Science Snippets: Shifts in World's Largest Ocean Current Linked to Southern Ocean Upwelling During Warm Intervals

Draft script:

Arguably the strongest current in the world, the Antarctic Circumpolar Current is the most important current in the Southern Ocean. It transports more water than any other current and it is the only current that flows completely around the world. Discovered by British astronomer Edmond Halley, famous mariners James Cook, Thaddeus Bellingshausen, and James Clark Ross described the Antarctic Circumpolar Current in their journals. I will refer to Antarctic Circumpolar Current as ACC except when I am quoting directly from a source.

An article published in Phys.Org on 6 January 2025 brings attention to the ACC and its role in regulating global climate patterns during the last 1.5 million years. The article is titled Past climate shifts altered Southern Ocean currents and carbon exchange: Study warns it may be happening again. Here’s the lede: “Human-induced climate change is causing shifts in the world’s largest ocean current and westerly wind systems also seen during periods of ice age and warmer intervals in Earth’s history, researchers claim.” Six paragraphs later, the importance of the Southern Ocean is revealed: “The Southern Ocean plays a central role in the global uptake of heat and carbon, with approximately 40% of annual global CO₂ emissions absorbed by the world’s oceans entering through this region.”

Forty percent is a lot. Two of every five molecules of carbon dioxide resulting from human activities are absorbed by the Southern Ocean. However, relatively few of the world’s human population live in areas adjacent to the Southern Ocean, which extends from the coast of Antarctica to 60 degrees south latitude. As a result, the Southern Ocean receives relatively little attention from corporate media outlets.

The following four sentences in the Phys.Org article provide an excellent overview of the research: “Their study highlights the role of the Antarctic Circumpolar Current in regulating dynamics in the Southern Ocean and global climate patterns over the past 1.5 million years. The international team … show[s] how southern migration of the westerly winds and the Antarctic Circumpolar Current towards the pole during periods of past global warming increased the amount of natural carbon released to the atmosphere by the Southern Ocean. The team warns that human-induced climate change has brought about a similar process, which is underway today and likely to continue under global warming without appropriate climate action. Their findings, published in Science Advances, offer vital insights into how heat, salt, and carbon-rich waters flow, filling a critical gap in the understanding of ocean circulation and its relationship with past and future global climate changes.”

The lead author of the peer-reviewed, open-access paper in Science Advances is then quoted: “Our study highlights the complex interplay between ocean currents and climate patterns.”

To understand the importance of the Southern Ocean, it is important to understand relevant terminology about large-scale global patterns of cooling and warming. When Earth is characterized by extensive ice sheets, this is called a glacial period or an Ice Age. Warmer periods are known as interglacial periods. Particularly warm periods are sometimes called super-interglacials when the ACC slows considerably. At the same time, marine flow accelerates in the high-latitude Drake Passage at the intersection of the Atlantic and Pacific Oceans, driving a poleward shift in the Southern Hemisphere’s westerly winds. This shift in warming coincides with a strengthening and southward shift of the ACC. This southward shift in the ACC and the associated shift to westerly winds has important implications for the way the Southern Ocean absorbs heat and carbon.

Well into the article at Phys.Org, we receive a customary message from the lead author: “The urgency for comprehensive climate action has never been clearer, given the delicate balance that exists within these oceanic systems. By linking ACC flow patterns with the flow of water from the deep ocean to the surface, we gain a clearer understanding of how these dynamics have varied over millennia and what this means for our current climate trajectory.”

There is no doubt that the lead author is correct that “linking ACC flow patterns with the flow of water from the deep ocean to the surface, we gain a clearer understanding of how these dynamics have varied over millennia and what this means for our current climate trajectory.” However, I am unconvinced that “the urgency for comprehensive climate action has never been clearer.” As I have pointed out many times in this space, the designed-to-fail Intergovernmental Panel on Climate Change indicated Earth was amid abrupt, irreversible climate change more than five years ago. At this point, non-stop pleas for the masses to reduce carbon emissions are pointless.

I turn now to the peer-reviewed, open-access paper in the renowned Science Advances. Published 1 January 2025, this paper was written by six scholars and titled Shifting Antarctic Circumpolar Current south of Africa over the past 1.9 million years.

The Abstract provides an excellent overview of the research and its findings: “The Antarctic Circumpolar Current dominates the transfer of heat, salt, and tracers around the Southern Ocean, driving the upwelling of carbon-rich deep waters around Antarctica. Paleoclimate reconstructions reveal marked variability in Southern Ocean circulation; however, few records exist coupling quantitative reconstructions of Antarctic Circumpolar Current flow with tracers of Southern Ocean upwelling spanning multiple Pleistocene glacial cycles. Here, we reconstruct near-bottom flow speed variability in the Southern Ocean south of Africa, revealing systematic glacial-interglacial variations in the strength and/or proximity of Antarctic Circumpolar Current jets. These are superimposed by warmer-than-present ‘super-interglacials,’ whereby extreme slowdown in the midlatitude Antarctic Circumpolar Current (41°S) is opposed by faster flow at higher latitudes (>54°S), implying poleward strengthening of the Antarctic Circumpolar Current. Coupled with reconstructions of the subsurface-deep stable carbon isotope gradient, we show that the reorganization of Antarctic Circumpolar Current coincides with the upwelling of isotopically light deep waters around Antarctica, likely contributing to the interglacial rise in atmospheric carbon dioxide (CO2) levels.”

Again, the article at Phys.Org indicates that “the urgency for comprehensive climate action has never been clearer.” The peer-reviewed paper to which it refers indicates that the “Antarctic Circumpolar Current dominates the transfer of heat, salt, and tracers around the Southern Ocean, driving the upwelling of carbon-rich deep waters around Antarctica.” In other words, the peer-reviewed paper indicates that the Antarctic Circumpolar Current is running the show. At this point, I doubt “comprehensive climate action” will save us from ourselves.