PP010-0003
Assessing the Reliability of the Coral Mn/Ca-based Trade-wind Proxy: Interpreting the Mn Signal Lag

Tuesday, 8 December 2020
Poster
Alice Chapman1, Diane M Thompson1, Jessica Carilli2, Thomas M Marchitto Jr3, Hussein R Sayani4 and Kim Cobb5, (1)University of Arizona, Department of Geosciences, Tucson, AZ, United States, (2)Scripps Institution of Oceanography, La Jolla, United States, (3)Univ Colorado, Boulder, CO, United States, (4)Georgia Institute of Technology, Earth and Atmospheric Sciences, Atlanta, MA, United States, (5)Georgia Institute of Technology Main Campus, Department of Earth and Atmospheric Sciences, Atlanta, GA, United States
Abstract:
Tropical Pacific trade-wind behavior has global influence due to its connection to Pacific climate phenomena such as the El Niño-Southern Oscillation (ENSO). By disrupting the Pacific's east-west air pressure gradient, ENSO leads to anomalous wind patterns and ocean heat uptake, thereby modulating the rate of climate change. Wind observations only date back 30-40 years, however, limiting the skill with which climate models can predict the future behavior of ENSO.

The manganese-to-calcium ratio (Mn/Ca) of corals growing at islands with large, west-facing lagoons is a promising new archive (“proxy") of Pacific trade-wind strength. At such sites, Mn/Ca variability is linked to the behavior of trade winds, which are thought to transport Mn-laden dust to the island's main lagoon. Intermittent strong, westerly wind events (WWEs) during El Niño years then mix lagoon waters and remobilize Mn-rich porewater from lagoon sediments, which can then be incorporated into coral skeletons.

However, considerable uncertainties remain in the processes by which this pulse of Mn-enriched porewater is advected and subsequently incorporated into the coral skeleton, impacting the timing and magnitude of the Mn/Ca signal. At Kiritimati and Butaritari atolls, coral Mn/Ca spikes do not occur concurrently with WWEs; there is a lag between islands and among sites within each island. Here we present the link between dissolved Mn concentrations in the lagoon and coral Mn/Ca at Kiritimati, as we trace their behavior through the recent 2015-2016 El Niño event. These results provide insight into the roles of elevated lagoon Mn concentration and lagoon morphology in the observed lag between WWEs and the spike in coral Mn/Ca at Kiritimati.

Ongoing work leverages a network of coral samples across the west-facing lagoons of Abaiang, Tarawa, and Jarvis atolls to further investigate how lagoon morphology impacts the magnitude and timing of the Mn/Ca wind signal. By establishing the cause of this Mn signal lag and elucidating key mechanisms, this study will help us assess the reliability of this coral Mn/Ca-based trade-wind proxy in its application across spatial and temporal scales, thus paving the way for reliable coral-based wind reconstructions in the future.

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