Climate research in the geologic past

Fig.1. Global map as published by Lyell in his "Principles of Geology" (8th edition 1850) to illustrate the past climatic changes.

The climate of a region, as experienced by daily observations of a cool morning and hot midday, was for very long time considered simply the result of the height of the sun above the horizon. This idea forced a very simple view of the distribution of climates on Earth, to the poles temperature dropped, to the equator it raised, forming so large parallel climatic belts. Such a static view of the Earth also didn’t need or even allow climate changes in the past or in the future time.
With the establishment of the deep geological time by the first geologists and naturalists it became clear that not only the distribution of sea and land changed over time, but so did climate.

Read on how Lyell explained climate change by shifting "pseudo"-continents over the globe in the post at the American Scientific Guest Blog.

Modeling Glacier Change 2000-2100

According to a simulation by researchers of the University of Alaska (RADIC, V. & HOCK, R.) and based on various scenarios of precipitation change and a temperature increase, with a mean value of ca. 2°C, as predicted by most climate models, until the year 2100 the 120.000 glaciers located (mainly) in middle latitudes will experience a massive loss of 21% of the actual ice volume.

Observing the reactions of more than 300 glaciers to the climatic change in the period of 1963 to 2004 the models were extrapolated to simulate a significant increase in temperature and slight increase in precipitation and the effects of these variables on the mass balance of the glaciers.
The projections show in the 19 chosen glacierized regions different glacier retreat values, depending from factors like elevation, surface properties and effective temperature rise in the region.
According to the proposed scenarios, mountain ranges in temperate climatic zones will experience the most massive volume change, in the European Alps glacier will loss up to 75% of the actual ice volume, similar values to the New Zealand Alps with 72% and the Caucasus.
In contrast mountain ranges with a high average altitude, like in Asia or the Andes, will experience much lower loss percentages, with an average value of 20%.

I discussed a previous research dealing with possible effects of such glacier retreat on human society in this post.

Fig.1. Regional twenty-first-century glacier volume change expressed in per cent from initial volume in year 2000, the results are presented for 19 regions based on temperature and precipitation projections from the ten applied climatic models, after RADIC & HOCK 2011.

Fig.2. Example of glacier retreat in the Alps in the past 100 years: The Waxegg-glacier in the Zillertaler Alps at the border between Austria and Italy ca. 1900-1903 and 2006. Historic image from ROTHPLETZ, A. & PLATZ, E. (1903): Alpine Majestäten und ihre Gefolge - Die Gebirgswelt der Erde in Bildern, 268 Ansichten aus der Gebirgswelt.
For the history of glacier monitor projects see this post.

Bibliography:

RADIC, V. & HOCK, R. (2011): Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise. Nature Geoscience doi:10.1038/ngeo1052

Geology and Cyclicity: Milankovitch´s idea

"I do not think that's my duty to teach to the ignorant the most basic things, and I have never forced anyone to accept my theory, on so far nobody could expose something."

Milutin Milankovitch in 1950

Milutin Milankovitch (1879 - 1958) was born in a relatively wealthy Serbian family, so it was almost a kind of obligation for him to archive a higher education degree and later take over the family business. So he studied agriculture, but following a passion for natural sciences he went to Vienna, where he in 1904 concluded his studies as an engineer.
Five years later he returned to Belgrad where he found employment as professor for mathematical studies at the University. Like Croll he was in search of a scientific problem worth his efforts, and in 1911, sharing some presumably good wine with a friend, he decided to develop a mathematical theory to explain climate changes on the planets of the solar system.

He studied the work of Croll, recognized his previous achievements but also noted his insufficient data. Milankovitch also consulted the work of the German mathematician Ludwig Pilgrim, who in 1904 published exact calculations of the orbital eccentricity, earth's obliquity and the rotation of the axis of earth (change of the perihelion). Pilgrim also tried to correlate the eccentricity with the occurrence of ice ages.
Between 1912 and the beginning of World War I Milankovitch published some preliminary abstracts of his developing theory, concluding that all three factors, in contrast to previous authors, are important to explain earth's climate. At the beginning of the War, Milankovitch was arrested as Serbian officer and imprisoned in his hometown Daly, but fortunately he was carrying with him his work, and so even in the first night as prisoner he continued to work. "When after midnight I looked around in the room, I needed some time to realize where I was. The small room seemed to me like an accommodation for one night during my voyage in the Universe."
Soon after he was released and travelled back to Belgrad, where he continued his work during the entire War and published some ideas about the climate of Mars and Venus.

Finally he published his theory in 1920 "Mathematische Theorie der durch Sonneneinstrahlung ausgelösten Wärmephänomene" (Mathematical theory of thermal phenomena caused by solar radiation).

Fig.1. Variations in the Earth's orbital parameters:
1. Eccentricity: the shape of the orbit around the sun.
2. Changes in obliquity: changes in the angle that Earth's axis makes with the plane of Earth's orbit.
3. Precession: the change in the direction of the Earth's axis of rotation, i.e., the axis of rotation behaves like the spin axis of a top that is winding down; hence it traces a circle on the celestial sphere over a period of time.
Together, the periods of these orbital motions have become known as Milankovitch cycles. These parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N).

In his theory he postulated:
- Glaciations are caused by variations of astronomical parameters
- The parameters influence the amount of solar energy on earth´s surface, especially during summer of the northern hemisphere (55°-65°N)
- It is possible to calculate these changes, and so calculate the climate in the past.

The German meteorologists Wladimir Köppen and Alfred Wegener supported the new theory, and noted the apparent coincidence of the calculated curve with the by Penck and Brückner postulated four European glaciations.

Fig. 2. Figure from KÖPPEN & WEGENER 1924, where they correlated the calculated cycles to the know ice ages at that time.

Fig.3. Outcrop of the Trubi-Formation at Capo Spartivento (South-Italy), a succession of Globigerina-marls from the Pliocene-Pleistocene transition. The regular stripes are caused by organic rich layers, thought to be caused by changes in the biological productivity in response of changes of the astronomical parameters - the Milankovitch cycles.

References:

CHORLTON, W. (ed) (1985): Ice Ages (Planet Earth). Time-Life Books: 176
KÖPPEN, W. & WEGENER, A. (1924): Die Klimate der geologischen Vorzeit. Borntraeger, Berlin: 256

Resources:

NASA Earth Observatory: Milutin Milankovitch (1879 - 1958). Accessed 26.06.2010

Megafauna Methane collapse

There are lots of hypothesis dealing with the extinction of the Pleistocene Megafauna. Now a research team of the University of New Mexico in Albuquerque adds a something different approach to the problem of climate change as extinction cause. SMITH et al. published a paper where they compared the production of methane of modern farm animals to extinct herbivores. Methane is a very effective green house gas. The research team observed in the geological record strong variations of the concentration of methane between the last glacial maximum, 18.000 years ago, and the Younger Dryas (13.000 years ago). Especially at the beginning of the temperature drop of the Younger Dryas the concentration of methane diminished considerable fast. The research team speculates that with the beginning extinction of large herbivores an important source of methane was removed from the climate system, destabilizing climate and environment end enforcing the extinction rate. The fast changes observed, faster than previously known variations, maybe are also related to human activity, disproving precedent research that excluded humans as triggers for the Pleistocene extinction.

References

SMITH, F.A.; ELLIOTT, S.M.. & YONS, K. (2010): Methane emissions from extinct megafauna. Nature Geoscience. Published online: 23. May 2010: doi:10.1038/ngeo877

Sea-Level Highstand disproves ice-age CO2 connection?

The ice ages on Earth could be influenced by CO2 levels differently than previously believed. The study of speleotherms in the cave of Vallgornera situated on the Spanish island of Mallorca revealed that the polar caps were as small as today 81,000 years ago - despite lower CO2 levels.
A team of scientists of the University of Iowa has studied aragonitic and calcitic mineral deposits from five caverns situated; depending of the sea level - itself varying by the amount of “captured” water in ice caps up to 130m - the caves were inundated and different mineralogical deposition occurred.

The dated samples suggest that the sea level around 81,000 years ago was about a meter above the current value. "We have reconstructed the sea level with really high precision," says researcher Doral to the German newspaper “SPIEGEL ONLINE”.Co-author Bogdan Onac from the University of South Florida explains that Mallorca is ideal for this kind of research because tectonically stable and the observed variations should be “true” variations of sea level, not falsified by geological movements or isostatic rebound.

If the sea level 81,000 years ago was actually where the researchers suggest, an interesting problem arises: it doesn’t support the calculated 100.000-year cycle of glacial advances. Also it contradicts the direct ice-CO2 connections - despite low CO2 concentrations, and weaker greenhouse effect, the ice caps on earth were not as great as previously tough, and in dimensions comparable to modern conditions.

So are climate denialists right, and is there no such thing as anthropogenic greenhouse effect?

No, the authors want to take the results in a scientific context: the research doesn’t make claims about the global temperature during this time, only about the possible ice volume, and the amount of ice is not only controlled by temperature, but also for example by insolation of the sun, stronger 80.000 years ago then today. "What happened 80,000 years ago, is not the same as what happened today," said Onac.

REFERENCES:

DORALE et al. (2010): Sea-Level Highstand 81,000 Years Ago in Mallorca. Science Vol.327(5967): 860 - 863

No more ice on Kilimanjaro ?

After Thompson et al. 2009, interview to Dr. Thompson mp3

The glacial record in Africa is restricted to the highest peaks of this continent, mainly to mountains of east Africa: Mount Kilimanjaro (5895m), Mount Kenya (5.199m), the Ruwenzori (5.119m) and on the northern margin of Africa in the High Atlas. Traces of two Pliocene-Pleistocene glaciations have been found on Mt Kilimanjaro, the oldest of which have been dated to about 2.0My (OSMASTON, 2004). Younger, in part uncertain glacier advances are dated to 1,0My, 0,4My and during the last glacial maximum (20.000y). Today three main glaciers persist on the summit of the volcano - the Northern Ice Field (NIF), the Southern Ice Field and the Furtwängler Glacier; some smaller glaciers are distributed on the slope of the mountain. Cores taken from all three glaciers showed that the ice cover on Kilimanjaro persisted for at least 11.700 years.

Isotopic record of oxygen isotopes from the Northern Ice Field (NIF), after THOMPSON et al. 2002

In modern times the dramatic loss of Kilimanjaro´s ice cover has attracted global attention, and has been a symbol for changing climate in Africa in popular media. The glaciers have considerable lost volume and surface, from 12,06 square kilometer in 1912 to 2,6-2,5 square kilometer in 2000. In the last 7 years ulterior 26% of this remaining ice are gone, leaving 1,85 square kilometer back. But not only the ice covered surface - easy to observe by aerial photographs - diminishes, but more important the glaciers are rapidly thinning, up to 0,5m thickness loss per year. This glacier mass lost is harder to determinate (mostly by measuring with stakes you got only punctual data) but crucial to understand the glacier balance.
If this melting rate persists, until 2022-2033 there will no more glacier ice left on the summit.

The widespread retreat of glaciers in Africa suggests a common driver, and not only local factors like deforestation, land use or humidity change on the slopes of Mount Kilimanjaro. The long record that this ice fields provided, demonstrate that for more then 11.000 years ice persisted without essential melting or mass lost, even during the end of the humid phase in Africa and change to more drier climate and subsequent droughts (p.e. 4.200 years ago). This seems to minimize the influence of changing precipitation on the glacier mass balance, and emphasizes changing in the temperature regime on the summit of the mountain.

References:

EHLERS, J. & GIBBARD, P.L. (2007): Glaciations. In (ed): ELIAS, S.A. (2006): Encyclopedia of Quaternary Science. Elsevier : 290-300

OSMASTON, H. (2004). Quaternary glaciations in the East African mountains. In J. Ehlers and P. L. Gibbard (eds): QuaternaryGlaciations - Extent and Chronology, Part III: South America, Asia, Africa, Australasia, Antarctica: 139-150.

THOMPSON, L.G. et al. (2009): Glacier loss on Kilimanjaro continues unabated. Proceedings of the National Academy of Sciences.

Caves and the dream of long term records

Within the Alps, long term climate records, ranging to the last or even to the penultimate interglacial are exceptionally rare. We are simply lacking sediments of these periods - sediments of interglacial's were systematically eroded by the (re)advance of glaciers, lay hidden under younger sediments (mostly postglacial alluvional river deposits) or are simply not yet recognised.

