ALBERT

Description: The waxy coating that protects the leaves and other soft tissues of plants includes n-alkane and n-alkanoic acid compounds that are commonly used as biomarkers to reconstruct past environment. Plant waxes have geological relevance given their persistence in soils and paleosols, as well as in lake and marine sediments, yet diagenesis may alter their molecular and isotopic signatures from synthesis to deposition. This study seeks to understand the fate of plant wax biomarkers in soils after leaf-fall as characterized by a series of tropical soil profiles. We investigate the changes in abundance, molecular distributions, and hydrogen (δD) and carbon isotopic compositions (δ13C) of plant waxes (n-alkanes and n-alkanoic acids) in six litter-to-soil profiles along a 2740 m elevation transect from the eastern flank of the Andes mountains down to the lowland Amazon floodplain in Peru. From litter to soil, we find acid/alkane ratios increase, while absolute abundances decrease. In contrast, within each soil, acid/alkane ratios are roughly constant and we find an equivalent exponential decline in concentration in both compound classes with depth; with molecular distributions indicating some new production. We observe a 4 - 6‰ 13C-enrichment from litter to deeper soils for both C29 n-alkanes and C30 n-alkanoic acids; of which the Suess effect accounts for ≤ 2‰. We infer that microbial degradation and production (or 'turnover') processes influence the δ13C of plant waxes that survive in soils; in contrast, no systematic change in δD values is observed. The plant wax signal in soils includes averaging of inputs and diagenetic effects, so this signature is particularly relevant for the interpretation of plant waxes archives in paleosols and the plant waxes eroded from soils and exported to downstream sedimentary archives. We show that soils represent the major stock of plant wax under living ecosystems, suggesting that soils may be a quantitatively-important source of plant waxes available for fluvial erosion, with implications for studies of carbon cycling and paleoenvironmental reconstructions from downstream geological archives.

Description: Geochemical data, brGDGT fractions and calculated indices for soils and river samples during the wet and dry season in the Madre de Dios catchment, Peru.

Description: Sedimentary records from California's Northern Channel Islands and the adjacent Santa Barbara Basin (SBB) indicate intense regional biomass burning (wildfire) at the Ållerød-Younger Dryas boundary (~13.0-12.9 ka) (All age ranges in this paper are expressed in thousands of calendar years before present [ka]. Radiocarbon ages will be identified and clearly marked "14C years".). Multiproxy records in SBB Ocean Drilling Project (ODP) Site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats. Abrupt ecosystem disruption is evident on the Northern Channel Islands at the Ållerød-Younger Dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape. These wildfires coincide with the extinction of Mammuthus exilis [pygmy mammoth]. The earliest evidence for human presence on these islands at 13.1-12.9 ka (~11,000-10,900 14C years) is followed by an apparent 600-800 year gap in the archaeological record, which is followed by indications of a larger-scale colonization after 12.2 ka. Although a number of processes could have contributed to a post 18 ka decline in M. exilis populations (e.g., reduction of habitat due to sea-level rise and human exploitation of limited insular populations), we argue that the ultimate demise of M. exilis was more likely a result of continental scale ecosystem disruption that registered across North America at the onset of the Younger Dryas cooling episode, contemporaneous with the extinction of other megafaunal taxa. Evidence for ecosystem disruption at 13-12.9 ka on these offshore islands is consistent with the Younger Dryas boundary cosmic impact hypothesis [Firestone et al., 2007, doi:10.1073/pnas.0706977104].

Description: Aerosol, seawater, and floodwater samples were taken during the 2017 California Thomas Fire and subsequent flash flood event. These samples were used to examine how fire-flood sequences affect metal and black carbon delivery to coastal waters, such as the Santa Barbara Basin (SBB). On day 11 of the Thomas Fire, aerosols sampled at sea level under a smoke plume over the SBB found high levels of PM2.5, levoglucosan, and black carbon (average: 49 μg/m^3, 1.05 μg/m^3, 14.93 μg/m^3, respectively) and both soluble and total aerosol metal concentrations were consistent with a forest fire signature. Metal, nutrient, and chlorophyll a concentrations in surface seawater (average: 2.42 nM Fe, 0.14 µM phosphate, and 0.44 µgChla/L) were similar to concentrations during non-fire conditions, thus we could not establish fire-related increases in the SBB surface waters. On days 37 to 40 of the fire, before, during, and after a flash flood in the Ventura River, dissolved organic carbon, dissolved black carbon, and dissolved metal concentrations were positively correlated with discharge. Our findings confirm that black carbon and metals were released by the Thomas Fire and transported by both atmospheric and fluvial pathways.