UC San Diego

This thesis advances the understanding of the global carbon cycle and atmospheric tracer transport by optimizing the use of CO2 and O2 measurements from global airborne campaigns and surface stations. The first three chapters provide toolboxes that leverage the use of airborne data in many aspects. Chapter 1 introduces a novel transformed isentropic coordinate system, Mθe, initially designed to organize airborne data, correct for meteorological variability, and calculate atmospheric inventories of trace gases. This system is versatile and has enabled the development of several toolboxes and models to assess large-scale atmospheric tracer transport and surface tracer flux rates. In Chapter 2, I present the first comprehensive application of Mθe coordinate, focusing on estimating atmospheric potential oxygen (APO ~ O2 + 1.1 CO2) and its seasonal air-sea fluxes, contributing valuable insights into oceanic carbon cycles, and benchmarking existing observation-based and modeled APO flux estimations. In chapter 3, I tackle the challenge of uncertainties in atmospheric transport models (ATMs), by developing two evaluative constraints based on atmospheric CO2 gradients across Mθe and parameterized diabatic mixing rates (tracer transport timescales across Mθe). These constraints lead to a more intuitive evaluation of ATMs, and more accurate descriptions of large-scale tracer transport, particularly over the extratropical Southern Ocean (SO). I also applied the diabatic mixing rates derived from reanalyses to improve seasonal air-sea CO2 flux estimations across different latitudes over the SO. In Chapter 4, I explore the role of large-scale CO2 transport in interpreting long-term CO2 variability at low-latitude stations like Mauna Loa (MLO). It identifies circulation changes as key contributors to variations in CO2 seasonal cycle amplitude at MLO and establishes correlations with climate modes like the Pacific Decadal Oscillation. The implications are significant for ecosystem studies, suggesting that using observed CO2 at low-latitude to constrain large-scale ecosystem changes requires a correct representation of large-scale CO2 transport.Collectively, this thesis represents a multifaceted approach to promote our understanding of the global carbon cycle and atmospheric tracer transport, by leveraging new data types and developing novel analytical tools. The findings support technical advancement in atmospheric science and have broad implications for carbon-climate feedback, climate variability, and global biogeochemical cycles.