Carbon storage mystery emerges in the Southern Ocean

Carbon storage in Earth’s deep seas continues to reveal surprising complexities, as scientists uncover more about the intricate processes of our oceans.

These vast underwater ecosystems play a pivotal role in regulating our planet’s climate, with microscopic organisms often driving major biogeochemical cycles.

One such discovery comes from a recent study led by the UK’s National Oceanography Centre (NOC).

The research team offers a fresh perspective on the role that a unique group of microscopic algae play in carbon sequestration – the natural storage of carbon in the ocean.

Carbon storage in the Southern Ocean

Microscopic algae known as diatoms play a significant role in pulling carbon down into the deep ocean, particularly in the Southern Ocean, which holds about a third of the organic carbon stored in the world’s oceans.

Diatoms carry distinct dense, silica-based structures that resemble petite glass houses.

Scientists have long believed these structures provide enough weight – or ballast – for the diatoms to sink into deeper waters, dragging carbon along with them into the deep blue depths.

“The ocean plays a key role in the global carbon cycle, with tiny, microscopic plants taking up billions of tons of carbon from the atmosphere every year,” said Dr. Sari Giering, Research Lead at NOC.

“For years, it has been believed that this group of plankton – diatoms – play a crucial role in efficiently transporting carbon to the deep ocean, where it is held out of contact with the atmosphere.”

Reconsidering the biological carbon pump

Diatoms and other types of phytoplankton absorb carbon near the sea surface. This process is part of what’s known as the biological carbon pump – a series of processes that funnel this carbon to the deep ocean.

But according to recent findings from the NOC study, the diatom skeletons don’t quite make the long descent. Instead, they linger near the surface, while carbon journeys to the deep ocean through other, yet unidentified means.

“We now understand that diatoms are not always contributing as heavily to the Southern Ocean’s carbon pump as we once thought,” said Dr. Giering. “This means there are unknown or poorly measured processes happening in the deep ocean that we need to learn more about.”

The future of ocean carbon storage

Scientists have been increasingly worried that ocean warming could impact diatom productivity and thus, reduce the effectiveness of the biological carbon pump in the Southern Ocean.

However, this recent study suggests that these changes might not greatly impact the carbon storage capacity of the Southern Ocean.

“The Southern Ocean is vulnerable to ocean warming, which may alter the availability of nutrients and reduce diatom numbers in the future,” said Jack Williams, a post-graduate researcher at the University of Southampton. “But our results suggest these changes may not impact the strength of Southern Ocean carbon storage as much as previously thought.”

Carbon continues to descend to the ocean’s depth, which suggests that there are yet undiscovered processes occurring in the “twilight zone” of the ocean.

Unveiling these processes is crucial for accurately predicting how the oceans may store carbon in the future.

The twilight zone: A frontier of discovery

The twilight zone, a mid-ocean layer spanning depths of 100 to 1,000 meters, has emerged as a critical area of interest for scientists studying carbon storage. Despite its name, this zone is far from a lifeless void.

It hosts a dynamic ecosystem of organisms and complex processes that are only beginning to be understood.

Recent findings suggest that much of the carbon transported into the deep ocean originates in this layer, bypassing the mechanisms traditionally associated with surface plankton like diatoms.

In this dimly lit zone, carbon is carried by sinking particles known as marine snow – aggregates of organic material, dead plankton, and other detritus. However, the exact processes enabling this descent remain elusive.

The twilight zone acts as a gatekeeper, determining how much carbon reaches the ocean depths. Understanding these pathways is vital for improving climate models and predicting how oceanic carbon storage will respond to global warming.

Ongoing research into the twilight zone could hold the key to unlocking the ocean’s full carbon sequestration potential, providing insights that may redefine conservation strategies and our approach to mitigating climate change.

The full study was published in the journal Nature.

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