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  • 1
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    Core-top calibration of the lipid-based UK'37 and TEX86 temperature proxies on the southern Italian shelf (SW Adriatic Sea, Gulf of Taranto) (2010)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 300, pp. 112-124, ISSN: 0012-821X
    Details
    Publikationsdatum: 2019-07-17
    Beschreibung: The Mediterranean Sea is at the transition between temperate and tropical air masses and as such of importance for studying climate change. The Gulf of Taranto and adjacent SW Adriatic Sea are at the heart of this region. Their sediments are excellently suited for generating high quality environmental records for the last millennia with a sub-decadal resolution. The quality of these records is dependent on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. Here, we examine and calibrate the UK′37 and TEX86 lipid-based temperature proxies in 48 surface sediments and relate these to ambient sea surface temperatures and other environmental data. The UK′37 -based temperatures in surface sediments reflect winter/spring sea surface temperatures in agreement with other studies demonstrating maximum haptophyte production during the colder season. The TEX86-based temperatures for the nearshore sites also reflect winter sea surface temperatures. However, at the most offshore sites, they correspond to summer sea surface temperatures. Additional lipid and environmental data including the distribution of the BIT index and remote-sensed chlorophyll-a suggest a shoreward increase of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal abundance by primary productivity, particle loading in surface waters and/or overprint by a cold-biased terrestrial TEX86 signal. As such the offshore TEX86 values seem to reflect a true summer signal to the effect that offshore UK′37 and TEX86 reconstruct winter and summer temperature, respectively, and hence provide information on the annual temperature amplitude.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 2
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    Radiocarbon and 230Th data reveal rapid redistribution and temporal changes in sediment focussing at a North Atlantic drift (2011)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 301, pp. 373-381, ISSN: 0012-821X
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    Publikationsdatum: 2019-07-17
    Beschreibung: In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transportedmaterial are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (230Thxs)measurements on four sediment cores retrieved in 1649–2879 mwater depth fromtwo such high accumulation drift deposits in the Northeast Atlantic, Björn and Gardar Drifts.While 230Thxs inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation ofmarine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results showthat although focussing factors calculated frombulk sediment 230Thxs inventoriesmay allowuseful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use ofmultiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 3
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    Long chain 1,13- and 1,15-diols as a potential proxy for palaeotemperature reconstruction (2012)
    ELSEVIER SCIENCE BV
    In:  EPIC3Geochimica et Cosmochimica Acta, ELSEVIER SCIENCE BV, 84, pp. 204-216, ISSN: 00167037
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    Publikationsdatum: 2019-07-17
    Beschreibung: Although commonly reported in marine and freshwater environments, little is known about the biological sources of long chain alkyl 1,13- and 1,15-diols, and factors controlling their distributions. Here we analyzed the occurrence and distribution of these lipids in a comprehensive set of marine surface sediments and compare their distributions with environmental conditions like sea surface temperature (SST), salinity and nutrient concentrations. Fractional abundances of the C28 1,13-, C30 1,13- and C30 1,15-diols show a strong correlation with SST and based on these results, we propose the Long chain Diol Index (LDI), which expresses the C30 1,15-diol abundance relative to those of C28 1,13-, C30 1,13- and C30 1,15-diols. The LDI shows a strong linear correlation with SST (LDI = 0.033 � SST + 0.095; R2 = 0.969, n = 162) over a temperature range of �3 to 27 �C. Long chain diol distributions in sediments from the South Atlantic close to the Congo River outflow (West Africa) provided a 43 kyr LDI SST record. This record reflects several known climatic events and shows similarities with an alkenone- derived SST record obtained using the same suite of sediments, both in trend and in terms of absolute SST. This confirms the potential of the LDI as a proxy for palaeo-SST reconstruction.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 4
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    The impact of Southern Ocean circulation on the global carbon cycle and Antarctic ice shelf stability (2018)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2018, Washington DC, 2018-12-10-2018-12-14Washington DC, American Geophysical Union
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    Publikationsdatum: 2019-01-06
    Repository-Name: EPIC Alfred Wegener Institut
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  • 5
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    An evaluation of 14C age relationships between co-occurring foraminifera, alkenones, and total organic carbon in continental margin sediments (2006)
    American Geophysical Union
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA1016, doi:10.1029/2004PA001103.