In cave systems we are not (so) affected by the destructive power of glaciers, so there maybe can be found sediments ranging much deeper in time, with a record much completer then in the outside world.

Speleothem growth depends strongly from temperature and water chemistry, and water in liquid form depends strongly by temperature of the environment outside the cave. During a cold period, water will be trapped in form of ice on the surface, and water percolation in the underground will be very restricted or completely missing - the speleothem will stop to growth. During warming, and melting of ice, again water is available, and the speleothem goes on growing. So just the presence of speleothems can provide a first clue to reconstruct past climates. But even better - the isotopic composition of the precipitation changes with the amount of water trapped in ice shields - so measuring the relationship between the two oxygen isotopes (the "light" 16O and the "heavy" 18O) in the- from the water deposited - carbonates, can give a direct information's of extend of ice shields, and so climate, during the past. And the carbon isotopes 13C and 12C, also found in the carbonate, give hinds on vegetation and soil cover of the catchment area of the cave. Plants assimilate preferred the lighter isotope - a high values of delta13C indicate low or even negligible input of soil-derived organic carbon into the dripwater.

Spannagel cave is a large high altitude (entrance to the cave 2.531m, extending down in two main branches to ca. 2.200m a.s.l.) cave network with approximately 10km of length in the Zillertal Alps of Austria.

The "Hintertux glacier" with the morain of the last highstand (1850). The entrance of the Spannagel caves - and also the Spannagel hut- lies on the upper end of the left morain.

It is the largest out of a series of more than 30 caves that developed within the Jurassic marble that covers the "Zentralgneiss" - the tectonic uplifted gneiss core of the "Tauern window", and is itself overlie by the phengitic gneisses.

The area above the cave today is ice free, but it was covered partially by the Hintertux glacier until 1850, and covered entirely by up to 250 thick ice during the past glacial. U/Th dates in the cave showed that deposition of the speleothems occurred repeatedly during the past few hundred thousand years, and is still ongoing, thanks of the constant temperature (1-2°C) in the cave slightly over the freezing point of water.


A stalagmite in the cave, composed of dense, columnar calcite, apparently grew without significant interruption for ca. 50 ka, albeit at a very slow rate, during the penultimate interglacial. The oxygen isotope record shows three prominent maxima, representing three warm phases, separated by a long earlier and a shorter later cold period. The mid points of the transitions into the three warm phases occurred at 240 ± 3 (correlated subsequently with the MarineIsotopicStadium 7.5), 215 ± 2 (MIS 7.3) and 200 ± 3 ka (MIS 7.1) and the end of the interglacial (MIS 7/6 transition) was dated to 190 ± 3 ka.

During full glacial periods no speleothem growth could be found. During the transition of interglacial to glacial conditions the sudden drop of the isotopes values suggest a cooling, but speleothems growth continues. Comparing the curve of the oxygen isotopes with the carbon isotopes shows a remarkable pattern - both curves appear very similar, relatively high delta18O values indicating warm atmospheric conditions coincide with high delta13C values. This suggests very little if any vegetation at this cave during the warm periods, and so less favourable conditions than today - were at least a thin soil developed.
The later interglacial (MIS 5), and also the Holocene show data with higher values of delta18O, and a low delta13C value during the "high stand" of oxygen - high temperature and thick soil and vegetation cover.

Continuous stable isotope record of speleothem growth during the Marine Isotope Stage 7 at the high-alpine Spannagel Cave, Central Alps. SPÖTL et al. (2008): Spannagel Cave, Austria MIS 7 Speleothem Stable Isotope Data. Age is given in kyr BP, isotope ratio per mil VPDB).
Relatively high (reaching -8 to -9 0/00) delta18O values indicating warm atmospheric conditions, these values during the observed interglacial coincide with relative high delta13C values (>2 0/00). The 13C isotope derives mostly of anorganic sources (p.e. dissolving limestone), so high values are sign of lacking vegetation or organic rich soil cover. During "cold periods" complete lack of soil and vegetation produces the high peak between 230-220kyrs.

