What is climate and how it works?
Climate it's a sensitive system which reflects the Earth weather behavior on a longer time interval (at least 30 years) and it depends on a various number of factors such as: distribution of water on Earth (oceans, seas, lakes and ice) and the way it interacts with land mases; wind patterns; temperature distribution; atmospheric pressure; quantity of sun radiation and varies with latitude and topography. Water is incredibly important for a number of reasons: it supports life; it creates vapours which result in clouds and then precipitations; ice caps or glaciers can trap or release water, thus they control the eustatic level (the water level of seas and oceans); ground water and sediments are also absorbing water which can be released after time or become entrapped in rocks as aquifers. Proximity- to equator or poles, is quite obvious because it controls insolation (exposure to sun).
Extremely important is also the quantity of greenhouse-potential gases and dust in the atmosphere which can destabilize the system and accelerate cooling or warming phases. This is possible through dust plumes from the big deserts (for us mostly from Sahara), methane (CH4) coming from melting ice, permafrost or from the bottom of the oceans aaannddd-volcanic eruptions, my favourite bastards. Volcanoes can release both dust (mostly ash) and gases (CO2, SO2, H2S, etc.) in very large quantities and destabilize the climate system quite fast.
As the introduction was done briefly, we know how the present day climate looks like (and we know the Earth is warming up!), but how do we know how it was in the past? Luckily, there are a lot of smart people who thought about this over time and found various methods to do determine and quantify it, from historical to deep time (geological time). The science that deal with reconstructing past climatic systems or events is called paleoclimatology and this is what I currently do.
Earth not only produces information but also records it. Imagine it like a big library with thousands of tomes, wrapped in various coverings, some complete and other with missing pages, some domains better described and others with scarce information. In the same way we found information recorded in nature and it gets scarcer and with less pages as we go deeper back in time. We call this information proxies or archives and they register various events, chemical components or physical features. In this article I will walk you through them, then in the future I will come with subject dedicated extended versions (at least for some of them).
Various types of data used in reconstructing past-climate (atmos.albany.edu)
What do they tell us?
▲ Pollen
A type of information becomes a proxy when it can be applied often and with a high rate of succes, that's why some of them are preferred on top of another, like pollen for example, which can be preserved relatively easy and usually in high quantities. So pollen is more than just the annoying thing that cause us allergies in the spring! Pollen is produced by all plants with any form of inflorescence and they are the sperm cells from male plants. Pollen grains are very small and thus they can be transported very easy by wind, birds or insects. Once the pollen grains reaches the soil or water bottom, they can be incorporated in the sediments and preserved in time. Every species of plant has a different shape and size of pollen, making our life easy when it comes to recognizing it. If we are able to recognize the pollen assemblages in our samples we are thus able to reconstruct the vegetation type and thus the type of environment. Pollen is a very useful tool for both historical and deep time, being able to be traced to the oldest pollen producer in Devonian (~400 million years ago).
Pollen grains from the Takarkori rock shelter, Lybia, showing the presence of a savana type vegetation and swamp/lake elements: A and B) Poaceae, C) Poaceae and phytolits, D) Ficus, E) Cyperaceae, F) Typha latifolia type, G) Cichorieae (left) and Brassicaceae (right).
During the last 10 ky Sahara lost its green due to widespred aridisation and slowly turned into what we see today-the largest desert of our planet.
Image from Cremaschi et al, 2014
▲ Tree rings
Trees are also a valuable resource for recent climate. Trees, as plants in general, respond to changes in
environment. If they have more humidity they grow faster, if is draught they grow more slowly or they don't grow at all. These responses can be seen in the trees structure by analyzing their rings. For this purpose there are used big trees which had a longer life so they could record more information. Dating the tree rings it's a whole science which is called dendrochronology. The method used for dating is radiocarbon which can be used for a wide array of other materials.
The tree material can be collected from sites as archaeobotanicl material (which material is quite scarce but extremely useful), from trees that died in our times from various reasons or from living trees. The dead trees are sliced open while the living trees are cored. Yes, cored like sediments but with a special type of coring device. After coring the samples are collected and taken to a lab for further analysis.
A 500 years old tree analysis (cdn.uanews.arizona.edu). You ca see the difference in rings thickness especially between 1560-1575 which was one of the worst drought registered by North America in human times. In Mexico, this drought was accompanied by an epidemic episode, the 3rd since the hispanic conquest (which began on april 21, 1519) and led to the complete collapse of aztec society.
▲ Ice cores
Ice cores are one of the most valuable and fancy data type you can get. As opposed to sediments which are more stable, coring ice and preserving it can be a pain in the ass because of melting issues. Ice from glaciers or ice caps are very good preserving environments being able to preserve dust, air bubbles and even organic material. The air trapped in ice gives us information about gases in the atmosphere at the moment our ice formed. The ice composition and structure itself gives us information about temperatures (based on oxygen isotopes), precipitations, water composition (based on hydrogen isotopes), while dust gives us information about wind patterns or volcanic eruptions (if ash is found). When volcanoes erupt, their ash can circle the planet and even disperse on latitude making it possible to be deposited in ice-sheets. Ash can also be dated and traced to the guilty volcano, which makes things quite awesome.
A core from western Antarctica with ice formed during the last ice age. In the right side can be seen a layer of ash (~1cm). Source: scripps.ucsd.edu.
▲ Coral reefs
Corals, just like trees, register the changes in the environment where they live, but they are able to build up structures for longer periods of time (even million of years for big reefs). Since corals are building their skeletons out of calcium carbonate (CaCO3) they are extremely sensitive to changes in the water chemistry or temperature and they can die easily if changes are happening fast. In order to retrieve data from corals these are drilled and cored, then cores are sectioned in order to be analyzed. As corals grow they add new CaCO3 layers which have different density and porosity depending on the season. The growing rings gives us information about the living conditions of the animals (temperature, pH) while the CaCO3 in their bodies allow us to date them. When they pass through stress periods or drastic changes they bleach or the test structure (coral's skeleton) changes. During big storms, hurricanes, typhoons, corals can be broken or choked with sediments. These events are also registered by these organisms and they can die or regenerate. If they regenerate, they seal the wounds and grow new branches.
Coral drilling, cores and cores description (flowergarden.noaa.gov)
▲ Speleothems
Speleothems are the beautiful structures that we see in caves: stalactites, stalagmites, columns or drapes. Stalactites form from the water drops that that infiltrates or condensates from ceilings. The counterpart are stalagmites and they grow on the floors from the carbonate that was dripped. When the two type of formations join together they form columns or pillars. In some caves the water is running across walls or collapsed rocks and form in time a wavy vertical structure called drape. Karst systems and cave structures gives use precious information about precipitations and water imput, thus about presence of rain, its abundance (rainy seasons, floods) or lack of it (droughts). When water is available the cave formations are growing adding new layers of carbonate. When the source dries out or is temporarily interrupted, they start to be eroded. While growing, they also trap the oxygen isotopes from water and this allows us to reconstruct precipitations and air temperature. While collecting data, if the structures are active, we are only allowed to core them and extract samples. Most of the time scientists are allowed to drill only formations that are naturally broken, especially in protected areas.
Drilling cave formations in Tú Làn cave system, Vietnam (eosvnu.net)
!!!! Cored corals and speleothems need to be filled back with cement so the natural process is not interrupted. Trees cored are also filled with a cellulose base or the tree is left to regenerate itself.
▲ Peats
Peat bogs are very common at higher latitudes but they can be found also in warmer areas and high elevation sites. They form in humid environments where water is stagnating and decayed vegetation accumulates over time. Stagnant conditions don't allow oxygen to be mixed and dissolved in water thus organic matter is preserved.