    Beschreibung: Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones and total organic carbon in sediments from the continental margins of Southern Chile, Northwest Africa and the South China Sea were compared with published results from the Namibian margin. Age relationships between the sediment components are site-specific and relatively constant over time. Similar to the Namibian slope, where alkenones have been reported to be 1000 to 4500 years older than co-occurring foraminifera, alkenones were significantly (~1000 yrs) older than co-occurring foraminifera in the Chilean margin sediments. In contrast, alkenones and foraminifera were of similar age (within 2σ error or better) in the NW African and South China Sea sediments. Total-organic-matter and alkenone ages were similar off Namibia (age difference TOC-alkenones: 200-700 years), Chile (100-450 years), and NW Africa (360-770 years), suggesting minor contributions of pre-aged terrigenous material. In the South China Sea total organic carbon is significantly (2000-3000 yrs) older due to greater inputs of pre-aged terrigenous material. Age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter. Physical characteristics of the depositional setting, such as sea-floor morphology, shelf width, and sediment composition, may control the age of co-occurring 2 sediment components. In particular, offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions. Aging of organic matter is promoted by transport. Age offsets are correlated with organic richness, suggesting that formation of organic aggregate is a key process.
    Beschreibung: GM and MK acknowledge financial support from the WHOI postdoctoral scholarship program. This work was funded by NSF grant OCE-0327405.
    Schlagwort(e): Compound-specific radiocarbon dating ; Alkenones ; High accumulation rate sediments
    Repository-Name: Woods Hole Open Access Server
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  • 6
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    On the sedimentological origin of down-core variations of bulk sedimentary nitrogen isotope ratios (2010)
    American Geophysical Union
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA2009, doi:10.1029/2004PA001081.
    Beschreibung: The bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the South China Sea (Site 17940 and Ocean Drilling Program (ODP) Site 1144) differs by up to 〉2‰ during the last glacial period. Given their close proximity, both core sites are located in the same biogeographic zone and nutrient regime, and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions. In an attempt to resolve this offset, we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary δ15N, namely, the variable contribution of inorganic N to bulk N in the sediment and the grain-size dependence of bulk δ15N. We find that neither effect, singly or in combination, is sufficient to explain the significant δ15N offset between the two down-core records. By elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site. This study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts, such as ODP Site 1144.
    Beschreibung: Funding from NSERC Canada (to S.E.C. and M.K.) and NSF (OCE-0214365 and OCE-0318371 to M.J.H. and OCE-0327405 to T.I.E.) is gratefully acknowledged, as well as Woods Hole Oceanographic Institution Postdoctoral Fellowships (M.K. and G.M.), the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry (M.J.H.), and a Geological Society of America student research grant (M.K.).
    Schlagwort(e): Sediment drift ; South China Sea ; Nitrogen isotopes
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 7
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    Aging of marine organic matter during cross-shelf lateral transport in the Benguela upwelling system revealed by compound-specific radiocarbon dating (2010)
    American Geophysical Union
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 8 (2007): Q09004, doi:10.1029/2007GC001603.
    Beschreibung: Organic matter accumulation and burial on the Namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers. Much of the material deposited in depo-centers on the slope ultimately derives from the shelf. Supply of organic matter from the shelf involves selective transport of organic matter. We studied these selective transport processes by analyzing the radiocarbon content of co-occurring sediment fractions. Here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity (phytoplankton-derived alkenones, membrane lipids of pelagic crenarchaeota (crenarchaeol), and calcareous microfossils of planktic foraminifera) in core-top and near-surface sediment samples. The samples were collected on the Namibian margin along a shelf-slope transect (85 to 1040 m) at 24°S and from the upper slope depo-center at 25.5°S. In core-top sediments, alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth. Crenarchaeol, while younger than alkenones, also increased in age with distance offshore. It was concluded that the observed ages were a consequence of cross-shelf transport and associated aging of organic matter. Radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied, pre-aged material present in a sample, highlighting the importance of nepheloid transport for the sedimentation of organic matter over the Namibian margin.
