Reconstructing Westerly Wind Bursts and Climate over Abaiang Atoll using Coral Mn/Ca and δ18O Records

The strength and direction of tropical Pacific zonal winds affect global surface warming. During Pacific climate patterns like the El Niño-Southern Oscillation (ENSO), weak easterly trade winds and strong westerly wind bursts (WWBs) accelerate surface warming. Strengthened trade winds correlate with greater ocean heat uptake and slowed warming. Zonal wind patterns thus inform near-term ENSO and global climate predictions. However, tropical Pacific wind observations remain scarce prior to 1970.

The manganese-to-calcium (Mn/Ca) ratio of coral skeletons at remote Pacific atolls demonstrate promise for extending zonal wind records. Trade winds carry Mn-laden dust to these remote atolls, depositing particulate Mn in large, west-facing lagoons. Over time, Mn in lagoon sediments dissolves and accumulates in the sediment porewater space. WWBs later mix lagoon waters and release the accumulated Mn from lagoon sediment porewater into the water column, allowing coral skeletons to incorporate Mn. Strong WWBs correspond to spikes in coral Mn/Ca at atolls like Tarawa, Butaritari, and Kiritimati. Here we apply this coral-based trade-wind proxy to a site with different lagoon morphology: Abaiang atoll. We present short Mn/Ca and δ18O records from two corals that span the very strong 1997-1998 El Niño event.

During this event, when WWBs became more frequent at Abaiang, Mn/Ca ratios in both cores increased. The corals' different positioning relative to Abaiang's central lagoon may explain small differences in the magnitude of Mn/Ca peaks. Additionally, during the 1997-1998 event, δ18O, Sr/Ca, and Li/Mg ratios in core ABG-11 declined, reflecting the warmer sea surface temperatures and wetter conditions expected during El Niño events in the west-central Pacific. During the event, heat stress to the corals likely caused Sr/Ca ratios to deviate from Li/Mg ratios. Our results at Abaiang further support the reliability of coral Mn/Ca in reconstructing Pacific trade wind behavior.