Water

Photo of the Week – Salt Coral

Matt Herod December 8, 2016

Walking along the shoreline of the Dead Sea, you can find some magnificent objects, like this coral made of salt. Combine that with the beautiful scenery and amazing lighting at dawn and you get this amazing photo. Source - Salt Coral by Zachi Shtain

The photo posted below is a really cool one. Interestingly, enough I have been getting into podcasts lately. They are great during my bus ride to and from work every day. One of the podcasts that I like is Neil de Grasse Tyson’s Star Talk Radio. Anyway, the other week Star Talk had a pretty good discussion about salt and the role it has played in developing human history. Check out the episode in two parts here. Arguably as one of the most important economic minerals of all time, although it may not seem so today.

That said, having read the book Sugar, Salt and Fat I would argue that salt retains its title as the most important of all economic minerals even to this very day! Anyone else have an opinion on this?

I digress though. The image below shows an incredible salt concretion on the shore of the hypersaline Dead Sea that has been formed by sea spray that has evaporated creating this magnifcent shape. Despite the title it is not actually coral.

Walking along the shoreline of the Dead Sea, you can find some magnificent objects, like this coral made of salt. Combine that with the beautiful scenery and amazing lighting at dawn and you get this amazing photo. Source - Salt Coral by Zachi Shtain

Bubbling Merrily: Artesian Springs

Matt Herod December 7, 2015

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I recorded the video above on a recent field camp near Deep River, Ontario. This video shows a great example of a flowing artesian spring which is bubbling up at the headwaters of a creek. The water is freezing, crystal clear and totally delicious! The classic textbook on groundwater, Freeze and Cherry, puts the attraction of groundwater springs nicely when they say “Flowing wells (along with springs and geysers) symbolize the presence and mystery of subsurface water, and as such they have always evoked considerable public interest.”

There are two types of artesian springs. Those that are controlled geologically, which are commonly taught as the only variety of artesian system, and topographically, which are often overlooked.

Geologically controlled artesian springs/wells result from a specific combination of hydrogeologic conditions. Specifically, the aquifer must be under pressure, which is usually caused by a steep elevation gradient in combination with relatively impermeable confining layers such as clay. This is called a confined aquifer. Recharge to this aquifer occurs on top of a hill, where the aquifer outcrops. This water then infiltrates through the permeable sediments to the water table and into the confined aquifer. However, this does not explain why a spring or a well drilled into and artesian aquifer often bubbles up with water, like the video above.

A conceptual model of a confined artesian aquifer in which the recharge area is exposed at higher elevation and the aquifer sediments are bounded by two aquitards. Source

The reason for this is somewhat abstract and has to do with water pressure. In an unconfined aquifer the water table and the potentiometric surface, which is the abstract line dictated by the water level in the well, are generally synonymous and are defined by the point at which the water pressure is equal to atmospheric pressure. However, in confined aquifers where artesian conditions exist this becomes more complicated. The reason for this is that within the confined aquifer the water pressure is often greater than atmospheric. Imagine diving down in a lake and feeling the pressure of the water above you. Therefore, when this aquifer is drilled or a pathway to conduct water to the surface exists the water will want to flow upward towards that point where the water pressure and the atmospheric pressure are equal. This point can be above the ground surface and this leads to flowing artesian conditions. The figure below illustrates this concept nicely.

Source: Minnesota Department of Health,

In this figure the water level in the well on the right, which is connected to the confined aquifer, is distinct from the water table in the unconfined aquifer. The water is not flowing because the potentiometric surface is not higher than the ground level. In the other artesian well, which is flowing, the water flows up to the potentiometric surface, well above the ground surface. This is because that surface represents the point where the water pressure, which is the pressure of the water within the confined aquifer, and the atmospheric pressure are equal.

The other type of artesian spring are topographically controlled and often occur in valleys. The reason for this is that as water recharges at the top of hills this can locally raise the potentiometric surface if there is a steep valley nearby. Therefore, at the base of the valley the potentiometric surface can be higher than the ground surface causing water to discharge.

So which type is the one in the video? Let’s start by checking the topo map of the region. The spring is located at the red star, which based on the terrain map is actually pretty flat, certainly much flatter than the opposite bank of the Ottawa river.

Based on this map it doesn’t look like the spring is topographically controlled. There may be some local elevation that does not show up at the map scale, although I don’t recall there being that much. One thing to keep in mind about this location is that there is a lot of bedrock exposed. It is possible that some of this bedrock aquifer is over-pressured and water flowing through fractures in the bedrock is discharging as a flowing artesian spring. In my mind, after about 10 minutes of looking around, this is the most likely scenario. It may also be completely wrong, but without a more detailed look around it is difficult to say.

Artesian springs and springs in general really represent the importance of protecting our groundwater resources. It is critical that places such as this artesian spring be protected from contamination and development as they are very fragile and represent important sources of clean, safe water as well as habitat to a large diversity of local flora and fauna. If you know of any artesian springs in your area please comment below and let me know if they are protected or if they have been compromised by contamination or development.

Matt

p.s. I’ve teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers.

It only take 5 minutes to complete the survey. Begin here: http://bit.ly/ScienceBorealisSurvey

If you complete the survey you will be entered to win one of eleven prizes! A $50 Chapters Gift Card, a $20 surprise gift card, 3 Science Borealis T-shirts and 6 Surprise Gifts! PLUS everyone who completes the survey will receive a free hi-resolution science photograph from Paige’s Photography!

Geology Photo of the Week #42

Matt Herod July 6, 2015

This week’s photo is a beautiful example of geochemistry in action. Briefly, travertine, which is composed of CaCO3 is often precipitated at hot springs as they emerge from the ground forming these gorgeous terraces. The reason for their formation is Henry’s gas law in action which states “the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid” which in this case is the open air. At depth, the superheated water contains lots of dissolved carbon dioxide, which lowers the water pH and allows it to dissolve carbonate minerals it comes in contact with. However, once the water reaches the surface the CO2 degasses because of the much lower partial pressure (concentration) of CO2 in the atmosphere à la Henry’s law. This causes the pH to rise which in turn leads to precipitation of dissolved carbonates such as aragonite and calcite (travertine).

By the way, I have always, always wanted to swim/lounge in one of these sorts of places but have never had the chance. Maybe one day!

Mammoth Hot Springs – travertine terrace – Credit: Joern Behrens (distributed via imaggeo.egu.eu)

Guest Lecture – Dr. Tim Lowenstein

Matt Herod January 25, 2013

Our department was recently lucky enough to have Dr. Tim Lowenstein from SUNY Binghamton come give a guest lecture on the changes in the chemistry of seawater throughout geologic time.

Originally, we thought that the major ion chemistry in the past was more or less the same as it is today. However, over the last 10 years this long standing belief has been challenged by many researchers and championed by Dr. Lowenstein. Honestly, when you see the changes in sea water chemistry over geologic time it is pretty mind blowing. Especially when these changes are related to some pretty important events in earth history. I know that the fact that the ocean is really important should not come as a surprise, but it is still amazing when you realize that small thinks like the concentration of magnesium relative to calcium can have a huge global impact.

I don’t want to steal Dr. Lowenstein’s thunder by revealing everything, but I would like to provide some of the key points of his talk and the paper’s that it came from, as well as the innovative methods that his lab uses to find these results.

The whole premise of this research is based on salt and more specifically, where does the salt come from and how does it change over time? The salt in the ocean comes from two main sources. The first is rivers. Rivers carry sediment and dissolved salts from weathering of the continent into the ocean. Should this input of salt to the ocean from the rivers of the world change, so would the salinity of the ocean. There is another important source as well: hydrothermal vents/black smokers/mid-ocean ridges. Basically, sea floor volcanic activity and spreading is responsible for dumping a lot of dissolved minerals and ions into the ocean. These two sources mix to create the salinity of the ocean and control the chemistry of seawater. Should these inputs change over time, so would the chemical composition of the oceans. This is not really that far-fetched an idea, but it is still catching on within the scientific community.

