Stable isotope paleoclimatology

Six carbon-dated late Holocene Queen Scallop (Aequipecten opercularis) shells from the southern North Sea, ranging in age from 2,535 to 965 years BP, were serially sampled and analysed for oxygen and carbon stable isotopic composition. Oxygen isotope profiles show substantial cyclical variation and reflect seawater temperature fluctuation , whose full seasonal range was recorded. Considered in relation to the dates of the shells, the temperature information does not support previous notions of late Holocene climatic change in the European area. Specifically, shells from allegedly warm periods provide evidence of relatively cool conditions; those from allegedly cool periods indicate relatively warm conditions. The data must, however, be treated with great circumspection because of the small number of shells analysed. Carbon isotope profiles exhibit relatively little variation, no consistent pattern, and are difficult to interpret in terms of environmental variables. There is, however, a statistically significant difference between the means of late Holocene and modern carbon isotopic compositions ; this probably reflects changes in the anthropogenic supply of CO 2 to the atmosphere. Late Holocene A. opercularis rarely exhibit the winter growth interruptions observed in modern shells from the North Sea, and are more abundant. This may reflect the absence of pollution.

Sampling a series of Glycymeris species shells from an age
transect in the well-dated Gatas excavation site, we found
δ18O isotope ratios that indicate a small gradual decrease in
mean sea surface temperatures between 27oo BC and
12oo BC. The sea surface temperature seasonality recorded in
the mollusk shells during this period was 7.o °C. While the
absolute temperatures are subject to the quality of the calibration
used for converting Glycymeris species isotope data
to temperatures, the signal itself and its relative magnitude
seem to be robust. Samples from 275o BC show mean temperatures
above 19.o °C decreasing to recent values around
17.5 °C in the youngest samples from the record at 12oo BC.
While we find indications for a transition from a warmer
phase before 25oo BC to a colder Holocene after 15oo BC, the
marine clams do not show a temperature peak around
22oo BC as it was recorded in high-resolution samples from
the North Greenland Ice Core Project (NGRIP).

The development of isotopic baselines for comparison with paleodietary data is crucial, but often overlooked. We review the factors affecting the carbon (δ13C) and nitrogen (δ15N) isotopic compositions of plants, with a special focus on the carbon and nitrogen isotopic compositions of twelve different species of cultivated plants (n = 91) and 139 wild plant species collected in northern Peru. The cultivated plants were collected from nineteen local markets. The mean δ13C value for maize (grain) was −11.8±0.4 ‰ (n = 27). Leguminous cultigens (beans, Andean lupin) were characterized by significantly lower δ15N values and significantly higher %N than non-leguminous cultigens. Wild plants from thirteen sites were collected in the Moche River Valley area between sea level and ~4,000 meters above sea level (masl). These sites were associated with mean annual precipitation ranging from 0 to 710 mm. Plants growing at low altitude sites receiving low amounts of precipitation were characterized by higher δ15N values than plants growing at higher altitudes and receiving higher amounts of precipitation, although this trend dissipated when altitude was >2,000 masl and MAP was >400 mm. For C3 plants, foliar δ13C was positively correlated with altitude and precipitation. This suggests that the influence of altitude may overshadow the influence of water availability on foliar δ13C values at this scale.

A giant carbonate vein (≥50 m thick; fissure ridge travertines) and nearby travertine plateaus in the Semproniano area (Mt. Amiata geothermal field, southern Tuscany, Italy) are investigated through a multidisciplinary approach, including field and laboratory geochemical analyses (U/Th geochronology, C, Nd, O and Sr isotope systematics, REE abundances, and fluid inclusion microthermometry). The main aim of this work is to understand: (1) modes and rates for the growth of the giant vein and nearby travertine deposits within a Quaternary volcano-tectonic domain; (2) implications in terms of the CO 2 leakage; and (3) possible relationships with Quaternary paleoclimate and hydrological oscillations. Results show that the giant vein was the inner portion of a large fissure ridge travertine and grew asymmetrically and ataxially through repeated shallow fluid injections between N650 and 85 ka, with growth rates in the 10 −2 –10 −3 mm/a order. The giant vein developed mainly during warm humid (interglacial) periods, partially overlapping with the growth of nearby travertine plateaus. Estimated values of CO 2 leakage connected with the vein precipitation are between about 5 × 10 6 and 3 × 10 7 mol a −1 km − 2 , approximately representing one millionth of the present global CO 2 leakage from volcanic areas. Temperature estimates obtained from O-isotopes and fluid inclusion microthermometry indicate epithermal conditions (90–50 °C) for the circulating fluid during the giant vein growth, with only slight evidence of cooling with time. Geochemical and isotope data document that the travertine deposits formed mainly during Pleistocene warm humid periods, within a tectonically-controlled convective fluid circuit fed by meteoric infiltration and maintained by the regional geothermal anomaly hosted by the carbonate reservoir of the Mt. Amiata field.

The application of stable isotope analysis in African archaeology has a long and distinguished pedigree. Many new developments were inspired by questions in the archaeology of the continent, helped considerably by the availability of African landscapes as natural laboratories for providing the essential underpinning of isotope ecology systematics. Stable isotopes are now regularly built into multi-disciplinary archaeological projects spanning the very long temporal and geographical span of human history on the African continent. On the fiftieth anniversary of Azania: Archaeological Research in Africa we evaluate these endeavours — the achievements, problems, constraints and potential of stable isotopic research in African archaeology. We begin with a discussion of the continent’s role in developing understandings of stable carbon, nitrogen, oxygen and strontium isotope systematics, as used to interpret change in the archaeological record. We discuss the application of these principles within several areas of archaeological research, drawing on case studies from among late Pleistocene/Holocene hunter-gatherers, early food producers, complex societies of the African Iron Age and the individual life histories of the African slave trade. There is clearly much potential for further application in African archaeology.

Stable isotope analyses have been performed on the bioapatite (d 13 C; d 18 O) and collagen (d 13 C; d 15 N) of four late Pleistocene South American megafaunal taxa (Notiomastodon platensis, Equus andium, cf. Hemiauchenia paradoxa and Xenarthra indet.) to evaluate paleoclimatic and paleoenvironmental conditions as well as paleoecological features of this time period. The analyzed megafauna was found at several locations in the northwestern Chilean Patagonia (38 e42 S, 74 e71 W). The bioapatite d 13 C values indicated the presence of C 3 vegetation ranging from forestal to woodland areas. The collagen d 15 N values pointed to temperate and humid ecosystems, and to the consumption of shrubs, trees, grasses and sedges. Mean annual temperatures estimated from bioapatite d 18 O PO4 values show a similarity to modern temperatures and suggested that the megafauna under study may have lived during warm stages (interstadials) of the late Pleistocene. When comparing our results with those obtained from other South American regions, we find that the diet of this particular Chilean megafauna appears to have been more influenced by resource availability than by the potential dietary range of the taxa.

In contrast to the coastal areas of the Iberian Peninsula, the Upper Palaeolithic settlement of central Iberia, dominated by the Spanish plateau, is poorly known. Traditional models assume a total or virtual depopulation of the interior of the Iberian Peninsula during the Last Glacial. In this paper we present a detailed investigation of human-environment interactions through the first zooarchaeological, tapho-nomic and isotopic study of the key site of Pe~ na Cap on, a rock shelter located in the southeastern foothills of the Central System range that contains a multi-layered deposit dated to marine isotope stage 2 (MIS 2). Analyses of the faunal assemblages of the Proto-Solutrean (3) and Middle Solutrean (2) layers show that human preferentially hunted horse, deer and iberian ibex living in the vicinity of the rock shelter. Isotope geochemistry of the animal remains of Pe~ na Cap on provides us with the first detailed intra-tooth multi-proxy analysis for this time period in southwestern Europe, providing estimates of climatic conditions, seasonal flucturation of diet, as well as patterns of seasonal mobility. Our results indicate that human presence at Pe~ na Cap on was apparently restricted to relatively warm intervals around the LGM or reflects the presence of an ecological refuge, and provide us with evidence of recurrent human presence in the Iberian interior during the Upper Paleolithic prior to the Magdalenian.

