58 research outputs found
A palynofacies study of past fluvio-deltaic and shelf environments, the Oligocene-Miocene succession, North Sea Basin:A reference data set for similar Cenozoic systems
The Jurassic-Cretaceous lithostratigraphy of Kilen, Kronprins Christian Land, eastern North Greenland
In situ observed relationships between snow and ice surface skin temperatures and 2 m air temperatures in the Arctic
To facilitate the construction of a satellite-derived 2 m air temperature
(T2 m) product for the snow- and ice-covered regions in the
Arctic, observations from weather stations are used to quantify the
relationship between the T2 m and skin temperature
(Tskin). Multiyear data records of simultaneous Tskin
and T2 m from 29 different in situ sites have been analysed for
five regions, covering the lower and upper ablation zone and the accumulation
zone of the Greenland Ice Sheet (GrIS), sea ice in the Arctic Ocean, and
seasonal snow-covered land in northern Alaska. The diurnal and seasonal
temperature variabilities and the impacts from clouds and wind on the
T2 m–Tskin differences are quantified.
Tskin is often (85 % of the time, all sites weighted equally)
lower than T2 m, with the largest differences occurring when the
temperatures are well below 0 ∘C or when the surface is melting.
Considering all regions, T2 m is on average
0.65–2.65 ∘C higher than Tskin, with the largest
differences for the lower ablation area and smallest differences for
the seasonal snow-covered sites. A negative net surface radiation balance generally cools
the surface with respect to the atmosphere, resulting in a surface-driven
surface air temperature inversion. However, Tskin and
T2 m are often highly correlated, and the two temperatures can
be almost identical (<0.5 ∘C difference), with the smallest
T2–Tskin differences around noon and early afternoon during
spring, autumn and summer during non-melting conditions. In general, the
inversion strength increases with decreasing wind speeds, but for the sites
on the GrIS the maximum inversion occurs at wind speeds of about
5 m s−1 due to the katabatic winds. Clouds tend to reduce the vertical
temperature gradient, by warming the surface, resulting in a mean overcast
T2 m–Tskin difference ranging from −0.08 to
1.63 ∘C, with the largest differences for the sites in the
low-ablation zone and the smallest differences for the seasonal snow-covered
sites. To assess the effect of using cloud-limited infrared satellite
observations, the influence of clouds on temporally averaged
Tskin has been studied by comparing averaged clear-sky
Tskin with averaged all-sky Tskin. To this end, we
test three different temporal averaging windows: 24 h, 72 h and 1 month.
The largest clear-sky biases are generally found when 1-month averages are
used and the smallest clear-sky biases are found for 24 h. In most cases,
all-sky averages are warmer than clear-sky averages, with the smallest bias
during summer when the Tskin range is smallest.</p
Paleocene/Eocene carbon feedbacks triggered by volcanic activity
The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state
Groundwater table fluctuations recorded in zonation of microbial siderites from end-Triassic strata
In a terrestrial Triassic–Jurassic boundary succession of southern Sweden, perfectly zoned sphaerosiderites are restricted to a specific sandy interval deposited during the end-Triassic event. Underlying and overlying this sand interval there are several other types of siderite micromorphologies, i.e. poorly zoned sphaerosiderite, spheroidal (ellipsoid) siderite, spherical siderite and rhombohedral siderite. Siderite overgrowths occur mainly as rhombohedral crystals on perfectly zoned sphaerosiderite and as radiating fibrous crystals on spheroidal siderite. Concretionary sparry, microspar and/or micritic siderite cement postdate all of these micromorphologies. The carbon isotope composition of the siderite measured by conventional mass spectrometry shows the characteristic broad span of data, probably as a result of multiple stages of microbial activity. SIMS (secondary ion mass spectrometry) revealed generally higher δ13C values for the concretionary cement than the perfectly zoned sphaerosiderite, spheroidal siderite and their overgrowths, which marks a change in the carbon source during burial. All the various siderite morphologies have almost identical oxygen isotope values reflecting the palaeo-groundwater composition. A pedogenic/freshwater origin is supported by the trace element compositions of varying Fe:Mn ratios and low Mg contents. Fluctuating groundwater is the most likely explanation for uniform repeated siderite zones of varying Fe:Mn ratios reflecting alternating physiochemical conditions and hostility to microbial life/activity. Bacterially mediated siderite precipitation likely incorporated Mn and other metal ions during conditions that are not favourable for the bacteria and continued with Fe-rich siderite precipitation as the physico-chemical conditions changed into optimal conditions again, reflecting the response to groundwater fluctuations
Magnetostratigraphically-calibrated dinoflagellate cyst bioevents for the uppermost Eocene to lowermost Miocene of the western North Atlantic (IODP Expedition 342, Paleogene Newfoundland sediment drifts)
Autothermal reforming of palm empty fruit bunch bio-oil: thermodynamic modelling
This work focuses on thermodynamic analysis of the autothermal reforming of palm empty fruit bunch (PEFB) bio-oil for the production of hydrogen and syngas. PEFB bio-oil composition was simulated using bio-oil surrogates generated from a mixture of acetic acid, phenol, levoglucosan, palmitic acid and furfural. A sensitivity analysis revealed that the hydrogen and syngas yields were not sensitive to actual bio-oil composition, but were determined by a good match of molar elemental composition between real bio-oil and surrogate mixture. The maximum hydrogen yield obtained under constant reaction enthalpy and pressure was about 12 wt% at S/C = 1 and increased to about 18 wt% at S/C = 4; both yields occurring at equivalence ratio Φ of 0.31. The possibility of generating syngas with varying H2 and CO content using autothermal reforming was analysed and application of this process to fuel cells and Fischer-Tropsch synthesis is discussed. Using a novel simple modelling methodology, reaction mechanisms were proposed which were able to account for equilibrium product distribution. It was evident that different combinations of reactions could be used to obtain the same equilibrium product concentrations. One proposed reaction mechanism, referred to as the ‘partial oxidation based mechanism’ involved the partial oxidation reaction of the bio-oil to produce hydrogen, with the extent of steam reforming and water gas shift reactions varying depending on the amount of oxygen used. Another proposed mechanism, referred to as the ‘complete oxidation based mechanism’ was represented by thermal decomposition of about 30% of bio-oil and hydrogen production obtained by decomposition, steam reforming, water gas shift and carbon gasification reactions. The importance of these mechanisms in assisting in the eventual choice of catalyst to be used in a real ATR of PEFB bio-oil process was discussed
Review of Survey activities 2012: Drowning of the Miocene Billund delta, Jylland: land–sea fluctuations during a global warming event
Review of Survey activities 2015: Miocene deposits at Silkeborg, Jylland, and their influence on hydrology
- …