Sensitivity of time lapse seismic data to the compliance of hydraulic fractures

We study the sensitivity of seismic waves to changes in the fracture normal and tangential compliances by analyzing the fracture sensitivity wave equation, which is derived by differentiating the elastic wave equation with respect to the fracture compliance. The sources for the sensitivity wavefield are the sensitivity moments, which are functions of fracture compliance, background elastic properties and the stress acting on the fracture surface. Based on the analysis of the fracture sensitivity wave equation, we give the condition for the weak scattering approximation to be valid for fracture scattering. Under the weak scattering approximation, we find that the percentage change of fracture compliance in hydraulic fracturing is equal to the percentage change of the recorded time-lapse seismic data. This could provide a means for monitoring the opening/closing of fractures in hydraulic fracturing through time-lapse seismic surveys.Eni-MIT Energy Initiative Founding Member Progra

The Weddelll Sea and Dronning Maud Land (WSDML) Regional Working Group Virtual Science Workshop, 20-23 October, 2020.

Workshop report from the Weddell Sea and Dronning Maud Land (WSDML) Regional Working Group virtual science workshop, held 20-23 October 2020

On the formation, ventilation, and erosion of mode waters in the North Atlantic and Southern Oceans

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94834/1/jgrc12564.pd

Physical controls of Southern Ocean deep-convection variability in CMIP5 models and the Kiel Climate Model

Global climate models exhibit large biases in the Southern Ocean. For example, in models Antarctic bottom water is formed mostly through open-ocean deep-convection rather than through shelf convection. Still, the timescale, region, and intensity of deep-convection variability vary widely among models. We investigate the physical controls of this variability in the Atlantic sector of the Southern Ocean, where most of the models simulate recurring deep-convection events. We analyzed output from eleven exemplary CMIP5 models and four versions of the Kiel Climate Model (KCM). Of several potential physical control parameters that we tested, the ones shared by all these models are: Stratification in the convection region influences the timescale of the deep-convection variability, i.e. models with a strong (weak) stratification vary on long (short) timescales. And, sea ice volume affects the modeled mean state in the Southern Ocean: large (small) sea ice volume is associated with a non-convective (convective) predominant regime

Carbon dynamics of the Weddell Gyre, Southern Ocean

The accumulation of carbon within the Weddell Gyre and its exchanges across the gyre boundaries are investigated with three recent full-depth oceanographic sections enclosing this climatically important region. The combination of carbonmeasurements with ocean circulation transport estimates from a box inverse analysis reveals that deepwater transports associated with Warm Deep Water (WDW) and Weddell Sea Deep Water dominate the gyre’s carbon budget, while a dual-cell vertical overturning circulation leads to both upwelling and the delivery of large quantities of carbon to the deep ocean. Historical sea surface pCO2 observations, interpolated using a neural network technique, confirm the net summertime sink of 0.044 to 0.058 ± 0.010 Pg C / yr derived from the inversion. However, a wintertime outgassing signal similar in size results in a statistically insignificant annual air-to-sea CO2 flux of 0.002± 0.007 Pg C / yr (mean 1998–2011) to 0.012 ± 0.024 Pg C/ yr (mean 2008–2010) to be diagnosed for the Weddell Gyre. A surface layer carbon balance, independently derived fromin situ biogeochemical measurements, reveals that freshwater inputs and biological drawdown decrease surface ocean inorganic carbon levels more than they are increased by WDW entrainment, resulting in an estimated annual carbon sink of 0.033 ± 0.021 Pg C / yr. Although relatively less efficient for carbon uptake than the global oceans, the summertime Weddell Gyre suppresses the winter outgassing signal, while its biological pump and deepwater formation act as key conduits for transporting natural and anthropogenic carbon to the deep ocean where they can reside for long time scales

The Zero Emissions Commitment and climate stabilization

How do we halt global warming? Reaching net zero carbon dioxide (CO2) emissions is understood to be a key milestone on the path to a safer planet. But how confident are we that when we stop carbon emissions, we also stop global warming? The Zero Emissions Commitment (ZEC) quantifies how much warming or cooling we can expect following a complete cessation of anthropogenic CO2 emissions. To date, the best estimate by the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report is zero change, though with substantial uncertainty. In this article, we present an overview of the changes expected in major Earth system processes after net zero and their potential impact on global surface temperature, providing an outlook toward building a more confident assessment of ZEC in the decades to come. We propose a structure to guide research into ZEC and associated changes in the climate, separating the impacts expected over decades, centuries, and millennia. As we look ahead at the century billed to mark the end of net anthropogenic CO2 emissions, we ask: what is the prospect of a stable climate in a post-net zero world

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Global Tipping Points 2023 Report: Ch1.4 – Tipping points in ocean and atmosphere circulations.

This chapter assesses scientific evidence for tipping points across circulations in the ocean and atmosphere. The warming of oceans, modified wind patterns and increasing freshwater influx from melting ice hold the potential to disrupt established circulation patterns. We find evidence for tipping points in the Atlantic Meridional Overturning Circulation (AMOC), the North Atlantic Subpolar Gyre (SPG), and the Antarctic Overturning Circulation, which may collapse under warmer and ‘fresher’ (i.e. less salty) conditions. A slowdown or collapse of these oceanic circulations would have far-reaching consequences for the rest of the climate system, such as shifts in the monsoons. There is evidence that this has happened in the past, having led to vastly different states of the Sahara following abrupt changes in the West African monsoon, which we also classify as a tipping system. Evidence about tipping of the monsoons over South America and Asia is limited, however large-scale deforestation or air pollution are considered as potential sources of destabilisation. Although theoretically possible, there is little indication for tipping points in tropical clouds or mid-latitude atmospheric circulations. Similarly, tipping towards a more extreme or persistent El Niño Southern Oscillation (ENSO) state is not sufficiently supported by models and observations. While the thresholds for many of these systems are uncertain, tipping could be devastating for many millions of people. Stabilising climate (along with minimising other pressures, like aerosol pollution and ecosystem degradation) is critical for reducing the likelihood of reaching tipping points in the ocean-atmosphere system