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  • 2020-2023  (4)
  • 1950-1954
  • 2021  (4)
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  • 1
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    Do massive Porites mirror the heavy metal concentration in the ambient seawater? – A culture study (2021)
    In:  [Poster] In: International Coral Reef Symposium 2021, 19.– 23.07.2021, Online, Bremen .
    Details
    Publication Date: 2022-01-27
    Description: Heavy metal pollution originating from anthropogenic sources, e.g. mining, industry and extensive land use, increasingly influence tropical marine environments. The elevated input of heavy metals into the marine system potentially affects the biota because of their toxicity, persistence and bioaccumulation. Corals are increasingly used as an indicator for reconstructions of past dynamics of environmental factors like temperature or carbonate system parameters. Especially the massive scleractinian coral Porites provides an excellent tool for reconstructions because of their wide distribution (e.g. Great Barrier Reef, Caribbean, Australia or the tropical region of the Indo – Pacific) and because of their high growth rates allowing measurements at sub - annual resolution as well as building environmental archives covering hundreds of years. Furthermore, recent studies demonstrated that the trace metal concentration in the coral skeleton is most likely linked to local (or global) seawater chemistry including contaminations at various scales. Therefore, the metal concentration in the coral skeleton offers the opportunity of monitoring the spatial and temporal distribution patterns of heavy metals in the environment so contemporary emission reduction measures can be evaluated. Here we will present the final results of culturing studies addressing the relationship of heavy metal concentrations in the seawater and those in the coral skeleton. The partitioning factor between the ambient seawater and the aragonite of the corals is constrained by continuous water monitoring with weekly to biweekly sampling intervals and laser ablation measurements of grown skeleton. Culturing experiments with Porites lobata, Porites lichen, Montipora sp., Seriatopora sp. and Stylophora sp. are performed. The concentrations of heavy metals in the culturing medium are increased in four phases by a factor between 5 and 10 over a time period of more than a year. The results will facilitate a new way to monitor anthropogenic footprints in presumably pristine tropical environments as well as areas of high human impact.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 2
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    Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes (2021)
    Details
    Publication Date: 2022-03-23
    Description: The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.
    Description: Plain Language Summary: The South Asian or Indian monsoon affects the lives of billions. Through the erosion and weathering of rocks, the monsoon also has the potential to remove carbon dioxide from the atmosphere through increased weathering in the region including the Himalaya Mountains. The late Miocene, between 9 and 5 million years ago, was a period of global cooling and proliferation of grasslands in different regions including South Asia. Here, we examine the composition of clays formed by rock weathering during the late Miocene to determine their source region around the Bay of Bengal. The results suggest a generally stable mixture of sources with the strongest sources being regions with the highest monsoon rainfall today. We identify slight changes in the mixture of sources, which accompany a global change in carbon cycling, highlighting the role monsoon climate likely played in these changes. Toward the end of the Miocene, we identify a change in the Sr isotopes, which was not caused by source changes but by the strength of the rock weathering. This change has been observed in global records and it seems likely that it was driven by rock weathering in the South Asian Monsoon region.
    Description: Highlights: Radiogenic isotope compositions of detrital clays from the Bay of Bengal indicate a generally stable provenance from 9 to 5 Ma. A step change in Nd and Pb isotope compositions at ∼7.3 Ma reflects a climatically driven eastward shift in precipitation patterns resulting in enhanced erosion of the Indo‐Burman Ranges. Elevated 87Sr/86Sr between 6 and 5 Ma was likely related to increased chemical weathering caused by thicker soils and by C4 plant expansion.
    Description: DFG
    Description: ANR
    Description: IODP
    Keywords: ddc:551.302 ; ddc:551.701
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
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    Provenance and weathering of clays delivered to the Bay of Bengal during the middle Miocene: linkages to tectonics and monsoonal climate (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bretschneider, L., Hathorne, E. C., Huang, H., Luebbers, J., Kochhann, K. G. D., Holbourn, A., Kuhnt, W., Thiede, R., Gebregiorgis, D., Giosan, L., & Frank, M. Provenance and weathering of clays delivered to the Bay of Bengal during the middle Miocene: linkages to tectonics and monsoonal climate. Paleoceanography and Paleoclimatology, 36(2), (2021): e2020PA003917, https://doi.org/10.1029/2020PA003917.
    Description: Tectonics and regional monsoon strength control weathering and erosion regimes of the watersheds feeding into the Bay of Bengal, which are important contributors to global climate evolution via carbon cycle feedbacks. The detailed mechanisms controlling the input of terrigenous clay to the Bay of Bengal on tectonic to orbital timescales are, however, not yet well understood. We produced orbital‐scale resolution geochemical records for International Ocean Discovery Program Site U1443 (southern Bay of Bengal) across five key climatic intervals of the middle to late Miocene (15.8–9.5 Ma). Our new radiogenic Sr, Nd, and Pb isotope time series of clays transported to the Ninetyeast Ridge suggest that the individual contributions from different erosional sources overall remained remarkably consistent during the Miocene despite major tectonic reorganizations in the Himalayas. On orbital timescales, however, high‐resolution data from the five investigated intervals show marked fluctuations of all three isotope systems. Interestingly, the variability was much higher within the Miocene Climatic Optimum (around 16–15 Ma) and across the major global cooling (~13.9–13.8 Ma) until ~13.5 Ma, than during younger time intervals. This change is attributed to a major restriction on the supply of High Himalayan erosion products due to migration of the peak precipitation area toward the frontal domains of the Himalayas and the Indo‐Burman Ranges. The transient excursions of the radiogenic isotope signals on orbital timescales most likely reflect climatically driven shifts in monsoon strength.
    Description: This research used samples and data provided by the International Ocean Discovery Program and was funded by the German Research Foundation (DFG) (grants HA 5751/6‐1 and HA 5751/6‐2, KU 649/36‐1, and TH 1317‐8 and TH 1317‐9). Open access funding enabled and organized by Projekt DEAL.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
  • 4
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    Unknown
    Enhanced late miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bretschneider, L., Hathorne, E. C., Bolton, C. T., Gebregiorgis, D., Giosan, L., Gray, E., Huang, H., Holbourn, A., Kuhnt, W., & Frank, M. Enhanced late miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes. Paleoceanography and Paleoclimatology, 36(9), (2021): e2021PA004252, https://doi.org/10.1029/2021PA004252.
    Description: The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo-Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.
    Description: This research used samples and data provided by the International Ocean Discovery Program and was funded by the German Research Foundation (DFG) (grants HA 5751/6-1 & -2). C. T. Bolton acknowledges funding from the French ANR project iMonsoon (ANR-16-CE01-0004-01) and IODP France. W. Kuhnt acknowledges funding from the DFG (grant Ku649/36-1).
    Keywords: Clay radiogenic isotopes ; Late Miocene ; South Asian Monsoon ; Chemical weathering
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
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