A Stormy Voyage Unveils Ocean's Carbon Cycle Secrets
In the midst of the global health crisis, a brave team of scientists embarked on a daring expedition to the North Atlantic, braving the elements to unravel the mysteries of the ocean's carbon cycle. Amidst bureaucratic hurdles and the relentless fury of nature, they emerged with groundbreaking insights that could reshape our understanding of Earth's climate.
The journey began with a series of storms that battered three state-of-the-art research vessels, threatening to derail the entire mission. Yet, the determined crew and researchers persevered, and their efforts yielded a treasure trove of knowledge. The study, led by David Siegel of UC Santa Barbara, was published in the prestigious journal Global Biogeochemical Cycles. It delves into the intricate dance of the ocean's biological pump, a vital player in the planet's carbon cycle.
Unraveling the Marine Snow Mystery
At the heart of this story is marine snow, a fascinating phenomenon. Tiny organic particles, larger than 0.5 millimeters, drift down from the ocean's surface, forming a fluffy blanket of detritus. Alice Alldredge and Mary Silver, oceanographers at UCSB and UC Santa Cruz, respectively, pioneered research on marine snow in the 1980s, revealing its rapid descent of up to 100 meters per day. This process is akin to a natural conveyor belt, transporting carbon from the sunlit surface to the ocean's depths, where it can be sequestered for months to millennia.
However, the dynamics of marine snow and its interaction with ocean currents and living organisms remained largely unknown. Uta Passow, a professor at Memorial University of Newfoundland, highlighted the gap in our understanding, emphasizing the need to explore marine snow's behavior in the vast ocean.
The EXPORTS Mission: Unlocking the Ocean's Secrets
To bridge this knowledge gap, NASA's EXPORTS (Export Processes in the Ocean from RemoTe Sensing) field campaign was born. This ambitious project aimed to link satellite measurements of photosynthetic activity to the fate of carbon in the ocean's biological pump. The mission involved three ships, the R/V Sarmiento de Gamboa, RRS Discovery, and RRS James Cook, and a dedicated team of scientists and researchers.
Despite the challenges posed by the pandemic, the EXPORTS team pulled off a remarkable feat. They coordinated safety plans across 40 institutions in over five countries, ensuring the health and safety of the crew and researchers. The project received an Administrator's Group Achievement Award in 2022 for its perseverance and innovative problem-solving.
Storms and Marine Snow: A Dynamic Duo
One of the most intriguing findings emerged from the storms that battered the research vessels. These storms, with wind speeds exceeding 50 knots and towering surface waves, acted as powerful blenders, shredding marine snow into smaller pieces. This process significantly reduced the flux of marine snow into the deep ocean. However, the team observed a fascinating phenomenon: just a couple of days after the storms subsided, a pulse of marine snow emerged from the surface ocean.
The researchers discovered that storms increased the depth of the ocean's mixed layer, a turbulent zone where water is homogenized. When calm conditions returned, the mixed layer shallowed, leaving a layer of shredded particles. These particles, freed from surface turbulence, could reaggregate into marine snow, ready to sink into the deep sea.
This observation provided the first field evidence of the intricate coupling between ocean turbulence, particle aggregation, and disaggregation, and sinking particle fluxes. The findings aligned closely with laboratory experiments conducted by Alldredge and the late Professor Tommy Dickey, challenging the assumption that lab data may not accurately represent ocean conditions.
Bites from Billions of Tiny Mouths
The team also investigated the fate of marine snow as it sank beyond the surface, at depths between 200 and 500 meters. They discovered that the number of particles smaller than 0.5 mm roughly doubled over the month-long experiment. However, these tiny particles couldn't sink fast enough to account for this increase, indicating that marine snow breakdown was the culprit.
The authors found that biological processes, primarily zooplankton, were responsible for breaking down large particles at a rate of approximately 12% per day. This revelation challenged the previous assumption that microbes played a more significant role in marine snow breakdown.
Zooplankton, the consumer counterparts to photosynthetic phytoplankton, were found to be the primary consumers of marine snow. This finding has significant implications for climate models, as it highlights the importance of zooplankton in the carbon cycle and their role in breaking down marine snow.
The Bigger Picture and Future Endeavors
The study's findings underscore the dynamic nature of the ocean's carbon cycle and the challenges in predicting carbon flux. The EXPORTS mission's second phase aims to integrate this newfound knowledge into carbon cycle models, which, in turn, feed into climate models. This integration will be a topic of discussion at an international workshop in Glasgow, UK, in March 2026, bringing together experts from around the world.
The journey to these scientific breakthroughs was a testament to the team's resilience and dedication. Siegel expressed his gratitude for NASA's support, acknowledging the decades of work that led to this pivotal moment in understanding the ocean's role in Earth's climate.
