| 1. |
- Schouten, Stefan, et al.
(författare)
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An interlaboratory study of TEX86 and BIT analysis of sediments, extracts, and standard mixtures
- 2013
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Ingår i: Geochemistry Geophysics Geosystems. - 1525-2027. ; 14:12, s. 5263-5285
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Tidskriftsartikel (refereegranskat)abstract
- Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility +/- 3-4 degrees C when translated to temperature) but a large spread in BIT measurements (reproducibility +/- 0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0 degrees C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the true (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
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| 2. |
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| 3. |
- Moros, Matthias, et al.
(författare)
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Giant saltwater inflow in AD 1951 triggered Baltic Sea hypoxia
- 2024
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Ingår i: Boreas. - : John Wiley & Sons. - 0300-9483 .- 1502-3885. ; 53:2, s. 125-138
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Tidskriftsartikel (refereegranskat)abstract
- A marked sedimentological change in subsurface sediments from the entire Baltic Proper, the Baltic Sea, has been previously noted. Our detailed work on a variety of multi-cores from basin-wide transects indicates that this sedimentological change was caused by a large shift in environmental conditions during the 1950s. Until the 1950s, the water column was rather weakly stratified and winter-time convection - although weakened during the post Little Ice Age warming - was still able to ventilate the bottom waters of the Baltic Proper. Therefore, complete sediment sequences only accumulated in calm waters deeper than 150-160 m. High-resolution benthic foraminiferal records of subsurface sediments obtained along the saline water inflow pathway in combination with historical data indicate that the depositional environment changed drastically owing to the giant saline water inflow in AD 1951. The accompanied sharpening of the halo(pycno)cline triggered a collapse in the ventilation of the basin, resulting in oxygen-deficient bottom waters. This deficiency, in turn, caused the onset of phosphate release from the sediments, which accelerated primary production. The ventilation collapse also enabled the onset of deposition of organic carbon-rich sediments also in shallower water areas as calm conditions prevailed up to the modern winter mixing depth (60-70 m). A slight return to Little Ice Age-type conditions was observed during the late 1980s when temperatures decreased and stratification weakened. These conditions gave rise to a reduction in hypoxic areas and to a bottom-water ventilation, most pronounced in the north of the so-called Baltic Sea Klint, a hydrographic and topographic barrier. However, the general environmental conditions essentially have not changed since the 1950s. Remarkably, external (temperature and stratification) in combination with internal factors (e.g. ventilation collapse and phosphate release) were able to change the redox conditions of the Baltic Proper from oxic to hypoxic within less than 10 years. A marked sedimentological change seen in sub-recent seabed sediment cores from the entire Baltic proper can be attributed to large hydrographic and environmental changes that started at the end of the Little Ice Age and were accelerated by a rapid change in stratification resulting from the massive inflow of saline water in AD 1951. The increase in stratification caused a collapse of the already weakened vertical winter-time deep water convection leading to hypoxia in the bottom waters, which in turn forced a sudden phosphate release from the sediments and increased primary production in the late 1950s.image
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| 4. |
- Moros, Matthias, et al.
(författare)
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Is 'deep-water formation' in the Baltic Sea a key to understanding seabed dynamics and ventilation changes over the past 7,000 years?
- 2020
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 550, s. 55-65
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Tidskriftsartikel (refereegranskat)abstract
- Numerous hydro-acoustic studies of the seabed of the Baltic Sea have revealed the unusual occurrence of sediment contourite drifts and re-suspension at greater water depths. In addition, radiocarbon dating of bulk sediments indicates significant age reversals. We present new geophysical, sediment proxy data (including extensive radiocarbon dating) and hydrographic measurements, which are combined with results of numerous marine geological studies performed during the last decades. These data indicate that a deep-water formation process significantly affected the seabed dynamics during regional climatically cold phases during the last c. 7,000 years. We propose that, during the colder periods (e.g. the Little Ice Age), newly formed bottom waters likely caused widespread re-suspension of organic carbon-rich laminated sediments that were deposited during the preceding warm periods in shallower areas, and this material was transported to and re-deposited in the deeper parts of the Baltic Sea sub-basins. In our scenario, a topographic feature, known as the Baltic Sea Klint, acted as a hydrographic barrier for deep-water formed in the northern Baltic. Thus, during the cold periods increased lateral matter influx from the northern Baltic led to the accumulation of much thicker macroscopically homogenous clayey sediments in sub-basins north of the Klint. Moreover, deep-water formation produced bottom currents that led to the formation of sediment contourite drifts at water depths of> 200 m in the Bothnian Sea, the Aland Deep and northern central Baltic Sea sub-basins. Bottom water ventilation in the Baltic Sea is generally assumed to be determined solely by the inflow of oxygen-rich, saline water from the North Sea, but we challenge this assumption and postulate that deep-water formation is a key process that ventilates the bottom waters of the Baltic Sea during climatically cold periods with substantial implications for its sedimentary archive.
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| 5. |
- van der Meer, Marcel T. J., et al.
(författare)
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Distribution and isotopic composition of bacterial lipid biomarkers in microbial mats from a sulfidic Icelandic hot spring
- 2008
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 1873-5290 .- 0146-6380. ; 39:8, s. 1015-1019
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Tidskriftsartikel (refereegranskat)abstract
- Green, nonsulfur-like bacteria (GNSLB) and cyanobacteria form major components of microbial mats in both sulfidic and non-sulfidic hot springs and have been mainly studied in hot springs of Yellowstone National Park (YNP). These organisms synthesize specific lipid biomarkers Such as wax esters and long chain polyunsaturated alkenes (GNSLB) and heptadecane (cyanobacteria). We analyzed the lipid distribution and their stable carbon isotopic composition in sulfidic Icelandic hot spring microbial mats known to contain GNSLB and cyanobacteria. Based on the lipid distribution, it seems that the GNSLB in these mats are closely related to Chloroflexus aurantiacus. The stable carbon isotopic composition of the bulk biomass and wax esters suggests mainly autotrophic growth by GNSLB in this sulfidic hot spring. However, the stable carbon isotopic composition of hentriacontatriene in the two GNSLB mats suggests an alternative carbon source for the C-31:3 alkene producing GNSLB from that in YNP. The isotopic composition of cyanobacterial biomarkers in the mat most distant from the source of the hot spring seems to suggest inorganic carbon limitation for cyanobacteria, possibly because they grow underneath the GNSLB in these sulfidic hot spring inverted microbial mats. (c) 2008 Elsevier Ltd. All rights reserved.
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