From Wind to Coral: Assessing the Mechanism Behind the Coral Mn/Ca-based Trade-wind Proxy
Abstract
Tropical Pacific trade-wind direction and strength have global repercussions due to their connection to Pacific climate phenomena such as El Niño-Southern Oscillation (ENSO). ENSO disrupts the Pacific's east-west air pressure gradient, leading to anomalous wind patterns and ocean heat uptake, which consequently modulate the rate of climate change. Scarce wind observations limit the ability of climate models to predict how the magnitude and frequency of future ENSO events will change.
A promising new archive ("proxy") of tropical Pacific wind strength consists of a link between the manganese to calcium ratio (Mn/Ca) of corals growing at islands with west-facing lagoons and the behavior of trade winds, which are thought to transport Mn-laden dust to the island's main lagoon. Intermittent strong, westerly wind bursts (WWBs) during El Niño years mix lagoon waters and remobilize Mn-rich lagoon sediments. This Mn is then incorporated into coral skeletons, leading to an increase in coral Mn/Ca. Kiritimati and Butaritari islands are equatorial Pacific atolls in the trade-wind belt with west-facing lagoons. The east side of Kiritimati consists of a network of shallow lakes, whose sediment porewater Mn concentration likely reflects the initial Mn reservoir of the main lagoon. The juxtaposition of the lagoon and lakes is advantageous for tracing the Mn signal from the primary dust and porewater reservoir (which accumulates in isolated lake sediments) to the coral record, via wind-driven remobilization and advection of lagoonal sediments. Mn/Ca spikes corresponding to WWBs in recently analyzed coral cores from Kiritimati and Butaritari demonstrate this proxy's reproducibility across colonies and sites. While we also detect a Mn spike in seawater during WWB events, the transformation and advection that Mn undergoes from porewater to water column to coral skeleton is still unknown. Here we present the results from a series of Kiritimati lake and lagoon sediment cores, which provide insight into this Mn advection pathway and how coral Mn/Ca can be affected by proximity to the lagoon's mouth. Establishing this Mn transfer mechanism will elucidate the individual pathways that constitute the coral Mn/Ca-based wind proxy, thus improving our understanding of the relationship between wind behavior and climate variability.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP33D1712C
- Keywords:
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- 1635 Oceans;
- GLOBAL CHANGE;
- 4825 Geochemistry;
- OCEANOGRAPHY: CHEMICAL;
- 4220 Coral reef systems;
- OCEANOGRAPHY: GENERAL;
- 4916 Corals;
- PALEOCEANOGRAPHY