No abstract

A femtosecond KrF excimer laser is focused into molecular hydrogen to generate a multifrequency laser beam, consisting of many vibrational and rotational lines, in a transient Raman regime. The intensity distribution is unchanged from 5 to 13 atm, in contrast to the case of nanosecond laser pump. The efficiency for generation of the rotational lines is improved by increasing the peak power, especially at longer wavelengths, indicating power-dependent and wavelength-dependent behavior of this effect, as expected from theory.

Marinoan snowball Earth offers us a set of sedimentary and geochemical records for exploring glacial isostatic adjustment (GIA) associated with one of the most severe glaciations in Earth history. An accurate prediction of GIA‐based relative sea level (RSL) change associated with a snowball Earth meltdown will help to explore sedimentary records for RSL changes and to place independent constraints on mantle viscosity and on the durations of syndeglaciation (Td) and cap carbonate deposition. Here we mainly examine postdeglacial RSL change characterized by an RSL drop and a resumed transgression inferred from the cap dolostones on the continental shelf in south China. Such a nonmonotonic RSL behavior may be a diagnostic GIA signal for the Marinoan deglaciation resulting from a significantly longer postdeglacial GIA response than that for the last deglaciation. A postdeglacial RSL drop followed by transgression in south China, which is significantly affected by Earth's rotation, is predicted over the continental shelf for models with Td ≤ 20 kyr and a deep mantle viscosity of ~5 × 1022 Pa s regardless of the upper mantle viscosity. The inferred GIA model also explains the postdeglacial RSL changes such as sedimentary‐inferred RSL drops on the continental shelf in northwestern Canada and California at low‐latitude regions insignificantly affected by Earth's rotation. Furthermore, the good match between the predicted and observed RSL changes in south China suggests an approximate duration of ~50 kyr for the Marinoan 17O depletion event, an atmospheric event linked to the post‐Marinoan drawdown of CO2 and the concurrent rise of O2.

No abstract

<p>Geodetic and geomorphological observations in the Antarctic coastal area generally indicate the uplift trend associated with the Antarctic Ice Sheet (AIS) change since the Last Glacial Maximum (LGM). The melting models of AIS derived from the comparisons between sea-level and geodetic observations and glacial isostatic adjustment (GIA) modeling show the monotonous retreat through the Holocene era (e.g., Whitehouse et al., 2012, <em>QSR</em>; Stuhne and Peltier, 2015, <em>JGR</em>). However, the observed crustal motion by GNSS in some regions of Antarctica cannot be explained as the deformation rates by only glacial rebound due to the last deglaciation of AIS (e.g., Bradley et al., 2015, <em>EPSL</em>). One reason for this mismatch is considered as the control of the uplift induced by the re-advance of AIS following a post-LGM maximum retreat, which was recently reported as the West AIS re-advance in the Ross and the Weddell Sea sectors (e.g., Kingslake et al., 2018, <em>Nature</em>).</p><p>On the other hand, the current crustal motion includes the elastic GIA component due to the present-day surface mass balance of AIS. To reveal the secular crustal movement induced by GIA, the separation of the elastic deformation induced by the current mass balance using GRACE data is essential. In the Lützow-Holm Bay, East Antarctica, GNSS observations have been carried out at several sites on the outcrop rocks since the 1990s to monitor recent crustal movements. Hattori et al. (2019, <em>SCAR</em>) precisely analyzed the GNSS data obtained from this area, which revealed the secular crustal movement by correcting the elastic deformation due to current mass balance. The results indicated the mismatch between secular current crustal motion and GIA calculations based on the previously published ice and viscosity models. Consequently, to represent the observed crustal deformation rates based on the GIA modeling, we must carefully investigate the numerical dependencies of various parameters such as local and global ice history in the AIS.</p><p>Recently, the study of glacial geomorphology and surface exposure dating (Kawamata et al., 2020, <em>QSR</em>) has suggested that the abrupt ice thinning and retreat occurred in Skarvsnes, located at the middle of the Lützow-Holm Bay, during 9 to 6 ka. We obtained the preliminary results related to the GIA effects induced by the abrupt thinning on the geodetic observations in this area. The numerical simulations that we examined are employed for a simple ice model with the thickness change by 400 m during 9 to 6 ka in this area based on the IJ05_R2 model grids (Ivins et al., 2013, <em>JGR</em>). The predictions based on the high-viscosity upper mantle (5x10<sup>20</sup> Pa s) show high uplift rates (~ +4.0 mm/yr), whereas the calculated uplift rates for the weaker viscosity (2x10<sup>20</sup> Pa s) show low value (~ +1.0 mm/yr). These results suggest that the viscoelastic relaxation due to the abrupt ice thinning in the mid-to-late Holocene may influence the current crustal motion and highly depend on the upper mantle viscosity profile. We will discuss the influences on the GIA-calculated crustal movement by AIS retreat history and mantle viscosity structure.</p>