About

Dr. Mark Albert Torres is an Assistant Professor at Rice University in the Department of Earth, Environmental, & Planetary Sciences. His professional contact is provided via email at mt61 (at) rice (dot) edu, and he maintains an updated CV as of February 2023 along with a Google Scholar page and a Twitter presence under the handle @Dr_Mark_Torres. The information available highlights his role as a faculty member leading a research group that includes postdoctoral researchers and graduate students working on various aspects of geochemistry and biogeochemical cycles. Although the page lists members of his lab and their research interests, it does not provide a detailed narrative of Dr. Torres's own research focus, background, or key contributions.

Research topics

• Environmental chemistry
• Chemistry
• Geology
• Geochemistry
• Paleontology
• Earth science
• Mineralogy
• Ecology
• Oceanography
• Organic chemistry
• Materials science
• Environmental science

Selected publications

• Hydrologic and geomorphic controls on bedrock organic carbon export

  2026-02-02

  article

  The top meter of the Earth’s crust holds nearly equal amounts of rock-derived organic carbon (OC petro ) and soil organic carbon. Due to this large reservoir size, the oxidation of OC petro may be an important flux of CO 2 to the atmosphere over geologic time. However, determining the magnitude and drivers of OC petro oxidation remains difficult at the watershed scale. To understand the balance of OC sources eroded from a landscape and prone to breakdown, we measured the OC concentrations, stable isotope ratios, and the radiocarbon content of suspended sediment samples from the East River: a shale-dominated alpine watershed near Crested Butte, Colorado. Suspended sediment samples were studied because they integrate multiple sources of sediment across a watershed. With these OC measurements, we employ a Monte Carlo mass balance inversion to constrain inputs of carbon from plants, soil, and bedrock. We find that along the main stem of the river, δ13C values range from -27 to -26 ‰ VPDB and fraction modern OC (FmC) ranges from 0.73 to 0.95, suggesting millennial-scale floodplain residence times. In contrast, lighter δ13C values (-29 to -27 ‰) and older FmC values are observed within tributaries. Notably, samples collected at different river stages at the downstream-most locality exhibit the widest variability in carbon isotope data. A decrease in sediment OC abundances and FmC values with increasing discharge is likely the result of an increased proportion in bedrock carbon in transport. These data illuminate hydrologic and geomorphic controls on the balance of OC export, which has consequences for watershed-scale OC fluxes. Whereas the river main stem primarily transports young, labile, plant- and soil-derived organic carbon, small steeper tributaries appear to transport older, rock-derived organic carbon, likely due to erosion of bedrock. However, the relative contributions of bedrock and soil-derived carbon in floodplains can fluctuate in response to changing hydrologic states, which are influenced by climate. Ongoing measurements of rhenium and carbon isotopes on suspended sediment, bedrock, and soil will help refine endmembers and shed light on the role of bedrock OC in riverine carbon fluxes.

  PublisherDOI

• Dependence of River Water Lithium Isotope Ratios on Watershed Attributes Complicates Interpretation of Weathering-Driven CO ₂ Drawdown

  American Journal of Science · 2026-03-30

  articleOpen access

  Chemical weathering produces alkalinity that, in conjunction with marine carbonate burial, mediates the return of carbon from planetary volcanism, metamorphism, and sedimentary recycling. However, clay formation during chemical denudation can result in reduced alkalinity fluxes. Because the 7 Li/ 6 Li ratio of dissolved lithium in river water (δ 7 Li river ) traces the degree of clay mineral formation following silicate dissolution at the watershed scale, fluvial Li isotope ratios and their expression in sedimentary archives can potentially convey the strength of silicate weathering-driven CO 2 drawdown. However, little attention has been given to the coupled dynamics that emerge when also considering the weathering of coexisting non-silicate minerals, such as carbonate and sulfide phases, that also modify alkalinity and carbon fluxes to the global ocean-atmosphere system. These additional phases potentially complicate attempts to relate δ 7 Li river values to changes in the partial pressure of atmospheric carbon dioxide (pCO 2 ). Here we address this complexity by compiling a global dataset of δ 7 Li river values and major and trace ion concentrations (n = 413), attributing solutes among lithologic sources and clay sinks with the MEANDIR inversion model and comparing numerical results to watershed properties. The analyses demonstrate that δ 7 Li river values correlate with alkalinity consumption by clay formation but do not simply relate to the net impact of weathering on atmospheric pCO 2 due to the weathering of carbonate and sulfide minerals. However, other weathering indices, like river Li/Na ratios, may more directly relate to pCO 2 change. A simple regolith model demonstrates that mineral supply, driven by bedrock composition and uplift, impacts the balance of sulfuric and carbonic acid weathering, the degree of clay mineral formation, and the fraction of Li incorporated from solution into clays. As a result, where measured or calculated δ 7 Li river trends have previously been interpreted in terms of clay mineral formation, we interpret δ 7 Li river as reflecting mineral supply modulated by climate.

