Impact of temperature on long chain diol and mid-chain hydroxy methyl alkanoate composition in Proboscia diatoms: Results from culture and field studies

Long chain 1,14-diols and 12-hydroxy methyl alkanoates are biomarker lipids for Proboscia diatoms and occur widely in Quaternary sediments. To determine the effect of temperature on the lipid composition of these algae, a new Proboscia sp. culture grown at 8 °C and Proboscia indica cultures grown at 18, 21, 24 and 27 °C were examined. The results were combined with lipid data from a P. indica culture and a Proboscia alata culture, grown at 20 and 2 °C, respectively, from previous studies. The data showed a strong relationship between long chain diol and 12-hydroxy methyl alkanoate composition and growth temperature, i.e. the chain length increases and the degree of unsaturation of long chain 1,14-diols decreases with increasing growth temperature. To determine the effect of temperature on Proboscia lipid compositions in natural environments, we also analyzed fossil long chain 1,14-diols and 12-hydroxy methyl alkanoates in surface sediments derived from Proboscia diatoms living in the water column of the eastern South Atlantic. The results indicate a significant relationship between sea surface temperature and chain length distribution of saturated long chain diols, but also suggest that the relative abundances of unsaturated long chain diols and 12-hydroxy methyl alkanoates in sediments are predominantly determined by factors other than temperature.     

Release of sulfur- and oxygen-bound components from a sulfur-rich kerogen during simulated maturation by hydrous pyrolysis

An immature sulfur-rich marl from the Gessosso-solfifera Formation of the Vena del Gesso Basin (Messinian, Italy) has been subjected to hydrous pyrolysis (160 to 330°C) to simulate maturation under natural conditions. The kerogen of the unheated and heated samples was isolated and the hydrocarbons released by selective chemical degradation (Li/EtNH₂ and HI/LiAlH₄) were analysed to allow a study of the fate of sulfur- and oxygen-bound species with increasing temperature. The residues from the chemical treatments were also subjected to pyrolysis–GC to follow structural changes in the kerogens. In general, with increasing hydrous pyrolysis temperature, the amounts of sulfide- and ether-bound components in the kerogen decreased significantly. At the temperature at which the generation of expelled oil began (260°C), almost all of the bound components initially present in the unheated sample were released from the kerogen. Comparison with an earlier study of the extractable organic matter using a similar approach and the same samples provides molecular evidence that, with increasing maturation, solvent-soluble macromolecular material was initially released from the kerogen, notably as a result of thermal cleavage of weak carbon–heteroatom bonds (sulfide, ester, ether) even at temperatures as low as 220°C. This solvent-soluble macromolecular material then underwent thermal cleavage to generate hydrocarbons at higher temperatures. This early generation of bitumen may explain the presence of unusually high amounts of extractable organic matter of macromolecular nature in very immature S-rich sediments.     

Estimation of impact of climate change on the peak discharge probability of the river Rhine

RHINEFLOW is a GIS based water balance model that has been developed to study the changes in the water balance compartments of the river Rhine basin on a monthly time basis. The model has been designed to study the sensitivity of the Rhine discharge to a climate change. The calculated discharge has been calibrated and validated on the period 1956 to 1980. For this period the model efficiency of RHINEFLOW is between 0.74 and 0.81 both for the entire Rhine and for its tributaries. Also calculated values for variations in other compartments, e.g. snow storage and actual evapotranspiration, were in good agreement with the measured values.Since a high correlation between monthly discharge and peak discharge was found for the period 1900–1980 The RHINEFLOW model is used to assess the probability of exceedence for discharge peaks under possible future climate conditions.The probabilities of exceedence were calculated from the conditional probabilities of peak discharges for a series of 15 classes of monthly discharges. Comparison of a calculated frequency distribution of high discharge peaks with observed peaks in a test series showed that the method performs well.Scenarios for temperature changes between 0 °C and plus 4 °C and precipitation changes between plus 20% and minus 20% have been applied. Within this range flood frequencies are more sensitive for a precipitation change than for a temperature change. The present two-year return period peak flow (6500–7000 m³/s) decreases by about 6% due to a temperature rise of 4 °C; a precipitation decrease of 20% leads to 30% lower two-year peaks whilst 20% precipitation increase raises them by approximately 30%.Application of a Business As Usual (BAU) and an Accelerated Policy (AP) climate scenario resulted in a significant increase in probability of peak flows for the BAU scenario, while for the AP scenario no significant change could be found. Due to sampling errors, accurate estimations of recurrence times of discharge peaks7000 m³/s require a longer sampling time series than 90 years. For management purposes the method can be applied to estimate changes of probabilities of events with a relatively long recurrence time.     

