42 research outputs found
Temperature seasonality in the North American continental interior during the Early Eocene Climatic Optimum
Paleogene greenhouse climate equability has long been a paradox in
paleoclimate research. However, recent developments in proxy and modeling
methods have suggested that strong seasonality may be a feature of at least
some greenhouse Earth periods. Here we present the
first multi-proxy record of seasonal temperatures during the Paleogene from
paleofloras, paleosol geochemistry, and carbonate clumped isotope thermometry
in the Green River Basin (Wyoming, USA). These combined temperature records
allow for the reconstruction of past seasonality in the continental interior,
which shows that temperatures were warmer in all seasons during the peak
Early Eocene Climatic Optimum and that the mean annual range of temperatures was high,
similar to the modern value (ââŒâ26 °C). Proxy data and
downscaled Eocene regional climate model results suggest amplified
seasonality during greenhouse events. Increased seasonality reconstructed for
the early Eocene is similar in scope to the higher seasonal range predicted
by downscaled climate model ensembles for future high-CO2 emissions
scenarios. Overall, these data and model comparisons have substantial
implications for understanding greenhouse climates in general, and may be
important for predicting future seasonal climate regimes and their impacts in
continental regions.</p
Temperature seasonality in the North American continental interior during the Early Eocene Climatic Optimum
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148644/1/Hyland_et_al_2018_CotP-Eocene_Climate_Equability.pd
Revisiting the Geographical Extent of Exceptional Warmth in the Early Paleogene Southern Ocean
To assess zonal temperature and biogeographical patterns in the Southern Ocean during the Paleogene, we present new multi-proxy air- and sea-surface temperature data for the latest Paleocene (âŒ57â56 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; âŒ56 Ma) from the northern margin of the Australo-Antarctic Gulf (AAG). The various proxy data sets document the well-known late Paleocene warming and, superimposed, two transient late Paleocene pre-cursor warming events, hundreds of kyr prior to the PETM. Remarkably, temperature reconstructions for the AAG and southwest Pacific during the latest Paleocene, PETM and Early Eocene Climatic Optimum (âŒ53â49 Ma) show similar trends as well as similar absolute temperatures east and west of the closed Tasmanian Gateway. Our data imply that the exceptional warmth as recorded by previous studies for the southwest Pacific extended westward into the AAG. This contrasts with modeling-derived circulation and temperature patterns. We suggest that simulations of ocean circulation underestimate heat transport in the southwest Pacific due to insufficient resolution, not allowing for mesoscale eddy-related heat transport. We argue for a systematic approach to tackle model and proxy biases that may occur in marginal marine settings and non-analog high-latitude climates to assess the temperature reconstructions
The global abundance of tree palms
Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., â„10 cm diameter at breast height) abundance relative to coâoccurring nonâpalm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of longâterm climate stability. Lifeâform diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many nonâtree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of aboveâground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests
The topographic evolution of the Tibetan Region as revealed by palaeontology
The Tibetan Plateau was built through a succession of Gondwanan terranes colliding with Asia during the Mesozoic. These accretions produced a complex Paleogene topography of several predominantly eastâwest trending mountain ranges separated by deep valleys. Despite this piecemeal assembly and resultant complex relief, Tibet has traditionally been thought of as a coherent entity rising as one unit. This has led to the widely used phrase âthe uplift of the Tibetan Plateauâ, which is a false concept borne of simplistic modelling and confounds understanding the complex interactions between topography climate and biodiversity. Here, using the rich palaeontological record of the Tibetan region, we review what is known about the past topography of the Tibetan region using a combination of quantitative isotope and fossil palaeoaltimetric proxies, and present a new synthesis of the orography of Tibet throughout the Paleogene. We show why âthe uplift of the Tibetan Plateauâ never occurred, and quantify a new pattern of topographic and landscape evolution that contributed to the development of todayâs extraordinary Asian biodiversity
Epiphyllous fungi and leaf physiognomy suggest an ever-wet humid mesothermal (subtropical) climate in the late Eocene of southern New Zealand
Abstract not availableJohn G. Conran, Jennifer M. Bannister, Tammo Reichgelt, Daphne E. Le
The early Miocene paleolake Manuherikia: vegetation heterogeneity and warm-temperate to subtropical climate in southern New Zealand
The Manuherikia Group in southern New Zealand represents terrestrial sediments associated with a large paleolake, Lake Manuherikia, formed during a period of basin subsidence in the early Miocene, ca. 18.7â15.1 Ma. Micro- and macrofloral assemblages collected throughout the Manuherikia Group were studied to derive terrestrial climate proxies, relying on leaf physiognomy (CLAMP) and taxonomic affinity (bioclimatic analysis). The assemblages were also analyzed for the component loading of the relative abundances of different leaf morphotypes and the results were interpreted in light of stratigraphic and lateral ecological variation. Independent paleoclimate proxies from a variety of depositional environments consistently indicate warm-temperate to marginally subtropical mean annual temperatures (16.5â20 C) and high annual precipitation (1,500â2,500 mm) during the Burdigalianâ Langhian of mid-latitude New Zealand. Leaf physiognomy reveals an amplified seasonal contrast in both precipitation and temperature, possibly caused by seasonal shifts in the position of the subtropical highpressure cells and westerly wind belts, causing overcast wet winters and dry summers. Regional and local vegetation variation was most likely caused by fluctuations in lake levels, which in turn may have been affected by enhanced seasonality from shortterm climate oscillations. Keywords Paleoenvironment Mid-latitudes Floral proxies Southern hemisphere SubtropicalTammo Reichgelt, Elizabeth M. Kennedy, John G. Conran, Dallas C. Mildenhall, Daphne E. Le
Diverse and abundant insect herbivory on Miocene Nothofagaceae of the Dunedin Volcano, Otago, New Zealand
Terrigenous sediments occurring within the mid/upper Miocene Dunedin Volcanic Group in southern New Zealand contain well-preserved leaf-beds, commonly dominated by Nothofagaceae leaf fossils. Abundant insect herbivory traces occur on Nothofagaceae leaf fossils from the Double Hill and Kaikorai Valley localities, including 28 types of external foliage feeding traces, 8 types of galling and a possible fungal trace, several not described previously. Relatively high diversity of insect herbivory traces on broad-leaved Nothofagaceae suggests a high diversity of insect herbivores. The high abundance and diversity of trace fossils in combination with evidence for plicate vernation suggests that Nothofagaceae growing on the mid/late Miocene Dunedin Volcano had shorter leaf retention times than modern New Zealand Nothofagaceae. The loss of Nothofagaceae diversity from New Zealand due to cooling climate in the late Neogene could also have meant the demise of an arthropod community adapted to living on broad-leaved Nothofagaceae. Insect damage diversity and amount at Double Hill was significantly higher than at Kaikorai Valley, as well as the occurrence of plicate vernation and leaves with stunted growth forms. This suggests that there may have been some difference in the insect diversity of the two sites, relating to local palaeoenvironment, such as higher temperatures at Double Hill during the warm season and/or differences in forest density.Tammo Reichgelt, Wyn A. Jones, David T. Jones, John G. Conran, Daphne E. Le
Quantitative palaeoclimate estimates for Early Miocene southern New Zealand: Evidence from Foulden Maar
A rich and diverse plant macrofossil assemblage from an earliest Miocene diatomite deposit in southern New Zealand provides a detailed record of mid-latitude, Southern Hemisphere terrestrial climate in an oceanic setting. Quantitative palaeoclimate estimates for temperature and precipitation variables were obtained using the Climate Leaf Analysis Multivariate Program (CLAMP) and the Bioclimatic Analysis approach. In addition, the surface area of fossil Podocarpus travisiae leaves preserved at the site was used as a proxy for mean annual temperature. CLAMP and Bioclimatic analysis both estimated mean annual temperatures at ~ 18.5-19.5 °C, with a moderate seasonal temperature range between summer and winter of ~ 10 °C and leaf size in Podocarpus suggested a MAT of about 21 °C. Precipitation rates were high at around 1700-2000. mm per year. CLAMP analysis suggested a ~ 600 mm difference between the dry and wet season, whereas Bioclimatic Analysis indicated a ~ 200-250 mm difference between summer and winter. When compared to CLAMP analysis on modern vegetation on subtropical oceanic islands, it would seem that CLAMP overestimates seasonal precipitation differences. © 2013 Elsevier B.V.Tammo Reichgelt, Elizabeth M. Kennedy, Dallas C. Mildenhall, John G. Conran, David R. Greenwood, Daphne E. Le