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  • 1
    Keywords: Hochschulschrift ; Peru ; Kontinentalabhang ; Benthos ; Foraminiferen ; Mikropaläontologie ; Biogeochemie
    Type of Medium: Online Resource
    Pages: Online-Ressource
    DDC: 550
    Language: English
    Note: Kiel, Univ., Diss., 2011
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  • 2
    Publication Date: 2021-03-19
    Description: Anthropogenic impacts are perturbing the global nitrogen cycle via warming effects and pollutant sources such as chemical fertilizers and burning of fossil fuels. Understanding controls on past nitrogen inventories might improve predictions for future global biogeochemical cycling. Here we show the quantitative reconstruction of deglacial bottom water nitrate concentrations from intermediate depths of the Peruvian upwelling region, using foraminiferal pore density. Deglacial nitrate concentrations correlate strongly with downcore δ13C, consistent with modern water column observations in the intermediate Pacific, facilitating the use of δ13C records as a paleo-nitrate-proxy at intermediate depths and suggesting that the carbon and nitrogen cycles were closely coupled throughout the last deglaciation in the Peruvian upwelling region. Combining the pore density and intermediate Pacific δ13C records shows an elevated nitrate inventory of 〉10% during the Last Glacial Maximum relative to the Holocene, consistent with a δ13C-based and δ15N-based 3D ocean biogeochemical model and previous box modeling studies.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 3
    Publication Date: 2021-05-07
    Description: Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats, where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. Large-scale genome and transcriptomes analyses reveal the presence of a denitrification pathway in foraminifera species of the genus Globobulimina. This includes the enzymes nitrite reductase (NirK) and nitric oxide reductase (Nor) as well as a wide range of nitrate transporters (Nrt). A phylogenetic reconstruction of the enzymes' evolutionary history uncovers evidence for an ancient acquisition of the foraminiferal denitrification pathway from prokaryotes. We propose a model for denitrification in foraminifera, where a common electron transport chain is used for anaerobic and aerobic respiration. The evolution of hybrid respiration in foraminifera likely contributed to their ecological success, which is well documented in palaeontological records since the Cambrian period.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2019-09-23
    Description: The discovery that foraminifera are able to use nitrate instead of oxygen as energy source for their metabolism has challenged our understanding of nitrogen cycling in the ocean. It was evident before that only prokaryotes and fungi are able to denitrify. Rate 5 estimates of foraminiferal denitrification were very sparse on a regional scale. Here, we present estimates of benthic foraminiferal denitrification rates from six stations at intermediate water depths in and below the Peruvian oxygen minimum zone (OMZ). Foraminiferal denitrification rates were calculated from abundance and assemblage composition of the total living fauna in both, surface and subsurface sediments, 10 as well as from individual species specific denitrification rates. A comparison with total benthic denitrification rates as inferred by biogeochemical models revealed that benthic foraminifera account for the total denitrification on the shelf between 80 and 250m water depth. They are still important denitrifiers in the centre of the OMZ around 320m (29–56% of the benthic denitrification) but play only a minor role at the lower OMZ 15 boundary and below the OMZ between 465 and 700m (3–7% of total benthic denitrification). Furthermore, foraminiferal denitrification was compared to the total benthic nitrate loss measured during benthic chamber experiments. Foraminiferal denitrification contributes 1 to 50% to the total nitrate loss across a depth transect from 80 to 700 m, respectively. Flux rate estimates ranged from 0.01 to 1.3 mmolm−2 d−1. Fur20 thermore we show that the amount of nitrate stored in living benthic foraminifera (3 to 705 μmolL−1) can be higher by three orders of magnitude as compared to the ambient pore waters in near surface sediments sustaining an important nitrate reservoir in Peruvian OMZ sediments. The substantial contribution of foraminiferal nitrate respiration to total benthic nitrate loss at the Peruvian margin, which is one of the main nitrate sink 25 regions in the world oceans, underpins the importance of previously underestimated role of benthic foraminifera in global biochemical cycles.
    Type: Article , PeerReviewed
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  • 5
    Publication Date: 2019-09-23
    Description: In this study we explore the correlation of I/Ca ratios in three calcitic and one aragonitic foraminiferal species. I/Ca ratios are evaluated as possible proxies for changes in ambient redox conditions across the Peruvian oxygen minimum zone to the ambient oxygen concentrations in the habitat of the foraminiferal species studied. We test cleaning and measurement methods to determine I/Ca ratios in benthic foraminifera from the Peruvian oxygen minimum zone. All species show a positive trend in their I/Ca ratios as a function of higher oxygen concentrations and these trends are all statistically significant except for the aragonitic species Hoeglundina elegans. The most promising species appears to be Uvigerina striata which shows a highly statistically significant correlation between I/Ca ratios and bottom water (BW) oxygenation (I/Ca = 0.032(± 0.004)[O2]BW + 0.29(± 0.03), R2 = 0.61, F = 75, P 〈 0.0001). Although I/Ca ratios in benthic foraminifera might prove to be a valuable proxy for changing redox-conditions the iodine volatility in acidic solutions, the species dependency ofI/Ca–[O2]BW correlations, and the individual variability of single tests severely interfere with the observed I/Ca–[O2]BW relationship.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2019-09-23
    Description: Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of 〈 7 μmol kg−1 under the Peruvian upwelling and 〈 5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at 〉 10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.
    Type: Article , PeerReviewed
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  • 7
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    In:  [Poster] In: 11. International Conference on Paleoceanography (ICP11) 2013, 01.-06.09.2013, Sitges - Barcelona, Spain .
