The Earth Story

Tree rings reveal historical megadroughts in US West

While some chunks of california are dying for rain, evidence has emerged that even the worst drought to strike the region, the Dust Bowl of the 1930's was a pipsqueak compared to some relatively recent events. A team from Brigham Young University in Utah used dendrochronology (the study of tree rings) to tease out records of droughts past from sensitive tree species. How it works is simple, if the tree is drought sensitive, it produces wide rings in years of plenty, and thin ones during dearth.

Their record now extends back to 1429, before the 'discovery' and settlement of America by Europeans. Some of the work involved trees by streams, allowing a gauge of past stream flows to be established. Focussing on the Weber river basin of Utah (though surrounding areas will have been experiencing similar conditions), they discovered several worrying multi-year events that imply much worse than currently experienced is possible. For example, in 1703, a 16 year drought started, that's a long time for even a resilient society like the modern USA to endure. The worst era was that of Columbus's lifetime, with 4 of the 5 worst recorded.

If climate change aggravates the situation further, we could start seeing events that go further than these already scary historic droughts. The work has revealed that the climate oscillates much more strongly in this area than we thought, since the 19th century, when the area was settled was wetter than the average. Water resource management workers will be using this research to help build the sort of resilience into the water use system that will take account of the newly revealed reality.

Our recent post on the current drought: https://www.facebook.com/TheEarthStory/posts/689930364401344 Loz

Image credit, galaxy above bristlecone pine: Rogelio Bernal Andreo (DeepSkyColors.com)

http://news.byu.edu/archive14-apr-dendrochronology.aspx

Iceland eruption caused a Dark Age famine in Europe

It is already a matter of record that the climatic effects of the 1783-4 Laki fissure eruption influenced the series of bad harvests that led to the rising societal tensions which exploded in the French Revolution some years later (see http://bit.ly/2w0Zmuc and http://bit.ly/2hQFFzv for a detailed expose), but evidence has emerged suggesting that a similar event from the misty region of European history known as the Dark Ages (roughly 400-1100 CE) was due to another Icelandic volcano, culprit pictured here: Katla. The mechanism is simple, large volumes of sulphurous aerosols erupt into the higher reaches of our globe's airy envelope and sit there, reflecting heat back into space and cooling the planet for several years. The story started in 2003, when spring floods on the Thverá River revealed a buried birch forest on Iceland. Preliminary evidence suggested that it might date from the early 9th century CE, piquing the interest of the team involved in this research: They are working on astrochronology, a new technique whereby C14 peaks in tree rings induced by major solar storms are used to help calibrate dendrochronology and C14 dating...what caught their attention was the possibility that this forest might put another data point into their database for an already well attested event, revealed by a 20x C14 spike in several locations measured in both hemispheres. Said event occurred in 775CE (for our past post on this research see here: http://bit.ly/2uw3P48).

This marker was indeed present in the tree rings, and the record revealed that the 775CE marker occurred some 47 years before the forest was engulfed in sediments from a huge flood in late 822 or early 823. This event was a Jokulhlaup (see http://bit.ly/2wD9G9f), a huge flood caused by an eruption under the Myrdalsjokull ice sheet growing and shrinking above Katla (currently some 700 m thick), lifting the ice off the underlying meltwater and allowing said liquid to escape downhill in one fell swoop. The trees had all been knocked over facing away from the mountain some 35km away in the flood, testifying to the intensity of the event.

Researchers had already found the chemical residue of this eruption in the relevant layers of the Greenland ice cores, but were unsure which smoking mountain might have been responsible. Since the Vikings hadn't arrived on the island yet (history on Iceland starts in 870CE, barring a few Irish monks who left no direct trace), there were no human records. Since then the smoker has awoken a dozen times, the most recent one to pierce the ice being in 1918.

Since the team are engaged in interdisciplinary research with archaologists and historians as well as researching past climates they went and checked the history books, and indeed such records as remain do mention hard times in the years immediately after, wet cold summers, poor harvests, winters so bitter that waterways that normally never froze through (such as Rhine, Danube and Seine) did so, and in such a way that horses and carts could cross directly over. Several years of nonexistent summers and bitter winters followed, characterised by widespread famine and plague, as they did the Laki event of 1783. This also makes the eruption the oldest precisely dated event, with a precision of a month or three.

