Climate Signals from 10Be Records of Marine Sediments Surrounded with Nearby a Continent

1. Introduction

Climate signals from ¹⁰Be records in marine environments have been studied for last two decades (Aldahan et al., 1997, Bourlès et al., 1989, Christl et al., 2003, Eisenhauer et al., 1994, Horiuchi et al., 2000, 2001, Kim and Nam, 2010, Knudsen et al., 2008, McHargue et al., 2010, McHargue and Donahue, 2005). Understanding of regional climate signals is feasible through not only ¹⁰Be but also ⁹Be from the sediment. This is because ⁹Be is terrigenous origin while ¹⁰Be signal is affected by climatic condition and production at the top of atmosphere. Recent study from the East Sea of Korea (05-GCRP-21) indicated that climate signals from ¹⁰Be records of Korean marine sediment are generally representing global climate variations during warm and cold periods from Last Glacial Maximum to Holocene and also MIS (marine isotope stage) 6 to Eemian. The ¹⁰Be records of the East Sea are well compared with those from the oxygen isotopic record of this marginal sea (Kim and Nam, 2010). During the warm interglacial periods the ¹⁰Be concentrations per sediment mass have significantly increased while during the cold glacial periods those have decreased (Aldahan et al., 1997, Eisenhauer et al., 1994). This result also shows that a vivid record of ¹⁰Be/⁹Be indicates a significant increase of ¹⁰Be at a time of 120 kyr, which might be an indication of the paleomagentic excursion.

Interestingly, it was found that the ¹⁰Be concentrations per 1g sediment of this region were about 30% lower than other ¹⁰Be records of largely open marine environment. We also found that ¹⁰Be concentrations of the Blake Outer Ridge were similar to those from Korean marine sediments (McHargue et al., 2000). Two study areas are located nearby large continents: the East Asia (the East Sea) vs North America (the Atlantic). This could be caused by sediment inflow to the marine environment which is close enough to the continent. Therefore, local marine environmental influence is revealed through the beryllium isotopes. Both cases would have similar climatic signals due to their geographical locations nearby continent. The lower ¹⁰Be concentrations for these regions could be also involved in ocean current and circulation. Relatively deep sea water of these regions may not be well mixed rapidly with the surface water and old sea water with relatively lower ¹⁰Be concentration remains in the sediment records. For this chapter, we investigated climatic signals from Be isotope records of the East Sea of Korea and the Mendeleev Ridge of the Arctic Ocean and compared with the records from the Blake Outer Ridge studied by McHargue et al., 2000. In addition, global ¹⁰Be records of marine sediments for various regions will be briefly discussed. This chapter would provide a new insight guide into understanding climate signals through ¹⁰Be records of various marine environments.

2. Beryllium isotopes in terrestrial environments

2.1. Cosmic ray induced ¹⁰Be production rate

Production rates of cosmogenic isotopes depend on geomagnetic latitude, altitude, and flux of incoming cosmic rays to the earth (Lal, 1988). The Earth’s geomagnetic field deflects incoming cosmic rays and has an effect on the production rate of in situ cosmogenic isotopes. This deflection affects the incident angle and the rigidity of cosmic rays. The rigidity is defined as r = pc/q, where p is the momentum, q is the charge of the particle, and c is the velocity of light (O’Brien, 1979). The vertical cutoff rigidity is the lowest at the geomagnetic poles and highest at the equator. Therefore, greater cosmic rays reach to the poles and attenuation length at low latitude is greater than at high latitude (Simpson and Uretz, 1953). Since geomagnetic latitude affects the production rate of cosmogenic isotopes, understanding of the secular variation of the Earth’s geomagnetic field is important. It is known that variations of geomagnetic field intensity cause changes in the flux of cosmic rays, in solar activity, and in shielding by the Earth’s magnetosphere. Laj et al., 1996 describes geomagnetic intensity and ¹⁴C abundance in the atmosphere and ocean during the past 50 kyr. This paper shows geomagnetic change effects on the ¹⁴C production, which is increased by the decrease of the Earth’s dipole moment. Similarly, the relationship between ¹⁰Be production rate and geomagnetic field intensity was studied using deep-sea sediments. These results also demonstrate the importance of the relationship between cosmogenic nuclide production and intensity of geomagnetic dipole moment variation (Frank et al., 1997). Thus, production of cosmogenic isotope should be corrected with the variation of geomagnetic dipole moment variation. It has been found that the Earth’s geomagnetic pole is essentially the geographic pole for periods greater than about 2 kyr (Champion, 1980, Ohno and Hamano, 1992). Therefore, a correction from geographic reading to geomagnetic reading is required. For most cases of ¹⁰Be or ²⁶Al surface exposure dating samples, the working range of age is from several thousand years to a few million years. Thus, in this case, the correction for geomagnetic reading may not be required, but the correction of production related to secular variation of geomagnetic dipole moment intensity is required. Masarik et al., 2001 demonstrated the correction of in situ cosmogenic nuclide production rates for geomagnetic field intensity variations during the past 800 kyr. This paper indicated that at the equator integrated production rates for exposure ages between ~40 and 800 kyr are 10 to 12% higher than the present day value, whereas at latitudes greater than 40 degree, geomagnetic field intensity variations have hardly influenced in situ cosmogenic nuclide production.

Production rates as a function of both latitude and altitude have been studied in the past. For a few decades, models from Lal and Peters, 1967 and Lal, 1988, have been widely used for the scaling factors for production rates of in situ produced cosmogenic nuclides. A third degree polynomial equation found in Lal, 1991, enables one to calculate the production rate of ¹⁰Be and ²⁶Al with respect to geomagnetic latitude and altitude. A reevaluation of scaling factors for these production rates has been attempted recently using non-dipole contributions of the geomagnetic field to the cosmic ray flux and observed attenuation lengths (Dunai, 2000). The scaling factors for the nuclear disintegration with respect to geomagnetic latitude and altitude from Lal’s work are involved in the geocentric axial dipole hypothesis and this is appropriate for time scales exceeding 200 kyr. The non-dipole components of the Earth’s magnetic field contribute up to 20% to the total field; therefore, they must be considered for short-term effects of cosmic rays. It is known that the new scaling factors and those of Lal are significantly different, by up to about 30%, especially at high altitude and at low latitude. Currently, a few other research groups have been involved in studying production rates of cosmogenic nuclide or measurement of neutron flux as a function of geomagnetic latitude and altitude. This additional research on this field may provide a confirmation of these scaling factors for the production of in situ cosmogenic isotopes. (Stone, 2000, Graham et al., 2005a,b,c, 2000, Lifton et al., 2001, Desilets et al., 2006).

2.1.1. Production rate in the atmosphere

¹⁰Be is produced in the atmosphere by nuclear interactions with oxygen and nitrogen (Peters, 1955, Goess and Phillips, 2001). The intensity of the cosmic ray flux depends on galactic and solar sources, and modulation by the heliomagnetic and geomagnetic fields. Both ¹⁰Be is produced by spallation reactions in the atmosphere, and then ¹⁰Be is well mixed up (Ueikkila et al., 2009) and removed from the atmosphere by precipitation scavenging of aerosol particles to land and sea. Eventually, these nuclides are deposited within ocean sediment. The ¹⁰Be concentration at 10.7 km of stratosphere and at 19.2 km in the tropospheric concentration are known to be 7 x 10⁶ atoms/m³, and 1.3 x 10⁷ atoms/m³, respectively. The global average ¹⁰Be production rate is found to be (1.21±70) x 10⁶ atoms/cm²/yr (Monaghan et al., 1985). Estimates of the ¹⁰Be production rate derived from measurements on ice cores, lake sediments, and deep-sea sediments range from 0.35 x 10⁶ atoms/cm²/yr to 1.89 x 10⁶ atoms/cm²/yr. (Monaghan et al., 1985). Castagnolie et al., 2003 demonstrated reconstruction of the modulation parameter M from the open solar magnetic flux proposed by Solanki et al., 2000, and experimental values calculated from the GCR spectra measured with balloons and spacecraft are compared well with ¹⁰Be concentration measured at the Dye3 ice core, assuming constant accumulation rate during the period of 1810-1997. The production rate of ¹⁰Be ranged from 0.015 to 0.025 atoms/cm²/s (Castagnolie et al., 2003).

The precipitation onto the surface of the Earth and the deposition of ¹⁰Be in soils is influenced by climate. In turn, the production of ¹⁰Be in the atmosphere is influenced by the magnetic dipole field of the Earth to which it is inversely related. This relationship between the production of ¹⁰Be and the geomagnetic field has been shown by the correlation between the variations of ¹⁰Be and those of the me paleo-asuredinclination data of the dipole field in sediments (Frank et al., 1997, Frank,2000, Masarik et al., 2001, Laj et al., 2000), and the concentrations of ¹⁰Be in marine sediments and the measured paleointensity (Carcaillet et al., 2004, McHargue and Donahue, 2005).

The influence of climate on the deposition of ¹⁰Be, otherwise is problematic for interpretations of the cosmic-ray flux, in itself is a worthy subject for study. For example, variations in the deposition rates of ¹⁰Be and sediments affect the ¹⁰Be/⁹Be ratio due to the uneven mixing of the two isotopes in the hydrological cycle. That, ¹⁰Be, produced largely in the atmosphere, is transported to the surface of the earth by rain and dry precipitation to the sea. In contrast, ⁹Be, derived from terrigenous materials, is transported to the sea largely by rivers, and to a lesser extent by atmospheric deposition.

Location	^10Be	Source	Reference
USA continent	(1.38±0.36) ~(3.96 ± 0.35) x 10^6atoms/cm^2/yr	rain	Monagahan et al., 1985
USA Hawaii	1.9 x 10^3 ~ 8.94 x 10^4 atoms/g	rain	Monagahan et al., 1985
Tropical region	Avg. 1.53 x 10^4atoms/g	rain	Monagahan et al., 1985
Illinois, USA	2 ~7 x 10^7atoms/g	soil	Brown et al., 1989
Japan, Kikari Is	(0.80 ~ 7.17) x 10^9atoms/g	soil	Maejima et al., 2005
Japan, Kikari Is	(2.0 ~ 3.5) x 10^6atoms/cm/yr	rain	Maejima et al., 2005
New Zealand	(2.1 ~ 2.9) x 10^4atoms/g	rain	Graham et al., 2003
Korea, Masanri	(0.67 ~ 1.47) x 10^8atom/g	soil	Kim et al., 2011a
India	(0.43~3.34) x 10^7 atoms/l	rain	Somayajulu et al., 1984
Global	(1.21 ±0.70) x 10^6atoms/cm^2/yr	rain	Monagahan et al., 1985

Table 1.

Production rate and concentration of ¹⁰Be in the rain and soil.

2.1.2. ¹⁰Be in land surface

Precipitation was collected for approximately one year during 1980 at seven localities in the continental U.S.A. (Monagahan et al., 1985). The ¹⁰Be flux ranged from (1.38±0.36) x 10⁶ to (3.96±0.35) x 10⁶ atoms/cm²/yr (Monagahan et al., 1985). In the case of Hawaii, ¹⁰Be concentration ranges from 1.9 x 10³ to 8.94 x 10⁴ atoms/g in rain water. The mean ¹⁰Be deposition rate in temperate latitude is determined to be 1.53 x 10⁴ atoms/g in rain water (20% error). Monagahan et al., 1985 indicated that the concentration of ¹⁰Be in surface soils and river sediments varies between 10⁷ and 10^{9 10}Be atoms/g soil with the modal concentration of ¹⁰Be lying between 4 x 10⁸ and 6 x 10⁸ atom/g. The relationship between annual rainfall and ¹⁰Be deposition rate is plotted to be linearly proportional to each other (Maejima et al., 2005). This study shows that ¹⁰Be fluxes (cm/day) for the two rain collection sites are relatively higher during a collection period of January 22 to April 22 than other collection period (Maejima et al., 2005).

Seasonal variations for ⁷Be and ¹⁰Be concentration in Tokyo and Hachijo-Island during a period of 2002 to 2003 were similar to each other. The peak value for ⁷Be and ¹⁰Be concentration appeared in April and October, respectively. Especially, in April when stratosphere-troposphere exchange occurs, peak values for the atomic ratio ¹⁰Be/⁷Be appeared. Low ⁷Be and ¹⁰Be concentrations and the atomic ratio of ¹⁰Be/⁷Be appeared in summer, July to August. Because the composition of the aerosol of Tokyo was almost same to the nearby soil, it is considered that Tokyo was strongly influenced by re-suspended soil contamination. Yamagata et al., 2005 indicated that using Al concentration in the aerosols, the enrichment of ¹⁰Be concentration by re-suspended soil contamination was estimated to be about 30%.

In the case of Southern Hemisphere, Graham et al., 2003 demonstrated ⁷Be and ¹⁰Be fluxes at 36 to 45ºS were determined to be (1.2~14) x 10⁷ atoms/kg and (2.1~2.9) x 10⁷ atoms/kg, respectively. These results are similar to those for rain sampled at mid-latitude sites across the USA from 1986 to 1994. The annual ⁷Be and ¹⁰Be flux rates are ~15 and ~27 x 10⁹ atoms/m², respectively, at the northern sites of Leigh and Gracefield, and are significantly lower at ~9 and ~19 x 10⁹ atoms/m², respectively, at the southern site of Denidin, because of the lower average rainfall there. Graham et al., 2003 indicated that ⁷Be/¹⁰Be in New Zealand ranged 0.47 to 0.61 and this is significantly lower than the ratio in USA (0.69~0.78). This is due to re-suspended dust to the primary atmospheric ¹⁰Be in the rain sample in New Zealand. Interestingly, the ratio of ⁷Be/¹⁰Be at three sites are 0.70 (Leigh), 0.65 (Gracefield) and 0.50 (Dunedin). These results suggest an overall reduction in the ⁷Be/¹⁰Be ratio from north to south, due to increasing residence time for Be isotopes in the atmosphere above New Zealand. The mean residence time for ⁷Be and ¹⁰Be in the atmosphere above New Zealand range from 77 to 109 days and are lower in the summer than the winter due to transfer of older stratospheric air to the tropopause in late spring-early summer (Graham et al., 2003).

Maejiam et al., 2005 demonstrated that ¹⁰Be concentrations of six soil samples on the raised coral reef terraces of Kikari Island, southwest Japan ranged from 0.80 to 7.17 x 10⁹ atoms/g. The annual deposition rate of ¹⁰Be from the atmosphere to Kikari Island from 2000 and 2002 ranged from 2.0 to 3.5 atoms/cm²/y. The minimum absolute age was calculated from the inventory of meteoric ¹⁰Be in the soil, and the annual deposition rates of ¹⁰Be are ranged from 8 to 136 kyr (Maejima et al., 2005). A 36 cm of soil depth profile from the Roberts Massif, Antarctica was studied to obtain the age of soil by Graham et al., 1997. The sampling site is located in the edge of the nearby East Antarctic Ice Sheet at an altitude of 2700 m. This site is considered to have been ice-free for an extremely long period of time, of the order of several million years. The results of Graham et al., 1997 determined its minimum soil age of 12 million years which is much older than other ⁴⁰Ar/³⁸Ar dating result of 8 million years for volcanic deposit, Scoria associated with soils on the tills laid down by the Meserve Glacier, Antarctica.

2.1.3. ¹⁰Be in the ocean

Using radiocarbon, the sedimentation rates during glacial periods and deglacial periods for the western Arctic Ocean were found to be 0.5 cm/kyr and 1-2 cm/kyr, respectively (Darby et al., 1997). A recent study shows that the concentration of ¹⁰Be in the authigenic fraction of the sediment normalized to the total sediment mass is indirectly correlated to the oxygen isotope curve (McHargue and Donahue, 2005). For example, a low ¹⁰Be/⁹Be ratio in sediments would imply that terrestrial source of ⁹Be has increased compared to the more oceanic ¹⁰Be. Correlation of ¹⁰Be with δ¹⁸O recorded in marine sediment from the Blake Outer Ridge (DSDP site 72) shows a climatic effect on the ¹⁰Be record in addition to cosmogenic effects. Age-corrected ¹⁰Be variability in the sediment cores studied in Aldahan et al., 1997 and the oxygen isotope stratigraphy with the climatic stages numbered from 1 to 10, is generated from Aldahan et al., 1997. ¹⁰Be from sediments of the Arctic Ocean covering the past 350 kyr shows well defined trends of Be isotopes coincident with interglacial/glacial climatic cycles and demonstrates that the sedimentation rates are higher during glacial periods and lower generally due to low sedimentation/accumulation rate during interglacial periods (Aldahan et al., 1997).

The ¹⁰Be records of four sediment cores, taken along a transect from the Norwegian Sea via the Fram Strait to the Arctic Ocean, demonstrate that high ¹⁰Be concentration are related to interglacial stages and that sediment sequences with low ¹⁰Be concentration are related to glacial stages. This study confirms that the sharp contrast of high and low ¹⁰Be concentrations at climatic stage boundaries are an independent proxy for climatic and sedimentary change, and can be applied for ¹⁰Be stratigraphic dating of sediment cores (Eisenhauer, 1994).

Figure 1.

Age corrected ¹⁰Be as a function of age (Aldahan et al., 1997).

Also, Carcaillet et al., 2004 produced high resolution authigenic ¹⁰Be/⁹Be records over the last 300 kyr from sedimentary cores off the Portuguese coast. Comparison of ¹⁰Be/⁹Be and benthic δ¹⁸O records from the two cores suggested that dipole moment lows may be associated with the end of interglacial episodes, and have a quasi-period of 100 kyr (Carcaillet et al., 2004). In a recent study, McHargue and Donahue, 2005 showed a strong correlation between ¹⁰Be and oxygen isotope stages from the Blake Outer Ridge in the Atlantic Ocean. This relationship between climate and ¹⁰Be deposition suggest that ¹⁰Be could be used, in addition to, or as proxy for δ¹⁸O in the studies of the climatic influences on marine sedimentation.

Other considerations are the carbonate flux in sediment which is strongly correlated to ¹⁰Be flux, and carbonate-free sediments from which δ¹⁸O is difficult to obtain from foraminifera. In addition, the two isotopes of beryllium, as stated above, are source dependent, thus the relationship of ¹⁰Be to ⁹Be in the sediments is a function of the relative contributions from atmospheric and terrestrial sources, and their mixing time in the sea.

Paleomagnetic intensity obtained from deep sea cores is well described in recent publications (Valet, 2001, Guyodo et al., 2000, Guyodo and Richter, 1999). However, it was found that climatic influence on ¹⁰Be deposition can be significant, obscuring those variations from its production in the atmosphere, and thus must be addressed (Frank et al, 1997, Kok, 1999). Scavenging corrected ¹⁰Be records compared to calculated variation of the global ¹⁰Be production based on paleomagnetic intensity records (Christl et al., 2003) (Figure 2) show the variation of ¹⁰Be flux in each location with general agreement of inversely proposal to the paleomagentic intensity from Mazaud et al., 1994, Yamazaki and Iokyr et al., 1994, and Guyodo and Valet, 1999.

Figure 2.

Scavenging corrected ¹⁰Be records compared to calculated variation of the global ¹⁰Be production based on paleomagnetic intensity records (Christl et al., 2003).

