What Is The Cause Of The Millennial Cycle?

[Mammo]

The 1-2 ky climate cycle is clearly evident in the paleoclimate records and is of primary importance in future predictions. But what actually is the driving mechanism of this cycle?
http://www.sciencemag.org/cgi/content/abstract/278/5341/1257

 

[Xnn]

That is a good paper.

In their paper, they argue that a rather substantial change in the North Atlantic's surface circulation brought about a series of ice-rafting events at a frequency of 1470 +- 500 years that was very pronounced during glacial maximum, but since then has occurred as follows:

YrsAgo AD/BC Delta
1400 597 1400
2800 -803 1400
4200 -2203 1400
5900 -3903 1700
8100 -6103 2200
9400 -7403 1300
10300 -8303 900
11100 -9103 800


Notice, the periodicity was poor during the de-glaciation between 11100 to 5900 years ago, but since then became more regular at exactly 1400 years for the last events.

So, by their reckoning we should be just about due for another event. However, with global warming going on as it has, I'd say it doesn't look good for ice rafting in the North Atlantic anytime soon.

 

[Andre]

Can't assess it but is the Ice rafting supported by ODP-core sediment evidence or is it yet a mere hypothesis?

 

[Xnn]

I took a closer look at the Science article. Overall, still a good paper, but there are some odd statements buried in there too.

For example, up front they state that the last significant ice-rafting event was 1400 years ago. Since they claim a 1470 year or so cycle, silly me thought that would imply we were due.

Then later on, they state that since the little ice age ended around the the year 1700, it was within +- 500 years of their expected cycle. That is 1100 years after the previous event. However, for some reason they weren't able to present any sediment data for the Little Ice age.

The problem with this is that the little ice age actually began much earlier than 1700 as pack ice began advancing southward starting around 1250. The little ice age is so loosely defined that one could point to any part of 400 year window and since there was no data, it is pure conjecture as to wether or not it was even an event in the first place.
Also, by some reconstructions, the little ice age didn't end until about the year 1750, when the industrial revolution was significantly increasing CO2 emissions.

So, who knows, maybe huge ice burgs would have been showing up off the coast of Ireland if it weren't for greenhouse gases.

 

[Andre]

Also, by some reconstructions, the little ice age didn't end until about the year 1750, when the industrial revolution was significantly increasing CO2 emissions.

However:

Pre-industrial carbon dioxide levels hovered around 280 ppm until 1850.

Emphazis mine

Better be careful, read https://www.physicsforums.com/showthread.php?t=280637:

Controversial claims must be supported by evidence that comes from a scientific, peer-reviewed journal or a similarly reliable source, i.e., unsubstantiated claims are not allowed.

 

[Mammo]

It's worth mentioning that the millennial cycle is also found in the cosmogenic isotope data. Wibjorn Karlen therefore believes that the Sun is the source of the cycle (personal communication). Unfortunately no clear millennial cycle is found in the Sun's radiation. The cosmogenic isotope data suggests either an increase in the Solar Wind or a decrease in the Earth's magnetosphere. My personal belief is that it is linked to a cyclical decrease in the Earth's magnetic field and is currently of an unknown cause.

 

[Xnn]

The thing is we are talking about are ice rafting events off the coast of Ireland.

A lot of things have to come together for that to happen.
Besides being cold enough, the currents have to shift significantly.

Remember, a warm Gulf Current flows from the south towards Ireland/Britain.
All the evidence they found was for iceburgs from Greenland.

So, either the Gulf current would have to shift away and it'd have to be so cold that an iceburg could survive it in for a long time.

My impression is that neither of these happened during the little ice age.

 

[Xnn]

Andre;

I agree; your claim about CO2 levels hovering until 1850 really needs to be be backed up.

It is overly vague and if you do the research, I'm sure you will find that there
were variations in CO2 levels.

 

[Skyhunter]

I don't have time to read the paper ATM. But is this ice rafted debris associated with http://en.wikipedia.org/wiki/Heinrich_event"

 

[Andre]

Andre;

I agree; your claim about CO2 levels hovering until 1850 really needs to be be backed up.

It is overly vague and if you do the research, I'm sure you will find that there
were variations in CO2 levels.

