1,721,094 research outputs found
Adenosyl-BHP abundances in Vancouver Island and Black Sea total suspended POM
No full textAdenosyl-BHP abundances in Vancouver Island and Black Sea total suspended particulate matter and Cariaco sinking particulate organic matter samples were analyzed to study in situ production in oxygen minimum zones. Water column suspended particulate matter samples were obtained using McLane WTS-LV (standard configuration) in situ filtration systems from Vancouver Island fjords aboard R/V Barnes in 2007 and the Black Sea aboard R/V Knorr (cruise 172/8) in 2003. Sinking particulate organic matter was sampled in sediment traps as part of the CARIACO Ocean Time-Series Program in Cariaco Basin. Adenosyl-BHPs were analyzed in trap A (275 m water depth) and trap B (455 m water depth) for 14-day opening intervals from November 1999 through April 2000 and July 2002 through October 2002
GDGT data in Siberian permafrost deposits
No full textCore lipid GDGT distributions were studied in different North Siberian permafrost deposits to study GDGT diversity and underlying environmental controls. Samples represent various deposit types such as active layer of polygonal tundra soils, fluvial terrace/floodplain sediments, Holocene and Pleistocene thermokarst sediments, and late Pleistocene Ice Complex (Yedoma) and were obtained on Samoylov Island, Kurungnakh Island, Arga Island, Bol'shoy Lyakhovsky Island, and Buor Khaya Peninsula during several field campaigns between 2009 and 2015. Active layer samples of polygonal tundra soils and fluvial terrace/floodplain sediments were sampled using shovels, Holocene and Pleistocene thermokarst sediments and late Pleistocene Ice Complex samples were obtained using drill rigs
Cariaco sinking POM samples
No full textAdenosyl-BHP abundances in Vancouver Island and Black Sea total suspended particulate matter and Cariaco sinking particulate organic matter samples were analyzed to study in situ production in oxygen minimum zones. Water column suspended particulate matter samples were obtained using McLane WTS-LV (standard configuration) in situ filtration systems from Vancouver Island fjords aboard R/V Barnes in 2007 and the Black Sea aboard R/V Knorr (cruise 172/8) in 2003. Sinking particulate organic matter was sampled in sediment traps as part of the CARIACO Ocean Time-Series Program in Cariaco Basin. Adenosyl-BHPs were analyzed in trap A (275 m water depth) and trap B (455 m water depth) for 14-day opening intervals from November 1999 through April 2000 and July 2002 through October 2002
Organic geochemical and palynological evidence for Holocene natural and anthropogenic environmental change at Lake Dojran (Macedonia/Greece)
No full textIn this study, we present lipid biomarker and palynological data for a sediment core from Lake Dojran (Macedonia/Greece), which covers the entire Holocene period. We analyzed vascular plant-derived n-alkanes, combustion-derived polycyclic aromatic hydrocarbons (PAHs), fecal steroids, and bacterial and archaeal glycerol dialkyl glycerol tetraether (GDGT) lipids in concert with microcharcoal and pollen assemblages to reconstruct climatic, environmental, and human impact in the Dojran catchment and the greater Dojran area. Overall, our results suggest a relationship between anthropogenic activity and environmental/climatic change since increased human impact corresponds to phases of higher humidity and high lake levels at Lake Dojran. During the early Holocene, the record reveals increasing temperatures and humidity and concurrent increasing vegetation cover and runoff/soil erosion, respectively. Following a thermal maximum during the middle early Holocene, temperatures decrease gradually until present. The middle-Holocene at Lake Dojran is characterized by relatively stable environmental conditions followed by greater climatic instability and strong anthropogenic overprint during the late-Holocene. The fecal stanol record reveals phases of increased human impact during the early Bronze Age, the late Bonze/early Iron Age, and the Middle Ages. A phase of low stanol and PAH concentrations from the late Iron Age until the early Middle Ages is either related to ecosystem changes and/or changes in settlement pattern since concurrent pollen data indicate intensified land use. Human impact re-intensified during the Middle Ages with some variability probably related to climatic variations of the Medieval Warm Period' and the Little Ice Age'
14C specific radiocarbon ages and bulk ages accompanied by geochemical proxys from surface sediment samples in the Black Sea
No full textTransfer of organic carbon (OC) from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport. Before transport, however, terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils. Using compound-specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated.