A good image showing both the modern salinity of sea water and the ionic composition of the salts. What if these proportions varied over time? (Source: Wikipedia)

In order to determine the chemistry of ancient seawater Dr. Lowenstein’s lab attempts to find places where seawater could have been trapped from its deposition to now. Obviously, this is a difficult task as there are very few ways to preserve water since, as we all know, it has a tendency to evaporate or flow away. To overcome this hurdle they use fluid inclusions in halite (salt) crystals.

This is pretty ingenious. Halite is formed from evaporating ocean water. As the crystals form they incorporate some of the water they’re forming from in tiny bubbles in the crystal structure, called fluid inclusions. This water is literally trapped forever, or until it is released by breaking the crystal. Therefore, in order to find old seawater all Dr. Lowenstein has to do is find old evaporite deposits, which are scattered all over the globe. I know of one that is Silurian in age not far from Ottawa, which means the fluid inclusions trapped in that halite are 445 million year old ocean water.

Halite from Potash Corporation of Saskatchewan Mine in Rocanville, Saskatchewan, Canada (Source: Wikipedia)

Once the halite has been collected it is examined under a microscope for the fluid inclusions, which occur along growth lines in the crystal. If they are present, the crystal is placed inside a scanning electron microscope, frozen using liquid N and cleaved along the growth line, exposing the frozen fluid inclusion to the electron beam. The microscope is able to analyse the composition of the ice bubble by producing x-ray spectra that vary based on dissolved ions. This is done 5 times for each inclusion. Using this method Dr. Lowenstein has been able to analyze ancient water throughout the geologic time scale and as far back as 830 million years!!

The scanning electron microscope at the University of Ottawa. (Source)

So what are the results and implications of knowing how the composition of seawater changes over time?

Dr. Lowenstein proposes a link between the chemistry of seawater and the types of skeletons that coral and benthic organisms such as molluscs can form. It is common knowledge to those familiar with the fossil record that the skeletal composition of corals and other reef building organisms has changed over time between calcite and aragonite. These cycles operate on roughly 100-200 million year timescales and it was believed that they were due to changes in the major ion chemistry of seawater in the past. However, these ideas were based on the rock record, which is subject to major chemical change during lithification, and as such the smoking gun to prove this was missing. Enter Dr. Lowenstein. The measurements presented by Dr. Lowenstein in his talk and his paper in Science show that the fluctuations in ancient seawater chemistry correlate very well with the timing of the calcite and aragonite seas and greatly reinforce our understanding of how important the chemistry of seawater is to sustaining and controlling life.

A graph showing the timing of calcite and aragonite seas. The graph by Lowenstein uses actual measurements to substantiate the timing. (Source)

The biggest implication of understanding the history of seawater is the fact that we now know that seawater chemistry has changed! The oceans play such an integral role in sustaining life on Earth and controlling the climate that understanding this system and how it can change over geologic time is crucial to making future predictions about the ocean and how things like climate change or tectonism could affect it. It is no longer acceptable to just think of the ocean as a salty bowl of soup. Indeed, we must now think of it in terms of a fluctuating system that has profound and basic linkages to the way our planet operates.

Thanks for reading,

Matt

References

Lowenstein, T. K., Timofeeff, M. N., Brennan, S. T., Hardie, L. A., & Demicco, R. V. (2001). Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions. Science (New York, N.Y.), 294(5544), 1086–8. doi:10.1126/science.1064280

Timofeeff, M. N., Lowenstein, T. K., Brennan, S. T., Demicco, R. V, Zimmermann, H., & Horita, J. (2008). Evaluating seawater chemistry from fluid inclusions in halite : Examples from modern marine and nonmarine environments. Geochimica et Cosmochimica Acta, 65(14), 2293–2300.