Geography Facts About the Southern Ocean

Caitlin Dempsey

Updated:

The waters that completely surround Antarctica is known as the Southern Ocean. The youngest named ocean in the world, the Southern Ocean, or Antarctic Ocean, was only recognized as a separate entity by the International Hydrographic Organization in 2000.

The Southern Ocean is the fourth largest ocean – out of the five world oceans, it is smaller than the Pacific, Atlantic, and Indian oceans but larger than the Arctic Ocean.

Where is the Southern Ocean located?

The boundary of Southern Ocean is generally recognized as stretching from the coastline of Antarctica up to 60 degrees south latitude. Its boundaries are not universally agreed upon, leading to variances in size estimates. This ocean is unique in that it’s the only ocean to encircle a continent. As the name indicates, the Southern Ocean is the southernmost ocean on Earth.

A natural shaded relief map of Antarctica showing in a bold line the 60° S extent of the Southern Ocean.
Map of Antarctica and the 60°S limited of the Southern Ocean surrounding Antarctica. Map: Caitlin Dempsey using Natural Earth data.

The Southern Ocean supports a rich biodiversity, including various species of penguins, whales, and seals, and is vital for the marine food chain, particularly for krill.

The Southern Ocean is the coldest ocean

The Southern Ocean is notably the coldest of all the ocean bodies. Its frigid waters are often at or below the freezing point, and it’s home to vast expanses of sea ice. The presence of sea ice is dynamic, expanding dramatically during the winter months and receding in the summer. The formation and melting of sea ice have profound effects on ocean salinity and density, driving oceanic circulation patterns.

The Antarctic Circumpolar Current (ACC)

The Antarctic Circumpolar Current (ACC) is the Earth’s largest and most powerful oceanic current. This massive flow of water moves from west to east, driven by the relentless westerly winds. The ACC, spanning a width of about 20,000 kilometers, acts as a significant conveyor belt, moving water masses between the world’s oceans and playing a pivotal role in global ocean circulation.

A blue toned map showing the path of an iceberg north and west off the coast of Antarctica.
The Antarctic Circumpolar Current (ACC) pushes icebergs northward and westward off the coast of Antarctica in the Southern Ocean. Path of Iceberg A-23A between August 2011 and November 2023. Map: NASA, public domain.

Also known as the “West Wind Drift,” this current is the world’s largest permanent current, with westerly winds driving the water eastward. Icebergs originating from the Weddell Sea are typically carried northward and eastward by the influence of this current.

The Southern Ocean helps to regulate the Earth’s climate

The role of the Southern Ocean in global climate regulation and serves as a major sink for atmospheric carbon dioxide, helping to mitigate the effects of climate change. The ocean’s deep waters absorb CO2 and transport it to the ocean floor, a process that has significant implications for global carbon cycles.

A map showing the major warm and cold ocean currents.
The primary ocean currents that carry warm water from the equator to the poles and cold water from the poles back toward the equator are referred to as the “great ocean conveyor belt.” Image: NASA/JPL.

The Southern Ocean is instrumental in distributing heat around the planet. The movement of warm water from the equator towards the poles and the reverse flow of cold, dense water influences climate patterns worldwide. This oceanic circulation is a critical component of the Earth’s climate system, affecting weather patterns far beyond the Antarctic region.

The Southern Ocean absorbs more carbon than it emits

A 2021 study published in Science analyzed aircraft observations of CO2 and found that the Southern Ocean absorbs far more CO2 than it releases, especially during the Southern Hemisphere summer. These findings looked at nearly a decade of data (2009-2018) from three field experiments, including NASA’s Atmospheric Tomography Mission (ATom) in 2016. Matthew Long, the lead author and a scientist at the National Center for Atmospheric Research (NCAR), explained that the lowered CO2 levels in the lower atmosphere above the Southern Ocean surface in summer indicate significant carbon uptake by the ocean.

Map showing a view of South America and parts of the Southern Ocean. Blue areas area carbon sinks in the world’s oceans. Red areas are areas in the ocean where carbon dioxide is released. Map: NASA.