    Publication Date: 2013-10-22
    Description: The distribution of dissolved oxygen in the world oceans mirrors deep circulation commencing where oxygen is exchanged with the atmosphere. Consumption by bacterial decay of organic matter reduces oxygenation of intermediate and deep waters along their pathways. Supply and consumption of oxygen at depth depend on circulation vigour and surface ocean primary productivity, both are sensitive to climate change. Reconstructions of past ocean ventilation from geological archives relied ratios of redox-sensitive elements and biotic indicators. Dissolved oxygen is a predominant environmental factor controlling the abundance and distribution of benthic organisms. In particular benthic foraminifera are sensitive to oxygenation changes but show a mutual response to both, an increase in particulate organic matter flux or a decrease in dissolved oxygen in near-bottom and pore waters. Reconstructions of ancient deep-water oxygen concentrations by using the ratio of species with oxic vs. suboxic or dysoxic environmental preferences showed a sufficient accuracy only at oxygen levels 〈65 µmol kg-1. Multivariate analyses and transfer functions improved the accuracy and robustness of the benthic foraminiferal proxy against changes in organic matter flux but they are applicable only between 180 and 270 µmol kg-1 and mainly rely on oxyphylic species. Recent approaches focussed on the pore density (PD) in foraminiferal tests, which covaries with the oxygen availability in the ambient seawater ([O2]). Calibrations of PDs versus [O2] for shallow endobenthic Bolivina spissa, B. pacifica, and Fursenkoina mexicana are constrained between 1 to 37, 4 to 130, and 50 to 200 µmol kg-1 repectively. The epibenthic Planulina limbata depicted a higher accuracy though only between 2 and 13 µmol kg-1. For the deep endobenthic Globobulimina turgida exists a calibration between 50 and 200 µmol kg-1, while Chilostomella oolina shows no significant relationship between PD and [O2].
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
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    In:  [Poster] In: 11. International Conference on Paleoceanography (ICP11) 2013, 01.-06.09.2013, Sitges - Barcelona, Spain .
    Publication Date: 2013-10-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 9
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    In:  [Poster] In: The Micropalaeontological Society's Foraminifera and Nannofossil Groups Joint Spring Meeting 2015, 14-18.06.2015, Plymouth, UK .
    Publication Date: 2019-09-23
    Description: The Peruvian Oxygen Minimum Zone (OMZ) is one of the strongest and most pronounced OMZs in today’s world oceans and thus is a key area to understand changing redox conditions in relation with changing climate. Vertical and horizontal changes or an extension of the OMZ through time and space are investigated using a sediment core from the lower OMZ boundary. This core has a complete record since the Last Glacial Maximum. We focus on time intervals Late Holocene, Early Holocene, Bølling Allerød, Heinrich-Stadial 1 and Last Glacial Maximum to investigate changes in bottom-water oxygen conditions by using benthic foraminiferal assemblages. Living benthic foraminiferal faunas are structured with the prevailing bottom-water oxygen concentrations today (Mallon et al., 2012). Bolivina species are frequent at the most oxygen-depleted conditions. Cassidulina and Uvigerina species dominate the faunas under higher oxygen concentrations. Downcore distribution of benthic foraminiferal assemblages showed fluctuations in the abundance of the indicator species depicting variations in past bottom-water oxygenation. In addition, changes in bottom-water nitrate concentrations are reconstructed by using the pore density in tests of Bolivina spissa (Glock et al., 2011) for the same time intervals. Combination of both proxies will provide information on past bottom-water conditions and changes of oxygen concentrations for the Peruvian margin.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2016-01-11
    Description: Benthic foraminifera have been used as proxies for the prevailing conditions at the sediment–water interface. Their distribution patterns are thought to facilitate reconstruction of past environmental conditions. Variations of bottom water oxygenation can be traced by the downcore distribution of benthic foraminifera and some of their morphological characters. Being one of the strongest and most pronounced OMZs in today’s world oceans, the Peruvian OMZ is a key area to study such variations in relation with changing climate. Spatial changes or an extension of the OMZ through time and space are investigated using sediment cores from the lower OMZ boundary. We focus on time intervals Late Holocene, Early Holocene, Bølling Allerød, Heinrich-Stadial 1 and Last Glacial Maximum (LGM) to investigate changes in bottom-water oxygen and redox conditions. The recent distributions of benthic foraminiferal assemblages provide background data for an interpretation of the past conditions. Living benthic foraminiferal faunas from the Peruvian margin are structured with the prevailing bottom-water oxygen concentrations today (Mallon et al., 2012). Downcore distribution of benthic foraminiferal assemblages showed fluctuations in the abundance of the indicator species depicting variations and a decreasing trend in bottom water oxygen conditions since the LGM. In addition, changes in bottom-water oxygen and nitrate concentrations are reconstructed for the same time intervals by the pore density in tests of Planulina limbata and Bolivina spissa (Glock et al., 2011), respectively. The pore densities also indicate a trend of higher oxygen and nitrate concentrations in the LGM compared to the Holocene. Combination of both proxies provide information on past bottom-water conditions and changes of oxygen concentrations for the Peruvian margin. Glock et al., 2011: Environmental influences on the pore density of Bolivina spissa (Cushman), Journal of Foraminiferal Research, v. 41, no. 1, p. 22–32. Mallon et al., 2012: The response of benthic foraminifera to low-oxygen conditions of the Peruvian oxygen minimum zone, in ANOXIA, pp.305-322.
    Type: Conference or Workshop Item , NonPeerReviewed
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