Folks who have been reading here for a while will notice certain themes that interweave. I look at climate and weather issues for a while, then wander off to economic issues, then spend some time looking at rocks and cements, and tour some old Egyptian tech, then…
This looks disconnected and like the various topics are quite orthogonal. They aren’t.
Everything is connected, just with variations of strength.
Geology tells us a great deal about our history. History tells us how our current society, and thus its economy, will unfold. Climate has had a drastic impact on that historical change (all from natural and extreme climate changes). The Egyptian history is particularly rich in records of economic, climate, and cultural changes. Rocks give a much longer term view of change. That the Egyptians likely had the technology to make ‘liquid stone’ is also an intrigue.
Today I was wandering down a similar connected path, and was reminded of a local soil condition where I grew up. Hardpan. Also called “Caliche”. It is a calcium carbonate sedimentary rock deposited inside soils.
In my home town region, we had a layer of ‘hardpan’ at about 10 feet down. It varied by location. Sometimes deeper, sometimes shallower. If you were unlucky to have hardpan at shallow depths, then tree roots could not penetrate it. The soil above the hardpan could become depleted in some minerals, too enriched in others. Locals grew a lot of peaches and that was one of two local major cash crops. (The other being rice). Rice farmers liked soils that held the water in place, so it was largely grown on the adobe clay soils out west of town. Peaches like loamy sandy soils, so tended to be grown east of town. But some folks wanted to grow peaches where the soils were not as deep as “east of town”…
So one of the odd bits of technology I learned about (at about 6 years old) was the process of “deep ploughing”. There were these very large very heavy steel plough wedges that had very heavy chains on them. They would be started into the dirt and dig themselves down in until they hit the hardpan layer. With some work (or starting at an already punctured area) they would break through. Then a Very Large Caterpillar Tractor would haul this steel plane back and forth through the field, using the chain to break up the hardpan layer. At that point, planted trees could send their roots through it and keep the layer open.
Has a nice write up of hardpan ‘deep tillage’ and pictures of some interesting plows they use. Their hardpan must be much shallower as the plows look to be about 1 meter or so deep. Maybe 1.5 at most.
Also talks about it. How, from a vintners point of view, it is important to give room for the grape roots to grow.
Until you have attempted to dig a hole in Hardpan you can only visualize it in an abstract sense how hard it is, concrete would be about right. Trees do not live in these hills, of this I am sure because the hardpan is so solid that without machines breaking through there is no way for them to obtain the nutrients and moisture to survive the summers. The hardpan is formed over millions of years by minerals being washed down during winter rains and having the right composition to bond with each other. The hardpan on our parcel varied in depth from 2-3 feet below the surface and varying thicknesses of 1 to 3 feet thick. The grapes need deeper soil than exists above the hardpan layer to succeed, they also need drainage or the roots will set in water and rot. Nothing, including water, will penetrate the hardpan layer, which meant something had to be done to break it up.
The most common way for a farmer to break up the hardpan is to hire a D-10 or larger Cat with a 7 feet deep ripping shank to rip the ground in two directions. This breaks the hardpan into chunks and does some mixing of the soils.
That pretty much sums it up. In my backyard, when I was about 8, my Dad showed me how to dig a well. Mostly, I think, as it was “old knowledge” and he just thought I ought to know it. Partly, I suspect, as a way to ‘play in the dirt’ and remember life back on the farm and share with his kid. We used a posthole digger. One of the kinds that you turn like an auger. It has a standard pipe for the shaft, so you can add sections between the handle and the blade. At 10 feet down, no water. We hit hardpan at 11 feet. The first 11 feet had been pretty easy. We’d do a foot or two at a time, and then do something else. The hardpan was a great discouragement, as we had no idea how thick it was. “Digging” through it was more like having the tartar removed from your teeth. Scrape scrape scrape scrape… (Speaking of calcium mineral deposits…)
After about a week more, we were at about 13 feet. We broke through the hardpan into a more sandy soil. Water rose to 10 feet down in the well. We ‘completed the well’ down to 14 or 15 feet and put in the well foot valve, screen and pipe. A small pump and shed over it completed the installation. So in the end we had 4 foot of water in a 14 foot well. We could pump at somewhere near 25 gallons per minute. ( I think that pump didn’t do much more than that). The water was very sweet and clean. (It had likely been trapped below that hardpan for a very long time…)
That well watered many summers of vegetable gardens. Eventually the town decided to put in water meters – we’d not had them most of my life; and the well had to go onto a ‘drop cord’ so as not to be obviously there. This simple act of bonding of father to son and both to the land had been made an illegal thing by government fiat. Several decades later, after my parents had died, I removed the well pipe and let the land reclaim the well when the home was sold. Yet that hole in the hardpan will continue providing water to trees for some large area around as it lets water rise into the soils above that hardpan layer.
The point behind this is pretty simple. I know hardpan. In that way you can only know something that you have grown up with, fought with, and heard the Cat Driver cussing about over lunch when the chain broke and a very expensive plough blade was 15 feet down. (Call the backhoe!)
Later in college I learned the word “Caliche”. At an Ag School geologists spend a bit more time on soils than at non-ag schools. But even there, they don’t like to use plain old English words as they don’t sound fancy enough. So Caliche it was.
Oh, and our vineyard above? He took the advice of my Alma Mater and did a very aggressive kind of hardpan treatment.
Having some experience with hardpan, I knew that if I wanted a special quality vineyard something more than the standard practice of ripping was in order. The University of California at Davis published a guide on dealing with hardpan in existing vineyards. The ripping only of vineyards sometimes leads to the hardpan reforming after several years and again blocking root development. The University recommended digging trenches thru the hardpan between the rows of the existing vineyard. The roots then would move into the trench and down deep. I also found an article about using this practice in new vineyards at Arciero Winery, in Paso Robles. I traveled there and met the farm manager who was nice enough to give me a tour and show me the results they have seen in the plant development compared with non-trenched vineyards.
The results seemed astounding, four year old plants in the trenched fields were more than twice the diameter of non-trenched fields. I was sold, the problem was cost. Renting a machine capable of doing this work would be more than $200.00 per hour and doing our forty acres would take more than 1,000 hours. We decided the only answer was to purchase a used excavator and I would learn to operate it.
Then again, his hardpan was only 2-3 feet down, not 10 to 15… But notice in particular that statement that it can reform in just a few years. That matters. It involves water, carbon dioxide, and mineral leaching. It directly ties rates of caliche formation to atmospheric CO2 consumption and precipitation.
Now caliche has a broader set of forms than the old hardpan. In some places you can get ‘nodules’ forming in the soil. Little balls of rock like things, just setting up in the soil. Caliche isn’t just a strange California thing, either. It is pretty much global. Search this document for “caliche” and it’s all through the thing. We also see here some of the many ways in which carbonates get deposited in normal day to day weather and biological processes:
Caliche–The prevalent occurrence of caliche in the Tertiary and Quaternary deposits of the southern High Plains has presented a puzzling problem since the early work on these beds. Caliche occurs abundantly in these deposits from Texas and New Mexico northward to Colorado and Nebraska. The earlier literature dealing with the caliche problem in Texas has been summarized by Sayre (1937, pp. 65-72) and, in western Kansas, by Smith (1940, pp. 90-92). In southwestern Kansas it has been common practice to refer to beds which contain only a small percentage of calcium carbonate as “caliche” and to use the term more or less interchangeably with “mortar bed.” It is my opinion that there occur in these strata two distinct types of calcium carbonate deposits, and that the origin of the two may or may not be similar. The first type consists of irregular beds and nodular bands of chalky calcium carbonate, occurring in both coarse and fine material and transgressing various types of material. This type, to which the use of the term “caliche” is here restricted, almost invariably contains some impurities either of silt, sand, or gravel, and locally contains some chert. The other type, which, for lack of a better name, will be referred to as “mortar bed,” consists of cemented zones, beds, or lenses of sand or of sand and gravel. The cementation may have been produced by percolating ground water, localized by the texture of the deposit, or it may have been produced in a manner similar to that described for caliche. Mortar beds locally occur as cemented lenses of sand within a thick sequence of sand and gravel or of fine sand and silt. The texture of the cemented bed may be either coarser or finer than that of the enclosing material.
