Evaluating the use of amber in palaeoatmospheric reconstructions: The carbon-isotope variability of modern and Cretaceous conifer resins.

Stable carbon-isotope geochemistry of fossilized tree resin (amber) potentially could be a very useful tool to infer the composition of past atmospheres. To test the reliability of amber as a proxy for the atmosphere, we studied the variability of modern resin d13C at both local and global scales. An amber d13C curve was then built for the Cretaceous, a period of abundant resin production, and interpreted in light of data from modern resins. Our data show that hardening changes the pristine d13C value by causing a 13C-depletion in solid resin when compared to fresh liquid-viscous resin, probably due to the loss of 13C-enriched volatiles. Modern resin d13C values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood. Resin d13C varies between plant species and localities, within the same tree and between different plant tissues by up to 6¿, and in general increases with increasing altitudes of the plant-growing site. We show that, as is the case with modern resin, Cretaceous amber d13C has a high variability, generally higher than that of other fossil material. Despite the high natural variability, amber shows a negative 2.5-3¿ d13C trend from the middle Early Cretaceous to the Maastrichtian that parallels published terrestrial d13C records. This trend mirrors changes in the atmospheric d13C calculated from the d13C and d18O of benthic foraminiferal tests, although the magnitude of the shift is larger in plant material than in the atmosphere. Increasing mean annual precipitation and pO2 could have enhanced plant carbon-isotope fractionation during the Late Cretaceous, whereas changing pCO2 levels seem to have had no effect on plant carbon-isotope fractionation. The results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions. Improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber d13C records and a wider understanding of the composition of the past atmosphere

Evaluating the use of amber in palaeoatmospheric reconstructions: The carbon-isotope variability of modern and Cretaceous conifer resins.

Stable carbon-isotope geochemistry of fossilized tree resin (amber) potentially could be a very useful tool to infer the composition of past atmospheres. To test the reliability of amber as a proxy for the atmosphere, we studied the variability of modern resin d13C at both local and global scales. An amber d13C curve was then built for the Cretaceous, a period of abundant resin production, and interpreted in light of data from modern resins. Our data show that hardening changes the pristine d13C value by causing a 13C-depletion in solid resin when compared to fresh liquid-viscous resin, probably due to the loss of 13C-enriched volatiles. Modern resin d13C values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood. Resin d13C varies between plant species and localities, within the same tree and between different plant tissues by up to 6¿, and in general increases with increasing altitudes of the plant-growing site. We show that, as is the case with modern resin, Cretaceous amber d13C has a high variability, generally higher than that of other fossil material. Despite the high natural variability, amber shows a negative 2.5-3¿ d13C trend from the middle Early Cretaceous to the Maastrichtian that parallels published terrestrial d13C records. This trend mirrors changes in the atmospheric d13C calculated from the d13C and d18O of benthic foraminiferal tests, although the magnitude of the shift is larger in plant material than in the atmosphere. Increasing mean annual precipitation and pO2 could have enhanced plant carbon-isotope fractionation during the Late Cretaceous, whereas changing pCO2 levels seem to have had no effect on plant carbon-isotope fractionation. The results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions. Improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber d13C records and a wider understanding of the composition of the past atmosphere

Amber inclusions from New Zealand

Amber is nearly ubiquitous in lignites from Otago and Southland, and elsewhere throughout New Zealand; however, until now no amber inclusions have been reported from these fossil tree resins. We have discovered and examined amber from 22 Cretaceous to Miocene sites in southern New Zealand and recovered inclusions in three localities: Cosy Dell (Late Oligocene), Roxburgh (Early Miocene), and Hyde (Early Miocene). Preparation of New Zealand amber and exposing its inclusions for study under incident and transmitted light is challenging and time-consuming, since most amber samples are brittle and opaque. Thus, we apply epoxy preparation under vacuum before grinding and imaging in order to stabilize the amber lumps and to clear the fossil resin for light-microscopy. To date we have recovered about 63 arthropods, as well as plant remains, fungi, and nematodes. Arachnids include diverse mites from the Mesostigmata, Oribatida, Astigmata, and Prostigmata, a variety of spiders and their web remains with prey, and a pseudoscorpion. Some Collembola were identified as belonging to the family Entomobryidae. Inclusions of insects comprise members of the families Dermestidae (Coleoptera), Mymaridae and Scelionidae (Hymenoptera), Veliidae (Heteroptera), Ceratopogonidae and Mycetophilidae (Diptera) as well as Psocoptera, and Lepidoptera. The most abundant fungi in New Zealand amber are hyphomycetes similar to the genus Casparyotorula from European Palaeogene ambers, and we discovered that such fungi still grow on resin of the extant Agathis australis, the iconic New Zealand kauri. Furthermore, specimens of the genus Metacapnodium (Capnodiales) represent the first southern hemispheric fossils of sooty moulds, a group of saprophytic ascomycetes with brown hyphae, often forming extensive subicula on living plant surfaces. These fungi are ubiquitous and diverse in New Zealand today. Many of the new amber fossils represent groups with an otherwise poor fossil record in the entire Southern Hemisphere. The systematic and ecological diversity of the inclusions highlights the potential of New Zealand amber for reconstructing past terrestrial ecosystems of Zealandia, one of the biogeographically crucial Gondwanan landmasses.Alexander R. Schmidt, Uwe Kaulfuss, Jennifer M. Bannister, Viktor Baranov, Christina Beimforde … John G. Conran … et al