Palaeoclimate

Stable isotope composition of Late Pleistocene-Holocene Eobania vermiculata (Müller, 1774) (Pulmonata, Stylommatophora) shells from the Central Mediterranean basin: Data from Grotta d’Oriente (Favignana, Sicily)

by Andre Carlo Colonese

On the sensitivity of the simulated European Neolithic transition to climate extremes

by Carsten Lemmen

Co-authored with Kai W. Wirtz, submitted to J. Archaeol. Sci, March 2012, do not cite without permission by authors.

Was the spread of agropastoralism from the Fertile Crescent throughout Europe influenced by rapid climatic shifts? We... more Was the spread of agropastoralism from the Fertile Crescent throughout Europe influenced by rapid climatic shifts? We here generate idealized climate events using palaeoclimate records. In a mathematical model of regional sociocultural development, these events disturb the subsistence base of simulated forager and farmer societies. We evaluate the regional simulated transition timings and durations against a published large set of radiocarbon dates for western Eurasia; the model is able to realistically hindcast much of the inhomogeneous space-time evolution of regional Neolithic transitions. Our study shows that the inclusion of climate events improves the simulation of typical lags between cultural complexes, but that the overall difference to a model without climate events is not significant. Climate events may not have been as important for early sociocultural dynamics as endogenous factors.

Early Pleistocene vegetation change in upland south-eastern Australia

by Kale Sniderman

Decline of a biome: evolution, contraction, fragmentation, extinction and invasion of the Australian mesic zone biota

by Kale Sniderman

Biased reptilian palaeothermometer?

by Kale Sniderman

Climate and vegetation in southeastern Australia respond to Southern Hemisphere insolation forcing in the late Pliocene-early Pleistocene

by Kale Sniderman

Enregistrement des variations climatiques au cours des interglaciaires d'après l'étude des isotopes stables de la calcite de tufs pléistocène du nord de la France : exemple des séquences de Caours (SIM 5e; Somme) et La-Celle-sur-Seine (MIS 11 ; Seine-et-Marne)

by Julie Dabkowski

Co-authored with N. Limondin-Lozouet, P. Antoine, A. Marca-Bell and J. Andrews.
Published in Quaternaire, 22 (4), 2011

RECORD OF CLIMATIC CHANGES DURING INTERGLACIALS FROM STABLE ISOTOPES IN NORTHERN FRANCE PLEISTOCENE TUFA CALCITE:... more RECORD OF CLIMATIC CHANGES DURING INTERGLACIALS FROM STABLE ISOTOPES IN NORTHERN FRANCE PLEISTOCENE TUFA CALCITE: EXAMPLES OF CAOURS (MIS 5e; SOMME) AND LA CELLE (MIS 11; SEINE ET MARNE).
Tufas are mainly composed of calcite (CaCO3) which makes them suitable for geochemical investigation, especially oxygen and carbon stable isotopes (δ18O and δ13C). These isotopic parameters have already been shown to record temperature and humidity variations in the Holocene tufas, proving their suitability as climatic proxies. This study focuses on two French Pleistocene sites, Caours and La Celle. Results are compared to palaeoenvironmental, especially malacological, data. This comparison shows that δ18O and δ13C in tufas are important proxies of palaeoclimatic variation during Pleistocene interglacials, just as they are during the Holocene.


La composition minéralogique des tufs calcaires, essentiellement constitués de CaCO3, permet l’utilisation d’indicateurs climatiques géochimiques et en particulier l’étude des isotopes stables de l’oxygène et du carbone (δ18O et δ13C). Ces derniers sont déjà bien connus dans les tufs holocènes comme marqueurs des variations de température et d’humidité. L’analyse des isotopes stables a été réalisée ici sur les séquences de tuf pléistocènes de Caours (SIM 5e, Somme) et de La Celle (SIM 11, Seine et Marne). Les résultats de cette étude géochimique ont été comparés aux données paléoenvironnementales, notamment malacologiques. Ces premières analyses montrent que, comme dans le cas des tufs holocènes, les variations des isotopes stables du carbone et de l’oxygène dans les tufs pléistocènes constituent des indicateurs fiables des variations climatiques au cours des interglaciaires pléistocènes.

