Subsurface filamentous fabrics: an evaluation of origins based on morphological and geochemical criteria, with implications for exopaleontology

The fossil record of the subsurface biosphere is sparse. Results obtained on subsurface filamentous fabrics (SFF) from >225 paleosubsurface sites in volcanics, oxidized ores, and paleokarst of subrecent to Proterozoic age are presented. SFF are mineral encrustations on filamentous or fibrous substrates that formed in subsurface environments. SFF occur in association with low-temperature aqueous mineral assemblages and consist of tubular, micron-thick (median 1.6 micron) filaments in high spatial density, which occur as irregular masses, matted fabrics, and vertically draped features that resemble stalactites. Micron-sized filamentous centers rule out a stalactitic origin. Morphometric analysis of SFF filamentous forms demonstrates that their shape more closely resembles microbial filaments than fibrous minerals. Abiogenic filament-like forms are considered unlikely precursors of most SFF, because abiogenic forms differ in the distribution of widths and have a lower degree of curvature and a lower number of direction changes. Elemental analyses of SFF show depletion in immobile elements (e.g., Al, Th) and a systematic enrichment in As and Sb, which demonstrates a relation to environments with high flows of water. Sulfur isotopic analyses are consistent with a biological origin of a SFF sample from a Mississippi Valley-Type deposit, which is consistent with data in the literature. Fe isotopes in SFF and active analogue systems, however, allow no discrimination between biogenic and abiogenic origins. The origin of most SFF is explained as permineralized remains of microbial filaments that possibly record rapid growth during phases of high water flow that released chemical energy. It is possible that some SFF formed due to encrustation of mineral fibers. SFF share similarities with Microcodium from soil environments. SFF are a logical target in the search for past life on Mars. The macroscopic nature of many SFF allows for their relatively easy in situ recognition and targeting for more detailed microstructural and geochemical analysis.     

High resolution limb observations of clouds by the CRISTA-NF experiment during the SCOUT-O3 tropical aircraft campaign

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere – New Frontiers (CRISTA-NF) experiment on board the Russian research aircraft Geophysica measures limb emission spectra with an unprecedented vertical and horizontal resolution in the 4–15 μm wavelength region. The IR spectra measured during the SCOUT-O3 Tropical Aircraft Campaign have been analysed with respect of cloud occurrence, cloud vertical and horizontal extent, cloud spatial structures and their utilisation for trace gas retrievals. In addition indicators for ice water content and optical thickness of the clouds have been adopted. These new kinds of measurements in the upper troposphere/lower stratosphere region are especially valuable for the design and development of future space borne high resolution limb sounders.     

Radiance calibration of CRISTA-NF

The CRISTA-NF instrument is the airborne version of the CRISTA satellite infrared limb sounder. It has been successfully flown on the Geophysica research airplane during a test campaign in July 2005, during the SCOUT-O3 Tropical Aircraft Campaign in November/December 2005 and during the AMMA campaign in August 2006. Radiance calibrations of the airborne instrument are more complex compared to the satellite instrument because the vacuum shell of CRISTA-NF is confined by a ZnSe (zinc–selenide) window and the detectors can thermally drift during measurement flights. By comprehensive radiance calibrations with a blackbody source the window’s emissivity and transmissivity are determined and the dependence of the instrument sensitivity on the detector temperature is characterized. Taking these effects into account, the remaining radiance error of the calibration is smaller than 3%.     

The Heliosphere in Time

The paleo-cosmic ray records are used to study the properties of the heliosphere and solar processes over the past 9300 years. They show that both varied greatly over that time, ranging from ～26 “Grand Minima” of duration 50–100 yr when the Sun was inactive, to periods similar to the past 50 years of strong solar activity. This shows that the detailed information regarding the heliosphere gained during the “space era” represents an extreme case, and is not representative of the majority of the past 9300 yr. The data confirm that the 11 and 22-year cycles of solar activity continued through the Spoerer and Maunder Grand Minima. Throughout the 9300 yr interval, “Grand Minima” usually occurred in groups of 2 to 4, similar to the group of four that occurred in the interval 1000–1800 AD. The groups are separated by ～1000 yr intervals without Grand Minima. Frequency spectra of the full 9300 yr record show that the heliospheric and solar phenomena exhibit >10 well-defined and persistent periodicities. We speculate that the solar dynamo exhibits a 2300 yr periodicity, wherein it alternates between two different states of activity. In the first (～800 yr duration) solar activity weakens greatly every 100–200 yr resulting in a sequence of Grand Minima, while in the other, the solar dynamo suffers smaller changes; the centenary scale solar and heliospheric changes are smaller, being similar to those that occurred in the interval 1890–1910. The paleo-cosmic ray evidence suggests that the Sun has now entered this more uniform period of activity, following the sequence of Grand Minima (Wolf, Spoerer, Maunder, and Dalton) that occurred between 1000 and 1800 AD.     

Positive pressure breathing by total body negative pressure: a new simulation model for fluid balance in weightlessness?

A systems study is proposed to explore correctly the effects of the combination of HDT (Head Down Tilt) and TBNP (Total Body Negative Pressure).