@article {2961,
	title = {Persistence of old soil carbon under changing climate: The role of mineral-organic matter interactions},
	journal = {Chemical Geology},
	volume = {587},
	year = {2022},
	month = {Jan-01-2022},
	pages = {120629},
	abstract = {Globally, soils store between 1500 and 2800 Pg of organic carbon (OC). The physical and chemical stability of these terrestrial soil carbon stores under plausible climate change scenarios is unclear. Soil organic carbon (SOC), especially in volcanic soils, is stabilized through mineral matrix interactions. How susceptible are these mineral-organic matter interactions to environmental change? Here we present a study of SOC age along a climate gradient of andisols from Kohala volcano on the Island of Hawai{\textquoteright}i. We measure carbon isotope composition (14C/12C, 13C/12C) in bulk samples and extracted biomarkers for 4{\textendash}8 horizons of 15 soil profiles to understand variability in SOC age and persistence across incremental differences in mean annual precipitation. Bulk OC in the subsoil has radiocarbon fraction modern (Fm) values as low as 0.28 to 0.16 (~10,160 to ~14,630 conventional radiocarbon years). Coexisting plant-derived long chain fatty acids (LCFAs) are older, over 22,500 yrs. (Fm = 0.060), implying that these are among the most stable compounds in the soil, while corresponding shorter-chain (C16) fatty acids are much younger, consistent with an origin from active microbial communities assimilating young OC percolating from surface horizons. There is significant Fe loss at higher mean annual precipitation (MAP) (>2200 mm yr-1) sites associated with episodic soil saturation and microbial Fe reduction. \%OC is higher at these sites, consistent with the expectation that saturated conditions promote SOC storage. However, in these higher MAP sites iron depletion is associated with much younger bulk SOC and LCFAs 14C ages (~2900 14C years) than at equivalent sample depths in sites that retain most Fe (~14,200 14C years). The remaining mineral matrix consists primarily of Si, Al, and Ti as SRO minerals. The data imply that modest increases in precipitation resulting from environmental change at locations near a potential saturation or redox threshold could result in destabilization of Fe-SOC complexes, rendering previously stabilized carbon available for rapid degradation, potentially irreversibly decreasing the size of the old SOC reservoir. The destabilization of an old, persistent Fe-SOC reservoir can decrease SOC storage and ultimately increase the amount of CO2 released to the atmosphere.},
	issn = {00092541},
	doi = {10.1016/j.chemgeo.2021.120629},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0009254121005726},
	author = {Grant, Katherine E. and Galy, Valier V. and Haghipour, Negar and Eglinton, Timothy I. and Derry, Louis A.}
}
@article {2921,
	title = {Climate control on terrestrial biospheric carbon turnover},
	journal = {Proceedings of the National Academy of Sciences},
	volume = {118},
	year = {2021},
	month = {Nov-02-2022},
	pages = {e2011585118},
	abstract = {Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon (C-14) ages on two groups of molecular tracers of plant-derived carbon-leaf-wax lipids and lignin phenols-from a globally distributed suite of rivers. We find significant negative relationships between the C-14 age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil C-14 ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change-induced perturbations of soil OC turnover and stocks.},
	keywords = {Carbon cycle, carbon turnover times, fluvial carbon, plant biomarkers, radiocarbon},
	issn = {0027-8424},
	doi = {10.1073/pnas.2011585118},
	url = {https://www.researchgate.net/publication/349357864_Climate_control_on_terrestrial_biospheric_carbon_turnover},
	author = {Eglinton, Timothy I. and Galy, Valier V. and Hemingway, Jordon D. and Feng, Xiaojuan and Bao, Hongyan and Blattmann, Thomas M. and Dickens, Angela F. and Gies, Hannah and Giosan, Liviu and Haghipour, Negar and Hou, Pengfei and Lupker, Maarten and McIntyre, Cameron P. and Montlu{\c c}on, Daniel B. and Peucker-Ehrenbrink, Bernhard and Ponton, Camilo and Schefu{\ss}, Enno and Schwab, Melissa S. and Voss, Britta M. and Wacker, Lukas and Wu, Ying and Zhao, Meixun}
}
@article {2764,
	title = {Mineral protection regulates long-term global preservation of natural organic carbon},
	journal = {Nature},
	volume = {570},
	year = {2019},
	month = {Jan-06-2019},
	pages = {228 - 231},
