Precessing cylinders at the second and third resonance: Turbulence controlled by geostrophic flow

Copyright © 2015 American Physical SocietyWe investigate, via both asymptotic analysis and direct numerical simulation, precessionally driven flow of a homogeneous fluid confined in fluid-filled circular cylinders that rotate rapidly about their symmetry axis and precess about a different axis and that are marked by radius-height aspect ratios Γ=1.045945 and Γ=1.611089 . At these radius-height aspect ratios, the Poincaré force resonates directly with the two special inertial modes that have the simplest vertical structure. An asymptotic analytical solution in closed form describing weakly precessing flow is derived in the mantle frame of reference for asymptotically small Ekman numbers, showing quantitative agreement with the result of direct nonlinear numerical simulation. Our numerical simulation makes use of a finite-element method with the three-dimensional tetrahedralization of a cylindrical cavity that allows the construction of dense nodes in the vicinity of the bounding surface of the cavity for resolving the thin viscous boundary layer. It is found that axisymmetric geostrophic flow in the alternating eastward and westward direction can be generated and maintained by nonlinear and viscous effects in the viscous boundary layer. It is also found that, when the precessing rate is moderate and, consequently, the geostrophic flow is weak, nonlinear interaction between the resonant inertial mode and the nonesonant inertial modes driven by the Poincaré force and the boundary-layer influx leads to strongly turbulent flow with irregular temporal-spatial fluctuation. When the cylinders are strongly precessing such that the geostrophic flow becomes predominant, however, the effect of the geostrophic flow controls/stabilizes its nonlinear dynamics, leading to weakly turbulent flow that can be largely described by a dominant quasisteady geostrophic component and a weak nonaxisymmetric component localized in the region where the geostrophic flow is weak.Leverhulme TrustMacau FDCTNSF

Testing the mantle plume hypothesis: An IODP effort to drill into the Kamchatka-Okhotsk Sea system

The great mantle plume debate (GPD) has been going on for ∼15 years (Foulger and Natland, 2003; Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006), centered on whether mantle plumes exist as a result of Earth’s cooling or whether their existence is purely required for convenience in explaining certain Earth phenomena (Niu, 2005). Despite the mounting evidence that many of the so-called plumes may be localized melting anomalies, the debate is likely to continue. We recognize that the slow progress of the debate results from communication difficulties. Many debaters may not truly appreciate (1) what the mantle plume hypothesis actually is, and (2) none of the petrological, geochemical and geophysical methods widely used can actually provide smoking-gun evidence for or against mantle plume hypothesis. In this short paper, we clarify these issues, and elaborate a geologically effective approach to test the hypothesis. According to the mantle plume hypothesis, a thermal mantle plume must originate from the thermal boundary layer at the core-mantle boundary (CMB), and a large mantle plume head is required to carry the material from the deep mantle to the surface. The plume head product in ocean basins is the oceanic plateau, which is a lithospheric terrane that is large (1000’s km across), thick (>200 km), shallow (2–4 km high above the surrounding seafloors), buoyant (∼1% less dense than the surrounding lithosphere), and thus must be preserved in the surface geology (Niu et al., 2003). The Hawaiian volcanism has been considered as the surface expression of a type mantle plume, but it does not seem to have a (known) plume head product. If this is true, the Hawaiian mantle plume in particular and the mantle plume hypothesis in general must be questioned. Therefore, whether there is an oceanic plateau-like product for the Hawaiian volcanism is key to testing the mantle plume hypothesis, and the Kamchatka-Okhotsk Sea basement is the best candidate to find out if it is indeed the Hawaiian mantle plume head product or not (Niu et al., 2003; Niu, 2004)

Metamorphic core complexes vs. synkinematic plutons in continental extension setting: insights from key structures (Shandong Province, eastern China)

International audienceContinental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust. Though a Metamorphic Core Complex (MCC) reveals a much stronger crustal extension than a synkinematic pluton, the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations. In eastern Asia, a major continental extensional event occurred during Mesozoic and early Cenozoic times. The resulting various extensional events described in previous studies consist in large intracontinental basins, important volcanism, emplacement of plutons in the upper-crust and exhumation of MCCs. An efficient description of MCCs and plutons in eastern Asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations. In that way, an integrated structural and geophysical study has been realized to precisely discriminate the structure in the Jiaodong Peninsula (Shandong Province, eastern China), previously regarded as simple sheared plutons. A succession of three main stages have been identified all pertaining to a NW-SE extensional setting: (1) the exhumation of the Late Jurassic-Early Cretaceous Linglong MCC below the SE-dipping Linglong detachment fault, (2) the emplacement of the Guojialing syntectonic pluton below the N-dipping extensional Guojialing intracrustal shear zone (130-124 Ma) and (3) a penetrative brittle normal faulting associated with gold mineralizations (not, vert, similar120 Ma). As a result, the maximum amount of extension in Jiaodong Peninsula, characterized by partially-melted lower to middle crust upward into the Linglong MCC should be revised to Late Jurassic-Early Cretaceous period

Autotransplantation of Inferior Parathyroid glands during central neck dissection for papillary thyroid carcinoma: A retrospective cohort study

AbstractIntroduction: The management of inferior parathyroid glands during central neck dissection (CND) for papillary thyroid carcinoma (PTC) remains controversial. Most surgeons preserve inferior parathyroid glands in situ. Autotransplantation is not routinely performed unless devascularization or inadvertent parathyroidectomy occurs. This retrospective study aimed to compare the incidence of postoperative hypoparathyroidism and central neck lymph node (CNLN) recurrence in patients with PTC who underwent inferior parathyroid glands autotransplantation vs preservation in situ. Methods: This is a retrospective study which was conducted in a tertiary referral hospital. A total of 477 patients with PTC (pN1) who underwent total thyroidectomy (TT) and bilateral CND with/without lateral neck dissection were included. Patients' demographical characteristics, tumor stage, incidence of hypoparathyroidism, CNLN recurrence and the number of resected CNLN were analyzed. Results: Three hundred and twenty-one patients underwent inferior parathyroid glands autotransplantation (autotransplantation group). Inferior parathyroid glands were preserved in situ among 156 patients (preservation group). Permanent hypoparathyroidism rate was 0.9% (3/321) versus 3.8% (6/156) respectively (p = 0.028). Mean numbers of resected CNLN were 15 ± 3 (6–23) (autotransplantation group) versus 11 ± 3 (7–21) (preservation group) (p < 0.001). CNLN recurrence rate was 0.3% (1/321) versus 3.8% (6/156) respectively (p = 0.003). Conclusion: Inferior parathyroid glands autotransplantation during CND of PTC (pN1) might reduce permanent hypoparathyroidism and CNLN recurrence. Further study enrolling more patients with long-term follow-up is needed to support this conclusion

Origin of microbial biomineralization and magnetotaxis during the Archean

Microbes that synthesize minerals, a process known as microbial biomineralization, contributed substantially to the evolution of current planetary environments through numerous important geochemical processes. Despite its geological significance, the origin and evolution of microbial biomineralization remain poorly understood. Through combined metagenomic and phylogenetic analyses of deep-branching magnetotactic bacteria from the Nitrospirae phylum, and using a Bayesian molecular clock-dating method, we show here that the gene cluster responsible for biomineralization of magnetosomes, and the arrangement of magnetosome chain(s) within cells, both originated before or near the Archean divergence between the Nitrospirae and Proteobacteria. This phylogenetic divergence occurred well before the Great Oxygenation Event. Magnetotaxis likely evolved due to environmental pressures conferring an evolutionary advantage to navigation via the geomagnetic field. Earth’s dynamo must therefore have been sufficiently strong to sustain microbial magnetotaxis in the Archean, suggesting that magnetotaxis coevolved with the geodynamo over geological time

Palaeomagnetic constraints from granodioritic plutons (Jiaodong Peninsula): New insights on Late Mesozoic continental extension in eastern Asia.

International audienceMechanism and kinematics of the Late Mesozoic continental extension event of eastern Asia are still debated. In order to better constrain its evolution, two granodioritic plutons of the Jiaodong Peninsula have been chosen as targets for a time-constrained palaeomagnetic study. Indeed, plutons are devoid of visible deformation, did not experience rotation along horizontal axis and are precisely dated by U/Pb and 40Ar/39Ar methods. Multidomain (MD) magnetite has been identified as the principal magnetic remanent carrier. The interpolation of existing and new U/Pb and 40Ar/39Ar ages revealed that characteristic remanent magnetisation was acquired in a narrow range of 116 ± 2 Ma. Twenty out of 27 sites present stable magnetic directions calculated from high-temperature or high-coercive components. The observations of the solo normal magnetic polarity for this palaeomagnetic collection and of the magnetic remanent age consistent with the Cretaceous Normal Superchron (CNS) argue that the characteristic magnetic remanence may be considered as primary. Detailed field observations of the intrusive relationship between the plutons and country rocks and Anisotropy of Magnetic Susceptibility (AMS) study reveal the absence of the subsequent deformation of plutons, or rigid rotation of plutons along a horizontal axis. Two palaeomagnetic poles have been therefore calculated from these plutons. Among 12 out 15 Cretaceous palaeomagnetic poles, including the two new poles provided by this study, from the Jiaodong Peninsula and on both sides of Tan-Lu and Muping-Jimo faults are statistically consistent. As a result, the Jiaodong Peninsula behaved as a rigid block as internal deformation appears negligible. The remaining three derived poles are probably due to the secular variation or/and the vicinity of fault zones near of the palaeomagnetic sampling site. Thus, they can not be applied to the peninsula-scaled tectonics. Comparison of these time52 constrained Cretaceous palaeomagnetic results of the Jiaodong Peninsula with those of North China Block (NCB) indicate that the Jiaodong Peninsula was rigidly attached to NCB since, 3 at least, the Cretaceous as residual difference is clearly insignificant with respect to the error brackets. These new palaeomagnetic results confirm that the relative clockwise (CW) rotation of Eastern Liaoning-Korea Block (ELKB) with respect to NCB does not affect the Jiaodong Peninsula as a rigid block, nevertheless, some tectonic structures have been reactivated since Cenozoic and local rotations could be produced. This palaeomagnetic study reveals that the Late Mesozoic extension in Eastern Asia is heterogeneously expressed in time and space. The complete understanding of the mechanism(s) of this extensional event needs further multidisciplinary investigations

Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China

Global and regional environmental changes have influenced the evolutionary processes of hominoid primates, particularly during the Miocene. Recently, a new Lufengpithecus cf. lufengensis hominoid fossil with a late Miocene age of ~6.2 Ma was discovered in the Shuitangba (STB) section of the Zhaotong Basin in Yunnan on the southeast margin of the Tibetan Plateau. To understand the relationship between paleoclimate and hominoid evolution, we have studied sedimentary, clay mineralogy and geochemical proxies for the late Miocene STB section (~16 m thick; ca. 6.7–6.0 Ma). Our results show that Lufengpithecus cf. lufengensis lived in a mildly warm and humid climate in a lacustrine or swamp environment. Comparing mid to late Miocene records from hominoid sites in Yunnan, Siwalik in Pakistan, and tropical Africa we find that ecological shifts from forest to grassland in Siwalik are much later than in tropical Africa, consistent with the disappearance of hominoid fossils. However, no significant vegetation changes are found in Yunnan during the late Miocene, which we suggest is the result of uplift of the Tibetan plateau combined with the Asian monsoon geographically and climatically isolating these regions. The resultant warm and humid conditions in southeastern China offered an important refuge for Miocene hominoids

Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia

The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8 ka and decrease at ~5.9 ka in Dali Lake coincided respectively with the onset and termination of the HWP, and are respectively linked to increased nutrient supply due to postglacial warming and poor nutrition due to drying at ~6 ka in the Asian interior. The two-stage transition at ~7.7 ka correlates well with increased organic carbon in middle HWP and suggests that improved climate conditions, leading to high quality nutrient influx, fostered magnetofossil proliferation. Our findings represent an excellent lake record in which magnetofossil abundance is, through nutrient availability, controlled by insolation driven climate changes.This research was supported by the NSFC grant 41330104 and the 973 program grant 2012CB821900. J.X. was supported by the 973 program grant 2010CB833400 and the NSFC grant 41130101. J.L. received support from the NSFC grant 41374004. C.D. acknowledges further support from the NSFC grant 40925012 and the CAS Bairen Program