The massive Pacific Ocean breathes slowly, exposing its deepest waters to the atmosphere only every few thousand years. Still, its sheer size enables it to absorb roughly 10% of global anthropogenic carbon dioxide emissions, as much as or more than any other ocean on the planet. New research shows that the Pacific has ramped up its carbon dioxide uptake in recent decades, in large part because of shifting ocean currents.
In the new study, Carter et al. took advantage of 3 decades of ocean observations in the Pacific Ocean conducted by the Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) oceanography survey. GO-SHIP scientists sail the world’s oceans collecting measurements of dissolved inorganic carbon, which serves as an indicator of how much carbon dioxide the water has absorbed from the atmosphere. GO-SHIP also measures other factors driving the exchange of carbon dioxide between the air and the sea surface, such as the availability of nutrients that feed carbon-capturing photosynthetic algae.
The team compared the Pacific Ocean’s absorption of carbon dioxide between two decades: 1995 to 2005 and 2005 to 2015. Between the first and second decades, carbon dioxide accumulation increased from 8.8 to 11.7 petagrams, or gigatons, of carbon. Although the biggest increase in carbon dioxide was due to mounting levels of the greenhouse gas in the atmosphere, variations in the rate of accumulation depended on the behavior of a system of ocean currents called the Southern Hemisphere Subtropical Gyre, they found.
This large counterclockwise eddy, which circulates between South America and Australia, appears to be responsible for the unexpected acceleration in carbon dioxide accumulation, the team writes. Careful, continued decadal surveys of the ocean’s interior are key to tracking ocean carbon in the future and understanding the ocean’s role in climate change, they say. (Global Biogeochemical Cycles, https://doi.org/10.1029/2018GB006154, 2019)
—Emily Underwood, Freelance Writer