	abstract = {The balance between photosynthetic organic carbon production and respiration controls atmospheric composition and climate1,2. The majority of organic carbon is respired back to carbon dioxide in the biosphere, but a small fraction escapes remineralization and is preserved over geological timescales3. By removing reduced carbon from Earth{\textquoteright}s surface, this sequestration process promotes atmospheric oxygen accumulation2 and carbon dioxide removal1. Two major mechanisms have been proposed to explain organic carbon preservation: selective preservation of biochemically unreactive compounds4,5 and protection resulting from interactions with a mineral matrix6,7. Although both mechanisms can operate across a range of environments and timescales, their global relative importance on 1,000-year to 100,000-year timescales remains uncertain4. Here we present a global dataset of the distributions of organic carbon activation energy and corresponding radiocarbon ages in soils, sediments and dissolved organic carbon. We find that activation energy distributions broaden over time in all mineral-containing samples. This result requires increasing bond-strength diversity, consistent with the formation of organo-mineral bonds8 but inconsistent with selective preservation. Radiocarbon ages further reveal that high-energy, mineral-bound organic carbon persists for millennia relative to low-energy, unbound organic carbon. Our results provide globally coherent evidence for the proposed7 importance of mineral protection in promoting organic carbon preservation. We suggest that similar studies of bond-strength diversity in ancient sediments may reveal how and why organic carbon preservation{\textemdash}and thus atmospheric composition and climate{\textemdash}has varied over geological time.},
	issn = {0028-0836},
	doi = {10.1038/s41586-019-1280-6},
	url = {http://www.nature.com/articles/s41586-019-1280-6},
	author = {Hemingway, Jordon D. and Rothman, Daniel H. and Grant, Katherine E. and Rosengard, Sarah Z. and Eglinton, Timothy I. and Derry, Louis A. and Galy, Valier V.}
}
@article {2788,
	title = {Thermal oxidation of carbon in organic matter rich volcanic soils: insights into SOC age differentiation and mineral stabilization},
	journal = {Biogeochemistry},
	volume = {144},
	year = {2019},
	month = {Jan-09-2019},
	pages = {291 - 304},
	abstract = {Radiocarbon ages and thermal stability measurements can be used to estimate the stability of soil organic carbon (OC). Soil OC is a complex reservoir that contains a range of compounds with different sources, reactivities, and residence times. This heterogeneity can shift bulk radiocarbon values and impact assessment of OC stability and turnover in soils. Four soil horizons (Oa, Bhs, Bs, Bg) were sampled from highly weathered 350 ka Pololu basaltic volcanics on the Island of Hawaii and analyzed by Ramped PyrOX (RPO) in both the pyrolysis (PY) and oxidation (OX) modes to separate a complex mixture of OC into thermally defined fractions. Fractions were characterized for carbon stable isotope and radiocarbon composition. PY and OX modes yielded similar results. Bulk radiocarbon measurements were modern in the Oa horizon (Fm = 1.013) and got progressively older with depth: the Bg horizon had an Fm value of 0.73. Activation energy distributions (p(E)) calculated using the {\textquoteleft}rampedpyrox{\textquoteright} model yielded consistent mean E values of 140 kJ mol-1 below the Oa horizon. The {\textquoteleft}rampedpyrox{\textquoteright} model outputs showed a mostly bimodal distribution in the p(E) below the Oa, with a primary peak at 135 kJ mol-1 and a secondary peak at 148 kJ mol-1, while the Oa was dominated by a single, higher E peak at 157 kJ mol-1. We suggest that mineral-carbon interaction, either through mineral surface-OC or metal-OC interactions, is the stabilization mechanism contributing to the observed mean E of 140 kJ mol-1 below the Oa horizon. In the Oa horizon, within individual RPO analyses, radiocarbon ages in the individual thermal fractions were indistinguishable (p > 0.1). The flat age distributions indicate there is no relationship between age and thermal stability (E) in the upper horizon (> 25 cm). Deeper in the soil profile higher {\textmu}Ef values were associated with older radiocarbon ages, with slopes progressively steepening with depth. In the deepest (Bg) horizon, there was the largest, yet modest change in Fm of 0.06 (626 radiocarbon years), indicating that older OC is slightly more thermally stable.},
