Eastern tropical north Pacific coral radiocarbon reveals North Pacific Gyre Oscillation variability

Abstract:

The North Pacific Oscillation (NPO) is possibly a major influence on global climate through its influence on the El Niño-Southern Oscillation (ENSO), but the decadal-scale cyclicity and limited observations (≈50 years) of the NPO make it difficult to explore this relationship. One approach to this problem is to use marine archives (e.g., corals and sediments) to build significantly longer records of the oceanic expression of the NPO—the North Pacific Gyre Oscillation (NPGO). For example, the strengthened winds associated with positive NPO sea level pressure distributions increase gyre circulation, increasing upwelling in the coastal northeastern Pacific and equatorward flow of the California Current. However, marine archives along the coast are potentially influenced by both NPGO and ENSO and are not ideal. Here we demonstrate that corals from the Revillagigedo Islands—in the Eastern Tropical North Pacific (ETNP)—provide a relatively “clean” record of NPGO variability. In particular, coral Δ¹⁴C and δ¹⁸O show fluctuations between salty / Δ¹⁴C “young” waters (native to the ETNP) and fresh / Δ¹⁴C “old” waters (similar to those upwelled off the California margin). This variability is highly coherent and consistent with the NPGO index, such that positive NPGO (and therefore NPO) corresponds to a increased presence of California Current waters in the ETNP. ENSO appears to have little influence on this record, probably because of minimal change in seawater Δ¹⁴C associated with the poleward propagating Kelvin waves associated with ENSO. Pre-instrumental records of NPGO, like these from the Revillagigedo Island corals, are necessary to begin understanding the tropical-subtropical drivers of NPO, ENSO, and other ocean-atmosphere climate phenomena.