Peats can be active over thousands of years which makes them an excelent candidate for time recording. They can record the changes in vegetation, precipitations, fire regimes, pollen, dust and animals around them. Peats can also preserve tools, artefacts and human or animal bodies, especially in the half northern side of Europe, but also sediments and heavy metals. Microscale material is obtain by coring the material, usually where they are the deepest so the record covers a wider time span. For pits can be used both a mechanical and a manual coring device, but is preferred the manual one because it keeps intact the core structure.
A perfect core from a sphagnum dominated pit (people.ales.ualberta.ca)
▲ Charcoal
When plants burn they produce a new type of organic matter that resists degradation called charcoal. Any part of plants can burn from pollen to roots. The larger fragments are usually deposited next to the fire source but smaller fragments can be transported by wind or water into swamps, lakes or seas and resedimented on the bottom. The quantity and type of burned biomass can help us detect fire sources and reconstruct past fire regimes. Fires are happening naturally during summer heat waves, long drought, lightning but also human induced. A rapid increase in fires is associated all over the world with human expansion and agriculture but it also gives us insight about events at geological time scale.
Holocene and Miocene charcoal from Russia (1 orage square=1mm), leaves fragments.
▲Phytolites
Phytolites are microscopic structures made out of silica that can be found in plants bodies. Plants are getting the soluble silica out of the soil and redistribute it though its body. Redistributed silica takes then the structure of the plant cells. Since their shape and structure vary from one plant to another this technique makes them easy to recognise and classify. Phytolites are extremely useful when no other type of organic material is preserved and remain preserved in sediments over thousands and millions of years just like pollen. They are very used in tracing plants presence or to their evolution in time. In archaeology they play a huge role in tracing the aclimatisation of different plants or plant hybridisation, thus agriculture and humans-plants interaction.
Various phytolite types (www.pourlascience.fr)
▲ Fossils
After cats and dogs, fossils are my next favourite thing in the universe. Fossils can come
from any form of life and it can be the body itself, an impression, feeding or motility tracks, eggs, you name it. Most of organic material is not preserved, but from time to time there are natural conditions which lead to fossilisation. In order to become fossil, the organism has to be covered rapidly in sediment and burried so it doesn't decompose. From paleontology (the science behind fossils) grew another branch called biostratigraphy, which dates sediments based on the fossils they contain. For about 2 centuries fossils were the only tool to date rocks. Certain species evolve only for short periods of time or they have population booms or disappear abruptly. These fossils that point very specific moments in time are called index fossils and they are were the dream of biostratigraphers, but nowadays is more important to understand how these organisms lived and behaved thus the environment conditions.
Depending on their size, fossils are divided into micro- and macrofossils. Microfossils are obviously all the tiny and microscopic ones (plankton, zooplankton, fish teeth and otholites, spores, pollen, phytolites, ostracods, tiny molluscs, etc.), while in macro- scale fits all the rest, from leaves to dinosaurs. Fossils are extremely precious to any scientist but in particular to geologists. Normally is considered a fossil any organism that is older than 10000 years, but there are other processes that takes less time like natural mummification, organisms caught in volcanic ash, coprolites, fibers. These organisms are on the limit because of age or poor preservation and they are often called sub-fossils.
Various types and ages of microfossils, both terrestrial and marine origins (foraminifera, fish vertebra, echinoid, radiolarian, ostracod, conodont, pollen, gastropod, coccolith, another gastropod-a Planorbis from my friend Danae Thivaiou, a fish otholite and another radiolarian). The marine fossils photos are taken from www.jsg.utexas.edu.
Various macrofossils: left a palm leaf and olive tree leaves preserved in ash from Santorini (the eruption that wiped out the Minoan civilisation 3600 years ago); right up- a burned tree from Turkey's miocene, right down- a cretaceous ammonite and a miocene bivalve from Bulgaria)
I would also add to the long list sediments in general, biomarkers and isotopes but it's a lot to say about each one of them so I will write separate articles.
See you next time!