The relative roles of CO2 and palaeogeography in determining Late Miocene climate: results from a terrestrial model-data comparison

The Late Miocene (∼11.6–5.3 Ma) palaeorecord provides evidence for a warmer and wetter climate than that of today and there is uncertainty in the palaeo-CO2 record of at least 150 ppmv. We present results from fully coupled atmosphere-ocean-vegetation simulations for the Late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of Late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that the data accurately reflects the Late Miocene climate, and that the Late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that the proxy-derived precipitation differences between the Late Miocene and modern can be largely accounted for by the palaeogeographic changes alone. However, the proxy-derived temperatures differences between the Late Miocene and modern can only begin to be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates

Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis

Late Miocene tectonic changes in Mediterranean–Atlantic connectivity and climatic changes caused Mediterranean salinity to fluctuate dramatically, including a ten-fold increase and near-freshening. Recent proxy- and model-based evidence suggests that at times during this Messinian Salinity Crisis (MSC, 5.96–5.33 Ma), highly saline and highly fresh Mediterranean water flowed into the North Atlantic Ocean, whilst at others, no Mediterranean Outflow Water (MOW) reached the Atlantic. By running extreme, sensitivity-type experiments with a fully coupled ocean–atmosphere general circulation model, we investigate the potential of these various MSC MOW scenarios to impact global-scale climate. The simulations suggest that although the effect remains relatively small, MOW had a greater influence on North Atlantic Ocean circulation and climate than it does today. We also find that depending on the presence, strength and salinity of MOW, the MSC could have been capable of cooling mid–high northern latitudes by a few degrees, with the greatest cooling taking place in the Labrador, Greenland–Iceland–Norwegian and Barents seas. With hypersaline MOW, a component of North Atlantic Deep Water formation shifts to the Mediterranean, strengthening the Atlantic Meridional Overturning Circulation (AMOC) south of 35° N by 1.5–6 Sv. With hyposaline MOW, AMOC completely shuts down, inducing a bipolar climate anomaly with strong cooling in the north (mainly −1 to −3 °C, but up to −8 °C) and weaker warming in the south (up to +0.5 to +2.7 °C). These simulations identify key target regions and climate variables for future proxy reconstructions to provide the best and most robust test cases for (a) assessing Messinian model performance, (b) evaluating Mediterranean–Atlantic connectivity during the MSC and (c) establishing whether or not the MSC could ever have affected global-scale climate

Quantifying the Mediterranean freshwater budget throughout the late Miocene:New implications for sapropel formation and the Messinian Salinity Crisis

The cyclic sedimentary record of the late Miocene Mediterranean shows a clear transition from open marine to restricted conditions and finally to evaporitic environments associated with the Messinian Salinity Crisis. This evolution has been attributed to changes in Mediterranean–Atlantic connectivity and regional climate, which has a strong precessional pulse. 31 Coupled climate simulations with different orbital configurations have been combined in a regression model that estimates the evolution of the freshwater budget of the Mediterranean throughout the late Miocene. The study suggests that wetter conditions occur at precession minima and are enhanced at eccentricity maxima. We use the wetter peaks to predict synthetic sapropel records. Using these to retune two Mediterranean sediment successions indicates that the overall net freshwater budget is the most likely mechanism driving sapropel formation in the late Miocene. Our sapropel timing is offset from precession minima and boreal summer insolation maxima during low eccentricity if the present-day drainage configuration across North Africa is used. This phase offset is removed if at least 50% more water drained into the Mediterranean during the late Miocene, capturing additional North African monsoon precipitation, for example via the Chad-Eosahabi catchment in Libya. In contrast with the clear expression of precession and eccentricity in the model results, obliquity, which is visible in the sapropel record during minimum eccentricity, does not have a strong signal in our model. By exploring the freshwater evolution curve in a box model that also includes Mediterranean–Atlantic exchange, we are able, for the first time, to estimate the Mediterranean's salinity evolution, which is quantitatively consistent with precessional control. Additionally, we separate and quantify the distinct contributions regional climate and tectonic restriction make to the lithological changes associated with the Messinian Salinity Crisis. The novel methodology and results of this study have numerous potential applications to other regions and geological scenarios, as well as to astronomical tuning

Precessional drivers of late Miocene Mediterranean sedimentary sequences: African summer monsoon and Atlantic winter storm tracks

Cyclic sedimentary patterns in the marine record of the Mediterranean Sea have been consistently correlated with orbitally‐driven shifts in climate. Freshwater input driven by the African summer monsoon is thought to be the main control of such hydrological changes, where the runoff signal is transferred from the eastern to the western Mediterranean. The geological record from the Atlantic margin also contains precession‐driven dilution cycles that have been correlated with the sedimentary sequences in the western and eastern Mediterranean despite the lack of a direct connection with the basin. In these regions, Atlantic winter storms have also been invoked to explain the wet phases. In the absence of seasonally‐resolved proxy data, climate simulations at high temporal resolution can be used to investigate the drivers of Mediterranean hydrologic changes both on precessional and seasonal timescales. Here, we use the results of 22 ocean‐atmosphere‐vegetation simulations through an entire late Miocene precession cycle. These show that the African summer monsoon drives the hydrologic budget in the Eastern Mediterranean during precession minima, while the western marginal basins are generally dominated by local net evaporative loss. During precession minima, the western Mediterranean and the Atlantic margin are also influenced by enhanced winter precipitation from the Atlantic storm tracks. We can, therefore, identify two different moisture sources affecting the circum‐Mediterranean area, characterized by the same phasing with respect to precession, but with opposite seasonality. This supports the interregional correlation of geological sections in these areas, as we show for the Messinian and speculate for other time periods

Differential inhibition of human cytomegalovirus (HCMV) by toll-like receptor ligands mediated by interferon-beta in human foreskin fibroblasts and cervical tissue

Human cytomegalovirus (HCMV) can be acquired sexually and is shed from the genital tract. Cross-sectional studies in women show that changes in genital tract microbial flora affect HCMV infection and/or shedding. Since genital microbial flora may affect HCMV infection or replication by stimulating cells through Toll-like receptors (TLR), we assessed the effects of defined TLR-ligands on HCMV replication in foreskin fibroblasts and ectocervical tissue. Poly I:C (a TLR3-ligand) and lipopolysaccharide (LPS, a TLR4-ligand) inhibited HCMV and induced secretion of IL-8 and Interferon-beta (IFNβ) in both foreskin fibroblasts and ectocervical tissue. The anti-HCMV effect was reversed by antibody to IFNβ. CpG (TLR9 ligand) and lipoteichoic acid (LTA, TLR2 ligand) also inhibited HCMV infection in ectocervical tissue and this anti-HCMV effect was also reversed by anti-IFNβ antibody. In contrast, LTA and CpG did not inhibit HCMV infection in foreskin fibroblasts. This study shows that TLR ligands induce an HCMV-antiviral effect that is mediated by IFNβ suggesting that changes in genital tract flora may affect HCMV infection or shedding by stimulating TLR. This study also contrasts the utility of two models that can be used for assessing the interaction of microbial flora with HCMV in the genital tract. Clear differences in the response to different TLR ligands suggests the explant model more closely reflects in vivo responses to genital infections

Age constraints on intra-formational unconformities in Upper Jurassic-Lower Cretaceous carbonates in northeast Turkey; geodynamic and hydrocarbon implications

Upper Jurassic-lowermost Cretaceous carbonate build-ups are imaged on seismic data in the Black Sea. They form important, untested, hydrocarbon reservoirs that are the focus of active exploration. Outcrop analogues to these build-ups around the Black Sea contain a series of subaerial exposure surfaces. The hiatuses associated with a number of these subaerial exposure surfaces have been dated in a well exposed Callovian or Upper Oxfordian to Barremian shallow-water inner platform carbonate succession (the Berdiga Formation) in the Eastern Pontides using strontium isotope stratigraphy and foraminiferal biostratigraphy. They span the latest Kimmeridgian to Tithonian or Berriasian, and the Hauterivian to Barremian. Less well constrained, but broadly contemporaneous stratigraphic gaps in multiple successions around the Black Sea provide additional insights and point to a regional driving mechanism. The timing of hiatus formation does not correspond to periods of eustatic lowstand. It does coincide, however, with Late Tithonian to Berriasian and Hauterivian to Early Aptian episodes of rifting in the Greater Caucasus Basin, located farther to the north. Thus, it is possible that subaerial exposure was caused by rift flank uplift during periods of regional extension. Uplift due to slab break off is discounted as a control because it post-dates (rather than pre-dates) locally developed Kimmeridgian magmatism. Rift-flank uplift is likely to have also affected carbonate build-ups on the intervening rift shoulders of the eastern Black Sea, the Shatskiy Ridge and the Mid Black Sea High. At outcrop, subaerial exposure is often associated with karstification and secondary porosity development. Similar processes may have occurred in the offshore helping to enhance the reservoir quality of these exploration targets