A Stormy Voyage Unveils Ocean's Carbon Cycle Secrets
In the midst of the COVID-19 pandemic, a team of scientists embarked on a daring research expedition to the North Atlantic, braving a series of storms and bureaucratic hurdles to uncover the mysteries of the ocean's carbon cycle. This journey, led by David Siegel from UC Santa Barbara, resulted in a groundbreaking study that sheds light on the crucial role of marine snow in the planet's climate regulation.
The Ocean's Biological Pump and Marine Snow
The ocean's carbon cycle is a complex process where photosynthetic plankton, or phytoplankton, convert inorganic carbon into organic compounds, forming the foundation of the marine food web. These tiny organisms fix an astonishing 55 to 60 billion metric tons of carbon annually. A significant portion of this carbon is transported to the ocean's depths through the biological carbon pump, largely carried by marine snow - tiny organic particles larger than 0.5 millimeters that drift down from the upper ocean.
Alice Alldredge and Mary Silver, oceanographers at UCSB and UC Santa Cruz, respectively, pioneered the study of marine snow in the 1980s. They discovered that marine snow sinks relatively quickly, up to 100 meters each day, compared to individual phytoplankton sinking only 1 meter per day. This rapid descent is crucial for long-term carbon sequestration.
Unraveling the Marine Snow Mystery
However, scientists had limited understanding of how ocean dynamics and interactions with living organisms affect marine snow. Uta Passow, a professor at Memorial University of Newfoundland, noted that while they knew much about marine snow composition, its real behavior in the ocean was largely unknown.
To address this, Siegel, Passow, and their colleagues built upon Alldredge and Silver's work, utilizing modern technology to enhance our models of the planet's carbon cycle. They proposed the Export Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign to NASA, aiming to link satellite measurements of photosynthetic activity to the fate of carbon in the ocean.
A Stormy Research Cruise
The EXPORTS North Pacific expedition in 2018 was highly productive, but the North Atlantic campaign faced a near-cancellation due to the COVID-19 pandemic. The team managed to set sail in April 2021, with all American scientists receiving their COVID-19 vaccines before departure. This logistical feat involved coordinating safety plans across 40 institutions in over five countries, ensuring the health of the crew and researchers.
During the research cruise, four major storms battered the team, with wind speeds exceeding 50 knots and surface waves reaching over 20 feet. These storms acted like blenders, shredding marine snow into smaller pieces, reducing its flux into the deep ocean. However, a few days after each storm, a pulse of marine snow left the surface ocean, indicating a complex interplay between ocean turbulence, particle aggregation, and sinking fluxes.
Zooplankton's Role in Marine Snow Breakdown
The team also investigated the fate of marine snow as it sank beyond the ocean surface, at depths between 200 and 500 meters. They found that the number of particles smaller than 0.5 mm roughly doubled over the month-long experiment, suggesting that marine snow breakdown occurs primarily through biological processes, with zooplankton playing a significant role.
This discovery challenges current Earth systems models, which underestimate the impact of zooplankton on marine snow breakdown. By incorporating this knowledge, climate models can be improved, leading to more accurate predictions of carbon flux.
The EXPORTS Mission's Impact
The EXPORTS mission has been a significant step forward in understanding the ocean's carbon cycle. The second phase aims to integrate this newfound knowledge into carbon cycle models, which are essential for climate modeling. The research community is now better equipped to address the complexities of the ocean's biological pump and its role in climate regulation.
As Siegel reflects, 'It’s a friggin’ miracle that we pulled this off.' The successful completion of the EXPORTS project has earned the NASA project office an Administrator’s Group Achievement Award, recognizing their perseverance and innovative thinking in the face of adversity.
