Ancient sediments show influence of southern ocean circulation on climate

Dec 05, 2005

About 34 million years ago, the Earth's climate transitioned from a "greenhouse climate" to the "icehouse climate" of today, forming a massive ice sheet on the Antarctic continent. A new study by Linda Anderson, an ocean sciences researcher at the University of California, Santa Cruz, suggests that oceanographic features in the Southern Ocean--the intensity of current flow and the amount of stratification (the formation of distinct layers at different depths)--may have played a key role in the transition.

Anderson will present her findings this week at the Fall Meeting of the American Geophysical Union in San Francisco.

Anderson analyzed the chemical properties of seafloor sediments laid down millions of years ago to piece together a picture of how Southern Ocean circulation may have looked deep in the past. The periods covered in her study include the transition from the Eocene to the Oligocene epochs about 33 million years ago and a similar transition between the Oligocene and Miocene epochs about 23 million years ago. These transitions coincided with a configuration of Earth's orbit around the Sun that facilitated ice growth. Some additional factor on Earth, however, amplified the climate response during these transitions.

The geological record suggests that this additional factor was a reduction of greenhouse warming due to a decrease in atmospheric carbon dioxide. The Southern Ocean may have played a role in the drawdown of atmospheric carbon dioxide through its influence on the global carbon cycle, Anderson said.

Her study suggests that, unlike today, the mixing of the Southern Ocean around the time of the climate shift was neither as intense nor as deep as it is now. As a result, the ocean was more stratified and regional characteristics of deep and intermediate waters were maintained. This layered structure may have had important consequences for global carbon cycling, setting the stage for the transition from greenhouse to icehouse.

Phytoplankton--tiny plants growing in the surface waters--use carbon dioxide from the atmosphere and transform it into organic carbon. When the plants (or animals that feed on them) die and decompose, most of the organic carbon is recycled but a small amount is buried within the deep ocean. In a layered ocean, dead organisms can drift into the deeper layers before they decompose, effectively burying the organic carbon in the depths.

Shifting continents have gradually changed the Southern Ocean over the past 30 million years so that water now whips around Antarctica in a strong current known as the Antarctic Circumpolar Current. The strength of the current blocks the influx of nutrient-poor surface water and, as this current squeezes through the narrow passage between South America and Antarctica, it mixes the water from top to bottom. As a result, most of the organic carbon formed within the Southern Ocean today is oxidized before it can be buried.

The impact of organic carbon burial on the atmospheric carbon dioxide depends on the relative burial of organic carbon to total carbon. The types of organisms that fix organic carbon are important, because some form shells of inorganic carbon in a process that releases carbon dioxide. Regional characteristics of the water affect which organisms are favored ecologically by controlling the nutrient content of the surface ocean. The integral relationship between biology (the organisms that fix the organic carbon) and the physical structure of the ocean (both the delivery of nutrients and removal of organic carbon for burial) ultimately control the atmospheric carbon dioxide, Anderson said.

As scientists search for ways to remove carbon from the atmosphere and reduce global warming, understanding organic carbon burial mechanisms of the past and the role of the structure of the ocean will give us important insights into how the global system may behave in the future, Anderson said.

"We have a long way to go to understand the modern Earth system, but because we only have one Earth, we must turn to the geological record to provide us with test cases," she said.

Source: University of California, Santa Cruz

Explore further: Storms threaten second launch try to space station

add to favorites email to friend print save as pdf

Related Stories

New study outlines 'water world' theory of life's origins

16 hours ago

(Phys.org) —Life took root more than four billion years ago on our nascent Earth, a wetter and harsher place than now, bathed in sizzling ultraviolet rays. What started out as simple cells ultimately transformed ...

Scientists explore one of Earth's deepest ocean trenches

Apr 11, 2014

What lives in the deepest part of the ocean—the abyss? A team of researchers funded by the National Science Foundation (NSF) will use the world's only full-ocean-depth, hybrid, remotely-operated vehicle, ...

Dissolving the future of coral reefs

Apr 10, 2014

Swimming through the liquid turquoise waters off the island of Viti Levu, Fiji, I am surrounded by iridescent fish of all colors, schooling around healthy branching corals. With a slight movement of my fins ...

Recommended for you

Ceres and Vesta Converge in Virgo

32 minutes ago

Don't let them pass you by. Right now and continuing through July, the biggest and brightest asteroids will be running on nearly parallel tracks in the constellation Virgo and so close together they'll easily ...

A full-spectrum Mars simulation in a box

1 hour ago

There are many reasons why Mars excels at destroying expensive equipment. For one thing, its entire surface is made of partially-magnetized dust. For another, Mars possesses just enough atmosphere so that ...

LADEE mission ends with planned lunar impact

1 hour ago

(Phys.org) —Ground controllers at NASA's Ames Research Center in Moffett Field, Calif., have confirmed that NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the surface ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

jeffsaunders
not rated yet Jun 16, 2009
good article. looking forward to things warming up again like they were in the good old days.

More news stories

LADEE mission ends with planned lunar impact

(Phys.org) —Ground controllers at NASA's Ames Research Center in Moffett Field, Calif., have confirmed that NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft impacted the surface ...

A full-spectrum Mars simulation in a box

There are many reasons why Mars excels at destroying expensive equipment. For one thing, its entire surface is made of partially-magnetized dust. For another, Mars possesses just enough atmosphere so that ...

Ceres and Vesta Converge in Virgo

Don't let them pass you by. Right now and continuing through July, the biggest and brightest asteroids will be running on nearly parallel tracks in the constellation Virgo and so close together they'll easily ...

Could 'Jedi Putter' be the force golfers need?

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...