CORRELATION BETWEEN LUMINESCENT SPELEOTHEM RECORDS OF SOLAR INSOLATION AND PALEOTEMPERATURE RECORDS

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Karst Processes and the Carbon Cycle ed. by Y. Daoxian & Z. Cheng, (2002)

Geological Publishing House, Beijing, China, IGCP379, pp. 136-144

CORRELATION BETWEEN LUMINESCENT SPELEOTHEM RECORDS OF

SOLAR INSOLATION AND PALEOTEMPERATURE RECORDS

Yavor Y. Shopov, Diana A. Stoykova, Gotse Tenchov, Ludmil Tsankov, Michael Sanambria, Leonid N. Georgiev, Derek C. Ford*,

Faculty of Physics, University of Sofia, James Bouchier 5, Sofia 1164, Bulgaria*Geography Dept., McMaster Univ., Hamilton,Ontario, L8S 1K4, Canada

E-Mail:[email protected]

1. Abstract

Calcite speleothems luminescence depends exponentially upon soil temperatures that are

determined primarily by solar visible and infrared radiation. So the microzonality of luminescence

of speleothems may be used as an indirect Solar Insolation proxy index. We obtained a luminescentsolar insolation proxy record in a speleothem (from Jewel Cave, South Dacota, US). The same

speleothem has been dated by 6 TIMS U/Th dates, which reveals determination of millennial andcentury cycles in the record. This record exhibits a very rapid increasing in solar insolation at 139

±5.5 kyrs BP responsible for the termination II (the end of the last glaciation). This increasing

precedes the one suggested by the Orbital (Milankovitch) theory with about 10 kyrs and is due to the

most powerful cycle of the solar luminosity with a period of 11.5 kyrs superposed on the orbital

variations curve. The Devils Hole18

O record suggests that termination II had happened at 140

±3 kyrs BP. It follows precisely the shape of our experimental solar insolation record. These

measurements do not reject the orbital theory, but suggest that the solar luminosity contribution to

the solar insolation curves has been severely underestimated. We demonstrated that the solar

luminosity variations contribute to Earth’s heating almost as much as the orbital variations of the

Earth’s orbit (Milankovitch cycles), since the most powerful cycle of the solar luminosity (11500 yrs)

is responsible for almost 1/2 of the variations in high resolution solar insolation experimental records.

Solar luminosity and orbital variations both cause variations of solar insolation affecting theclimate by the same mechanism.

Rapid temperature changes as the well known “The Little Ice Ages” and “Medieval

Maximum” are often connected with changes of solar activity and understanding of these processes

leading to formation and melting of the ice sheets is of great significance for prediction of possible

disasters.

2. Validity of the Milankovitch Theory

M.Milankovitch (1920) demonstrated that orbital variations of the Earth’s orbit cause

significant variations of the amount of solar radiation received by the Earth’s surface (solar insolation-SI) and assumed the idea that glacial periods (ice ages) are result of such variations. The orbital

components which cause variations of solar insolation are:1. Variations of the tilt (obliquity) of the Earth’s axis with respect to the vertical to the ecliptic

plane (the plane of the Earth’s orbit). It varies to about ±1.5o

on either side of its average angle of 23.5

owith period of about 41 000 years.

2. Precession - owing to the gravitational pull of the Sun and the Moon on the equatorial bulge

of the Earth, its axis of rotation moves slowly around a circular path and completes one turn every 23

000 years. It causes also precession of the equinoxes and the solstices with the same period.

Precessional motion is similar to rotation of the axis of a top.



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3. Eccentricity - the ratio between the distance from the centre of the orbit to one of its focal

points versus the semimajor axis of the Earth’s orbit. It varies with a number of periods around 100

000 years. They cause small variations of the total Solar energy received by the Earth.Recent measurements (Winograd et al, 1988, 1992) of a cave deposit from Devils Hole (DH),

USA, which is the best dated paleoclimatic record, demonstrated that the end of the former glaciation(Termination II) came 10 kyrs before that suggested by the orbital theory. Some scientists consider

this as a denial of the orbital origin of glaciations, because it demonstrates that the result appears farbefore the reason.

The Orbital theory has 2 presumptions:1. That the solar luminosity is constant during geological periods of time.

2. That the Earth behaves as an absolute solid body independently of the orbital variations.

Recent studies demonstrate that both these presumptions are not precise. Direct satellite

measurements of the solar constant demonstrated that it varies with time as much as 0.4% during the

observation time span (Hickey et al., 1980), but there are experimental data suggesting that it varied

much greater during geological periods (Sonett, 1984, Stuiver & Braziunas, 1989).

Formation and melting of the ice sheets affect the Sea Level, but they influence also the

rotation speed of the Earth (Moerner, 1993), the obliquity (Wlliams et al., 1998; Bills, 1998) and the

precession as well. The orbital theory (Berger, Loutre 1992) does not consider these influences.

Increasing of the ice volume and related sea level change during glaciations produces changes

in the inertial moment of the Earth and resulting changes in the speed of Earth’s rotation (Tenchov et

al., 1993). These changes must affect in some degree the amplitude and may be even the frequency of the orbital variations. Orbital variations cause also some deformation of the solid Earth and

redistribution of the Ocean masses (Moerner, 1976, 1983). In result theoretical curves can be usedonly for qualitative reference. For quantitative correlation it is necessary to use experimental records

of the solar insolation, because they contain also variations of the solar luminosity and number of others not covered by the Orbital theory.

3. Experimental Methods

Calcite speleothems (stalagmites etc.) usually display luminescence which is produced by

calcium salts of humic and fulvic acids derived from soils above the cave (White, Brennan, 1989,

Shopov, 1989). These acids are released by the decomposition of humic matter. Rates of decomposition depend exponentially upon soil surface temperatures that are determined primarily by

solar infrared radiation (Shopov et al., 1997). So the microzonality of luminescence of speleothems

can be used as an indirect Solar Activity (SA) index (Shopov et al., 1990). From a speleothem from

Cold Water cave, (Iowa, USA) it was obtained a high correlation coefficient of 0.90 between the

luminescence record and the Solar Luminosity Sunspot index measured since 1700 AD (fig.1), and

with the reconstructed sunspot numbers since 1000 AD with a precision within the experimental error

of the measurements. Intensity of luminescence in the record was not dependent on actual

precipitation (zero correlation).

Time series of the SA index "Microzonality of Luminescence of Speleothems" are obtained by

Laser Luminescence Microzonal analysis (LLMZA) of cave flowstones (Shopov, 1987). LLMZAallows measurement of luminescence time series with duration of hundreds of thousands years, and

nevertheless the time step for short time series can be as small as 6 hours (Shopov et al., 1994)allowing resolution of 3 days (Shopov, et al., 1988).

Striking correlation (with a correlation coefficient of 0.8) is demonstrated between thecalibration residue delta 14-C record and a LLMZA speleothem record (Shopov et al.,1994). Cosmic

rays flux and inverted sunspot numbers demonstrate the same correlation coefficient of 0.8 (Beer,1991).The 14-C record represents the Cosmic Ray Flux (CRF) and modulation of the CRF by the solar

wind.



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Figure 1. (a) 20 yr. average sunspot record (Solar Luminosity Sunspot index) since 1700 AD (b) Luminecent speleothem record from Cold Water cave, Iowa, USA with step of 3.78 years. Sunspot

record has been transformed digitally in the format of the luminescent record in order to calculatecorrelation between both curves.

4. Luminescent Speleothem Proxy Record of Solar Insolation

We measured a luminescent solar insolation proxy record in a speleothem (JC11) from Jewel

Cave, South Dakota, USA (Shopov et al.,1998, Stoykova et al., 1998). This record covers 89300-

138600 yrs BP (fig.2b) with high resolution (34 years) and precision of measurements better than 1%.

It reveals determination of millennial and century cycles in the record.

This TIMS U/Th dated JC11 record exhibits a very rapid increasing in solar insolation at 139

kyrs ±5.5 kyrs BP (95% confidence level) responsible for the termination II. This increasing proceedsthat one suggested by the Orbital theory with about 10 kyrs and is due to the most powerful cycle of

the solar luminosity with period of 11.5 kyrs superposed on the orbital variations curve. This cycle

was found previously to be the most intensive one in the ∆14C calibration record (Damon & Sonett,

1991) and was interpreted to be of geomagnetic origin. Our studies suggest that this is a solar cyclemodulating the geomagnetic field. The Devils Hole

18O record (fig.2a) suggests that termination II had

happened at 140 ±3 kyrs B.P. It follows precisely the shape of our experimental solar insolation

record. This result is confirmed by an other U/Th dated luminescent solar insolation proxy record in a

speleothem from a Duhlata cave, Bulgaria (fig.2c) 10 000 km far form the JC11 site. These records do

not deny the orbital theory, but they suggest that the solar luminosity contribution to the solar

insolation curves has been severely underestimated.



