One of the most useful paleoclimate proxies used to reconstruct conditions in Earth’s history is tiny shell fossils within the layers of sediment on the seafloor. Planktonic foraminifera, or forams, float in ocean water during their lifetimes and exhibit changes in the chemistry of their shell as well as the abundance and range of communities based on ocean variability through time. Scientists use foram records to reconstruct past sea surface temperature, primary productivity, and other conditions, but an unresolved question is how forams will be affected by marine heatwaves, which are predicted to become more frequent and intense with future climate change.
A new study, partially funded by the Climate Program Office’s Climate Observations and Monitoring (COM) Program, documented forams that were collected in nets (pictured above) in 2010, 2012, and 2014-2019 along a Northern California Current transect and compared them to recent marine heatwave conditions which occurred in 2014-2016, with a shorter duration event in 2019. Earlier on in this project, NOAA Fisheries shared a story detailing how the samples were collected. The results, published in Frontiers in Marine Science, show that during times of typical ocean temperatures, specific cold-water foram species were most prevalent in the study region, but warm-water species from areas toward the tropics became more abundant during marine heatwaves. The study shows that these changes were directly correlated with changes in temperature and salinity in the ocean water’s upper 100 meters, and not related to the distance from a coastline or upwelling processes. The paper, led by Oregon State University doctoral student Kelsey Lane, with support from COM-funded scientist Melanie Fewings, contributes to a COM initiative to develop datasets for a changing climate, providing the first detailed record of foram variations in association with marine heatwave events in this region.