Reproducibility of Coral Mn/Ca-Based Wind Reconstructions at Kiritimati Island and Butaritari Atoll

Abstract

Global surface temperatures during the twentieth century are characterized by multidecadal periods of accelerated or reduced warming, which are thought to be driven by Pacific decadal variability, specifically changes in trade-wind strength. However, the relationship between trade-wind strength and global surface warming remains poorly constrained due to the scarcity of instrumental wind observations. Previous work has shown that corals growing at Tarawa Atoll (1.3°N, 173°E) incorporate dissolved Mn flushed from lagoon sediments by El Niño-related westerly wind events (WWEs), providing records of both westerly wind variability and trade-wind strength (on decadal time scales). Here, we explore the utility of this novel coral Mn/Ca-wind proxy at two nearby islands that also feature west-facing lagoons. Short coral Mn/Ca records from Butaritari (3°N, 173°E) and Kiritimati (2°N, 157.5°W) track WWEs, albeit with some intercolony variability in the magnitude and timing of the signal. Variability in coral Mn/Ca signal intensity among records from Butaritari suggests that wind-driven mixing of the sediment Mn reservoir may be finite and/or localized. At Kiritimati, a coral growing outside the lagoon shows higher Mn/Ca concentrations during the 1997/1998 El Niño event, suggesting that nearshore sediments may be an overlooked dissolved Mn reservoir. Taken together, these results highlight a need for additional studies of Mn reservoir variability within and across atolls that hold promise for recording WWEs. These results also suggest that Mn/Ca records from multiple coral colonies and sites are needed to generate robust coral-based wind reconstructions, particularly from sites with unknown or complex Mn transport pathways. © 2021. American Geophysical Union. All Rights Reserved.