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Figure 2. (a) The theoretical insolation curve compared to Devils Hole (DH-11), Vostok, and

SPECMAP stack stable isotope curves (Winograd et al.,1992). Shading represents high sea levelstands (at or above modern levels). (b) JC11. It is TIMS U/Th dated in 6 points with 2σ error varyingfrom 0.8 kyrs (for 89.3 kyrs BP) to 5.5 kyrs (for 138.7 kyrs BP). (c) Duhlata Cave (Bulgaria), DC-2

luminescence Solar Insolation proxy record. It is TIMS U/Th dated in 4 points with 2σ error varying

from 1 kyr (for 89.3 kyrs BP) to 23 kyrs (140 kyrs BP).

We extracted orbital variations from the JC11 record by a band-pass Tukey filter set for

frequencies of 41, 23 and 19 kyrs (fig. 3). So the remaining signal contains only SL self-variations

(fig. 3). The most powerful cycle in this record with period of 11.5 kyrs appears to be a bit more

powerful than the precession cycle and a bit less than the total orbital component of the SI variations.



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Figure 3. (c) Solar Luminosity variations extracted from Jewel Cave (South Dakota) JC11luminescence Solar Insolation proxy record (a) by subtracting of the sum of the orbital variations (b)extracted from the JC11 record by a band- pass Tukey filter set for frequences of 42, 23 and 19 kyrs

orbital components of the JC11 luminescent record. All curves are presented in % from the solarinsolation.

Intensity of this part of the solar insolation variations due to tilt variations appear to be more

than twice more intensive, than the one due to precession variations. It disapproves the suggestion of

the orbital theory that precession variations are responsible for almost entire solar insolation variation

for this time and place (Berger and Loutre, 1992). The theoretical curves (A. Berger, 1978, 1992)

explain about 1/2 of the signal in the existing proxy paleotemperature records (Imbrie et al.,1992,



141

1993) derived from sea cores and polar ice. But a more precise correlation demonstrates that a

significant part of it is not due to the components of the orbital variations (Imbrie et al., 1992,1993) in

such proportions as in the theoretical solar insolation curves. In order to overcome this disagreementImbrie (1985) introduced his ETP index of orbital variations, which is a sum of separate components

of orbital variations in proportions other than those suggested by Milankovitch theory. Imbrie (1985)does not offer an explanation why the real ratio between the orbital variations is different from the

theoretical one.Paleoclimatic records also contain tilt, precession and eccentricity components, but with

different proportions than in the theoretical solar insolation curves (Imbrie, 1985; Imbrie at all. 1992a,b). There are 2 possible explanations of this disagreement:

1.That variations of the solar insolation caused by the precession is far less than the one

suggested by theory (this is very unlikely).

2. That amplitude of obliquity variation was greater than theoretical. Such greater variations are

possible and may be caused by redistribution of the ocean masses in result of the variations of

obliquity; variations of the inertial moment of the Earth (due to mass redistribution caused by

precipitation of ice and lowering of the sea level during glacial periods) and resulting variations of the

rotation speed and oblateness of the Earth (Tenchov& Tenchov, 1993).

5. Solar Cycles found in Luminescent Speleothem Record

Sonett (1984) analysing the 14-C solar proxy record found that the cycle with a period of about900 yrs has intensity 5- 7 times higher than that of the century cycle. Stuiver & Braziunas (1989)

calculated MEM spectra of the same record and claimed that “changes occur in the Sun’s convectivezone with a fundamental oscillatory mode of about 420 yr period...” and that century and sub- century

cycles are about one twentieth of the strength of this 420-yr cycle. Although the uncertainty of theproportion between intensities of different cycles in spectra calculated by these authors can not be

estimated they demonstrate, that longer solar cycles are more than one order of magnitude stronger,than the solar cycles covered by direct measurements.

We used periodogramme analyses to determine the solar insolation cycles contained in theluminescent speleothem record (JC11), Jewel Cave (South Dakota).

