Year: 2006
Type: article
Abstract: The accident of geography that creates a circumpolar channel of ocean at the latitude of Drake Passage has a profound impact on global ocean circulation patterns and climate. The strong eastward flow of the Antarctic Circumpolar Current (ACC) connects the ocean basins, allowing the existence of a global-scale overturning circulation that dominates ocean heat transport. The tilting of density surfaces associated with the geostrophic flow of the ACC brings dense water to the surface at high latitudes. Water mass transformations where these layers outcrop link the upper and lower limbs of the overturning circulation. Water masses exported from the Southern Ocean ventilate the deep and intermediate layers of the ocean and play an important part in global budgets of heat, freshwater, carbon and nutrients. As well as influencing mean climate, the Southern Ocean plays a role in climate variability and is likely to both drive and respond to climate change. The existence of high quality atmospheric reanalyses at high southern latitudes has helped to clarify the main modes of southern hemisphere climate variability. The extent to which the ocean circulation is an active or passive partner in these modes remains a topic of active research. Climate models suggest the Southern Ocean overturning circulation is sensitive to climate change and that reductions in the strength of the overturning may result in positive feedback through a reduction in heat and carbon uptake by the ocean. Changes in Antarctic sea ice provide another potential climate feedback. Evidence is growing that changes are underway in the Southern Ocean system. The most dramatic changes have been observed on the Antarctic Peninsula, where air temperatures have increased more rapidly than anywhere else in the southern hemisphere in recent decades. The collapse of the Larsen B ice shelf and increased melt rates of floating glaciers on the western peninsula have been linked to increases in both water and air temperatures. Water mass changes over several decades have been observed through much of the Southern Ocean water column, with the rate of change in some near-bottom waters comparable in magnitude to the well-documented freshening observed in the deep North Atlantic. However, the short and gappy observational record makes it difficult to distinguish natural variability from climate change. Many of these changes may ultimately be linked to the positive trend of the Southern Annular Mode (SAM) in recent decades. The source of the trend in the SAM is itself a topic of debate, with candidate explanations including depletion of ozone in the stratosphere, enhanced greenhouse warming, and natural variability..
Author: Stephen R. Rintoul
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W2185237358