Here we show compound-specific radiocarbon (14C) ages of terrigenous biomarkers and bulk 14C ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the Black Sea. 14C ages of long chain n-alkanes, long chain n-fatty acids and total organic carbon (TOC) are highest in front of the river mouths, correlating well with BIT (branched and isoprenoid tetraether) indices, which indicates contribution of pre-aged, soil-derived terrigenous organic matter. The radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter. Average terrestrial residence times of vascular plant biomarkers deduced from n-C29+31 alkanes and n-C28+30 fatty acids ages from stations directly in front of the river mouths range from 900 ± 70 years to 4400 ± 170 years. These average residence times correlate with size and topography in climatically similar catchments, whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the Black Sea catchment. Along-transect data imply petrogenic contribution of n-C29+31 alkanes and input via different terrigenous biomarker transport modes, i.e., riverine and aeolian, resulting in aged biomarkers at offshore core locations. Because n-C29+31 alkanes show contributions from petrogenic sources, n-C28+30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers. Moreover, sedimentary n-C28 and n-C30 fatty acids appear clearly much less influenced by autochthonous sources than n-C24 and n-C26 fatty acids as indicated by increasing radiocarbon ages with increasing chain-length and are, thus, more representative as vascular plant biomarkers
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Elemental composition of marine and terrestrial sedimentary archives from sub-Antarctic South Georgia
No full textThe dataset comprises elemental data that was obtained on sediment samples from sub-Antarctic South Georgia. The sediments were collected from a range of different sites, including lakes, peat deposits, a marine inlet and a fjord during RV Polarstern expedition PS81 in 2013. Prior to the geochemical analyses reported here, the sediments were freeze-dried and ground. More details on the study sites, sampling and data evaluation can be found in Berg et al. (submitted manuscript).
Total organic carbon (TOC) was analyzed with a DIMATOC 200 (DIMATEC Corp., Canada) analyser. The TOC concentration is derived from the difference between total carbon (TC) and total inorganic carbon (TIC). Total carbon (C), total nitrogen (N) and sulfur (S) were analyzed using a Vario Micro Cube combustion elemental analyser (Elementar, Germany)
Alkanol composition of marine and terrestrial sedimentary archives from sub-Antarctic South Georgia
No full textThe dataset comprises alkanol composition data that was obtained on sediment samples from sub-Antarctic South Georgia. The sediments were collected from a range of different sites, including lakes, peat deposits, a marine inlet and a fjord during RV Polarstern expedition PS81 in 2013. Prior to the geochemical analyses reported here, the sediments were freeze-dried and ground. More details on the study sites, sampling and data evaluation can be found in Berg et al. (submitted manuscript).
Alkyl lipid biomarkers were extracted by accelerated solvent extraction (ASE 300, Thermo, USA) with dichloromethane and methanol (DCM, MeOH; 9:1, v/v at 120°C, 75 bar) (cores Co1305, PS81/283, and Co1308) or via consecutive ultrasonication in DCM:Hexan (1:1), MeOH:DCM (1:1) and MeOH (core Co1306 and the peat and soil samples).
The total lipid extract (TLE) was saponified with 0.5 M KOH in MeOH and water (9:1, v/v) at 80°C for 2 h. Neutral lipids (NL) were extracted from the TLE with dichloromethane by liquid-liquid phase separation. Alkanes were purified from NL by silica gel column chromatography (SiO2, deactivated, mesh-size 60) by elution with hexane and alkanols by elution with chloroform. Prior to analysis by gas chromatography (GC, Agilent 7890B, Agilent Technologies, USA) equipped with a flame ionization detector (FID), alkanols were acetylated. Alkanols were identified and quantified against authentic external standards. Concentrations are given as fractional abundances for the compound class
N-alkane composition of marine and terrestrial sedimentary archives from sub-Antarctic South Georgia
No full textThe dataset comprises N-alkane composition data that was obtained on sediment samples from sub-Antarctic South Georgia. The sediments were collected from a range of different sites, including lakes, peat deposits, a marine inlet and a fjord during RV Polarstern expedition PS81 in 2013. Prior to the geochemical analyses reported here, the sediments were freeze-dried and ground. More details on the study sites, sampling and data evaluation can be found in Berg et al. (submitted manuscript).
Alkyl lipid biomarkers were extracted by accelerated solvent extraction (ASE 300, Thermo, USA) with dichloromethane and methanol (DCM, MeOH; 9:1, v/v at 120°C, 75 bar) (cores Co1305, PS81/283, and Co1308) or via consecutive ultrasonication in DCM:Hexan (1:1), MeOH:DCM (1:1) and MeOH (core Co1306 and the peat and soil samples).
The total lipid extract (TLE) was saponified with 0.5 M KOH in MeOH and water (9:1, v/v) at 80°C for 2 h. Neutral lipids (NL) were extracted from the TLE with dichloromethane by liquid-liquid phase separation. Alkanes were purified from NL by silica gel column chromatography (SiO2, deactivated, mesh-size 60) by elution with hexane. Analysis was conducted by gas chromatography (GC, Agilent 7890B, Agilent Technologies, USA) equipped with a flame ionization detector (FID). Alkanes were identified and quantified against authentic external standards. Concentrations are given as fractional abundances for the compound class
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