Department of Geography at Northumbria University
Although modern lakes cover only about 3.7% of the non-glaciated Earth surface and contain only 0.013% of the global water, their sediments record millions of years of climate and environmental history. This history is fascinating, but often difficult to recover and to decipher. Dr Kwiecien explained how she retrieves and works with lake sediments and what can be learnt from the results.
The following are notes from the on-line lecture. Even though I could stop the video and go back over things there are likely to be mistakes because I haven’t heard things correctly or not understood them. I hope Dr Kwiecien, and my readers will forgive any mistakes and let me know what I got wrong.
I would also like to thank Dr Kwiecien for allowing me to use her slides. Please ask her permission if you wish to use them.
Dr Kwiecien is a geoscientist and she is interested in the environmental response to climate change. Her work involves researching light sediments i.e. mud, as they can tell wonderful stories (and mud is very tasty, I ate a lot as a child).
Why the environmental response to climate change is important.
Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years
J. Jouzel et al. 2007
A high-resolution deuterium profile is now available along the entire European Project for Ice Coring in Antarctica Dome C ice core, extending this climate record back to marine isotope stage 20.2, ∼800,000 years ago. Experiments performed with an atmospheric general circulation model including water isotopes supported its temperature interpretation. They assessed the general correspondence between Dansgaard-Oeschger events and their smoothed Antarctic counterparts for this Dome C record, which revealed the presence of such features with similar amplitudes during previous glacial periods. They suggested that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records.
High-resolution carbon dioxide concentration record 650,000–800,000 years before present
Lüthi et al 2008
Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years. The paper presents results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data and the present work, they found that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. They have reported the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172–300 p.p.m.v.
The following graphs show the natural background changes of the last 800 thousand years indicating glacial and interglacial periods
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The Last Glacial Period ended about 15,000 years ago. The Holocene is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state.
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.
The Dome C temperature anomaly record with respect to the mean temperature of the last millennium (based on original deuterium data interpolated to a 500-yr resolution). Data for CO2 are from Dome C.
The graphs are coming from ices cores taken from Antarctica and show the temperature and carbon dioxide concentration.
Antarctica is Earth’s southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean.
The graphs are extremely good climate records and they are very valuable as they give information about the natural changes of the background over the last 800,000 years. Glacial-interglacial cycles are shown and indicate the natural variability over the time period. The grey columns show the interglacials and the white columns are the glacials. The records are coming from Antarctica ice which means they don’t give any information about what was happening with the other continents. This is a major problem because humans don’t tend to live around the South Pole (or the North Pole).
There is definitely a need for looking at different environmental archives and trying to figure out how the environment and climate in the past
PAGES (Past Global Changes) supports research which aims to understand the Earth’s past environment in order to obtain better predictions of future climate and environment, and inform strategies for sustainability. We encourage international and interdisciplinary collaborations and seek to promote the involvement of scientists from developing countries in the global paleo-community discourse.
Holocene global mean surface temperature, a multi-method reconstruction approach
Kaufman et al 2020
An extensive new multi-proxy database of paleo-temperature time series (Temperature 12k) enables a more robust analysis of global mean surface temperature (GMST) and associated uncertainties than was previously available. They applied five different statistical methods to reconstruct the GMST of the past 12,000 years (Holocene). Each method used different approaches to averaging the globally distributed time series and to characterizing various sources of uncertainty, including proxy temperature, chronology and methodological choices. The results were aggregated to generate a multi-method ensemble of plausible GMST and latitudinal-zone temperature reconstructions with a realistic range of uncertainties. The warmest 200-year-long interval took place around 6500 years ago when GMST was 0.7 °C (0.3, 1.8) warmer than the 19th Century (median, 5th, 95th percentiles). Following the Holocene global thermal maximum, GMST cooled at an average rate −0.08 °C per 1000 years (−0.24, −0.05). The multi-method ensembles and the code used to generate them highlighted the utility of the Temperature 12k database, and they are now available for future use by studies aimed at understanding Holocene evolution of the Earth system.
