| 1. |
- Barras, Christine, et al.
(författare)
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Experimental calibration of manganese incorporation in foraminiferal calcite
- 2018
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 237, s. 49-64
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Tidskriftsartikel (refereegranskat)abstract
- In the context of recent climate change and increased anthropogenic activities in coastal areas, which both may have a negative impact on dissolved oxygen concentration, there is an increased interest to better understand the mechanisms and evolution leading to hypoxia in marine environments. The development of well calibrated proxies is crucial to obtain reliable environmental reconstructions of past oxygen content and of historical development of hypoxia. Manganese is a redox element of interest for this purpose because manganese oxides are reduced to soluble Mn2+ in oxygen-depleted conditions, which can be incorporated in biogenic calcite. The Mn/Ca ratio in benthic foraminiferal calcite is therefore a promising proxy to reconstruct past oxygen variations. In this study, we calibrate this proxy by measuring (with Laser Ablation ICP-MS) the Mn/Ca ratio of benthic foraminifera calcified under controlled conditions in laboratory experiments. Two benthic foraminiferal species (Ammonia tepida and Bulimina marginata) calcified in 4 different dissolved manganese concentrations (from 2.4 to 595 µmol L−1) corresponding to in situ Mn concentrations encountered in bottom and/or pore waters in low oxygen marine environments. There is a statistically significant positive linear correlation (R2 > 0.9) between Mn/Cacalcite and Mn/Caseawater. However, the two species show different partitioning coefficients (DMn of 0.086 and 0.621, for A. tepida and B. marginata, respectively), although they calcified in exactly the same stable conditions. These results highlight a strong species specific effect on Mn incorporation, which is probably due to different biological controls during biomineralisation processes. There is also ontogenetic variability (determined through a comparison of successive chambers) that is different between the two species and also varies as a function of the dissolved Mn concentration. A conceptual model is proposed to explain these data.
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| 2. |
- Brinkmann, Inda, et al.
(författare)
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Benthic Foraminiferal Mn/Ca as Low-Oxygen Proxy in Fjord Sediments
- 2023
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 37:5
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Tidskriftsartikel (refereegranskat)abstract
- Fjord systems are typically affected by low-oxygen conditions, which are increasing in extent and severity, forced by ongoing global changes. Fjord sedimentary records can provide high temporal resolution archives to aid our understanding of the underlying mechanisms and impacts of current deoxygenation. However, such archives can only be interpreted with well-calibrated proxies. Bottom-water oxygen conditions determine redox regime and availability of redox-sensitive trace elements such as manganese, which in turn may be recorded by manganese-to-calcium ratios (Mn/Ca) in biogenic calcium carbonates (e.g., benthic foraminifera tests). However, biological influences on Mn incorporation (e.g., species-specific Mn fractionation, ontogeny, living and calcification depths) are still poorly constrained. We analyzed Mn/Ca of living benthic foraminifera (Bulimina marginata, Nonionellina labradorica), sampled at low- to well-oxygenated conditions over a seasonal gradient in Gullmar Fjord, Swedish West coast (71–217 μmol/L oxygen (O2)), by laser-ablation ICP-MS. High pore-water Mn availability in the fjord supported Mn incorporation by foraminifera. B. marginata recorded contrasting Mn redox regimes sensitively and demonstrated potential as proxy for low-oxygen conditions. Synchrotron-based scanning X-ray fluorescence nanoimaging of Mn distributions across B. marginata tests displayed Mn/Ca shifts by chambers, reflecting bottom-water oxygenation history and/or ontogeny-driven life strategy preferences. In contrast, Mn/Ca signals of N. labradorica were extremely high and insensitive to environmental variability. We explore potential biologically controlled mechanisms that could potentially explain this species-specific response. Our data suggest that with the selection of sensitive candidate species, the Mn/Ca proxy has potential to be further developed for quantitative oxygen reconstructions in the low-oxygen range.
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| 3. |
- Brinkmann, Inda, et al.
(författare)
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Drought recorded by Ba/Ca in coastal benthic foraminifera
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:9, s. 2523-2535
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Tidskriftsartikel (refereegranskat)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 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.
