Cultural Responses to Climate Change During the Late Holocene

This study describes the effect of drought on past civilizations and peoples and their response as civilizations or cultures. The site includes four case studies drawn from New and Old World civilizations that document societal responses to prolonged drought, including population dislocations, urban abandonment, and state collapse. Further study of past cultural adaptations to persistent climate change may provide valuable perspective on possible responses of modern societies to future climate change. Educational levels: High school, Undergraduate lower division

The "African humid period" and the record of marine upwelling from excess ^(230)Th in Ocean Drilling Program Hole 658C

Using a high-resolution ^(230)Th normalized record of sediment flux, we document the deglacial and Holocene history of North African aridity and coastal upwelling at Ocean Drilling Program Hole 658C. At both the end of the Younger Dryas and after the 8.2 ka event, there are significant drops in terrigenous accumulation at our site, indicating an increase in the monsoon moisture flux over Africa at this time. At 5.5 ka, there is an abrupt end to the “African humid period” and a return to stronger upwelling conditions. For carbonate and opal fluxes the ^(230)Th normalization completely changes the shape of each record based on percentage variations alone. This site is a clear example of how variations in one sediment component can obscure changes in the others, and it demonstrates the need for radionuclide measurements more generally in paleoceanography. By taking our new records and a large amount of previous data from this site we conclude that increases in African moisture are tightly coupled to decreases in coastal upwelling intensity

Climate Shocks

Changes in climate are emerging as elements that shaped human evolution over millions of years, as scientists learn that such alteration coincided with the extinction of some of our ancestors and the success of others. Evidence from ancient soils in East Africa, deep-sea sediments and fossil teeth from our forerunners combines to reveal rapid swings between wet and dry environments, as well two distinct periods when grasslands replaced more wooded areas. The emergence of our own genus, Homo, our varied diet, advances in stone tool technology and the very human trait of adaptability in the face of ongoing change may be tied to these episodes, according to one theory

High- and low-latitude climate interactions: evidence for enhanced aridity of Asian monsoon dust source areas after 2.4 MYR from ODP Leg 117 magnetic susceptibility data

EXTRACT (SEE PDF FOR FULL ABSTRACT): Whole-core magnetic susceptibility can sometimes be used as a rapid and sensitive indicator of variations in the concentration of terrigenous material. We apply this approach to study the evolution of Plio-Pleistocene climatic cycles of terrigenous sedimentation at Ocean Drilling Program Site 721, on the Owen Ridge in the Arabian Sea

Human migration: Climate and the peopling of the world

The human dispersal out of Africa that populated the world was probably paced by climate changes. This is the inference drawn from computer modelling of climate variability during the time of early human migration

The evolution of neogene terrestrial ecosystems in Europe

Journal ArticleThe Pliocene-Pleistocene chronology of hominid and other vertebrate evolution in East Africa is largely constrained by isotopic dating and regional intercorrelation of volcanic ash layers. Some eruptions were of sufficient magnitude or duration that their widespread tephra dispersal defines a series of dated marker horizons throughout the fossil-bearing sedimentary deposits of Tanzania, Uganda, Kenya, and Ethiopia (Brown, 1982; Feibel et al, 1989; Haileab&Brown, 1992,1994; Pickforderal, 1991; WoldeGabrieler al, 1994). Although many of the larger eruptive events have been dated directly the ages of many tephra are only constrained by indirect stratigraphic interpolation between dated levels. The geochcmica! compositions of volcanic glasses from each eruption are unique, providing a definitive means to establish broad tephrostratigraphic correlations linking the regional climatic, tectonic, and biologic histories of this distinctive archive of Earth history

Ocean-atmosphere climate shift during the mid-to-late Holocene transition

Climate records of the mid-to-late Holocene transition, between 3–4 thousand years before present (ka), often exhibit a rapid change in response to the gradual change in orbital insolation. Here we investigate North Atlantic Central Water circulation as a possible mechanism regulating the latitudinal temperature gradient (LTG), which, in turn, amplifies climate sensitivity to small changes in solar irradiance. Through this mechanism, sharp climate events and transitions are the result of a positive feedback process that propagates and amplifies climate events in the North Atlantic region. We explore these linkages using an intermediate water temperature record reconstructed from Mg/Ca measurements of benthic foraminifera (Hyalinea balthica) from a sediment core off NW Africa (889 m depth) between 0 to 5.5 ka. Our results show that Eastern North Atlantic Central Waters (ENACW) cooled by ~1°±0.7 °C~1°±0.7 °C and densities decreased by σθ=0.4±0.2σθ=0.4±0.2 between 3.3 and 2.6 ka. This shift in ENACW hydrography illustrates a transition towards enhanced mid-latitude atmospheric circulation after 2.7 ka in particular during cold events of the late-Holocene. The presented records demonstrate the important role of ENACW circulation in propagating the climate signatures of the LTG by reducing the meridional heat transfer from high to low latitudes during the transition from the Holocene Thermal Maximum to the late-Holocene. In addition, the dynamic response of ENACW circulation to the gradual climate forcing of LTGs provides a prime example of an amplifying climate feedback mechanism

Depth of post-depositional remanence acquisition in deep-sea sediments: a case study of the Brunhes-Matuyama reversal and oxygen isotopic Stage 19.1

Although post-depositional remanent magnetization (PDRM) in deep-sea sediments appears to be acquired during the earliest stages of sediment compaction, the natural variability of the PDRM lock-in depth in deep-sea sediments is poorly understood and as yet unquantified. Here we consider variations in the relative stratigraphic positions of oxygen isotopic interglacial Stage 19.1 and the Brunhes-Matuyama (B/M) Chronozone reversal for eight deep-sea sediment cores. Results from a similar study of the displacement between a widespread microtektite layer and the B/M boundary are also included [1]. The PDRM lock-in depth and the temporal relationships between the B/M and Stage 19.1 datums can be determined from the offsets between the paleomagnetic and the isotopic (and microtektite) stratigraphies. For cores with sedimentation rates greater than 1 cm kyr−1, the depth offset between the paleomagnetic and isotopic datums is a linear function of sedimentation rate. A simple model (r2 = 0.77) demonstrates that (1) PDRM acquisition occurs ∼ 16 cm below the sediment surface, and (2) the B/M reversal occurs 6 kyr (±2 kyr) after the Stage 19.1 datum, and the Stage 19.1 datum occurs 9 kyr (±3 kyr) after the deposition of the Australasian microtektite strewnfield. This example argues against simple geophysical models linking geomagnetic field reversals to climate change or impact events. The B/M boundary is anomalously deep (30–50 cm) in very low accumulation rate sediments ( < 1 cm kyr−1) and this may reflect the unusual physical properties of these sediments. A review of the geotechnical literature suggests that very low accumulation rate sediments have sufficient time to develop enhanced interparticle rigidity (structural strength) which inhibits early compaction and, hence, PDRM acquisition

Rainfall regimes of the Green Sahara

During the “Green Sahara” period (11,000 to 5000 years before the present), the Sahara desert received high amounts of rainfall, supporting diverse vegetation, permanent lakes, and human populations. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. We present a quantitative reconstruction of western Saharan precipitation derived from leaf wax isotopes in marine sediments. Our data indicate that the Green Sahara extended to 31°N and likely ended abruptly. We find evidence for a prolonged “pause” in Green Sahara conditions 8000 years ago, coincident with a temporary abandonment of occupational sites by Neolithic humans. The rainfall rates inferred from our data are best explained by strong vegetation and dust feedbacks; without these mechanisms, climate models systematically fail to reproduce the Green Sahara. This study suggests that accurate simulations of future climate change in the Sahara and Sahel will require improvements in our ability to simulate vegetation and dust feedbacks

Relationship between individual chamber and whole shell Mg/Ca ratios in Trilobatus sacculifer and implications for individual foraminifera palaeoceanographic reconstructions

Precisely targeted measurements of trace elements using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) reveal inter-chamber heterogeneities in specimens of the planktic foraminifer Trilobatus (Globigerinoides) sacculifer. We find that Mg/Ca ratios in the final growth chamber are generally lower compared to previous growth chambers, but final chamber Mg/Ca is elevated in one of thirteen sample intervals. Differences in distributions of Mg/Ca values from separate growth chambers are observed, occurring most often at lower Mg/Ca values, suggesting that single-chamber measurements may not be reflective of the specimen’s integrated Mg/Ca. We compared LA-ICPMS Mg/Ca values to paired, same-individual Mg/Ca measured via inductively coupled plasma optical emission spectrometry (ICP-OES) to assess their correspondence. Paired LA-ICPMS and ICP-OES Mg/Ca show a maximum correlation coefficient of R = 0.92 (p \u3c 0.05) achieved by applying a weighted average of the last and penultimate growth chambers. Population distributions of paired Mg/Ca values are identical under this weighting. These findings demonstrate that multi-chamber LA-ICPMS measurements can approximate entire specimen Mg/Ca, and is thus representative of the integrated conditions experienced during the specimen’s lifespan. This correspondence between LA-ICPMS and ICP-OES data links these methods and demonstrates that both generate Mg/Ca values suitable for individual foraminifera palaeoceanographic reconstructions