Palaeoclimate reconstructions from Arctic and Nordic Shelf seas: development and application of multiple proxies

Although Holocene climate changes are significantly smaller in amplitude than the Pleistocene Glacial-Interglacial cycles (Dansgaard et al., 1993), they have affected human civilisations over at least the last 4000 years (Buntgen et al., 2011; Lamb, 1995; Mayewski & White, 2002). The study of Holocene climate variations is increasingly important to disentangle climate change caused by anthropogenic influences from natural climate change. Furthermore, Holocene climate change provides the geological context in which to place contemporary climatic observations. Studying sedimentary records stemming from marine biotopes located close to land, such as fjords, affords the opportunity to study marine and terrestrial paleo-climatic variability, and therein linking the two together. Additionally, fjordic environments typically have a higher sediment accumulation rate than deeper ocean sites, facilitating resolution of rapid climate change events. The fjords of Northwest Iceland are ideal for studying Holocene climate change as they receive warm water from the Irminger current, an end member of the Atlantic current, but are also influenced by the east Greenland current, which brings cold polar waters to the region (Jennings et al., 2011). Furthermore, the coring site is located beneath one of the dipoles of the North Atlantic Oscillation (Hurrell, 1995). Therefore, oceanic and atmospheric Holocene variability should be recorded in the sediments studied. Alkenones, terrestrial leaf wax n-alkanes, branched and archaeal glycerol tetraethers and C/N ratios from a sediment core from the mouth of the Ísafjarðardjúp fjord (MD99-2266; location: 66° 13' 77'' N, 23° 15' 93'' W; 106 m water depth) were analysed. These terrestrial and marine biomarkers were used to produce biomarker based palaeoclimatic records with the highest resolution to date (one sample every ~ 32 years), covering the Holocene from ~ 10,700 calibrated years before present (cal. a BP) to ~ 300 cal. a BP. The terrestrial and marine organic carbon contributions to the sediment and the palaeoproductivity of the fjord vary throughout the Holocene forced by changing climate. While the amount of terrestrial organic carbon is primarily controlled by the development of vegetation as glaciers retreat, the primary productivity is controlled by varying influxes of nutrient rich water masses. By combining the reconstructed sea surface temperature, air temperature and precipitation records, climatic changes that affect the terrestrial and marine realm are uncovered. Two periods in the Holocene where major climatic shifts in the North Atlantic region occur, one at ~ 7700 cal. a BP, and one at ~ 2900 cal. a BP, are observed. Meltwater events and decreasing summer insolation drive climatic change throughout the early Holocene. The middle Holocene climate, from 7700 to 2900 cal. a BP is driven by decreasing summer insolation, and meridional overturning circulation. The climate variability is decoupled from insolation change in the late Holocene, and the sea surface temperature and air temperature, and precipitation changes are driven by NAO-type fluctuations and variations in the heat transport via the meridional overturning circulation. The TEX86 palaeo-SST thermometer does not work in Ísafjarðardjúp fjord. The TEX86-SSTs are adversely affected by GDGTs associated with archaea mediating anaerobic oxidation of methane, as indicated by the methane index. Methane indices as low as 0.1 indicate anaerobic oxidation of methane at the site studied. The palaeo-sea-ice proxy IP25 was not detected in the sediments of MD99-2266 even though the northwest Icelandic coast has been affected by drift ice, particularly in the late Holocene. Therefore, the use of carbon isotopic signatures from sedimentary fatty acids, derived from ice and pelagic algae was investigated as a sea-ice proxy. Ice algae, ice core, water column particulate organic matter and sediment samples were collected on the ICE CHASER 2010 research cruise. The carbon isotopic signature of the ice algal C16 fatty acid is significantly heavier than that of the pelagic derived organic matter. Furthermore, the carbon isotopic signature of the fatty acid in the samples from the sediment core located at the ice edge is isotopically heavier, compared to the fatty acid isotopic signature from the sediment core from a pelagic site. It appears that the isotopic signature of algal fatty acids can be used to elucidate sea-ice cover, however, more research is needed

Preventing drift of oxygen isotopes of CO₂-in-air stored in glass sample flasks:new insights and recommendations

It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.</p

Preventing drift of oxygen isotopes of CO₂-in-air stored in glass sample flasks:new insights and recommendations

It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.</p

Preventing drift of oxygen isotopes of CO₂-in-air stored in glass sample flasks:new insights and recommendations

It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.</p

Preventing drift of oxygen isotopes of CO₂-in-air stored in glass sample flasks:new insights and recommendations

It is known that the oxygen isotope composition of CO2-in-air, when stored over longer time periods in glass sample flasks, tends to drift to more negative values while the carbon isotope composition remains stable. The exact mechanisms behind this drift were still unclear. New experimental results reveal that water already inside the flasks during sampling plays a major role in the drift of the oxygen isotopes. A drying method to remove any water sticking to the inner walls by evacuating the flasks for more than 72 h while heating to 60 °C significantly decreases drift of the oxygen isotopes. Moreover, flasks not dried with this method showed higher differences among drift rates of individual flasks. This is explained through the buildup of H2O molecules sticking to the inner walls. Humidity of the air samples in the flasks as well as surface characteristics will lead to differences among flasks. Results also show that permeability of water is higher through Viton O-ring flask seals than through polychlorotrifluoroethylene (PCTFE) shaft seals, and that the stability of flasks sealed with the latter is significantly better over time.</p

Production Systems and Rete Algorithm Formalisation

Rapport de contrat.The rete algorithm is a well-known algorithm for efficiently addressing the many patterns/many objects match problem, and it has been widely used and implemented in several applications, mainly production systems. But despite of the wide usage of production systems and the rete algorithm, to the best of our knowledge there has been just one proposition for a formal definition of the rete algorithm given by Fages and Lissajoux~\cite{Fages92}, but no attempt to give a formal description of production systems as a whole, giving rise to lots of ambiguities and incompatibilities between the different implementations. Therefore, the need for a formalisation is clear and we present in this report a first approach to it, refining Fages and Lissajoux's approach to fit it in our general model of production systems

Neighbourhood species richness and drought-tolerance traits modulate tree growth and delta¹³C responses to drought

International audienceMixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. In particular, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. Using tree cores from a large-scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; delta C-13) to changes in climate-induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases delta C-13 and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterised the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance versus resource acquisition and stomatal control.Tree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods. The effects of neighbourhood species richness and climate on growth and delta C-13 were modulated by the traits of focal trees and the traits of their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during dry and wet years.We show that species' drought-tolerance traits can explain the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress