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Measuring the strength of the ocean’s biological carbon pump

Springtime in the Bering Sea brings reduced sea ice cover and increased phytoplankton production. As the climate warms, productivity may contribute to oxygen depletion in these waters. The image is a composite of Aqua/MODIS data collected over two days in May 2021. Credit: NASA.

Scientists are investigating the movement of carbon from the atmosphere to the deeper ocean via ecological processes.

Microscopic organisms known as phytoplankton in the upper ocean play a critical role in Earth’s carbon cycle and climate, transporting carbon from the surface to the deeper ocean where it is stored for months to millennia. This movement of carbon—known as the biological carbon pump— represents a significant sink for atmospheric carbon dioxide, but measuring it remains a challenge. A better understanding of what influences the function of the ocean's biological pump, and how this may be altered under changing ocean conditions, is critical to predicting how oceans respond to and influence climate change.

The joint NASA-NSF EXPORTS (EXport Processes in the Ocean from RemoTe Sensing) field campaign is one of the most comprehensive studies on the biological carbon pump ever conducted. EXPORTS uses research vessels, underwater robotic platforms, and satellite imagery to study the role of ocean ecosystems in the global carbon cycle and its implications for Earth’s climate. Results from the 2018 EXPORTS North Pacific field campaign, published in 2020, described how carbon flux varies over space and time and measured the strength of the biological carbon pump in an area characterized by its low ecosystem productivity.1

In addition, results highlight the importance of small organic particles in sustaining deep ocean communities and the critical role microorganisms play in removing and altering organic carbon as it sinks.2 Data from the 2021 EXPORTS field campaign, deployed in the North Atlantic, will complement the 2018 findings. These results improve understanding of how the biological pump works, including how it may change in the future under different climate change scenarios, and could lead to more accurate climate models.

1 Buesseler, KO, et al. 2020. High-resolution spatial and temporal measurements of particulate organic carbon flux using thorium-234 in the northeast Pacific Ocean during the EXport Processes in the Ocean from RemoTe Sensing field campaign. Elem Sci Anth, 8:1.

2 Stephens BM, Opalk K, Petras D, Liu S, Comstock J, Aluwihare LI, Hansell DA and Carlson CA (2020) Organic Matter Composition at Ocean Station Papa Affects Its Bioavailability, Bacterioplankton Growth Efficiency and the Responding Taxa. Front. Mar. Sci. 7:590273.