2.2. ¹⁰Be chemistry

Generally, to extract authigenic beryllium isotopes from sediments, the procedure of Bourles et al., 1989 is used. About one gram of sediment is leached in a solution of 25% acetic acid and hydroxlyamine-HCl to separate the “authigenic” fraction of the sediment from the “terrigenous” fraction. Most samples had more than 1 g of dry sediment; however, in the case of less than 1 g, two or three neighbouring samples were combined for the analysis. When ¹⁰Be is normalized to the mass of the authigenic fraction, it should more accurately reflect its concentration in ocean water than ¹⁰Be normalized to the total mass of the sediment (McHargue and Donahue, 2005, McHargue et al., 2010). This fraction is mostly composed of exchangeable ions, carbonates, and Fe-Mn hydroxides. Two aliquots of the leachate are prepared, one for the elemental analysis with ICP-MS/ICP-AES, and one for the preparation of AMS samples.

Figure 3 shows the flow chart of ¹⁰Be chemistry to extract authigenic beryllium from sediment. This chemistry includes two steps of purification procedures using perchloric acid and nitric/hydrochloric acid. These steps are important to extract authigenic brylllium isotopes. Sometimes, this step is repeated to remove unwanted organic materials. When the unwanted organic materials are not completely removed, the residue sample is often difficult to dissolve in weak acidic solution for ICP analysis. This also causes a further problem in the step of Be separation using Na-EDTA. The concentration level for Be is mostly in ppb range; therefore, Be analysis was performed using ICP-MS. For AMS, the Be fraction is precipitated as Be(OH)₂ and combusted to BeO. ¹⁰Be/⁹Be ratios for chemical blank are found to be less than ~ 1 x 10^-14 with 2 mg of ⁹Be carrier. ⁹Be and other elements can be measured by ICP-MS and ICP-AES.

Figure 3.

Description of authigenic Be isotope extraction method.

2.3. The climate signal of ¹⁰Be from nearby a continent

The signal of ¹⁰Be from the East Sea in the Pacific Ocean and the Black Outer Ridge in the North Atlantic Ocean may give similar climatic influence because of its proximity to continents (Kim and Nam, 2010, McHargue et al., 2000). The depths of basins where sediment core collected were about 3,700 m and 3,818 m in the East Sea and Blake Outer Ridge, respectively. Because both cores were collected in the basin of the ocean, we might expect water circulation could be weaker. This could allow rather older waters can remain at the bottom of the basin. In this case, we may expect lower concentration of ¹⁰Be in sediment compared to samples collected from other open seas (Bourlès et al., 1989, Knudsen et al., 2008). Also, the influence from the continent would be similar in both regions. The terrestrial origin of ¹⁰Be over glacial/deglacial time period may similarly appear.

As shown in Figure 4, three locations were examined with respect to ¹⁰Be concentration as a function of time and any related proxies for each site. Mostly, maximum ¹⁰Be concentrations in various marine sediment samples appear to be above 1 x 10⁹ atoms/g sediment (Bourlès et al., 1989, Knudsen et al., 2008). Both the East Sea and Blake Outer Ridge, ¹⁰Be concentrations are reached at 8 x 10⁸ atoms/g. This value is at least 30 percent lower than the most maximum value of ¹⁰Be in each marine sediment core. Also, when ⁹Be is investigated with ¹⁰Be, ⁹Be signal may be another indicator as a signal of sediment input from the land to the offshore. In the case of the study of the East Sea, the ⁹Be values also show similar trend to those of ¹⁰Be. his shows that both warmer periods of the Holocene and the Eemian,

Figure 4.

Locations of the coring sites of the East Sea, Black Outer Ridge, and Mendeleev Ridge in the western Arctic Ocean.

wetter and warmer climate influenced ⁹Be to be transported from the land to the ocean. ¹⁰Be is transported from the both land and atmosphere. The signal of ¹⁰Be/⁹Be especially stands for lack of either lack of ⁹Be transport or higher production rate of ¹⁰Be, possibly associated with paleomagnetic intensity. In Figure 5, A, B, and C are associated with relatively higher ¹⁰Be/⁹Be compared to neighbouring ¹⁰Be/⁹Be values. A could be partially due to lowered value of ⁹Be; B and C could be due to production rate of ¹⁰Be. This study shows high production rate of Be at 15.5 and near 120 kyr. Also, lower ¹⁰Be production rate is shown at 130.6 kyr during MIS 6 (Figure 5) (Kim and Nam, 2010). These three points can be identified easily with ¹⁰Be/⁹Be rations. In the Figure 5, the regions associated with climatic influence are clearly shown as the ¹⁰Be/⁹B ratios to be within the value between 2 and 3. This observation could be useful in future analysis. Based on Wagner et al., 2000, lower paleomagnetic intensities are associated with the ages at 1.5, 2.5, 4.0, and 6.5 kyr (Christl et al., 2003). Therefore, B could be likely involved in higher production rate of ¹⁰Be at 1.5 kyr (Kim and Nam, 2010) (Figure 5).

Figure 6 shows the ¹⁰Be concentration and M/Mo as determined from measured NRM/ARM of core CH88-10P with respect to depth and time. This figure shows that ¹⁰Be concentration is inversely proportional to the relative paleomagnetic intensity. The production rate of ¹⁰Be occurred at about 40 and 65 kyr. The peak values of ¹⁰Be/⁹Be reached at maximum at about 40 kyr. This time period is named as Laschamp paleomagnetic excursion where the expected ¹⁰Be reaches at a maximum value. These paleomagnetic excursions are well compared with GRIP records.

A recent investigation on ¹⁰Be and ⁹Be from the Mendeleev ridge in the Arctic Ocean shows that ¹⁰Be record at 75 kyr reveals production rate decrease evidently for at least 35 kyr of duration (Kim et al., 2011b). At this time the paleomagnetic intensity is found to be at maximum (Figure 2) (Christl et al., 2003; Flank et al., 1997). Interestingly, the values of magnetic susceptibility (Guyodo and Valet, 1996) obtained from a lake (Lac du Bouchet, France) are high as well as δ¹⁸O. Also, ⁹Be is relatively high which stands for a warm climate. The results of this study confirm that ¹⁰Be reveals predominantly paleomagnetic features over the δ¹⁸O at the extreme point of paleomagnetic intensity. This situation brings us to have precaution in a misuse of ¹⁰Be as a climatic tracer. This study confirms the fact that the ¹⁰Be record for climatic tracer, comparison with ⁹Be is essential. When both beryllium isotopes behaves similarly, the pattern of Be can be used to determine whether the record of Beryllium isotopes is associated with colder or warmer climate based on their consistent concentration trend. The total authigenic ¹⁰Be and ⁹Be (⁹Be>>¹⁰Be) can be referred as ⁹Be because of their amount ratio in terrestrial environment. The ⁹Be can be used as another climatic indicator like Sr, Ca, opal, TOC. The study at The Mendeleev Ridge confirms that ⁹Be generally has a positive correlation with opal, TOC, δ¹³C_org and negative correlation with CaCO₃ (Nam unpublished) (Figure 7). General trend of ⁹Be clearly show the anti-correlation between ⁹Be and Ca or Sr (Boulrès et al., 1989, Kim et al., 2011b). Therefore, we can conclude that ¹⁰Be has a positive correlation with δ¹⁸O which gives ¹⁰Be to be used as a climate indicator, however, this is only true when ⁹Be reveals similar climatic pattern with ¹⁰Be. Both ¹⁰Be and ⁹Be show lower concentration at a cold/dry climate and higher concentration at a warm/wet climate period (Kim and Nam, 2010).

Figure 5.

Authigenic beryllium isotope records from the East Sea, Korea (Kim and Nam, 2010).

Figure 6.

The ¹⁰Be concentration and M/Mo as determined from measured NRM/ARM (Schwartz et al., 1998) of core CH88-10P versus depth and time (McHargue et al., 2000).

2.4. Current problem and future research

A number of investigations show that there has been positive correlation between oxygen isotope and ¹⁰Be concentration (Aldahan et al., 1997). Also, a positive correlation between oxygen isotopes and paleomagnetic intensity and also magnetic susceptibility is investigated (Carcaillet et al., 2004). During the Holocene, paleomagnetic intensity was gradually increased since the time of Laschamp excursion. This confirmed that production rate of 10Be at present is the lowest value since Laschamp excursion. However, the 10Be values recent years are higher than the 10Be concentration and the trend of 10Be is similar to that of δ18O value. This implies that 10Be is closely related to climatic and temperature variation. Because of this contradictory fact, confining the cause of climate change using nuclides which sun’s activity related became important.

Although there have been a number of investigation on climate study using above parameters, obscurity in finding the cause of climate change is still remain. The relationship among production rate of 10Be, paleomagenetic intensity, and Sun-climate connection was studied (Sharma, 2002). This study estimated changes in 10Be production rate and the geomagnetic field intensity, variations in solar activity were calculated for the last 200 kyr., and confirms that the production of ¹⁰Be in the Earth’s atmosphere depends on the galactic cosmic ray influx that is affected by the solar surface magnetic activity and the geomagnetic dipole strength. However, large variations in the solar activity are evident. The marine δ¹⁸O record and solar modulation are strongly correlated at the 100 kyr timescale. This proposes that variation in solar activity control the 100 kyr glacial-interglacial cycles. Sharma, 2002 suggested that the ¹⁰Be production rate variations may have been under-estimated during the interval between 115 kyr and 125 kyr, and may have biased the results (Sharma, 2002).

Figure 7.

Multi-proxy record from the core (PS72/396-3) from Mendeleev Ridge, the Arctic Ocean (Kim et al., 2011b).

Usoskin et al., 2004 indicated that the reconstructed sunspot record exhibits a prominent period of about 600 years, in agreement with earlier observations based on cosmogenic isotopes. Also, there is evidence for the century scale Gleissberg cycle and a number of shorter quasi-periodicities whose periods seem to fluctuate on millennium time scale. This invalidates the earlier extrapolation of multi-harmonic representation of sunspot activity over extended time intervals and the present high level of sunspot activity is unprecedented on the millennium time scale (Usoskin et al., 2004). Accepting solar forcing of Holocene and galacial climatic shift implies that the climate system is far more sensitive to small variation in solar activity than generally believed. In order to fully understand how sensitive climate really is for variations in solar activity, we need to look for additional evidence and to quantify such evidence, both in paleorecords and in observations of present climate with models to estimate climate change in the future (Geel et al., 1999).

3. Conclusions

As a climate indicator, ¹⁰Be has been frequently investigated because of its property associated with rainfall, dust fallout and its production mechanism in the atmosphere by cosmic-rays. Similar patterns of ¹⁰Be and δ¹⁸O, magnetic susceptibility records show climatic influence, however, ¹⁰Be is incorporated with the production rate which is inversely proportional to the paleomagenetic intensity. The cyclic orbital forcing effect toward ¹⁰Be, δ¹⁸O, and paleomagenetic intensity are connected, ¹⁰Be signal is clearly mixed with climatic component and earth’s paleo magnetic strength. Scrutinizing authigenic ¹⁰Be with ⁹Be, a region either climatic or production related zone can be evidently identified by looking at the ¹⁰Be/⁹Be ratios. Investigation of ⁹Be is another useful tracer to examine climatic influence of marine environments with other multi-proxies which have positive or anti-correlated with ⁹Be. Marine environments like the East Sea of Korea, Blake Outer Ridge, and Mendeleev Ridge are associated with significant terrigeous input during deglacial periods. Examining both beryllium isotopes together with other multi-proxy stratigraphy will provide understanding the pattern of environmental change at various glacial/interglacial events much more evidently.

Acknowledgments

This study is partially supported by Korean-IODP at Korea Institute of Geoscience and Mineral Resources and also funded by K-Polar (PP11070) at Korea Polar Research Institute.