Plant wax integration and transport from the Mississippi River Basin to the Gulf of Mexico inferred from GIS-enabled isoscapes and mixing models. (15th July 2019)

• Record Type: Journal Article
• Authors: Suh, Yeon Jee; Diefendorf, Aaron F.; Bowen, Gabriel J.; Cotton, Jennifer M.; Ju, Se-Jong
• Is Part Of: Geochimica et cosmochimica acta. Volume 257(2019)
• Page Start: 131
• Page End: 149
• Publication Date: 2019-07-15
• Subjects: Compound-specific δ13C -- Compound-specific δ2H -- Biomarker proxies -- n-Alkane -- C3 -- C4 -- Spatial analysis; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2019.04.022
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Understanding the fate of terrestrial plant waxes from source to sink is critical for improving paleoclimate interpretations from sedimentary plant waxes. However, there is limited knowledge about the controls on plant wax integration and transport in large catchments with multiple biomes and climates. To address this lack of understanding, we investigated the vegetation and climatic controls on plant wax integration and transport from the Mississippi River Basin (MRB), the largest river in the U.S., to the Gulf of Mexico (GOM). We first estimated the geographic distribution of n -alkane carbon (δ 13 Calk ) and hydrogen (δ 2 Halk ) isotopic compositions (i.e. isoscapes) in the MRB using plant isotope fractionation calibrations from North America and similar climate regions for the pre-industrial. We utilized two different vegetation maps (i.e. biome map and %C4 map) and two plant isotope fractionation estimation approaches, and discussed advantages and disadvantages of each method. Then, we developed mixing models weighting the isotope values by biological and climatic parameters (i.e. vegetation area, n -alkane concentration by chain lengths, net primary productivity (NPP), and runoff) and their combinations to test the sensitivity of basin-integrated plant wax isotopic compositions to these variables. Our approach does not factor in soil stocks of plant wax nor degradation in transit, as future work will need to constrain these factors for the MRB for the period of interest. Vegetation area weighting alone predicted relatively high C4 plant contributions to the pool of waxes exported from the basin. When n -alkane concentration in leaves, NPP, or runoff was considered, the contribution of forest-derived plant waxes increased. Sensitivity of plant wax isotopic compositions to productivity and transport efficiency varied among models and chain lengths. For example, n -C29 alkanes were sensitive to plant wax contribution increases from forests whereas n -C33 alkanes were more sensitive to increases in C4 grassland productivity. The plant wax concentration and NPP were combined as an estimate for total wax productivity, and a combination of this total wax productivity and runoff were used to simulate both production and transport. These multi-parameter models estimated the highest plant wax contribution from C3 forests because these areas were calculated to have the highest productivity and greatest runoff. Despite large differences in δ 13 Calk and δ 2 Halk values across the MRB, variation in the predicted δ 13 C and δ 2 H of exported n -alkanes is small across all models. This small range is consistent with a calculated predominance of plant wax export from wet and tree-dominated biomes and suggests that drier and C4 grass-dominated biomes may be under-represented in the sedimentary plant wax record.