The incised valley of Baffin Bay,Texas: a tale of two climates

Baffin Bay, Texas is the flooded Last Glacial Maximum incised valley of the Los Olmos, San Fernando and Petronila Creeks along the north‐western Gulf of Mexico. Cores up to 17 m in length and high‐resolution seismic profiles were used to study the history of Baffin Bay over the last 10 kyr and to document the unusual depositional environments within the valley fill. The deposits of the Baffin Bay incised valley record two major and two minor events. Around 8·0 ka, the estuarine environments backstepped more than 15 km in response to an increase in the rate of sea‐level rise. Around 5·5 ka, these estuarine environments changed from environments similar to other estuaries of the northern Gulf of Mexico to the unusual suite of environments found today. Another minor flooding event occurred around 4·8 ka in which several internal spits were flooded. Some time after 4·0 ka, the upper‐bay mud‐flats experienced a progradational event. Because of its semi‐arid climate and isolation from the Gulf of Mexico, five depositional environments not found in the other incised‐valley fills of the northern Gulf of Mexico are found today within Baffin Bay. These deposits include well‐laminated carbonate and siliciclastic open‐bay muds, ooid beaches, shelly internal spits and barrier islands, serpulid worm‐tube reefs and prograding upper‐bay mud‐flats. Based on these unusual deposits, and other characteristics of Baffin Bay, five criteria are suggested to help identify incised valleys that filled in arid and semi‐arid climates. These criteria include the presence of: (i) hypersaline‐tolerant fauna; (ii) aeolian deposits; and (iii) carbonate and/or evaporite deposits; and the absence of: (iv) peat or other organic‐rich deposits in the upper bay and bay‐margin areas; and (v) well‐developed fluvially dominated bayhead deltas.     

Noble gases in enstatite chondrites released by stepped crushing and heating

Abstract– Enstatite chondrites (ECs) were subjected to noble gas analyses using stepped crushing and pyrolysis extraction methods. ECs can be classified into subsolar gas‐carrying and subsolar gas‐free ECs based on the ³⁶Ar/⁸⁴Kr/¹³²Xe ratios. For subsolar gas‐free ECs, elemental ratios, and Xe isotopic compositions indicate that Q gas is the dominant trapped component, the Q gas concentration can be correlated with the petrologic type, reasonably explained by gas release from a common EC parental material during subsequent heating. Atmospheric Xe with sub‐Q elemental ratios is found in Antarctic E3s at 600–800 °C and through crushing. The ¹³²Xe released in these fractions accounts for 30–60% of the bulk concentrations. Hence, the sub‐Q signature is generally due to contamination of elementally fractionated atmosphere. Subsolar gas is mainly released (up to 78% of the bulk ³⁶Ar) at 1300–1600 °C and through crushing, suggesting that enstatite and friable phases are the host phases. Subsolar gas is isotopically identical to solar gas, but elementally fractionated. These observations are consistent with a previous study, which suggested that subsolar gas could be fractionated solar wind having been implanted into chondrule precursors ( Okazaki et al. 2001 ). Unlike subsolar gas‐free ECs, the primordial gas concentrations of subsolar gas‐carrying ECs are not simply correlated with the petrologic type. It is inferred that subsolar gas‐rich chondrules were heterogeneously distributed in the solar nebula and accreted to form subsolar gas‐carrying ECs. Subsequent metamorphic and impact‐shock heating events have affected noble gas compositions to various degrees.     

The critical stage for inducing oviparity and embryonic diapause in parthenogenetic Artemia(Crustacea: Anostraca): an experimental study

The brine shrimp Artemia exhibits two reproductive modes: 1) oviparity, producing diapause embryos;and 2) ovoviviparity, producing free-swimming nauplii. Previous studies have suggested the existence of a critical stage that determines the reproductive mode. Physicochemical factors, such as photoperiod, temperature, and salinity, have been suggested to irreversibly aff ect the reproductive mode of oocytes during this critical stage. In this study, experiments were carried out using a photoperiod and temperature-sensitive parthenogenetic Artemia clone where maternal Artemia were shifted bidirectionally between ovoviviparity (18 h L:6 h D, 27℃) and oviparity (6 h L:18 h D, 19℃) culture conditions. In the main experiment ( Artemia shifted at six diff erent stages including the post-larva Ⅱ to adult Ⅱ), the reproductive mode of fi rst brood was converted when shifting was performed on post-larva Ⅱ and Ⅲ but was not converted when females were shifted after post-larva Ⅲ. A supplementary experiment further revealed that the reproductive mode of fi rst brood could be altered when shifting females at an "early phase of postlarva Ⅳ", characterized by a developing ovisac reaching the middle of the third abdominal segment, ventral spines, and some oocytes growing larger than the others. In both experiments, reproductive modes of the second brood were signifi cantly aff ected when the shifting was performed on post-larva Ⅳ. These results suggest that the critical stage for inducing oviparity and embryonic diapause is at the previtellogenic stage of oocytes, or at maternal "early phase of post-larva Ⅳ" for the first-brood off spring. During this stage, diff erential gene expression patterns of the two destined oocytes may be triggered by the token stimuli signals received by the oocytes.     