	issn = {0168-2563},
	doi = {10.1007/s10533-019-00586-1},
	url = {http://link.springer.com/10.1007/s10533-019-00586-1},
	author = {Grant, Katherine E. and Galy, Valier V. and Chadwick, Oliver A. and Derry, Louis A.}
}
@article {2789,
	title = {The effect of sample drying temperature on marine particulate organic carbon composition},
	journal = {Limnology and Oceanography: Methods},
	volume = {16},
	year = {2018},
	month = {Jan-05-2018},
	pages = {286 - 298},
	abstract = {Compositional changes in marine particulate organic carbon (POC) throughout the water column trace important processes that underlie the biological pump{\textquoteright}s efficiency. While labor-intensive, particle sampling efforts offer potential to expand the empirical POC archive at different stages in the water column, provided that organic composition is sufficiently preserved between sampling and analysis. The standard procedure for preserving organic matter composition in marine samples is to immediately store particles at -80{\textdegree}C to -20{\textdegree}C until they can be freeze-dried for analysis. This report investigates the effect of warmer drying and storage temperatures on POC composition, which applies to the majority of POC samples collected in the field without intention for organic analysis. Particle samples collected off Woods Hole, Massachusetts were immediately dried at 56{\textdegree}C, at room temperature, or stored in a freezer until freeze-drying. Results show that oven- and air-drying did not shift the bulk composition (i.e., carbon and nitrogen content and stable isotope composition) of POC in the samples relative to freeze-drying. Similarly, warmer drying temperatures did not affect POC thermal stability, as inferred by ramped pyrolysis/oxidation, a growing technique that uses a continuous temperature ramp to differentiate components of organic carbon by their decomposition temperature. Oven- and air-drying did depress lipid abundances relative to freeze-drying, the extent of which depended on compound size and structure. The data suggest that field samples dried at room temperatures and 56{\textdegree}C are appropriate for assessing bulk POC composition and thermal stability, but physical mechanisms such as molecular volatilization bias their lipid composition.},
	doi = {10.1002/lom3.v16.510.1002/lom3.10245},
	url = {https://www.researchgate.net/publication/324893072_The_effect_of_sample_drying_temperature_on_marine_particulate_organic_carbon_composition},
	author = {Rosengard, Sarah Z. and Lam, Phoebe J. and McNichol, Ann P. and Johnson, Carl G. and Galy, Valier V.}
}
@article {2763,
	title = {Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils},
	journal = {Science},
	volume = {360},
	year = {2018},
	month = {Jan-04-2019},
	pages = {209 - 212},
	abstract = {Lithospheric organic carbon ({\textquotedblleft}petrogenic{\textquotedblright}; OCpetro) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO2) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 {\textpm} 11\% of the OCpetro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OCpetro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emission fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial.},
	issn = {0036-8075},
	doi = {10.1126/science.aao6463},
	url = {https://www.sciencemag.org/lookup/doi/10.1126/science.aao6463},
	author = {Hemingway, Jordon D. and Hilton, Robert G. and Hovius, Niels and Eglinton, Timothy I. and Haghipour, Negar and Wacker, Lukas and Chen, Meng-Chiang and Galy, Valier V.}
}
@article {2765,
	title = {Hydrologic controls on seasonal and inter-annual variability of Congo River particulate organic matter source and reservoir age},
	journal = {Chemical Geology},
	volume = {466},
	year = {2017},
	month = {Jan-09-2017},
	pages = {454 - 465},