Click links

However:

 

[Monique]

Xnn, read this post by the administrator: https://www.physicsforums.com/showthread.php?t=280637

It is not clear from what publication the above graph was taken and thus how the data was acquired.

Update:
Since the graph is not directly reproduced from a peer-reviewed source it has been deleted. Please stick to the forum guidelines to maintain a uniform standard of discussion.

 

[Xnn]

Here is the link to the National Climate Data Center for the Law Dome CO2 record over the past 1000 years:

http://www1.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/law/law_co2.txt

Just put it into Excel.

I used the 75 year smoothed value.

 

[Mammo]

The thing is we are talking about are ice rafting events off the coast of Ireland.

A lot of things have to come together for that to happen.
Besides being cold enough, the currents have to shift significantly.

Remember, a warm Gulf Current flows from the south towards Ireland/Britain.
All the evidence they found was for iceburgs from Greenland.

So, either the Gulf current would have to shift away and it'd have to be so cold that an iceburg could survive it in for a long time.

My impression is that neither of these happened during the little ice age.

Exactly what is your explanation of Heinrich Events? It is obviously closely linked to the millennial cycle and both need a simultaneous explanation. My best guess is that the Labrador current gains in strength and height due to an increase in the Gulf Stream reaching the Arctic basin.

 

[Xnn]

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

These more modern 1.47K events involved the Greenland ice sheet. The last once occurred around the year 597 (according to the paper).

For one to occur again, there would have to be enough ice burgs with cool enough sea temperatures for them to reach the area just east of Ireland.

Correct me if I'm wrong, but the Labrador current flows south westward doesn't it?

So, for an ice burg to get to Ireland, either the gulf current would have to cool, or it would have to shift direction so that ice burgs could travel direct.

 

[Andre]

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

Actually the first Heinrich event occurred 60,000 years ago

 

[Mammo]

Heinrich Events involved the Laurentide ice sheet and occurred relatively infrequently between 7 to 15 thousand years. Since the Laurentide ice sheet is history, we are not about to see any more Heinrich events.

These more modern 1.47K events involved the Greenland ice sheet. The last once occurred around the year 597 (according to the paper).

For one to occur again, there would have to be enough ice burgs with cool enough sea temperatures for them to reach the area just east of Ireland.

Correct me if I'm wrong, but the Labrador current flows south westward doesn't it?

So, for an ice burg to get to Ireland, either the gulf current would have to cool, or it would have to shift direction so that ice burgs could travel direct.

The Labrador Current flows south eastward Wikipedia Labrador Current. The idea that I had would be an increase in the strength of this current due to an additional Arctic current during Heinrich Events. The size of the icebergs is also a crucial factor. Perhaps the trans-Atlantic route was not a direct one, but rather a southeast course which is then later picked up by the stronger Gulf Stream and carried northeast.

I also tentatively suggest that the weaker Heinrich Events H3 and H6 Wikipedia Heinrich Events occur during periods of high sea level, which allows the proposed additional Arctic current to overflow through the Bering Strait rather than be primarily channelled down the north Canadian island channels Arctic Map. The average depth of the Bering Strait is only between 30 and 50 meters below current sea level. Wikipedia Bering Strait. This idea seems more applicable to H6 at 60,000 BP, since this is shown to coincide with a sea level just below the land bridge of the Bering Strait. Could this be the reason that there is no evidence of Heinrich Events before 60,000 BP, due to sea levels generally being above 50m? Incidentally, I have just realized that it is even possible that icebergs flowed from the Queen Elizabeth Islands along Greenland's north coast!

 

[Xnn]

I was looking at an old map of the seasonal extent of sea ice that included lines for normal and maximum ranges of ice burgs. Unfortuantely, I don't have the link readily available, but it showed that Ireland is within the maximum range. The normal range was over a 1000 miles to the east, but at least in recent history, Iceburgs could make it to Ireland.

The map appeared somewhat dated, and the NH sea ice has changed dramatically in the last decade, so I have no idea as to when the last iceburg made it that far or how many ice burgs are necessry to call it one of these 1450 year cycle events.

I believe that Ice burgs are no where nears as common as they were back in the time of the Titanic.

 

[Mammo]

Xnn, going back to the Original Post, do you have any ideas or inclinations as to the actual driving mechanism of the 1-2 kyr cycle?