Hayabusa‐returned sample curation in the Planetary Material Sample Curation Facility of JAXA

Abstract– The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa‐returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round‐trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses.     

Acid‐susceptive material as a host phase of argon‐rich noble gas in the carbonaceous chondrite Ningqiang

Abstract— A fine‐grained dark inclusion in the Ningqiang carbonaceous chondrite consists of relatively pristine solar nebular materials and has high concentrations of heavy primordial rare gases. Trapped 36Ar concentration amounts to 6 times 10^?6 cc STP/g, which is higher than that of Ningqiang host by a factor of three. Light HF‐HCl etching of the dark inclusion removed 86, 73, and 64% of the primordial ³⁶Ar, ⁸⁴Kr, and ¹³²Xe, respectively. Thus, the majority of the noble gases in this inclusion are located in very acid‐susceptive material. Based on the elemental composition, the noble gases lost from the dark inclusion during the acid‐treatments are Ar‐rich, and the noble gases remaining in the inclusion are Q and HL gases. Transmission electron microscopy showed that the acid treatments removed thin Si, Mg, and Fe‐rich amorphous rims present around small olivine and pyroxene grains in the dark inclusion, suggesting that the Ar‐rich gases reside in the amorphous layers. A possible origin of the Ar‐rich gases is the acquisition of noble‐gas ions with a composition fractionated relative to solar abundance favoring the heavy elements by the effect of incomplete ionization under plasma conditions at 8000 K electron temperature.     

Thermal history of the enstatite chondrites from silica polymorphs

Abstract— Here we report the results of our petrologic and mineralogical study of enstatite (E) chondrites in order to explore their thermal histories. We studied silica phases in 20 E chondrites by laser micro Raman spectroscopy to determine the silica polymorphs they contain. Silica phases are commonly present in E chondrites and their polymorphs reflect the physical conditions of formation. The samples studied here include EH3–5, EL3–6, E chondrite melt rocks, and an anomalous E chondrite. We identified quartz, tridymite, cristobalite, and silica glass in the samples studied. EH4–5 and EH melt rocks are divided into high and low temperature classes based on niningerite‐alabandite solid solutions. EH3, EL3, and some EH melt rocks of the high temperature class contain tridymite and cristobalite. We suggest that tridymite and cristobalite crystallized in chondrules and E chondrite melts, followed by rapid cooling, leading to the survival of these silica polymorphs. EH4 and EL4 chondrites also contain tridymite and cristobalite in their chondrules, indicating that these silica polymorphs survived low temperature metamorphism (as estimated from opaque mineral geothermometers) because of the sluggishness of the transition to a more stable polymorph. Tridymite and cristobalite in EL6 chondrites reflect the high temperature processes experienced by these meteorites. On the other hand, some EH5 chondrites and EH melt rocks of the low temperature class contain quartz, which may be a product of the transition from tridymite or cristobalite during a long period of low temperature metamorphism. Although the thermal history of E chondrites have been previously estimated from opaque minerals, such compositions mainly reflect low temperature processes. However, we can reconstruct the primordial thermal processes and subsequent cooling histories of E chondrites from their silica polymorphs. The E chondrites have complicated thermal histories, which produced the observed variations among them.     

The critical stage for inducing oviparity and embryonic diapause in parthenogenetic Artemia(Crustacea: Anostraca): an experimental study

The brine shrimp Artemia exhibits two reproductive modes:1)oviparity,producing diapause embryos;and 2)ovoviviparity,producing free-swimming nauplii.Previous studies have suggested the existence of a critical stage that determines the reproductive mode.Physicochemical factors,such as photoperiod,temperature,and salinity,have been suggested to irreversibly affect the reproductive mode of oocytes during this critical stage.In this study,experiments were carried out using a photoperiod and temperature-sensitive parthenogenetic Artemia clone where maternal Artemia were shifted bidirectionally between ovoviviparity(18 h L:6 h D,27℃)and oviparity(6 h L:18 h D,19℃)culture conditions.In the main experiment(Artemia shifted at six different stages including the post-larva Ⅱ to adult Ⅱ),the reproductive mode of first brood was converted when shifting was performed on post-larva II and III but was not converted when females were shifted after post-larva Ⅲ.A supplementary experiment further revealed that the reproductive mode of first brood could be altered when shifting females at an "early phase of postlarva Ⅳ",characterized by a developing ovisac reaching the middle of the third abdominal segment,ventral spines,and some oocytes growing larger than the others.In both experiments,reproductive modes of the second brood were significantly affected when the shifting was performed on post-larva Ⅳ.These results suggest that the critical stage for inducing oviparity and embryonic diapause is at the previtellogenic stage of oocytes,or at maternal "early phase of post-larva Ⅳ" for the first-brood offspring.During this stage,differential gene expression patterns of the two destined oocytes may be triggered by the token stimuli signals received by the oocytes.