Did the Drake Passage Alone Freeze Antarctica?
Did the Drake Passage Alone Freeze Antarctica?
I've had the same best friend since we were kids. We're lucky if we see each other once every two or three years anymore. Somehow there's never any warming back up between us; we just pick up where we left off.
He went to a maritime academy, then straight into a shipping career. His body drifted away from mine — the conversation never did. Every time we sit down, it circles back to the ocean. At first it was dolphins: pods trailing his ship for miles, a tall tale that got a little better with each telling.
These days he works out of an Antarctic research station, and his stories have moved with the job. Almost all of them lead to the same stretch of water now, the Drake Passage. "Real men are born in the Drake Passage," he told me last time, half joking. It stuck anyway.
Two lifelong friends reunite at a seaside café as an Antarctic research sailor shares stories about the legendary Drake Passage, with ships visible through a rainy harbor window.
The Sea That Made My Friend Tough Wasn't Always So Cruel
My friend has crossed the Drake Passage more times than he can count, and he still calls it the meanest water he knows. It raises an obvious question: did the Drake Passage alone freeze Antarctica, or is that too tidy a story for what the evidence shows?
I went looking for the short version my friend gives — gateway opens, current forms, continent freezes — expecting it to mostly hold up. It doesn't, not entirely.
Antarctica's coastline once sat under seas warmer than the ones battering it today. That much the fossil and isotope record settles without much argument. Whether the Drake Passage is the reason that warmth disappeared is where researchers start to diverge, and that's exactly where this gets interesting.
The moment scientists point to is the Eocene-Oligocene transition, roughly 34 million years ago, when the global climate cooled sharply and Antarctica's ice sheets expanded fast enough to leave a clear mark in the sediment record. The question is what actually drove it.
Climate models complicate the easy answer: the Drake Passage's opening did not, by itself, guarantee that cooling. Its effect on Antarctica depended on sea ice, wind patterns, and ocean gateway depth acting together.
A geological reconstruction shows South America separating from Antarctica as the Drake Passage gradually opens and seawater begins flowing through the newly formed ocean gateway millions of years ago.
How Scientists Actually Watch a 34-Million-Year-Old Question
Nobody was standing on a beach when the Drake Passage opened, and no source anywhere names the day it happened, because it wasn't a day. It was a process, and a slow one.
One detailed plate-reconstruction traces the start of it to roughly 50 million years ago, when the crust between South America and the Antarctic Peninsula began to stretch and separate. The channel between them deepened gradually, over millions of years, not in a single geological event.
The closest thing to a witness showed up almost 50 million years later, and it wasn't a geologist. From 2007 to 2011, each October through December, the research vessel Nathaniel B. Palmer crossed the Drake Passage and deployed current meters and seafloor mooring equipment as part of an effort called cDrake. The goal wasn't to watch the passage open; that had already taken place. It was to measure, in real numbers, the transport and physical balance of the current now moving through the gap the ancient rifting created.
The data that came back doesn't carry a single hero's name. It's the product of ship crews, marine technicians, and equipment operators doing the same unglamorous work, haul after haul, year after year.
That's not the version of science I grew up picturing, the lone genius with the breakthrough moment. It's slower and far less photogenic, and it's probably closer to how most of this actually gets known.
The same unhurried timeline shows up elsewhere in Earth science too. It's part of why predictions about the world running out of oil keep missing their own deadlines; resources laid down over geologic time simply don't operate on human-scale schedules.
Powerful Antarctic Circumpolar Current encircles Antarctica while expanding ice sheets transform the continent from a warm ancient landscape into today's frozen wilderness.
The Cooling Wasn't Guaranteed. Models Show It Could Have Gone the Other Way
I'd assumed, going in, that opening a gap between two icy landmasses would obviously cool everything down. Pour cold water into a warm system, and the temperature has to drop. That's not quite what the models say.
Three sets of researchers, working the same 34-million-year-old question, each foreground a different piece of what did the cooling: the passage, the carbon, or the ice that showed up depending on which one came first.
The traditional version goes like this: rapid separation between South America and Antarctica, beginning around 50 million years ago, opened the passage. A current eventually wrapped around the continent, cutting off warm water that used to reach Antarctic shores.
The British Antarctic Survey's 2005 research supports part of that chain. It found that even a shallow gateway, opened by that same separation, could have significantly affected Southern Ocean circulation and climate. It's a clean story, and it's the one most articles stop at.
A 2014 climate-model study published in Nature complicated the order of events. Rather than the passage driving the cooling, the researchers' models suggested the reverse: falling atmospheric carbon dioxide likely triggered Antarctic ice-sheet growth first, and that growth reorganized ocean circulation afterward, not the other way around.
