The expression of the end-Cenomanian oceanic anoxic event (OAE 2) in the Helvetic Alps

Upper Cenomanian pelagic sediments from the northern Alpine Helvetic fold-and-thrust belt (northern Tethyan margin) coeval with Oceanic Anoxic Event (OAE) 2 are characterized by the temporal persistence of micrite sedimentation and lack of organic carbon-rich layers. We studied an expanded section in the Chrummflueschlucht (east of Euthal, Switzerland), which encompasses the OAE 2 time interval. In order to identify the paleoceanographic and paleoenvironmental conditions during OAE 2 in this part of the northern Tethyan margin, and more specifically to trace eventual changes in nutrient levels and oxic conditions, we investigated the biostratigraphy (planktonic foraminifera), the bulk-rock mineralogy, and measured stable carbon- and oxygen-isotopes, total phosphorus (P) and redox-sensitive trace-element (RSTE) contents. We were able to determine – with some remaining uncertainties – the different planktonic foraminiferal biozones characteristic of the Cenomanian–Turonian boundary interval (Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones). In the lower part of the section (R. cushmani total range zone), the bulk-rock δ13C record shows a long-term increase. Within sediments attributed to the W. archaeocretacea partial range zone, δ13C values reach a maximum of 3.3‰ (peak “a”). In the following the values decrease and increase again to arrive at a plateau with high δ13C values of around 3.1‰, which ends with a peak of 3.3‰ (peak “c”). At the top of the section, in sediments belonging to the H. helvetica total range zone, δ13C values decrease to post-OAE values of around 2.2‰. The last occurrence of R. cushmani is observed just above the positive δ13C shift characterizing OAE 2. P contents display small variations along the section with a long-term decreasing trend towards the top. Before the OAE 2 interval, P values show higher values and relatively good covariation with detrital input, indicating higher nutrient input before OAE 2. In sediments corresponding to the onset of the δ13C positive excursion, P content is marked by a sharp peak probably linked to a slowdown in sedimentation rates and/or the presence of a small hiatus, as is shown by the presence of glauconite and phosphatic grains. In the interval corresponding to OAE 2, P values remain low and increase slightly at the end of the positive shift in the δ13C record (in the H. helvetica total range zone). The average contents of RSTE (U, V, As, Co, Mo and Mn) remain low throughout the section and appreciable RSTE enrichments have not been observed for the sedimentary interval corresponding to OAE 2. No correlation is observed with stratigraphic trends in RSTE contents in organic-rich deeper-water sections. The presence of double-keeled planktonic foraminifera species during most of the Cenomanian/Turonian boundary event is another evidence of relatively well-oxygenated conditions in this part of the northern Tethyan outer shelf. Our results show that the Chrummflueschlucht section corresponds to one of the most complete section for the Cenomanian–Turonian boundary interval known from the Helvetic realm even if a small hiatus may be present at the onset of the δ13C record (peak “a”). The evolution of P contents suggests an increase in input of this nutritive element at the onset of OAE2. However, the trends in RSTE contents and the planktonic foraminifera assemblages show that the Helvetic realm has not been affected by strongly depleted oxygen conditions during OAE 2.

Reframing 'crisis' in fair trade coffee production: trajectories of agrarian change in Nicaragua

A focus on crisis provides a methodological window to understand how agrarian change shapes producer engagement in fair trade. This orientation challenges a seperation between the market and development, situating fair trade within global processes that incorporate agrarian histories of social change and conflict. Reframing crisis as a condition of agrarian life, rather than emphasizing its cyclical manifestation within the global economy, reveals how market-driven development encompasses the material conditions of peoples' existence in ambiguous and contradictory ways. Drawing on the case of coffee production in Nicaragua, experiences of crisis demonstrate that greater attention needs to be paid to the socioeconomic and political dimensions of development within regional commodity assemblages to address entrenched power relations and unequal access to land and resources. This questions moral certainties when examining the paradox of working in and against the market, and suggests that a better understanding of specific trajectories of development could improve fair trade's objective of enhancing producer livelihoods.

Wild pollinators enhance fruit set of crops regardless of honey bee abundance

Diversity and abundance of wild-insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. Here, we show universally positive associations of fruit set with wild-insect visits to flowers in 41 crop systems worldwide, and thus clearly demonstrate their agricultural value. In contrast, fruit set increased significantly with visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively, because increase in their visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Further, visitation by wild insects and honey bees promoted fruit set independently, so high abundance of managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild-insect assemblages will enhance global crop yields.

A high resolution late Holocene palaeo environmental record from the central Adriatic Sea

A multi-proxy study of a Holocene sediment core (RF 93-30) from the western flank of the central Adriatic, in 77 m of water, reveals a sequence of changes in terrestrial vegetation, terrigenous sediment input and benthic fauna, as well as evidence for variations in sea surface temperature spanning most of the last 7000 yr. The chronology of sedimentation is based on several lines of evidence, including AMS 14C dates of foraminifera extracted from the core, palaeomagnetic secular variation, pollen indicators and dated tephra. The temporal resolution increases towards the surface and, for some of the properties measured, is sub-decadal for the last few centuries. The main changes recorded in vegetation, sedimentation and benthic foraminiferal assemblages appear to be directly related to human activity in the sediment source area, which includes the Po valley and the eastern flanks of the central and northern Appenines. The most striking episodes of deforestation and expanding human impact begin around 3600 BP (Late Bronze Age) and 700 BP (Medieval) and each leads to an acceleration in mass sedimentation and an increase in the proportion of terrigenous material, reflecting the response of surface processes to widespread forest clearance and cultivation. Although human impact appears to be the proximal cause of these changes, climatic effects may also have been important. During these periods, signs of stress are detectable in the benthic foram morphotype assemblages. Between these two periods of increased terrigeneous sedimentation there is smaller peak in sedimentation rate around 2400BP which is not associated with evidence for deforestation, shifts in the balance between terrigenous and authigenic sedimentation, or changes in benthic foraminifera. The mineral magnetic record provides a sensitive indicator of changing sediment sources: during forested periods of reduced terrigenous input it is dominated by authigenic bacterial magnetite, whereas during periods of increased erosion, anti-ferromagetic minerals (haematite and/or goethite) become more important, as well as both paramagnetic minerals and super-paramagnetic magnetite. Analysis of the alkenone, U37k′, record provides an indication of possible changes in sea surface temperature during the period, but it is premature to place too much reliance on these inferred changes until the indirect effects of past changes in the depth of the halocline and in circulation have been more fully evaluated. The combination of methods used and the results obtained illustrate the potential value of such high resolution near-shore marine sedimentary sequences for recording wide-scale human impact, documenting the effects of this on marine sedimentation and fauna and, potentially, disentangling evidence for human activities from that for past changes in climate.

Fractal spatialities

This paper argues for the use of ‘fractals’ in theorising sociospatial relations. From a realist position, a nonmathematical but nonmetaphoric and descriptive view of ‘fractals’ is advanced. Insights from the natural sciences are combined with insights on the position of the observer from Luhmann and notions of assemblages and repetitions from Deleuze. It is argued that the notion of ‘fractals’ can augment current understanding of sociospatialities in three ways. First, it can pose questions about the scalar position of the observer or the grain of observation; second, as a signifier of particular attributes, it prompts observation and description of particular structuring processes; and third, the epistemic access afforded by the concept can open up possibilities for transformative interventions and thereby inform the same. The theoretical usefulness of the concept is demonstrated by discussing the territory, place, scale, and networks (TPSN) model for theorising sociospatial relations advanced by B Jessop, N Brenner, and M Jones in their 2008 paper “Theorizing sociospatial relations”, published in this journal (volume 26, pages 389–401). It is suggested that a heuristic arising from a ‘fractal’ ontology can contribute to a polymorphous, as opposed to polyvalent, understanding of sociospatial relations.

An improved methodology for the recovery of Zea mays and other large crop pollen, with implications for environmental archaeology in the Neotropics

We present a simple sieving methodology to aid the recovery of large cultigen pollen grains, such as maize (Zea mays L.), manioc (Manihot esculenta Crantz), and sweet potato (Ipomoea batatas L.), among others, for the detection of food production using fossil pollen analysis of lake sediments in the tropical Americas. The new methodology was tested on three large study lakes located next to known and/or excavated pre-Columbian archaeological sites in South and Central America. Five paired samples, one treated by sieving, the other prepared using standard methodology, were compared for each of the three sites. Using the new methodology, chemically digested sediment samples were passed through a 53 µm sieve, and the residue was retained, mounted in silicone oil, and counted for large cultigen pollen grains. The filtrate was mounted and analysed for pollen according to standard palynological procedures. Zea mays (L.) was recovered from the sediments of all three study lakes using the sieving technique, where no cultigen pollen had been previously recorded using the standard methodology. Confidence intervals demonstrate there is no significant difference in pollen assemblages between the sieved versus unsieved samples. Equal numbers of exotic Lycopodium spores added to both the filtrate and residue of the sieved samples allow for direct comparison of cultigen pollen abundance with the standard terrestrial pollen count. Our technique enables the isolation and rapid scanning for maize and other cultigen pollen in lake sediments, which, in conjunction with charcoal and pollen records, is key to determining land-use patterns and the environmental impact of pre-Columbian societies.

