A group of researchers has found evidence of an abrupt, mid-latitude cooling of seawater during the Jurassic period, around 174 million years ago.
University of Copenhagen researcher Christoph Korte and his colleagues have shed light on the causes behind an ‘Ice Age’ that took place on our planet 174 million years ago. Image credit: Gerhard Boeggemann / CC BY-SA 2.5.
The group, headed by Christoph Korte of the University of Copenhagen in Denmark, found that the cooling coincided with a massive volcanic event, the North Sea Dome, which restricted the flow of seawater and the associated heat that it carried from the equator towards the North Pole region.
“We tend to think of the Jurassic as a warm greenhouse world where high temperatures were governed by high atmospheric carbon dioxide contents,” said team member Prof. Stephen Hesselbo, of the University of Exeter, UK.
“Our study suggests that re-organization of oceanic current patterns may also have triggered large scale climate changes.”
Dr Korte, Prof. Hesselbo and their colleagues suggest that it’s the North Sea Dome, preventing the ocean flow, rather than a change in carbon dioxide in the atmosphere, that led to an extended Ice Age.
The researchers spent ten years constructing a record of seawater temperature change using fossil bivalve and brachiopod shells.
They found that during the same period that the North Sea Dome event occurred, the planet experienced a significant and fast cooling in temperature.
Upper image: map shows the connection between the equatorial Tethys Ocean and the Boreal Sea via the Laurasian Seaway; the latter including the Viking Corridor which was several hundred miles wide. Red arrows mark generalized paleocurrents. Bottom image: detail of Laurasian Seaway paleogeography with the region affected by North Sea Dome as determined by the generalized outer limit of the Toarcian subcrop. Brown arrows represent the siliciclastic sediment supply/transport in relation to domal uplift. Sample locations are numbered and identified by stars (Hebrides Basin (I; Scotland), Cleveland Basin (II; England), Swabo-Franconian Basin (III; Germany) and Lusitanian (IV; Portugal)/Basque-Cantabrian basins (V; Spain)). SNS, Southern North Sea Basin, W, Wessex Basin. Image credit: Korte, C. et al.
“Our results show an especially abrupt earliest Middle Jurassic mid-latitude cooling of seawater by as much as 10 degrees Celsius in the north-south Laurasian Seaway, a marine passage that connected the equatorial Tethys Ocean to the Boreal Sea,” the scientists wrote in a paper published last week in the journal Nature Communications.
The evidence indicates that this cold period lasted many millions of years, until the North Sea Dome subsided.
“Although we have known about the occurrence of cold periods during greenhouse times for a while, their origins have remained mysterious,” Prof. Hesselbo said.
“This work suggests a mechanism at play that may also have been important for driving other climate change events in the Jurassic and at other times in Earth history.”
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Korte, C. et al. 2015. Jurassic climate mode governed by ocean gateway. Nature Communications 6: 10015; doi: 10.1038/ncomms10015