A 2021 study in Scientific Reports tested the passage-opening idea directly, and this is where the reversal sits. Strip sea ice out of the model, and opening the Drake Passage did not reliably cool the Southern Ocean; in some runs, it produced slight warming instead. Add sea ice and the ice-albedo feedback it creates back into the same model, and the open passage suddenly ran colder than the closed one. The passage itself never changed. What changed the outcome was whether ice was already there to react to it.
It's tempting to read this as scientists simply disagreeing with each other. It's more likely that each study is holding one piece of a system that only makes sense once wind, ice, carbon, and geography get put back together, which is a less satisfying answer, and probably the truer one.
Antarctica has a habit of complicating tidy stories. The freshwater world sealed under Lake Vostok for millions of years complicated a similar set of assumptions about hidden oceans on moons like Enceladus.
Scientists aboard an Antarctic research vessel deploy oceanographic instruments into the stormy Drake Passage to measure one of Earth's strongest ocean currents.
The same underlying physics that makes some coastal tides dramatically bigger than others is at work in the Drake Passage too, just amplified by geography that squeezes the Antarctic Circumpolar Current through its narrowest major bottleneck.
A Passage 500 Miles Wide, Moving an Ocean Every Second
Stand at the tightest stretch of the Drake Passage and you're looking across roughly the distance between New York and Detroit. Not a small stretch of water. Not an ocean, either. What's harder to picture is what's actually moving through it.
I tried imagining that whole distance moving as one body of water and couldn't quite do it, so I went looking for the actual numbers instead.
Estimates cluster around 130 to 134 Sverdrups in the long-standing measurements — a Sverdrup is a million cubic meters of water a second, so roughly 130 million cubic meters push through the gap every second. Even that figure turned out to be incomplete: a 2016 reanalysis that finally combined the current's steady near-bottom flow with its more variable upper-ocean flow put full transport closer to 173 Sverdrups, about 30 percent above the number long treated as standard. The exact number still shifts with measurement method and sampling years, itself a clue to how hard this current is to pin down. One tracking instrument, aboard a supply ship called the Laurence M. Gould, doesn't catch the whole water column at once; its first reading starts about 46 meters down, watching the upper ocean, not the depths below.
What's almost stranger than the current's size is how stubbornly consistent it's stayed.
NOAA's Atlantic Oceanographic and Meteorological Laboratory puts one long-term average at about 134, plus or minus 11.2, Sverdrups, drawn from current-meter and bottom-pressure records from the late 1970s and early '80s; a separate analysis of 1975–2000 data put baroclinic transport above 3,000 meters depth at 107.3, plus or minus 10.4, Sverdrups. The exact figure depends on how deep you measure and which years you catch — which turns out to be the more interesting finding. A 2023 study using shipboard measurements from the Laurence M. Gould since 2005 found no statistically significant speed-up in the upper 760 meters of the current, even as wind conditions over the Southern Ocean shifted.
Maybe the simplest reading is that, over the upper 760 meters and the years measured, opposing trends among the current's separate fronts canceled each other out while eddy activity between them increased. Net transport looked steady less because nothing changed and more because those trends were pulling in opposite directions. Whether that holds through the full water column or over longer stretches of time is still an open question.
Scientific visualization illustrates how ocean gateways, atmospheric carbon dioxide, sea ice, winds, and ocean circulation together shaped Antarctica's ancient climate.
Antarctica's Freeze Might Not Be Finished Being Explained
If there's one thing this keeps circling back to, it's that "open" and "finished" are not the same word in deep time. I wanted one clean moment to point to when I started digging into this, and that timescale just doesn't deal in those.
Even as the Drake Passage kept deepening and the Southern Ocean's other gateways shifted, at least three more variables rewrote how cold Antarctica actually got, and when.
Gateway depth was one of them. A 2021 modeling study found that once a second Southern Ocean gateway deepened beyond roughly 300 meters, the warm-water gyres that had been reaching Antarctica weakened sharply, cooling Antarctic margin waters by as much as 5°C. A separate sediment-based reconstruction of Southern Ocean temperatures adds a timing detail to that threshold effect: cooling near Antarctica intensified again around 26 million years ago — a second wave, not a single moment.
Wind position was another. A 2022 modeling study found that with both the Drake Passage and the Tasman Gateway open, shifting the Southern Hemisphere's westerly winds could flip the outcome at the Antarctic coast entirely. With the Tasman Gateway modeled at a shallow 300 meters, southward-shifted winds warmed the coastal water by up to 2°C. Deepen that same gateway to 1,500 meters, and the identical wind shift cooled the coast by 3 to 4°C instead. Same winds, opposite result, depending on how deep one side channel ran.