Pediastrum species as potential indicators of lake-level change in tropical South America

We explored the potential for using Pediastrum (Meyen), a genus of green alga commonly found in palaeoecological studies, as a proxy for lake-level change in tropical South America. The study site, Laguna La Gaiba (LLG) (17°45′S, 57°40′W), is a broad, shallow lake located along the course of the Paraguay River in the Pantanal, a 135,000-km2 tropical wetland located mostly in western Brazil, but extending into eastern Bolivia. Fourteen surface sediment samples were taken from LLG across a range of lake depths (2-5.2 m) and analyzed for Pediastrum. We found seven species, of which P. musteri (Tell et Mataloni), P. argentiniense (Bourr. et Tell), and P. cf. angulosum (Ehrenb.) ex Menegh. were identified as potential indicators of lake level. Results of the modern dataset were applied to 31 fossil Pediastrum assemblages spanning the early Holocene (12.0 kyr BP) to present to infer past lake level changes qualitatively. Early Holocene (12.0-9.8 kyr BP) assemblages do not show a clear signal, though abundance of P. simplex (Meyen) suggests relatively high lake levels. Absence of P. musteri, characteristic of deep, open water, and abundance of macrophyte-associated taxa indicate lake levels were lowest from 9.8 to 3.0 kyr BP. A shift to wetter conditions began at 4.4 kyr BP, indicated by the appearance of P. musteri, though inferred lake levels did not reach modern values until 1.4 kyr BP. The Pediastrum-inferred mid-Holocene lowstand is consistent with lower precipitation, previously inferred using pollen from this site, and is also in agreement with evidence for widespread drought in the South American tropics during the middle Holocene. An inference for steadily increasing lake level from 4.4 kyr BP to present is consistent with diatom-inferred water level rise at Lake Titicaca, and demonstrates coherence with the broad pattern of increasing monsoon strength from the late Holocene until present in tropical South America.

Pollen-based differentiation of Amazonian rainforest communities and implications for lowland palaeoecology in tropical South America

An ongoing controversy in Amazonian palaeoecology is the manner in which Amazonian rainforest communities have responded to environmental change over the last glacial–interglacial cycle. Much of this controversy results from an inability to identify the floristic heterogeneity exhibited by rainforest communities within fossil pollen records. We apply multivariate (Principal Components Analysis) and classification (Unweighted Pair Group with Arithmetic Mean Agglomerative Classification) techniques to floral-biometric, modern pollen trap and lake sediment pollen data situated within different rainforest communities in the tropical lowlands of Amazonian Bolivia. Modern pollen rain analyses from artificial pollen traps show that evergreen terra firme (well-drained), evergreen terra firme liana, evergreen seasonally inundated, and evergreen riparian rainforests may be readily differentiated, floristically and palynologically. Analogue matching techniques, based on Euclidean distance measures, are employed to compare these pollen signatures with surface sediment pollen assemblages from five lakes: Laguna Bella Vista, Laguna Chaplin, and Laguna Huachi situated within the Madeira-Tapajós moist forest ecoregion, and Laguna Isirere and Laguna Loma Suarez, which are situated within forest patches in the Beni savanna ecoregion. The same numerical techniques are used to compare rainforest pollen trap signatures with the fossil pollen record of Laguna Chaplin.

Differentiation between Neotropical rainforest, dry forest and savannah ecosystems by their modern pollen spectra and implications for the fossil pollen record

Accurate differentiation between tropical forest and savannah ecosystems in the fossil pollen record is hampered by the combination of: i) poor taxonomic resolution in pollen identification, and ii) the high species diversity of many lowland tropical families, i.e. with many different growth forms living in numerous environmental settings. These barriers to interpreting the fossil record hinder our understanding of the past distributions of different Neotropical ecosystems and consequently cloud our knowledge of past climatic, biodiversity and carbon storage patterns. Modern pollen studies facilitate an improved understanding of how ecosystems are represented by the pollen their plants produce and therefore aid interpretation of fossil pollen records. To understand how to differentiate ecosystems palynologically, it is essential that a consistent sampling method is used across ecosystems. However, to date, modern pollen studies from tropical South America have employed a variety of methodologies (e.g. pollen traps, moss polsters, soil samples). In this paper, we present the first modern pollen study from the Neotropics to examine the modern pollen rain from moist evergreen tropical forest (METF), semi-deciduous dry tropical forest (SDTF) and wooded savannah (cerradão) using a consistent sampling methodology (pollen traps). Pollen rain was sampled annually in September for the years 1999–2001 from within permanent vegetation study plots in, or near, the Noel Kempff Mercado National Park (NKMNP), Bolivia. Comparison of the modern pollen rain within these plots with detailed floristic inventories allowed estimates of the relative pollen productivity and dispersal for individual taxa to be made (% pollen/% vegetation or ‘p/v’). The applicability of these data to interpreting fossil records from lake sediments was then explored by comparison with pollen assemblages obtained from five lake surface samples.

Palynological differentiation between genera of the Moraceae family and implications for Amazonian palaeoecology

The Moraceae family is one of the most abundant and ecologically important families in Neotropical rainforests and is very well-represented in Amazonian fossil pollen records. However, difficulty in differentiating palynologically between the genera within this family, or between the Moraceae and Urticaceae families, has limited the amount of palaeoecological information that can be extracted from these records. The aim of this paper is to analyse the morphological properties of pollen from Amazonian species of Moraceae in order to determine whether the pollen taxonomy of this family can be improved. Descriptive and morphometric methods are used to identify and differentiate key pollen types of the Moraceae (mulberry) and Urticaceae (nettle) families which are represented in Amazonian rainforest communities of Noel Kempff Mercado National Park (NKMNP), Northeast Bolivia. We demonstrate that Helicostylis, Brosimum, Pseudolmedia, Sorocea and Pourouma pollen can be identified in tropical pollen assemblages and present digital images of, and a taxonomic key to, the Moraceae pollen types of NKMNP. Indicator species, Maquira coriacea (riparian evergreen forest) and Brosimum gaudichaudii (open woodland and upland savanna communities), also exhibit unique pollen morphologies. The ability to recognise these ecologically important taxa in pollen records provides the potential for much more detailed and reliable Neotropical palaeovegetation reconstructions than have hitherto been possible. In particular, this improved taxonomic resolution holds promise for resolving long-standing controversies over the interpretation of key Amazonian Quaternary pollen records.

Species richness declines and biotic homogenization have slowed down for NW-European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20-year periods, comparing periods of rapid land-use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post-1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large-scale land-use intensification and natural habitat loss has ceased.

Ecosystem effects of CO2 concentration: evidence from past climates

Atmospheric CO2 concentration has varied from minima of 170-200 ppm in glacials to maxima of 280-300 ppm in the recent interglacials. Photosynthesis by C-3 plants is highly sensitive to CO2 concentration variations in this range. Physiological consequences of the CO2 changes should therefore be discernible in palaeodata. Several lines of evidence support this expectation. Reduced terrestrial carbon storage during glacials, indicated by the shift in stable isotope composition of dissolved inorganic carbon in the ocean, cannot be explained by climate or sea-level changes. It is however consistent with predictions of current process-based models that propagate known physiological CO2 effects into net primary production at the ecosystem scale. Restricted forest cover during glacial periods, indicated by pollen assemblages dominated by non-arboreal taxa, cannot be reproduced accurately by palaeoclimate models unless CO2 effects on C-3-C-4 plant competition are also modelled. It follows that methods to reconstruct climate from palaeodata should account for CO2 concentration changes. When they do so, they yield results more consistent with palaeoclimate models. In conclusion, the palaeorecord of the Late Quaternary, interpreted with the help of climate and ecosystem models, provides evidence that CO2 effects at the ecosystem scale are neither trivial nor transient.

Landscape evolution and ice-sheet behaviour in a semi-arid polar environment: James Ross Island, NE Antarctic Peninsula

This study of landscape evolution presents both new modern and palaeo process-landform data, and analyses the behaviour of the Antarctic Peninsula Ice Sheet through the Last Glacial Maximum (LGM), the Holocene and to the present day. Six sediment-landform assemblages are described and interpreted for Ulu Peninsula, James Ross Island, NE Antarctic Peninsula: (1) the Glacier Ice and Snow Assemblage; (2) the Glacigenic Assemblage, which relates to LGM sediments and comprises both erratic-poor and erratic-rich drift, deposited by cold-based and wet-based ice and ice streams respectively; (3) the Boulder Train Assemblage, deposited during a Mid-Holocene glacier readvance; (4) the Ice-cored Moraine Assemblage, found in front of small cirque glaciers; (5) the Paraglacial Assemblage including scree, pebble-boulder lags, and littoral and fluvial processes; and (6) the Periglacial Assemblage including rock glaciers, protalus ramparts, blockfields, solifluction lobes and extensive patterned ground. The interplay between glacial, paraglacial and periglacial processes in this semi-arid polar environment is important in understanding polygenetic landforms. Crucially, cold-based ice was capable of sediment and landform genesis and modification. This landsystem model can aid the interpretation of past environments, but also provides new data to aid the reconstruction of the last ice sheet to overrun James Ross Island.

Modern pollen samples from alpine vegetation on the Tibetan Plateau.

1  A set of 316 modern surface pollen samples, sampling all the alpine vegetation types that occur on the Tibetan Plateau, has been compiled and analysed. Between 82 and 92% of the pollen present in these samples is derived from only 28 major taxa. These 28 taxa include examples of both tree (AP) and herb (NAP) pollen types. 2  Most of the modern surface pollen samples accurately reflect the composition of the modern vegetation in the sampling region. However, airborne dust-trap pollen samples do not provide a reliable assessment of the modern vegetation. Dust-trap samples contain much higher percentages of tree pollen than non-dust-trap samples, and many of the taxa present are exotic. In the extremely windy environments of the Tibetan Plateau, contamination of dust-trap samples by long-distance transport of exotic pollen is a serious problem. 3  The most characteristic vegetation types present on the Tibetan Plateau are alpine meadows, steppe and desert. Non-arboreal pollen (NAP) therefore dominates the pollen samples in most regions. Percentages of arboreal pollen (AP) are high in samples from the southern and eastern Tibetan Plateau, where alpine forests are an important component of the vegetation. The relative importance of forest and non-forest vegetation across the Plateau clearly follows climatic gradients: forests occur on the southern and eastern margins of the Plateau, supported by the penetration of moisture-bearing airmasses associated with the Indian and Pacific summer monsoons; open, treeless vegetation is dominant in the interior and northern margins of the Plateau, far from these moisture sources. 4  The different types of non-forest vegetation are characterized by different modern pollen assemblages. Thus, alpine deserts are characterized by high percentages of Chenopodiaceae and Artemisia, with Ephedra and Nitraria. Alpine meadows are characterized by high percentages of Cyperaceae and Artemisia, with Ranunculaceae and Polygonaceae. Alpine steppe is characterized by high abundances of Artemisia, with Compositae, Cruciferae and Chenopodiaceae. Although Artemisia is a common component of all non-forest vegetation types on the Tibetan Plateau, the presence of other taxa makes it possible to discriminate between the different vegetation types. 5  The good agreement between modern vegetation and modern surface pollen samples across the Tibetan Plateau provides a measure of the reliability of using pollen data to reconstruct past vegetation patterns in non-forested areas.

Pollen-based reconstructions of Japanese biomes at 0, 6000 and 18,000 14C yr bp

A biomization method, which objectively assigns individual pollen assemblages to biomes ( Prentice et al., 1996 ), was tested using modern pollen data from Japan and applied to fossil pollen data to reconstruct palaeovegetation patterns 6000 and 18,000 14C yr bp Biomization started with the assignment of 135 pollen taxa to plant functional types (PFTs), and nine possible biomes were defined by specific combinations of PFTs. Biomes were correctly assigned to 54% of the 94 modern sites. Incorrect assignments occur near the altitudinal limits of individual biomes, where pollen transport from lower altitudes blurs the local pollen signals or continuous changes in species composition characterizes the range limits of biomes. As a result, the reconstructed changes in the altitudinal limits of biomes at 6000 and 18,000 14C yr bp are likely to be conservative estimates of the actual changes. The biome distribution at 6000 14C yr bp was rather similar to today, suggesting that changes in the bioclimate of Japan have been small since the mid-Holocene. At 18,000 14C yr bp the Japanese lowlands were covered by taiga and cool mixed forests. The southward expansion of these forests and the absence of broadleaved evergreen/warm mixed forests reflect a pronounced year-round cooling.