Arnoud Boom

CO2 and temperature controlled altidudinal shifts of C4 and C3-dominated grasslands allow reconstruction of paleo-atmospheric pCO2

Abstract During the Pleistocene the vegetation changes in the high Colombian Andes included changes from C3 to C4 plants. This is inferred from δ13C values of the C31 n-alkane from the Funza-2 sedimentary record taken from the high plain of Bogota at 2550 m elevation. The environmental factors thought to be responsible for these changes were investigated using a single point simulation of the BIOME3 vegetation model, including changes in precipitation, temperature and atmospheric CO2 concentrations. The model shows that changes are for a major part caused by these latter two factors. The isotopic signature of the n-alkanes of several extant C3 and C4 grasses from the area were determined to calibrate the interpretation of the isotopic record. From the geochemical record, we estimated the altitudinal distribution of C3 and C4 plants, using present grass distribution patterns based on floristic data as a template. This information, in combination with palaeotemperature estimates, enabled the reconstruction of atmospheric CO2 concentrations. The reconstructed CO2 concentrations follow the trends of the Vostok Antarctic ice core through three glacial and two interglacial stages. The lowest calculated CO2 concentration is ca. 210 ppmV for the glacial maxima and within the range of lowest values from Vostok, our highest value (310 ppmV) is for interglacial MIS 7. This represents a new method to reconstruct palaeoatmospheric pCO2. It is less accurate than measurements from ice cores, but has potential to be used for sediments that are much older than the ice cores.

High altitude C4 grasslands in the northern Andes: relicts from glacial conditions?

The altitudinal vegetation distribution in the northern Andes during glacial time differed from the present-day conditions as a result of temperature and precipitation change. New evidence indicate that as a response to a reduced atmospheric partial CO(2) pressure (pCO(2)), the competitive balance between C(3) and C(4) plants have changed. Effects may have remained virtually undetected in pollen records, but can be observed using a stable carbon isotope analysis. Vegetation dominated by C(4) taxa, belonging to the families Cyperaceae (e.g. Bulbostylis and Cyperus) and Poaceae (e.g. Muhlenbergia, Paspalum and Sporobolus), may have been able to replace for a significant part the modern type C(3) taxa (e.g. species belonging to Carex, Rhynchospora, Aciachne, Agrostis, Calamagrostis, and Chusquea). Impact of reduced glacial atmospheric pCO(2) levels and lower glacial temperatures on the composition and the elevational distribution of the vegetation types is discussed. The present high Andean vegetation communities may differ from the glacial equivalents (non-modern analogue situation). We identified dry Sporobolus lasiophyllus tussock grassland and Arcytophyllum nitidum dwarfshrub paramo as the possible relict communities from glacial time. The effect on previous estimates of paleo-temperatures is estimated to be small.

Studies towards the synthesis of (+)-ptilomycalin A; Stereoselective N-acyliminium ion coupling reactions to enantiopure C-2 substituted lactams

Abstract Highly stereoselective N -acyliminium ion coupling reactions of β-ketoester derived silyl enol ethers with enantiopure lactams derived from ( S )-malic acid are reported. This reaction type is applied in the synthesis of the enantiopure C-2 substituted lactam 27 , a plausible intermediate in a projected synthesis of ptilomycalin A.

On the 13C/12C isotopic signal of day and night respiration at the mesocosm level.

While there is currently intense effort to examine the (13)C signal of CO(2) evolved in the dark, less is known on the isotope composition of day-respired CO(2). This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure c(i)/c(a) effect) from respiratory effect (production of CO(2) with a different delta(13)C value from that of net-fixed CO(2)) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO(2)]. We show that whole mesocosm-respired CO(2) is slightly (13)C depleted in the light at the mesocosm level (by 0.2-0.8 per thousand), while it is slightly (13)C enriched in darkness (by 1.5-3.2 per thousand). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the (13)C abundance in day- and night-evolved CO(2). We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO(2) production may change, thereby explaining the different (12)C/(13)C respiratory fractionations in the light and in the dark.

Pollen-based biome reconstructions for the past 450 000 yr from the Funza-2 core, Colombia: comparisons with model-based vegetation reconstructions

Abstract The 586-m Funza-2 sequence from the high plain of Bogota, Colombia has provided one of the longest pollen-based vegetation reconstructions in the world. Affinity scores to seven biomes are compared to the record of CO2 fluctuation from the Vostok ice core for the period spanning from approximately 25 000 to 450 000 yr before present (BP). Results are compared to output from the BIOME-3 vegetation model run under different environmental scenarios at regional and local scales. The model is run with temperature and precipitation reductions, relative to the present values, of up to −10°C and −700 mm yr−1 respectively. For this particular investigation we are interested in the role of CO2 as a forcer of vegetation change; we run the model with concentrations of atmospheric CO2 ([CO2]atm.) within the range of 170 to 340 ppmV. During glacial periods, the cool grass/shrubland biome is highly dominant, less so during interglacial periods when the cool evergreen and cool mixed forest biomes become co-dominant. In addition to this climate-driven altitudinal oscillation of the vegetation, there is also a signal that indicates longer term evolution of the vegetation. The cool grass/shrubland and cool evergreen and cool mixed forest biomes become co-dominant for the first time over the 450 000-yr record at approximately 170 000 yr BP, become completely anti-phase (during a period of extreme low [CO2]atm.) and then become co-dominant from approximately 120 000 yr BP until the core top, just prior to the last glacial maximum. The model results for the Funza area indicate that changes in [CO2]atm., temperature and precipitation are inter-linked by the vegetation response. A shift of 5.5°C is required to lower the cool grass/shrubland biome to altitudes about the Funza catchment where the Andean forest biome dominant. At low [CO2]atm. concentrations, particularly below 180 ppmV, the composition of the high latitudinal tropical vegetation about the Funza catchment changed. It is suggested that this low [CO2]atm., combined with a period when the climate was characterised by extreme cooling and drying, caused a readjustment of the tropical high altitudinal vegetation zonation and the formation of plant communities that are presently recorded.

Improving estimates of tropical peatland area, carbon storage, and greenhouse gas fluxes

Our limited knowledge of the size of the carbon pool and exchange fluxes in forested lowland tropical peatlands represents a major gap in our understanding of the global carbon cycle. Peat deposits in several regions (e.g. the Congo Basin, much of Amazonia) are only just beginning to be mapped and characterised. Here we consider the extent to which methodological improvements and improved coordination between researchers could help to fill this gap. We review the literature on measurement of the key parameters required to calculate carbon pools and fluxes, including peatland area, peat bulk density, carbon concentration, above-ground carbon stocks, litter inputs to the peat, gaseous carbon exchange, and waterborne carbon fluxes. We identify areas where further research and better coordination are particularly needed in order to reduce the uncertainties in estimates of tropical peatland carbon pools and fluxes, thereby facilitating better-informed management of these exceptionally carbon-rich ecosystems.Our limited knowledge of the size of the carbon pool and exchange fluxes in forested lowland tropical peatlands represents a major gap in our understanding of the global carbon cycle. Peat deposits in several regions (e.g. the Congo Basin, much of Amazonia) are only just beginning to be mapped and characterised. Here we consider the extent to which methodological improvements and improved coordination between researchers could help to fill this gap. We review the literature on measurement of the key parameters required to calculate carbon pools and fluxes, including peatland area, peat bulk density, carbon concentration, above-ground carbon stocks, litter inputs to the peat, gaseous carbon exchange, and waterborne carbon fluxes. We identify areas where further research and better coordination are particularly needed in order to reduce the uncertainties in estimates of tropical peatland carbon pools and fluxes, thereby facilitating better-informed management of these exceptionally carbon-rich ecosystems.

Biogeological Analysis of Desert Varnish Using Portable Raman Spectrometers

Desert varnishes are thin, dark mineral coatings found on some rocks in arid or semi-arid environments on Earth. Microorganisms may play an active role in their formation, which takes many hundreds of years. Their mineral matrix may facilitate the preservation of organic matter and is therefore of great relevance to martian exploration. Miniaturized Raman spectrometers (which allow nondestructive analysis of the molecular composition of a specimen) will equip rovers in forthcoming planetary exploration missions. In that context, and for the first time, portable Raman spectrometers operating in the green visible (532 nm as currently baselined for flight) and in the near-infrared (785 nm) were used in this study to investigate the composition (and substrate) of several samples of desert varnish. Rock samples that were suspected (and later confirmed) to be coated with desert varnish were recovered from two sites in the Mojave Desert, USA. The portable spectrometers were operated in flight-representative acquisition modes to identify the key molecular components of the varnish. The results demonstrate that the coatings typically comprise silicate minerals such as quartz, plagioclase feldspars, clays, ferric oxides, and hydroxides and that successful characterization of the samples can be achieved by using flightlike portable spectrometers for both the 532 and 785 nm excitation sources. In the context of searching for spectral signatures and identifying molecules that indicate the presence of extant and/or extinct life, we also report the detection of β-carotene in some of the samples. Analysis complications caused by the presence of rare earth element photoluminescence (which overlaps with and overwhelms the organic Raman signal when a 785 nm laser is employed) are also discussed.

Climatic controls on Later Stone Age human adaptation in Africa’s southern Cape

Africas southern Cape is a key region for the evolution of our species, with early symbolic systems, marine faunal exploitation, and episodic production of microlithic stone tools taken as evidence for the appearance of distinctively complex human behavior. However, the temporally discontinuous nature of this evidence precludes ready assumptions of intrinsic adaptive benefit, and has encouraged diverse explanations for the occurrence of these behaviors, in terms of regional demographic, social and ecological conditions. Here, we present a new high-resolution multi-proxy record of environmental change that indicates that faunal exploitation patterns and lithic technologies track climatic variation across the last 22,300 years in the southern Cape. Conditions during the Last Glacial Maximum and deglaciation were humid, and zooarchaeological data indicate high foraging returns. By contrast, the Holocene is characterized by much drier conditions and a degraded resource base. Critically, we demonstrate that systems for technological delivery - or provisioning - were responsive to changing humidity and environmental productivity. However, in contrast to prevailing models, bladelet-rich microlithic technologies were deployed under conditions of high foraging returns and abandoned in response to increased aridity and less productive subsistence environments. This suggests that posited links between microlithic technologies and subsistence risk are not universal, and the behavioral sophistication of human populations is reflected in their adaptive flexibility rather than in the use of specific technological systems.

Using Paleoecological Data to Define Main Vegetation Dynamics Along the Savanna–Forest Ecotone in Colombia: Implications for Accurate Assessment of Human Impacts

In recent decades there has been increasing interest, from scientists of many disciplines, in the origins and dynamics of tropical savanna–forest boundaries. These boundaries are rarely present as a smooth gradient from tropical forests to scattered trees and open grassland (Bond and Parr 2010); rather, they are often patchy and irregular, occurring where at first sight no apparent driver for an ecosystem shift is apparent (Sarmiento 1984). In general terms, savanna ecosystems cover approximately 40% of the tropics or 23 million km2 (Cole 1986; Gardner 2006) and host around one-fifth of the world’s human population (Young and Solbrig 1993). These people are imparting a growing impact on savanna systems, as agriculture and other subsistence activities occupy increasingly larger land areas (Gardner 2006).

Questioning the Influence of Sunspots on Amazon Hydrology: Even a Broken Clock Tells the Right Time Twice a Day

It was suggested in a recent article that sunspots drive decadal variation in Amazon River flow. This conclusion was based on a novel time series decomposition method used to extract a decadal signal from the Amazon River record. We have extended this analysis back in time, using a new hydrological proxy record of tree ring oxygen isotopes (δ¹⁸OTR). Consistent with the findings of Antico and Torres, we find a positive correlation between sunspots and the decadal δ¹⁸OTR cycle from 1903 to 2012 (r = 0.60, p < 0.001). However, the relationship does not persist into the preceding century and even becomes weakly negative (r = −0.30, p = 0.11, 1799–1902). This result casts considerable doubt over the mechanism by which sunspots are purported to influence Amazon hydrology.