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  • Other Sources  (5)
  • Nature Research  (3)
  • Frontiers  (2)
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  • Other Sources  (5)
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  • 1
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    Coupling of oceanic carbon and nitrogen facilitates spatially resolved quantitative reconstruction of nitrate inventories (2018)
    Nature Research
    In:  Nature Communications, 9 (Article number 1217).
    Details
    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
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  • 2
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    Organic Heterogeneities in Foraminiferal Calcite Traced Through the Distribution of N, S, and I Measured With NanoSIMS: A New Challenge for Element-Ratio-Based Paleoproxies? (2019)
    Frontiers
    In:  Frontiers in Earth Science, 7 (175).
    Details
    Publication Date: 2022-01-31
    Description: Oceanic oxygen decline due to anthropogenic climate change is a matter of growing concern. A quantitative oxygen proxy is highly desirable in order to identify and monitor recent dynamics as well as to reconstruct pre-Anthropocene changes in amplitude and extension of oxygen depletion. Geochemical proxies like foraminiferal I/Ca ratios seem to be promising redox proxies. Nevertheless, recent studies on microanalyses of benthic foraminiferal I/Ca ratios at the Peruvian oxygen minimum zone (OMZ) measured with secondary-ion mass spectrometry (SIMS) revealed a possible association of iodine with organic accumulations within the test. Here, we present a new study on the micro-distribution of nitrogen, sulfur, and iodine within the test walls of Uvigerina striata from the Peruvian OMZ measured with Nano-SIMS. A quantification of the foraminiferal I/Ca ratios from our NanoSIMS study is in good agreement with quantitative results from a previous SIMS study. Additionally, we compared uncleaned specimens with specimens that have been treated with an oxidative cleaning procedure. Both nitrogen and sulfur, which are used as tracer for organic matter, show a patchy distribution within the test walls of the uncleaned specimens and a statistically significant correlation with the iodine distribution. This patchy organic-rich phase has a different geochemical signature than the pristine calcitic parts of the test and another phase that shows a banding-like structure and that is characterized by a strong sulfur enrichment. All three elements, sulfur, nitrogen, and iodine, are strongly depleted in the cleaned specimens, even within the massive parts of the test walls that lack the connection with the test pores. These results indicate that the organic parts of the test walls are located inside a microporous framework within the foraminiferal calcite. This has to be considered in the interpretation of geochemical proxies on foraminiferal calcite, especially for microanalytical methods, since the chemical signature of these organic parts likely alters some element-to-calcium ratios within the foraminiferal test.
    Type: Article , PeerReviewed
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  • 3
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    A deep-learning automated image recognition method for measuring pore patterns in closely related bolivinids and calibration for quantitative nitrate paleo-reconstructions (2023)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Eutrophication is accelerating the recent expansion of oxygen-depleted coastal marine environments. Several bolivinid foraminifera are abundant in these oxygen-depleted settings, and take up nitrate through the pores in their shells for denitrification. This makes their pore density a possible nitrate proxy. This study documents three aspects related to the porosity of bolivinids. 1. A new automated image analysis technique to determine the number of pores in bolivinids is tested. 2. The pore patterns of Bolivina spissa from five different ocean settings are analysed. The relationship between porosity, pore density and mean pore size significantly differs between the studied locations. Their porosity is mainly controlled by the size of the pores at the Gulf of Guayaquil (Peru), but by the number of pores at other studied locations. This might be related to the presence of a different cryptic Bolivina species in the Gulf of Guayaquil. 3. The pore densities of closely related bolivinids in core-top samples are calibrated as a bottom-water nitrate proxy. Bolivina spissa and Bolivina subadvena showed the same correlation between pore density and bottom-water nitrate concentrations, while the pore density of Bolivina argentea and Bolivina subadvena accumeata is much higher.
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  • 4
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    The Peruvian oxygen minimum zone was similar in extent but weaker during the Last Glacial Maximum than Late Holocene (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Quantifying past oxygen concentrations in oceans is crucial to improving understanding of current global ocean deoxygenation. Here, we use a record of pore density of the epibenthic foraminifer Planulina limbata from the Peruvian Oxygen Minimum Zone to reconstruct oxygen concentrations in bottom waters from the Last Glacial Maximum to the Late Holocene at 17.5°S about 500 meters below the sea surface. We found that oxygen levels were 40% lower during the Last Glacial Maximum than during the Late Holocene (about 6.7 versus 11.1 µmol/kg, respectively). A comparison with other reconstructions of oxygen concentrations in the region reveals a shallow Oxygen Minimum Zone during the Last Glacial Maximum that was similar in water depth and extent but weaker than during the Late Holocene. Increased glacial oxygen concentrations are probably related to lower temperatures (higher oxygen solubility), decreased nutrient and increased oxygen supply by source waters, and a decrease in coastal upwelling.
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  • 5
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    Climate-Biogeochemistry Interactions in the Tropical Ocean: Data collection and legacy (2021)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: From 2008 through 2019, a comprehensive research project, SFB 754, Climate - Biogeochemistry Interactions in the Tropical Ocean, was funded by the German Research Foundation to investigate the climate-biogeochemistry interactions in the tropical ocean with a particular emphasis on the processes determining the oxygen distribution. During three 4-year long funding phases, a consortium of more than 150 scientists conducted or participated in 34 major research cruises and collected a wealth of physical, biological, chemical, and meteorological data. A common data policy agreed upon at the initiation of the project provided the basis for the open publication of all data. Here we provide an inventory of this unique data set and briefly summarize the various data acquisition and processing methods used.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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