Inorganic carbon dynamics at the land-ocean interface

Matthews, Ruth (2022) Inorganic carbon dynamics at the land-ocean interface. Doctoral thesis, University of East Anglia.

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Recent studies have recognised the importance of estuaries in the context of land-ocean carbon cycling, but large uncertainties around estuarine CO2 outgassing estimates remain. Furthermore, there is debate about the relative contribution of different factors to estuarine dissolved inorganic carbon (CT) and total alkalinity (AT) concentrations.
This thesis contributes measurements of CT and AT in 16 UK estuaries, covering range of sizes, weather regimes and geologies. Estuarine CT and AT concentrations are found to vary from 0 – 5000 µmol kg-1 at the freshwater inflow. Between-estuary differences are controlled by catchment lithology; chalk bedrock weathering drives the highest freshwater CT and AT concentrations, moderate freshwater CT and AT concentrations are driven by limestone weathering, and estuaries draining non-carbonate bedded catchments have low freshwater CT and AT concentrations. Mixing is the dominant control on estuarine carbonate chemistry along the salinity gradient.
Given that estuarine CT and AT dynamics are controlled ultimately by their riverine concentrations, a range of geochemical tracer variables were measured in four rivers and end member mixing models are constrained to determine the quantitative contribution of different bedrock types to river flow. Chalk and limestone bedrock weathering have measurably different geochemical signatures. Secondary geological data are well-described by the models, so future UK studies may avoid this complex analysis entirely.
The partial pressure (pCO2) and water-to-air fluxes of CO2 (FCO2) are calculated. pCO2 is related to temperature and organic carbon concentration, suggesting that outgassing is driven by river-derived organic carbon degradation. UK-wide estuarine outgassing is estimated, using FCO2 interpolation and upscaling, to be equivalent to approximately ¼ of the current UK fossil fuel emission.
This study presents the first full examination of the factors that drive carbonate chemistry between estuaries, which was only made possible because of the uniquely large number of estuaries sampled.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Kitty Laine
Date Deposited: 27 Jun 2023 11:23
Last Modified: 27 Jun 2023 11:23


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