Loz

Image credit: 1: Alamy, others Ulf Büntgen/University of Cambridge

http://econ.st/2vtbrp6 http://bit.ly/2s95mvA Original paper, free access: http://bit.ly/2uuQRaY

Tree rings contain records of solar storms

A new form of dating has just entered the lexicon of archaeology using a refinement of dendrochronolgy, long used to calibrate radiocarbon dating and determine when a piece of wood found at a dig was felled. The authors propose a new technique that they call astrochronology, and hope that it will help fix some long sought after key dates that are at present poorly constrained. The width of tree rings already give us climate proxies for years of plenty or drought and in many cases the database allows the precise season and year of felling to be determined (though wood can be reused so the date is the oldest possible, archaeological context is vital to increase the degree of certainty).

Radiocarbon dating is based on the formation of C14 by cosmic rays and charged particles streaming off the sun as 'solar wind' that is then absorbed by plants and animals during growth. On death the radioactive unstable carbon starts to decay, and the ratio of this isotope to C12 (a carbon atom with 2 less neutrons in its nucleus) gives us a rough date for organic matter up to a certain age limit by which point the C14 has decayed to a level below the detection limit of the measuring instruments. Some years though the sun has huge electromagnetic storms which blast the Earth resulting in much higher levels (up to 20x) of C14 in the tree ring for that year in every tree then alive on the planet.

The first such event was found in 2012 dating from 775CE and named a Miyake event after the Japanese scientist that spotted it. Recently a paper was published identifying a second in 994CE and the search is on for more, hoping that the presence of such rings in archaeological material will build up into another database allowing some chronologies to be better constrained. Known as floating chronologies they can have internal consistency without being pinned down to a precise date (since the accuracy range in radiocarbon dating is typically a century either side of the date, depending on the availability of other datasets such as tree rings).

Mayan dates are an example, we have their calendar, can read their writing but have few tie points to accurately measured dates in our calendar system. Another is the precise dates of Old Kingdom Egypt, the epoch of pyramid building. We have reasonably established king lists and reign lengths, rough radiocarbon dates, but the discovery of a spike during this period would allow the first precise dating. Since the dating of other Bronze age civilisations in the Near East is hung of the better established Egyptian one the potential for new discoveries would be great, allowing many histories to be precisely tied to our calendar for the first time. China's first accurate date is 841BCE and Europe's 763, both based on observed and dated astronomical events, mostly solar eclipses.

Previous dendrochronology looked at rings on a decade by decade basis, but now scientists are working hard on recalibrating the entire system on a year by year basis (partly using statistical methods as analysing every ring in the record would be expensive and time consuming) and seeking out further Miyake moments. In reference to the first discovered, the Anglo-Saxon chronicle records a weird red crucifix in the sky in 774 that might well by the display of aurora borealis that blasted our planet with extra radiation and the spike has been found in wood from Russia, New Zealand, Germany and the USA, proving the global nature of the event.

This is a very exciting development, with the potential to revolutionise ancient world dating and allow us to finally constrain what happened when in the more distant past of our varied human cultures.

Loz

Image credit: Arnoldius

http://bit.ly/2bGFGTS http://bit.ly/2b11p6k Original paper, paywall access: http://bit.ly/2cZBslH

What are tree rings?

When you look at a fresh cut piece of wood, you see concentric rings. One can count these rings in order to deduce the age of the tree. In fact, an entire branch of study known as dendrochronology pursues answers to questions about past climate simply by analyzing variations in tree rings. So what exactly are tree rings?

The answer to this question lies in the physiology of wood formation. Trees are most photosynthetically active during a period referred to as the “growing season”, when the sun is strong and resources are abundant. For most of the US, the growing season is April – September (give or take a month or two). For the first portion of the growing season, trees put on new growth in the form of “earlywood”. Earlywood is less dense (thinner cell walls, and wider lumen [cell wall opening]) with wider vessel elements. At some point during the growing season trees begin putting on new growth in the form of “latewood”. Latewood is denser (thicker cell walls, narrow lumen), with narrower vessels, and is visually darker in color. The point in which a tree transitions from earlywood to latewood production throughout the growing season varies both within and between species. This transition point is particularly important to scientists because the percentage of latewood is the most important factor controlling the density of wood (averaged across a tree), the mechanical strength and structure of the wood, as well as the yield and quality of paper pulp.