The image below shows all the different environmental archives but it would be difficult to study all of them so Dr Kwiecien specialises in sediment studies.
The thing about lakes … … … and why should people care?
Only 2.5% of the Earth’s water is freshwater. Only 52% of this 2.5% is found in lakes
In 2014 there were around 117 million lakes around the Earth, but this only constituted 0.013% of the Earth’s water.
Some lake world records:
The oldest, deepest and largest volume lake is Lake Baikal
Lake Baikal is a rift lake, formed from an ancient rift valley, and is located in southern Siberia, Russia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast. It has a long, crescent shape, with a surface area of 31,722 km2 and its mean temperature varies from a winter minimum of −19 °C to a summer maximum of 14 oC.
It is the largest freshwater lake by volume in the world, containing 22 to 23% of the world’s fresh surface water. With 23,615.39 km3 of fresh water, it contains more water than all of the North American Great Lakes combined. With a maximum depth of 1,642 m, Baikal is the world’s deepest lake. It is considered among the world’s clearest lakes and is considered the world’s oldest lake, at 25–30 million years. It is the seventh-largest lake in the world by surface area.
The lake with the largest surface area is Lake Superior
Above left: The top of the Giant trail in Sleeping Giant Provincial Park. Credit: Sam Greer.
Lake Superior is the largest of the Great Lakes of North America, the world’s largest freshwater lake by surface area (82100km2), and the third largest freshwater lake by volume. It is shared by the Canadian province of Ontario to the north, the U.S. state of Minnesota to the west, and Wisconsin and the Upper Peninsula of Michigan to the south. Superior is the farthest north and west of the Great Lakes chain, and the highest in elevation, draining through the St. Mary’s River into Lake Huron.
The thing about lakes is that they may be, mostly, freshwater, but they will all have different settings, sediments and water chemistries
Different lakes from different climate zones. The sediments deposited in them will all be different.
Recording environmental signals – background deposits
How do scientists figure out what is being deposited in the lake?
Where do the sediments originate?
The following images present case scenarios of what lake scientists would like to see.
Imagine a lake with a deep basin where the bottom is anoxic (in the following images it is the darkest blue layer)
Anoxic waters are areas of sea water, fresh water, or groundwater that are depleted of dissolved oxygen and are a more severe condition of hypoxia. The US Geological Survey defines anoxic groundwater as those with dissolved oxygen concentration of less than 0.5 milligrams per litre. This condition is generally found in areas that have restricted water exchange.
In most cases, oxygen is prevented from reaching the deeper levels by a physical barrier as well as by a pronounced density stratification, in which, for instance, heavier hypersaline waters rest at the bottom of a basin. Anoxic conditions will occur if the rate of oxidation of organic matter by bacteria is greater than the supply of dissolved oxygen.
Anoxic waters are a natural phenomenon, and have occurred throughout geological history. In fact, some postulate that the Permian–Triassic extinction event, a mass extinction of species from world’s oceans, resulted from widespread anoxic conditions. At present anoxic basins exist, for example, in the Baltic Sea, and elsewhere. Recently, there have been some indications that eutrophication has increased the extent of the anoxic zones in areas including the Baltic Sea, the Gulf of Mexico, and Hood Canal in Washington State.
In the winter there will be some precipitation. Materials from the catchment area and detrital materials, like clastic materials will be transported with the precipitation into the lake. These materials will be deposited into the dark anoxic layer.
In meteorology, precipitation is any product of the condensation of atmospheric water vapour that falls under gravity from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor (reaching 100% relative humidity), so that the water condenses and “precipitates” or falls.
A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from rain runoff, snowmelt, hail, sleet and nearby streams that run downslope towards the shared outlet, as well as the groundwater underneath the earth’s surface. Drainage basins connect into other drainage basins at lower elevations in a hierarchical pattern, with smaller sub-drainage basins, which in turn drain into another common outlet.
