ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Glock, Nicolaas; Eisenhauer, Anton; Liebetrau, Volker; Wiedenbeck, M; Hensen, Christian; Nehrke, Gernot (2012): EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols. Biogeosciences, 9, 341-359, https://doi.org/10.5194/bg-9-341-2012
    Publication Date: 2019-02-13
    Description: In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox conditions. Foraminiferal tests are often contaminated by diagenetic coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings. Thus, it is substantial to assure that the cleaning protocols are efficient or that spots chosen for microanalyses are free of contaminants. Prior to the determination of the element/Ca ratios, the distributions of several elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow infaunal species Uvigerina peregrina and Bolivina spissa were mapped with an electron microprobe (EMP). To visualize the effects of cleaning protocols uncleaned and cleaned specimens were compared. The cleaning protocol included an oxidative cleaning step. An Fe rich phase was found on the inner test surface of uncleaned U. peregrina specimens. This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was found at the inner test surface of B. spissa. Specimens of both species treated with oxidative cleaning show the absence of this phase. Neither in B. spissa nor in U. peregrina were any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca and Fe/Ca ratios of single specimens of B. spissa from different locations have been determined by secondary ion mass spectrometry (SIMS). Bulk analyses using solution ICP-MS of several samples were compared to the SIMS data. The difference between SIMS analyses and ICP-MS bulk analyses from the same sampling sites was 14.0-134.8 µmol mol-1 for the Fe/Ca and 1.68(±0.41) µmol mol-1 for the Mn/Ca ratios. This is in the same order of magnitude as the variability inside single specimens determined with SIMS at these sampling sites (1sigma[Mn/Ca] = 0.35-2.07 µmol mol-1; 1sigma[Fe/Ca] = 93.9-188.4 µmol mol-1). The Mn/Ca ratios in the calcite were generally relatively low (2.21-9.93 µmol mol-1) but in the same magnitude and proportional to the surrounding pore waters (1.37-6.67 µmol mol-1). However, the Fe/Ca ratios in B. spissa show a negative correlation to the concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca ratios (87.0-101.0 µmol mol-1) were found at 465 m water depth, a location with a strong sharp Fe peak in the pore water next to the sediment surface and respectively, high Fe concentrations in the surrounding pore waters. Previous studies found no living specimens of B. spissa at this location. All these facts hint that the analysed specimens already were dead before the Fe flux started and the sampling site just recently turned anoxic due to fluctuations of the lower boundary of the OMZ near the sampling site (465 m water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for redox conditions, if cleaning protocols are carefully applied. The data presented here may be rated as base for the still pending detailed calibration.
    Type: Dataset
    Format: application/zip, 5 datasets
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-02-06
    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
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    facet.materialart.
    Unknown
    In:  [Poster] In: Ocean Sciences Meeting 2010 "Oxygen Minimum Zones and Climate Change: Observations and Prediction IV", 22.02.-26.02.2010, Portland, Oregon, USA .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    Unknown
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    Unknown
    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
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-08-20
    Description: Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO3−) or oxygen (O2)—makes them important mediators of benthic nitrogen cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O2 respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). Denitrification and O2 respiration rates significantly scale sublinearly with the cell volume. The scaling is lower for O2 respiration than for denitrification, indicating that NO3− metabolism during denitrification is more efficient than O2 metabolism during aerobic respiration in foraminifera from the Peruvian OMZ. The negative correlation of the O2 respiration rate with the surface/volume ratio is steeper than for the denitrification rate. This is likely explained by the presence of an intracellular NO3− storage in denitrifying foraminifera. Furthermore, we observe an increasing mean cell volume of the Peruvian foraminifera, under higher NO3− availability. This suggests that the cell size of denitrifying foraminifera is not limited by O2 but rather by NO3− availability. Based on our findings, we develop a mathematical formulation of foraminiferal cell volume as a predictor of respiration and denitrification rates, which can further constrain foraminiferal biogeochemical cycling in biogeochemical models. Our findings show that NO3− is the preferred electron acceptor in foraminifera from the OMZ, where the foraminiferal contribution to denitrification is governed by the ratio between NO3− and O2.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Glock, Nicolaas; Schönfeld, Joachim; Eisenhauer, Anton; Hensen, Christian; Mallon, Jürgen; Sommer, Stefan (2013): The role of benthic foraminifera in the benthic nitrogen cycle of the Peruvian oxygen minimum zone. Biogeosciences, 10(7), 4767-4783, https://doi.org/10.5194/bg-10-4767-2013
    Publication Date: 2019-08-29
    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 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, 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 250 m water depth. They are still important denitrifiers in the centre of the OMZ around 320 m (29-56% of the benthic denitrification) but play only a minor role at the lower OMZ boundary and below the OMZ between 465 and 700 m (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 mmol m-2 d-1. Furthermore we show that the amount of nitrate stored in living benthic foraminifera (3 to 705 µmol L-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 regions in the world oceans, underpins the importance of previously underestimated role of benthic foraminifera in global biochemical cycles.
    Type: Dataset
    Format: application/zip, 6 datasets
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...