Subduction initiation often takes advantage of previously weakened lithosphere and may preferentially nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and inherited lithospheric structure might lead to self-sustaining subduction, we present an analysis of the Puysegur Trench, a young subduction zone with a rapidly evolving tectonic history. The Puysegur margin, south of New Zealand, has experienced a transformation from rifting to seafloor spreading to strike-slip, and most recently to incipient subduction, all in the last ~45 million years. Here we present deep-penetrating multichannel reflection (MCS) and ocean-bottom seismometer (OBS) tomographic images to document crustal structures along the margin. Our images reveal that the overriding Pacific Plate beneath the Solander Basin contains stretched continental crust with magmatic intrusions, which formed from Eocene-Oligocene rifting between the Campbell and Challenger plateaus. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading in the Solander Basin as previously thought. Subsequent strike-slip deformation translated continental crust northward causing an oblique collisional zone, with trailing ~10 Myr old oceanic lithosphere. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust the continent-collision zone. We suggest that subduction initiation at the Puysegur Trench was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. The Puysegur margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation scenario and should be considered throughout Earth’s history.

Microbial decomposition of carbon and biogenic methane in coal is one of the most important issues in CBM exploration. Microbial C-N-S functional genes in different hydraulic zones of high rank coal reservoirs was studied, demonstrating high sensitivity of this ecosystem to hydrodynamic conditions. The results shows that hydrodynamic strength of the 3# coal reservoir in Shizhuangnan block gradually weakened from east to west, forming the transition feature from runoff area to stagnant area. Compared with runoff area, the stagnant area has higher reservoir pressure, gas content and ion concentrations. The relative abundance of genes associated to C, N and S cycling was increased from the runoff area to stagnant area, including cellulose degrading genes, methane metabolism genes, N cycling genes and S cycling genes. This indicates that the stagnant zone had more active microbial C-N-S cycle. The machine learning model shows that these significantly different genes could be used as effective index to distinguish runoff area and stagnant area. Carbon and hydrogen isotopes indicate that methane in the study area was thermally generated. The methanogens compete with anaerobic heterotrophic bacteria to metabolize limited substrates, resulting in low abundance of methanogens. Meanwhile, the existence of methane oxidizing bacteria suggests biogenic methane was consumed by methanotrophic bacteria, which is the main reason why biogenic methane in the study area was not effectively preserved. In addition, weakened hydrodynamic conditions increased genes involved in nutrient cycling contributed to the increase of CO2 and consumption of sulfate and nitrate from runoff area to stagnant area.

In this study, the price elasticity of water demand was estimated using disaggregated data of approximately 30,000 households recorded over five years: two years before and three years after a tariff revision. From the results of the latent class analysis, the mean price elasticity was -0.1. The households were divided into three groups: 35%–55% of the households did not respond to the tariff revision, and households with high water demand prior to the revision had higher elasticity. In addition, no statistically significant difference was observed in elasticity between the first and third years after revision.

Anthropogenic climate change footprints in the ocean go beyond the mixed layer depth, with considerable impacts throughout mesopelagic and deep-ocean ecosystems. Yet, little is known about the timing of these environmental changes, their spatial extent, and the associated timescales of recovery in the ocean interior when strong mitigation strategies are involved. Here, we simulate idealized rapid climate change and mitigation scenarios using the Norwegian Earth System Model (NorESM) to investigate timescales of climate change onset and recovery and the extent of change in the North Atlantic (NAtl) interior relative to Pre-industrial (PI) variability across a suite of environmental drivers (Temperature – T; pH; Dissolved Oxygen – DO; Apparent Oxygen Utilization - AOU; Export Production - EP; and Calcite saturation state - Ωc). We show that, below the subsurface domains, responses of these drivers are asymmetric and detached from the anthropogenic forcing with large spatial variations. Vast regions of the interior NAtl experience detectable anthropogenic signal significantly earlier and over a longer period than those projected for the subsurface. In contrast to surface domains, the NAtl interior remains largely warmer relative to PI (up to +50%) following the mitigation scenario, with anomalously lower EP, pH and Ωc (up to -20%) south of 30°N. Oxygenation in the upper mesopelagic of up to +20% is simulated, mainly driven by a decrease in consumption during remineralization. Our study highlights the need for long-term commitment focused on pelagic and deep-water ecosystem monitoring to fully understand the impact of anthropogenic climate change on the North Atlantic biogeochemistry.

