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Microfossils Reveal Secrets of Ancient Ocean Changes

NSF, microfossils, forams, ACC, Arctic Circumpolar Current, fossils
Microfossils like these, the remains of tiny seafloor-dwelling organisms, contain chemical information about major changes in the world’s oceans. (Image credit: Miriam Katz, Rensselaer Polytechnic Institute. (Originally published by Micropress.))

This Research in Action article was provided to LiveScience in partnership with the National Science Foundation.

No matter how many times you've been in the ocean, you've probably never noticed foraminifera. But "forams," as scientists call these microscopic organisms for short, are everywhere — from the water surface to the seafloor, all around the world. They've been here since before the time of the dinosaurs, and now they're revealing vital information about the history of the world we live in.

Here's how: As forams grow, their tiny shells record the chemical and physical conditions of the ocean, which are tightly linked to those of the atmosphere. When they die, they collect on the seafloor, where settling sediment and other dead organisms eventually bury them. Some forams are preserved as microfossils. Over hundreds of millions of years, these microfossils have stacked up on the seafloor to form an incredible natural archive of ocean and climate data.

Scientists use this foram "bioarchive" as a historical field guide to everything from marine biology to climate change. Research programs like the Integrated Ocean Drilling Program, sponsored by the National Science Foundation and international partners, have been instrumental in making foram microfossils accessible, drilling and recovering sediment cores from deep in the ocean floor. Recently, an NSF-funded, multi-institution research team led by Miriam Katz of Rensselaer Polytechnic Institute used microfossils preserved in cores to investigate a major turning point in ocean history: the development of the Antarctic Circumpolar Current (ACC).

As the name suggests, the ACC encircles Antarctica, flowing clockwise (west to east). It is a major force in ocean circulation, or the movement of ocean water via a global network of large-scale currents. The ACC links the Atlantic, Indian and Pacific Oceans, aiding the exchange of water, heat and salt between these otherwise disconnected water bodies. It began flowing about 38 million years ago, when the ocean passages separating Antarctica from South America and Australia started to widen and deepen. As the ACC "engine" gained momentum, the current isolated Antarctica from warmer waters to the north, allowing the great Antarctic ice sheets to form. Without the ACC, these ice sheets — which have a strong influence on present-day climate and sea level — could not continue to survive.

The research team discovered that the churning of the ACC forced a reorganization of water temperatures and densities, separating the ocean into the four distinct layers that characterize it today: surface, intermediate, deep and bottom waters. Each of these layers is distinguished by a different set of physical and chemical conditions, and this ocean stratification powerfully affects global circulation patterns and the diversity and distribution of marine life.

Forams live in all of the ocean's layers, even at the bottom of the deepest ocean trenches. Without their microfossils, there are countless things we might not know today — like how the modern ocean developed, and the crucial part that the ACC played. Thanks to these miniscule, unassuming creatures, scientists are continually making new discoveries that change the way we understand the history of the ocean-climate system, and guide the way we look at its future.

Editor's Note: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. See the Research in Action archive.