Other terms for drainage basin are catchment area, catchment basin, drainage area, river basin, water basin, and impluvium. In North America, the term watershed is commonly used to mean a drainage basin, though in other English-speaking countries, it is used only in its original sense, that of a drainage divide.
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.
Detritus is particles of rock derived from pre-existing rock through processes of weathering and erosion. A fragment of detritus is called a clast. Detrital particles can consist of lithic fragments (particles of recognisable rock), or of monomineralic fragments (mineral grains). These particles are often transported through sedimentary processes into depositional systems such as riverbeds, lakes or the ocean, forming sedimentary successions. Diagenetic processes can transform these sediments into rock through cementation and lithification, forming sedimentary rocks such as sandstone. These rocks can then in turn again be weathered and eroded to form a second generation of sediment.
In biology, detritus is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and faecal material. Detritus typically hosts communities of microorganisms that colonize and decompose (i.e. remineralize) it. In terrestrial ecosystems it is present as leaf litter and other organic matter that is intermixed with soil, which is denominated “soil organic matter”. The detritus of aquatic ecosystems is organic material that is suspended in the water and accumulates in depositions on the floor of the body of water; when this floor is a seabed, such a deposition is denominated “marine snow”.
In the summer some pollen may be transported into the lake and because the water will be warmer there is a possibility of an algal bloom occurring
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems, and is often recognised by the discolouration in the water from their pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic, multicellular organisms like seaweed and microscopic, unicellular organisms like cyanobacteria. Algal bloom commonly refers to rapid growth of microscopic, unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.
Algal blooms are the result of a nutrient, like nitrogen or phosphorus from fertiliser runoff, entering the aquatic system and causing excessive growth of algae. An algal bloom affects the whole ecosystem. Consequences range from the benign feeding of higher trophic levels, to more harmful effects like blocking sunlight from reaching other organisms, causing a depletion of oxygen levels in the water, and, depending on the organism, secreting toxins into the water. The process of the oversupply of nutrients leading to algae growth and oxygen depletion is called eutrophication. Blooms that can injure animals or the ecology are called “harmful algal blooms” (HAB), and can lead to fish die-offs, cities cutting off water to residents, or countries having to close fisheries.
Taken from orbit in October 2011, the worst algae bloom that Lake Erie has experienced in decades. Record torrential spring rains washed fertiliser into the lake, promoting the growth of microcystin-producing cyanobacteria blooms.
Algal blooms can induce precipitation of carbonates in the lake known as a whiting event.
A whiting event is a phenomenon that occurs when a suspended cloud of fine-grained calcium carbonate precipitates in water bodies, typically during summer months, as a result of photosynthetic microbiological activity or sediment disturbance. The phenomenon gets its name from the white, chalky color it imbues to the water. These events have been shown to occur in temperate waters as well as tropical ones, and they can span for hundreds of meters. They can also occur in both marine and freshwater environments. The origin of whiting events is debated among the scientific community, and it is unclear if there is a single, specific cause. Generally, they are thought to result from either bottom sediment re-suspension or by increased activity of certain microscopic life such as phytoplankton. Because whiting events affect aquatic chemistry, physical properties, and carbon cycling, studying the mechanisms behind them holds scientific relevance in various ways.
An aerial view of a whiting event precipitation cloud in Lake Ontario.
In the above example whitings will result in the lighter layer in the lake. When there are different conditions during the seasons, these conditions will be reflected in the composition and colour of the sediments. The colours of the sediments are actually a good indication of their composition.
The above image is showing a second winter with a bit more detrital and clastic materials in the catchment area. This is how the sequence of layers are built up. There are events that might happen.
A lot of precipitation might lead to floods, which might lead to a greater quantity of detrital material entering the lake. This would give a different, more homogenous, slightly chaotic, thicker layer from what would normally be deposited during a cycle.
