Tree Ring Reconstruction Of Modern Radiocarbon Dioxide Variability Over The Southern Ocean

• Main Author: Rachel Corran
• Format: Thesis
• Language: unknown
• Published: 2021
• Subjects: Climate change processes; Atmospheric radiocarbon; Tree ring; Southern Ocean; 040104 Climate Change Processes; School: School of Geography; Environment and Earth Sciences; Unit: Antarctic Research Centre; Degree Discipline: Geology; Degree Level: Doctoral; Degree Name: Doctor of Philosophy; Antarctic; New Zealand; Rafter; Antarc*
• Online Access: https://doi.org/10.26686/wgtn.14703831.v2; https://figshare.com/articles/thesis/TREE_RING_RECONSTRUCTION_OF_MODERN_RADIOCARBON_DIOXIDE_VARIABILITY_OVER_THE_SOUTHERN_OCEAN/14703831

The Southern Ocean is the largest ocean carbon sink region. However, its trend of increasing carbon uptake has shown variability over recent decades. It is important to understand the underlying mechanisms of anthropogenic carbon uptake such that the future response of the Southern Ocean carbon sink under climate forcing can be predicted. The carbon uptake of the Southern Ocean is characterised by the balance of outgassing of CO2 from carbon-rich deep water and sequestration of anthropogenic carbon into surface waters. Atmospheric radiocarbon dioxide (Del14CO2) in the Southern Hemisphere is sensitive to the release of CO2 from the upwelling of ‘old’ 14C-depleted carbon-rich deep water at high southern latitudes, but is insensitive to CO2 uptake into the ocean. Thus Del14CO2 has the potential to be used as a tracer of the upwelling observed, thereby isolating the outgassing carbon component. The Southern Ocean Region has limited atmospheric Del14CO2 measurements, with sparse long-term sampling sites and few shipboard flask measurements. Therefore in this PhD project I exploit annual growth tree rings, which record the Del14C content of atmospheric CO2, to reconstruct Del14CO2 back in time. Within tree ring sample pretreatment for 14C measurement I automate the organic solvent wash method at the Rafter Radiocarbon Laboratory. I present new annual-resolution reconstructions of atmospheric Del14CO2 from tree rings, from coastal sites in New Zealand and Chile, spanning a latitudinal range of 44 S to 55 S, for the period of interest, 1985 – 2015. Data quality analysis using a range of replicate 14C measurements conducted within this project leads to assignment of apx 1.9 ‰ uncertainties for all results, in line with atmospheric measurements. In this project I also develop a harmonised dataset of atmospheric Del14CO2 measurements in the Southern Hemisphere for this period from different research groups, including the new tree ring Del14CO2 records alongside existing data. The harmonised atmospheric Del14CO2 dataset has ...