A 50,000-year history of current flow yields new climate clues

Posted: May 12, 2021 by oldbrew in climate, Ocean dynamics, research, Temperature
Tags:
atlantic1

Credit: NASA – GISS

They refer here to the same AMOC that was recently claimed by Mann et al to be of no significance, or even not to exist at all. But empirical evidence has its uses.
– – –
From 50,000 to 15,000 years ago, during the last ice age, Earth’s climate wobbled between cooler and warmer periods punctuated by occasional, dramatic ice-melting events, says Phys.org.

Previous research has suggested that these oscillations were likely influenced by changes in the Atlantic Meridional Overturning Circulation (AMOC), a pattern of currents that carry warm, tropical water to the North Atlantic, where it cools, sinks, and flows back south. However, the precise role played by the AMOC in ancient climate fluctuations has been unclear.

Now Toucanne et al. have reconstructed the historical flow of a key current in the upper part (the northward flow) of the AMOC, the Glacial Eastern Boundary Current (GEBC), shedding new light on how the AMOC can drive sudden changes in climate.

The GEBC flowed northward along Europe’s continental margin during the last ice age (it persists today as the European Slope Current). To better understand the GEBC’s role in the AMOC, the researchers collected six seafloor sediment cores off the coast of France.

Analysis of grain sizes and isotope levels in the core layers revealed the current’s strength when each layer was deposited, yielding the first high-resolution, 50,000-year historical record of the current.

This new historical record shows that the GEBC flowed faster during warmer intervals of the last ice age but weakened during the coldest periods.

The timing of these changes aligns well with previously established records on AMOC speed and the southward return flow of deep waters to the west.

Comparing the history of the GEBC with other records also shows that major ice-melting events, in which ice age glaciers released huge amounts of freshwater into the Atlantic, correspond with periodic weakening of the current and of the AMOC in general.

Full article here.

Comments
  1. oldbrew says:

    periodic weakening of the current and of the AMOC in general.

    Periodic – due to what?

  2. JB says:

    “the researchers collected six seafloor sediment cores off the coast of France.”

    So, the assumption is, the coast of France did not change over the last 50K yrs.

    But there is evidence, around for decades, that the coastline was NOT the same as today, that it along with the entire Atlantic coast line on both continents went through catastrophic changes, especially around 12KBCE.

    Me thinks more than 6 samples are in order here.

  3. Gamecock says:

    ‘Analysis of grain sizes and isotope levels in the core layers revealed the current’s strength when each layer was deposited, yielding the first high-resolution, 50,000-year historical record of the current.’

    And what is that resolution?

    ‘This new historical record shows’

    It’s not ‘historical’ nor a ‘record’ in any way. Not written, not significant, not superlative.

    ‘the researchers outline a mechanism by which the GEBC could have carried cold glacial meltwater northward and contributed to changes in the AMOC that may have driven warm-cold climate oscillations in the North Atlantic.’

    21st century definitive science: ‘could have’ and ‘may have.’

  4. Phil Salmon says:

    This is an important study, it could pin down the role of the AMOC in northern hemisphere periodic warming and cooling.

    And stop the warmists trying to have it both ways, to impossibly have their cake and eat it. Up to now they have claimed that both a slowing down and a speeding up of the AMOC, will both cause warming. Not apparently seeing any logical problem with this.

    This study stops that nonsense. As would be expected from elementary thermodynamics, faster AMOC moves more heat poleward, warming the NH. Slower AMOC does the opposite, moving less heat and cooling the high latitudes of the NH.

    Oceanographers have known for ages that the AMOC is responsible for the big difference in climate stability between the Northern and Southern Hemispheres; that is, the NH being unstable with more frequent climate and ice cover fluctuations, while the SH is more stable with slower and less frequent climate changes. The DO events recorded in Greenland are a good example of this. They don’t happen in the SH.

  5. Phoenix44 says:

    Earth’s climate went between warmer and cooler periods. How and why.

    Answer that and maybe I will take claims about current climate seriously.

  6. From 50,000 to 15,000 years ago, during the last ice age, Earth’s climate wobbled between cooler and warmer periods punctuated by occasional, dramatic ice-melting events, says Phys.org.

    Greenland ice core records are easy to understand. Meltwater from the great ice sheets on the continents broke through the ice dams and emptied into the Arctic and caused these apparent dramatic ice-melting events, actually the meltwater surges did cause ice-melting events. Ocean circulations outside the ice dams around the Arctic could not have caused these events, but water escaping from these meltwater surges could have caused ocean circulation changes.

  7. oldmanK says:

    popesclimatetheory says: May 24, 2021 at 12:29 am
    “Greenland ice core records are easy to understand. Meltwater from the great ice sheets on the continents broke through the ice dams and emptied into the Arctic and caused these apparent dramatic ice-melting events”

    Can meltwater at near zero degrees provide the latent heat (of fusion or freezing) to ice – at zero degrees?

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