1995, Spatial and temporal variability of late Neogene equatorial Pacific carbonate

High-resolution, continuous records of GRAPE wet bulk density (a carbonate proxy) from Ocean Drilling Program Leg 138 provide one the opportunity for a detailed study of eastern equatorial Pacific Ocean carbonate sedimentation during the last 6 m.y. The transect of sites drilled spans both latitude and longitude in the eastern equatorial Pacific from 90° to 110°W and from 5°S to 10°N. Two modes of variability are resolved through the use of Empirical Orthogonal Function (EOF) analysis. In the presence of large tectonic and climatic boundary condition changes over the last 6 m.y., the dominant mode of spatial variability in carbonate sedimentation is remarkably constant. The first mode accounts for over 50% of the variance in the data, and is consistent with forcing by equatorial divergence. This mode characterizes both carbonate concentration and carbonate mass accumulation rate time series. Variability in the first mode is highly coherent with insolation, indicating a strong linear relationship between equatorial Pacific car bonate sedimentation and Milankovitch variability. Frequency domain analysis indicates that the coupling to equatorial divergence in carbonate sedimentation is strongest in the precession band (19-23 k.y.) and weakest though present at lower frequencies. The second mode of variability has a consistent spatial pattern of east-west asymmetry over the past 4 m.y. only; prior to 4 Ma, a different mode of spatial variability may have been present, possibly suggesting influence by closure of the Isthmus of Panama or other tectonic changes. The second mode of variability may indicate influence by CaCO3 dissolution. The second mode of variability is not highly coherent with insolation. Comparison of the modes of carbonate variability to a 4 m.y. record of benthic δ 1 8 indicates that although overall correlation between carbonate and δ 1 8 is low, both modes of variability in carbonate sedimentation are coherent with δ 1 8 changes at some frequencies. The first mode of carbonate variability is coherent with Sites 846/849 δ 1 8 at the dominant insolation periods, and the second mode is coherent at 100 k.y. during the last 2 m.y. The coherence between carbonate sedimentation and δ 1 8 in both EOF modes suggests that multiple uncorrelated modes of variability operated within the climate system during the late Neogene

Millennial-scale variability of deep-water temperature and δ18Odwindicating deep-water source variations in the Northeast Atlantic, 0-34 cal. ka BP

Paired measurements of Mg/Ca and δ18Occ (calcite δ18O) in benthic foraminifera from a deep-sea core recovered on the Iberian Margin (MD99-2334K; 37°48′N, 10°10′W; 3,146 m) have been performed in parallel with planktonic δ18Occ analyses and counts of ice-rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic δ18Occ allows the proxy records from MD99-2334K to be placed confidently on the GISP2 time-scale. This correlation is further corroborated by AMS 14C-dates. Benthic Mg/Ca measurements in MD99-2334K permit the reconstruction of past deep-water temperature (Tdw) changes since ∼34 cal. ka BP (calendar kiloyears before present). Using these Tdw estimates and parallel benthic δ18Occ measurements, a record of deep-water δ18O (δ18Odw) has been calculated. Results indicate greatly reduced Tdw in the deep Northeast Atlantic during the last glaciation until ∼15 cal. ka BP, when Tdw warmed abruptly to near-modern values in parallel with the onset of the Bølling-Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ∼13.4 and ∼11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice-rafting event. Similar millennial-scale Tdw changes also occurred during the last glaciation. Indeed, throughout the last ∼34 cal. ka, millennial δ18Odw and Tdw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower Tdw and δ18Odw conditions occurred. In general, millennial Tdw and δ18Odw variations recorded in MD99-2334K describe an alternation between colder, low-δ18Odw and warmer, high δ18Odw conditions, which suggests the changing local dominance of northern-sourced North Atlantic Deep Water (NADW) versus southern-sourced Antarctic Bottom Water (AABW). The observed similarity of the Tdw and GISP2 δ18Oice records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low-δ18Odw AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic δ18Occ signal since ∼34 cal. ka BP

History of Plio-Pleistocene Climate in the Northeastern Atlantic, Deep Sea Drilling Project Hole 552A

DSDP Hole 552A, cored with the HPC on Hatton Drift, represents an almost complete and undisturbed sediment section spanning the late Neogene and Quaternary. Lithologic, faunal, isotopic, and paleomagnetic analyses indicate that the section represents the most complete deep sea record of climatic evolution hitherto recovered at high latitudes in the northern hemisphere. A glacial record of remarkable resolution for the late Pliocene and Pleistocene is provided by oxygen and carbon isotope ratios in benthic foraminifers. In the upper part of the section, the whole of the standard oxygen isotope record of the past million years is well preserved. The onset of ice-rafting and glacial-interglacial alternations occurs at about 2.4 m.y. ago

Contribution of Baobab Production Activities to Household Livelihoods.

IES Working paper.Baobab production activities play a crucial role in contributing to the livelihoods of rural households. In the face of increasing village populations, commercial use of baobab has been steadily increasing to the point where currently, 43% of sampled households participate in baobab production activities. Commercial use of baobab products is especially important to the poorer households arid women. In terms of contributing to household livelihoods, baobab activities are ranked second only to some kinds of agricultural production. Numerical estimates of contribution to livelihoods bear out this result with cash income of approximately Z$5000 per annum received for each participating person, well above the official minimum wage. Opportunity costs of labour make up about four-fifths of this value, leaving one-fifth of the cash income accruing as economic rent. The rent available to households seems to vary widely, as there are households that are well located close to baobab trees, which greatly reduces production costs and increases economic rents captured. The importance of baobabs to livelihoods, combined with the potential ecological importance of these trees in contributing to biodiversity, makes the sustainability of this resource vital. Accordingly, if current use rates are not sustainable (see Romero et al., (in prep) there is scope for investigations into policies and management options that could foster sustainable use

Benthic foraminiferal stable isotope stratigraphy of Site 846 : 0-1.8 Ma

A stable-isotope stratigraphy at Site 846 (tropical Pacific, 3°06'S, 90°49'W, 3307 m water depth), based on the benthic foraminifers Cibicides wuellerstorfi and Uvigerina peregrina, yields a high-resolution record of deep-sea δ¹⁸O and δ¹³C over the past 1.8 Ma, with an average sampling interval of 3 k.y. Variance in the δ¹⁸O and δ¹³C records is concentrated in the well-known orbital periods of 100, 41, and 23 k.y. In the 100-k.y. band, both isotopic signals grow from relatively low amplitudes prior to 1.2 Ma, to high amplitudes in the late Quaternary since 0.7 Ma. The amplitude of δ¹⁸O and especially of δ¹³C decreases in the 41-k.y. band as it grows in the 100-k.y. band, consistent with a transfer of energy into an orbitally-paced internal oscillation. A weak 30-k.y. rhythm, present in both δ¹⁸O and δ¹³C, may reflect nonlinear interaction between the 41-k.y. and 100-k.y. bands in the evolving climate system. In the 23-k.y. and 19-k.y. bands associated with orbital precession, δ¹⁸O and δ¹³C are not coherent with each other on long time scales, and do not evolve like the 100-k.y. and 41-k.y. bands. This suggests that the source of the growing 100-k.y. oscillation is not a nonlinear response to precession, in contrast to predictions of some climate models. Sedimentation rates at this site also vary with a strong 100-k.y. cycle. Unlike the isotope records, the amplitude of 100-k.y. variations in sedimentation rate is relatively constant over the past 1.8 Ma, ranging from about 15 to 70 m/m.y. Prior to 0.9 Ma, sedimentation rates co-vary with orbital eccentricity, rather than with global climate as reflected by δ¹⁸O or δ¹³C. A source of this 100-k.y. cycle of sedimentation rate in the absence of similar ice volume fluctuations may be precessional heating of equatorial land masses, which in an energy balance climate model drives variations of monsoonal climates with a 100-k.y. rhythm. For the interval younger than 0.9 Ma, high sedimentation rates in the 100-k.y. band are consistently associated with glacial stages. This change of pattern suggests that when the amplitude of glacial cycles become large enough, their global effects overpower a local monsoon-driven variation in sedimentation rate at Site 846

Late Quaternary paleoceanography in the Eastern Equatorial Pacific Ocean from Planktonic Foraminifiers : a high-resolution record from Site 846

High-resolution records of δ¹⁸0 and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic δ¹⁸0 record to the SPECMAP and ODP Site 677 δ¹⁸0 time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with δ¹⁸0 at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the δ¹⁸0 record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial “cool tongue” was also possibly stronger

Policy brief, number 11, 2014

[From Introduction] Urbanisation in sub-Saharan Africa: changing the locus of poverty. Urbanisation is a global phenomenon that is changing the face of the Earth, as well as how people earn a living and secure their livelihoods. In 2006 the number of urban people in the world surpassed the number of rural people, and this gap will continue to grow. In only 16 years (by 2030) just under two-thirds of the world's people will be urban dwellers. Whilst most of the developed world and large parts of Latin America already have more than threequarters of their populations living in cities and towns, most countries in Asia and sub-Saharan Africa are still catching up. This means that they are experiencing massive migrations from rural to urban areas as rural people wish to swap the insecurities of rural living for the allure of secure employment and better services for health, education, sanitation and transport in towns and cities. Sub-Saharan Africa (SSA) is the most rapidly urbanising region of the globe. According to UN-Habitat, in 1990, only 28 % of the region's inhabitants lived in towns and cities; that increased to approximately 32 % in 2001 and 41 % in 2010. The size of the urban population is likely to surpass the rural one around 2025. Contrary to popular belief, most urban residents in SSA (and globally) live in small towns rather than massive megacities; with just over half living in towns of less than 200,000 people and 78 % living in towns of less than 500,000 residents. Only 14 % of urban dwellers live in cities of more than one million people. Many new urban households maintain strong links to relatives and clans in rural areas, with circular migration patterns emerging as the urban transition takes place over several decades. The implications of this extremely rapid urbanisation in SSA countries for livelihoods and poverty are widely debated. UN-Habitat highlights a relatively unique aspect of urbanisation in SSA as being the accompanying high rate of growth in informal settlements or slums. In other words, not all rural migrants to towns and cities find secure incomes or shelter. Some slum areas have become permanent features where inter-generational poverty is reproduced. Although urban areas are producing an increasing share of national wealth in SSA countries, some argue that slowly the nexus of poverty is shifting towards urban areas. Rates of poverty are high in rural areas of SSA, but migration and internal population growth means that in some countries the number of urban poor almost matches the number of rural poor, and it is likely to grow. The informal economy contributes an average of 40 – 45 % of total urban GDP, which is higher than any other region of the world

Pliocene-Pleistocene marine cyclothems, Wanganui Basin, New Zealand: a lithostratigraphic framework

The Rangitikei River valley between Mangaweka and Vinegar Hill and the surrounding Ohingaiti region in eastern Wanganui Basin contains a late Pliocene to early Pleistocene (c. 2.6-1.7 Ma), c. 1100 m thick, southward-dipping (4-9deg.), marine cyclothemic succession. Twenty sedimentary cycles occur within the succession, each of which contains coarse-grained (siliciclastic sandstone and coquina) and fine-grained (siliciclastic siltstone) units. Nineteen of the cycles are assigned to the Rangitikei Group (new). Six new formations are defined within the Rangitikei Group, and their distribution in the Ohingaiti region is represented in a new geologic map. The new formations are named: Mangarere, Tikapu, Makohine, Orangipongo, Mangaonoho, and Vinegar Hill. Each formation comprises one or more cyclothems and includes a previously described and named distinctive basal horizon. Discrete sandstones, siltstones, and coquinas within formations are assigned member status and correspond to systems tracts in sequence stratigraphic nomenclature. The members provide the link between the new formational lithostratigraphy and the sequence stratigraphy of the Rangitikei Group. Base of cycle coquina members accumulated during episodes of sediment starvation associated with stratigraphic condensation on an open marine shelf during sea-level transgressions. Siltstone members accumulated in mid-shelf environments (50-100 m water depth) during sea-level highstands, whereas the overlying sandstone members are ascribed to inner shelf and shoreface environments (0-50 m water depth) and accumulated during falling eustatic sea-level conditions. Repetitive changes in water depth of 50-100 m magnitude are consistent with a glacio-eustatic origin for the cyclothems, which correspond to an interval of Earth history when successive glaciations in the Northern Hemisphere are known to have occurred. Moreover, the chronology of the Rangitikei River section indicates that Rangitikei Group cyclothems accumulated during short duration, 41 ka cycles in continental ice volume attributed to the dominance of the Milankovitch obliquity orbital parameter. The Ohingaiti region has simple postdepositional structure. The late Pliocene formations dip generally to the SSW between 4deg. and 9deg.. Discernible discordances of c. 1deg. between successively younger formations are attributed to synsedimentary tilting of the shelf concomitant with migration of the tectonic hingeline southward into the basin. The outcrop distribution of the Rangitikei Group is strongly influenced by this regional tilt and also by three major northeast-southwest oriented, high-angle reverse faults (Rauoterangi, Pakihikura, and Rangitikei Faults)

Late Neogene chronology: New perspectives in high-resolution stratigraphy

We present an integrated geochronology for late Neogene time (Pliocene, Pleistocene, and Holocene Epochs) based on an analysis of data from stable isotopes, magnetostratigraphy, radiochronology, and calcareous plankton biostratigraphy. Discrepancies between recently formulated astronomical chronologies and magnetochronologies for the past 6 m.y. have been resolved on the basis of new, high-precision Ar/Ar ages in the younger part of this interval, the so-called Brunhes, Matuyama, and Gauss Epochs (= Chrons C1n-C2An; 0-3.58 Ma), and revised analysis of sea floor anomalies in the Pacific Ocean in the older part, the so-called Gilbert Epoch (= Chron C2Ar-C3r; 3.58-5.89 Ma). The magneto- and astrochronologies are now concordant back to the Chron C3r/C3An boundary at 5.89 Ma. The Neogene (Miocene, Pliocene, Pleistocene, and Holocene) and Paleogene are treated here as period/system subdivisions of the Cenozoic Era/Erathem, replacements for the antiquated terms Tertiary and Quaternary. The boundary between the Miocene and Pliocene Series (Messinian/Zanclean Stages), whose global stratotype section and point (GSSP) is currently proposed to be in Sicily, is located within the reversed interval just below the Thvera (C3n.4n) Magnetic Polarity Subchronozone with an estimated age of 5.32 Ma. The Pliocene/Pleistocene boundary, whose GSSP is located at Vrica (Calabria, Italy), is located near the top of the Olduvai (C2n) Magnetic Polarity Subchronozone with an estimated age of 1.81 Ma. The 13 calcareous nannoplankton and 48 planktonic foraminiferal datum events for the Pliocene, and 12 calcareous nannoplankton and 10 planktonic foraminiferal datum events for the Pleistocene, are calibrated to the newly revised late Neogene astronomical/geomagnetic polarity time scale