Particle triggered reactions as an important mechanism of alkalinity and inorganic carbon removal in river plumes

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(11), (2021): e2021GL093178, https://doi.org/10.1029/2021GL093178.The effects of heterogeneous reactions between river-borne particles and the carbonate system were studied in the plumes of the Mississippi and Brazos rivers. Measurements within these plumes revealed significant removal of dissolved inorganic carbon (DIC) and total alkalinity (TA). After accounting for all known DIC and TA sinks and sources, heterogeneous reactions (i.e., heterogeneous CaCO3 precipitation and cation exchange between adsorbed and dissolved ions) were found to be responsible for a significant fraction of DIC and TA removal, exceeding 10% and 90%, respectively, in the Mississippi and Brazos plume waters. This finding was corroborated by laboratory experiments, in which the seeding of seawater with the riverine particles induced the removal of the DIC and TA. The combined results demonstrate that heterogeneous reactions may represent an important controlling mechanism of the seawater carbonate system in particle-rich coastal areas and may significantly impact the coastal carbon cycle.This research was funded by the National Science Foundation (NSF) and the Bi-National Science Foundation U.S-Israel award number OCE-BSF 1635388.2021-11-2

High resolution, in-situ studies of seawater carbonate chemistry and carbon cycling in coastal systems using CHANnelized Optical System II

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2022.Study of the marine CO2 system is critical for understanding global carbon cycling and the impacts of changing ocean chemistry on marine ecosystems. This thesis describes the development of a near-continuous, in-situ dissolved inorganic carbon (DIC) sensor, CHANnelized Optical System (CHANOS) II, suitable for deployment from both mobile and stationary platforms. The system delivers DIC measurements with an accuracy of 2.9 (laboratory) or 9.0 (field) μmol kg-1, at a precision of ~4.9-5.5 μmol kg-1. Time-series field deployments in the Pocasset River, MA, revealed seasonal and episodic biogeochemical shifts in DIC, including two different responses to tropical storm and nor’easter systems. Towed surface mapping deployments across Waquoit Bay, MA, highlighted the export of DIC from salt marshes through tidal water. High resolution (<100 m) data collected during ROV deployments over deep coral mounds on the West Florida Slope revealed a much wider DIC range (~1900 – 2900 μmol kg-1) across seafloor and coral habitats than was observed through the few bottle samples collected during the dives (n = 5, 2190.9 ± 1.0 μmol kg-1). These deployments highlight the need to investigate deep sea biogeochemistry at high spatial scales in order to understand the range of environmental variation encountered by benthic communities.Funding for this work was provided by the National Science Foundation (OCE Award No. 1233654, OCE 1635388, OCE 1841092), National Oceanic and Atmospheric Administration Office of Ocean Exploration and Research (NA18OAR0110352), MIT Seagrant (2017-R/RCM-51), and Woods Hole Oceanographic Institution (Ocean Ventures Fund, Grassle Fellowship)

Influence of vegetation type and site-to-site variability on soil carbonate clumped isotope records, Andean piedmont of Central Argentina (32-34°S)

The clumped isotope geothermometer estimates the formation temperature (T(Δ47)) of carbonates and has great potential to enhance the extraction of environmental data from pedogenic (soil) carbonate in the geologic record. However, the influence of vegetation type and site-specific conditions on carbonate formation processes and T(Δ47) records remains poorly understood. This study examines the potential for variability in T(Δ47) data between nearby, same elevation sites with different C3/C4 biomass. Pedogenic carbonates (undercoatings and nodules) were collected from five modern soil pits in the semi-arid eastern Andean piedmont of Argentina under a summer precipitation regime. Three pits were instrumented with temperature and moisture sensors to 1 m depth, and a fourth was instrumented with additional soil CO2 and atmospheric (temperature, relative humidity, insolation, and rainfall) sensors. T(Δ47) values (mean: 30±6°C (±1SE)) are invariant with depth and are statistically indistinguishable between the four instrumented sites, though a 10 °C difference between our T(Δ47) values and those of a nearby Peters et al. (2013, EPSL) study suggests the potential for significant site-to-site variability, likely due to local soil hydrology. The results of this study suggest that deeper (≥40 cm) T(Δ47) values are consistent with carbonate formation during the early part of soil drying immediately after large mid-summer rainstorms. Carbonate formation ≤ 40 cm depth may be biased to soil drying after small, frequent precipitation events occurring throughout the spring, summer, and fall months, averaging to shallow summer T(Δ47) values and resulting in a near-isothermal T(Δ47) profile.Fil: Ringham, Mallory C.. Syracuse University; Estados UnidosFil: Hoke, Gregory D.. Syracuse University; Estados UnidosFil: Huntington, Katharine W.. University of Washington; Estados UnidosFil: Aranibar, Julieta Nelida. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin