High-resolution upper Pliocene to Pleistocene calcareous nannofossil biostratigraphy in Ocean Drilling Program Hole 1146A in the South China Sea

We established a high-resolution calcareous nannofossil biostratigraphy for the late Pliocene–Pleistocene by analyzing a 242 m-thick, continuous sedimentary succession from Ocean Drilling Program Site 1146, Hole A, in the South China Sea (SCS). A total of 14 calcareous nannofossil datums were detected in the SCS succession. They are, in descending order: first occurrence (FO) of Emiliania huxleyi, last occurrence (LO) of Pseudoemiliania lacunosa, LO of Reticulofenestra asanoi, FO of Gephyrocapsa parallela, FO of R. asanoi, LO of large Gephyrocapsa spp., FO of large G. spp., FO of Gephyrocapsa oceanica, FO of Gephyrocapsa caribbeanica, LO of Calcidiscus macintyrei, LO of Discoaster brouweri, LO of Discoaster pentaradiatus, LO of Discoaster surculus, and LO of Discoaster tamalis. The FO of E. huxleyi was not precisely detected due to poor preservation and dissolution of nannofossils in the underlying strata. We refined the previous calcareous nannofossil biostratigraphy in the SCS by identifying Gephyrocapsa species and four evolutionary extinction events of the genus Discoaster. The proposed calcareous nannofossil biostratigraphy correlates with those reported in other terrestrial and marine areas/sites and global benthic foraminiferal δ18O records. The age–depth curves based on nannofossil biostratigraphy indicate a significant increase in the sedimentation rates at the LO of R. asanoi (0.91–0.85 Ma). The timing of this increase corresponds to reef expansion in the Ryukyu Islands linked to a stepwise increase in Kuroshio Current intensity. This timing is broadly coeval with a sea surface temperature increase of ∼2°C in the northwestern Pacific due to expansion of the Western Pacific Warm Pool towards the north and south subtropical regions. This can be explained by increased weathering and erosion of terrestrial areas in glacial periods and increased rainfall causing higher sediment transport in interglacial periods, which were both linked to Middle Pleistocene Transition-related climatic changes

GRB 091208B: First Detection of the Optical Polarization in Early Forward Shock Emission of a Gamma-Ray Burst Afterglow

We report that the optical polarization in the afterglow of GRB 091208B is measured at t = 149 - 706 s after the burst trigger, and the polarization degree is P = 10.4% +/- 2.5%. The optical light curve at this time shows a power-law decay with index -0.75 +/- 0.02, which is interpreted as the forward shock synchrotron emission, and thus this is the first detection of the early-time optical polarization in the forward shock (rather than that in the reverse shock reported by Steele et al. (2009). This detection disfavors the afterglow model in which the magnetic fields in the emission region are random on the plasma skin depth scales, such as amplified by the plasma instabilities, e.g., Weibel instability. We suggest that the fields are amplified by the magnetohydrodynamic instabilities, which would be tested by future observations of the temporal changes of the polarization degrees and angles for other bursts.Comment: 12 pages, 4 figures, accepted for publication in ApJ Letter

Early phase observations of extremely luminous Type Ia Supernova 2009dc

We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is $\Delta m_{15}(B)=0.65\pm 0.03$, which is one of the slowest among SNe Ia. The peak $V$-band absolute magnitude is $M_{V}=-19.90\pm 0.15$ mag even if the host extinction is $A_{V}=0$ mag. It reaches $M_{V}=-20.19\pm 0.19$ mag for the host extinction of $A_{V}=0.29$ mag as inferred from the observed Na {\sc i} D line absorption in the host. Our $JHK_{s}$-band photometry shows that the SN is one of the most luminous SNe Ia also in near-infrared wavelengths. These results indicate that SN 2009dc belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We estimate the ejected $^{56}$Ni mass of $1.2\pm 0.3$ \Msun for no host extinction case (or 1.6$\pm$ 0.4 M$_{\odot}$ for the host extinction of $A_{V}=0.29$ mag). The C {\sc ii} $\lambda$6580 absorption line keeps visible until a week after maximum, which diminished in SN 2006gz before its maximum brightness. The line velocity of Si {\sc ii} $\lambda$6355 is about 8000 km s$^{-1}$ around the maximum, being considerably slower than that of SN 2006gz, while comparable to that of SN 2003fg. The velocity of the C {\sc ii} line is almost comparable to that of the Si {\sc ii}. The presence of the carbon line suggests that thick unburned C+O layers remain after the explosion. SN 2009dc is a plausible candidate of the super-Chandrasekhar mass SNe Ia

Discovery of a WZ Sge-Type Dwarf Nova, SDSS J102146.44+234926.3: Unprecedented Infrared Activity during a Rebrightening Phase

Several SU UMa-type dwarf novae, in particular, WZ Sge-type stars tend to exhibit rebrightenings after superoutbursts. The rebrightening phenomenon is problematic for the disk instability theory of dwarf novae since it requires a large amount of remnant matter in the disk even after superoutbursts. Here, we report our optical and infrared observations during the first-ever outburst of a new dwarf nova, SDSS J102146.44+234926.3. During the outburst, we detected superhumps with a period of 0.056281 +/- 0.000015 d, which is typical for superhump periods in WZ Sge stars. In conjunction with the appearance of a long-lived rebrightening, we conclude that the object is a new member of WZ Sge stars. Our observations, furthermore, revealed infrared behaviors for the first time in the rebrightening phase of WZ Sge stars. We discovered prominent infrared superhumps. We calculate the color temperature of the infrared superhump source to be 4600-6400 K. These temperatures are too low to be explained with a fully-ionized disk appearing during dwarf nova outbursts. We also found a Ks-band excess over the hot disk component. These unprecedented infrared activities provide evidence for the presence of mass reservoir at the outermost part of the accretion disk. We propose that a moderately high mass-accretion rate at this infrared active region leads to the long-lived rebrightening observed in SDSS J102146.44+234926.3.Comment: 11 pages, 10 figures. Accepted for publication in PAS

Hazardous explosive eruptions of a recharging multi-cyclic island arc caldera

Caldera-forming eruptions of silicic volcanic systems are among the most devastating events on Earth. By contrast, post-collapse volcanic activity initiating new caldera cycles is generally considered less hazardous. Formed after Santorini’s latest caldera-forming eruption of ~1600 bce, the Kameni Volcano in the southern Aegean Sea enables the eruptive evolution of a recharging multi-cyclic caldera to be reconstructed. Santorini’s eruptive record has been documented by onshore products and historical descriptions of mainly effusive eruptions dating back to 197 bce. Here we combine high-resolution seismic reflection data with cored lithologies from International Ocean Discovery Program Expedition 398 at four sites to determine the submarine architecture and volcanic history of intra-caldera deposits from Kameni. Our shore-crossing analysis reveals the deposits of a submarine explosive eruption that produced up to 3.1 km3 of pumice and ash, which we relate to a historical eruption in 726 ce. The estimated volcanic explosivity index of magnitude 5 exceeds previously considered worst-case eruptive scenarios for Santorini. Our finding that the Santorini caldera is capable of producing large explosive eruptions at an early stage in the caldera cycle implies an elevated hazard potential for the eastern Mediterranean region, and potentially for other recharging silicic calderas

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic

Phenotypes of SMA patients retaining SMN1 with intragenic mutation

Background: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by homozygous deletion or intragenic mutation of the SMN1 gene. It is well-known that high copy number of its homologous gene, SMN2, modifies the phenotype of SMN1-deleted patients. However, in the patients with intragenic SMN1 mutation, the relationship between phenotype and SMN2 copy number remains unclear. Methods: We have analyzed a total of 515 Japanese patients with SMA-like symptoms (delayed developmental milestones, respiratory failures, muscle weakness etc.) from 1996 to 2019. SMN1 and SMN2 copy numbers were determined by quantitative polymerase chain reaction (PCR) method and/or multiplex ligation-dependent probe amplification (MLPA) method. Intragenic SMN1 mutations were identified through DNA and RNA analysis of the fresh blood samples. Results: A total of 241 patients were diagnosed as having SMA. The majority of SMA patients showed complete loss of SMN1 (n = 228, 95), but some patients retained SMN1 and carried an intragenic mutation in the retaining SMN1 (n = 13, 5). Ten different mutations were identified in these 13 patients, consisting of missense, nonsense, frameshift and splicing defect-causing mutations. The ten mutations were c.275G > C (p.Trp92Ser), c.819820insT (p.Thr274Tyrfs*32), c.830A > G (p.Tyr277Cys), c.5C > T (p.Ala2Val), c.826 T > C (p.Tyr276His), c.79C > T (p.Gln27*), c.188C > A (p.Ser63*), c.422 T > C (p.Leu141Pro), c.835-2A > G (exon 7 skipping) and c.835-3C > A (exon 7 skipping). It should be noted here that some patients with milder phenotype carried only a single SMN2 copy (n = 3), while other patients with severe phenotype carried 3 SMN2 copies (n = 4). Conclusion: Intragenic mutations in SMN1 may contribute more significantly to clinical severity than SMN2 copy numbers. © 2021 The Japanese Society of Child Neurolog