Trends in wood formation are fairly well studied. Between the ages of one to about 10-15 years of age, a tree is putting on a large percentage of earlywood each year (with percent latewood increasing each year). This portion of the tree is known as the “juvenile core”. Once the tree transitions to the “mature core”, the percentage of latewood produced each year stabilizes. Mature wood of trees is structurally superior to the juvenile wood since it contains the highest percentage of latewood.

So when you look at a fresh cut piece of wood and begin counting the rings to deduce the age; remember, you are not simply counting rings, but macroscopic differences in the physiology of earlywood and latewood!

-Greg Aegis

Further Reading http://wapo.st/1fKleym http://bit.ly/1I3Birk http://1.usa.gov/1I3Bnv7 Previous posts: http://bit.ly/1OgHvPO http://bit.ly/1LcDnlq

Image http://bit.ly/1RA8qve

Did a Gamma Ray Burst Irradiate Earth in the 8th Century?

In 2012 scientist Fusa Miyake announced the detection of high levels of the isotopes Carbon-14 and Beryllium-10 in tree rings formed in 775 CE, suggesting that a burst of radiation struck the Earth in the year 774 or 775. These isotopes form when radiation from space collides with nitrogen atoms, which then decay into these heavier forms of carbon and beryllium.

A nearby supernova was ruled out as the cause of the burst, as no observations were recorded at this time, aside from a possible sighting in 776 CE, which was too late to account for the C-14 data. Miyake also ruled out solar flares because they are not powerful enough to account for the observed excess of C-14.

Astronomers Valeri Hambaryan and Ralph Neuhӓuser of the Astrophysics Institute of the University of Jena in Germany may have a better answer: a nearby short duration gamma burst. They suggest that two compact stellar remnants (black holes, white dwarfs or neutron stars) collided together, releasing a gamma ray burst. In these mergers the burst is short and intense, lasting less than two seconds. This explanation would be consistent with both the C-14 measurements and the absence of any recorded events in the sky. The merging stars could not have been closer than 3,000 light years away, of the burst would have led to the extinction of some terrestrial life. Hambaryan and Neuhӓuser believe the gamma ray burst originated 3,000 - 12,000 light years from the Sun.

-JF

Image: artist's impression of the merger of two neutron stars (Credit: NASA/Dana Berry) Larger image: http://www.ras.org.uk/images/stories/press/114914main_neutcollidecloseup_strip.jpg Sources: http://www.sciencedaily.com/releases/2013/01/130121083255.htm http://www.ras.org.uk/news-and-press/224-news-2013/2215-did-an-8th-century-gamma-ray-burst-irradiate-the-earth

UK National Tree Week Music from Trees! Trees have a unique physiology where each year’s growth is represented as a new layer between the wood and the bark: as a ring. The inner portion (“spring wood”) of a growth ring forms early in the season, when growth is comparatively fast, and the wood formed is less dense. The outer portion (“summer wood”) forms slower, during the second half of the growing season, and is comparatively denser. In the early 1900’s an astronomer named A. E. Douglass developed a method of dating based on tree ring growth patterns known as dendrochronology. Lately, this science is primarily used in paleoecology, the study of past ecologies, to learn about our past climates.  Tree rings have also inspired an intriguing art project called “Years” by German artist Bartholomaus Traubeck. He created a record player that interprets slices of wood (known as “cookies”) much the same way a conventional record player interprets a vinyl record. This is accomplished using a set of cameras that read the width of rings that pass under its view, and translates it into piano music. Traubeck described fir trees as a dark c-minor sound, ash as “compressed and complex”, and walnut as a stressed artistic sound.  While this does not relate to dendrochronology scientifically, it offers anyone who appreciates art, music, and a handsome tree, another interpretation of tree rings.  -Greg Aegis Sources with videos http://climate.nasa.gov/blogs/index.cfm?FuseAction=ShowBlog&NewsID=740 http://traubeck.com/years/ Sources without videos http://www.shef.ac.uk/archaeology/research/dendrochronology Photo Credit http://www.redorbit.com/

