Ringham Mallory C.

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Ringham
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Mallory C.
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  • Article
    Particle triggered reactions as an important mechanism of alkalinity and inorganic carbon removal in river plumes
    (American Geophysical Union, 2021-05-20) Wurgaft, Eyal ; Wang, Zhaohui Aleck ; Churchill, James H. ; Dellapenna, Timothy M. ; Song, Shuzhen ; Du, Jiabi ; Ringham, Mallory C. ; Rivlin, Tanya ; Lazar, Boaz
    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.
  • Thesis
    High resolution, in-situ studies of seawater carbonate chemistry and carbon cycling in coastal systems using CHANnelized Optical System II
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2022-05) Ringham, Mallory C. ; Wang, Zhaohui Aleck
    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.
  • Article
    Development of the channelized optical system II for in situ, high-frequency measurements of dissolved inorganic carbon in seawater
    (American Chemical Society, 2024-03-25) Ringham, Mallory C. ; Wang, Zhaohui Aleck ; Sonnichsen, Frederick ; Lerner, Steven A. ; McDonald, Glenn ; Pfeifer, Jonathan A.
    This study describes the development of the CHANnelized Optical System II (CHANOS II), an autonomous, in situ sensor capable of measuring seawater dissolved inorganic carbon (DIC) at high frequency (up to ∼1 Hz). In this sensor, CO2 from acidified seawater is dynamically equilibrated with a pH-sensitive indicator dye encapsulated in gas-permeable Teflon AF 2400 tubing. The pH in the CO2 equilibrated indicator is measured spectrophotometrically and can be quantitatively correlated to the sample DIC. Ground-truthed field data demonstrate the sensor’s capabilities in both time-series measurements and surface mapping in two coastal sites across tidal cycles. CHANOS II achieved an accuracy and precision of ±5.9 and ±5.5 μmol kg–1. The mean difference between traditional bottle and sensor measurements was −3.7 ± 10.0 (1σ) μmol kg–1. The sensor can perform calibration in situ using Certified Reference Materials (CRMs) to ensure measurement quality. The coastal time-series measurements highlight high-frequency variability and episodic biogeochemical shifts that are difficult to capture by traditional methods. Surface DIC mapping shows multiple endmembers in an estuary and highlights fine-scale spatial variabilities of DIC. The development of CHANOS II demonstrates a significant technological advance in seawater CO2 system sensing, which enables high-resolution, subsurface time-series, and profiling deployments.