Famous for their tortoises and important role in the fiction of Kurt Vonnegut, the Galápagos Islands are often lauded as a home for a variety of species that exist nowhere else and thus contribute to the overall biodiversity on Earth. Among the list of animals endemic to the archipelago are the Galápagos penguins, which are typically around 49 centimeters in length and the only penguins found in the Northern Hemisphere.
The bird’s ability to thrive at this tropical latitude is a result of ocean upwelling, the confluence of processes that cause cold water from the depths to be pushed closer to the surface. Most upwelling—like the kind that takes place along continental coastlines like California—is wind driven (also known as Ekman upwelling). In contrast, upwelling in the Galápagos is driven by topography. The Equatorial Undercurrent flows eastward at anywhere between 50 and 300 meters beneath the surface, hugging the equator all the way from Papua New Guinea to the Galápagos. When it reaches the islands, the waters are pushed around to the north or south—but also upward, piling up like water behind a dam. This forces colder, nutrient-rich waters up from the depths toward the islands, resulting in cooler surface temperatures and an ideal habitat for the penguins.
Here Karnauskas et al. investigate the impact of multidecadal climate variability on this upwelling and its implications for the penguin population. Using relatively high resolution satellite observations, the scientists analyzed sea surface temperatures in the region adjacent to the Galápagos between 1982 and 2014. Although it seems counterintuitive, the warming of Earth’s climate actually coincides with a decrease in average sea surface temperature along the west coast of the Galápagos Islands. The team attributes the finding to a strengthening of the Equatorial Undercurrent.
Trends in the tropical trade winds, according to the scientists, have gradually nudged the Equatorial Undercurrent farther to the north—aligning it more squarely with the Galápagos Islands and thus causing sea surface temperatures to drop by as much as 0.8°C over the study period. The penguin habitats appear to have shifted accordingly, and the populations have thrived most where the waters are coldest. The authors suggest that their study represents an example of how global climate change can have important and variable effects at local scales, especially where the viability of ecosystems is concerned. (Geophysical Research Letters, doi:10.1002/2015GL064456, 2015)
—David Shultz, Freelance Writer
Citation: Shultz, D. (2015), Cooling Galápagos sea surface temperatures affect local penguins, Eos, 96, doi:10.1029/2015EO039721. Published on 23 November 2015.
Correction, 23 December 2015: An earlier version of this article stated that the Galápagos Islands are lauded for their biodiversity and species richness. The text has been updated to state instead that they are home to species that exist nowhere else and thus contribute to the overall biodiversity on Earth.