  PublisherOA PDFDOI

• Glacially Enhanced Silicate Weathering Revealed by Holocene Lake Records

  Geophysical Research Letters · 2025-09-26

  articleOpen accessSenior author

  Abstract How glaciation affects drawdown by chemical weathering influences the weathering‐climate feedback strength, which controls the exogenic carbon cycle and planetary habitability. However, the role of glaciers remains elusive as glaciation alters multiple factors controlling weathering, the net effect of which is ambiguous even in directionality. To isolate and quantify the effect of glaciers, we developed a novel multi‐proxy system for constraining catchment‐scale weathering fluxes in the past. This approach utilizes the correlation between Ge/Si and Si isotope ratios in modern rivers and the preservation of these signals in lacustrine sediments. Reconstructed weathering fluxes in two Icelandic catchments with different glacial histories during the past 10,000 years show that chemical weathering fluxes are roughly 10 times higher when a catchment is glaciated versus ice‐free. The synchronous variations in weathering fluxes with the expansion and contraction of glaciers indicate that glaciation may rapidly amplify climatic variations via a positive feedback.

  PublisherOA PDFDOI

• Glacially enhanced silicate weathering revealed by Holocene lake records

  2025-02-08 · 1 citations

  preprintOpen accessSenior author

  How glaciation affects CO2 drawdown by chemical weathering sets the strength of the weathering-climate feedback, which controls the exogenic carbon cycle and planetary habitability (Kump et al., 2000). However, the exact role of glaciers remains elusive as glaciation alters multiple factors controlling weathering, the net effect of which is ambiguous even in directionality. While illustrative, modern observations have limited ability to constrain time-dependent behavior, which is thought to be important to glacial weathering (Vance et al., 2009; Kemeny et al., 2021). To isolate and quantify the effect of glaciers over millennial timescales, we developed a novel multi-proxy system for constraining catchment-scale fluxes in the past. This approach utilizes the correlation between Ge/Si and Si isotope ratios in modern rivers, which sensitively tracks weathering processes, and the preservation of these signals in biogenic silica in lake sediments. We report changes in weathering fluxes in two catchments with different glacial histories during the past ten thousand years from two lacustrine records in Iceland. We find that the chemical weathering fluxes are an order of magnitude higher in the same catchment when glaciated compared to when ice free. The synchronous variations in weathering fluxes with the expansion and contraction of glaciers indicate a rapid effect of glaciation that may amplify climatic variations via a positive feedback.

  PublisherOA PDFDOI

• Editorial preface to special issue: Chemical weathering as a key mechanism sustaining Earths habitability

  Global and Planetary Change · 2025-09-07

  article
  PublisherDOI

• Equitable Access, Open Science, and the Future of Publishing in Geochemistry and Cosmochemistry

  Advances in Geochemistry and Cosmochemistry · 2025-04-23 · 1 citations

  articleOpen access

  The landscape of academic publishing, including in geochemistry and cosmochemistry, is evolving toward greater openness and accessibility. This editorial outlines the vision for Advances in Geochemistry and Cosmochemistry, a diamond open access journal that eliminates article processing charges and prioritizes equitable access to scientific knowledge. The journal’s commitment to Open Science as well as diversity in authorship and editorial representation aims to address systemic inequities in research publishing. Drawing on the success of journals like Volcanica, we emphasize the importance of fostering inclusivity and interdisciplinary research in Earth and planetary sciences. By adopting a community-driven approach, Advances in Geochemistry and Cosmochemistry seeks to create a publishing platform that reflects the values of excellent and cutting-edge science, equity, diversity, and innovation, ensuring that knowledge is accessible to all, regardless of geographical or financial limitations.

  PublisherOA PDFDOI

• Reactive-transport models and isotopic tracers reveal the spatial pattern of riverine CO ₂ emissions and suggest cooperative inorganic-organic carbon cycling

  2025-01-01

  article1st authorCorresponding
  PublisherDOI

• The Clumped Isotope Signatures of Multiple Methanogenic Metabolisms

  Environmental Science & Technology · 2025-07-03 · 8 citations

  articleOpen access

  Methane is a potent greenhouse gas, an important energy source, and an important part of the global carbon cycle. The relative abundances of doubly substituted (“clumped”) methane isotopologues (13CH3D and 12CH2D2) offer important information on the sources and sinks of methane. However, the clumped isotope signatures of microbially produced methane from different methanogenic pathways lack a systematic investigation. In this study, we provide a data set encompassing isotopic signatures of hydrogenotrophic, methylotrophic, acetoclastic, and methoxydotrophic methanogenesis. We find that a statistical “combinatorial effect” generates significant differences in 12CH2D2 compositions between hydrogenotrophic methanogenesis and the other pathways, while variations in the fractionation factors of clumped isotopologues result in differences in 13CH3D compositions between the methylotrophic, acetoclastic, and methoxydotrophic pathways. The energy yield of methanogenesis and the energy conservation approaches implemented by different microbial strains may also influence the isotope values of methane. Further analysis suggests that previously observed isotopic signatures of methane in freshwater environments are potentially due to mixing between hydrogenotrophic and other methanogenesis pathways. This study provides new experimental constraints on the isotope signatures of different microbial methanogenic pathways and evidence of the mechanisms responsible for the observed differences. This enables a better understanding of the sources and sinks of methane in the environment.

