Constant weathering
Surprisingly stable behavior despite glacial and interglacial periods
That weathering has to do with the weather is obvious in itself. All the more astonishing, therefore, are the research results of a group of scientists from the GFZ German Research Center for Geosciences in Potsdam and Stanford University, USA, which show that variations in the weathering of rocks over the past 2 million years have been relatively uniform despite the distinct glacial and interglacial periods and the associated fluctuations in the Earth’s climate.
The researchers have observed a most stable behavior in marine sediments, fed year after year through the rivers of the world with silicate rocks, the product of weathering – variations in the weathering rates were actually less than ten percent.
The surface of the Earth is under constant change: chemical reactions between water and rocks dissolve minerals, form soil and wash removed component parts in the form of sediments into the oceans. Hereby, carbon dioxide is extracted from the atmosphere and deposited in the oceans rendering global temperatures favourable for human life.
Scientists actually expect high fluctuation in weathering rates during the cold and warm periods. If scientists measure the transport of weathered rocks in the rivers worldwide today, they find slower rates in the drier and colder regions. During the glacial period, temperatures and rainfall were lower and vegetation cover was reduced in many regions of the world i.e. weathering rates are reduced during the glacial periods. On the contrary, increased weathering reactions due to increased rainfall, highter temperatures, more vegetation and melting glacial ice are expected during the warm periods. “If you look at how these climate attributes control weathering rates today, you would expect that weathering and sedimentation rates also varied widely between glacial to interglacial times,” explains the Geochemist Friedhelm von Blanckenburg of the GFZ Potsdam. “But what we found was the complete absence of resolvable variations though the last two million years”.
Together with his GFZ colleague, Julien Bouchez, a research scientist now at the Global Institue of Physics in Paris, they applied a geochemical technique, which has been playing a central role in determing the rate of Earth surface processes at the GFZ during the past few years. One compares the concentration of two forms, or isotopes, of the element beryllium (Be). 9Be is found naturally in silicate rocks on Earth; 10Be is a radioactive cosmogenic isotope produced by the collision of cosmic rays with nitrogen and oxygen molecules in the atmosphere. “Because 10Be rains down onto the Earth’s continents and oceans at more or less a constant rate, it is like a clock that can be used to time processes,” von Blanckenburg said. “9Be, on the other hand, can be used to calculate how much dissolved rock has been washed into the oceans from rivers.”
By determining the ratio of 10Be to 9Be in marine sediment layers, it was possible to reconstruct the weathering flux for the last two million years with the surprising result that there was little change between glacial and interglacial periods.
And now, scientists Kate Maher and Daniel Ibarra from Stanford University (USA), who specialize in using computer models to understand how the flow of water controls weathering, have compiled data on river-to-ocean flow from an ensemble of climate models and have calculated the average discharge from rivers at different latitudes during glacial and interglacial times. The Stanford scientists reached the same results. Because the global water discharge is strongly controlled by the large tropical rivers, whose water volume hardly varied between the glacial and interglacial periods, the global rock weathering showed only moderate fluctuation.
In spite of this explanation questions still remain open: Why did the melting of glaciers and the release of large amounts of finely ground rock at the end of the glacial period have no influence on weathering and why can the effect of globally varying vegetation not be observed?
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Friedhelm von Blanckenburg, Julien Bouchez, Daniel E. Ibarra, Kate Maher: „Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles”, Nature Geoscience, Advance online Publication, 08.06.2015, DOI: 10.1038/ngeo2452
Weathering is a “magic” word in climate science.
One just has to write “weathering” in any paper and the faithful are mesmerized into believing CO2 causes everything. No evidence or data needs to be presented, just the idea of weathering.
I would expect geochemical weathering rates to respond to the big Earth tectonic changes, such as the Andes uplift that occurred 15 Million years ago, or the Himalayan uplift that started 40 Mya. Those big uplifts are what would present new, unweathered rock to erosion and sedimentation layering. Their time scale is looking for a signal far, far down in the noise at 2 Mya to present.
