Coring Expedition to Palmyra Atoll
Recently, a team of USGS and U.S. Fish and Wildlife Service scientists traveled to Palmyra Atoll to collect sediment cores. Analyzing the cores and other sources of data will help managers better understand pre-human vegetation, climate variability, and sea level changes.
Where in the World is Palmyra?
Palmyra Atoll is a remote island in the Line Islands near the equator in the central Pacific Ocean (latitude 5˚53΄N, longitude 162˚05΄W). It is a coral atoll with several islets surrounding a deep (up to ~50 m) inner lagoon with 12 km2 of land and 14 km2 of sea-facing coral reef.
The atoll provides habitat and breeding grounds for many different species of seabirds. In the past, the atoll was used to farm coconuts for profit. This led to coconut tree monocultures across the atoll, that replaced parts of the native rainforest and wetland ecosystems.
The atoll is a national wildlife refuge currently owned by The Nature Conservancy and managed by the U.S. Fish and Wildlife Service (USFWS) and is part of the Pacific Remote Islands Marine National Monument.
The atoll is uninhabited, but The Nature Conservancy manages a science station for visiting research teams that includes wet and dry labs, screened-in huts for sleeping, and a galley where the temporary residents can gather for meals.
Managers are working to improve shorebird habitat by restoring the atoll’s native wetlands and forests.
Partnership between the USGS and the U.S. Fish and Wildlife Service
In order to inform ecosystem climate adaptation strategies, the USFWS is partnering with USGS researchers. The team is working to better understand what pre-human lowland vegetation communities on the atoll looked like in the context of climate variability and sea level changes.
So in late March 2024, a team of USGS and USFWS scientists traveled to Palmyra Atoll to collect sediment cores from the atoll's lagoon. Various fossils and biomarkers buried in the sediments will be able to shine light on what environmental and climate conditions were present in the past. Because of its location in the central Pacific Ocean, Palmyra is the ideal place from which to study a major climate pattern of the Pacific Ocean that can affect weather worldwide: El Niño–Southern Oscillation (ENSO).
During El Niño years, trade winds that blow west along the equator relax and sea surface temperatures increase in the ocean surrounding Palmyra, bringing wetter conditions to the atoll. During La Niña years, the trade winds blow even stronger, pushing warm water towards Asia and bringing ocean upwelling and cooler sea surface temperatures to the region.
Because of the remote nature of the work, the team had to plan months in advance to ship larger items and scale down coring equipment to be lightweight and compact enough to fit on a small Falcon 50 jet. The team spent 10 days on the atoll, building the coring platform from an aluminum frame pontoon, situating the raft in the deepest part of the lagoon, and finally, collecting a core. All of this was made more exciting by curious black tipped reef sharks that routinely circled the raft with curiosity. The team ultimately recovered over 5 meters of core, bottoming out in an unexpected coral rubble deposit.
Back to the Lab
Previous work on a short sediment core collected in 2009 from the atoll shows that the isotopic composition of fossil larval bivalve shells has a strong correlation with changes in both sea surface temperature and salinity, which changes with precipitation amounts. Moreover, the sediment accumulation rate in the lagoon is very high, on the order of .66 cm/yr. As a result, the team is hopeful these fossil shells may be the key to producing a long-term reconstruction of ENSO activity directly from where it expresses the strongest.
Other datasets that will be produced from the sediment cores will shed light on changes in vegetation by studying fossil pollen and biomarkers, and changes in bird populations by studying nitrogen isotopes in the core. One question the study will address using fossil pollen grains is whether Cocos nucifera (coconut palms), which are being eradicated through a USFWS effort in favor of more shorebird friendly Pisonia forest habitat, are in fact a part of the pre-human environment.
The work is part of a larger ongoing project in partnership with the USFWS to understand pre-human lowland vegetation communities in the context of ENSO climate variability and sea level changes to inform wetland climate smart adaptation strategies with the goal of improving shorebird habitat.
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