dataset of heater temperature into different types of kerogens. Developed ANN and SVM models show great performances in the inversion and classification. The suggested characterization method provides a simple tool of estimating reactivity and type of kerogens. It will be used as a proxy for the inverse modeling of geochemical characterization of organic matter coupled with forward numerical simulations, by reducing the number of simulation runs required in the traditional inverse modeling.

Lee, S.-A., Kim, T.-H., Kim, G., 2020. Tracing terrestrial versus marine sources of dissolved organic carbon in a coastal bay using stable carbon isotopes. Biogeosciences 17, 135-144.

https://www.biogeosciences.net/17/135/2020/ The sources of dissolved organic matter (DOM) in coastal waters are diverse, and they play different roles in the biogeochemistry and ecosystems of the ocean. In this study, we measured dissolved organic carbon (DOC) 13 δ and nitrogen (DON), the stable carbon isotopic composition of dissolved organic carbon ( C-DOC), and fluorescent dissolved organic matter (FDOM) in coastal bay waters surrounded by large cities (Masan Bay, Republic of Korea) to determine the different DOM sources in this region. The surface seawater samples were collected in two sampling campaigns (August 2011 and August 2016). The salinities were in the range of 10 - 21 in 2011 and 25 - 32 in 2016. In 2011, excess DOC was observed in high-salinity (16 - 21) waters; the excess 13 δ DOC source was found to be mainly from marine autochthonous production according to the C-DOC values (-23.7 ‰to -20.6 ‰), the higher concentrations of protein - like FDOM, and the lower DOC∕DON (C∕N) ratios (8 - 15). In contrast, excess DOC observed in high-salinity waters in 2016 was characterized by low FDOM, 13 δ more depleted C values (-28.8 ‰to -21.1 ‰), and high C∕N ratios (13- 45), suggesting that the source of excess DOC is terrestrial C plants by direct land - seawater interactions. Our results show that multiple DOM 3 13 δ tracers such as C- DOC, FDOM, and C∕N ratios are powerful for determining different sources of DOM occurring in coastal waters.

Lehmer, O.R., Catling, D.C., Buick, R., Brownlee, D.E., Newport, S., 2020. Atmospheric CO levels from 2.7 2 billion years ago inferred from micrometeorite oxidation. Science Advances 6, eaay4644.

http://advances.sciencemag.org/content/6/4/eaay4644.abstract Earth's atmospheric composition during the Archean eon of 4 to 2.5 billion years ago has few constraints. However, the geochemistry of recently discovered iron-rich micrometeorites from 2.7 billion - year - old limestones could serve as a proxy for ancient gas concentrations. When micrometeorites entered the atmosphere, they melted and preserved a record of atmospheric interaction. We model the motion, evaporation, and kinetic oxidation by CO of micrometeorites entering a CO -rich atmosphere. We consider a CO -rich 2 2 2 rather than an O -rich atmosphere, as considered previously, because this better represents likely atmospheric 2 conditions in the anoxic Archean. Our model reproduces the observed oxidation state of micrometeorites at 2.7 Ga for an estimated atmospheric CO concentration of >70% by volume. Even if the early atmosphere was 2 thinner than today, the elevated CO level indicated by our model result would help resolve how the Late 2 Archean Earth remained warm when the young Sun was ~20% fainter.

Lengger, S.K., Rush, D., Mayser, J.P., Blewett, J., Schwartz-Narbonne, R., Talbot, H.M., Middelburg, J.J., Jetten, M.S.M., Schouten, S., Sinninghe Damsté, J.S., Pancost, R.D., 2019. Dark carbon fixation in the Arabian Sea oxygen minimum zone contributes to sedimentary organic carbon (SOM). Global Biogeochemical Cycles 33, 1715-1732.

https://doi.org/10.1029/2019GB006282 Abstract: In response to rising CO concentrations and increasing global sea surface temperatures, oxygen 2 minimum zones (OMZ), or 'dead zones', are expected to expand. OMZs are fueled by high primary productivity, resulting in enhanced biological oxygen demand at depth, subsequent oxygen depletion, and