Recent developments in ocean-bottom pressure gauge (OBP) networks have enabled us to continuously monitor various waves in the ocean. On 1 July, 2020, an OBP network, S-net, recorded tsunami-like pressure changes, although no earthquake was reported. These waves were well explained by a numerical simulation supposing a northward-moving atmospheric low pressure system with a maximum pressure depression of −0.5 ± 0.1 hPa and an apparent speed of 100–110 m/s. This simulation suggested that these waves were meteotsunamis. The simulation also suggested that the maximum amplitudes of the sea-surface height of ~ 2 cm were up to ~30% larger than those expected from the observed pressure if we do not consider the effect of the atmospheric pressure change. Our study showed that the S-net can detect the generation and propagation of meteotsunamis, which could not be achieved in the past when OBP networks with only a few stations were available.

For the past five+ years, The GLOBE Program has hosted an International Virtual Science Symposium (IVSS). This annual event invites primary through undergraduate GLOBE (Global Learning and Opportunities to Benefit the Environment) students to showcase their Earth science research in an entirely online platform. With GLOBE, students learn the practices of science through hands-on investigations in their own communities, sparking their curiosity and interest in science. This often leads to inquiries that help solve real-world problems and further understanding of our global environment. Students from around the world submit their research projects to a panel of international scientists, teachers, subject matter experts, graduate students, and other interested community members for scoring and valuable feedback which will help them improve as scientists. As well, students are awarded digital badges if they demonstrate specific scientific practices such as collaboration, data science, and engineering. Badges are also awarded to students who work with STEM professionals, explore STEM careers, demonstrate community impacts, and share their research in creative ways such as through storytelling. By the time the pandemic started shutting down schools across the world, the 2020 IVSS was already underway and was able to continue with few interruptions. This helped to reinforce the IVSS as a model for virtual student engagement on a global scale. As well, we now have five years of data to help assess the efficacy of the IVSS, analyze its growth, and help direct future engagement opportunities. Planning for the 2021 IVSS is already underway and we are currently working on how to incorporate COVID-19-related restrictions into the model by encouraging a focus on using previously collected GLOBE data and creating student resources aimed at improving data science skills.

Use of ensemble rainfall forecasts has gained popularity in providing detailed uncertainty information and improving hydrologic prediction skill. India Meteorological Department (IMD) provides medium-range multi-model ensemble (MME) forecasts for all over India with 1- to 5-day lead time. In this study, we bias correct the IMD MME rainfall forecasts using a modified version of Kohonen Self-Organizing Maps (KSOM) and analyse the effect of bias correction on the streamflow prediction skill of MIKE 11 Hydrodynamic (HD) model for the years 2012-2014. We have selected the upper region of the Mahanadi River basin as the test bed. The results indicate improvement of rainfall forecasts after bias correction. Subsequently, use of bias corrected rainfall forecasts as input forcing to the MIKE 11 HD model provides better streamflow forecasts at all the lead times (Nash Sutcliffe Efficiency, NSE ranging from 0.89 to 0.41) compared to the use of raw forecasts (NSE ranging from 0.89 to -0.51). To further improve the streamflow forecasts, we have applied the recently developed robust wavelet-based non-linear autoregressive with exogenous inputs dynamic neural network model, WNARX. This post-processing operation tends to improve the streamflow forecast quality to an acceptable range (NSE = 0.92-0.71). The results encourage us to conclude that the IMD MME forecasts has great potential to improve streamflow prediction skill of a hydrodynamic model.

Six ALAMO floats are deployed within the tropical warm pool of the eastern Indian Ocean, to study the thermal stratification in the diurnal warm layer (DWL) during strong diurnal SST variation (DV SST) prior to the onset of Madden-Julian Oscillations (MJO). Strong DV SST of > 2 °C is measured by four floats before the passage of a MJO event (i.e., during the suppressed phase), when the peak insolation > 1000 W m-2 and the wind speed < 3 m s-1. Even after the occurrence of daytime peak SST, the temperature gradient in the DWL can still extend to > 10 m until the midnight, which may be driven by the turbulent mixing at the base of DWL. Interestingly, the foundation SST (SSTfnd) at three floats increases rapidly from 26.4 °C to > 27.6 °C over two days, coincident with the shoaling of surface mixed layer depth (MLD) by more than 20 m. The strongly stratified near surface layer may sustain higher SSTs and enhance air-sea heat fluxes until the onset of stronger winds. The KPP mixing scheme used in a 1-D model can simulate the observed DV SST magnitude reliably, but fail to predict the rapid increase of SSTfnd. The magnitude of DV SST is affected by the near surface stratification, but the SSTfnd is modulated by the evolution of stratification above the MLD. Future field measurements in the upper ocean during diurnal warming are proposed to help improve air-sea flux simulations and the forecast of MJOs.