The origin of caliche will not be discussed in detail here. However, one hypothesis that seems to fit the conditions existing in this area will be presented. During the latter part of the Pliocene and the Pleistocene, the time during which caliche was being formed in this area, the Rocky Mountain region to the west stood high above the adjacent plains and was being vigorously eroded by competent streams. The streams transporting sediments to the plains area carried in solution calcium carbonate, derived from the igneous and sedimentary rocks being eroded. In the plains region these streams were aggrading–filling their channels, which often shifted in position, and overflowing and spreading deposits over their flood plains. Although it is possible that the first effect of a cold Pleistocene climate was not felt in the Rocky Mountain region until after some caliche formation had taken place, it seems certain that the water flowing from these mountain streams was relatively cold. It is a well-known fact that cold water heavily charged with calcium carbonate will, when heated, lose part of this dissolved material. When floodwaters from these streams spread over their broad flood plains the temperature of the water must have been raised sufficiently to cause some precipitation of the dissolved lime. It is also well known that calcium carbonate will be precipitated from an aqueous solution at constant temperature if carbon dioxide is removed. It is certain that grass or other forms of vegetation covered the extensive plain of alluviation, and it is possible that the plants may be able to extract carbon dioxide from the water flooding the surface. Thus, the factors producing deposition of caliche in these sediments seem to be a rise in temperature of the waters of the depositing streams plus the possible extraction of additional carbon dioxide by vegetation. These factors probably were augmented by evaporation and concentration of the solution by drying winds and sun.
Dissolved carbonates deposit out of normal runoff waters when there are any of: warming, evaporation, plants, loss of CO2, …
That’s why it’s found pretty much world wide.
Where does that dissolved carbonate come from? Well, some might come from carbonate rocks, but other comes from non-carbonate rocks plus CO2 from the air. In “climate science” this is assumed to be a constant process, but it isn’t. What happens in the soils is highly variable over time. Often heavily dependent on rainfall or rain acidity.
Per the Army, you get more of it in semi-arid conditions.
Caliche is a general term for any secondary calcium carbonate (CaCO3) that forms in sediments or in voids and crevices within bedrock just below the surface in semiarid regions, as a result of soil-forming processes (pedogenic caliche) or ground-water evaporation (ground-water caliche); it is material left behind by the evaporation of ground water or soil moisture that is no longer present at that level, although ground water may be present at much lower depths beneath the caliche.
Caliche has several forms:
. thin, white crusts or rinds on individual pebbles and fillings in pores and crevices in soil or bedrock;
. discrete, hard, white nodules or lumps;
. or thick, massive, rock-hard accumulations that cement gravel, sand, and fines of a sediment, producing a dense and impermeable layer that resembles fresh-water limestone. Such massive caliche layers (calcretes) are common in deserts at depths of a few centimeters to about 2 m. The layers are a few centimeters to several meters thick.
Occasionally, caliche acts as a barrier to percolation of soil moisture from precipitation, helping to retain seasonal moisture near the root zone in vegetated areas. Some alluvial fans eventually become so plugged with caliche that surface runoff can no longer percolate into the gravel, producing short-lived but disastrous flooding in their terminal regions.
Now think about this for just a minute. It happens fast enough for individual farmers to notice in their lifetimes. It can be from “soil forming processes” or “groundwater evaporation” both of which vary widely with changes in precipitation (that in turn varies widely with climate changes and the Ice Age cycle) and it depends on carbonate to happen.
Think maybe an Ice Age Glacial might just make things more dry and arid, causing more carbonate to be trapped in caliche deposits and less making it back to the oceans? Think maybe when the interglacial comes, all that added water might just erode more carbonate back into the sea, and have more of it consumed by plants as the biosphere rebounds, eventually to be put back into the air by the animals eating those plants and the decay of dead ones over, oh, about 800 years?
