Trends in grain size and BET surface area in cold–arid versus warm–semiarid fluvial systems Kristen R. Marra a, ⁎, Gerilyn S. Soreghan a , Megan E. Elwood Madden a , Leslie J. Keiser a , Brenda L. Hall b a School of Geology and Geophysics, University of Oklahoma, 100 E Boyd St, Suite 710, Norman, OK 73072, USA b Climate Change Institute, University of Maine, 303 Bryand, Orono, ME 04469, USA abstract article info Article history: Received 25 September 2012 Received in revised form 16 October 2013 Accepted 18 October 2013 Available online 26 October 2013 Keywords: Eolian Clark Glacier Polar desert Chemical weathering Clays Antarctica Sediment grain size and surface area impose critical controls on the rates of chemical weathering, even in cold- based (i.e., polar) glacial systems, where extensive chemical weathering traditionally has been considered minimal owing to low temperatures. Production of fine-grained material increases the surface area of sediments, priming mineral surfaces for chemical weathering. Comparison among grain size and reactive surface area of sediments along granitoid-sourced fluvial transects between a cold–arid, glacial (Wright Valley, Antarctica) and a warm– semiarid, nonglacial (Wichita Mountains, Oklahoma) environment indicates opposing trends downstream within the silt and clay (b 63 μm) fraction. In the polar glacial transect, the silt and clay fraction coarsens and exhibits a corresponding decrease in mineral surface area with fluvial transport. This is inferred to reflect rapid dissolution of fine-grained eolian material trapped on a glacier surface and released during summer melting. Fluvial sediments from the warm, nonglacial system exhibit the opposite trend, wherein a downstream decrease in grain size and increase in surface area suggest incongruent chemical weathering resulting in clay-sized secondary weathering phases. The observed trends highlight the important roles of reactive surface area and solute chemistry, which are closely linked to climate, in determining chemical weathering rates. Such trends are potentially discernible in the sediment record, providing a means to refine climatic inferences from proximal fluvial strata and further constrain the influence of chemical weathering on modern and on ancient global carbon cycles. Published by Elsevier B.V. 1. Introduction Intensity of chemical weathering generally correlates with tempera- ture and precipitation, such that warmer and wetter climates should exhibit higher weathering rates (White and Blum, 1995; Riebe et al., 2004; Van de Kamp, 2010). Sediment surface area is critical to deter- mining mineral–water reaction rates and cation exchange capacities during natural weathering processes. However, sediment surface area is not commonly reported for natural systems, and most weathering studies focus on trends in solutes rather than sediments (Anderson et al., 1997; Nezat et al., 2001; Maurice et al., 2002; Lyons et al., 2003; Rawlins et al., 2010). Chemical fluxes from temperate glacial systems are larger than previously assumed owing to the production of freshly abraded, fine-grained mineral particles with high surface areas resulting from glacial grinding (Anderson et al., 1997; Anderson, 2005, 2007). Ad- ditionally, significant chemical weathering has been established in polar glacial streams (Dry Valleys, Antarctica), where increases in multiple cations (specifically Ca, Na, K, and Mg) occur along the stream channel during the summer melt season as a result of hyporheic zone exchange with underlying unconsolidated sediments (Gooseff et al., 2011; Stumpf et al., 2012). In contrast to temperate glacial systems, however, the role of surface area in cold-based, polar systems remains relatively unexplored and considered negligible because of a lack of physical grinding to create strained mineral textures and enhanced surface roughness (Anbeek, 1992; Hallet et al., 1996; Anderson et al., 1997; Anderson, 2007). Fine-grained sediments have particularly high surface areas owing to small particle sizes, which increase the proportion of mineral surfaces readily available for chemical weathering. High-surface-area sediments also enhance partitioning between the more labile mineral phases (i.e., hornblende, anorthite, and K-feldspar) and more resistant phases (i.e., quartz), even over relatively short exposure times to the weathering environment. The importance of surface area in chemical weathering and the link between surface area production and climate implies that the production and fate of fine-grained sediment may be diagnostic of climate. Here we quantify sediment size distributions and corresponding surface area as conducted by the Brunauer, Emmett, Teller (BET) method (Brunauer et al., 1938) within the finest (b 63 μm; silt and clay), and thus potentially most reactive, sediment fraction along proximal fluvial Geomorphology 206 (2014) 483–491 ⁎ Corresponding author at: U.S. Geological Survey, Denver, CO 80225, USA. Tel.: +1 303 236 7756. E-mail address: kmarra@ou.edu (K.R. Marra). 0169-555X/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.geomorph.2013.10.018 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph