C. Taricco

Evidence for enhanced 10Be deposition in Mediterranean sediments 35 kyr BP

In this letter, we report the profiles (∼160 samples) of 10Be, 9Be, Zn in a Mediterranean sediment core spanning the last 60 kyr. We show the existence of a 10Be peak, whose absolute age is estimated to be 34±3 kyr BP, based on its stratigraphic position between two tephra layers originating from two volcanic eruptions (Campanian Ignimbrite and Citara), dated by K-Ar, 40Ar-39Ar and 14C methods. This peak is similar to the increase in the 10Be concentration observed in Vostok and Dome C ice cores at the same age. The increase with approximately similar amplitude in both ice and sediment cores at different latitudes and hemispheres cannot be explained by changes in the archives. The present result supports the view of a well defined global enhancement of the 10Be flux, related to an increase of the 10Be production rate and not to a redistribution of the 10Be fallout between different latitudes.

Behavior of the Heliosphere over Prolonged Solar Quiet Periods by 44Ti Measurements in Meteorites

The heliospheric magnetic field (HMF) is controlled by solar activity, as established by measurements over the last few decades, but its characteristics when the sun was quiet for prolonged periods, such as during Gleissberg or Maunder minima, are not known. Titanium-44, produced in meteorites, provides a monitor of the galactic cosmic ray (GCR) flux and allows estimation of the modulation effect of the sun for the period 1883 to 1992. The titanium-44 activity is consistent with the expected value, but the increase, due to the last Gleissberg minimum, is four times greater than expected for a GCR modulation based solely on sunspot numbers. This result implies that the HMF was weaker than at present and as a result the GCR flux (for energy greater than 1 gigaelectron volt) was higher between 2.2 to 3.6 protons per square centimeter per second per 4π steradians at 1 to 3 astronomical units in solar cycles 12 to 15.

Galactic cosmic ray flux decline and periodicities in the interplanetary space during the last 3 centuries revealed by 44Ti in meteorites

[1]xa044Ti and 26Al activities and heavy nuclei tracks produced by cosmic rays have been measured in 19 stone meteorites that fell during the period 1766 to 2001. The gamma activity measurements of cosmogenic isotopes were performed using a highly specific and selective large volume Ge-NaI (Tl) spectrometer. The 44Ti activity, corrected for the target element abundances and shielding effects, shows a decrease of about 43% over the past 235 years. Superimposed on this declining trend, the 44Ti activity shows a centennial oscillation. The variations in 44Ti activity are related to changes in cosmic ray intensity caused by heliospheric magnetic field modulation in the interplanetary space between heliocentric distances of 1 and 3 AU. Using the relations between solar open magnetic flux, modulation parameter, and galactic cosmic ray flux, we have calculated the variation in production rates of 44Ti in meteorites back to about 1700 AD. We show that the measured 44Ti activity in meteorites over the past 235 years and the calculated production rates are in agreement. Our results are consistent in phase and magnitude with doubling of the solar open magnetic field intensity over the past century. The data also imply that the centennial scale oscillation deduced by 44Ti is in phase with Gleissberg solar cycle, but its amplitude is larger than expected from the calculated cosmic ray flux.

Solar radiation variability in the last 1400 years recorded in the carbon isotope ratio of a mediterranean sea core

Abstract We present measurements and data analysis of the carbon stable isotopes (δ 13 C) in the planktonic Globigerinoides ruber extracted from the GT90/3 shallow water Ionian sea core, dated with high precision. It is commonly accepted that δ 13 C variations in symbiontic foraminifera mainly record the effects of productivity and of photosynthetic activity, varying with the ambient light level. Therefore from this time series we can deduce information on the sea surface illumination at the time of the planktonic foraminifera growth. The profile (359 points) covers the period 590–1979 AD, with a resolution of 3.87 years and it is an extension of the time series (215 points) previously published in this journal. The spectral analysis of the longer time series confirms the presence of the 11 y signal, with amplitude ∼0.08‰ (peak-to-trough), found in the shorter time series in phase with the sunspot solar cycle; furthermore it shows the presence of two centennial cycles of 100 and 200 years, with amplitude 0.08‰ and 0.02‰ respectively. These components are identified at high significance level by Monte Carlo singular spectrum analysis (MC-SSA). A comparison between the δ 13 C profile and the historical aurorae series (600–1500 AD) shows that the long-term δ 13 C variations are at least partially generated by the solar activity modulation and in phase with the solar output, as represented by the solar wind interaction with the magnetosphere.

Solar activity in the last millennium recorded in the δ18O profile of planktonic foraminifera of a shallow water Ionian Sea core

In this paper we present the δ18O profile of Globigerinoides ruber measured in the GT90/3 shallow water Ionian sea core, dated with high precision. The δ18O profile covers the period 1200–1900xa0AD, with a resolution of 3.87xa0years. This long record of 700xa0years of δ18O allows us to identify the imprint of the solar cycle in a climatic record. In fact, the spectral analysis of the time series performed with different methods shows a dominant periodicity of about 11xa0years with an amplitude of ≈0.07‰. The signal is in opposition to the sunspot number cycle. This component is identified at a high significance level by Monte Carlo Singular Spectrum Analysis (MC-SSA).

