These are a couple of papers that do have the dreaded CO2 in one of them, but refreshingly, more as consequence than as causal. (Though it is a bit ambiguous about cause and effect…)
First up, a paper that claims to find that Antarctic ice growth causes the reduction in CO2 seen at ice age glacial maximum. Essentially that ice covers the place in the Southern Ocean where deep water CO2 can out gas. Not sure I completely buy into the theory (there’s a lot of ocean where, IMHO, CO2 could diffuse and enter / exit the water; and that is not accounted here). But still, quite refreshing to see CO2 as effect, not cause. It does sort of imply a CO2 causal involvement in the write up / description, but not in the description from the referenced paper (that I’ve not got in hand, though…)
The paleoclimate record for the last ice age—a time 21,000 years ago called the “Last Glacial Maximum” (LGM)—tells of a cold Earth whose northern continents were covered by vast ice sheets. Chemical traces from plankton fossils in deep-sea sediments reveal rearranged ocean water masses, as well as extended sea ice coverage off Antarctica. Air bubbles in ice cores show that carbon dioxide in the atmosphere was far below levels seen before the Industrial Revolution.
The researchers focused on the Southern Ocean, which encircles Antarctica—a critical part of the carbon cycle because it provides a connection between the atmosphere and the deep ocean abyss. Ruffled by the winds whipping around Antarctica, the Southern Ocean is one of the only places where the deepest carbon-rich waters ever rise to the surface, to “breathe” CO2 in and out.
This question demanded the use of the field’s accumulated knowledge of ocean physics. Using a mathematical equation that describes the wind-driven ocean circulation patterns around Antarctica, the researchers calculated the amount of water that was trapped under the sea ice by currents in the LGM. They found that the shock to the entire Earth from this added ice cover was massive: The ice covered the only spot where the deep ocean ever got to breathe. Since the sea ice capped these deep waters, the Southern Ocean’s CO2 was never exhaled to the atmosphere.
The researchers then saw a link between the sea ice change and the massive rearrangement of ocean waters that is evident in the paleoclimate record. Under the expanded sea ice, a greater amount of upwelled deep water sank back downward. Southern Ocean abyssal water eventually filled a greater volume of the entire midlevel and lower ocean—lifting the interface between upper and lower waters to a shallower depth, such that the deep, carbon-rich waters lost contact with the upper ocean. Breathing less, the ocean could store a lot more carbon.
A Southern Ocean suffocated by sea ice, the researchers say, helps explain the big drop in atmospheric CO2 during the LGM.
So the description of the ‘finding’ is that ice limited the CO2 flux. Ice first, then flux change. Only the ‘lead in’ sideways hints at CO2 being needed as a kicker to solar changes. And yeah, it looks like it is Yet Another Model… but maybe it’s ‘right enough’…
“This study is an elegant, straightforward explanation that pulls all these pieces together into one place like no one has managed to do before,” says Daniel Sigman, a professor of geological and geophysical sciences at Princeton, who was not involved in the study.
Sigman, who tries to understand carbon fluxes in the last ice age, says that this new framework narrows his focus to a smaller range of possibilities. “What it really does is tune me in to the sea ice and biochemical conditions that I need to see at the Southern Ocean’s surface for the full CO2 drop to be realized.”
And here, a person who read the paper says that it is about understanding what drives CO2 to drop, and that it is ice changing CO2, not CO2 changing ice…
This one finds that ocean currents change up to 1000 years prior to the change of temperatures. The “thaw” came after ocean circulation changed. Gee…. So oceans shift, then temperatures (and per the above ‘ice changes CO2’, one presumes that even later the CO2 changes…)
The Atlantic Ocean at mid-depths may have given out early warning signals – 1,000 years in advance – that the last Ice Age was going to end, scientists report today in the journal Paleoceanography.
Scientists had previously known that at the end of the last Ice Age, around 14,700 years ago, major changes occurred to the Atlantic Ocean in a period known as the Bolling-Allerod interval. During this period, as glaciers melted and the Earth warmed, the currents of the Atlantic Ocean at its deepest levels changed direction.
The researchers have analysed the chemistry of 24 ancient coral fossils from the North Atlantic Ocean to learn more about the circulation of its waters during the last Ice Age. They found that the corals recorded a high variability in the currents of the Atlantic Ocean at mid-depths, around 2km below the surface, up to 1,000 years prior to the Bolling-Allerod interval. The team suggests that these changes may have been an early warning signal that the world was poised to switch from its glacial state to the warmer world we know today, and that the changes happened first at mid-depths.
They use neodymium isotopes in corals and other sea skeletons to indicate source of waters in the currents, thus infer the currents. Nice.
Dr David Wilson, from the Department of Earth Science and Engineering at Imperial College London, said: “The world’s oceans have always been an important barometer when it comes to changes in our planet. Excitingly, the coral fossils we’ve studied are showing us that the North Atlantic Ocean at mid-depths was undergoing changes up to 1,000 years earlier than we had expected. The tantalising prospect is that this high variability may have been a signal that the last Ice Age was about to end.”
The fossil corals analysed by the team come from a species called Desmophyllum dianthus, which are often around 5cm in diameter and look like budding flowers. They typically only live for 100 years, giving the team a rare insight into what was happening to the ocean’s currents during this relatively brief time. Thousands of years ago they grew on the New England Seamounts, which are a chain of undersea mountains approximately 1000km off the east coast of the US, located at mid-depths 2km beneath the surface. This underwater area is important for understanding the North Atlantic’s currents.
So once again we have a cause / effect arrow that points to ocean changes first, then temperature and ice changes. Coupled with the above paper that finds ice controlling CO2, we have the CO2 change last on the list AFTER ocean currents and ice melt. Golly.
And published in 2014.