Simulated retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

Rapid retreat of Greenland's marine-terminating glaciers coincides with regional warming trends, which have broadly been used to explain these rapid changes. However, outlet glaciers within similar climate regimes experience widely contrasting retreat patterns, suggesting that the local fjord geometry could be an important additional factor. To assess the relative role of climate and fjord geometry, we use the retreat history of Jakobshavn Isbræ, West Greenland, since the Little Ice Age (LIA) maximum in 1850 as a baseline for the parameterization of a depth- and width-integrated ice flow model. The impact of fjord geometry is isolated by using a linearly increasing climate forcing since the LIA and testing a range of simplified geometries.We find that the total length of retreat is determined by external factors – such as hydrofracturing, submarine melt and buttressing by sea ice – whereas the retreat pattern is governed by the fjord geometry. Narrow and shallow areas provide pinning points and cause delayed but rapid retreat without additional climate warming, after decades of grounding line stability. We suggest that these geometric pinning points may be used to locate potential sites for moraine formation and to predict the long-term response of the glacier. As a consequence, to assess the impact of climate on the retreat history of a glacier, each system has to be analyzed with knowledge of its historic retreat and the local fjord geometry.</p

The key role of topography in altering North Atlantic atmospheric circulation during the last glacial period

The Last Glacial Maximum (LGM; 21 000 yr before present) was a period of low atmospheric greenhouse gas concentrations, when vast ice sheets covered large parts of North America and Europe. Paleoclimate reconstructions and modeling studies suggest that the atmospheric circulation was substantially altered compared to today, both in terms of its mean state and its variability. Here we present a suite of coupled model simulations designed to investigate both the separate and combined influences of the main LGM boundary condition changes (greenhouse gases, ice sheet topography and ice sheet albedo) on the mean state and variability of the atmospheric circulation as represented by sea level pressure (SLP) and 200-hPa zonal wind in the North Atlantic sector. We find that ice sheet topography accounts for most of the simulated changes during the LGM. Greenhouse gases and ice sheet albedo affect the SLP gradient in the North Atlantic, but the overall placement of high and low pressure centers is controlled by topography. Additional analysis shows that North Atlantic sea surface temperatures and sea ice edge position do not substantially influence the pattern of the climatological-mean SLP field, SLP variability or the position of the North Atlantic jet in the LGM

Eemian Greenland SMB strongly sensitive to model choice

Understanding the behavior of the Greenland ice sheet in a warmer climate, and particularly its surface mass balance (SMB), is important for assessing Greenland's potential contribution to future sea level rise. The Eemian interglacial period, the most recent warmer-than-present period in Earth's history approximately 125&thinsp;000 years ago, provides an analogue for a warm summer climate over Greenland. The Eemian is characterized by a positive Northern Hemisphere summer insolation anomaly, which complicates Eemian SMB calculations based on positive degree day estimates. In this study, we use Eemian global and regional climate simulations in combination with three types of SMB models – a simple positive degree day, an intermediate complexity, and a full surface energy balance model – to evaluate the importance of regional climate and model complexity for estimates of Greenland's SMB. We find that all SMB models perform well under the relatively cool pre-industrial and late Eemian. For the relatively warm early Eemian, the differences between SMB models are large, which is associated with whether insolation is included in the respective models. For all simulated time slices, there is a systematic difference between globally and regionally forced SMB models, due to the different representation of the regional climate over Greenland. We conclude that both the resolution of the simulated climate as well as the method used to estimate the SMB are important for an accurate simulation of Greenland's SMB. Whether model resolution or the SMB method is most important depends on the climate state and in particular the prevailing insolation pattern. We suggest that future Eemian climate model intercomparison studies should include SMB estimates and a scheme to capture SMB uncertainties.</p

Sea Surface Temperature of the mid-Piacenzian Ocean:A Data-Model Comparison

The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction

Detection of ice core particles via deep neural networks

Insoluble particles in ice cores record signatures of past climate parameters like vegetation, volcanic activity or aridity. Their analytical detection depends on intensive bench microscopy investigation and requires dedicated sample preparation steps. Both are laborious, require in-depth knowledge and often restrict sampling strategies. To help overcome these limitations, we present a framework based on Flow Imaging Microscopy coupled to a deep neural network for autonomous image classification of ice core particles. We train the network to classify 7 commonly found classes: mineral dust, felsic and basaltic volcanic ash (tephra), three species of pollen (Corylus avellana, Quercus robur, Quercus suber) and contamination particles that may be introduced onto the ice core surface during core handling operations. The trained network achieves 96.8 % classification accuracy at test time. We present the system’s potentials and limitations with respect to the detection of mineral dust, pollen grains and tephra shards, using both controlled materials and real ice core samples. The methodology requires little sample material, is non destructive, fully reproducible and does not require any sample preparation step. The presented framework can bolster research in the field, by cutting down processing time, supporting human-operated microscopy and further unlocking the paleoclimate potential of ice core records by providing the opportunity to identify an array of ice core particles. Suggestions for an improved system to be deployed within a continuous flow analysis workflow are also presented

Mid-Pliocene Atlantic Meridional Overturning Circulation Not Unlike Modern

In the Pliocene Model Intercomparison Project (PlioMIP), eight state-of-the-art coupled climate models have simulated the mid-Pliocene warm period (mPWP, 3.264 to 3.025 Ma). Here, we compare the Atlantic Meridional Overturning Circulation (AMOC), northward ocean heat transport and ocean stratification simulated with these models. None of the models participating in PlioMIP simulates a strong mid-Pliocene AMOC as suggested by earlier proxy studies. Rather, there is no consistent increase in AMOC maximum among the PlioMIP models. The only consistent change in AMOC is a shoaling of the overturning cell in the Atlantic, and a reduced influence of North Atlantic Deep Water (NADW) at depth in the basin. Furthermore, the simulated mid-Pliocene Atlantic northward heat transport is similar to the pre-industrial. These simulations demonstrate that the reconstructed high-latitude mid-Pliocene warming can not be explained as a direct response to an intensification of AMOC and concomitant increase in northward ocean heat transport by the Atlantic

Regulator of G-protein signaling 5 (RGS5) protein: a novel marker of cancer vasculature elicited and sustained by the tumor’s proangiogenic microenvironment

We previously identified regulator of G-protein signaling 5 (RGS5) among several genes expressed by tumor-derived endothelial cells (EC). In this study, we provide the first in vivo/ex vivo evidence of RGS5 protein in the vasculature of ovarian carcinoma clinical specimens and its absence in human ovaries. Consistent with this, we show higher amounts of Rgs5 transcript in EC isolated from human cancers (as opposed to normal tissues) and demonstrate that expression is sustained by a milieu of factors typical of the proangiogenic tumor environment, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2). Supporting these findings, we show elevated levels of Rgs5 mRNA in the stroma from strongly (as opposed to weakly) angiogenic ovarian carcinoma xenografts and accordingly, we also show more of the protein associated to the abnormal vasculature. RGS5 protein predominantly colocalizes with the endothelium expressing platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31) and to a much lesser extent with perivascular/mural cells expressing platelet-derived growth factor receptor-beta (PDGFR-β) or alpha smooth muscle actin (αSMA). To toughen the relevance of the findings, we demonstrate RGS5 in the blood vessels of other cancer models endowed with a proangiogenic environment, such as human melanoma and renal carcinoma xenografts; to the contrary, it was undetectable in the vasculature of normal mouse tissues. RGS5 expression by the cancer vasculature triggered and retained by the proangiogenic microenvironment supports its exploitation as a novel biomarker and opens the path to explore new possibilities of therapeutic intervention aimed at targeting tumor blood vessels

Mid-Pliocene West African Monsoon Rainfall as simulated in the PlioMIP2 ensemble

International audienceAbstract. The mid-Pliocene warm period (mPWP; ∼3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar to modern geography and ∼400 ppmv atmospheric CO2 concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble, we analyse changes of the WAM rainfall during the mPWP by comparing them with the control simulations for the pre-industrial period. The ensemble shows a robust increase in the summer rainfall over West Africa and the Sahara region, with an average increase of 2.5 mm/d, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara and deepening of the Saharan Heat Low, seen in >90 % of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Though previous studies of future projections indicate a west–east drying–wetting contrast over the Sahel, PlioMIP2 simulations indicate a uniform rainfall increase in that region in warm climates characterized by increasing greenhouse gas forcing. We note that this effect will further depend on the long-term response of the vegetation to the CO2 forcing

Persistence of phylogeographic footprints helps to understand cryptic diversity detected in two marine amphipods widespread in the Mediterranean basin

Amphipods of the genus Gammarus are a vital component of macrozoobenthic communities in European inland and coastal, marine and brackish waters of the Mediterranean and the Black Sea. Exceptional levels of cryptic diversity have been revealed for several widespread freshwater Gammarus species in Europe. No comprehensive assessment has yet been made for brackishwater counterparts, such as Gammarus aequicauda and G. insensibilis, which are among the most widely dispersed members of the so-called “G. locusta group” in the Mediterranean and in the Black Sea. Here we probe the diversity of these morphospecies examining the partitioning of mtDNA and nDNA across multiple populations along their distribution range and discuss it within the regional paleogeographic framework. We gathered molecular data from a collection of 166 individuals of G. aequicauda and G. insensibilis from 47 locations along their distribution range in the Mediterranean including the Black Sea. They were amplified for both mitochondrial COI and 16S rRNA as well as the nuclear 28S rRNA. All five MOTU delimitation methods (ABGD, BIN, bPTP, GMYC single and multiple threshold models) applied revealed deep divergence between Black Sea and Mediterranean populations in both G. aequicauda and G. insensibilis. There were eight distinct MOTUs delimited for G. aequicauda (6–18% K2P) and 4 MOTUs for G. insensibilis (4–14% K2P). No sympatric MOTUs were detected throughout their distribution range. Multimarker time-calibrated phylogeny indicated that divergence of both G. aequicauda and G. insensibilis species complexes started already in the late Oligocene/early Miocene with the split between clades inhabiting eastern and western part of the Mediterranean occurring in both species at the similar time. Our results indicate a high cryptic diversity within Mediterranean brackishwater Gammarus, similar to that observed for freshwater counterparts. Moreover, the phylogenetic history combined with the current geographic distribution indicate that the evolution of botThis work was supported by Polish National Science Center (projects no. 2014/15/B/NZ8/00266 and 2015/17/N/NZ8/01628) and partially by the statutory funds of the Department of Invertebrate Zoology and Hydrobiology of University of Lodz. F. Costa and the University of Minho contribution was supported by the strategic programme UID/BIA/04050/2013 (POCI-01-0145-FEDER-007569) funded by national funds through the FCT I.P. and by the ERDF through the COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI). There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Atlantic Deep-water Response to the Early Pliocene Shoaling of the Central American Seaway

The early Pliocene shoaling of the Central American Seaway (CAS), ~4.7–4.2 million years ago (mega annum-Ma), is thought to have strengthened Atlantic Meridional Overturning Circulation (AMOC). The associated increase in northward flux of heat and moisture may have significantly influenced the evolution of Pliocene climate. While some evidence for the predicted increase in North Atlantic Deep Water (NADW) formation exists in the Caribbean and Western Atlantic, similar evidence is missing in the wider Atlantic. Here, we present stable carbon (δ13C) and oxygen (δ18O) isotope records from the Southeast Atlantic-a key region for monitoring the southern extent of NADW. Using these data, together with other δ13C and δ18O records from the Atlantic, we assess the impact of the early Pliocene CAS shoaling phase on deep-water circulation. We find that NADW formation was vigorous prior to 4.7 Ma and showed limited subsequent change. Hence, the overall structure of the deep Atlantic was largely unaffected by the early Pliocene CAS shoaling, corroborating other evidence that indicates larger changes in NADW resulted from earlier and deeper shoaling phases. This finding implies that the early Pliocene shoaling of the CAS had no profound impact on the evolution of climate