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| 4. |
- Brinkmann, Inda, et al.
(författare)
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Through the eDNA looking glass: Responses of fjord benthic foraminiferal communities to contrasting environmental conditions
- 2023
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Ingår i: Journal of Eukaryotic Microbiology. - : Wiley. - 1066-5234 .- 1550-7408. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- The health of coastal marine environments is severely declining with global changes. Proxies, such as those based on microeukaryote communities, can record biodiversity and ecosystem responses. However, conventional studies rely on microscopic observations of limited taxonomic range and size fraction, missing putatively ecologically informative community components. Here, we tested molecular tools to survey foraminiferal biodiversity in a fjord system (Sweden) on spatial and temporal scales: Alpha and beta diversity responses to natural and anthropogenic environmental trends were assessed and variability of foraminiferal environmental DNA (eDNA) compared to morphology-based data. The identification of eDNA-obtained taxonomic units was aided by single-cell barcoding. Our study revealed wide diversity, including typical morphospecies recognized in the fjords, and so-far unrecognized taxa. DNA extraction method impacted community composition outputs significantly. DNA extractions of 10 g sediment more reliably represented present diversity than of 0.5-g samples and, thus, are preferred for environmental assessments in this region. Alpha- and beta diversity of 10-g extracts correlated with bottom-water salinity similar to morpho-assemblage diversity changes. Sub-annual environmental variability resolved only partially, indicating damped sensitivity of foraminiferal communities on short timescales using established metabarcoding techniques. Systematically addressing the current limitations of morphology-based and metabarcoding studies may strongly improve future biodiversity and environmental assessments.
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| 5. |
- van Dijk, Inge, et al.
(författare)
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Chemical Heterogeneity of Mg, Mn, Na, S, and Sr in Benthic Foraminiferal Calcite
- 2019
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The chemical composition of fossil foraminiferal shells (tests) is widely used as tracers for past ocean chemistry. It is, therefore, important to understand how different (trace) elements are transported and incorporated into these tests from adjacent seawater. The elemental distribution within the walls of foraminiferal tests might be used to differentiate between proposed transport mechanisms. Here, the microdistribution of Mg, Mn, Na, S, and Sr in tests of three species of foraminifera, known to have contrasting test chemistry, is investigated by a combination of electron probe microanalysis (EPMA) and nanoscale secondary ion mass spectrometry (nanoSIMS), micro-X-ray fluorescence (μXRF), and micro-X-ray absorption near-edge structure (μXANES) analyses. The three investigated species are the symbiont-barren Ammonia sp. T6 and Bulimina marginata, which precipitate a low-Mg calcite test, and the symbiont-bearing species Amphistegina lessonii, which produces a test with intermediate Mg content. Because all analyzed tests were formed under controlled and identical laboratory conditions, the observed distributions of elements are not due to environmental variability but are a direct consequence of the processes involved in calcification or, in the case of A. lessonii, possibly symbiont activity. Despite some variability in elemental microdistribution between specimens from a given species, our combined dataset shows species-specific distributions of the elements (e.g., peak heights and/or band-widths) and also a systematic colocation of Mg, Na, S, and Sr for all three species, suggesting a coupled or simultaneous uptake, transport, and incorporation of these elements during chamber addition. The observed trace element patterns generally reflect a laminar calcification model, suggesting that heterogeneity of these elements is intrinsically linked to chamber addition. Although the incorporation of redox-sensitive Mn depends on the Mn concentration of the culture medium, the Mn distribution observed in Ammonia sp. suggests that Mn transport is similarly linked to laminar calcification dynamics. However, for B. marginata, Mn banding was sometimes anticorrelated with Mg banding, suggesting that (bio)availability, uptake, and transport of Mn differ from those for Ammonia sp. Our results from symbiont-bearing A. lessonii suggest that the activity of symbionts (i.e., photosynthesis/respiration) may influence the incorporation of Mn owing to alternation of the chemistry in the microenvironment of the foraminifera, an important consideration in the development of this potential proxy for past oxygenation of the oceans.
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