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

Abstract

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.