 

[Mammo]

I've just found an interesting article from an IPCC member, http://209.85.229.132/search?q=cach...storf+(2003).+timing&hl=en&ct=clnk&cd=5&gl=uk. (click on the html version at the top for a better format with graphs)

 

[Xnn]

Mammo;

Missed your post back on January 9...

The Rahmstorf paper points to the LIA as possibly the most recent event. However, it also suggest that if the mechanism is internal to the earth, then it could be disrupted ocassionally. Since there is evidence for an event around the year 597, this suggest that there was a recent disruption of the 1470 year cycle. Also, there is evidence that the cycle was disrupted between 11000 to 5900 years ago.

Based on the number of disruptions, it looks like an internal mechanism. However, I suspect that there is an external component as well. In other words, a combination.

 

[Mammo]

However, I suspect that there is an external component as well. In other words, a combination.

Xnn, I have drawn the same conclusions. I'm still reading up on the subject. What about the cosmogenic isotope data? The 1,500 year cycle shows up here as well.

 

[Xnn]

A 2005 article from Nature.

http://www.nature.com/nature/journal/v438/n7065/abs/nature04121.html

Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard–Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of 87 and 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation.

 

[Mammo]

The Rahmstorf report quotes:

There is some evidence that this cycle may also be present in the Holocene
but does not trigger DO events then [Bond et al., 1997], possibly because the Atlantic ocean circulation is not close to a threshold in a warm climate [Ganopolski and Rahmstorf,2001]. The so-called ‘‘little ice age’’ of the 16th–18th century may be the most recent cold phase of this cycle. The origin of the ‘‘mystery 1,500 year cycle’’ is thus one of the key issues in climatology that needs to be explained.

This seems at odds with the above paper. The Bond cycle suggests the mechanism is independent of glacial or interglacial conditions. It's a tricky one, for sure.

 

[Xnn]

Mammo;

I think the mistake is to assume that the Little Ice age is one of the 1470 year events.

As I understand it, every 1470 years almost like clockwork, the sun may get into a highly excited state which can drive a short warm pulse on the Earth that is followed by a rapid cooling. So, the event is relatively short. However, sometimes it does't happen, but then at another period following the 1470 year cycle an event will eventually happen.

Based on the dozen or so of these events, the most recent period period was around the year 1580. Of course we know that that was near the little ice age. In other words, there was no rapid warming/cooling Dansgaard like event, just a period of gradual cooling. So, it looks to me that the sun missed a beat.

Maybe in 1580+1470 = 3050, there will be an event, but I can't get too excited about something that far off.

However, what is interesting is the notion that 1470 years is a combination of 87 and 210 year cycles.

1470/210 = 7 complete multiples.
1470/87=16.89 an incomplete multiple
While 1470/17=86.47.

This is getting a little off topic, but what is going on with the sun is rather interesting.

The next 87 (86.47) year cycle if 2012. I don't know what this may look like during the current solar cycle (which is at an extened minimum). Maybe, since it's not combined with the 210 year cycle, it will be a non-event.

 

[Andre]

Great link Mammo Need to study

Sound application of physics to for instance the instantaneous reaction of the isotopes of the Santa Barbara Basin may reveal that some too hasty conclusions are drawn

More later

 

[Mammo]

Mammo;

I think the mistake is to assume that the Little Ice age is one of the 1470 year events

We have a difference of opinion on this, then Xnn. I woke up today with a new idea about the millennial cycle. I think that it is a permanent feature of the dynamical difference between the inner and outer core of the Earth. Irregularities in the composition of the inner core could cause it to oscillate against the fluid outer core. This bulging of the outer core could account for the cycle showing in the geomagnetic field variation and is also, I believe, responsible for a 1,470 year Earth tidal cycle. This additional tidal force could be the reason for an extended warm Atlantic Gulf Stream to penetrate into the Arctic Basin. This would inhibit the formation of sea-ice and lead to warming due to a reduction in polar albedo, i.e. the D-O events. Heinrich events could be caused by this stronger warm current circling the basin to melt the glaciers of north east Canada and Greenland.

Great link Mammo Need to study
Sound application of physics to for instance the instantaneous reaction of the isotopes of the Santa Barbara Basin may reveal that some too hasty conclusions are drawn
More later

I look forward to your input Andre.