| 1. |
- 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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| 2. |
- Brinkmann, Inda
(författare)
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Coastal signals of environmental changes: foraminifera as benthic monitors
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate changes, tightly linked to anthropogenic activities, are significantly altering environments and ecosystems globally, such as by increasing marine and coastal deoxygenation or occurrences of extreme weather events. The significance of paleoenvironmental and -climate reconstructions, as well as monitoring of current conditions, for unravelling baseline natural variation, today’s changes and potential future impacts, has been recognised by the Intergovernmental Panel on Climate Change (IPCC) reports. However, to access past records of physical and chemical environmental variables, and comprehensively assess ecosystem reactions, reliable and sensitive proxies are critical. This thesis’ focus lies on benthic foraminifera—unicellular protists with mineralised or organic test, abundantly inhabiting ocean and coastal sediments—and their calibration as indicator for a variety of environmental conditions in field-sampling approaches. The research projects follow two general strategic tracks: (I) a biogeochemical assessment of trace-elemental ratios in foraminiferal calcium-carbonate tests using high-resolution, micro-analytical techniques; (II) a molecular approach investigating foraminiferal environmental DNA derived from coastal sediments. Papers I and II concern the calibration of the benthic foraminiferal Mn/Ca proxy for marine oxygenation conditions in modern field studies. Trace-element concentrations and distributions were measured by plasma-, laser- and synchrotron-based analyses in a high-resolution, individual-foraminifera approach, and interpreted in the context of ambient physical and chemical conditions of the water column, pore-waters and sediments (including oxygen and manganese concentrations). Investigating two coastal systems with almost permanently severely oxygen-deficient bottom-waters (Santa Barbara Basin, Paper I), and undergoing a seasonal oxygenation cycle across the low- to well-oxygenated range (Gullmar Fjord, Paper II), respectively, demonstrated the utility of the Mn/Ca proxy for indicating low-oxygen conditions specifically. Continued calibration efforts under consideration of ambient oxygenation and redox regimes may open further possibilities of quantitative oxygen reconstructions. Paper III explores the use of coastal, benthic Ba/Ca records as indicator of riverine runoff and drought on land across the years 2018 and 2019, characterised by severe heat and drought, and warm and wet conditions, respectively. Benthic Ba/Ca correlated significantly with the hydroclimate conditions, as inferred from extensive meteorological and hydrological data sets of the region, highlighting qualitative proxy potential for paleo-drought reconstructions. Based on ambient sediment and pore-water geochemistry, we discuss mediation of water-column transport and pore-water Ba cycling by Fe and Mn oxides. All three investigations of these geochemical proxies (Paper I–III) highlighted the significance of biological controls on foraminiferal TE/Ca, which are species-specific and, thus, should be a deciding factor in choosing proxy candidate species. In particular the influences of micro-habitat distribution and utilised metabolic pathways by foraminifera are discussed in detail. In Paper IV foraminiferal biodiversity and assemblage responses to natural and anthropogenic environmental trends in a fjord system (Swedish west coast) are documented in a metabarcoding approach. Environmental DNA successfully tracked biodiversity and community composition changes associated with contrasting ecosystems but showed damped sensitivity to environmental variability on sub-annual time-scales. Overlaps and discrepancies between molecular and traditional, observation-based assessment techniques, as well as future trajectories to resolve uncertainties are discussed. Overall, this thesis solidifies and expands the currently available proxy toolbox for reconstructions of both coastal low-oxygen, as well as terrestrial hydroclimate conditions. The findings contribute towards filling current knowledge gaps pertaining to biotic impacts on foraminifera-derived biogeochemical signals and methodological uncertainties in metabarcoding approaches and highlight the significance of implementing molecular techniques in conventional foraminiferal assemblage studies.
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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. |
- Paul, K. Mareike, et al.
(författare)
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Revisiting the applicability and constraints of molybdenum- and uranium-based paleo redox proxies : comparing two contrasting sill fjords
- 2023
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Ingår i: Biogeosciences Discussions. - 1810-6277 .- 1810-6285. ; 20:24, s. 5003-5028
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentary molybdenum (Mo) and uranium (U) enrichments are often used as redox proxies to reconstruct bottom water redox changes. However, these redox proxies may not be equally reliable across a range of coastal settings due to varying depositional environments. Fjords vary greatly in their depositional conditions, due to their unique bathymetry and hydrography, and are highly vulnerable to anthropogenic and climatic pressures. Currently, it is unknown to what extent Mo and U sequestration is affected by variable depositional conditions in fjords. Here, we use pore water and sequential extraction data to investigate Mo and U enrichment pathways in sediments of two sill fjords on the Swedish west coast with contrasting depositional environments and bottom water redox conditions. Our data suggest that sedimentary authigenic Mo and U pools differ between the two fjords. At the (ir)regularly dysoxic (oxygen = 0.2–2 mL L−1) Gullmar Fjord, authigenic Mo largely binds to manganese (Mn) oxides and to a lesser extent to iron (Fe) oxides; Mo sulfides do not play a major role due to low sulfate reduction rates, which limits the rate of Mo burial. Authigenic U largely resides in carbonates. At the (ir)regularly euxinic (oxygen = 0 mL L−1; total hydrogen sulfide ≥ 0 mL L−1) Koljö Fjord, authigenic Mo is significantly higher due to binding with more refractory organic matter complexes and Mo-Fe-sulfide phases. Uranium is moderately enriched and largely bound to organic matter. We found no direct evidence for temporal changes in bottom water redox conditions reflected in Mo and U enrichments at either Gullmar Fjord or Koljö Fjord. While sulfidic bottom waters favor Mo sequestration at Koljö Fjord, enrichment maxima reflect a combination of depositional conditions rather than short-term low-oxygen events. Our data demonstrate that secondary pre- and post-depositional factors control Mo and U sequestration in fjords to such an extent that bottom water redox conditions are either not being systematically recorded or overprinted. This explains the large variability in trace metal enrichments observed in fjords and has implications for applying Mo and U as proxies for environmental redox reconstructions in such systems.
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