PP010-0013
Reinforcing the Mn/Ca Trade-Wind Proxy: A Closer Look at Manganese Redox in Kiritimati’s Lagoon

Tuesday, 8 December 2020
Poster
Sophia Bautista1, Alice Chapman1, Diane M Thompson1, Jessica Carilli2, Stephan Hlohowskyj3, Gwyneth Williams Gordon4 and Tyler Goepfert4, (1)University of Arizona, Department of Geosciences, Tucson, AZ, United States, (2)Scripps Institution of Oceanography, La Jolla, United States, (3)Central Michigan University, Department of Earth and Ecosystem Science, Mount Pleasant, United States, (4)Arizona State University, METAL Lab, Tempe, AZ, United States
Abstract:
The strength and location of the tropical Pacific trade winds are associated with global warming and climate variability patterns, such as El Niño-Southern Oscillation (ENSO) and Pacific Decadal Variability. Despite the importance of wind data for predicting future critical climate patterns such as ENSO, wind observations only date back ~30 years.

It was recently discovered that the Mn/Ca ratio of equatorial Pacific coral skeletons reflect and can therefore reconstruct westerly wind events (WWEs). Originally developed at Tarawa atoll, this proxy has since been reproduced at Kiritimati and Butaritari, with the potential of being applied to other Pacific islands. These islands receive Mn-laden dust via trade winds throughout the year; Mn settles, is reduced, and accumulates in the porewater space of lagoon sediments. Intermittent WWEs mix the lagoon and remobilize dissolved Mn from the porewater into the water column, which is then subsequently integrated into coral skeletons.

Applying this novel proxy to corals from other islands requires a closer look at the individual components of this mechanism by which Mn is transferred from dust to coral. A recent investigation of porewater Mn concentration, redox potential, and organic matter content (% OM) of a sediment core in Kiritimati’s main lagoon has provided key insights into the process of Mn accumulation in sediment porewater. First, the transition from oxic to anoxic environment occurs at ~5.5-6.5 cm, shallow enough to permit sufficient mixing and remobilization of porewater Mn during WWEs. Second, the oxidation of sediment OM (on average 7.6-8.2%) promotes the dissolution of reduced Mn, suggesting that % OM influences the amount of dissolved Mn produced in sediment porewater. Leveraging the strong relationship between sediment OM and the porewater Mn reservoir, we present a complete analysis of surface sediment % OM in a network of lagoon cores to infer the spatial distribution of the porewater Mn reservoir across the Kiritimati lagoon. These results will improve the interpretation of the timing and magnitude of coral Mn/Ca anomalies following WWEs, and identify sites most suitable for the application of this novel wind proxy.

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