    Beschreibung: This work was funded by NSF grant OCE- 0327405 to T.I.E. and by a Spinoza grant to J.S.S.D. from NWO.
    Schlagwort(e): Compound-specific radiocarbon dating ; Sediment transport
    Repository-Name: Woods Hole Open Access Server
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  • 8
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    Multi-proxy reconstruction of terrigenous input and sea-surface temperatures in the eastern Gulf of Guinea over the last ~35 ka (2012)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 319-32, pp. 35-46, ISSN: 0025-3227
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    Publikationsdatum: 2019-07-17
    Beschreibung: The tight coupling between the atmospheric and oceanic circulation in the equatorial Atlantic region makes this area an important region for paleoclimatic research. Previous studies report the occurrence of large amounts of terrigenous material and soil organic carbon (SOC) within the marine sediments of the eastern Gulf of Guinea. We use the accumulation rates (AR) of branched glycerol dialkyl glycerol tetraethers (GDGTs) to identify variations in SOC delivery to the Niger Fan over the last 35 ka, and compare these records to long-chain n-alkanes as a proxy for higher plant material, to an inorganic proxy for terrigenous input (aluminum AR) and to indicators for the marine productivity (AR of carbonate and crenarchaeol). In addition, sea surface temperatures (SSTs) are calculated based on the TEX86H index and environmental factors affecting the SST-reconstructions are discussed. Our results indicate that Al AR are closely connected to the rate of mean sea level change after 15 ka BP, with an additional influence of the increased monsoonal precipitation and extended vegetation cover corresponding to the African Humid Period (14.8–5.5 ka BP). Branched GDGT AR appears to be determined by shelf erosion in addition to the interplay of monsoonal precipitation and vegetation cover controlling soil erosion. Long-chain n-alkane concentrations clearly show a different trend than the other proxies, which might be due to their predominant eolian transport. Paleo-SSTs show a clear shift from colder temperatures during the last glacial period (20–22 °C) to warmer temperatures during the Holocene (24–26 °C). However, TEX86H -based SSTs are cold-biased compared to recent SSTs and Mg/Ca-based SST reconstructions, which is probably caused by a high seasonality of the Thaumarchaeota, with a maximum productivity of these organisms during the cold summer months. However, a sub-surface production of GDGTs and/or a potential bias of SST reconstruction by terrestrial input could not be completely excluded.
    Repository-Name: EPIC Alfred Wegener Institut
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  • 9
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    Estimating Bioturbation From Replicated Small‐Sample Radiocarbon Ages (2021)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 36(7), ISSN: 2572-4517
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    Publikationsdatum: 2024-06-22
    Beschreibung: Marine sedimentary records are a key archive when reconstructing past climate; however, mixing at the seabed (bioturbation) can strongly influence climate records, especially when sedimentation rates are low. By commingling the climate signal from different time periods, bioturbation both smooths climate records, by damping fast climate variations, and creates noise when measurements are made on samples containing small numbers of individual proxy carriers, such as foraminifera. Bioturbation also influences radiocarbon-based age-depth models, as sample ages may not represent the true ages of the sediment layers from which they were picked. While these effects were first described several decades ago, the advent of ultra-small-sample $^{14}$C dating now allows samples containing very small numbers of foraminifera to be measured, thus enabling us to directly measure the age-heterogeneity of sediment for the first time. Here, we use radiocarbon dates measured on replicated samples of 3-30 foraminifera to estimate age-heterogeneity for five marine sediment cores with sedimentation rates ranging from 2-30 cm kyr$^{-1}$. From their age-heterogeneities and sedimentation rates we infer mixing depths of 10-20 cm for our core sites. Our results show that when accounting for age-heterogeneity, the true error of radiocarbon dating can be several times larger than the reported measurement. We present estimates of this uncertainty as a function of sedimentation rate and the number of individuals per radiocarbon date. A better understanding of this uncertainty will help us to optimise radiocarbon measurements, construct age models with appropriate uncertainties and better interpret marine paleo records.
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    Materialart: Article , isiRev , info:eu-repo/semantics/article
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