Biomarker lipids of the freshwater fern Azolla and its fossil counterpart from the Eocene Arctic Ocean

Eocene sediments recovered from the Lomonosov Ridge in the central Arctic Ocean during Integrated Ocean Drilling Program Expedition 302 contain high amounts of fossil remains of the free floating freshwater fern Azolla. Both extant Azolla and the sediments from the Arctic Azolla interval were found to contain relatively high quantities of compounds identified as 1,ω20 C₃₀–C₃₆ diols. Furthermore, structurally related mid-chain hydroxy fatty acids, long chain n-alkanols and keto-ols were discovered. The different series have a common feature: there is always a hydroxy group at the ω20 position. In addition, structurally related C₂₉ ω20,ω21 diols, C₂₉ 1,20,21 triols, C₂₉ dihydroxy fatty acids as well as a series of wax esters containing these mono- and dihydroxy lipids are reported. Selective extraction of Azolla surface lipids revealed that these compounds are most likely present in the leaf waxes of the fern. The suite of long-chain, mid-chain ω20 hydroxy wax constituents is described for the first time. As they are well preserved in the Eocene sediments, these lipids may serve as palaeo-environmental indicators of the Arctic Azolla interval and as markers for the past occurrence of Azolla in general.     

Occurrence of gorgosterol in diatoms of the genus Delphineis

The presence of the C₃₀ sterol gorgosterol (22,23-methylene-23,24-dimethylcholest-5-en-3ß-ol) and its analogues in some marine and freshwater environments is generally associated with invertebrate animals or dinoflagellates since there have been no reports of them in other microalgal classes. Here we show that two unialgal cultures of different species of the marine diatom Delphineis contain gorgosterol in addition to sterols more commonly found in diatoms. Our findings suggest that some reports of gorgosterol in seawater and marine sediments may well have an origin, at least in part, from diatoms.     

The influence of oxic degradation on the sedimentary biomarker record I: evidence from Madeira Abyssal Plain turbidites

Free and ester-bound lipid biomarkers were analysed in oxidised and unoxidised parts of four distinct turbidites from the Madeira Abyssal Plain (MAP), which contained 1 to 2% organic carbon homogeneously distributed throughout the turbidites at the time they were deposited. These turbidites are well suited to study the effects of oxic degradation on lipid biomarkers without the complicating influence of varying organic matter sources, sedimentation rates, or bioturbation. One sample from the oxidised turbidite was compared with two samples from the unoxidised part of each turbidite. Postdepositional oxic degradation decreased concentrations of biomarkers by several orders of magnitude. The ester-bound lipids were degraded to a far lesser extent than their free counterparts were. The extent of degradation of different compounds differed substantially. Within a specific class of biomarkers, degradation also took place to a different extent, altering their distributions. This study shows that oxic degradation of the organic matter may have a profound effect on the biomarker fingerprint and may result in a severe bias in, for example, the interpretation of organic matter sources and the estimation of the palaeoproductivity of specific groups of phytoplankton.     

Modeling permafrost distribution over the river basins of Mongolia using remote sensing and analytical approaches

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