## Past and Future Pole Shifts

Introduction

Pole Shift is a controversial subject and is debated passionately. During these discussions people tend to forget the basic physics, the law of the conservation of angular momentum which dictates that the average axial tilt angle with respect to the solar axis will remain constant. The axial tilt angle oscillates with a 41 kyr periodicity but it will always be between 22.2 and 24.5 degrees. Another consequence of the law of the conservation of angular momentum is that the Earth’s rotation around its axis will always be counterclockwise as seen from above the ecliptic plane. These facts can only change if Earth collides with a large asteroid. That object has to be at least as big as Mars. Mechanisms internal to Earth may widen the range (amplitude) of the tilt oscillation but they cannot change the average axial tilt.

Based on the law of the conservation of angular momentum, we can say that the Sun will always rise from the East. That would be a logical statement based on the fact that Earth spin rotation will always be counterclockwise. According to some mythological stories Sun started rising from a different direction 11.5 kyr ago. There is the usual difference between summer and winter of course but the mythologies are talking about a major shift. There is no reason to believe that mythological stories are literally true but for the sake of argument let’s assume that these stories have an element of truth in them; let’s ask what is possible within the restrictions of the law of the conservation of angular momentum?

TPW (true-polar-wander)

In the reference frame of the Solar system the average axial tilt angle does not change (the tilt oscillation stays within a range), the spin rotation speed may change slightly but the rotation is always counterclockwise. The relative orientation of a particular spot on Earth with respect to the axial poles, however, can shift. Geophysicists call this type of polar shift TPW (true-polar-wander) [1].

The polar shift of the TPW kind does not involve a slippage of the crust at the lithosphere-mantle boundary as in Hapgood’s theory [2].  In TPW there is no slippage at the core-mantle boundary either.  The TPW is also different from continental drifts.

In TPW the whole Earth shifts relative to the rotational axis which is fixed in celestial coordinates. In other words, the relative position of a city on Earth with respect to the axial pole is shifting without any crustal slippage, continental drift or core-mantle slippage. This is hard to visualize but it can be explained as follows.

Earth is not a perfect sphere.  Earth’s equatorial circumference is 82 miles longer than the polar circumference. Earth is an oblate sphere. The equatorial bulge was formed from the centrifugal forces when the Earth’s spin rotation was established billions of years ago. More importantly, Earth’s mantle (the huge molten rock layer below the crust) is denser around the equator. This makes Earth a gyroscope. This is why the axial tilt angle is so stable.

Let’s assume for a moment that the densities in Earth’s mantle change. This actually happens because there are convection currents within the liquid mantle and there are also super-plumes (liquid core rising into the mantle). The mantle is liquid rock and the outer core is mostly liquid iron. Currently there are 2 super-plume activities beneath the Pacific Ocean basin (near Hawaii) and beneath the African continent [3] [4] [5] [6]. Interestingly both super-plumes are positioned close to the equator. Because of super-plumes the average mantle density near the equator is decreasing. This has dramatic consequences. This means the Earth is becoming less of a gyroscope. The super-plumes also push the crust (lithosphere) up. From the angular momentum point of view, the rising crust (Africa) counters the destabilizing effect of the density change. The overall effect is probably a decrease in the gyroscope property.

The law of the conservation of angular momentum forces the equator to be near the denser regions of the mantle or near the raised continents or raised ice sheets. Often the continent Antarctica is ignored in these discussions but we know that Antarctica is the most raised continent. The off-axis parts of Antarctica contribute to Earth’s angular momentum significantly. When the distribution of mass density changes for whatever reason the equator will gravitate towards the areas that contribute most to Earth’s angular momentum. Since the axial orientation in space cannot change, the sphere (Earth) will shift so that the denser regions will move towards the axial equator as defined in the reference frame of the Solar System. This is a real shift. In this regard consider the melting of the polar ice caps due to current global warming. If the North Pole ice sheet melts completely the equator will probably move towards Australia. In the absence of super-plumes, this kind of mass redistribution would not cause a large TPW but under the current circumstances it might.

2.5 cm TPW Pole Shift due to 2004 Sumatra Earthquake

Not just the mantle super-plumes but any change in the distribution of mass on Earth will cause TPW kind of polar shift. We know from measurements that the December 2004 Sumatra earthquake [7] [8] [9] [10] [11] shortened the day by 0.000003 seconds (0.003 milliseconds). In regular earthquakes the tectonic plates grind against each other. When one of the plates moves with an angle under the other plate big disasters happen. These regions are known as subducting zones. The 2004 Sumatra earthquake caused a 2.5 cm TPW polar shift because of the subduction activity. The subducting plate motion shortens the day because it is like the skater moving his arms closer to his chest. The post-glacial bounce of the continents has the opposite effect. The rising continents slow down the earth rotation thus lengthening the day. The Earth day has been getting longer because of the rising continents and other reasons. On Dec 31, 2008, 1 second was added to the atomic clocks to reflect this change.

8 cm TPW Pole Shift due to 2010 Chile Earthquake

Geophysicist Richard Gross of NASA’s Jet Propulsion Laboratory in California estimated that the February 27, 2010 earthquake in Chile (8.8 on Richter scale) caused a 8 cm TPW pole shift and also shortened an Earth day by 1.26 millionths of a second.

500 meter TPW Pole Shift due to Uneven Rise in Sea Levels

Recent research suggests that the melting of the West Antarctic ice sheet would raise the sea level by 5 meters. There is huge amount of water contained in the Antarctic ice sheet (25 million $km^3$). The West Antarctic ice sheet is only a small portion of it (2.2 million $km^3$). The 5 meter rise in the sea level would devastate all coastal areas globally. In addition to this devastation we would have the additional problem of a TPW pole shift because of the huge redistribution of mass. Researchers at the University of Toronto and Oregon State University estimate a 500 meter TPW pole shift from the melting of West Antarctic ice sheet [12]. They also estimate that the sea level rise will be uneven in northern and southern hemispheres.

A Possible Scenario

Under a TPW all cities will shift their positions with respect to the axial poles but their relative distances will remain the same. For the reasons mentioned above Earth would shift in such a way that the cities in Central Asia would be closer to the new axial North Pole. The explanation for this is the fact that the continent of Australia is the only large land mass that is denser than the surrounding ocean and the mantle beneath Australia will be denser compared to the mantle at the super-plume location. The direction is also aided by the high-altitude and large mass of Antarctica. Under the current global warming conditions the Antarctic ice sheet will take longer to melt compared to the Arctic ice sheet. This enhances the redistribution of mass density and amplifies the TPW.

My estimate is that if the current warming continues the equator will tilt towards the “Tropic of Capricorn” in Australia and towards the “Tropic of Cancer” on the western hemisphere. The city of Miami will be very close to the new equator. The new North Pole will be in Siberia. All Asian cities will experience colder climates. New York climate will be very similar to the current Miami climate. It is hard to predict the climate of Europe after such pole shift because Europe’s climate is very dependent on the Atlantic Ocean currents. It is very difficult to predict the future of the ocean currents in the wake of a polar shift of the TPW kind.

Commentary on Hapgood’s Theory

Hapgood and his followers argued that accumulation of ice in the Polar Regions could cause changes in the distribution of mass resulting in slippage of lithosphere over the liquid mantle. The argument is that the crust (lithosphere) is very thin compared to the depth of the mantle. Crustal slippage would require less energy compared to the mantle slippage over the core. Hapgood did not know about the convection currents in the mantle and the super-plumes and he did not consider the true-polar-wander which requires even less energy than the crustal slippage. The accumulation of ice in the Polar Regions during the last ice age decreased the ocean level by 120 meters and therefore represented significant redistribution of mass on Earth’s surface. The polar ice accumulation could cause the type of polar shift I explained above if the center of gravity of the ice sheets were off axis. This is the key concept. What caused the off-axis ice sheet formations? One possibility is often ignored: the special astronomical configuration I explained in the article titled “Rapid Climate Change 11.5 Thousand Years Ago”.

TPW 11.5 Thousand Years Ago

Let’s re-examine the special phase 11.5 kyr ago. Axial tilt was at maximum. When the tilt is at maximum both the North and South hemispheres receive more solar insolation during summer and less during winter. The interesting thing about this period (11.5 kyr ago) was that the summer solstice in the Northern Hemisphere was happening at perihelion causing even more heat during summer. The summer solstice in the southern hemisphere, however, was happening at aphelion causing summers in the Southern Hemisphere to be much colder compared to the summers in the Northern Hemisphere. When you consider the amplifying feedback effects caused by the ice sheet reflections and the CO2 and methane gases an imbalance was created between the ice amounts accumulated in the North and South Polar Regions. This meant that the ice sheets in the Northern Hemisphere melted and the ice sheets in the Southern Hemisphere increased. During this processes the ice accumulation and melting tends to be off axis because of the feedback mechanisms mentioned before. The equator angled towards the new center of gravity of the ice sheets in the southern hemisphere resulting in a pole shift. The TPW 11.5 kyr ago moved Greenland away from the rotation axis which is fixed in celestial coordinates.

The Post-Glacial Rebound and TPW

The continents have been in “post-glacial rebound’” since the global warming 11.5 kyr ago. As the ice sheets decreased the continents rose on the mantle. This is one of the reasons why days are getting longer. The rising continent is like the ice-skater extending her arms. That motion slows down the ice skater. Same thing happens to Earth. Another consequence of ice-melt is of course the rising of ocean levels.

The contribution of the “post-glacial rebound’”  to mass redistribution is hard to calculate. Let’s assume that the “post glacial rebound” is the only contributor so that Greenland and Antarctica are rising on the mantle. The immediate consequence will be that the equator in the western hemisphere will tilt towards Greenland. This is purely dictated by the law of conservation of angular momentum. This contribution to the true-polar-wander is reinforcing the contribution from the super-plumes. The two independent phenomena will be contributing to the true-polar-wander in the same direction; as a result the north rotational pole will be located in Siberia in the future. Also, the axial tilt angle is decreasing. Assuming all else is constant, simply due to smaller tilt angle, the summers would be cooler and winters would be warmer in the future. This effect would actually accelerate polar melting, yet another factor contributing to true-polar-wander in the same direction.

Other Factors

It is worth mentioning that even a volcano eruption can cause a TPW. Any mass distribution due to volcanoes or earthquakes or density changes in the mantle will cause a TPW while the gyroscope effect of the equatorial bulge strongly resisting these forces.

Another possibility is the plastic deformation of Earth’s shape and consequent relaxation to normal. An elastic deformation/relaxation is too fast to cause a mass redistribution long enough to cause a polar shift. Only a plastic deformation will do. What are the possible causes of plastic deformation? Gravitational pull from a large astronomical object is needed to cause such a plastic deformation. Pole Shifts of the TPW kind may have happened in the past when large asteroids came close to Earth.

Coupling With the Magnetic Pole

The Pole Shift of the TPW kind is independent of the Magnetic Pole shifts. I hope to write a separate article on the Magnetic Pole shifts. The geodynamo creates the magnetic field of Earth. Contrary to common belief the magnetic field of Earth is not like a bar magnet. There is an overall dipole component but the overall magnetic energy is non-uniformly distributed on the surface. The magnetic poles reversed in the past. The magnetic poles move daily. In the last 50 years the magnetic north pole has been drifting towards Siberia. If this drift continues the magnetic north pole will certainly be in Siberia in the next few decades [13] [14].

We do not understand the details of the geodynamics of this magnetic pole drift. One possibility, however, is that the rotational north pole and the magnetic north pole will be aligned due to coupling created by the geodynamics.

All factors pointing to Siberia as the next location of the North Pole.

A picture is worth a thousand words

Take a look at this picture from NASA and pay attention to North Asia (Siberia). In the future the temperatures may look like this. Blue represents colder, red represents warmer temperatures relative to their norm in the past.

The pole shift of the TPW kind may already be in progress.

References

[1] V. Courtillot and J. Besse, “Magnetic Field Reversals, Polar Wander, and Core-Mantle Coupling”, Science Vol.237 pp.1140-1147 (Science Classic Paper),
[2] Charles Hapgood, “Path of the Pole”, Adventures Unlimited Press, Kempton, Illinois (1999)
[3] E.J.Garnero and A.K.McNamara, “Structure and Dynamics of Earth’s Lower Mantle”, Science Vol.320, No.5876 (2008), pp.626-628 (Review Paper),
[4] B. Romanowicz and Y. Gung, “Superplumes from the Core-Mantle Boundary to the Lithosphere: Implications for Heat Flux”, Science Vol.296, No.5567 (2002), pp.513-516
[5] M. Panning and B. Romanowicz, “Inferences on Flow at the Base of Earth’s Mantle Based on Seismic Anisotrophy”, Science Vol.303, No.5656 (2004), pp.351-353
[6] S. Ni, E. Tan, M. Gurnis, D. Helmberger, “Sharp Sides to the African Superplume”, Science Vol.296, No.5574 (2002), pp.1850-1852
[7] T. Lay et al, “The Great Sumatra-Andaman Earthquake of 26 December 2004”, Science Vol.308 No.5275 (2005), pp.1127-1133
[8] S-C. Han, C.K. Shum, M.Bevis, C.Ji, C-Y Kuo, “Crustal Dilation Observed by GRACE After the 2004 Sumatra-Andaman Earthquake”, Science Vol.313, No.5787 (2006), pp.658-662
[9] http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake
[10] G.Scalera, “The Geodynamic Meaning of the Great Sumatran Earthquake: Inferences from Short Time Windows”, New Concepts in Global Tectonics Newsletter, No.35
[11] R. Sabadini, R.E.M. Riva, G.D. Via, “Coseismic rotation changes from the 2004 Sumatra earthquake: the effects of Earth’s compressibility versus earthquake induced topography”, Geophysical Journal International, Vol.171 No.1, pp.231-243
[12] Scientific American, April 2009, pp.16
[13] http://en.wikipedia.org/wiki/North_Magnetic_Pole
[14] http://news.bbc.co.uk/2/hi/science/nature/4520982.stm