Geophysical Research Letters
ISSN / EISSN : 0094-8276 / 1944-8007
Published by: American Geophysical Union (AGU) (10.1029)
Total articles ≅ 42,700
Latest articles in this journal
Geophysical Research Letters; https://doi.org/10.1029/2021gl094366
The equatorial Pacific Warm-Water-Volume (WWV) and western equatorial Pacific WWV (WWVw) are two important long-lead time El Nin∼o–Southern Oscillation (ENSO) event precursors. Here we utilize the recharge-discharge oscillator framework to obtain the analytical solution of WWV and WWVw lead times to ENSO sea surface temperatures (SSTs). Both WWV and WWVw lead times show a strong dependence on the inherent ENSO periodicity, whereas WWV lead time is further modulated by the air-sea coupling strength and ENSO SST spatial pattern. The derived solution is able to explain observed decadal variations in lead times of WWV to SST in terms of variations in ENSO periodicity and air-sea coupling strength.
Geophysical Research Letters; https://doi.org/10.1029/2021gl093738
The contributions of phytoplankton and bacteria cells to alkalinity (AT) were measured in seawater samples obtained from 205 locations including the East Sea, the North Pacific Ocean, the Bering Sea, the Chukchi Sea, and the Arctic Ocean. We attributed the differences in AT values measured for unfiltered versus filtered samples to AT components contributed by phytoplankton (retained on a 0.7 μm filter) and by phytoplankton and bacteria combined (AT−BIO; retained on a 0.45 μm filter). The AT−BIO values reached 10−19 μmol kg−1 in the East Sea and the North Pacific Ocean, and progressively decreased to a level of 1 μmol kg−1 with distance towards the Arctic Ocean. The study shows that the AT−BIO values are non-negligible in coastal and open ocean environments and need to be considered when assessing the accuracy of carbon parameters calculated using the thermodynamic models that use measured AT as an input parameter.
Geophysical Research Letters; https://doi.org/10.1029/2021gl093462
Methods commonly used to estimate net primary production (NPP) from satellite observations are now being applied to biogeochemical (BGC) profiling float observations. Insights can be gained from regional differences in float and satellite NPP estimates that reveal gaps in our understanding and guide future NPP model development. We use seven years of BGC profiling float data from the Northeast Pacific Ocean to quantify discrepancies between float and satellite NPP estimates and decompose them into contributions associated with the platform sensing method and depth resolution of observations. We find small, systematic seasonal discrepancies in the depth-integrated NPP (iNPP) but much larger (>±100%) discrepancies in depth-resolved NPP. Annual iNPP estimates from the two planforms are significantly, positively correlated, suggesting that they similarly track interannual variability in the study region. Using the long-term satellite iNPP record, we identify elevated annual iNPP during two recent marine heatwaves and gain insights about ecosystem functionality.
Geophysical Research Letters; https://doi.org/10.1029/2021gl092957
Under tropical climates, mineral assemblages composing lateritic weathering profiles offer precious records of past weathering conditions. Silicon (Si) isotope signatures in the clay fractions of a deep lateritic profile in central Amazonia, Brazil, in combination with previously determined kaolinite ages, suggest that the surrounding region underwent two major weathering episodes, distinct in their intensity. The first episode (ca. 35-20 Ma) of moderate intensity produced well-crystallized kaolinites from the parent sediment with limited Si isotope fractionation. A more recent (8-6 Ma) and shorter phase caused the replacement, from top to bottom of the profile, of the first kaolinite generation by a new population characterized by higher crystallographic disorder and stronger Si isotope fractionation, suggesting weathering under conditions of rapid water percolation. These inferences are supported by results from an isotope-enabled reactive transport model, and they are consistent with paleoclimatic and paleogeographic evidences recorded over the Amazon Basin.
Geophysical Research Letters; https://doi.org/10.1029/2021gl094880
From 29 June to 1 July, 2015, a phreatic eruption occurred in Owakudani, the largest fumarole area in Hakone volcano, Japan. In this study, an interferometric synthetic aperture radar (InSAR) time series analysis of the Advanced Land Observing Satellite-2 (ALOS-2)/Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) data was performed to measure deformation after the eruption. The results show that the central cones of the volcano have subsided since the eruption and its deflation source is located beneath the previously estimated bell-shaped conductor, which is considered as a sealing layer confining a pressurized hydrothermal reservoir. Therefore, the InSAR results demonstrate the deflation of the hydrothermal system beneath the volcano. One possible cause of this deflation is compaction due to a decrease in pore pressure caused by rupture and fluid migration during and after the eruption.
Geophysical Research Letters; https://doi.org/10.1029/2021gl094726
This study examines the effects of the vertical structure of polar warming on the remote atmospheric circulation. We apply thermal forcing at different vertical levels in the Northern Hemisphere polar region in two atmospheric global climate models of different complexity, both coupled to an aquaplanet slab ocean. The efficacy of polar heating in perturbing the remote climate increases with the altitude at which it is applied. This robust sensitivity arises from the dominance of surface temperature contribution to the outgoing longwave radiation owing to the large emissivity of the polar troposphere. An upper-level polar heating has a smaller fraction of forcing balanced by radiative flux changes and a larger contribution from atmospheric energy transport changes, which provokes larger shifts in the extratropical jet and Hadley circulation. Our results suggest increasingly far-reaching impacts of Arctic warming as a less surface-trapped profile is projected for seasonally ice-free conditions in the near future.
Geophysical Research Letters; https://doi.org/10.1029/2021gl093977
The InSight mission to Mars is currently monitoring the seismic activity of the planet. Interpretation of seismological observations in terms of composition and mineralogy requires the knowledge of density and thermo-elastic properties of constituent materials at pertinent conditions. We thus performed phase equilibria experiments and carried out sound velocity and density measurements on aggregates representative of the Martian mantle over pressures and temperatures directly relevant for Mars’ upper and mid mantle. Our results indicate the stability of magnetite, although in a small amount, in phase assemblages at upper mantle conditions, especially in an oxidized environment. The measured pressure and temperature derivatives of compressional and shear velocities show that the temperature-induced reduction of seismic wave speeds dominates over pressure-induced effects at Mars’ shallow mantle conditions for the predicted areotherms and, independently from mineralogy, support the presence of a low-shear-wave-velocity layer between 150 and 350 km depth, in agreement with seismic observations.
Geophysical Research Letters; https://doi.org/10.1029/2021gl094784
Earth’s inner core anisotropy is widely used to infer the deep Earth's evolution and present dynamics. Many compressional-wave anisotropy models have been proposed based on seismological observations. In contrast, inner-core shear-wave (J-wave) anisotropy – on a par with the compressional-wave anisotropy – has been elusive. Here we present a new class of the J-wave anisotropy observations utilizing earthquake coda-correlation wavefield. We establish that the coda-correlation feature I2-J, sensitive to J-wave speed, exhibits time and amplitude changes when sampling the inner core differently. J-waves traversing the inner core near its center travel faster for the oblique than equatorial angles relative to the Earth’s rotation axis by at least ∼5 s. The simplest explanation is the J-wave cylindrical anisotropy with a minimum strength of ∼0.8%, formed through the lattice-preferred-orientation mechanism of iron. Although we cannot uniquely determine its stable iron phase, the new observations rule out one of the body-centered-cubic iron models.
Geophysical Research Letters; https://doi.org/10.1029/2021gl094737
This proof-of-concept study couples machine learning and physical modelling paradigms to develop a computationally efficient simulator-emulator framework for generating super-resolution ( < 250 m) urban climate information, that is required by many sectors. To this end, a regional climate model/simulator is applied over the city of Montreal, for the summers of 2019 and 2020, at 2.5 km (LR) and 250 m (HR) resolutions, which are used to train and validate the proposed super-resolution deep learning (DL) model/emulator. The DL model uses an efficient sub-pixel convolution layer to generate HR information from LR data, with adversarial training applied to improve physical consistency. The DL model reduces temperature errors significantly over urbanized areas present in the LR simulation, while also demonstrating considerable skill in capturing the magnitude and location of heat stress indicators. These results portray the value of the innovative simulator-emulator framework, that can be extended to other seasons/periods, variables and regions.
Geophysical Research Letters; https://doi.org/10.1029/2021gl094776
Surface effects of sea-level rise (SLR) in permafrost regions are obvious where increasingly iceless seas erode and inundate coastlines. SLR also drives saltwater intrusion, but subsurface impacts on permafrost-bound coastlines are unseen and unclear due to limited field data and the absence of models that include salinity-dependent groundwater flow with solute exclusion and freeze-thaw dynamics. Here, we develop a numerical model with the aforementioned processes to investigate climate change impacts on coastal permafrost. We find that SLR drives lateral permafrost thaw due to depressed freezing temperatures from saltwater intrusion, whereas warming drives top-down thaw. Under high SLR and low warming scenarios, thaw driven by SLR exceeds warming-driven thaw when normalized to the influenced surface area. Results highlight an overlooked feedback mechanism between SLR and permafrost thaw with potential implications for coastal infrastructure, ocean-aquifer interactions, and carbon mobilization.