Konstantin Pustovoytov

Drought stress variability in ancient Near Eastern agricultural systems evidenced by δ13C in barley grain

Significance Collapse and resilience of ancient Near Eastern societies is intrinsically tied to agricultural production. Despite intensive palaeoclimate research, the role of environmental conditions in ancient agricultural production is little understood. Stable carbon isotope analysis on cereal grains from archaeological sites provides a direct evidence for drought stress. This paper demonstrates that drought stress correlated with major climatic fluctuations and affected many agricultural settlements in the ancient Near East but that its regional impact was diverse and influenced by geographic factors and human technology. The results lead to a better understanding of how ancient agricultural societies performed under fluctuating climate and regionally diverse environmental conditions. The collapse and resilience of political systems in the ancient Near East and their relationship with agricultural development have been of wide interest in archaeology and anthropology. Despite attempts to link the archaeological evidence to local paleoclimate data, the precise role of environmental conditions in ancient agricultural production remains poorly understood. Recently, stable isotope analysis has been used for reconstructing site-specific ancient growing conditions for crop species in semiarid and arid landscapes. To open the discussion of the role of regional diversity in past agricultural production as a factor in societal development, we present 1.037 new stable carbon isotope measurements from 33 archaeological sites and modern fields in the geographic area of the Fertile Crescent, spanning the Aceramic Neolithic [10,000 calibrated years (cal) B.C.] to the later Iron Age (500 cal B.C.), alongside modern data from 13 locations. Our data show that drought stress was an issue in many agricultural settlements in the ancient Near East, particularly in correlation with the major Holocene climatic fluctuations, but its regional impact was diverse and influenced by geographic factors. Although cereals growing in the coastal areas of the northern Levant were relatively unaffected by Holocene climatic fluctuations, farmers of regions further inland had to apply irrigation to cope with increased water stress. However, inland agricultural strategies showed a high degree of variability. Our findings suggest that regional differences in climatic effects led to diversified strategies in ancient subsistence and economy even within spatially limited cultural units.

Growth rates of pedogenic carbonate coatings on coarse clasts

Abstract Growth rates of pedogenic carbonate coatings on clasts can be used as a simple quantitative index of soil and sediment age, as well as a chronological framework for palaeoecological reconstructions. They are also probably connected with general intensity of formation of Bk horizons in soils. Previously, data on coating growth rates were restricted ecologically and geographically to desert regions of North America. This paper presents growth rates of Holocene pedogenic carbonate coatings on clasts within an extended range of environments, calculated on the basis of archaeological and radiocarbon dating. The rates, in this study, are higher than in earlier reports. Carbonate coatings can thicken with rates up to 1 mm /1000 years or higher in semi-arid and semi-humid climates. At least five factors are likely to control growth rates: (1) climate, (2) lithology of carbonate parent material, (3) depth under the soil surface, (4) clast size, (5) bulk density and composition of cutans. Favorable factors for comparatively rapid coating thickening seems to be climatic conditions, ranging from semi-arid to semi-humid, high carbonate content of parent material and large size of clasts. There is also an optimal depth of carbonate coating growth in a soil profile. Little information on bulk density and composition of cutans is available, but they appear to play an important role as one of the factors governing growth rates of pedogenic carbonate coatings on clasts.

Pedogenic carbonate formation: Recrystallization versus migration—Process rates and periods assessed by 14C labeling

[1]xa0Under arid to semihumid climatic conditions, dissolution of primary carbonate and recrystallization with carbon (C) from soil CO2 leads to accumulation of significant amounts of pedogenic (secondary) carbonate. Most soils of arid and semiarid regions contain a carbonate accumulation horizon, the depth of which is related to climatic conditions and properties of parent material. It remains unclear whether this carbonate migrates from the upper horizons before or after recrystallization with soil CO2. The aim of this study was to determine recrystallization rates during initial pedogenesis and to estimate the accumulation depth of secondary carbonate based on C isotopic exchange during secondary carbonate formation in an experiment with alternating moisture conditions. Maize grown on 1xa0m high loess-filled columns was pulse labeled in14CO2 atmosphere every 3xa0weeks. After 6xa0months, portions of secondary (recrystallized) CaCO3 were determined in 5xa0cm segments, based on 14C respired in the rhizosphere and subsequently incorporated into newly formed secondary carbonate. More than 80% of recrystallized carbonate (Ca14CO3) was leached from the uppermost 15xa0cm of the loess column, and more than 70% of total secondary carbonate were accumulated in a depth between 15 and 50xa0cm. Based on the recrystallization rate calculated for the uppermost 15xa0cm of the loess column (1.77 ± 0.26 ⋅ 10−5 day−1), between 300 and more than 1,700xa0years are necessary for complete decalcification of the upper 15xa0cm. Our modeled data are consistent with formation of calcic horizons under relatively humid conditions.

Pedogenic carbonate cutans on clasts in soils as a record of history of grassland ecosystems

Pedogenic carbonate cutans (coatings, pendants, rinds) on coarse clasts are common in stony soils of arid and semiarid regions dominated by open vegetation. This paper gives an overview of the potential of the carbonate cutans for paleograssland research using data from literature and personal observations. Carbonate coatings are stratified into distinct microlamina, which can provide a record of local environmental changes. Lamina made of a rather pure calcium carbonate with better formed and parallel oriented crystals seem to be indicative of relatively dry phases that were less favorable for biological activity. A high content of admixtures, poorer formed and randomly oriented calcite crystals presumably mark wetter periods characterized by climatic amelioration. At a most general level, N 13 C of the cutan carbonate can provide information on the type of photosynthesis of local vegetation, whereas N 18 O in carbonate material of the coatings correlates with oxygen isotopic composition of precipitation water at the site and is sensitive to fluctuations in temperature. To obtain chronological evidence on cutan formation the 14 C and Th/U methods can be applied with certain limitations. Additionally, cutan growth rates can be used to evaluate the age of these features. fl 2002 Elsevier Science B.V. All rights reserved.

Carbon Sources in Fruit Carbonate of Buglossoides arvensis and Consequences for 14C Dating

Fruit carbonate of Buglossoides arvensis (syn. Lithospermum arvense) is a valuable dating and paleoenvironmental proxy for late Quaternary deposits and cultural layers because CaCO3 in fruit is assumed to be accumulated from photosynthetic carbon (C). However, considering the uptake of HCO3 – by roots from soil solution, the estimated age could be too old depending on the source of HCO3 – allocated in fruit carbonate. Until now, no studies have assessed the contributions of photosynthetic and soil C to the fruit carbonate. To evaluate this, the allocation of photo-assimilated carbon and root uptake of HCO3 – was examined by radiocarbon (C) labeling and tracing. B. arvensis was grown in carbonate-free and carbonate-containing soils (sand and loess, respectively), where C was provided as (1) CO2 in the atmosphere (5 times shoot pulse labeling), or (2) Na2 CO3 in soil solution (root-labeling; 5 times by injecting labeled solution into the soil) during one month of fruit development. Distinctly different patterns of C distribution in plant organs after rootand shoot labeling showed the ability of B. arvensis to take up HCO3 – from soil solution. The highest C activity from root labeling was recovered in roots, followed by shoots, fruit organics, and fruit carbonate. In contrast, C activity after shoot labeling was the highest in shoots, followed by fruit organics, roots and fruit carbonate. Total photo-assimilated C incorporated via shoot labeling in loess-grown plants was 1.51mg lower than in sand, reflecting the presence of dissolved carbonate (i.e. CaCO3) in loess. Loess carbonate dissolution and root-respired CO2 in soil solution are both sources of HCO3 – for root uptake. Considering this dilution effect by carbonates, the total incorporated HCO3 – comprised 0.15% of C in fruit carbonate after 10 hr of shoot labeling. However, if the incorporated HCO3 – during 10 hr of shoot labeling is extrapolated for the whole month of fruit development (i.e. 420-hr photoperiod), fruit carbonate in loess-grown plants incorporated approximately 6.3% more HCO3 – than in sand. Therefore, fruit carbonates from plants grown on calcareous soils may yield overestimated C ages around 500 yr because of a few percentage uptake of HCO3 – by roots. However, the age overestimation because of HCO3 – uptake becomes insignificant in fruits older than approximately 11,000 yr due to increasing uncertainties in age determination.

Reply to Maxwell et al.: Stable isotopes and their potential for interpreting archaeobotanical remains

We thank Maxwell et al. (1) for their interest in our study and agree that multielement isotopic analysis helps interpret ancient agricultural systems. Measurements of δ15N on archaeobotanical crop seeds have corroborated hypotheses of Near Eastern cultivation under gradually less-fertile soil conditions (2) and that early farmers used livestock manure to enhance crop yields (3). It is also understood that soil fertility along with salinity, evapotranspiration, and crop density causes variation in δ13C.