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 ( ∼ 26&thinsp;°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

Climate variability, heat distribution, and polar amplification in the warm unipolar “icehouse” of the Oligocene

The Oligocene (33.9–23.03 Ma) had warm climates with flattened meridional temperature gradients, while Antarctica retained a significant cryosphere. These may pose imperfect analogues to distant future climate states with unipolar icehouse conditions. Although local and regional climate and environmental reconstructions of Oligocene conditions are available, the community lacks synthesis of regional reconstructions. To provide a comprehensive overview of marine and terrestrial climate and environmental conditions in the Oligocene, and a reconstruction of trends through time, we review marine and terrestrial proxy records and compare these to numerical climate model simulations of the Oligocene. Results, based on the present relatively sparse data, suggest temperatures around the Equator that are similar to modern temperatures. Sea surface temperatures (SSTs) show patterns similar to land temperatures, with warm conditions at mid- and high latitudes (∼60–90°), especially in the Southern Hemisphere (SH). Vegetation-based precipitation reconstructions of the Oligocene suggest regionally drier conditions compared to modern times around the Equator. When compared to proxy data, climate model simulations overestimate Oligocene precipitation in most areas, particularly the tropics. Temperatures around the mid- to high latitudes are generally underestimated in models compared to proxy data and tend to overestimate the warming in the tropics. In line with previous proxy-to-model comparisons, we find that models underestimate polar amplification and overestimate the Equator-to-pole temperature gradient suggested from the available proxy data. This further stresses the urgency of solving this widely recorded problem for past warm climates, such as the Oligocene.</p

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 (∼57–56 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; ∼56 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 (∼53–49 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., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm 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 long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground 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 east–west 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 ‘the uplift of the Tibetan Plateau’, 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 ‘the uplift of the Tibetan Plateau’ never occurred, and quantify a new pattern of topographic and landscape evolution that contributed to the development of today’s 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. 18.7–15.1 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 (16.5–20 C) and high annual precipitation (1,500–2,500 mm) during the Burdigalian– 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