Variability in Pacific trade winds inferred from coral Mn/Ca: Implications for the rate of global warming

Abstract:

Zonal wind strength and direction are fundamental components of the El Niño-Southern Oscillation (ENSO) and likely play an important role in global temperature modulation. However, historical observations of tropical Pacific winds are limited, and existing datasets disagree on long-term trends, emphasizing the need for independent data to assess zonal wind variability. Earlier work using a 17-year dataset from Tarawa Atoll suggests that Mn/Ca in corals near west-facing lagoons record westerly winds associated with the onset and maintenance of El Niño events. These westerly wind anomalies trigger strong physical mixing and release of Mn from the Mn-enriched lagoonal sediments, which is incorporated into the coral skeleton. Here we present a new ~90 year Mn/Ca record from Tarawa that allows us to assess westerly wind anomalies before the mid-20^th century, when instrumental data from the tropical Pacific are scarce. We compare this new Mn/Ca record with 20^th-century reanalysis zonal wind and demonstrate a strong association between the frequency of westerly winds and Tarawa Mn/Ca from 1890-1982. This new wind reconstruction also corroborates and extends the idea, developed from models and analyses of the well-observed late 20^th century, that periods of strong Pacific trade winds are associated with cooler equatorial Pacific SSTs and a slower rate of global warming, and vice versa. By adding Mn/Ca to the suite of coral tracers measured for paleoclimate reconstructions from appropriate sites, we can expand our view of past climate variability to include westerly winds, along with the more commonly reconstructed variables of SST and salinity. Development of additional Mn/Ca records from other equatorial atolls with westerly facing lagoons will be used to obtain a broader multivariate perspective on the dynamics of recent climate variability.