A submarine canyon is in essence a canyon cutting down into the seabed (it’s got nothing to do with the submarine vehicle). Although they offer very interesting challenges when it comes to modelling the flow of the water on the ocean floor it won’t be fluid mechanics we’re looking at today. Instead it is their importance as marine habitats especially as locations of intense biodiversity which is under study.
Methane (CH4) is listed with carbon dioxide (CO2) and nitrous oxide (N2O) as one of the most important greenhouse gasses. Geological records seem to show the connection between methane and global temperature over a time scale of a few thousand years. A large quantity of methane is currently trapped at the bottom of the ocean as deposits of gas hydrate. Estimates give a value of about 1015 kg of carbon being stored in marine sediments in the form of methane. This methane can escape from its prison through physical mechanisms. Currently the main causes of methane seepage are changes in pressure caused by sea level changes and sea bed water temperature changes. As pressure decreases and temperature rises the agitation bottom ocean currents can release many tonnes of CH4 into the ocean.
Models which predict the how the Earth will change under various intensities of global warming need to look at a variety of features. Ocean currents and plankton activity, storm rates and atmospheric flows have all been studied in great detail. The complex models employed to foresee these changes give us a reasonably accurate prediction over time scales between 10 and 100 years, the time scale in which changes will have a direct impact on us. It would be of great scientific interest to be able to estimate the impact of current changes on the long term time scale of over 1000 years and all the way to the millions of years. But there is a problem. Like I said, the current models are very complex which means that there is a limit imposed by our current computing power of how far these models can be extended into the future.
When it comes to greenhouse gasses it is undeniable that the most famous has to be carbon dioxide (CO2). It is clear why this is the case, 80% of the greenhouse gas we emit is carbon dioxide with the other 20% being made up of methane (CH4), water vapour (H2O) and nitrous oxide (N2O). It’s this nitrous oxide that we’ll be looking at today as despite making up 5% of the total produced greenhouse gas it is estimated to be a few hundred times more effective at trapping heat than CO2 and quite annoyingly it has an atmospheric lifetime of 121 years while CO2 has a lifetime of about 30 to 95 years which means the N2O produced now will be blighting us far into the next century. To make matters worse the removal pathway of nitrous oxide also removes ozone so it acts to destroy the ozone layer while it’s stifling the planet.
Sea level rise is one of the more worrying aspects of global warming. Due to a general energy imbalance the ocean has been gaining energy at a rate of about one W/m2 for the last few decades. Some predictions claim that the sea level will have risen an average of about a metre by the end of the century. But a concept that is overlooked is the idea of the average sea level rise. The ocean is a bit more complicated than a tub of water, there is no guarantee the sea level rise in California will be the same as that in Mozambique.
The precise measurement of Earth’s gravitational field is very important. By timing the period of a simple pendulum it might be possible to get a measurement for the field with accuracies to three significant figures but not much more than that. A key part of geophysics is to use variations in gravitational field strength at different points around the surface of the Earth to estimate subterranean densities. These variations can be found to such resolution that they can be used to study tectonic plates, volcanoes and even the decrease in mass of melting glaciers.
Last week I produced this post which begins with a quick sum up of a few times I’ve talked about air pollution in China. Now today we’re actually talking about air pollution not in China but in the second most populous country in the world: India. The air pollution in India is considered pretty bad and is likely a main contributor to health defects in the country. In the Indo-Gangetic Plain, the span of the country bordering Bangladesh and China, you will find PM2.5 concentrations of up to 150 μg m−3 (remember that the World Health Organisation recommends a limit of 10 μg m−3) due to this strip containing Delhi, Dhaka, Kolkata and about 50% of the country’s population.