700 year record of the 11 year solar cycle by planktonic foraminifera of a shallow water Mediterranean core

Abstract In this paper we present the δ 18 O and δ 13 C profiles of Globigerinoides Ruber measured in the GT90/3 shallow water Ionian sea core, dated with high precision. They are records respectively of the sea surface temperature (SST) and of the biomass amount present at the time of the planktonic forams growth. The profiles cover the period 1200–1900 AD, with a resolution of 3.87 years. The spectral analysis of the δ 18 O time series performed with different methods shows a dominant periodicity of 11.4 years with an amplitude of ∼0.07‰, in antiphase with the sunspot solar cycle, while the δ 13 C time series shows a dominant periodicity of 11.2 years with an amplitude of ∼0.04‰, in phase with the sunspot cycle. These components are identified at high significance level by Monte Carlo singular spectrum analysis (MC-SSA). These 700 year long records of δ 18 O and δ 13 C disclose the presence of a clear and statistically significant imprint of the solar cycle in a terrestrial archive.

Long term solar-terrestrial records from sediments: carbon isotopes in planktonic foraminifera during the last millennium

Abstract We show the δ13C profile of Globigerinoides ruber measured in the GT90/3 shallow-water Ionian sea core. This core is dated with high accuracy (better than 1%) using radiometric and tephroanalysis methods, for the last 2000 years. The core, extracted from the Gallipoli platform, was sampled at contiguous steps of thickness 2.5 mm, corresponding to 3.87 years. The δ13C profile covers the period 1147–1975 AD. During the first seven centuries it appears fairly flat, while it shows a steep increase between 1760 and 1950 of ∼0.3‰. The analysis of the time series performed using different methods shows a dominant decadal periodicity throughout the record. The 11-year component is identified at high significance level by Monte Carlo singular spectrum analysis (MC-SSA); the SSA-reconstructed-11-year component is in phase with the sunspot solar cycle. The average amplitude of this component is A11y=0.04‰. It is commonly accepted that δ13C variations in symbiontic foraminifera mainly record the effects of symbiont density and of photosynthetic activity, varying with ambient light level. The δ13C peak-to-trough 11-year variation (0.08‰) can be related to solar irradiance variation of 0.1% on decadal time scale, like that measured in space in the last 20 years. By supposing that the observed δ13C modern increase of ∼0.3‰ is also produced by a solar irradiance variability on a longer time scale, through the same mechanisms, we estimate a secular increase of the total solar irradiance between 1760 and 1950 of (0.3/0.08)∗0.1% ≅ 0.37%. This value is at the higher limit of the long term variability estimates (0.25%–0.35%) that are currently proposed. Finally, in the light of the available experimental evidences, we discuss possible ways in which direct solar forcing can be modified by atmospheric processes in order to give the observed δ13C signal.

Solar magnetic and bolometric cycles recorded in sea sediments

The total carbonate and thermoluminescence (TL) profiles of the GT89-3 Ionian sea sediment core have been measured in the upper 200 cm of the core spanning the last 3100 years in order to test the presence of the Gleissberg (80–90 yr) cycle in the two different time series recorded in the same archive. Two different sampling intervals respectively of 2.5 mm and 2 mm have been chosen for the measurements in order to obtain results independent from sampling effects in the time series. We have revealed the Gleissberg cycle at 83 and 92 yr in both records.

Cosmogenic 44Ti in meteorites and century scale solar modulation.

The galactic cosmic ray (GCR) flux is modulated by solar activity: 11 and 22 year cycles are well established. Meteorites offer the possibility of studying longer cycles in the interplanetary space, due to GCR nuclear interactions. 44Ti cosmogenic isotope produced in meteorites is suitable for detecting a century scale modulation. So far reliable measurements of 44Ti in the samples are scarce, the radioisotope concentration being very low. A gamma-ray sensitive spectrometer has been set up in the underground laboratory of Monte dei Cappuccini. The system consists of a 2 kg HPGe detector inside a 28 kg NaI well. The system has a background of approximately 1 count/day (in coincidence mode) in the 44Ti region. We present here the results obtained on the Rio Negro meteorite, which fell in the year 1934.

Galactic cosmic ray variations in the last two centuries recorded by cosmogenic 44Ti in meteorites

We have previously shown that the very low activity of the cosmogenic 44Ti in meteorites records the galactic cosmic ray (GCR) flux over a century time-scale (Bonino et al., 1995). The heliospheric magnetic field (HMF) variations are the principal source of the GCR modulation in the heliosphere. We present here new measurements which extend our investigation over the last two centuries. The 44Ti activity at the time of fall has been obtained on the basis of the recently revised value of its half-life of 59.2 years. We basically confirm our earlier findings (Bonino et al., 1997). The 44Ti profile, with the time of fall of the meteorites, shows variations in phase in agreement with those expected. The magnitude of oscillations is ∼ 4 times higher than expected (∼ 6%) on the basis of the GCR flux over the past centuries deduced from sunspot number since 1700 and by the neutron monitor and balloon measurements in the last decades. The higher 44Ti production rate during prolonged solar quiet periods (Gleissberg minima) may imply that during these minima the HMF was weaker than during the recent minima of the 11-year solar cycle.