Search

Climate variability is typically amplified towards polar regions. The underlying causes, notably albedo and humidity changes, are challenging to accurately quantify with observations or models, thus hampering projections of future polar amplification. Polar amplification reconstructions from the ice-free early Eocene (∼56 –48 Ma) can exclude ice albedo effects, but the required tropical temperature records for resolving timescales shorter than multi-million years are lacking. Here, we reconstruct early Eocene tropical sea surface temperature variability by presenting an up to ∼4 kyr resolution biomarker-based temperature record from Ocean Drilling Program (ODP) Site 959, located in the tropical Atlantic Ocean. This record shows warming across multiple orbitally paced carbon cycle perturbations, coeval with high-latitude-derived deep-ocean bottom waters, showing that these events represent transient global warming events (hyperthermals). This implies that orbital forcing caused global temperature variability through carbon cycle feedbacks. Importantly, deep-ocean temperature variability was amplified by a factor of 1.7–2.3 compared to the tropical surface ocean, corroborating available long-term estimates. This implies that fast atmospheric feedback processes controlled meridional temperature gradients on multi-million year, as well as orbital, timescales during the early Eocene. Our combined records have several other implications. First, our amplification factor is somewhat larger than the same metric in fully coupled simulations of the early Eocene (1.1–1.3), suggesting that models slightly underestimate the non-ice-related – notably hydrological – feedbacks that cause polar amplification of climate change. Second, even outside the hyperthermals, we find synchronous eccentricity-forced temperature variability in the tropics and deep ocean that represent global mean sea surface temperature variability of up to 0.7 °C, which requires significant variability in atmospheric p CO 2. We hypothesize that the responsible carbon cycle feedbacks that are independent of ice, snow, and frost-related processes might play an important role in Phanerozoic orbital-scale climate variability throughout geological time, including Pleistocene glacial–interglacial climate variability. [ABSTRACT FROM AUTHOR]

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO.sub.2 concentrations are crucial for developing better projections of future climate change. Deep-ocean.sup.1,2 and high-latitude.sup.3 palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data.sup.4-6 to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing.sup.7,8, rather than changes in ocean circulation.sup.9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO.sub.2 reconstructions.sup.8 yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates.sup.11.A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification., Author(s): Margot J. Cramwinckel [sup.1] , Matthew Huber [sup.2] , Ilja J. Kocken [sup.1] , Claudia Agnini [sup.3] , Peter K. Bijl [sup.1] , Steven M. Bohaty [sup.4] , Joost [...]

Model simulations of past climates are increasingly found to compare well with proxy data at a global scale, but regional discrepancies remain. A persistent issue in modeling past greenhouse climates has been the temperature difference between equatorial and (sub‐)polar regions, which is typically much larger in simulations than proxy data suggest. Particularly in the Eocene, multiple temperature proxies suggest extreme warmth in the southwest Pacific Ocean, where model simulations consistently suggest temperate conditions. Here, we present new global ocean model simulations at 0.1° horizontal resolution for the middle‐late Eocene. The eddies in the high‐resolution model affect poleward heat transport and local time‐mean flow in critical regions compared to the noneddying flow in the standard low‐resolution simulations. As a result, the high‐resolution simulations produce higher surface temperatures near Antarctica and lower surface temperatures near the equator compared to the low‐resolution simulations, leading to better correspondence with proxy reconstructions. Crucially, the high‐resolution simulations are also much more consistent with biogeographic patterns in endemic‐Antarctic and low‐latitude‐derived plankton, and thus resolve the long‐standing discrepancy of warm subpolar ocean temperatures and isolating polar gyre circulation. The results imply that strongly eddying model simulations are required to reconcile discrepancies between regional proxy data and models, and demonstrate the importance of accurate regional paleobathymetry for proxy‐model comparisons. Plain Language Summary: Climate models are widely used to understand warm climates in the geologic past such as the late Eocene (38 million years ago; ∼8°C warmer than today). To determine the quality of these models, simulations are often compared to measured proxies representing the regional environment. Here, we show that a finer‐than‐typical detail in the ocean model causes a profoundly different regional ocean flow and environmental conditions. The improved correspondence to proxy data implies that high‐resolution simulations are required for a meaningful point‐by‐point data‐model comparison. Key Points: Eddying ocean simulations provide a profoundly different local flow compared to noneddying simulationsHeat transport is enhanced in eddying simulations leading to reduced equator‐to‐pole sea surface temperature gradientsEddying simulations reduce model‐data mismatches for sea surface temperature and ocean flow [ABSTRACT FROM AUTHOR]

Considered one of the most significant climate reorganizations of the Cenozoic period, the Eocene–Oligocene Transition (EOT; ca. 34.44–33.65) is characterized by global cooling and the first major glacial advance on Antarctica. In the southern high latitudes, the EOT cooling is primarily recorded in the marine realm, and its extent and effect on the terrestrial climate and vegetation are poorly documented. Here, we present new, well-dated, continuous, high-resolution palynological (sporomorph) data and quantitative sporomorph-based climate estimates recovered from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene (37.97 Ma) to the early Oligocene (33.06 Ma). Our results indicate three major climate transitions and four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) a warm-temperate Nothofagus–Podocarpaceae-dominated rainforest with paratropical elements from 37.97 to 37.52 Ma; (ii) a cool-temperate Nothofagus-dominated rainforest with secondary Podocarpaceae rapidly expanding and taking over regions previously occupied by the warmer taxa between 37.306 and 35.60 Ma; (iii) fluctuation between warm-temperate–paratropical taxa and cool temperate forest from 35.50 to 34.49 Ma, followed by a cool phase across the EOT (34.30–33.82 Ma); and (iv) a post-EOT (earliest Oligocene) recovery characterized by a warm-temperate forest association from 33.55 to 33.06 Ma. Coincident with changes in the stratification of water masses and sequestration of carbon from surface water in the Southern Ocean, our sporomorph-based temperature estimates between 37.52 and 35.60 Ma (phase ii) showed 2–3 ∘ C terrestrial cooling. The unusual fluctuation between warm and cold temperate forest between 35.50 to 34.59 Ma is suggested to be linked to the initial deepening of the Tasmanian Gateway, allowing eastern Tasmania to come under the influence of warm water associated with the proto-Leeuwin Current (PLC). Further to the above, our terrestrial data show the mean annual temperature declining by about 2 ∘ C across the EOT before recovering in the earliest Oligocene. This phenomenon is synchronous with regional and global cooling during the EOT and linked to declining p CO 2. However, the earliest Oligocene climate rebound along eastern Tasmania is linked to a transient recovery of atmospheric p CO 2 and sustained deepening of the Tasmanian Gateway, promoting PLC throughflow. The three main climate transitional events across the studied interval (late Eocene–earliest Oligocene) in the Tasmanian Gateway region suggest that changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation dynamics; a series of regional and global events, including a change in the stratification of water masses, sequestration of carbon from surface waters, and changes in p CO 2 , may have also played vital roles. [ABSTRACT FROM AUTHOR]

Terrestrial organic carbon (TerrOC) acts as an important CO2 sink when transported via rivers to the ocean and sequestered in coastal marine sediments. This mechanism might help to modulate atmospheric CO2 levels over short‐ and long‐ timescales (103–106 years), but its importance during past warm climates remains unknown. Here we use terrestrial biomarkers preserved in coastal marine sediment samples from Wilkes Land, East Antarctica (∼67°S) to quantify TerrOC burial during the early Eocene (∼54.4–51.5 Ma). Terrestrial biomarker distributions indicate the delivery of plant‐, soil‐, and peat‐derived organic carbon (OC) into the marine realm. Mass accumulation rates of plant‐ (long‐chain n‐alkane) and soil‐derived (hopane) biomarkers dramatically increase between the earliest Eocene (∼54 Ma) and the early Eocene Climatic Optimum (EECO; ∼53 Ma). This coincides with increased OC mass accumulation rates and indicates enhanced TerrOC burial during the EECO. Leaf wax δ2H values indicate that the EECO was characterized by wetter conditions relative to the earliest Eocene, suggesting that hydroclimate exerts a first‐order control on TerrOC export. Our results indicate that TerrOC burial in coastal marine sediments could have acted as an important negative feedback mechanism during the early Eocene, but also during other warm climate intervals. Plain Language Summary: Organic matter from the terrestrial biosphere can be transferred into rivers and eventually deposited in the ocean. This process helps to remove carbon dioxide from the atmosphere over long (>1,000 years) timescales. However, the importance of this process in warm climates is one of the most poorly understood aspects of the climate system. One way to test the behavior of the Earth in warmer‐than‐present climate states is to examine the geological record. Here we analyzed marine sediments deposited close to the Antarctic shoreline to quantify organic carbon burial during an ancient warm interval (the early Eocene, 56 to 48 million years ago). We analyzed biomolecules from plants and microbes to determine how much organic matter was derived from the terrestrial biosphere. We found evidence for increased terrestrial organic carbon burial in marine sediments during the early Eocene. This process could help to remove carbon dioxide from the atmosphere and is relevant to other episodes of climate change during Earth's history. Key Points: Terrestrial organic carbon is an important CO2 sink when transported via rivers to the ocean and sequestered in coastal marine sedimentsBiomarkers indicate enhanced terrestrial organic carbon burial during early Eocene—this could have acted as a negative feedback mechanismHydrology regulates organic carbon export from the terrestrial biosphere at this site [ABSTRACT FROM AUTHOR]

The role and climatic impact of the opening of the Drake Passage and how it affected both marine and terrestrial environments across the Eocene–Oligocene transition (EOT ∼34 Ma) period remains poorly understood. Here we present new terrestrial palynomorph data compared with recently compiled lipid biomarker (n -alkane) data from Ocean Drilling Program (ODP) Leg 113, Site 696, drilled on the margin of the South Orkney Microcontinent (SOM) in the Weddell Sea, to investigate changes in terrestrial environments and palaeoclimate across the late Eocene and early Oligocene (∼37.6 –32.2 Ma). Early late Eocene floras and sporomorph-based climate estimates reveal Nothofagus-dominated forests growing under wet temperate conditions, with mean annual temperature (MAT) and precipitation (MAP) around 12 ∘ C and 1802 mm respectively. A phase of latest Eocene terrestrial cooling at 35.5 Ma reveals a decrease in MAT by around 1.4 ∘ C possibly linked to the opening of the Powell Basin. This is followed by an increase in reworked Mesozoic sporomorphs together with sedimentological evidence indicating ice expansion to coastal and shelf areas approximately 34.1 Myr ago. However, major changes to the terrestrial vegetation at Site 696 did not take place until the early Oligocene, where there is a distinct expansion of gymnosperms and cryptogams accompanied by a rapid increase in taxon diversity and a shift in terrestrial biomarkers reflecting a change from temperate forests to cool temperate forests following 33.5 Ma. This surprising expansion of gymnosperms and cryptogams is suggested to be linked to environmental disturbance caused by repeat glacial expansion and retreat, which facilitated the proliferation of conifers and ferns. The timing of glacial onset at Site 696 is linked to the global cooling at the EOT, yet the latest Eocene regional cooling cannot directly be linked to the observed vegetation changes. Therefore, our vegetation record provides further evidence that the opening of the Drake Passage and Antarctic glaciation were not contemporaneous, although stepwise cooling in response to the opening of ocean gateways surrounding the Antarctic continent may have occurred prior to the EOT. [ABSTRACT FROM AUTHOR]

Declining atmospheric CO2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO2. The role of Southern Ocean gateways contributing to the Eocene-Oligocene climate transition is still debated. Here, the authors present high-resolution ocean simulations to show that gateways opening led to a reorganization of ocean circulation, heat transport and Antarctic surface water cooling. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (SW) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects on the isoGDGT distribution in marine sediments. Here, we use the current proxy insights to (re-)assess the reliability of the isoGDGT-based SST signal in 69 newly analyzed and 242 reanalyzed sediments at Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We compare our results with paleoenvironmental and paleoclimatologic reconstructions based on dinoflagellate cysts. The resulting ∼ 130 kyr resolution Maastrichtian–Oligocene SST record based on the TetraEther indeX of tetraethers with 86 carbon atoms (TEX 86) confirms previous conclusions of anomalous warmth in the early Eocene SW Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and assemblages show a strong response to the local SST evolution, supporting the robustness of the TEX 86 record. Soil-derived branched GDGTs stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land using the Methylation index of Branched Tetraethers with 5-methyl bonds (MBT' 5me) proxy. MAAT is consistently lower than SST during the early Eocene, independent of the calibration chosen. General trends in SST and MAAT are similar, except for (1) an enigmatic absence of MAAT rise during the Paleocene–Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and (2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocysts and GDGT signals suggest a mid-shelf depositional environment with strong river runoff during the Paleocene–early Eocene progressively becoming more marine thereafter. This trend reflects gradual subsidence and more pronounced wet/dry seasons in the northward-drifting Australian hinterland, which may also explain the subdued middle Eocene MAAT cooling relative to that of SST. The overall correlation between dinocyst assemblages, marine biodiversity and SST changes suggests that temperature exerted a strong influence on the surface-water ecosystem. Finally, we find support for a potential temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in marine sediments. It is encouraging that a critical evaluation of the GDGT signals confirms that most of the generated data are reliable. However, this also implies that the high TEX 86 -based SSTs for the Eocene SW Pacific and the systematic offset between absolute TEX 86 -based SST and MBT' 5me -based MAAT estimates remain without definitive explanation. [ABSTRACT FROM AUTHOR]

The early and late Eocene have both been the subject of many modelling studies, but few have focused on the middle Eocene. The latter still holds many challenges for climate modellers but is also key to understanding the events leading towards the conditions needed for Antarctic glaciation at the Eocene–Oligocene transition. Here, we present the results of CMIP5-like coupled climate simulations using the Community Earth System Model (CESM) version 1. Using a new detailed 38 Ma geography reconstruction and higher model resolution compared to most previous modelling studies and sufficiently long equilibration times, these simulations will help to further understand the middle to late Eocene climate. At realistic levels of atmospheric greenhouse gases, the model is able to show overall good agreement with proxy records and capture the important aspects of a warm greenhouse climate during the Eocene. With a quadrupling of pre-industrial concentrations of both CO 2 and CH 4 (i.e. 1120 ppm and ∼2700 ppb, respectively, or 4 × PIC; pre-industrial carbon), sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ∼ Bartonian) proxies. Being generally cooler, the simulated climate under 2 × PIC forcing is a good analogue for that of the late Eocene (38–34 Ma; ∼ Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are in agreement with the available information. Our simulated middle to late Eocene climate has a reduced Equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation, and ice account for a global average 5–7 ∘ C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. This helps to explain Eocene warmth in general, without the need for greenhouse gas levels much higher than indicated by proxy estimates (i.e. ∼500 –1200 ppm CO 2) or low-latitude regions becoming unreasonably warm. High-latitude warmth supports the idea of mostly ice-free polar regions, even at 2 × PIC, with Antarctica experiencing particularly warm summers. An overall wet climate is seen in the simulated Eocene climate, which has a strongly monsoonal character. Equilibrium climate sensitivity is reduced (0.62 ∘ C W -1 m 2 ; 3.21 ∘ C warming between 38 Ma 2 × PIC and 4 × PIC) compared to that of the present-day climate (0.80 ∘ C W -1 m 2 ; 3.17 ∘ C per CO 2 doubling). While the actual warming is similar, we see mainly a higher radiative forcing from the second PIC doubling. A more detailed analysis of energy fluxes shows that the regional radiative balance is mainly responsible for sustaining a low meridional temperature gradient in the Eocene climate, as well as the polar amplification seen towards even warmer conditions. These model results may be useful to reconsider the drivers of Eocene warmth and the Eocene–Oligocene transition (EOT) but can also be a base for more detailed comparisons to future proxy estimates. [ABSTRACT FROM AUTHOR]

Integrated Ocean Drilling Program (IODP) Expedition 318 recovered lower Eocene sediments in Hole U1356A from the continental rise of the Wilkes Land Margin, Antarctica. These sediments yielded a new genus of organic-walled dinoflagellate cysts ( Adeliesphaera gen. nov.). We tentatively place this new genus within the suborder Gonyaulacineae, family Areoligeraceae, based on the obligate apical archeopyle, the asymmetric antapical geometry and the left-side offset sulcal notch. We herein describe the type species of Adeliesphaera gen. nov., Adeliesphaera ohanlonii sp. nov., as well as a new species of Turbiosphaera , Turbiosphaera guersteinae sp. nov. The short stratigraphic range of both species (53.7–53.4 Ma and 53.1–52.9 Ma, respectively) qualifies them as potentially important regional Southern Ocean stratigraphic markers for high-resolution age control. [ABSTRACT FROM AUTHOR]

The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth's climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene 'greenhouse world', however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing. [ABSTRACT FROM AUTHOR]

The middle Eocene climatic optimum (ca. 40 Ma) stands out as a transient global warming phase of ~400 k.y. duration that interrupted long-term Eocene cooling; it has been associated with a rise in atmospheric CO2 concentrations that has been linked to a flare-up in Arabia-Eurasia continental arc volcanism. Increased organic carbon burial in the Tethys Ocean has been proposed as a carbon sequestration mechanism to bring the middle Eocene climatic optimum to an end. To further test these hypotheses, we assessed the sedimentary and geochemical expression of the middle Eocene climatic optimum in the northern Peri-Tethys, specifically, the organic-rich Kuma Formation of the Belaya River section, located on the edge of the Scythian Platform in the North Caucasus, Russia. We constructed an age-depth model using nannofossil chronobiostratigraphy. Throughout the studied middle Eocene interval (41.2-39.9 Ma), we documented sea-surface temperatures of 32-36 °C based on the tetraether index of tetraethers consisting of 86 carbons (TEX86), depending on proxy calibration, and during the early middle Eocene climatic optimum, we observed sea-surface warming of 2-3 °C. Despite the proximity of the section to the Arabia-Eurasia volcanic arc, the hypothesized source of volcanic CO2, we found no evidence for enhanced regional volcanism in sedimentary mercury concentrations. Sedimentary trace-element concenconcentrations and iron speciation indicate reducing bottom waters throughout the middle Eocene, but the most reducing, even euxinic, conditions were reached during late middle Eocene climatic optimum cooling. This apparent regional decoupling between ocean warming and deoxygenation hints at a role for regional tectonics in causing basin restriction and anoxia. Associated excess organic carbon burial, extrapolated to the entire regional Kuma Formation, may have been ~8.1 Tg C yr-1, comprising ~450 Pg C over this ~55 k.y. interval. Combined with evidence for enhanced organic carbon drawdown in the western Peri-Tethys, this supports a quantitatively significant role for the basin in the termination of the middle Eocene climatic optimum by acting as a large organic carbon sink, and these results collectively illustrate that the closing Tethys Ocean might have affected global Paleogene climate. Moreover, this study highlights the importance of the interplay between global climate and regional oceanic gateway evolution in determining local climate and oceanographic change. [ABSTRACT FROM AUTHOR]

Abstract: The early Eocene epoch was characterized by extreme global warmth, which in terrestrial settings was characterized by an expansion of near-tropical vegetation belts into the high latitudes. During the middle to late Eocene, global cooling caused the retreat of tropical vegetation to lower latitudes. In high-latitude settings, near-tropical vegetation was replaced by temperate floras. This floral change has recently been traced as far south as Antarctica, where along the Wilkes Land margin paratropical forests thrived during the early Eocene and temperate Nothofagus forests developed during the middle Eocene. Here we provide both qualitative and quantitative palynological data for this floral turnover based on a sporomorph record recovered at Integrated Ocean Drilling Program (IODP) Site U1356 off the Wilkes Land margin. Following the nearest living relative concept and based on a comparison with modern vegetation types, we examine the structure and diversity patterns of the Eocene vegetation along the Wilkes Land margin. Our results indicate that the early Eocene forests along the Wilkes Land margin were characterized by a diverse canopy composed of plants that today occur in tropical settings; their richness pattern was similar to that of present-day forests from New Caledonia. The middle Eocene forests were characterized by a canopy dominated by Nothofagus and exhibited richness patterns similar to modern Nothofagus forests from New Zealand. [Copyright &y& Elsevier]

While many palaeoclimate studies have focussed on the Eocene-Oligocene transition (EOT), little is known about the timing and drivers of the post-EOT climate recovery. To better understand and reconstruct terrestrial climate and vegetation dynamics from the late Eocene to late Oligocene (35.5–27.46 Ma), we use a new, high-resolution palynological record and quantitative sporomorph-based climate estimates recovered from ODP Site 1168 on the western Tasmanian margin. Late Eocene (35.50–34.81 Ma) floras reveal Nothofagus -dominated temperate forests with secondary Gymnostoma and minor thermophilic plant elements growing under wet conditions, with mean annual temperatures (MATs) of ∼13 °C. This is followed by a small decrease in terrestrial temperatures across the EOT by ∼2 °C. Apart from a slight decline in abundance of Gymnostoma , increases in the Fuscospora and Lophozonia -type Nothofagus, and the disappearance of palms (Arecaceae), vegetation remained relatively stable across the EOT. However, a prolonged interval of warm-temperate conditions after 33.0 Ma, independent of fluctuations in the current p CO 2 record, imply additional regional controls on local climate. Changes in surface oceanographic currents, due to sustained deepening of the Tasmanian Gateway, may have played a significant role in sustaining warm-temperate vegetation in southern Australia post-EOT. The early Oligocene (PZ 3; 30.5–27.46 Ma) vegetation record still maintains the Nothofagus -dominated forest with a recovery in Gymnostoma. Gymnosperms (especially Araucariaceae, Dacrydium , and Podocarpus) and cryptogams expanded alongside an increase in overall species diversity. Sporomorph-based MATs averaged ∼11 °C in this interval. The expansion of cool-temperate forest (sustained cool-temperate climate conditions in our terrestrial records) matches the general declining p CO 2 concentrations in the early Oligocene. The synchroneity between terrestrial and marine temperatures (MATs and SSTs gradually decline) and atmospheric p CO 2 highlight the importance of p CO 2 in driving terrestrial climate and vegetation change in the Tasmanian region during the early Oligocene. • Tasmanian record shows climate recovery after the Eocene-Oligocene Transition (EOT). • Sporomorph-based MATs indicate cooling at EOT. • Mesothermic climate persisted post-EOT until 30.4 Ma. • Tectonic and atmospheric p CO 2 are main controls of vegetation change. [ABSTRACT FROM AUTHOR]

Abstract: We examine ocean changes in response to changes in paleogeography from the Cretaceous to present in an intermediate complexity model and in the fully coupled CCSM3 model. Greenhouse gas concentrations are kept constant to allow a focus on effects arising from changing continental configurations. We find consistent and significant geography-related Cenozoic cooling arising from the opening of Southern Ocean (SO) gateways. Both models show significant deep ocean cooling arising from tectonic evolution alone. Simulations employing continental configurations associated with greenhouse climates, namely the Turonian and the Eocene simulations, systematically exhibit warm deep ocean temperatures at elevated pCO2 close to 10°C. In contrast, continental configurations associated with (later) icehouse climates are associated with cooler deep ocean temperatures at identical pCO2, arising from a progressive strengthening of the Antarctic Circumpolar Current. This suggests that a component of the Cenozoic benthic cooling trend recorded in oxygen isotopes could arise directly from changes in continental configuration, and so be partially decoupled from the Cenozoic greenhouse gas history. In this paper we will present our model results against the background of an extensive review of previous work on ocean gateways and additional modelling results from several other global climate models. [Copyright &y& Elsevier]

The scarcity of paleo-records from the Antarctic Peninsular region of the Southern Ocean hinders our understanding of the timing of the opening of Drake Passage, specifically in the region of the South Orkney Microcontinent (SOM) and Powell Basin, between the Scotia and Antarctic plates. At Ocean Drilling Program (ODP) Hole 696B, SOM sediments recovered from the upper Eocene-lower Oligocene (~37.6–32.2 Ma) enable us to gain insight into paleoceanographic and paleoclimatic changes during gateway opening across the major Cenozoic climate shift —the Eocene-Oligocene transition— when the Antarctic ice sheet first reached sea-level. We propose the following sequence of events, based on a multi-proxy analysis of sediment facies, mineralogy, and organic matter geochemistry (TOC, TN, C/N ratio, δ13C, δ15N, and n -alkanes). During the late Eocene (~37.6–35.5 Ma) the SOM was attached to the Antarctic Peninsula, and terrigenous sediments of likely local origin were deposited in shallow waters under conditions of reduced‑oxygen/low-salinity, and temperate climate. In the latest Eocene (~35.5–34.1 Ma), terrigenous input was reduced due to the separation of the SOM from the Antarctic Peninsula by proto-Powell Basin opening. Decreased sediment supply during continuous deepening of the SOM led to deposition of a condensed section with significant glauconitization, recurrent winnowing by bottom currents, and suboxic conditions near the sediment-water interface. At the time of the Eocene-Oligocene transition (EOT; ~34.1–33.6 Ma) two upward-coarsening sediment sections were deposited within an overall upward-fining section, which we interpret as records of regressive phases due to ice sheet expansion. During the early Oligocene (~33.6–33.2 Ma) the SOM deepened further because of continued opening of Powell Basin, and organic-rich sediments were deposited as a result of enhanced biological production, partially driven by enhanced upwelling. Major cooling caused a change from forests indicating relatively humid temperate conditions in the late Eocene, to forests indicative of dry and cool conditions in the Oligocene, as shown by biomarker records, which also indicate weakening contributions of terrestrial organic matter to the marine sedimentary record. We thus conclude that a shallow gateway, the proto-Powell Basin, formed at ~35.5 Ma, as seen in the decreased delivery of proximal, coarse terrigenous sediments to the SOM margin; this was followed by a long-term deepening trend, interrupted by EOT regression due to continent-wide ice sheet build-up. Opening of the proto-Powell Basin could have provided a shallow-water pathway for water flowing from the Drake Passage-Scotia Sea towards the northern Weddell Sea, enhancing upwelling at the southern SOM shelf margin. Hence, increased marine productivity across the EOT might have resulted from the combined effects of the opening of Powell Basin and climate cooling. • Eocene-Oligocene sediments at Site 696 evidences a sustained relative sea-level rise in the SOM. • Our results point to the formation of the proto-Powell Basin at ~35.5 Ma. • Opening of Powell Basin provided a shallow-water pathway for water flowing towards the Weddell Sea. • We describe enhancing upwelling at the southern margin of the SOM shelf. • A shift from relatively humid temperate to dry and cool forests occurs between the Eocene and Oligocene. [ABSTRACT FROM AUTHOR]

The Early Eocene is extensively studied due to its extremely warm climate and highatmospheric pCO2 conditions (e.g. Bijl et al., 2009; Evans et al., 2018); and in spite of thediffering paleogeography is often seen as potential analog for future climate projections.Existing studies show significantly warmer sea surface temperatures at high latitudes and ingeneral a more flatter meridional temperature gradient than modern times (e.g. Evans et al.,2018). However, most of these high latitude temperature estimates are derived solely of theTEX86 proxy where complications with the different calibrations bring in a certainuncertainty. In this study we show with carbonate clumped isotope (Δ47) thermometry analternative proxy to add further temperature estimates and insights to Early Eocene highlatitude climate reconstructions. We collected fossil corals and gastropods from shallow marine beds of the Dilwynformation that formed during the Early Eocene climatic optimum (∼54.5 Ma) in the Otwaybasin, at a paleolatitude of ∼60 ˚ S. The application of Δ47 thermometry on fossil corals ischallenging due to the high content of organics within the aragonitic skeleton, potentialdis-equilibrium effects during skeleton formation, aragonite specific acid fractionation duringisotope analysis and importantly, a potential diagenetic overprint on the primaryaragonitic skeleton. In order to select well preserved corals we performed an extendedscreening of the material using a combination of multiple geochemical techniques(XRD, EBSD and μXRF), before analyzing the finely powdered fossils for theirΔ47. Our Δ47 temperature estimates on the fossil corals show approximately 10 ˚ C colderwaters than nearby sea surface temperature records based on TEX86 (Bijl et al., 2013; Prosset al., 2012) whereas T estimates from a gastropod shell align well with the TEX86 data. Wediscuss the observed offset between the different reconstructions taking into account differentformation depths and local circulation of a relatively cold intermediate water mass in theOtway basin, matching bottom water temperature estimates from the nearby, but deeperPacific site U1172 based on oxygen isotope thermometry of benthic foraminifera (Bijl et al.,2013). References: Bijl P.K., Schouten S., Sluijs A., Reichart G.-J., Zachos J.C. and Brinkhuis H. (2009)Early Paleogene temperature evolution of the southwest Pacific Ocean. Nature 461,776-779. Bijl P.K., Bendle J.A.P., Bohaty S.M., Pross J., Schouten S., Tauxe L., Stickley C.E.,McKay R.M., Röhl U., Olney M., Sluijs A., Escutia C., Brinkhuis H. and Expedition 318Scientists (2013) Eocene cooling linked to early flow across the Tasmanian Gateway. PNAS110, 9645-9650. Evans D., Sagoo N., Renema W., Cotton L.J., Müller W., Todd J.A., Saraswati P.K.,Stassen P., Ziegler M., Pearson P.N., Valdes P.J. and Affek H.P. (2018) Eocene greenhouseclimate revealed by coupled clumped isotope-Mg/Ca thermometry. PNAS 115,1174-1179. Pross J., Contreras L., Bijl P.K., Greenwood D.R., Bohaty S.M., Schouten S., BendleJ.A., Röhl U., Tauxe L., Raine J.I., Huck C.E., van de Flierdt T., Jamieson S.S.R.,Stickley C.E., van de Schootbrugge B., Escutia C., Brinkhuis H. and IntegratedOcean Drilling Program Expedition 318 Scientists (2012) Persistent near-tropicalwarmth on the Antarctic continent during the early Eocene epoch. Nature 488, 73-77. [ABSTRACT FROM AUTHOR]