In order to compare quantitatively intensities of all cycles presented in our data we designed a

special algorithm and relevant computer program, which plots the periodogramme in coordinates

(Cycle Intensity/Period). Calculated periodogrammes of the JC11 luminescent record demonstrated,that the solar cycle about 900 years has intensity only 3-4% of the 11500-yr cycle and the solar cycle

about 420 years has intensity less than 2.5 % of the 11500-yr cycle. So the 11500-yr cycle should have

intensity of several orders of magnitude higher, than the observed century and sub- century cycles.

We obtained many cycles of solar insolation, more intensive of them are with duration of 6000,

4400, 3300, 2500, 2300, 1900 and 1460, years (in order of decreasing intensity) with amplitude

ranging respectively from 3 to 0.7 % of the Solar Constant (tab.1).

A cycle with duration 10026 (+1254/ -834) yrs. was found in records of the intensity of the

geomagnetic field of the Earth (Tric et al., 1992). We identified this cycle with the 11500 yrs. one in

the luminescent record and we calibrated all other cycles in the geomagnetic record to this luminescent

cycle. There were found many cycles contained in both records. They are with duration of 4400, 2500,3950, 2770, 1950,1460,2090, 1200, 900 yrs (in order of decreasing intensity), (tab. 1).

6. Solar Insolation, Solar Luminosity and Sea Level

John Imbrie et al.(1985) demonstrated, that orbital variations cause major changes of the global

sea level, because of the melting of polar ice caps by the solar radiation. He even expressed units of orbital variations in resulting sea level changes in meters regarding the modern sea level. Accordingly

Fairbanks (1989) during the last glacial maximum 18000 years ago global sea level was 120 meters

below the modern one. The reason for this is that water and ice adsorbs strongly infrared solar

radiation, resulting in melting of the ice. Lower solar insolation during glaciations allow higher ratio

between ice precipitation and melting, resulting in increasing of ice accumulation and preservation,



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and also in advance of the ice shields in direction to the equator. Melting of this ice during interglacials

cause rising of the sea level.

Cycle VSC PSC GEOM C14

[Yrs] [W/m2] [%] [%] [%]11500 100.6 7.33 7.33 7.33

7800 27.5 2.006160 41.5 3.02

4400 24.4 1.78 6.2

3950 25.1 1.83 4.32

3400 24.1 1.76

2770 12.6 0.92 3.25

2500 16.3 1.19 4.70

2300 12.5 0.91

2090 7.28 0.53 2.26

1958 11.26 0.82 2.82

1770 8.5 0.62

1670 9.1 0.66 1.01 0.73

1460 10.0 0.73 2.421280 4.8 0.35 0.71

1195 4.5 0.33 1.22 0.401145 4.5 0.33 1.92

1034 4.26 0.31 1.62935 3.02 0.22 1.2

835 3.6 0.26 0.6 0.56814 2.6 0.19

775 2.3 0.17750 2.6 0.19 0.56

670 2.06 0.15

660 2.47 0.18

610 1.78 0.13 0.48570 2.06 0.15

550 1.78 0.13

538 2.06 0.15

Table 1 Cycles of the Solar Luminosity (in Years), relevant variations of the Solar Constant expressed in W/m2

(VSC) and in % from the Solar Constant (PSC) compared to cycles of Solar Wind proxies- Intensity of the Dipole of the

Geomagnetic Field (GEOM) and inverted rate of production of 14C

7. Conclusions

The Milankovich theory has 2 presumptions:1. That the solar luminosity is constant during geological periods of time.

2. That the Earth behaves as an absolute solid body independently of the orbital variations.Recent studies demonstrate that both these presumptions are not relayable.

Solar luminosity variations contribute to Earth’s heating almost as much as the variations of the Earth’s orbit (Milankovitch cycles). Their most prominent cycle (with period of 11500 yrs) must

be also taken into account for a proper explanation of the timing of the last deglaciation.Speleothem records (being the best dated paleoclimatic records) may serve as a reliable tool for

studying the mechanisms of formation and precise timing of glaciations.



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7. AcknowledgementsThis research was funded by Bulgarian Science Foundation by research grant 811/98 to Y. Shopov and by a NSERC

strategic research grant to D.C.Ford.

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CORRELATION BETWEEN LUMINESCENT SPELEOTHEM RECORDS OF SOLAR INSOLATION AND PALEOTEMPERATURE RECORDS