Graduate Thesis Or Dissertation
 

High-frequency measurements of total CO₂ : Method development and first oceanographic observations

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  • As concern grows about the long-term effects of increasing atmospheric CO₂ concentrations, it becomes increasingly important to understand the cycling of carbon on Earth, particularly in the dynamic marine reservoir. Gas exchange and relatively rapid ocean mixing times mean that the oceans play a significant role in determining the atmospheric CO₂ concentrations on annual and longer timescales. Over the last forty years, several large-scale projects have provided valuable marine carbon data, increasing the understanding of carbon cycling in ocean basin-scale processes. As more targeted projects are developed, traditional water column sampling techniques do not readily provide the high spatial resolution data necessary to understand small-scale processes. Towed instruments, such as the Lamont Pumping SeaSoar, have been developed which are capable of pumping a continuous sample stream to the shipboard laboratory for analysis. In order to maximize the amount of information obtained from the continuously flowing stream and achieve high spatial resolution, shipboard analyses must be performed at high temporal resolution. This work describes the development of an analytical system to measure the total carbon dioxide (TCO₂) in a continuously flowing seawater stream at high temporal resolution. The system uses a gas-permeable membrane contactor to extract the evolved CO₂ from an acidified stream and a non-dispersive infrared detector to analyze the CO₂ in the resulting gas stream. Laboratory tests have shown that the system responds with a time constant of 6 seconds and is able to resolve changes in signal with better than ±0.1% precision. Coulometric analyses of check samples collected in the field as well as analyses of internal check samples have shown the internal accuracy of the system to be reliable to ±0.1%, and analyses of certified reference materials have shown the absolute accuracy to be better than ±0.1%. Coupled with the Lamont Pumping SeaSoar, the TCO₂ system has yielded high spatial resolution distributions of TCO₂ across the New England shelfbreak front. These TCO₂ data, in conjunction with collocated PCO₂ measurements of similar resolution, allowed us to calculate high spatial resolution distributions of alkalinity. Differences in distributions of alkalinity relative to TCO₂ shoreward and seaward of the front indicated a shift in phytoplankton assemblages as the front was crossed. Our measurements implicated biogenic calcium carbonate production on the seaward side of the front, as indicated by a near equivalence of TCO₂ and alkalinity depletion, and its absence shoreward of the front, as indicated by the absence of alkalinity depletion in areas of significant biological TCO₂ uptake. These high-resolution data can be coupled with collocated high-resolution physical data to calculate mixing and biological rates of production and calcite formation.
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file details BandstraLeahM2005.pdf 2017-10-20 Pubblico Scaricare