This is just a huge unexplored part of the carbon cycle. The size is large enough to account for the known variation of CO2 levels with the glacial / interglacial cycles. The things that drive it are directly related to the changes of climate that happen over those events.
But someone will undoubtedly say that “it’s from carbonate rocks, not from the air”… and besides, it isn’t THAT much drier during a glacial, certainly not enough to cause a lot more caliche to form and taking a lot more CO2 out of the air faster…
Spanish and American researchers have conducted a mineralogical and chemical analysis to ascertain the origin of “terra rossa” soil in the Mediterranean. The results of the study reveal that mineral dust from the African regions of the Sahara and Sahel, which emit between 600 and 700 tons of dust a year, brought about the reddish soil in Mediterranean regions such as Mallorca and Sardinia between 12,000 and 25,000 years ago.
The study, which has been published in Quaternary Science Reviews, finds that African mineral dust additions “play an important role” in the origin of the soils (palaeosols) in the Mediterranean region, namely on the island of Mallorca. The results resemble those published regarding the soils on Sardinia, “which indicates the likelihood of Africa being a common source”.
In turn, “African dust explains the origin of the ‘terra rossa’ soils in the Mediterranean region located on top of mother carbonate rock,” Ãvila added.
Now think about THAT for a minute. it was so dry and dusty that all that Sahara dust was making soil layers in Europe. ( That also implies a lot of wind headed north too…) Just at the last, deepest part of the glacial period. Then it all ended…
The wiki has a lot to say about it, including a rather remarkable section on uses for it. (Who knew? You can actually use it for things)
Caliche (pronounced kuh-lee-chee) generally forms when minerals are leached from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon), at depths of approximately 3 to 10 feet under the surface. Caliche generally consists of carbonates in semiarid regions, while in arid regions, less soluble minerals will form caliche layers after all the carbonates have been leached from the soil. The calcium carbonate that is deposited accumulates, first forming grains, then small clumps, then a discernible layer, and finally a thicker, solid bed. As the caliche layer forms, the layer gradually becomes deeper, eventually moving into the parent material, which lies under the upper soil horizons.
However, caliche can also form in other ways. It can form when water rises through capillary action. In an arid region, rainwater will sink into the ground very quickly. Later, as the surface dries out, the water below the surface will rise, carrying dissolved minerals from lower layers upward with it. This water movement forms a caliche that tends to grow thinner and branch out as it nears the surface. Plants can contribute to the formation of caliche as well. The plant roots take up water through transpiration, leaving behind the dissolved calcium carbonate, which precipitates to form caliche. Caliche can also form on outcrops of porous rocks or in rock fissures where water is trapped and evaporates. In general, caliche deposition is a slow process, but if enough moisture is present in an otherwise arid site, it can accumulate fast enough to block a drain pipe.
The point here is that in human terms it may mostly be a slow process, but in geologic terms this is a fairly fast process ( plug a drain pipe!) and is highly dependent on the amount of water (both as a leaching agent and as an evaporative process). If that carbonate isn’t going into making minerals, some of it would be ‘otherwise engaged’. Either staying in groundwater solutions, or draining back into the oceans.
Is a typical soils chemistry kind of paper. Where do the minerals come from, where do they go. How do we get potassium and calcium into soils and on into drainage water. It’s not long, and not hard to read. Buried down in the middle of it is a small reference to where the Carbonate comes from. It’s that bit that matters here. Mostly the paper is just showing that weathering of feldspars is the source of most of the associated mineral ions and that there is a net balance. “ANC” is Acid Neutralizing Capacity. It takes acid to weather the rocks.
The annual ANC arising from primary mineral hydrolysis is approximately 1500 to 1700 mol(c) ha-1 yr-1 (Tables 1, 2, 3; H* consumed). The current annual acid input estimated from pH of bulk precipitation is about 70 mol ha-1 yr-1. Van Breeman et al. (1984) suggest that the ratio of external proton inputs (acid deposition) to internal proton production (mainly net cation uptake and oxidation reactions such as nitrification) is a good measure of ecosystem sensitivity to acid. The EIPR values > 0.5 generally show Al mobilization and SO4 2- retention in soil, and result in Al export and pH depressions. The EIPR ratio has a value of < 0.1 in watershed SC-5 under current conditions (inputs of 70 mol ha-1 yr-1; uptake and nitrification estimated at 800 mol ha-1 yr-1 from Clayton and Kennedy, 1985; the other source of protons is from carbonic acid dissociation).
So the amount of “carbonic acid” directly drives the rate of hydrolysis of the feldspars. That hydrolysis directly drives the soil fertility for needed minerals like K and Ca and the levels in the runoff water. Water that enters the groundwater carrying that CO2 as carbonates.
Add more CO2, you get more rock decomposition for feldspars (and others) and more formation of carbonate rocks IN THE SOILS of the world. I’ve not seen much mention of CO2 as contributing to greater availability of soil minerals to plants. I’ve not seen much discussion of CO2 sequestration in SOIL being directly related to atmospheric CO2 levels.
I’ve seen even less discussion of how normal cyclical variation in precipitation might cause atmospheric CO2 to rise and fall with the precipitation changes of glacial / interglacial cycles. Does the level of caliche formation, globally, drop off during profound cold periods due to less rock decomposition in the drought? Or does it increase due to more evaporation of ground waters through the now arid soils? How does this influence global CO2 levels? It is presently warm and relatively wet (but was warmer and wetter just a few thousand years ago). Does the greater erosion of rocks lead to more CO2 in the air from carbonate rock erosion and lower caliche formation in areas that are no longer having excess evaporation? Or does it lead to less from “carbonic acid” being consumed in the feldspar erosion?
I suspect that we get more, as the more rapid water cycle causes more net erosion of all those global carbonates into the ocean where it can form carbonic acid and emit CO2 (that then causes even faster erosion of feldspars, and cycle more carbonates into the water cycle). During cooling drying times, I’d expect less carbonate flux into the oceans, thus less CO2 flux to the air and less carbonic acid breaking down minerals. That would then lead to less plant life as everything it needs becomes more dear. Less water, less minerals dissolved in the waters, and less CO2 in the air.
All in all, it looks to me like a water driven carbonate cycle, with rocks and caliche as important storage places.
People are just not very important to all that.
As a sidebar on feldspar:
It looks like it breaks down in the presence of acid solutions. This confirms the idea that you could use alkaline / base solutions to form a cement between rock particles. So taking a load of ‘rotted granite’ (that they had in Egypt) or similar feldspar rich sands; perhaps treating it briefly with an acid, then mixing with some clay (hydrolyzed feldspar product) some quartz sand (similar origins) and then making the whole thing basic (with Natron and / or quicklime) ought to cause the formation of cementing materials of feldspar derived minerals between the grains. Simply trying to run the weathering process backwards might well form a very nice stone like material.
Hopefully this article shows how unexplored and ignored the question of soil carbonates has been in the “cimate science” we’ve been subjected to so far.
It is a major issue, and it is largely swept under the rug with a wave of the CO2 wand and assumption that “nothing changes”.
But we KNOW things change. Europe is not under a constant barrage of red dust from Africa. Caliche forms in farmers fields in years, not centuries. Rainfall on forests can directly modulate the decomposition of feldspars and the consumption of CO2 in the process.
All this DOES matter. To ignore it just means we’re making decisions based on ignorance of what is really driving CO2 and what CO2 really does. It feeds plants. Not just directly AS CO2, but indirectly via carbonic acid helping to break down rocks for minerals the plants need.
Hopefully, too, I’ve managed to show just a little bit how these things interweave. The Egyptian chemistry of ‘liquid stone’ ties directly to the CO2 cycle and weathering. The European red soil ties directly to the extreme desert conditions at the end of the last glacial, ending in the warming that created a wet Sahara, that then turned back to desert in the cooling catastrophe that drove the proto-Egyptians out of the central / southern Sahara and into the Nile valley about 6,000 years ago. The coming Ice Age Glacial that will return those extreme droughts, and the African red dusts to Europe. Perhaps itself driven by some cosmic dust.
“All we are is dust in the wind”…
And a bit of water and CO2…