The study also highlights the complex process of CO2 absorption by the ocean. Cold water rises from the ocean’s depths through upwelling, absorbing atmospheric CO2, often assisted by photosynthesizing phytoplankton, before sinking back. This process results in the Southern Ocean absorbing approximately 40% of the human-produced CO2 in the ocean worldwide, making it one of the planet’s most crucial carbon sinks.

Accurately measuring the CO2 flux at the air-sea interface has been challenging. The research team overcame this by analyzing CO2 measurements from various airborne campaigns, including ATom, HIPPO, and ORCAS. These campaigns provided crucial data on the vertical gradient of CO2 in the atmosphere, allowing the scientists to create a detailed picture of CO2 absorption and release by the Southern Ocean over time and throughout the seasonal carbon cycle. This comprehensive approach, supported by atmospheric computer models, has been instrumental in quantifying the Southern Ocean’s role as a carbon sink.

The effect of climate change on the Southern Ocean

Numerous studies have looked at the effect of climate change on the Southern Ocean. Due to rising levels of CO2 and global warming, the Southern Ocean (SO) is likely to undergo several changes. It is expected to become warmer and lose some of its sea ice. The region will also probably become windier, which will lead to shifts in the polar fronts (the boundaries between cold polar air and warmer air) and changes in the Southern Annular Mode (a climate pattern affecting the southern hemisphere).

Tabular icebergs in the Southern Ocean. Photo: Mike Goebel, NOAA NMFS SWFSC Antarctic Marine Living Resources (AMLR) Program, 1992, public domain.
Tabular icebergs in the Southern Ocean. Photo: Mike Goebel, NOAA NMFS SWFSC Antarctic Marine Living Resources (AMLR) Program, 1992, public domain.

The Southern Ocean is also likely to become more acidic and see alterations in the average depth of its mixed layer, which is the upper layer of the ocean where the temperature and salinity are relatively uniform. Research by NASA and University of North Carolina published in Geophysical research letters in 2019 noted that data from two satellites operated by NASA have shown clear increases in the levels of chlorophyll (a green pigment found in plants and algae) across the Southern Ocean. These researchers concluded that rising chlorophyll levels throughout the year and in winter could affect the Southern Ocean’s ability to absorb carbon and support marine life, including larger animals higher up in the food chain.

An important regulator of the Earth’s biogeochemistry, Weather Systems, and Ocean circulation

The Southern Ocean’s geography plays a vital role in Earth’s environmental health. Its unique features, such as the Antarctic Circumpolar Current and its status as a significant carbon sink, have far-reaching impacts on global climate and marine ecosystems. The ocean’s influence on weather patterns and its rich biodiversity highlight its importance. Preserving the Southern Ocean is crucial for environmental stability worldwide. As a focus for ongoing scientific research, it remains essential in understanding and responding to global environmental challenges.

Icebergs float in the Southern Ocean, Antarctica. Photo: Kristina Jacob. Used with permission.
Icebergs float in the Southern Ocean, Antarctica. Photo: Kristina Jacob. Used with permission.

References

Bates, S. (2021, December 8). NASA-supported study confirms importance of Southern Ocean in absorbing carbon dioxide – Climate change: Vital signs of the planet. Climate Change: Vital Signs of the Planet. https://climate.nasa.gov/news/3136/nasa-supported-study-confirms-importance-of-southern-ocean-in-absorbing-carbon-dioxide/

Del Castillo, C. E., Signorini, S. R., Karaköylü, E. M., & Rivero‐Calle, S. (2019). Is the Southern Ocean getting greener?. Geophysical research letters46(11), 6034-6040.

Long, M. C., Stephens, B. B., McKain, K., Sweeney, C., Keeling, R. F., Kort, E. A., … & Wofsy, S. C. (2021). Strong Southern Ocean carbon uptake evident in airborne observations. Science374(6572), 1275-1280. DOI: 10.1126/science.abi435

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.

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