Geography was a third. An earlier climate-modeling study, from 2013, found that Oligocene-era geography, specifically where the Australian continent sat at the time, likely prevented a strong, continuous circumpolar current from forming even with both gateways connected at depth. Having an open channel wasn't the same as having the current people associate with Antarctica today.
Timing may be the biggest variable of all. Lead isotopes preserved in a seafloor mineral crust, analyzed in a 2024 study, suggest the current's modern configuration may not have settled into place until around 5 million years ago.
It's hard not to read that long gap, between the start of tectonic separation and the current reaching the shape it holds today, as the real story the simple version buries: opening the gateway mattered, but on its own it was never close to the whole explanation.
Laid side by side, the conditions that flip the outcome are easier to see than they are to explain in a single paragraph:
| Model Condition | Effect on Southern Ocean / Antarctic Coastal Temperature |
|---|---|
| Drake Passage open, sea ice excluded (Vincze et al., 2021) | No reliable cooling; slight warming possible |
| Drake Passage open, sea ice and ice-albedo feedback included (Vincze et al., 2021) | Southern Ocean notably colder than closed-passage case |
| Second Southern Ocean gateway deeper than ~300 m (Sauermilch et al., 2021) | Antarctic margin waters up to 5°C cooler |
| Tasman Gateway at 300 m depth, westerlies shifted south (Xing et al., 2022) | Antarctic coastal water up to 2°C warmer |
| Tasman Gateway at 1,500 m depth, same wind shift (Xing et al., 2022) | Antarctic coastal water 3–4°C cooler |
One more distinction is worth making before this closes: none of this is the mechanism behind the Antarctic sea ice headlines of the past few years. That's a separate, much faster story, unfolding under conditions — wind, ocean warming, year-to-year variability — that have little to do with what froze the continent 34 million years ago in the first place.
The Drake Passage is where the Pacific and the Atlantic meet, squeezing one of the planet's largest volumes of moving water through a gap only about 500 miles wide. Force that much ocean through that little space, and the reputation for brutal seas stops being surprising.
Harder to imagine is the other version: a warmer Antarctica, before this passage existed, when the coastline my friend now studies looked nothing like the frozen, storm-battered edge of the world he flies south to reach. The freeze itself turns out to be less a single event than a slow argument, written into sediment and disagreement, that scientists are still working through.
Today, like most days, he's probably out on that water. I hope for a calm crossing. And when I think about that line of his, that real men are born in the Drake Passage, I find myself, against my better judgment, agreeing with him.
An Antarctic research ship sails through the massive waves of the Drake Passage at sunrise, symbolizing the courage of sailors navigating one of the world's roughest seas.
Sources & References
- Van de Lagemaat et al., plate-reconstruction study on Scotia Sea subduction and Drake Passage opening, Earth-Science Reviews (2021)
- British Antarctic Survey, "Early Drake Passage opening led to global change" (2005)
- Goldner, Herold & Huber, climate-model study on Antarctic glaciation and ocean circulation, Nature (2014)
- Vincze et al., study on sea ice, gateway opening, and Southern Ocean cooling, Scientific Reports (2021)
- Sauermilch et al., modeling study on Southern Ocean gateway depth and gyre-driven Antarctic cooling, Nature Communications (2021)
- Hoem et al., sediment-based reconstruction of the Oligocene Southern Ocean temperature gradient, Communications Earth & Environment (2022)
- Xing et al., modeling study on wind stress and Eocene-Oligocene Southern Ocean sensitivity, Climate of the Past (2022)
- Hill et al., climate-model study on paleogeographic controls on the Antarctic Circumpolar Current, Geophysical Research Letters (2013)
- Huang et al., seawater lead isotope study on Southern Ocean circulation dynamics, Paleoceanography and Paleoclimatology (2024)
- Donohue et al., study on mean Antarctic Circumpolar Current transport measured in Drake Passage, Geophysical Research Letters (2016)
- NOAA National Centers for Environmental Information, cDrake dataset metadata (2020)
- NOAA Atlantic Oceanographic and Meteorological Laboratory, Southern Ocean transport data
- Cunningham et al., study on transport and variability of the Antarctic Circumpolar Current in Drake Passage, Journal of Geophysical Research: Oceans (2003)
- Gutierrez-Villanueva, Chereskin & Sprintall, study on Drake Passage transport trends using Laurence M. Gould shipboard ADCP data, Nature Communications (2023)
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