Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
Search results
55 records were found.
The distribution of glycerol dibiphytanyl glycerol tetraethers (GDGTs), predominantly derived from planktonic Crenarchaeota,
were studied in three age-equivalent Pliocene sapropels as well as in the homogeneous intervals, below and above the sapropel. In
both the homogeneous intervals and sapropels the dominance of GDGT-0 and crenarchaeol among the GDGTs indicated their
origin from planktonic Crenarchaeota as it was found in many other marine sediments. In the homogeneous intervals highest
GDGT abundances (normalized to TOC) were measured at the easternmost study Site 967 of the eastern Mediterranean Sea and
decreased at the central and western Sites 969 and 964. Within the three studied sapropels large variations in GDGT abundance
were observed. The newly established sea surface temperature (SST) proxy, the TEX86 index, derived from G...
Marine organic-rich sediments are important for long-term carbon sequestration, and as a source of fossil
hydrocarbons, but the processes underlying their formation remain elusive. We present a multiproxy analysis of
a relatively recent, well-preserved Mediterranean organic-rich deposit known as sapropel S5, which formed
124–119 thousand years ago (ka B.P., where B.P. references year 1950). Combining planktonic foraminiferal
abundance records with stable isotope and organic biomarker data, we reconcile the apparently contradicting
coexistence of deep-dwelling foraminiferal faunas with green sulphur bacteria that indicate photic zone euxinia.
S5 started with a rapid freshwater-induced increase of density stratification that inhibited vertical mixing and
deepwater ventilation. Through the first 900 years, anoxic to euxinic deepwater cond...
Recently we proposed a new organic sea surface temperature proxy, TEX86, based on the distribution of archaeal tetraether lipids. Here, we have examined the effect of oxic degradation and maturity on this new temperature proxy. Our results show that oxic degradation does not appear to affect the TEX86 values within the analytical error. Hydrous pyrolysis experiments suggest that thermal maturity does have an effect on TEX86. Sediments with relatively high amounts of 22S-hopanes [22S/(22S+22R) ratios > 0.1] or 17,21(H)-hopanes [/(++) ratios <0.5] may have TEX86 values which are biased towards lower values and, thus, lower sea surface temperatures.
Marine organic-rich sediments are important for long-term carbon sequestration, and as a source of fossil hydrocarbons, but the processes underlying their formation remain elusive. We present a multiproxy analysis of a relatively recent, well-preserved Mediterranean organic-rich deposit known as sapropel S5, which formed 124–119 thousand years ago (ka B.P., where B.P. references year 1950). Combining planktonic foraminiferal abundance records with stable isotope and organic biomarker data, we reconcile the apparently contradicting coexistence of deep-dwelling foraminiferal faunas with green sulphur bacteria that indicate photic zone euxinia. S5 started with a rapid freshwater-induced increase of density stratification that inhibited vertical mixing and deepwater ventilation. Through the first 900 years, anoxic to euxinic deepwater cond...
The Black Sea and the Cariaco Basin are both large, euxinic marine basins in which methane concentrations are high and where anaerobic oxidation of methane (AOM) is an important part of the carbon cycle. AOM can be recognized by lipid biomarkers that are specific to methanotrophic archaea involved and by strongly 13C-depleted isotope compositions consistent with uptake of 13C-depleted methane-derived carbon. The working hypothesis for our investigation was that AOM in both the Black Sea and Cariaco Basin would generate measurable diagnostic biomarkers and isotope depletions. To test this hypothesis, we analyzed particulate matter and surface sediments for intact glycerol dialkyl glycerol tetreaethers (GDGTs), components of archaeal membrane lipids, and measured stable carbon isotope compositions of their constituent biphytanes. Several...
It has recently been shown that membrane lipids of marine crenarchaeota, a ubiquitous and abundant component of plankton, occur in relatively high concentrations in recent and ancient sediments. In this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments. We especially focussed on temperature, as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature. Indeed, a significant linear correlation (r2=0.92) is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures. This suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to t...
Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and branched glycerol dialkyl diethers are main membrane constituents of cultured hyperthermophilic archaea and eubacteria, respectively, and are found in environments with temperatures >60°C. Recently, we developed a new technique for the analysis of intact core tetraether lipids in cell material and sediments. The application of this technique to recent sediments shows that known and newly identified isoprenoid and branched GDGTs are widespread in low-temperature environments (<20°C) and are structurally far more diverse than previously thought. Their distribution indicates the ubiquitous environmental presence of as yet uncultivated, nonthermophilic organisms that may have independently evolved from hyperthermophilic archaea and eubacteria. The structures of some of the new GD...
High performance liquid chromatography with photodiode array UV–Vis detection and atmospheric pressure chemical
ionization mass spectrometry was used to analyze sediment samples from the meromictic Ace Lake (Antarctica), as
well as a Pliocene sapropel from the Mediterranean Sea and a Miocene marl from the Vena del Gesso formation (Italy).
The Ace Lake samples contained intact chlorobactene, isorenieratene, γ- and β-carotene and two series of carotenoid
breakdown products. The first and more abundant series was identified as aryl (φ)-carotenals of increasing chain length
(C13, C15, C18, C20, C22, C25, C27, C30, and C32) on the basis of their UV–Vis and mass spectra. They appear to be
formed from chlorobactene through oxidative cleavage of the double bonds of the polyene chain. The minor series
(β-carotenals) was also identified, and may...
Repeated semi-preparative normal-phase HPLC was performed to isolate selected biomarkers from sediment extracts for radiocarbon analysis. Flow injection analysis mass spectrometry was used for rapid analysis of collected fractions to evaluate the separation procedure, taking only 1 min per fraction. In this way 100 1000 g of glycerol dialkyl glycerol tetraethers, sterol fractions and chlorophyll-derived phytol were isolated from typically 100 g of marine sediment, i.e., in sufficient quantities for radiocarbon analysis, without significant carbon isotopic fractionation or contamination.
