A new study published by researchers at the University of Hawai'i (UH) at Mānoa sheds light on the critical role of iron in Earth's climate history, revealing how its sources in the South Pacific Ocean have shifted over the past 93 million years. This groundbreaking research , based on the analysis of deep-sea sediment cores, provides crucial insights into the interplay between iron, marine life, and atmospheric carbon dioxide levels.
Iron is a vital nutrient for marine life and plays a significant role in regulating atmospheric carbon dioxide by influencing the growth of phytoplankton, which absorb carbon dioxide. Although the importance of iron today is well-established, researchers have a limited understanding of how past iron availability may have shaped the marine ecosystem.
To investigate the long-term history of oceanic iron, the researchers meticulously analyzed iron isotopes in three deep-sea sediment cores from the South Pacific, far removed from continental influences.
"Over the past 93 million years, we found that five primary sources of iron have influenced the South Pacific Ocean: dust, iron from far off ocean sources, two distinct hydrothermal sources, and a volcanic ash," explained Logan Tegler, the lead author and oceanography postdoctoral researcher in the UH Mānoa School of Ocean and Earth Science and Technology . "These sources shifted over time as the sites gradually migrated away from mid-ocean ridges."
The study revealed an evolution in iron supply: initially, hydrothermal sources were the dominant source, but dust gradually took over, becoming the primary contributor around 30 million years ago.
Iron's influence on the ecosystem, carbon removal
"Understanding this historical context helps us comprehend how iron has shaped ecosystems," said Tegler. "It also raises questions about how the iron cycle might have favored certain microbes over others—an ecosystem with persistently low iron could favor microbes adapted to survive under iron-limited conditions, such as diatoms."
In many regions of the Pacific Ocean, iron availability limits the growth of phytoplankton, thereby limiting the amount of carbon dioxide removed from the atmosphere.
"Modern dust deposition in the South Pacific is extremely low," said Tegler. "However, our findings surprisingly suggest that the South Pacific is currently receiving more dust than it has at any point in the last 90 million years, which is remarkable given its current reputation as an iron poor region!"
This study sheds light on iron cycling across the broader Pacific basin and enhances understanding of how essential nutrients like iron shape ocean ecosystems and climate over millions of years.
"As human activities increase iron input to the oceans through industrial emissions and biomass burning, understanding past perturbations of the iron cycle is crucial for predicting and mitigating adverse effects," added Tegler.
