Carbon chemistry of cretaceous marine organic matter

Geochemical studies of Cretaceous strata rich in organic carbon (OC) from Deep Sea Drilling Project (DSDP) sites and several land sections reveal several consistent relationships among amount of OC, hydrocarbon generating potential of kerogen (measured by pyrolysis as the hydrogen index, HI), and the isotopic composition of the OC. First, there is a positive correlation between HI and OC in strata that contain more than about 1% OC. Second, percent OC and HI often are negatively correlated with carbon isotopic composition (delta13C) of kerogen. The relationship between HI and OC indicates that as the amount of organic matter increases, this organic matter tends to be more lipid rich reflecting the marine source of the organic matter. Cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter. Average delta13C values for organic matter from most Cretaceous sites are between -26 and -28 per mil, and values heavier than about -25 per mil occur at very few sites. Most of the delta13C values of Miocene to Holocene OC-rich strata and modern marine plankton are between -16 to -23 per mil. Values of delta13C of modern terrestrial organic matter are mostly between -23 and -33 per mil. The depletion of terrestial OC in 13C relative to marine planktonic OC is the basis for numerous statements in the literature that isotopically light Cretaceous organic matter is of terrestrial origin, even though other organic geochemical and(or) optical indicators show that the organic matter is mainly of marine origin. A difference of about 5 per mil in delta13C between modern and Cretaceous OC-rich marine strata suggests either that Cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis, or that OC derived from Cretaceous marine plankton was isotopically lighter by about 5 per mil relative to modern plankton OC. Diagenesis does not produce a significant shift in delta13C in Miocene to Holocene sediments, and therefore probably did not produce the isotopically light Cretaceous OC. This means that Cretaceous marine plankton must have had delta13C values that were about 5 per mil lighter than modern marine plankton, and at least several per mil lighter than Cretaceous terrestrial vegetation. The reason for these lighter values, however, is not obvious. It has been proposed that concentrations of CO2 were higher during the middle Cretaceous, and this more available CO2 may be responsible for the lighter delta13C values of Cretaceous marine organic matter.

Seawater carbonate chemistry and particulate organic particles during an incubation experiments with natural phytoplankton community, 2002

Incubation experiments with natural phytoplankton revealed a relationship between CO2 concentration and the production of transparent exopolymer particles (TEP), with TEP production being linearly related to theoretical CO2 uptake rates. The effect of different CO2 concentrations on TEP production was examined during incubation experiments with natural phytoplankton sampled at two different locations in the central Baltic Sea in summer 1999.

Desiccant capability of organic xerogels: Surface chemistry vs porous texture

Resorcinol-Formaldehyde xerogels are organic polymers that can be easily tailored to have specific properties. These materials are composed of carbon, hydrogen and oxygen, and have a surface that is very rich in oxygen functionalities, and is therefore very hydrophilic. Their most interesting feature is that they may have the same chemical composition but a different porous texture. Consequently, the influence of porous characteristics, such as pore volume, surface area or pore size can be easily assessed. In this work, a commonly used desiccant, silica gel, is compared with organic xerogels to determine their rate and capacity of water adsorption, and to evaluate the role of surface chemistry versus porous texture. It was found that organic xerogels showed a higher rate of moisture adsorption than silica gel. Pore structure also seems to play an important role in water adsorption capacity. The OX-10 sample, whose porosity was mainly composed of micro-mesoporosity displayed a water adsorption capacity two times greater than that of the silica gel, and three times higher than that of the totally macroporous xerogel OX-2100. The presence of feeder pores (mesopores) that facilitate the access to the hydrophilic surface was observed to be the key factor for a good desiccant behaviour. Neither the total pore volume nor the high surface area (i.e. high microporosity) of the desiccant sample, is as important as the mesopore structure.