Global Backup Generator For Past Climate Change

I would love to see vastly more resolution and coverage.  Yet this is a good start in confirming that major circulation changes are possible to the extent of ending circulation into the Atlantic.  The reasons given are premature guesses until we have a lot more data.

It does not rule out a crustal shift as such would have disrupted the Atlantic during that same era.  As posted before, the purpose of the shift was to deliver tropical water into the Arctic to end the Northern Ice Age forever.  The possible flow was simply insufficient prior to that occurring.

It also reaffirms my conjecture that long term climatic cycles are driven by long term adjustments in the primary global current systems.

Besides all that, prior to the Hekla blast in 1159 BCE that ended Atlantis and the Bronze Age, the Gulf Stream was two degrees warmer.  For some reason I do not believe it has ever recovered.  The ash impacted for twenty years allowing a twenty year build up of sea ice.  That obviously was sufficient to drop Atlantic temperatures also and it appears to have never really changed since.

Of course we need better data to confirm that.

Global Backup Generator For Past Climate Change

by Staff Writers

Honolulu HI (SPX) Jul 13, 2010

The top panel shows the glacial conveyor belt flow 21,000 years ago. The bottom panel shows a reorganized conveyor belt flow 17,500-15,000 years ago with deep-water sinking in the North Pacific. Credit: IPRC/SOEST

Toward the end of the last ice age, a major reorganization took place in the current system of the North Pacific with far-reaching implications for climate, according to a new study published in the July 9, 2010, issue ofScience by an international team of scientists from Japan, Hawaii, and Belgium.
Earth's climate is regulated largely by the world ocean's density-driven circulation, which brings warm surface water to the polar regions and transports cold water away from there at depth. As poleward flowing salty waters cool in the North Atlantic, they become so heavy that they sink. This sinking acts as a pump for the ocean's conveyor belt circulation.
A well-established fact by now is that there have been times in the past when the North Atlantic branch of the conveyor belt circulation was shut down by melting ice sheets, which released so much fresh glacial meltwater that the sinking of cold water in the Nordic Seas stopped and the Northern Hemisphere was plunged into a deep freeze.
The last time such a collapse took place was toward the end of the last ice age, from around 17,500 to 15,000 years ago, the first stage of what scientists call the Mystery Interval.
About that time, the North Pacific branch of the conveyor belt changed drastically, according to this study in Science.
"The reconstructed changes in the North Pacific current system may have buffered the global impacts of the collapsed circulation in the Atlantic and possibly prevented further cooling of the Northern Hemisphere," says Axel Timmermann at the International Pacific Research Center, University of Hawaii at Manoa, and corresponding author of the paper.
"Around 17,000 years ago, the North Pacific surface waters grew saltier, and the resulting higher density there caused massive sinking. Newly formed icy deep water spilled out of the subarctic North Pacific at depths of 2000-3000 meters merging into a southward flowing deep western boundary current. A warm, strong poleward current, moreover, formed at the surface. It released much heat into the atmosphere and supplied water for the Pacific deep overturning circulation," explains Yusuke Okazaki of the Japan Agency for Marine-Earth Science and Technology and lead author on the paper.
The deep overturning circulation in the Pacific may have also stirred up old carbon-rich deep waters, contributing to the increase in atmospheric CO2 concentration during the last glacial termination. "This could have catalyzed further warming and accelerated the glacial meltdown," says Laurie Menviel, also at the International Pacific Research Center and a co-author on this study.
The observational evidence for these circulation changes comes from analyses of radiocarbon data taken from 30 sediment cores at various locations in the North Pacific.
A comparison of the concentrations of radioactively decaying carbon in marine organisms (foraminifera) living at the surface and ocean bottom in various regions of the North Pacific Ocean yields information about the ages of water masses over this time period. From this data, the scientists could reconstruct and draw a map of the altered circulation.
To complement these observational analyses, the authors used a computer model that simulates the interactions among the ocean basins, seaice, the atmosphere, land vegetation, and the global marine-carbon cycle.
This "earth system model" was run under conditions that mimicked the catastrophic meltwater discharge from the retreating ice sheets 17,500 - 15,000 years ago and disrupted the heat engine in the North Atlantic.
The computer simulation pointed to the same reorganization of the North Pacific overturning circulation as the sediment core data. And both suggest that during this period, the North Pacific Ocean served as a kind of global backup generator to partly offset the global effects of plunging temperatures in the North Atlantic.
"An ultimate test for the proposed mechanisms would be a sediment-core transect through Kamchatka Strait. It would show changes in the water mass ages and flow rates in what would have been a bottleneck for the southward flowing deep currents in the Pacific during the early Mystery Interval," concludes Timmermann.
"In the meantime our findings caution against the Atlantic-centric view of abrupt climate change that has prevailed amongst climate scientists for the last 20 years. They highlight the complicated adjustments happening in the global ocean during these periods of climate change, in which the North Pacific was definitely a player to be considered."

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