Caribbean and Pacific moisture sources on the Isthmus of Panama revealed from stalagmite and surface water <i>δ</i>¹⁸O gradients

Abstract

We test the hypothesis that the Pacific Ocean contributes moisture to the Intertropical Convergence Zone (ITCZ) over southern Central America, by spatial analysis of surface water δ 18 O values from Panama and Costa Rica. The δ 18 O values decrease with distance from the Caribbean Sea to the isthmian divide then gradually increase from the divide toward the Pacific slope, which suggests a contribution of both Caribbean and Pacific sourced moisture to the isthmus. We estimated the Pacific moisture contribution for Pacific slope regions of 22% to 64%. The δ 18 O values from stalagmites from five cave systems demonstrate decreasing δ 18 O values with distance from the Caribbean, implicating the Atlantic Basin as a dominant moisture source. Constraining modern moisture sources is important for the interpretation of stable isotopic proxy records of past rainfall, because of the combined influence of Pacific and Atlantic ocean‐atmosphere phenomena on ITCZ rainfall over the Isthmus of Panama.