These facts let conclude that the penultimate interglacial posess three major climatic phases, with warmer periods separated by cooler periods. On average this interglacial was less warmer then the last interglacial or the Holocene in this altitude, with consequent lower equilibrium lines for glaciers. The catchment area of the Spannagel cave must be covered by ice, but the ongoing growths of speleothems demonstrate the presence of water - this implies warm based conditions beneath the ice. Only during full glacial conditions no speleothem deposit occurred.

References:

SPÖTL, C.; MANGINI, A.; BURNS, S.J., FRANK, N. & PAVUZA, R. (2002): Speleothems from the high-alpine Spannagel cave, Zillertal Alps (Austria). In (ed.) SASOWSKY & MYLROIE: Studies of Cave Sediments: Physical and Chemical Records of Paleoclimate
SPÖTL et al.(2006): The last and the Penultimate Interglacial as Recorded by Speleothems From a Climatically Sensitive High-Elevation Cave Site in the Alps. In SIROCKO, F. et al. (ed): The climate of past interglacial. Developments in Quaternary Science 7.
VOLLWEILER, N.; MANGINI, A.; SPÖTL, C.; SCHOLZ, D. & MÜHLINGHAUS, C. (2009: Stalagmites from Spannagel cave (Austria) and holocene climate. Geophysical Research Abstracts. Vol.11

Glacier Change

Waxeggkees (Zillertaler Alps) ca. 1900-1906 and 2006

Dinosaurs on the rocks?

In this week's issue of Science (Science 11 January 2008:Vol. 319. no. 5860, p. 145), paleoceanographers present new data that make the case for polar ice at the height of the Cretaceous hothouse 90 million years ago.

The study by researchers at Scripps Institution of Oceanography at UC San Diego provides strong evidence that a glacial antarctic ice cap, about half the size (until 60%) of the modern day glacial ice sheet, existed 91 million years ago during a period of high mean global temperatures.

The new study is titled, “Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse,” and examines geochemical and sea level data retrieved from marine microfossils deposited on the ocean floor 91 million years ago during the Cretaceous Thermal Maximum.

This extreme warming event in Earth’s history raised tropical ocean temperatures to 35-37°C, about 10°C warmer than today, thus creating an intense greenhouse climate. But 90 milion years ago the sealevel dropped worldwide by 40 m - how, and why?

Using two independent isotopic techniques, researchers at Scripps Oceanography studied the microfossils to gather geochemical data on the growth and eventual melting of large Cretaceous ice sheets (Stable isotopes of oxygen molecules (d18O) in bottom-dwelling and near-surface marine foraminifera as proxy for large waterstorages other than the oceans, and the chemical composition of fossil archeobacteria-membranes as proxy for water-temperatures).

These independent methods provided Andre Bornemann, lead author of the study, with strong evidence to conclude that an ice sheet about 50-60 percent the size of the modern Antarctic ice cap existed for about 200,000 years. Bornemann conducted this study as a postdoctoral researcher at Scripps Oceanography and continues this research at Universitat Leipzig in Germany.

“Until now it was generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago,” said Richard Norris, professor of paleobiology at Scripps Oceanography and co-author of the study. “This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth.”

Researchers are still unclear as to where such a large mass of ice could have existed in the Cretaceous or how ice growth could have started. The temperatures where much to high for icefields in or on the oceans. So the authors suggest that climate cycles may have favored ice growth during a few times in the Cretaceous when natural climate variations produced unusually cool summers, likewise on high mountains or on the continent of Antarctica.

But anyway ice sheets were much less common during the Cretaceous Thermal Maximum than during more recent “icehouse” climates. Paradoxically, past greenhouse climates may have aided ice growth by increasing the amount of moisture in the atmosphere and creating more winter snowfall at high elevations and high latitudes, according to the paper’s authors.

The results from the study are consistent with other studies from Russia and New Jersey that show sea level fell by about 25-40 m at the same time that the ice sheets were growing during the Cretaceous period. Sea level is known to fall as water is removed from the oceans to build continental ice sheets; conversely, sea level rises as ice melts and returns to the sea.
The presence or absence of sea ice has major environmental implications, specifically in terms of sea level rise and global circulation patterns.