  PublisherDOI

• Using Peak Geometry and Shifts in the X‐Ray Spectrum of Carbon from Electron Probe Microanalysis to Determine Thermal Maturity of Organic Matter

  Geostandards and Geoanalytical Research · 2025-05-15

  articleSenior author

  During the burial of mudstones, the associated organic matter undergoes gradual thermal maturation, a key process that can influence the reactivity of organic matter during catagenesis, the formation of hydrocarbon deposits and the chemical weathering of mudstones. Conventional methods for assessing the thermal maturity of organic matter often fail to reflect the geochemical heterogeneity between individual organic phases in mudstone samples. Here, we report an alternative, non‐destructive, surficial and micro‐scale (analytical spot size of ~ 300 nm with about 4 μm diffusion depth for micrometre‐size organic grains) method to evaluate the thermal maturity of organic matter in mudstones using the carbon K α X‐ray spectrum measured by field emission‐electron probe microanalyser (FE‐EPMA). Using this method, we observed correlations between parameter values derived from FE‐EPMA spectra, including the peak position, the peak area and the intra‐sample heterogeneity of these measurements, and independently measured vitrinite/solid bitumen reflectance for a suite of mudstones, representing different age, geological context and burial depth. With the increased values in peak area and position, we identified an increase in the carbon mass fraction of organic matter and the mean nominal oxidation state of carbon approaching zero. These trends, which are consistent with aromatisation and graphitisation, provide the rationale for using FE‐EPMA to estimate the thermal maturity of organic matter. To explore some of these trends in more detail, we employed time‐of‐flight secondary ionisation mass spectrometry, X‐ray photoelectron spectroscopy and optical reflectance measurements on a subset of samples.

  PublisherDOI

• Flowpath Partitioning Controls Chemical Weathering Fluxes in the Tropics

  Water Resources Research · 2025-04-01 · 3 citations

  articleOpen access

  Abstract Tropical watersheds are thought to exert a strong control on the global carbon cycle because elevated temperature and rainfall rates promote the chemical weathering of silicate rocks. However, the critical factors that control tropical weathering, such as the role of subsurface flowpaths in setting the sensitivity of weathering to climate change, remain obscure. Here, we relate solute dynamics to flowpath partitioning using new and existing data from the Luquillo Critical Zone Observatory (LCZO) in the tropical forests of eastern Puerto Rico. We used new measurements of deuterium excess in streamflow and rainfall to show that the fraction of young water (F yw , fraction of streamflow less than 1–3 months old) for each catchment increases with increasing discharge. We attribute F yw ‐Q behavior to the activation of shallow flowpaths that efficiently route incident rainfall to streamflow. Results from this 2‐year sampling period are comparable to results from end‐member mixing analysis of longer‐term solute records, suggesting that water routed via shallow flowpaths acquires little additional solutes from weathering reactions. Our findings of apparent mixing between flowpaths can be unified with time‐dependent weathering reactions and time‐variable transit time distributions. To estimate the response of the LCZO to climatic change, we compare F yw ‐Q behavior between sites that experience different mean annual precipitation amounts. Intriguingly, we find that climatically driven changes in flowpath partitioning reconcile watershed fluxes with regolith‐based studies. This suggests that shallow flowpath activation is the mechanism for maintaining constant weathering rates despite variable rainfall rates in the supply limited regions where weathering is already maximized.

  PublisherDOI

Recent grants

• Does Sediment Storage Set the Pace of the Terrestrial Organic Carbon Cycle?

  NSF · $414k · 2021–2024

Frequent coauthors

• A. Joshua West

  University of Southern California

  31 shared

• Kathryn E. Clark

  26 shared

• Preston C. Kemeny

  University of Chicago

  23 shared

• Science Party IODP Expedition

  Mitchell Institute

  18 shared

• J. Jotautas Baronas

  Durham University

  17 shared

• Woodward W. Fischer

  California Institute of Technology

  14 shared

• Jess F. Adkins

  California Institute of Technology

  13 shared

• Guillaume Paris

  13 shared

Labs

• Torres LabPI

  The Torres Lab conducts research on the biogeochemical cycles of elements such as lithium, sulfur, and carbon, and their role in Earth's climate and environmental systems.

Education

• Ph.D., Earth Sciences

  University of Southern California

  2015

Awards & honors

• Texaco Postdoctoral Fellow (2015-17)