Palmyra Atoll Coring Expedition

A collaboration between the U.S. Geological Survey and the U.S. Fish and Wildlife Service

To develop ecosystem climate adaptation strategies, the U.S. Fish and Wildlife Service is working with researchers from the U.S. Geological Survey. The team is working to better understand what pre-human lowland vegetation communities on atolls look like in the context of climate change and sea level change.

So, in late March 2024, a team of scientists from the U.S. Geological Survey and the U.S. Fish and Wildlife Service traveled to Palmyra Atoll to collect sediment cores from the atoll’s lagoon. The various fossils and biomarkers buried in the sediments will be able to shed light on past environmental and climate conditions. Because of its location in the central Pacific Ocean, Palmyra is an ideal location to study a major Pacific climate pattern that affects global weather: the El Niño-Southern Oscillation (ENSO).

In El Niño years, the trade winds that blow westward along the equator weaken, warming sea surface temperatures around Palmyra and making the atoll wetter. In La Niña years, the trade winds are stronger, pushing warm water toward Asia, causing ocean upwelling in the region and cooling sea surface temperatures.

Due to the remote location of the work, the team had to plan months in advance to transport larger items and reduce the size of the coring equipment to be light and compact enough to fit on a small Falcon 50 jet. The team spent 10 days on the atoll, building the coring platform with aluminum frame pontoons, positioning the raft in the deepest part of the lagoon, and finally collecting the cores. Curious black tip reef sharks often circled the raft curiously, making it all the more exciting. The team ultimately recovered more than 5 meters of core, which sank into an unexpected coral rubble deposit.

Back to the lab

Previous studies of short sediment cores collected from the atoll in 2009 showed that the isotopic composition of fossil larval bivalve shells correlates strongly with changes in sea surface temperature and salinity, which vary with precipitation. In addition, the sediment accumulation rate in the lagoon is very high, about 0.66 cm/year. Therefore, the team hopes that these fossil shells may be the key to reconstructing El Niño-Southern Oscillation (ENSO) activity directly from where it is most intense.

By studying the sediment cores, the researchers will have additional data sets to understand changes in vegetation (by studying fossil pollen and biomarkers), as well as changes in bird populations (by studying nitrogen isotopes in the cores). One question this study will address using fossil pollen grains is, coconut (Coconut palm), which the U.S. Fish and Wildlife Service is working to eliminate in favor of trees that are more friendly to shorebirds. Pisonia Forest habitats are actually part of the pre-human environment.