Subantarctic

Lore & Background

The subantarctic region is defined by both geographic and political boundaries. Geographically, it lies between the Subtropical Front and the Antarctic Convergence, encompassing the Subantarctic Zone and the Polar Frontal Zone. This current, along with thermohaline circulation, strongly influences global climate and underwater biodiversity. Politically, the Antarctic Treaty defines Antarctica as all land and ice shelves south of 60° south latitude, so islands north of that line—even if south of the Antarctic Convergence—are considered subantarctic. This creates a distinction between scientific definitions (based on hydrology and biology) and political ones. Islands such as the Kerguelen Islands, Heard Island, and South Georgia are subantarctic, while those south of 60°, like the South Shetlands, are Antarctic. The region's islands vary in climate and vegetation. Some, like the Falkland Islands, have trees and arable land, while others, like Heard Island, feature tundra, permafrost, and active volcanoes. Subantarctic glaciers are retreating significantly due to climate change, and the Subantarctic Mode Water (SAMW) acts as a carbon sink, though its capacity may decrease with warming.

Reader's Guide

The subantarctic region holds significance as a transitional zone between the temperate and Antarctic worlds, influencing global ocean circulation and climate. The Antarctic Circumpolar Current, which flows through the region, is the only current to circle the Earth, connecting three ocean basins and driving thermohaline circulation. This current and the formation of Antarctic Bottom Water affect heat distribution and carbon cycling worldwide. Biologically, the convergence of water masses near the Antarctic Convergence creates high marine productivity, particularly for Antarctic krill, supporting vast seabird and marine mammal populations. Heard Island, for example, is a biological hot spot with large colonies of penguins, petrels, elephant seals, and fur seals, as well as diverse benthic habitats. Climate change poses a threat to the region's role as a carbon sink. The Subantarctic Mode Water absorbs atmospheric CO2, but warming could reduce its density and salinity, decreasing its capacity to store carbon. Additionally, glaciers on subantarctic islands are retreating, creating new ice-free areas for colonization by plants and animals. The political definition under the Antarctic Treaty (south of 60°S) also shapes governance and conservation efforts, distinguishing subantarctic islands from Antarctic territory.

Did You Know?

• The subantarctic region includes islands in the Roaring Forties, Furious Fifties, and Shrieking Sixties latitude bands.
• The Subantarctic Mode Water and Antarctic Intermediate Water act as a carbon sink, absorbing atmospheric carbon dioxide.