Identification of frequent La Niña events during the early 1800s in the east equatorial Pacific

Ellen R.M Druffel,Robert B Dunbar,Sheila Griffin,Desiree Vetter,David M Mucciarone

doi:10.1002/2014gl062997

Ellen R.M Druffel, Robert B Dunbar + Show 3 more

Open Access

https://doi.org/10.1002/2014gl062997

Copy DOI

Abstract

AbstractWe report measurements of near monthly Δ14C and δ18O during selected decades from an east equatorial Pacific coral that grew during the past four centuries. We find that El Niño events occurred regularly during the late 1700s. During the early 1800s, El Niño events occurred less often, and La Niña conditions prevailed, which were accompanied by unprecedented, low cool season Δ14C values and high cool season δ18O values. These results indicate that shallow overturning water (e.g., Central Mode Water) from the North Pacific was likely an important source of water to the Galapagos area during the early 1800s.

Highlights

Radiocarbon (14C) in dissolved inorganic carbon (DIC) in seawater is primarily a tracer of water mass circulation and upwelling
During the early 1800s, El Niño events occurred less often, and La Niña conditions prevailed, which were accompanied by unprecedented, low cool season Δ14C values and high cool season δ18O values
It was reported that two thirds of the Equatorial Undercurrent (EUC) water arriving in the east equatorial Pacific was from the Southern Hemisphere [Rodgers et al, 2003]

Summary

Introduction

Radiocarbon (14C) in dissolved inorganic carbon (DIC) in seawater is primarily a tracer of water mass circulation and upwelling. Subsurface DIC contains lower Δ14C values than those in the surface, because of isolation from the atmosphere and radioactive decay. From a model study of surface Δ14C values from the tropical Pacific, Toggweiler et al [1991] showed that the source of low Δ14C water at the Galapagos (À72‰) was from Subantarctic Mode Water (SAMW) formed in the convergence zone at 40°S–50°S. It was reported that two thirds of the Equatorial Undercurrent (EUC) water arriving in the east equatorial Pacific was from the Southern Hemisphere [Rodgers et al, 2003]. A second source of low 14C water to the east equatorial Pacific is shallow overturning water from the subpolar North Pacific [Druffel et al, 2014; Rodgers et al, 2004], which has lower Δ14C values than waters from SAMW

Methods

Results

Conclusion