The Jurassic-Cretaceous transition of the Fårarp-1 core, southern Sweden: Sedimentological and phytological indications of climate change

by Sofie Lindström

Published in Palaeo3 2011
Co-authored with M. Erlström

The 116 m deep Fårarp-1 core drilled in the Vomb Trough in southernmost Sweden is dated by integrated terrestrial and... more The 116 m deep Fårarp-1 core drilled in the Vomb Trough in southernmost Sweden is dated by integrated terrestrial and marine palynostratigraphy. The lower part of the succession (ca 84 m) encompasses uppermost Jurassic to lowermost Cretaceous (uppermost Tithonian to Valanginian) strata. An unconformity separates the Valanginian strata from an overlying ca 1 m thick interval of upper Albian to Cenomanian Arnager Greensand Formation. The uppermost part of the core is a repetitive succession of lowermost Cretaceous sediments.

During the Jurassic–Cretaceous (J/K) transition NW Europe was located in mid latitudes, and comprised an archipelago of large and small islands separated by deeper grabens and epicontinental seaways that connected the Boreal Sea to the north with the warmer Tethys Ocean to the south. Boundary strata in England, France, the Netherlands and Germany are characterised by relatively prominent climatic change from arid/semi arid to subhumid/humid conditions. Southernmost Sweden was located on the margin of a large landmass comprising most of the Fennoscandian Shield bordering a large epicontinental sea to the west. By combining sedimentology, clay mineralogy and palynofacies the Tithonian to Valanginian cored succession of the Fårarp-1 core provides complementary information on how marginal deposits from the eastern part of the epicontinental sea reflect the climatological and environmental changes observed in other parts of NW Europe.

The Fårarp-1 core shows that during the Tithonian to earliest Berriasian deposition took place in a terrestrial but near-marine depositional setting, in coastal lakes or lagoons with little marine influence. A dry climatic regime favoured stagnant water conditions with common algal blooms of primarily Botryococcus and zygnemataceae. Palynofacies and sedimentology indicate limited transport of freshwater and material to the basin. The stagnant depositional environment was terminated by a marine flooding in the early Berriasian. During the remaining Berriasian and the early Valanginian conditions shifted between near marine and marine settings in a dynamic coastal environment, similar to contemporaneous assemblages reported from the Danish Island of Bornholm.

A shift in clay mineralogy, from a dominance of 10 Å minerals to increasing amounts of mixed layer and kaolinite indicates a change to more humid conditions in the latest Tithonian. Cheirolepidacean pollen (Classopollis) are present but never common in the cored succession, and a similar conspicuous decrease of these pollen, as previously reported from England, Germany and France, is not evident in the Fårarp-1 core. Instead a subsequent shift in both palynofacies and palynoflora, marked by an increase in abundance of heavy terrigenous material, i.e. wood and coal particles, upland pollen grains and reworked palynomorphs is also observed in the uppermost Tithonian–lowermost Berriasian interval. At the same level spores and pollen classified as warmer/drier elements decrease in abundance. This is interpreted as representing a shift to more humid climatic conditions with increased runoff from the hinterland. Thus, the combined sedimentological and palynological data from the Fårarp-1 core suggest that climatic conditions in the area changed from more seasonally dry (semi-arid) to more humid (semi-humid) across the J/K boundary (latest Tithonian to earliest Berriasian) and hence earlier than the mid-Berriasian climatic shift recorded from e.g. England and the Netherlands.

Macrofloras and palynomorphs as possible proxies for palaeoclimatic and palaeoecological studies: A case study from the Pelsonian (Middle Triassic) of Kühwiesenkopf/Monte Prà della Vacca (Olang Dolomites, N-Italy)

by Evelyn Kustatscher

authors: Evelyn Kustatscher, Johanna H.A. van Konijnenburg-van Cittert & Guido Roghi, 2010
Palaeogeography, Palaeoclimatology, Palaeoecology 290 (2010) 71–80