Understanding the sequence of events that take place during glacial-interglacial climate transitions is important for improving our knowledge of abrupt climate change. Here, we present a new stacked, high-resolution, precisely-dated speleothem stable isotope record from the northern Alps, which provides an important record of temperature and moisture-source changes between 134 and 111 ka for Europe and the wider North Atlantic realm. The record encompasses the penultimate deglaciation (Termination II (TII)), which lies beyond the limit of radiocarbon dating, thus providing an important new archive for a crucial period of rapid paleoclimate change. Warmer and wetter ice-free conditions were achieved by 134.1 ± 0.7 ka (modelled ages) as indicated by the presence of liquid water at the site. Temperatures warmed further at 133.7 ± 0.5 ka and led into an interstadial, synchronous with slightly elevated monsoon strength during the week monsoon interval. The interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in Atlantic Meridional Overturning Circulation (AMOC) and a reduction in North Atlantic Deep Water (NADW) formation. The interstadial ended with a more extreme cold reversal lasting 500 years in which NADW formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards. The main warming associated with TII was very rapid, taking place between 130.9 ± 0.9 and 130.7 ± 0.9 ka coeval with initial monsoon strengthening. Temperatures then plateaued before being interrupted by a 600-year cold event at 129.1 ± 0.6 ka, associated once again with penetration of polar waters southwards into the North Atlantic and a slowdown in monsoon strengthening. Sub-orbital climate oscillations were thus a feature of TII in the north Atlantic realm, which broadly resemble the Bølling/Allerød-Younger Dryas-8.2 ka event pattern of change observed in Termination I despite monsoon records indicating strong differences between the last and penultimate deglaciation.

Eolian input fluctuations and paleoceanographic conditions in the western Mediterranean have been reconstructed by using a multi-proxy approach to infer climate variability for the last 20,000 yr. A sediment core from the East Alboran Sea basin provides high-resolution geochemical, mineralogical and grain size distribution records from the Last Glacial Maximum onward. The accurate chronology obtained, closely related with the North Greenland Ice core Project, has provided a detailed paleoclimate reconstruction at the centennialemillennial time scale. Mineral and chemical compositions as well as sediment grain size distribution have been used to establish both fluvial and eolian input variations, deep-water current intensity, and ventilation and productivity conditions at the time of deposition. During the cold period Greenland Stadial-2a, the analyzed proxies evidence significant climate oscillations. Redox proxies, showing marked Mn/Al and Fe/Al peaks, as well as granulometric parameters, support major changes in thermohaline circulation, with active circulation triggered by the Western Mediterranean Deep Water formation. Ba/Al ratios and the presence of authigenic barite point to high productivity during the Last Heinrich event. At this time, Zr/Al, Si/Al and Ti/Al ratios as well as quartz and palygorskite contents also corroborate dryer conditions in the Alboran borderlands, with a major reorganization of atmospheric circulation at the beginning of the deglaciation and during the Last Heinrich event. In contrast, a decreasing trend in the Zr/Al ratio and increasing Mg/Al, K/Al and illite þ chlorite/kaolinite ratios would indicate enhanced river runoff and supporting lower eolian dust input and wetter periods during the Bölling eAlleröd. Short-term and abrupt climate oscillations such as the Intra-Alleröd Cold Period are likewise reflected by minor yet conspicuous changes in eolian proxies. During the Younger Dryas, we distinguish an initial cold and dry phase, with major westerlies intensity, thermohaline reactivation, and high productivity levels, and a second wetter phase characterized by sporadic rainfalls over poorly vegetated surrounding continental areas. Then, during the Holocene, alternating phases of major humidity and aridity were recorded by major fluctuations in detrital input. These are also correlated with recurrent forest cover declines reported from pollen records, with a noteworthy early decline in the African Humid Period. During the Holocene, an initial demise of the Last Organic-Rich Layer is also evidenced, tentatively associated with aspiration forces promoted by intense thermohaline circulation through the Gibraltar Strait.

The interpretation of δ18O and δ13C analyses of extinct foraminifera is hampered by insufficient knowledge on the contribution of environmental versus biological factors on the measured values. We present single-species stable isotope data for 18 benthic and 11 planktic foraminiferal species and one calcareous dinoflagellate cyst species from a Turonian equatorial record measured on samples collected in SE Tanzania. All microfossils analyzed were excellently preserved and results are compared to isotopic measurements from bulk sediment of the same material. Remarkably low intra-specific variability (standard deviations <0.2‰) across the studied interval and consistently large benthic / planktic offsets in δ18O (~2.8‰) and δ13C (~1.5‰) indicate absence of major long-term environmental fluctuations and presence of a well stratified water column. Stratigraphic isotopic trends show small shifts that are parallel in all studied benthic species (with the exception of the δ13C record of Lenticulina species), but within-sample inter-specific offsets reflect a combination of habitat differences and species-specific isotopic disequilibrium fractionation. Among planktic taxa closely related taxa tend to have similar isotopic values. Biserial taxa have the lowest δ18O values (~-4.7‰) but also have relatively low δ13C values (~1.6‰) indicating that, for the assumption of a surface water habitat, additional metabolic effects need to be involved, which supports the concept of their opportunistic life style. Among trochospiral planktics the keeled taxa with compressed chambers have slightly higher δ18O (~-4.2‰) and lower δ13C (~2.3‰) values than taxa with globular chambers (~-4.4‰ and ~2.4‰, respectively), suggesting differences in habitat or in peak seasonal abundance. Benthic taxa are subdivided into three isotopically distinct groups with differences reflecting mineralogy, life strategy and habitat; Group I: aragonitic taxa (Epistomina, Colomia africana), Group II: calcitic trochospiral taxa with isotopic values seemingly close to equilibrium (Berthelina berthelini, Oridorsalis umbonatus, Lingulogavelinella globosa, Lingulogavelinella convexa) and Group III: calcitic taxa with low δ18O values and large scatter in δ13C values (Lenticulina). Four other benthic species show values between Groups II and III.

The wealth and consistency of data, especially for benthic taxa, permits refined conclusions. The five studied species of Epistomina have a similar isotopic signature and are inferred to form their aragonitic shells with close to equilibrium values. Small isotopic offsets are seen among species that differ in orientation of the septal foramen, but no offsets are seen that seem to co-vary with test shape or ornamentation. The conical species C. africana has δ18O values ~0.2‰ lower and δ13C values ~0.7‰ lower than species of Epistomina. The latter offset probably reflects an infaunal habitat for C. africana. Epistomina and Group II species are recommended for paleoenviromental studies. Mono-specific Lenticulina δ18O values may be used if increased by correction factors of 0.4‰ to 0.9‰, but this taxon’s low and variable δ13C values are interpreted to reflect incorporation of respiratory CO2, possibly combined with fast growth rates related to opportunism, rather than equilibrium with benthic dissolved inorganic carbon. The observed stability of inter-specific isotopic offsets suggest disequilibrium isotopic effects are relatively consistent for many taxa in this section, and correction factors are proposed that may help to generate more robust Upper Cretaceous foraminiferal isotopic records. However, δ18O / δ13C covariance in some benthic inter-specific comparisons suggest offsets might vary with changes in temperature, food supply or other factors so the appropriateness of the correction factors should be confirmed before being applied at different sites. Similarities between the observed single-species isotopic patterns from this and other studies are used to present a summarizing scheme of influences on the stable isotopic composition in foraminiferal tests. By applying the new insights from our study to data from other Cretaceous studies we demonstrate that the selection of species for isotopic analysis and understanding these signals are critical to the outcome of paleoceanographic interpretations.

Droughts have had large impacts on past and present societies. High-resolution paleoclimate data are essential to place recent droughts in a meaningful historical context and to predict regional future changes with greater accuracy. Such records, however, are very scarce in the Middle East in general, and the Fertile Crescent in particular. Here we present a 2400 year long speleothem-based multiproxy record from Gejkar Cave in northern Iraq. Oxygen and carbon isotopes and magnesium are faithful recorders of effective moisture. The new Gejkar record not only shows that droughts in 1998–2000 and 2007–2010, which have been argued to be a contributing factor to Syrian civil war, were extreme compared to the current mean climate, but they were also superimposed on a long-term aridification trend that already started around or before 950 C.E. (Common Era). This long-term trend is not captured by tree ring records and climate models, emphasizing the importance of using various paleoclimate proxy data to evaluate and improve climate models and to correctly inform policy makers about future hydroclimatic changes in this drought-prone region.

Climatic and ecological conditions during Marine Oxygen Isotope Stage (MIS) 3 are complex and the impact of cold spells on the ecosystems in Central Europe still needs to be investigated thoroughly. Ziegeleigrube Coenen (ZC) is a late Pleistocene MIS 3 locality in the Lower Rhine Embayment of Germany, radiocarbon-dated to > 34 14C ka BP. The site yielded a broad spectrum of mammal species. We investigated the carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope signatures of bone collagen, since these are valuable tools in characterizing ecological niches, environmental conditions and aspects of climate and mobility. By comparison with pre- and post-Last Glacial Maximum (LGM) sites in Central Europe we show that ZC belongs in a cold event of MIS 3 and was climatically more similar to post-LGM sites than to pre-LGM sites. However, the trophic structure resembled that of typical pre-LGM sites in Belgium. This cold event in MIS 3 changed the bottom of the foodweb, but do not seem to have had a direct impact on the occurrence of the mammalian species and their ecological distribution. Apparently the (mega-) faunal community could adapt also to harsher environmental conditions during MIS 3.