Antonio Longinelli

Eight glacial cycles from an Antarctic ice core

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

Oxygen isotope analyses of co-existing carbonate and phosphate in biogenic apatite: a way to monitor diagenetic alteration of bone phosphate?

Abstract The oxygen isotopic composition of phosphate (δ 18 Op) and structural carbonate (δ 18 Oc) of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries. These two variables are highly correlate (r 2 = 0.98) and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations [1,2]. According to previous measurements [3–6] on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between δ 18 Op and δ 18 Oc, as is the case with modern samples. It therefore seems possible, at least in some cases, to use these measurements for monitoring fossil bone and tooth diagenetic alteration. When a set of points lie on the equilibrium line or close to it, the δ 18 O values could be considered close to the original values. In contrast, when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified, due to interaction with meteoric water or 18 O-enriched water, respectively.

Holocene climate variability in Europe: Evidence from δ18O, textural and extension-rate variations in three speleothems

Time-series O isotope profiles for three U–Th dated stalagmites have revealed that for much of the Holocene, a site on the Atlantic seaboard (SW Ireland) exhibits first-order δ18O trends that are almost exactly out of phase with coupled δ18O curves from two southern European sites (SE France and NW Italy). In the Irish stalagmite (CC3 from Crag Cave, SW Ireland), low δ18O at 10,000 cal yr BP reflects cool conditions. By the early to mid-Holocene (9000–6000 cal yr BP) δ18O had increased, reflecting the onset of warmer conditions on the Atlantic seaboard. This shift to higher δ18O was accompanied by a marked increase in the stalagmite extension rate, reinforcing our interpretation that this was a period of relative warmth. Except for an episode of increased extension rate about 5500 yr ago, δ18O in the Crag stalagmite exhibits a gradual decrease, accompanied by declining extension rates between 7800 and 3500 cal yr BP, interpreted as a cooling trend. There is evidence for increases in both δ18O and stalagmite extension rate in the period from 3500 cal yr BP to the present day suggesting a return to warmer conditions on the Atlantic seaboard. In the stalagmite from NW Italy (ER76, Grotta di Ernesto, Trentino province) the early-Holocene (c. 9200-7800 cal yr BP) is characterised by high δ18O, probably indicative of warm and/or dry conditions. Exceptionally low δ18O from 7800 to 6900 cal yr BP at this site reflects a well-defined wet phase (Cerin wet phase). In the last three millennia, this stalagmite exhibits a shift to lower δ18O, interpreted as some combination of cooler and/or wetter conditions. Unlike the Irish stalagmite, the Italian sample does not show a correlation between δ18O and extension rate. Instead, its extension rate correlates roughly with δ13C, presumably reflecting a climate-driven vegetation change. In the early Holocene, δ18O in the French stalagmite (CL26, Grotte de Clamouse, Herault province, SE France) was low relative to its Holocene average. For much of the period since c. 3500 cal yr BP this stalagmite exhibits higher δ18O than in the early Holocene, suggesting warmer conditions. Like the Irish stalagmite, the French sample exhibits a well-defined correlation between δ18O and extension rate. Had drip-water availability been the dominant control on δ18O at this semi-arid site then higher δ18O would have been accompanied by lower, not higher extension rates. This suggests strongly that temperature rather than rainfall amount was the dominant control at this site. While conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early Holocene warm conditions on the Atlantic seaboard (Irish site) coincided with relatively cool conditions at the Clamouse site. By c. 3500 yr ago the pattern appears to have been reversed.

Oxygen isotopes in living mammal's bone phosphate: Further results

Abstract The potential use of oxygen isotopes in mammal bone phosphate to study paleoclimates has been recognized since a few years. It has been proven that the δ 18 O(PO 4 3− ) of some mammal species is related to the mean δ 18 O of local meteoric water, each species showing a specific linear relationship. We report here some measurements of the oxygen isotopic composition of bone phosphate from living specimens of deer, mice, cattle and sheep coming from different areas with different mean annual values of local meteoric water. The oxygen isotopic composition of body water (blood water) of some of these specimens has also been measured. Linear relationships between the δ 18 O of bone phosphate, the δ 18 O of blood water and the mean δ 18 O of local meteoric water have been found, as in the case of the previously studied specimens of humans, pigs and rats. The slopes of the calculated equations for the bone phosphate-meteoric water relationships are the following: 0.79 (wood mice), 1.01 (cattle), 1.13 (deer) and 1.48 (sheep). The calculated phosphate-water fractionation factors are quite homogeneous, ranging from 1.0172 to 1.0175. These values are very close to those which may be calculated for isotopic equilibrium conditions between bone phosphate and body water. Fossil bones from the studied species may now be used for paleoclimatological and paleohydrological studies.

A new 27 ky high resolution East Antarctic climate record

The ice core recently drilled at the Dome Concordia site on the East Antarctic plateau provides a new high resolution isotope record covering part of the last glacial, the last transition and the Holocene. The two step shape of the deglaciation is remarkably similar for all the ice cores now available on the East Antarctic plateau. The first warming trend ends about 14000 years ago and is followed by the well marked Antarctic Cold Reversal (ACR) with a secondary peak common to all records. During the deglaciation, there are more similarities between the near coastal site of Taylor Dome and inland East Antarctica than between Taylor Dome and central Greenland. However, the results for EPICA do appear to confirm the Taylor Dome timescale after about 14 ka, showing cooling into the ACR roughly in phase between Greenland and Antarctica. While the overall deglacial pattern is asynchronous, this suggests that the now classical picture of a temperature seesaw between Antarctica and Greenland may be too simplistic.

OXYGEN ISOTOPE VARIATIONS OF PHOSPHATE IN MAMMALIAN BONE AND TOOTH ENAMEL

About eighty specimens from ten different species of mammals, collected from different areas under different climatic and environmental conditions, were measured for the oxygen isotopic composition of their bone and tooth phosphate. The equations relating these values to the mean oxygen isotopic composition of local meteoric water were also derived. The same equation can be used for goats, roe-bucks, and mouflons, despite the biological differences among these species. Measurements were made on about fourty different specimens of rabbit and hare from Europe, Africa, and Canada, but in this case the data obtained clearly show no direct relationship between the oxygen isotopic composition of local meteoric water and the isotopic composition of the skeletal phosphate. However, there seems to be an inverse relationship between the relative humidity of the studied areas and the δ 18O(PO43−) of the skeletal phosphate, thus suggesting the use of fossil bones of these mammal species as recorders of palaeoenvironmental relative humidity. Finally, a new equation was derived for the isotopic scale for horses, on the basis of all the previous data and of a few newly obtained results.

An isotopic palaeoenvironmental study of human skeletal remains from the Nile Valley

Stable isotope measurements were carried out on human skeletal remains from the Nile Valley, ranging in age from about 7000 to 1750 yr B.P. and on a set of other samples among which are archaeological food remains. Bone samples were analyzed for δ18O(PO3−4), δ18O(CO2−3) and δ13C(CO−3) of carbonate hydroxylapatite and δ13C and δ15N of collagen. Food remains and tissue samples were analyzed for their δ13C and δ15N values. The isotopic composition of bone collagen, apatite and food remains (partially representative of the diet in ancient Egypt) suggest a mixed diet including C3 plant food and, probably, animal resources (both fresh-water fish and C3 animals). A rather surprising observation is the lack of differences between isotopic composition of remains of different social classes spanning from the very poor village of Gebelein to the middle class of the rich town of Asyut to the distinguished people who underwent mummification processes after their death. From the palaeoclimatological point of view, the δ18O(PO3−4) values, ranging from 20.6 to 24.5‰, seem to reflect the isotopic composition of Nile river water (also related to relative humidity) rather than real climatic (temperature) variations through time. The oxygen isotope compositions of carbonate and phosphate of the same samples (from 30.2 to 32.5 and from 20.6 to 22.2, respectively) suggest isotopic equilibrium conditions, thus confirming the possibility of also using the carbonate measurements for palaeoclimatological studies, at least in the case of recent and well preserved samples.

Irreversible water–rock mass transfer accompanying the generation of the neutral, Mg–HCO3 and high-pH, Ca–OH spring waters of the Genova province, Italy

In a recent survey of the spring waters of the Genova province, many neutral Mg–HCO3 waters and some high-pH, Ca–OH waters were found in association with serpentinites. All the springs are of meteoric origin as indicated by the stable isotopes of water and dissolved N2 and Ar. Interaction of these meteoric waters with serpentinites determines a progressive evolution in the chemistry of the aqueous phase from an immature Mg-rich, SO4–Cl facies of low salinity to an intermediate Mg–HCO3 facies (pH 7.0–8.5, PCO210−3.5–10−2.5 bar, Eh 150–250 mV), and to a mature Ca–OH facies (pH 10–12, PCO2 10−9.4−10−10.6 bar, Eh-390 to-516 mV). The irreversible water–rock mass transfer leading to these chemical changes in the aqueous phase was simulated through reaction path modeling, assuming bulk dissolution of a local serpentinite, and the precipitation of gibbsite, goethite, calcite, hydromagnesite, kaolinite, a montmorillonite solid mixture, a saponite solid mixture, sepiolite, and serpentine. The simulation was carried out in two steps, under open-system and closed-system conditions with respect to CO2, respectively. The calculated concentrations agree with analytical data, indicating that the computed water-rock mass transfer is a realistic simulation of the natural process. Moreover, the simulation elucidates the role of calcite precipitation during closed-system serpentinite dissolution in depleting the aqueous solution of C species, allowing the concurrent increment in Ca and the acquisition of a Ca–OH composition. Calcium–OH waters, due to their high pH, tend to absorb CO2, precipitating calcite. Therefore, these waters might be used to sequester anthropogenic CO2, locally preventing environmental impact to the atmosphere.

Oxygen isotopic composition of fossil equid tooth and bone phosphate: an archive of difficult interpretation

Abstract Variation in the concentration of the stable isotopes of hydrogen, oxygen and carbon have been tested in continental records as tools for quantitative or semi-quantitative paleoclimatological studies. Among the different methods, the potential use of oxygen isotopes in mammal bone and tooth phosphate has recently been recognized. Measurements carried out on fossil mammal bones of Holocene age and their paleoclimatological interpretation corresponded well with paleontological and paleobotanical records. In the case of considerably older fossils, diagenetic processes may change the primary oxygen isotopic composition of phosphate. Fossil horse bones and teeth (principally of the species Equus stenonis) were studied to ascertain how far back in time fossil mammal remains may be considered reliable material for paleoclimatological studies. The samples come from 13 different locations in southeastern Spain, their age ranging from Maspinian (late Pleistocene) to Middle Villafranchian (Pliocene). Apart from the variations of the δ18O(PO43−) values which may be related to climatic changes, it is apparent that the isotopic composition of bones and teeth from the same deposit are frequently rather different from one another. The isotopic differences range from a few tenths of one % to several %. This suggests a strong influence of taphonomy over the measured isotopic values of fossils in each deposit. Time can be considered neither the only variable nor the most important one responsible for the change of the primary isotopic composition of fossils. Under these conditions it is rather difficult to establish lower or upper limits for the age of fossils to be studied for reliable paleoclimatological information since the limits are directly related to taphonomic history. This, in turn, is related to local environmental conditions and not only to the age of fossils.

A late-glacial high-resolution site and source temperature record derived from the EPICA Dome C isotope records (East Antarctica)

The timing and synchronisation of Greenland and Antarctic climate events that occurred during the last glacial period are still under debate, as is the magnitude of temperature change associated with these events. Here we present detailed records of local and moisture-source temperature changes spanning the period 27-45 kyr BP from water stable isotope measurements (deltaD and delta(18)O) in the recently drilled EPICA Dome C ice core, East Antarctic plateau. Using a simple isotopic model, site (DeltaT(site)) and source (DeltaT(source)) temperatures are extracted from the initial 50-yr high-resolution isotopic records, taking into account the changes in seawater isotopic composition. The deuterium isotope variability is very similar to the less precise deltaD record from the Vostok ice core, and the site temperature inversion leads to a temperature profile similar to the classical palaeothermometry method, due to compensations between source and ocean water corrections. The reconstructed DeltaT(site) and DeltaT(source) profiles show different trends during the glacial: the former shows a decreasing trend from the warm Al event (38 kyr BP) toward the Last Glacial Maximum, while the latter shows increasing values from 41 to 28 kyr BP. The low-frequency deuterium excess fluctuations are strongly influenced by obliquity fluctuations, controlling the low- to high-latitude temperature gradients, and show a remarkable similarity with a high-resolution southeast Atlantic sea surface temperature record. A comparison of the temperature profiles (site and source) and temperature gradient (DeltaT(source)-DeltaT(site)) with the non-sea-salt calcium and sodium records suggests a secondary influence of atmospheric transport changes on aerosol variations.