwanResearch Unit Potsdam, Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung, Potsdam, GermanyMARUM—Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen, Bremen, GermanyMarine sedimentary archives are routinely used to reconstruct past environmental changes. In many cases, bioturbation and sedimentary mixing affect the proxy time-series and the age-depth relationship. While idealized models of bioturbation exist, they usually assume homogeneous mixing, thus that a single sample is representative for the sediment layer it is sampled from. However, it is largely unknown to which extent this assumption holds for sediments used for paleoclimate reconstructions. To shed light on 1) the age-depth relationship and its full uncertainty, 2) the magnitude of mixing processes affecting the downcore proxy variations, and 3) the representativity of the discrete sample for the sediment layer, we designed and performed a case study on South China Sea sediment material which was collected using a box corer and which covers the last glacial cycle. Using the radiocarbon content of foraminiferal tests as a tracer of time, we characterize the spatial age-heterogeneity of sediments in a three-dimensional setup. In total, 118 radiocarbon measurements were performed on defined small- and large-volume bulk samples ( ∼ 200 specimens each) to investigate the horizontal heterogeneity of the sediment. Additionally, replicated measurements on small numbers of specimens (10 × 5 specimens) were performed to assess the heterogeneity within a sample volume. Visual assessment of X-ray images and a quantitative assessment of the mixing strength show typical mixing from bioturbation corresponding to around 10 cm mixing depth. Notably, our 3D radiocarbon distribution reveals that the horizontal heterogeneity (up to 1,250 years), contributing to the age uncertainty, is several times larger than the typically assumed radiocarbon based age-model error (single errors up to 250 years). Furthermore, the assumption of a perfectly bioturbated layer with no mixing underneath is not met. Our analysis further demonstrates that the age-heterogeneity might be a function of sample size; smaller samples might contain single features from the incomplete mixing and are thus less representative than larger samples. We provide suggestions for future studies, optimal sampling strategies for quantitative paleoclimate reconstructions and realistic uncertainty in age models, as well as discuss possible implications for the interpretation of paleoclimate records.https://www.frontiersin.org/articles/10.3389/feart.2022.871902/fullpaleoceanographyradiocarbonage-heterogeneitymarine sedimentsplanktonic foraminiferabioturbation |
| spellingShingle | Alexandra M. Zuhr Alexandra M. Zuhr Andrew M. Dolman Sze Ling Ho Jeroen Groeneveld Ludvig Löwemark Hendrik Grotheer Chih-Chieh Su Thomas Laepple Thomas Laepple Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements Frontiers in Earth Science paleoceanography radiocarbon age-heterogeneity marine sediments planktonic foraminifera bioturbation |
| title | Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements |
| title_full | Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements |
| title_fullStr | Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements |
| title_full_unstemmed | Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements |
| title_short | Age-Heterogeneity in Marine Sediments Revealed by Three-Dimensional High-Resolution Radiocarbon Measurements |
| title_sort | age heterogeneity in marine sediments revealed by three dimensional high resolution radiocarbon measurements |
| topic | paleoceanography radiocarbon age-heterogeneity marine sediments planktonic foraminifera bioturbation |
| url | https://www.frontiersin.org/articles/10.3389/feart.2022.871902/full |
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