	abstract = {We present dissolved organic carbon (DOC) concentrations, particulate organic matter (POM) composition (δ13C, δ15N, ∆14C, N/C), and particulate glycerol dialkyl glycerol tetraether (GDGT) distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model using δ13C and N/C indicates that exported POM is consistently dominated by C3 rainforest soil sources, with increasing contribution from C3 vegetation and decreasing contribution from phytoplankton at high discharge. Large C4 inputs are never observed despite covering ≈ 13\% of the catchment. Low and variable ∆14C values during 2011 [annual mean = (- 148 {\textpm} 82) {\textperthousand}], when discharge from left-bank tributaries located in the southern hemisphere reached record lows, likely reflect a bias toward pre-aged POM derived from the Cuvette Congolaise swamp forest. In contrast, ∆14C values were stable near - 50{\textperthousand} between January and June 2013, when left-bank discharge was highest. We suggest that headwater POM is replaced and/or diluted by C3 vegetation and pre-aged soils during transit through the Cuvette Congolaise, whereas left-bank tributaries export significantly less pre-aged material. GDGT distributions provide further evidence for seasonal and inter-annual variability in soil provenance. The cyclization of branched tetraethers and the GDGT-0 to crenarchaeol ratio are positively correlated with discharge (r >= 0.70; p-value <= 4.3 {\texttimes} 10- 5) due to the incorporation of swamp-forest soils when discharge from right-bank tributaries located in the northern hemisphere is high. Both metrics reach record lows during 2013, supporting our interpretation of increased left-bank contribution at this time. We conclude that hydrologic variability is a major control of POM provenance in the Congo River Basin and that tropical wetlands can be a significant POM source despite their small geographic coverage.},
	keywords = {biomarkers, Congo River, GDGTs, Particulate organic matter, radiocarbon},
	issn = {00092541},
	doi = {10.1016/j.chemgeo.2017.06.034},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0009254117303935},
	author = {Hemingway, Jordon D. and Schefu{\ss}, Enno and Spencer, Robert G.M. and Dinga, Bienvenu Jean and Eglinton, Timothy I. and McIntyre, Cameron and Galy, Valier V.}
}
@article {2608,
	title = {Technical note: An inverse method to relate organic carbon reactivity to isotope composition from serial oxidation},
	journal = {Biogeosciences},
	volume = {14},
	year = {2017},
	month = {Jan-01-2017},
	pages = {5099 - 5114},
	doi = {10.5194/bg-14-5099-201710.5194/bg-14-5099-2017-supplement},
	url = {https://www.biogeosciences.net/14/5099/2017/https://www.biogeosciences.net/14/5099/2017/bg-14-5099-2017.pdfhttps://www.biogeosciences.net/14/5099/2017/bg-14-5099-2017-supplement.zip},
	author = {Hemingway, Jordon D. and Rothman, Daniel H. and Rosengard, Sarah Z. and Galy, Valier V.}
}
@article {2585,
	title = {Indonesian vegetation response to changes in rainfall seasonality over the past 25,000 years},
	journal = {Nature Geoscience},
	volume = {7449278721172063253871891072011563523665412739429544323},
	year = {2014},
	month = {Jan-06-2014},
	pages = {513 - 517},
	abstract = {The hydrologic response to climate forcing in the Indo-Pacific warm pool region has varied spatially over the past 25,000 years1, 2, 3, 4, 5. For example, drier conditions are inferred on Java and Borneo for the period following the end of the Last Glacial Maximum, whereas wetter conditions are reconstructed for northwest Australia4. The response of vegetation to these past rainfall variations is poorly constrained. Using a suite of 30 surface marine sediment samples from throughout the Indo-Pacific warm pool, we demonstrate that today the stable isotopic composition of vascular plant fatty acids (δ13Cfa) reflects the regional vegetation composition. This in turn is controlled by the seasonality of rainfall consistent with dry season water stress6. Applying this proxy in a sediment core from offshore northeast Borneo, we show broadly similar vegetation cover during the Last Glacial Maximum and the Holocene, suggesting that, despite generally drier glacial conditions1, 7, there was no pronounced dry season. In contrast, δ13Cfa and pollen data from a core off the coast of Sumba indicate an expansion of C4 herbs during the most recent glaciation, implying enhanced aridity and water stress during the dry season. Holocene vegetation trends are also consistent with a response to dry season water stress. We therefore conclude that vegetation in tropical monsoon regions is susceptible to increases in water stress arising from an enhanced seasonality of rainfall, as has occurred8 in past decades.},
	keywords = {Palaeoclimate, Palaeoecology},
	issn = {1752-0894},
	doi = {10.1038/ngeo2182},
	url = {http://www.nature.com/doifinder/10.1038/ngeo2182},
	author = {Dubois, Nathalie and Oppo, Delia W. and Galy, Valier V. and Mohtadi, Mahyar and van der Kaars, Sander and Tierney, Jessica E. and Rosenthal, Yair and Eglinton, Timothy I. and L?ckge, Andreas and Linsley, Braddock K.}
}
