Multiple plant-wax compounds record differential sources and ecosystem structure in large river catchments

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 184 (2016): 20-40, doi:10.1016/j.gca.2016.04.003.The concentrations, distributions, and stable carbon isotopes (δ13C) of plant waxes carried by fluvial suspended sediments contain valuable information about terrestrial ecosystem characteristics. To properly interpret past changes recorded in sedimentary archives it is crucial to understand the sources and variability of exported plant waxes in modern systems on seasonal to inter-annual timescales. To determine such variability, we present concentrations and δ13C compositions of three compound classes (n-alkanes, n-alcohols, n-alkanoic acids) in a 34-month time series of suspended sediments from the outflow of the Congo River. We show that exported plant-dominated n-alkanes (C25 – C35) represent a mixture of C3 and C4 end members, each with distinct molecular distributions, as evidenced by an 8.1 ± 0.7‰ (±1σ standard deviation) spread in δ13C values across chain-lengths, and weak correlations between individual homologue concentrations (r = 0.52 – 0.94). In contrast, plant-dominated n-alcohols (C26 – C36) and n-alkanoic acids (C26 – C36) exhibit stronger positive correlations (r = 0.70 – 0.99) between homologue concentrations and depleted δ13C values (individual homologues average ≤ -31.3‰ and -30.8‰, respectively), with lower δ13C variability across chain-lengths (2.6 ± 0.6‰ and 2.0 ± 1.1‰, respectively). All individual plant-wax lipids show little temporal δ13C variability throughout the time-series (1σ ≤ 0.9‰), indicating that their stable carbon isotopes are not a sensitive tracer for temporal changes in plant-wax source in the Congo basin on seasonal to inter-annual timescales. Carbon-normalized concentrations and relative abundances of n-alcohols (19 – 58% of total plant-wax lipids) and n-alkanoic acids (26 – 76%) respond rapidly to seasonal changes in runoff, indicating that they are mostly derived from a recently entrained local source. In contrast, a lack of correlation with discharge and low, stable relative abundances (5 – 16%) indicate that n-alkanes better represent a catchment-integrated signal with minimal response to discharge seasonality. Comparison to published data on other large watersheds indicates that this phenomenon is not limited to the Congo River, and that analysis of multiple plant-wax lipid classes and chain lengths can be used to better resolve local vs. distal ecosystem structure in river catchments.J.D.H. was supported by the National Science Foundation Graduate Research Fellowship under Grant No. 2012126152. V.V.G. was partly supported by the US National Science Foundation, grants OCE-0851015 and OCE-0928582. Parts of this work were supported by the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System” at MARUM - Center for Marine Environmental Science, University of Bremen.2017-04-0

Particulate multi-element geochemical concentrations, dissolved barium concentrations and barium-isotopic data collected during the R/V Blue Heron cruise BH15-11 in Lake Superior during August 2015

Dataset: Particulate and dissolved Lake Superior geochemistryParticles are important vectors of nutrients, carbon, and several trace metals within large bodies of water. Broadly speaking, particle distributions can be classified into three major groups on the basis of their multi-element geochemistry: biogenic (organic matter-associated phases and tests); lithogenic (highly refractory rock-derived materials); and authigenic (formed in situ below the euphotic zone). We collected particulate samples spanning the full water column of Lake Superior at Stations FWM (46.998528, -91.246250) and WM (47.331611, -89.821389) during the height of 2015 summer thermal stratification (cruise BH15-11). We analyzed particle leachates for their multi-element geochemistry using ICP-MS (inductively-coupled plasma mass spectrometry) at the Woods Hole Oceanographic Institution Plasma Facility. We report elemental concentrations in Lake Superior particulate matter in (nano or pico) moles per liter, defined by a 0.44 um filter cutoff. Lithogenic cycles are resolved by Al, Fe, Ti, V, and Y; biogenic phases by Ca, Cd, P, and Sr; and authigenic processes by Ba, Cd, and Mn. Several elements exhibit hybrid-type distributions depending on the depth range under investigation. Also reported are stable barium-isotopic distributions for particulate and total dissolvable Ba, measured using multiple-collector ICP-MS and reported relative to NIST SRM 3104a in permill. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/680091NSF Division of Ocean Sciences (NSF OCE) OCE-1430015, NSF Division of Ocean Sciences (NSF OCE) OCE-144357

Pelagic barite precipitation at micromolar ambient sulfate

The question of how significant barite deposits were able to form from early Earth’s low-sulfate seas remains controversial. Here, the authors show pelagic barite precipitation within a strongly barite-undersaturated ecosystem, highlighting the importance of particle-associated microenvironments

Publisher Correction : Pelagic barite precipitation at micromolar ambient sulfate

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 9 (2018): 305, doi:10.1038/s41467-017-02701-y.Correction to: Nature Communications https://doi.org/10.1038/s41467-017-01229-5, Article published online 07 November 201

The influence of glacial cover on riverine silicon and iron exports in Chilean Patagonia

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (0.45 mu m) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems

Seasonal changes in dissolved organic matter composition in a Patagonian fjord affected by glacier melt inputs

Biogeochemical processes in fjords are likely affected by changes in surrounding glacier cover but very little is known about how meltwater directly influences dissolved organic matter (DOM) in fjords. Moreover, the data available are restricted to a handful of northern hemisphere sites. Here we analyze seasonal and spatial variation in dissolved organic carbon (DOC) concentration and DOM composition (spectrofluorescence, ultrahigh resolution mass spectrometry) in Baker-Martinez Fjord, Chilean Patagonia (48°S), to infer the impacts of rapid regional deglaciation on fjord DOM. We show that surface layer DOC concentrations do not vary significantly between seasons, but DOM composition is sensitive to differences in riverine inputs. In summer, higher protein-like fluorescence reflects increased glacial meltwater inputs, whilst molecular level data show weaker influence from marine DOM due to more intense stratification. We postulate that the shifting seasonal balance of riverine and marine waters affects the supply of biolabile peptides and organic nitrogen cycling in the surface layer. Trends in DOM composition with increasing salinity are consistent with patterns in estuaries (i.e. preferential removal of aromatic compounds and increasing relative contribution of unsaturated and heteroatom-rich DOM from marine sources). Preliminary estimates also suggest that at least 10 of the annual organic carbon stock in this fjord is supplied by the four largest, glacially fed rivers and that these inputs are dominated by dissolved (84) over particulate organic carbon. Riverine DOC may therefore be an important carbon subsidy to bacterial communities in the inner fjord. The overall findings highlight the biogeochemical sensitivity of a Patagonian fjord to changes in glacier melt input, which likely has relevance for other glaciated fjords in a warming climate