Nowadays, many of the world cities and its peripheral areas are under constant threat of flooding due to high rainfall events. Increased rate of severe flood hazards world-wide have created a demand for understanding the flooding behaviour across various urban and peri-urban catchments. However, simulating the flooding scenarios under limited hydrological data condition is a great challenge for the urban water planners and managers, especially in developing countries. To this, in this study, a combined modelling approach is proposed with the physically based Variable Parameter Muskingum Stage (VPMS) routing model to develop a local rating curve for generating the discharge data from the available stream stage data, which was subsequently used as an input to the Storm Water Management Model (SWMM). The coupled methodology is applied in a typical ungauged urban and peri-urban catchment of eastern India. The proposed SWMM-VPMS model is calibrated for the monsoon (rainy) season of the year 2009, and validated for the monsoon seasons of 2011 and 2014. The performance of the model is satisfactory with the Nash-Sutcliffe efficiency (NSE) estimates of 0.82, 0.89, and 0.89 for the years 2009, 2011, and 2014, respectively. The proposed SWMM-VPMS model can be used for a catchment where the tributary is ungauged while the main river is gauged at a downstream location of the confluence point. This methodology can also be adopted in catchments with missing rating curves. Additionally, the information regarding spatial distribution of channel flow depth at different time can be utilised to have an initial assessment of the flood-vulnerable areas. Keywords: VPMS; SWMM; Urban and peri-urban catchment; Ungauged catchment

Water Balance Components (WBCs), the most fundamental processes of a river basin, are getting disturbed by climate change and land-use alterations in the present scenario. These two factors are the major driving force behind the spatio-temporal variation of the WBCs that creates an alarming concern for fulfilling water demand by different sectors. The popular hydrological model Soil and Water Assessment Tool (SWAT) is applied to the Baitarani River basin (12,095 km2) of eastern India for evaluating the dominance of the above factors on the WBCs deviations at a decadal scale (1980-1989, 1990-1999, and 2000-2009). A quantile regression-based stochastic approach has been used to analyze the uncertainties resulting from different simulations accounting the combined responses of climate change and land-use alterations as well as model parameters. However, such analysis has not been explored more for the present study area. The model performance results reveal that the statistical performance indices (NSE and R2) are within the acceptable limit. The WBCs in terms of evapotranspiration, surface runoff, lateral flow, water yield, soil moisture storage, and deep aquifer recharge has been quantified at a decadal scale from the simulated model outcomes. The result shows that the water yield component is more (680.36 mm) for mid-decade (1990-1999) as compared to other decades, which is favourable to fulfill sectoral water demand. Further, the uncertainty analysis explains that climate change impact plays a vital role in WBCs variation. The developed approach can portray the variability of WBCs of other river basins that are vulnerable to climate change. The outcomes of this study can be used to maintain an appropriate balance between water availability and demand to avoid water scarcity. Keywords: Water balance components; Climate change; Land-use Alterations, Brahmani; Baitarani

Biological processes in Southern Ocean surface waters have widespread impacts on global productivity and oceanic CO2 storage. Here, we demonstrate that biological calcification in the Southern Ocean exerts a strong control the global distribution of alkalinity. The signature of Southern Ocean calcification is evident in observations as a depletion of potential alkalinity within portions of Subantarctic Mode and Intermediate water. Experiments with an ocean general circulation model indicate that calcification and subsequent sinking of biogenic carbonate in this region effectively transfers alkalinity between the upper and lower cells of the meridional overturning circulation. Southern Ocean calcification traps alkalinity in the deep ocean; decreasing calcification permits more alkalinity to leak out from the Southern Ocean, yielding increased alkalinity in the upper cell and low-latitude surface waters. These processes have implications for the atmosphere-ocean partitioning of carbon. Reductions in Southern Ocean calcification increase the buffer capacity of surface waters globally, thereby enhancing the ocean’s ability to absorb carbon from the atmosphere. This study highlights the critical role of Southern Ocean calcification in determining global alkalinity distributions, demonstrating that changes in this process have the potential for widespread consequences impacting air-sea partitioning of CO2.

Following observations of a drop in the West Antarctic Ice Sheet (WAIS) mass balance over the last few decades with the possibility to reach a tipping point leading to ineluctable glaciers outlets instability in the region, understanding the driving processes has become a priority. In particular, the Circumpolar Deep Water (CDW) intrusion onto the continental shelf in the Amundsen Sea is, nowadays, in the spotlight, and gathers the attention of both the observers and the modellers. This modelling study presents the analysis of a 1/12° simulation of the Amundsen Sea sector reproducing well the interannual-to-decadal variability of the ice-shelves basal melt rates. The development of a methodology to study the ocean state in the reference frame of the continental shelf break enables us to distinguish and characterize a western fresh shelf zone and an eastern warm shelf zone in the region. Connecting it with the more regional circulation, we try to shed light on the different mechanisms driving the CDW inflow onto the continental shelf in the region. In particular, we draw attention to the sea ice effect in terms of Ekman pumping along the shelf break, and we point out the possible initiation of a southern Antarctic Circumpolar Current (ACC) branch to the south-east of the Ross Gyre, which could control part of the variability along the Amundsen Sea shelf. Finally, we discuss correlations between the ocean variability at the shelf break and the one of the melt activity underneath the ice-shelves.

High altitude ecosystems react sensitively to climatic changes. To evaluate hydroclimate dynamics and ecosystem responses since the late glacial in a typical glacier influenced, high-altitude, lacustrine ecosystem, we analysed concentrations and hydrogen isotopic composition of different aquatic (alkenones, nC23:1, HBIs) and terrestrial (nC31) biomarker groups in Hala Hu. The lake is located on the northern margin of the Tibetan Plateau, i.e. in the transitioning zone between the East Asian summer monsoon (EASM) and westerlies influence. According to species association of ostracods, it experienced a lake level rise of ca. 45 m during the late glacial and early Holocene and reached its highest stand during early mid-Holocene (8 - 6.1 cal. kyr BP) followed by lake level decline. The organic geochemical data reveal asynchronous responses of the aquatic and terrestrial ecosystem in Hala Hu and its catchment to hydroclimatic forcing. We interpret δD values of terrestrial biomarkers as indicative for δD of growing season precipitation, with a potential contribution of surface meltwater runoff. Hence, most negative values during 9 - 7 cal. kyr BP indicate changes in moisture source, possibly related to EASM intensification. In contrast, rapid appearance and disappearance of aquatic biomarkers and shifts in theirs δD values between ca. 8 – 5 kyr BP, revealed distinct mid-Holocene aquatic regime-shifts and changes in lake hydrology. Maxima of terrestrial biomarker concentrations also occurred between 8 - 5 cal. kyr BP, suggesting expansion of terrestrial grasses and eventually increased biomarker flux via surface runoff. These results give evidence that neither shifts of vapour source nor increased precipitation amounts were the major triggers of ecosystem responses. Instead we hypothesize, that warmer temperatures during the Holocene climate optimum, receding glaciers and consequently increased meltwater discharge into the lake, caused the pronounced ecological changes. The rapid regime-shifts within phytoplankton communities in the mid-Holocene illustrate the sensitivity of high altitude mountain ecosystems within the marginal Asian monsoon region to climatic changes. This is of relevance in context with future changes as response to global warming.

One of the largest tropical tidal ranges in the world occurs in King Sound, a semi-enclosed embayment in the tropical Kimberley region of Western Australia. Incubations of phytoplankton within King Sound displayed reduced photosynthetic efficiency, elevated maximum photosynthetic rates, and no measurable photo-inhibition. A response typical of high light adapted phytoplankton despite decreased water clarity and low ambient nutrient concentrations in the estuary. This is in contrast with the adjacent shelf where phytoplankton, associated with a deep chlorophyll maximum, display high photosynthetic efficiency, and strong light inhibition typical of low light adaptation. Remote sensing and numerical modelling suggest that spatial and temporal variations in tidal mixing drive changes in light variability and in photo-acclimation. In King Sound phytoplankton experience the largest variations in light over short timescales where diatoms dominate since they can rapidly acclimate to water column light conditions by adjusting pigment within the cell. The photo-physiological response of the phytoplankton in the Sound, suggests that acclimation to alternate weak and strong mixing exposes them to cyclical changes in light intensity delaying the onset of photo-inhibition, allowing higher maximum photosynthetic rates to be attained. These findings highlight the importance of a multifaceted approach to understanding the links between physics and photo-acclimation strategies employed by phytoplankton to more accurately determine rates of depth-integrated productivity in complex coastal areas.

A high-resolution (1.25 m) LES simulation of the nocturnal cloud-topped marine boundary layer is used to evaluate random error as a function of continuous track length L for virtual aircraft measurements of turbulent fluxes of sensible heat, latent heat, and horizontal momentum. Results are compared with the theoretically derived formula of Lenschow and Stankov (1986). In support of these comparisons , we also evaluate and document the relevant integral length scales and correlations and show that for heights up to approximately 100 m (z/z i = 0.12), the length scales are accurately predicted by empirical expressions of the form I f = Az^b. The Lenschow and Stankov expression is found to be remarkably accurate at predicting the random error for shorter flight tracks, but our empirically determined errors decay more rapidly with L than the L^−1/2 relationship predicted from theory. Consistent with earlier findings, required track lengths to obtain useful precision increase sharply with altitude.

Using ionograms from the Brazilian equatorial region of São Luís (SL, 2° S; 44° W, I =-3.8°), the relation between the uplift of the intermediated layers (ILs) at sunset and the prereversal enhancement of the zonal electric field (PRE) is investigated. The ILs were studied during periods of maximum (2003) and minimum solar activity (2009). The presence of the ILs during the PRE occurrence time was very low for both years. In 2003, six ILs’ events were observed, being four of them in the summer solstice and one in the March equinox. In 2009, only a single event was registered and occurred during the December month. The results show that depending on the height at which the ILs are located, their upward movement at sunset can be in some way related to the normal F layer rise at sunset due to the PRE. Additionally, the eastward prompt penetration electric fields (PPEF) during weak magnetic storms can also contribute to the IL’s rise. An interesting case of uplift of a sporadic-E layer from ~120 to 290 km of altitude probably due to the PPEF is investigated. The absence of answers of the F layer to the same disturbed electric field reveals the complex nature of the layers located in the ionosphere valley region.

We present a new high resolution empirical model for the ionospheric total electron content (TEC). TEC data are obtained from the global navigation satellite system (GNSS) receivers with a 1 x 1 spatial resolution and 5 minute temporal resolution. The linear regression model is developed at 45N, 0E for the years 2000 - 2019 with 30 minute temporal resolution, unprecedented for typical empirical ionospheric models. The model describes dependency of TEC on solar flux, season, geomagnetic activity, and local time. Parameters describing solar and geomagnetic activity are evaluated. In particular, several options for solar flux input to the model are compared, including the traditionally used 10.7cm solar radio flux (F10.7), the Mg II core-to-wing ratio, and formulations of the solar extreme ultraviolet flux (EUV). Ultimately, the extreme ultraviolet flux presented by the Flare Irradiance Spectral Model, integrated from 0.05 to 105.05 nm, best represents the solar flux input to the model. TEC time delays to this solar parameter on the order of several days as well as seasonal modulation of the solar flux terms are included. The Ap_3 index and its history are used to reflect the influence of geomagnetic activity. The root mean squared error of the model (relative to the mean TEC observed in the 30-min window) is 1.9539 TECu. A validation of this model for the first three months of 2020 shows excellent agreement with data. The new model shows significant improvement over the International Reference Ionosphere 2016 (IRI-2016) when the two are compared during 2008 and 2012.

We document the implementation of the Common Representative Intermediates Mechanism version 2, reduction 5 (CRIv2-R5) into the United Kingdom Chemistry and Aerosol model (UKCA) version 10.9. The mechanism is merged with the stratospheric chemistry already used by the StratTrop mechanism, as used in UKCA and the UK Earth System Model (UKESM1), to create a new CRI-Strat mechanism. CRI-Strat simulates a more comprehensive treatment of non-methane volatile organic compounds (NMVOCs) and provides traceability with the Master Chemical Mechanism (MCM). In total, CRI-Strat simulates the chemistry of 233 species competing in 613 reactions (compared to 87 species and 305 reactions in the existing StratTrop mechanism). However, while more than twice as complex than StratTrop, the new mechanism is only 75% more computationally expensive. CRI-Strat is evaluated against an array of in situ and remote sensing observations and simulations using the StratTrop mechanism in the UKCA model. It is found to increase production of ozone near the surface, leading to higher ozone concentrations compared to surface observations. However, ozone loss is also greater in CRI-Strat, leading to less ozone away from emission sources and a similar tropospheric ozone burden compared to StratTrop. CRI-Strat also produces more carbon monoxide than StratTrop, particularly downwind of biogenic VOC emission sources, but has lower burdens of nitrogen oxides as more is converted into reservoir species. The changes to tropospheric ozone and nitrogen budgets are sensitive to the treatment of NMVOC emissions, highlighting the need to reduce uncertainty in these emissions to improve representation of tropospheric chemical composition.