An important fossil flora has been collected in the middle-upper Pelsonian mainly marine locality at Kühwiesenkopf... more An important fossil flora has been collected in the middle-upper Pelsonian mainly marine locality at Kühwiesenkopf (NE-Dolomites, Italy). The fossil plants are briefly described and ecological reconstructions of coastal, lowland, river and upland plant assemblages were made. The composition of the rich and diversified macroflora indicates a typically warm and humid climate. The entire section was also subject of detailed
palynological sampling for biostratigraphy and quantitative analyses. The palynological data confirm the macrofloral reconstructions and also suggest a warm and humid climate for this interval in the Dolomites (probably also on a more regional scale). Moreover, these results were subjected to two different
palynological methods to obtain more detailed palaeoecological and palaeoclimatological data for the whole section. Palynological data suggest, that major oscillations observed in the middle part of the section are related to eustatic oscillations rather than to climatic changes.

Ladinian palynofloras in the Norwegian-Danish Basin: a regional marker reflecting a climate change

by Sofie Lindström

Reference:
Lindström, S., Vosgerau, H., Piasecki, S., Nielsen, L.H., Dybkjær, K. Erlström, M., 2009. Ladinian palynofloras in the Norwegian-Danish Basin: a regional marker reflecting a climate change. GEUS Bulletin 17, 21-24.

Late Jurassic climate change in the Volga Basin (SE Russia): clay mineral and calcareous nannofossil evidence

by Darren Gröcke

A study of clay mineral and calcareous nannofossil abundances in late Jurassic – early Cretaceous sediments from the... more A study of clay mineral and calcareous nannofossil abundances in late Jurassic – early Cretaceous sediments from the Volga Basin, SE Russia, is presented. From these results, we are able to compare some general patterns of mineralogical and palaeontological change for the Volga Basin to the palaeoclimate models developed for northern Europe and beyond. The two successions examined comprise calcareous mudstones with black organic-rich shale horizons, overlain by a series of phosphatic silty sands. Clay mineralogical results show a progressive decrease in kaolinite and the concomitant increase of smectite and illite through the middle Volgian, followed by an abrupt increase in kaolinite in the late Volgian. The clay mineral evidence suggests increasing aridity at the end of the Jurassic, similar, in part, to many western European successions. Because of differential settling of clay minerals, superimposed upon this possible climatic signature is likely to be the effect of relative sea-level change. Calcareous nannofossil analysis from a single section reveals a shift through the middle Volgian from low nutrient, warm water assemblages dominated by Watznaueria to cooler surface water and high nutrient assemblages dominated by Biscutumconstans. These observations suggest that increased aridity is also associated with climatic cooling. Black shales are associated with increased productivity, higher sea levels and increases in smectite content. Hence, periods of low (chemical) hinterland weathering during semi-arid conditions are paradoxically associated with relatively nutrient-rich waters, and organic-richshales. Comparison of published carbon and oxygen stable isotope results from this and other sections to the clay mineral and nannofossil data confirms the palaeoclimatic interpretation. This study significantly improves the published biostratigraphically constrained clay mineral database for this time period, because other European and North American successions are either non-marine (and thus poorly dated), absent (through penecontemporaneous erosion) or condensed.

Paleoklimatoloji ve kültürler: Arkeolojide iklim-medeniyet ilişkisi

by Canan Cakirlar

popüler bilim

....Son yıllarda yapılan arkeolojik ve paleoklimatolojik araştırmalar iklim değişikliklerinin geçmiş uygarlıkların... more ....Son yıllarda yapılan arkeolojik ve paleoklimatolojik araştırmalar iklim değişikliklerinin geçmiş uygarlıkların şekillenmesinde de belirleyici bir rol oynadığını, insanların da küresel boyutta olmasa bile bölgesel boyutta çevre şartlarını etkilemiş olduklarını ortaya koyuyor. Bu araştırmalar uygarlık tarihindeki kesintiler olarak da görebileceğimiz karanlık çağlara sebep olan faktörlerin de daha iyi anlaşılmasını sağlıyor....

Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum

by William Gosling

Mayle, F.E., Beerling, D.J., Gosling, W.D. and Bush, M.B. (2004). Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum. Philosophical Transactions of the Royal Society, London, (B), 359: 499-514.

The aims of this paper are to review previously published palaeovegetation and independent palaeoclimatic datasets... more The aims of this paper are to review previously published palaeovegetation and independent palaeoclimatic datasets together with new results we present from dynamic vegetation model simulations and modern pollen rain studies to: (i) determine the responses of Amazonian ecosystems to changes in temperature, precipitation and atmospheric CO2 concentrations that occurred since the Last Glacial Maximum (LGM), ca. 21 000 years ago; and (ii) use this long–term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although the combination of reduced temperatures, precipitation and atmospheric CO2 concentrations resulted in forests structurally and floristically quite different from those of today. Cold–adapted Andean taxa mixed with rainforest taxa in central areas, while dry forest species and lianas probably became important in the more seasonal southern Amazon forests and savannahs expanded at forest–savannah ecotones. Net primary productivity (NPP) and canopy density were significantly lower than today. Evergreen rainforest distribution and NPP increased during the glacial—Holocene transition owing to ameliorating climatic and CO2 conditions. However, reduced precipitation in the Early–Mid–Holocene (ca. 8000–3600 years ago) caused widespread, frequent fires in seasonal southern Amazonia, causing increased abundance of drought–tolerant dry forest taxa and savannahs in ecotonal areas. Rainforests expanded once more in the Late Holocene owing to increased precipitation caused by greater austral summer insolation, although some of this forest expansion (e.g. in parts of the Bolivian Beni) is clearly caused by palaeo Indian landscape modification. The plant communities that existed during the Early–Mid–Holocene may provide insights into the kinds of vegetation response expected from similar increases in temperature and aridity predicted for the twenty–first century. We infer that ecotonal areas near the margins of the Amazon Basin are liable to be most sensitive to future environmental change and should therefore be targeted with conservation strategies that allow ‘natural’ species movements and plant community re–assortments to occur.

Assessing pedogenic calcite stable-isotope values: Can positive linear covariant trends be used to quantify palaeo-evaporation rates?

by Darren Gröcke

Chemical Geology, 256, 46–51, doi:10.1016/j.chemgeo.2008.07.022

Palaeoclimate models suggest enhanced evaporation rates in subtropical regions (15–30° latitude) during... more Palaeoclimate models suggest enhanced evaporation rates in subtropical regions (15–30° latitude) during greenhouse-world conditions, however, there are no empirical data to support these estimates. Laboratory evaporation experiments have shown that calcites precipitated from variably saturated solutions yield a positive linear covariant trend (PLCT) in δ18Ocalcite versus δ13Ccalcite values. The goal of the present controlled laboratory experiments is to develop a method to quantify regional palaeo-evaporation rates from palaeosol calcrete PLCTs. Samples of powdered CaCO3 were dissolved in de-ionized water in pressure sealed containers with a range of elevated atmospheric pCO2 concentrations for 24 h. The solution was then allowed to evaporate completely from an open container within an incubator with the time of calcite crystallization noted, and aliquots removed for analysis every 24 h. The precipitated calcite produced an array of δ18Ocalcite versus δ13Ccalcite values that fall upon a PLCT projected from a theoretical meteoric calcite line (MCL). Water analyses yielded δ18Owater enrichments from an initial value of −4.75‰ VSMOW ranging up to between +10.0‰ and +14.8‰. The experimental results show that solutions formed under higher pCO2 conditions precipitated calcite very early on during evaporation, and thus have δ18Ocalcite and δ13Ccalcite values that are slightly enriched relative to the MCL. The solutions that formed under low pCO2 conditions precipitated calcite after much of the fluid had evaporated, and thus yield more enriched δ18Ocalcite and δ13Ccalcite values. Repeat trials with varying temperature and relative humidity show that the PLCT is steeper under both higher temperature and low relative humidity. The wide range of pCO2, temperature and relative humidity conditions used simulate meteoric phreatic and meteoric vadose conditions that may affect a calcrete horizon over time during numerous dissolution/precipitation reactions. The results of these experiments show that a dominant factor in the precipitation of vadose calcite is the saturation state of the fluid with respect to CaCO3, while the primary factors affecting the magnitude and steepness of the PLCT are vadose zone temperature, relative humidity, the starting δ18Owater value and saturation state of the fluid with respect to CaCO3. Since the pCO2 of the rooting zone is cross-controlled by the local soil and surface ecology, the magnitude of the PLCT enrichment may not be a direct proxy for palaeo-evaporation rates.

Vegetation, climate and fire in the eastern Andes (Bolivia) during the last 18,000 years

by Joseph Williams

Joseph J Williams, William D Gosling, Stephen J Brooks, Angela L Coe and Sheng Xu. 2011, Palaeogeography, Palaeoclimatology, Palaeoecology. 312(1-2). pp.115-126.

A c. 18 ka cal BP long sediment record from Laguna Khomer Kocha Upper (4153 m asl), Bolivia, shows that fire regime,... more A c. 18 ka cal BP long sediment record from Laguna Khomer Kocha Upper (4153 m asl), Bolivia, shows that fire regime, governed by climatic variation, has long been a transformative agent in the eastern Andes. Before c. 14.5 ka cal BP, warming and relatively moist conditions free from fire, facilitated the expansion of high Andean Polylepis woodland. Fire onset at c. 14.5.ka cal BP, quickly transformed the local vegetation and the woodlands became restricted to areas protected from fire. A major increase in burning, c. 10.1 − 6.4 ka cal BP removed Polylepis woodland locally and this coincided with a region-wide Holocene dry event (HDE) which caused falling lake levels and allowed fire intensification. A decline in burning at c. 6.4 ka cal BP and an increase in marsh-woodland (Alnus) marked the termination of the HDE and a return to wetter conditions. As well as recording the environmental history of local vegetation dynamics, long-distance pollen transport provides evidence of changes in the Yungas montane forests, highlighting their sensitivity to climate and burning regimes. Simultaneous adjustments in both Andean and Yungas montane taxa suggests that vegetation dynamics in the two environments are linked to a common climatic driver. There is no evidence to indicate that human activity had any impact on the local landscape.

Highlights
► Fossil pollen, charcoal and spores provided an 18 ka year record of climate change. ► Charcoal revealed that fire was a transformative agent in the eastern Andes. ► A major increase in burning occurred in the early Holocene (10.1 ka cal BP). ► Pollen and charcoal indicated a shift to wetter conditions at 6.4 ka cal BP. ► The sensitivity of Polylepis woodland to fire is confirmed.

Keywords: Fossil pollen; Fossil charcoal; Deglaciation; Holocene dry event (HDE); Polylepis woodland; Temperature; Precipitation

(Not so) Distant Mirrors: a complex macro-comparison of polities and political, economic and religious systems in the crisis of the 14th century

by Johannes Preiser-Kapeller

Paper for the International Conference "THE ANGEVIN DYNASTY (14TH CENTURY)" in Targoviste (Romania), October 21st-23rd 2011.
Slides here: http://oeaw.academia.edu/JohannesPreiserKapeller/Talks/58247/_Not_so_Distant_Mirrors_a_complex_macro-comparison_of_polities_and_political_economic_and_religious_systems_in_the_crisis_of_the_14th_century

In the “calamitous” 14th century, as Barbara Tuchman called it in her classic „A Distant Mirror“ (1978) , the medieval... more In the “calamitous” 14th century, as Barbara Tuchman called it in her classic „A Distant Mirror“ (1978) , the medieval world entered a period of severe crisis in demography, economy, politics and religion. This crisis took hold in all regions, ranging from China in the East to England in the West. Even before the catastrophic pandemic of the Black Death (1346-1352), deteriorating climatic conditions had ended the period of demographic and economic expansion that began in the 10th century.
The local and regional impacts and consequences of these general potentially crisis-laden conditions may have differed; outcomes ranged from actual societal collapse to the emergence of powerful new polities – while Byzantium´s power dwindled away, Hungary entered a period of strong rulership and external power in the reign of Louis I of Anjou (1342-1382), for instance. But these conditions provide a framework for global perspective on this period and allow us to use the 14th century-crisis as a field of “natural experiments of history”, as Jared Diamond and James A. Robinson have called them ; accordingly, we analyse how similar crisis phenomena influenced the development of societies with different (or similar) traditions, religions, institutions, geographies or ecologies.
In order to be able to capture the local variations and complexities, we adopt concepts and tools provided by the field of complexity science. Mono-causal or linear explanations are inadequate for the analysis and the description of crisis, transformation or collapse of pre-modern polities. Within this framework, complex systems are understood as large networks of individual components, whose interactions at the microscopic level produce “complex” changing patterns of behaviour of the whole system on the macroscopic level. In the last decades, historians and social scientists who became interested in complexity theory tried to use its concepts and terminology for the conceptualisation and description of phenomena in their own fields, but often only in a “metaphoric” way. Less frequently, though, historians have tried to make use of the mathematical foundations of complexity theory or of quantitative tools provided by this field. Recent scholarship has implemented some of these tools especially for the construction of macro-models of socio-economic development. While these studies help us construct analytical tools for the macro-level of our own research, they run the same risk as earlier scholarship of neglecting complex variations at the local and regional levels.
Therefore, we combine complexity theory with the analytical framework of „systems theory“ developed by the German sociologist Niklas Luhmann in order to capture the interveawements between politics, economy and religion within a polity and with the political, economic and ecological environment. In addition, we employ the methods and tools of network analysis, which allow us to capture, analyse and model linkages and cause-effect correlations in society, economy, politics and religion on the macro- and micro-level down to groups and individuals.
Overall, as a complement to earlier studies our analytical
approach shall allow us to capture the “diversité véritable” of our period without losing track of essential commonalities (the “strange parallels”, as Victor Liebermann has called them in his remarkable study on Southeast Asia in Global Context, 2009 ) of this “first world crisis” across all cultures and societies. The scientic value of this approach will be demonstrated for some specific cases.

Intra-tooth oxygen isotope variation in a known population of red deer: Implications for past climate and seasonality reconstructions

by Rhiannon Stevens

Model, proxy and isotopic perspectives on the East African Humid Period

by Sophie Lewis

Tierney, J.E., S.C. Lewis, B.I. Cook, A.N. LeGrande, and G.A. Schmidt, 2011: Model, proxy and isotopic perspectives on the East African Humid Period. Earth Planet. Sci. Lett., 307, 103-112, doi:10.1016/j.epsl.2011.04.038.

Both North and East Africa experienced more humid conditions during the early and mid-Holocene epoch (11,000-5,000 yr... more Both North and East Africa experienced more humid conditions during the early and mid-Holocene epoch (11,000-5,000 yr BP; 11-5 ka) relative to today. The North African Humid Period has been a major focus of paleoclimatic study, and is now understood to represent a response of the hydrological cycle to the increase in boreal summer insolation and associated ocean, atmosphere and land surface feedbacks. Meanwhile, the mechanisms responsible for the coeval East African Humid Period are poorly understood. Here, we use results from isotope-enabled coupled climate modeling experiments to investigate the cause of the East African Humid Period. The modeling results are interpreted alongside proxy records of both water balance and the isotopic composition of rainfall. Our simulations show that the orbitally-induced increase in dry season precipitation and the subsequent reduction in precipitation seasonality can explain the East African Humid Period, and this scenario agrees well with regional lake level and pollen paleoclimate data. Changes in zonal moisture flux from both the Atlantic and Indian Ocean account for the simulated increase in precipitation from June through November. Isotopic paleoclimate data and simulated changes in moisture source demonstrate that the western East African Rift Valley in particular experienced more humid conditions due to the influx of Atlantic moisture and enhanced convergence along the Congo Air Boundary. Our study demonstrates that zonal changes in moisture advection are an important determinant of climate variability in the East African region.

High-resolution stalagmite reconstructions of Australian–Indonesian monsoon rainfall variability during Heinrich stadial 3 and Greenland interstadial 4

by Sophie Lewis

Lewis, S.C., Gagan, M.K., Ayliffe, L.K., Zhao, J.-x., Hantoro, W.S., Treble, P.C., Hellstrom, J.C., LeGrande, A.N., Kelley, M., Schmidt, G.A., Suwargadi, B.W., 2011. High-resolution stalagmite reconstructions of Australian-Indonesian monsoon rainfall variability during Heinrich stadial 3 and Greenland interstadial 4. Earth Planet. Sci. Lett. 303, 133-142. doi: 10.1016/j.epsl.2010.12.048.