TREE RINGS! Most of us know that by counting the rings inside cross-cuttings of trees, we can obtain an age for a tree. However, the childhood practice of counting rings is just the start. Dendrochronology and its sub-varieties have garnered a great deal of respect in the scientific community for going above and beyond simply looking at age. Dendrochronology is the all-encompassing term for the study of tree rings and their structure to interpret information of historical events and processes, but is now accompanied by many branches (ba-dum-tsh!) like dendroclimatology, dendroarchaeology, dendrovolcanology, dendrochemistry, dendrogeomorphology, and the list goes on! It’s all from those itty bitty rings we used to count as children. As of now, dendrochronology gives us an unbroken tree-ring record of 11,000 years into the past (1), so the “dendro” sciences are certainly a force to be respected!  A lot of the basis for dendro studies comes from the idea that ideal growing conditions for the tree will produce a larger ring (by width), and poor conditions will produce a smaller ring. The same principle applies to farm crops. The crops need water, nutrients, sun, and the right temperatures. When you’ve got the right combination, your crops grow larger, but when you don’t, they suffer. Trees essentially lock in information about that growing seasons’ microclimate conditions when they produce a ring. Trees begin forming any given years’ ring at the start of the growing season, and as temperatures drop and the growing season comes to an end, we get a visible ring where the following year will commence growth.  Trees are fairly accurate as estimates of former climate as well as nutrient levels in soil, but are still tricky to read. Some trees may present false rings, where perhaps some large storm or disturbance event happened late in the growing season, but the tree continued to grow a bit after the event happened. Many trees in a similar situation will show a false ring at the point in time where the event occurred as if the tree is saying “just kidding! Not done growing yet.”  Although it is a difficult (and sometimes tedious) pursuit, the study of tree-rings has certainly earned its spot on the scientific global stage, and continues to astound scientists and amateurs alike!  -BN Photo Credit: Compton’s Pictured Encyclopedia and Fact Index (1947) Image hosted by: http://massmirage.tumblr.com/tagged/Compton%27s-Pictured-Encyclopedia-and-Fact-Index%281947%29 Further Reading:  (1)Becker, Kromer. 1993. The continental tree-ring record — absolute chronology, 14C calibration and climatic change at 11 ka. Elsevier B.V http://scienceline.org/2007/03/ipcc-driscoll-treerings/ http://www.ncdc.noaa.gov/paleo/slides/slideset/18/18_355_slide.html http://www.yale.edu/fes519b/saltonstall/trmethods.htm

Tree rings reveal historical megadroughts in US West While large chunks of the US are dying for rain, evidence has emerged that even the worst drought to strike the region, the Dust Bowl of the 1930's was a pipsqueak compared to some relatively recent events. A team from Brigham Young University in Utah used dendrochronology (the study of tree rings) to tease out records of droughts past from sensitive tree species. How it works is simple, if the tree is drought sensitive, it produces wide rings in years of plenty, and thin ones during dearth. Their record now extends back to 1429, before the 'discovery' and settlement of America by Europeans. Some of the work involved trees by streams, allowing a gauge of past stream flows to be established. Focussing on the Weber river basin of Utah (though surrounding areas will have been experiencing similar conditions), they discovered several worrying multi-year events that imply much worse than currently experienced is possible. For example, in 1703, a 16 year drought started, that's a long time for even a resilient society like the modern USA to endure. The worst era was that of Columbus's lifetime, with 4 of the 5 worst recorded. If climate change aggravates the situation further, we could start seeing events that go further than these already scary historic droughts. The work has revealed that the climate oscillates much more strongly in this area than we thought, since the 19th century, when the area was settled was wetter than the average. Water resource management workers will be using this research to help build the sort of resilience into the water use system that will take acocunt of the newly revealed reality. Our recent post on the current drought:https://www.facebook.com/TheEarthStory/posts/689930364401344 Loz Image credit, galaxy above bristlecone pine: Rogelio Bernal Andreo (DeepSkyColors.com) http://news.byu.edu/archive14-apr-dendrochronology.aspx