Too many variables with unknown changes, 10Be is not constant, big variation in sedimentation rates between glacial and interglacial periods, and …………. = not a plausible conclusion.
The surface of the Earth is under constant change: chemical reactions between water and rocks dissolve minerals, form soil and wash removed component parts in the form of sediments into the oceans. Hereby, carbon dioxide is extracted from the atmosphere and deposited in the oceans rendering global temperatures favourable for human life.
Wrong. It has gone too far. CO2 starvation caused by geological weathering is predicted to be a future cause of biosphere extinction:
https://hal.archives-ouvertes.fr/hal-00297542/
The best CO2 level for life on Earth is somewhere in the range 1000-1500 ppm.
Would that not implicate that the atmospheric CO2 did NOT change during those periods?
A surprising finding:
The analysis goes in circles when there are multiple fundamental errors as to what is the physical cause of what is observed.
The physical cause in this case (what is the cause of the glacial/interglacial cycle and what is the cause of the cyclic changes within both periods of climate) affects the proxies such Be10 and most certainly effects erosion rates.
There are cyclic massive changes in precipitation (increase in precipitation when the planet warms and decreases in precipitation when the planet cools) and there is a massive increase in wind speed and increase material ejected from the continental sized ice sheets that cover the planet for 100,000 years during the glacial phase and when the planet cools cyclically (smaller cycles) during both the glacial phase and interglacial phase.
The increase erosion caused by increased wind speed and grinding of rock by the massive ice sheets will partially offset the change in erosion due to precipitation changes.
As noted above Be10 is not constant as the geomagnetic field strength is not constant which invalidates the analysis which asserts that erosion rates do not change when the planet gets colder. The geomagnetic field strength and orientation (location of the geomagnetic north and south poles on the earth’s surface) is the principal factor that cause variation of the amount and intensity of the high speed cosmic particles that strike the earth which in turn affects the production of cosmogenic isotopes such as Be10.
As noted in the papers quoted above in the last 10 years the geomagnetic field specialists have found that there are immense cyclic changes to the geomagnetic field. The immense cyclic changes to the geomagnetic field in turn causes immense cyclic changes to the earth’s climate by changing the amount of high speed cosmic particles that strike the earth’s atmosphere. The high speed particles create ions in the earth’s atmosphere which changes the amount of clouds, the life time of clouds, and the albedo of clouds. The immense cyclic changes in cosmic particles that strike the earth’s atmosphere also cause immense cyclic changes in wind speed.
These cyclic immense changes in the earth’s climate explain why dust in the Green Ice cores (the dust is coming from Asia) varies by a factor of 100 with massive increases during cyclic Heinrich events. The Heinrich events occur during the glacial periods and which interglacial periods. This explains why interglacial periods end abruptly after a period of no more than 10,000 years. The periodicity of Heinrich events is 8000 to 10,000 years.
http://onlinelibrary.wiley.com/doi/10.1029/1999JD900929/full
Anyone looking at the last 2 million years can clearly see from all the data that no Interglacial lasts much longer than 12,000 years which is approximately the length of our present Interglacial.
Why people are worried that it will be warmer and warmer baffles me. Since all the declines into Ice Ages are abrupt and steep, the warning signs for these events must be very obscure until the hour it begins.
I’ll see your variations in 10Be and raise you partial pressures in water.
If there is an abundance of 10Be (or 9Be) in the atmosphere then the absorption into the rivers may depend on the concentration already there.
Self-smoothing signal.
Does partial pressure still apply if the molecule in question is not a gas?
Fair point. Technically, no it doesn’t.
But I would have thought that there was more chance for Be to escape the liquid at a higher
water / atmosphere concentration than at lower a lower water / atmosphere concentration.
And as it takes time to deposit, that makes the principle still apply. The signal would be smoothed.
So long as Be can escape solution again.
It has been pointed out to me that most weathering of silicates is by hydrolysis, not carbonation. The rate of hydrolysis will increase with temperature and increase with decreasing pH. But I think that biological processes in the near surface environment would have the biggest impact on silicate weathering. How that could explain the stability seen in the beryllium 10 data I don’t know.