Little is known about the possible teleconnections between abrupt climatic changes originating in the North Atlantic... more Little is known about the possible teleconnections between abrupt climatic changes originating in the North Atlantic and precipitation dynamics in the Australian–Indonesian summer monsoon (AISM) domain. We examine the climatic impacts of Heinrich stadial 3 (HS3) and Greenland interstadials 4 and 3 (GIS4/3) on AISM-associated precipitation through a high resolution analysis of stable isotope (δ18O, δ13C) and trace element (Mg/Ca, P/Ca) ratios in a stalagmite from Liang Luar cave, Flores, Indonesia. Sixteen high precision 230Th dates indicate that stalagmite LR07-E1 grew rapidly (~0.3–1.0 mm/yr) in two phases between ~31.5– 30.1 ka and ~27.8–25.6 ka, separated by a ~2.3 kyr unconformity. Temporally consistent abrupt responses occur in the Flores record during HS3 and GIS4, which are coherent with changes in stalagmite δ18O records from China and Brazil. The response of low-latitude precipitation to HS3 cooling and GIS4 warming, as demonstrated by the widely separated sites, comprises three distinct simplified phases: (1) a strong southward migration of the ITCZ during HS3 is associated with a decrease in rainfall at Liang Luar cave and in China, while wetter conditions are reconstructed from Brazil, (2) represents the peak of HS3 impacts and an extended hiatus begins in the Flores record and (3) where suggested dry conditions at Liang Luar throughout GIS4 form part of a coherent north–south anti-phasing in precipitation changes. The reconstructed changes are also broadly consistent with NASA GISS ModelE-R simulations of a Heinrich-like freshwater perturbation in the North Atlantic basin, which produces a southward shift in the ITCZ. The relationship between the palaeoclimate records indicates that atmospheric teleconnections rapidly propagate and synchronise climate change across the hemispheres during periods of abrupt climate change. Our findings augment recent proposals that large-scale atmospheric re-organisations during stadials and interstadials play a key role in driving changes in atmospheric CO2 concentration, air temperature and global climate change.

Water vapour source impacts on oxygen isotope variability in tropical precipitation during Heinrich events

by Sophie Lewis

Lewis, S.C., LeGrande, A.N., Kelley, M., Schmidt, G.A., 2010. Water vapour source impacts on oxygen isotope variability in tropical precipitation during Heinrich events. Clim. Past 6, 325-343. doi: 10.5194/cp-6-325-2010.

Water isotope records such as speleothems provide extensive evidence of past tropical hydrological changes. During... more Water isotope records such as speleothems provide extensive evidence of past tropical hydrological changes. During Heinrich events, isotopic changes in monsoon regions have been interpreted as implying a widespread drying through the Northern Hemisphere tropics and an antiphased precipitation response in the south. Here, we examine the sources of this variability using a water isotope-enabled general circulation model, Goddard Institute for Space Studies ModelE. We incorporate a new suite of vapour source distribution tracers to help constrain the impact of precipitation source region changes on the isotopic composition of precipitation and to identify nonlocal amount effects. We simulate a collapse of the North Atlantic meridional overturning circulation with a large freshwater input to the region as an idealised analogue to iceberg discharge during Heinrich events. An increase in monsoon intensity, defined by vertical wind shear, is modelled over the South American domain, with small decreases simulated over Asia. Simulated isotopic anomalies agree well with proxy climate records, with lighter isotopic values simulated over South America and enriched values across East Asia. For this particular abrupt climate event, we identify which climatic change is most likely linked to water isotope change – changes in local precipitation amount, monsoon intensity, water vapour source distributions or precipitation seasonality. We categorise individual sites according to the climate variability that water isotope changes are most closely associated with, and find that the dominant isotopic controls are not consistent across the tropics – simple local explanations, in particular, fall short of explaining water isotope variability at all sites. Instead, the best
interpretations appear to be site specific and often regional in
scale.