Aluminum extracts in Antarctic paleosols: Proxy data for organic compounds and bacteria and implications for Martian paleosols William C. Mahaney a, ⁎, Kris M. Hart b , James M. Dohm c , Ronald G.V. Hancock d , Pedro Costa e , Shane S. O'Reilly b , Brian P. Kelleher b , Stephane Schwartz f , Bruno Lanson f a Quaternary Surveys, 26 Thornhill Ave., Thornhill, Ontario, Canada, L4J 1J4 b School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland c Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ, 85721, USA d Medical Physics and Applied Radiation Sciences, and Department of Anthropology, McMaster University Hamilton, Ontario, Canada L8S 4K1 e Departmento de Geologia, University of Lisbon, Lisbon, Portugal f IS Terre, CNRS, Université of Grenoble I, Grenoble, France abstract article info Article history: Received 12 December 2010 Received in revised form 2 February 2011 Accepted 16 February 2011 Available online 23 February 2011 Editor: M.R. Bennett Keywords: Antarctic and Martian paleosols Fe–Al extracts Al p vs. C Organic proxy data Pyrophosphate-extractable Al has been used to establish the presence of organically-complexed compounds in middle latitude and tropical soils and paleosols on Earth. As proxy data used to establish the presence of organic molecules and trace movement within proﬁles, it has proved an accurate indicator of downward translocation in Spodosols (podzols). Antarctic paleosols, dating from Middle to Early Miocene age (15– 20 Ma), are mineralic weathering proﬁles lacking A and B horizons. These proﬁles exhibit pavement/Cox/Cz/Cu horizons, largely with sandy silt textures, little clay, and exceedingly low concentrations of organic matter. Recent chemical investigations of 33 soil samples from the New Mountain and Aztec Mountain areas near the Inland Ice, adjacent to the Taylor Glacier, show that pyrophosphate-extractable Al concentrations vary in phase with organic carbon as determined by loss-on-ignition. While Al-extract concentrations in selected samples are low (b 0.15%), increasing values above nil approximately correlate positively with increases in bacterial populations of several common phylum, the extreme high numbers with more advanced biota including fossil Coleoptera. Available data suggest Al p extracts may target samples which may have undergone minor chelation, and which over long periods of time might have a cumulative weathering effect resulting in the accumulation of small concentrations of organic matter. As such, Al p extracts may prove useful in targeting the presence of life once in situ investigations of paleosols begin on Mars. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Major requirements for terrestrial and presumably extraterrestrial microbial life are liquid water, carbon, nitrogen, and iron, the latter as Fe +2 or Fe +3 (Falkowski et al., 2008). While these requirements complement each other with regard to physiological processes, perhaps more importantly, water increases the mobility of C, N, and to some degree Fe, the latter accelerating the oxidation potential of mineral grains by importing O to sites where Fe +2 is converted to Fe +3 . Both forms of Fe are important in microbial respiration, although Fe +3 is more easily taken up by microorganisms such as bacteria and fungi (Pitt, 1979). Fluctuations of organic C and N as organically-complexed material are seen to move in concert with pyrophosphate-extractable Al (Al p )(Mahaney et al., 1999, 2009, 2010a), such that Al p might be used to signal the presence of microbes when C and N are at detection limits. Previous work with Cryosols (cold-desert paleosols) in the Antarctic (Fig. 1 for location; Fig. 2A for stratigraphy) showed the presence of microbes in horizons with a Fe/salt mixed composition or in salt-rich zones [(Claridge and Campbell, 1968; Claridge, 1977)(Fig. 2A, arrows indicate the presence of microbial life) rather than other horizons, including ones that are Fe-enriched (Mahaney et al., 2000, 2001)]. Cryosols exist either as discrete proﬁles or as pedostratigraphic columns, the latter consisting of two or more proﬁles in succession with the older proﬁle at base descending in age closer to the land surface. The structure of each proﬁle proliferates in space and time as Fe horizon(s) over salt rich horizon(s), the most recent proﬁle in place since at least the mid-Miocene and topped with a pebble pavement depleted of ﬁnes by near constant action of wind. Colonies Sedimentary Geology 237 (2011) 84–94 ⁎ Corresponding author. E-mail addresses: arkose@rogers.com (W.C. Mahaney), hart.kris2@mail.dcu.ie (K.M. Hart), jmd@hwr.arizona.edu (J.M. Dohm), ronhancock@ca.inter.net (R.G.V. Hancock), ppcosta@fc.ul.pt (P. Costa), shane.oreilly8@mail.dcu.ie (S.S. O'Reilly), brian.kelleher@dcu.ie (B.P. Kelleher), schwartz@ujf-grenoble.fr (S. Schwartz), bruno.lanson@ujf-grenoble.fr (B. Lanson). 0037-0738/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2011.02.007 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo