Multi-proxy speleothem-based reconstruction of mid-MIS 3 climate in South Africa

The southern coast of South Africa displays a highly dynamical climate as it is at the convergence of the Atlantic and Indian oceans, and it is located near the subtropical/temperate zone boundary with seasonal influence of easterlies and westerlies. The region hosts some key archeological sites with records of significant cognitive, technological and social developments. Reconstructions of the state and variability of past climate and environmental conditions around sites of archeological significance can provide crucial context for understanding the evolution of early humans. Here we present a short but high-resolution record of hydroclimate and temperature in South Africa. Our reconstructions are based on trace elements, calcite and fluid inclusion stable isotopes, as well as fluid inclusion microthermometry, from a speleothem collected in Bloukrantz cave, in the De Hoop Nature Reserve in the southern Cape region of South Africa. Our record covers the time period from 48.3 to 45.2 ka during marine isotope stage 3. Both δ18Oc and δ13Cc show strong variability and covary with Sr/Ca. This correlation suggests that the control on these proxies originates from internal cave processes such as prior carbonate precipitation, which we infer to be related to precipitation amount. The hydroclimate indicators furthermore suggest a shift towards overall drier conditions after 46 ka, coincident with cooling in Antarctica and drier conditions in the eastern part of South Africa corresponding to the summer rainfall zone (SRZ). Fluid inclusion-based temperature reconstructions show good agreement between the oxygen isotope and microthermometry methods, and results from the latter display little variation throughout the record, with reconstructed temperatures close to the present-day cave temperature of 17.5 ∘C. Overall, the BL3 speleothem record thus suggests relatively stable temperature from 48.3 to 45.2 ka, whereas precipitation was variable with marked drier episodes on sub-millennial timescales.</p

Radiomic analysis of MRI to Predict Sustained Complete Response after Radiofrequency Ablation in Patients with Hepatocellular Carcinoma - A Pilot Study

OBJECTIVES: To investigate whether quantitative textural features, extracted from pretreatment MRI, can predict sustained complete response to radiofrequency ablation (RFA) in patients with hepatocellular carcinoma (HCC). METHODS: In this IRB-approved study, patients were selected from a maintained six-year database of consecutive patients who underwent both pretreatment MRI imaging with a probable or definitive imaging diagnosis of HCC (LI-RADS 4 or 5) and loco-regional treatment with RFA. An experienced radiologist manually segmented the hepatic nodules in MRI arterial and equilibrium phases to obtain the volume of interest (VOI) for extraction of 107 quantitative textural features, including shape and first- and second-order features. Statistical analysis was performed to evaluate associations between textural features and complete response. RESULTS: The study consisted of 34 patients with 51 treated hepatic nodules. Sustained complete response was achieved by 6 patients (4 with single nodule and 2 with multiple nodules). Of the 107 features from the arterial and equilibrium phases, 20 (18%) and 25 (23%) achieved AUC &gt;0.7, respectively. The three best performing features were found in the equilibrium phase: Dependence Non-Uniformity Normalized and Dependence Variance (both GLDM class, with AUC of 0.78 and 0.76, respectively) and Maximum Probability (GLCM class, AUC of 0.76). CONCLUSIONS: This pilot study demonstrates that a radiomic analysis of pre-treatment MRI might be useful in identifying patients with HCC who are most likely to have a sustained complete response to RFA. Second-order features (GLDM and GLCM) extracted from equilibrium phase obtained highest discriminatory performance

Characterization and Correction of Evaporative Artifacts in Speleothem Fluid Inclusion Isotope Analyses as Applied to a Stalagmite From Borneo

Abstract Fluid inclusion water isotope measurements in speleothems have great potential for paleoclimate studies as they enable the reconstruction of precipitation dynamics and land temperatures. Several previous observations, however, suggest that inclusion waters do not always reflect the isotopic composition of surface precipitation. In such cases, dripwaters are thought to be modified by evaporation in the cave environment that results in more positive δ2H and δ18O values and shallow δ2H/δ18O slopes. Although evaporation can occur in cave systems, water can also be lost to evaporation during analysis but before water extraction. Here, we examine the likelihood of this possibility with a stalagmite from Borneo. We demonstrate that many samples lose water, and that water loss is controlled by the type and size of inclusions. With multiple replicate measurements of coeval samples, we calculate an evaporative δ2H/δ18O slope of 1.0 ± 0.6 (2SE). This value is consistent with model predictions of evaporative fractionation at high analytical temperature and low humidity. Finally, we propose a method to correct for this effect. We find that fluid–calcite δ18O paleotemperatures calculated with corrected δ18O data show excellent agreement with recent microthermometry temperature estimates for Borneo, supporting the validity of our approach and implying limited stalagmite δ18O disequilibrium variations. Corrected fluid inclusion δ18O and δ2H values follow the expected hydroclimate response of Borneo to periods of reduced Atlantic Ocean meridional overturning circulation. Our results suggest that careful petrographic examination and multiple replicate measurements are necessary for reliable paleoclimate reconstructions with speleothem fluid inclusion water isotopes

Radiogenic isotope (Nd, Pb, Sr) signatures of surface and sea ice-transported sediments from the Arctic Ocean under the present interglacial conditions

Under modern conditions, sediments from the large continental shelves of the Arctic Ocean are mixed by currents, incorporated into sea ice and redistributed over the Arctic Basin through the Beaufort Gyre and Trans-Polar Drift major sea-ice routes. Here, compiling data from the literature and combining them with our own data, we explore how radiogenic isotopes (Sr, Pb and Nd) from Arctic shelf surface sediment can be used to identify inland and coastal sediment sources. Based on discriminant function analyses, the use of two-isotope systematics introduces a large uncertainty (ca. 50%) that prevents unequivocal identifications of regional shelf signatures. However, when using all three isotopic systems, shelf provinces can be distinguished within a ca. 23% uncertainty only, which is mainly due to isotopic overlaps between the Canadian Arctic Archipelago and the Barents–Kara seas areas. Whereas the Canadian Arctic shelf seems mostly influenced by Mackenzie River supplies, as documented by earlier studies, a clear Lena River signature cannot be clearly identified in the Laptev–Kara seas area. The few available data on sediments collected in sea-ice rafts suggest sea ice originating mostly from the Laptev Sea area, along with non-negligible contributions from the East Siberian and Kara seas. At last, whereas a clear radiogenic identity of the Mackenzie River in sediments can be identified in the Beaufort Sea margin, isotopic signatures from major Russian rivers cannot be deciphered in modern Siberian margin sediments because of an intense mixing by sea ice and currents of inland and coastal supplies