Discours III.

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to reconstruct past terrestrial temperature and soil pH. Here we compare all available modern soil brGDGT data (n=350) to a wide range of environmental parameters to obtain new global temperature calibrations. We show that soil moisture index (MI), a modeled parameter that also takes potential evapotranspiration into account, is correlated to the 6-methyl brGDGT distribution but does not significantly control the distribution of 5-methyl brGDGTs. Instead, temperature remains the primary control on 5-methyl brGDGTs. We propose the following global calibrations: MAAT soil = 40.01 x MBT’5me − 15.25 (n=350, R2 22 = 23 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 x MBT’5me - 4997.5 (n=350, R2 24 = 0.63, RMSE = 1779 °C). Recent studies have suggested that factors other than temperature can impact arid and/or alkaline soils dominated by 6-methyl brGDGTs. As such, we develop new global temperature calibrations using samples dominated by 5-methyl brGDGTs only (IR6me<0.5). These new calibrations have significantly improved correlation coefficients and lower root mean square errors (RMSE) compared to the global calibrations: MAATsoil’ = 39.09 x !"#!!" ! − 14.50 (n=177, R2 30 = 0.76, RMSE = 4.1 °C) and GDD0 soil’ = 13498.8 x !"#!!" ! − 4444.5 (n=177, R2 31 = 0.78, RMSE = 1326). We suggest that these new calibrations should be used to reconstruct terrestrial climate in the geological past; however, care should be taken when employing these calibrations outside the modern calibration rangThis research was funded through the advanced ERC grant `The greenhouse earth 412 system' (T-GRES, project reference 340923). R.D.P. acknowledges the Royal Society 413 Wolfson Research Merit Award

The latitudinal temperature gradient and its climate dependence as inferred from foraminiferal δ18O over the past 95 million years

The latitudinal temperature gradient is a fundamental state parameter of the climate system tied to the dynamics of heat transport and radiative transfer. Thus, it is a primary target for temperature proxy reconstructions and global climate models. However, reconstructing the latitudinal temperature gradient in past climates remains challenging due to the scarcity of appropriate proxy records and large proxy–model disagreements. Here, we develop methods leveraging an extensive compilation of planktonic foraminifera δ18O to reconstruct a continuous record of the latitudinal sea-surface temperature (SST) gradient over the last 95 million years (My). We find that latitudinal SST gradients ranged from 26.5 to 15.3 °C over a mean global SST range of 15.3 to 32.5 °C, with the highest gradients during the coldest intervals of time. From this relationship, we calculate a polar amplification factor (PAF; the ratio of change in >60° S SST to change in global mean SST) of 1.44 ± 0.15. Our results are closer to model predictions than previous proxy-based estimates, primarily because δ18O-based high-latitude SST estimates more closely track benthic temperatures, yielding higher gradients. The consistent covariance of δ18O values in low- and high-latitude planktonic foraminifera and in benthic foraminifera, across numerous climate states, suggests a fundamental constraint on multiple aspects of the climate system, linking deep-sea temperatures, the latitudinal SST gradient, and global mean SSTs across large changes in atmospheric CO2, continental configuration, oceanic gateways, and the extent of continental ice sheets. This implies an important underlying, internally driven predictability of the climate system in vastly different background states

Distributions of geohopanoids in peat: Implications for the use of hopanoid-based proxies in natural archives

This is the final version of the article. Available from Elsevier via the DOI in this record.Hopanoids are pentacyclic triterpenoids produced by a wide range of bacteria. Within modern settings, hopanoids mostly occur in the biological 17β,21β(H) configuration. However, in some modern peatlands, the C31 hopane is present as the ‘thermally-mature’ 17α,21β(H) stereoisomer. This has traditionally been ascribed to isomerisation at the C-17 position catalysed by the acidic environment. However, recent work has argued that temperature and/or hydrology also exert a control upon hopane isomerisation. Such findings complicate the application of geohopanoids as palaeoenvironmental proxies. However, due to the small number of peats that have been studied, as well as the lack of peatland diversity sampled, the environmental controls regulating geohopanoid isomerisation remain poorly constrained. Here, we undertake a global approach to investigate the occurrence, distribution and diagenesis of geohopanoids within peat, combining previously published and newly generated data (n = 395) from peatlands with a wide temperature (−1 to 27 °C) and pH (3–8) range. Our results indicate that peats are characterised by a wide range of geohopanoids. However, the C31 hopane and C32 hopanoic acid (and occasionally the C32 hopanol) typically dominate. C32 hopanoic acids occur as αβ- and ββ-stereoisomers, with the ββ-isomer typically dominating. In contrast, C31 hopanes occur predominantly as the αβ-stereoisomer. These two observations collectively suggest that isomerisation is not inherited from an original biological precursor (i.e. biohopanoids). Using geohopanoid ββ/(αβ + ββ) indices, we demonstrate that the abundance of αβ-hopanoids is strongly influenced by the acidic environment, and we observe a significant positive correlation between C31 hopane isomerisation and pH (n = 94, r2 = 0.64, p 1 pH unit) and longer-term (>1 kyr) variation. Overall, our findings demonstrate the potential of geohopanoids to provide unique new insights into understanding depositional environments and interpreting terrestrial organic matter sources in the geological record.This research was funded through the advanced ERC grant ‘The Greenhouse Earth System’ (T-GRES. Project reference: 340923). RDP acknowledges the Royal Society Wolfson Research Merit Award. YZ thanks the National Natural Science Foundation of China (Project reference: 41372033). ELM acknowledges the Philip Leverhulme Prize. We also thank the NERC Life Sciences Mass Spectrometry Facility (Bristol) for analytical support and D. Atkinson for help with the sample preparation. GNI thanks Janet Dehmer and Philippe Schaeffer for helpful discussions. Members of the T-GRES Peat Database collaborators are M.J. Amesbury, H. Biester, R. Bindler, J. Blewett, M.A. Burrows, D. del Castillo Torres, F.M. Chambers, A.D. Cohen, S.J. Feakins, M. Gałka, A. Gallego-Sala, L. Gandois, D.M. Gray, P.G. Hatcher, E.N. Honorio Coronado, P.D.M. Hughes, A. Huguet, M. Könönen, F. Laggoun-Défarge O. Lähteenoja, M. Lamentowicz, R. Marchant, X. Pontevedra-Pombal, C. Ponton, A. Pourmand, A.M. Rizzuti, L. Rochefort, J. Schellekens, F. De Vleeschouwer. Finally, we thank Darci Rush, Phil Meyers and an anonymous reviewer for their comments and thoughtful suggestions which greatly improved this manuscript

Bleu Arabia: Palaeolithic and underwater survey in SW Saudi Arabia and the role of coasts in Pleistocene dispersals

The role of coastal regions and coastlines in the dispersal of human populations from Africa and across the globe has been highlighted by the recent polarisation between coastal and interior models. The debate has been clouded by the use of the single term ‘coastal dispersal’ to embrace what is in fact a wide spectrum of possibilities, ranging from seafaring populations who spend most of their time at sea living off marine resources, to land-based populations in coastal regions with little or no reliance on marine foods. An additional complicating factor is the fact of Pleistocene and early Holocene sea-level change, which exposed an extensive coastal region that is now submerged, and may have afforded very different conditions from the modern coastal environment. We examine these factors in the Arabian context and use the term ‘Blue’ to draw attention to the fertile coastal rim of the Arabian Peninsula, and to the now submerged offshore landscape, which is especially extensive in some regions. We further emphasise that the attractions of the coastal rim are a product of two quite different factors, ecological diversity and abundant water on land, which have created persistently ‘Green’ conditions throughout the vagaries of Pleistocene climate change in some coastal regions, especially along parts of the western Arabian escarpment, and potentially productive marine environments around its coastline, which include some of the most fertile in the world. We examine the interplay of these factors in the Southwest region of Saudi Arabia and the southern Red Sea, and summarise some of the results of recent DISPERSE field investigations, including survey for Palaeolithic sites on the mainland, and underwater survey of the continental shelf in the vicinity of the Farasan Islands. We conclude that coastlines are neither uniformly attractive nor uniformly marginal to human dispersal, that they offer diverse opportunities that were spatially and temporally variable at scales from the local to the continental, and that investigating Blue Arabia in relation to its episodically Green interior is a key factor in the fuller understanding of long-term human population dynamics within Arabia and their global implications

Antidepressant stimulation of CDP-diacylglycerol synthesis does not require monoamine reuptake inhibition

<p>Abstract</p> <p>Background</p> <p>Recent studies demonstrate that diverse antidepressant agents increase the cellular production of the nucleolipid CDP-diacylglycerol and its synthetic derivative, phosphatidylinositol, in depression-relevant brain regions. Pharmacological blockade of downstream phosphatidylinositide signaling disrupted the behavioral antidepressant effects in rats. However, the nucleolipid responses were resistant to inhibition by serotonin receptor antagonists, even though antidepressant-facilitated inositol phosphate accumulation was blocked. Could the neurochemical effects be additional to the known effects of the drugs on monoamine transmitter transporters? To examine this question, we tested selected agents in serotonin-depleted brain tissues, in PC12 cells devoid of serotonin transporters, and on the enzymatic activity of brain CDP-diacylglycerol synthase - the enzyme that catalyzes the physiological synthesis of CDP-diacylglycerol.</p> <p>Results</p> <p>Imipramine, paroxetine, and maprotiline concentration-dependently increased the levels of CDP-diacylglycerol and phosphatidylinositides in PC12 cells. Rat forebrain tissues depleted of serotonin by pretreatment with <it>p</it>-chlorophenylalanine showed responses to imipramine or maprotiline that were comparable to respective responses from saline-injected controls. With fluoxetine, nucleolipid responses in the serotonin-depleted cortex or hippocampus were significantly reduced, but not abolished. Each drug significantly increased the enzymatic activity of CDP-diacylglycerol synthase following incubations with cortical or hippocampal brain tissues.</p> <p>Conclusion</p> <p>Antidepressants probably induce the activity of CDP-diacylglycerol synthase leading to increased production of CDP-diacylglycerol and facilitation of downstream phosphatidylinositol synthesis. Phosphatidylinositol-dependent signaling cascades exert diverse salutary effects in neural cells, including facilitation of BDNF signaling and neurogenesis. Hence, the present findings should strengthen the notion that modulation of brain phosphatidylinositide signaling probably contributes to the molecular mechanism of diverse antidepressant medications.</p

The DeepMIP contribution to PMIP4: methodologies for selection, compilation and analysis of latest Paleocene and early Eocene climate proxy data, incorporating version 0.1 of the DeepMIP database

This is the final version of the article. Available from European Geosciences Union via the DOI in this record.Data availability. The data referenced in this manuscript are provided as Supplement Data Files 1 to 8. In the final version, these files will form DeepMIP database version 0.1 and will be accessible online via a citable DOI reference.The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than those of the present day. As such, the study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model–model and model–data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene–Eocene thermal maximum (PETM) and early Eocene climatic optimum (EECO). A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate “atlas” will be used to constrain and evaluate climate models for the three selected time intervals and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.Natural Environment Research Council (NERC)GNS Science Global Change through Time ProgrammeNational Science Foundation (NSF)KU Leuve

Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate

The Early Eocene Climate Optimum (EECO, which occurred about 51 to 53 million years ago)1, was the warmest interval of the past 65 million years, with mean annual surface air temperature over ten degrees Celsius warmer than during the pre-industrial period2–4. Subsequent global cooling in the middle and late Eocene epoch, especially at high latitudes, eventually led to continental ice sheet development in Antarctica in the early Oligocene epoch (about 33.6 million years ago). However, existing estimates place atmospheric carbon dioxide (CO2) levels during the Eocene at 500–3,000 parts per million5–7, and in the absence of tighter constraints carbon–climate interactions over this interval remain uncertain. Here we use recent analytical and methodological developments8–11 to generate a new high-fidelity record of CO2 concentrations using the boron isotope (δ11Β) composition of well preserved planktonic foraminifera from the Tanzania Drilling Project, revising previous estimates6. Although species-level uncertainties make absolute values difficult to constrain, CO2 concentrations during the EECO were around 1,400 parts per million. The relative decline in CO2 concentration through the Eocene is more robustly constrained at about fifty per cent, with a further decline into the Oligocene12. Provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the Eocene was similar to that of the late Quaternary period13, this CO2 decline was sufficient to drive the well documented high- and low-latitude cooling that occurred through the Eocene14. Once the change in global temperature between the pre-industrial period and the Eocene caused by the action of all known slow feedbacks (apart from those associated with the carbon cycle) is removed2–4, both the EECO and the late Eocene exhibit an equilibrium climate sensitivity relative to the pre-industrial period of 2.1 to 4.6 degrees Celsius per CO2 doubling (66 per cent confidence), which is similar to the canonical range (1.5 to 4.5 degrees Celsius15), indicating that a large fraction of the warmth of the early Eocene greenhouse was driven by increased CO2 concentrations, and that climate sensitivity was relatively constant throughout this period

Optically stimulated luminescence dating as a geochronological tool for late quaternary sediments in the Red Sea region

This chapter concerns the use of luminescence methods as geochronological tools for dating Late Quaternary sediments in the Red Sea region. The dating methods all use stimulated luminescence to register signals developed in mineral systems in response to long term exposure to ionising radiation in the environment. The principles of luminescence dating are outlined followed by discussion of its application to the Arabian Peninsula, where, particularly in SE Arabia and parts of the interior, a growing corpus of work is emerging, which is helping to define past arid or humid periods of importance to palaeoclimatology and to archaeology. Turning to the Red Sea, studies conducted within the DISPERSE project are presented both in marine and terrestrial settings. The motivation for much of this work concerns definition of the environmental conditions and chronologies for hominin and human dispersion through Arabia. Data are presented which identify, for the first time, late Pleistocene evidence on the inner continental shelf near the Farasan Islands, using material from the 2013 cruise of RV AEGAEO . Results are also presented from the littoral fringe of southwest Saudi Arabia, identifying units associated with MIS5 which have palaeo-environmental and archaeological significance. It is to be hoped that further research in coming decades will continue to extend the regional chronology for the littoral fringe of the Red Sea. In this respect luminescence dating has potential to help define the environmental history of this important area, to assist with assigning marine and terrestrial features into unique stages of Quaternary climate cycles, and to promote better understanding of human-environment interactions in this dynamic area