The Pacific coast of northern South America, from Panama to Ecuador, also known as the Chocó biogeographic region, is one of the wettest and more biodiverse places on Earth. These wet conditions are caused by the presence of a tropical low-level atmospheric current known as the Chocó low level Jet that transports moisture from the Pacific Ocean to the Andes of Colombia and is responsible for a large portion of moisture entering the continent, reaching as far as the Eastern Cordillera. In order to understand better the climate and ecosystem dynamics of such a wet region, we investigated the past hydroclimate and environmental conditions of a yet an unexplored area, the Medellincito wetland at 2020 m above sea level, located on the water divide of the Western Cordillera of Colombia, under the direct influence of the Chocó Jet. Our results indicate that between ∼6680 and 3710 cal yr BP the wetland had permanent waters and was surrounded by forest. This suggests wet conditions with a strong and persistent Chocó Jet. From ∼3710 to ∼1560 cal yr BP, the wetland dried out and open vegetation dominated by grasses replaced the forest. Later on, between ∼1200 and 750 cal yr BP the wetland formed again although with shallow waters, while open vegetation continued to expand. Humid conditions and the forest were re-established after 750 cal yr BP. We hypothesize that dry conditions in an otherwise very wet area were caused by the weakening of the Chocó Jet, possibly associated with ENSO-moderated changes in the temperature of the Pacific Ocean that coincided with changes in the position, relative to today’s, of the Intertropical Convergence Zone. This record highlights that the ecosystems’ dynamics in the Chocó biogeographic region are highly responsive to variations in moisture from the Chocó Jet, which in turn depends on temperatures in the Pacific Ocean. With current global change leading to the warming of the oceans, this highly biodiverse region can potentially be transformed into grass-rich ecosystems as it had occurred in the past.

南美洲北部的太平洋海岸，从巴拿马到厄瓜多尔，也被称为Chocó生物地理区域，是地球上最潮湿，生物多样性最丰富的地方之一。这些潮湿的条件是由热带低空大气流（称为Chocó低空急流）引起的，该低空急流将水分从太平洋输送到哥伦比亚的安第斯山脉，并导致大部分水分进入非洲大陆，达到远至东部山脉。为了更好地了解这种湿润地区的气候和生态系统动态，我们调查了尚未开发的地区，即位于西部山脉山脉水域的海拔2020 m的麦德林奇托湿地的过去水文气候和环境条件在ChocóJet的直接影响下。我们的研究结果表明，在约6680到3710 cal BP之间，湿地具有永久水域，被森林包围。这表明强劲而持久的ChocóJet可以在潮湿的条件下使用。在BP的大约3710年至大约1560年之间，湿地变干了，以草为主的开阔植被取代了森林。后来，在约1200到750 cal BP之间，尽管水浅，湿地又形成了，而开放的植被继续扩大。在750 cal BP之后，重新建立了潮湿的环境和森林。我们假设，在原本非常潮湿的地区，干旱条件是由ChocóJet的减弱引起的，这可能与ENSO调节的太平洋温度变化有关，这与相对于当今热带地区的位置变化相吻合会聚区。该记录突出表明，乔科生物地理区域内的生态系统动态对乔科喷流的水分变化有高度响应，而乔科喷流的水分变化又取决于太平洋的温度。随着当前的全球变化导致海洋变暖，这个高度生物多样化的地区可能像过去一样潜在地转变为富含草的生态系统。