Looking carefully at the sediment sequences it is possible to figure out how often such a flood happens which is what some of Dr Kwiecien’s colleagues are doing in the lakes that are found in the Alps.
The Alps are the highest and most extensive mountain range system that lies entirely in Europe, and stretch approximately 1,200 km across eight Alpine countries (from west to east): France, Switzerland, Monaco, Italy, Liechtenstein, Austria, Germany, and Slovenia.
Alpine lakes are classified as lakes at high altitudes, usually starting around 3km in elevation above sea level or above the tree line.
The Alpine lake of Oeschinen, overlooked by the Blüemlisalp and the Doldenhorn
Recording environmental signals – events
A volcanic eruption can lead to ashes being deposited in the sediments. This is indicated by the reddish layer seen in the above image.
These layers are very important because they are good marker layers for dating. So sometimes you can simply correlate the presence of the marker layer in the “red layer” sediment with an eruption that deposits material on the land. Sometimes the layer can be dated using a radioactive isotopic system. This involves looking at the “mother-daughter” isotopic ratio. An example of this is carbon dating.
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
In nature, carbon exists as two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C), and a radioactive isotope, carbon-14 (14C), also known as “radiocarbon”. The half-life of 14 C (the time it takes for half of a given amount of 14C to decay) is about 5,730 years, so its concentration in the atmosphere might be expected to decrease over thousands of years, but 14C is constantly being produced in the lower stratosphere and upper troposphere, primarily by galactic cosmic rays, and to a lesser degree by solar cosmic rays. These cosmic rays generate neutrons as they travel through the atmosphere which can strike nitrogen-14 (14N) atoms and turn them into 14C.
Once produced, the 14C quickly combines with the oxygen in the atmosphere to ultimately form carbon dioxide (CO2).
Radioactive carbon dioxide diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis. Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere. The ratio of 14C to 12C is approximately 1.25 parts of 14C to 1012 parts of 12C. In addition, about 1% of the carbon atoms are of the stable isotope 13C.
Carbon 14 decays via beta emission (e–) to form a stable non-radioactive isotope of nitrogen.
By emitting a beta particle (an electron, e−) and an electron antineutrino (νe bar), one of the neutrons in the 14C nucleus changes to a proton and the 14C nucleus reverts to the stable (non-radioactive) isotope 14N.
During its life, a plant or animal is in equilibrium with its surroundings by exchanging carbon either with the atmosphere or through its diet. It will, therefore, have the same proportion of 14C as the atmosphere, or in the case of marine animals or plants, with the ocean. Once it dies, it ceases to acquire 14C, but the 14C within its biological material at that time will continue to decay, and so the ratio of 14C to 12C in its remains will gradually decrease. Because 14C decays at a known rate, the proportion of radiocarbon can be used to determine how long it has been since a given sample stopped exchanging carbon – the older the sample, the less 14C will be left.
The equation governing the decay of a radioactive isotope is
where N0 is the number of atoms of the isotope in the original sample (at time t = 0, when the organism from which the sample was taken died), and N is the number of atoms left after time t. λ is a constant that depends on the particular isotope; for a given isotope it is equal to the reciprocal of the mean-life – i.e. the average or expected time a given atom will survive before undergoing radioactive decay. The mean-life, denoted by t, of 14C is 8,267 years, so the equation above can be rewritten as
The sample is assumed to have originally had the same 14C/12C ratio as the ratio in the atmosphere, and since the size of the sample is known, the total number of atoms in the sample can be calculated, yielding N0, the number of 14C atoms in the original sample. Measurement of N, the number of 14C atoms currently in the sample, allows the calculation of t, the age of the sample, using the equation above.
The half-life of a radioactive isotope (usually denoted by t1/2) is a more familiar concept than the mean-life, so although the equations above are expressed in terms of the mean-life, it is more usual to quote the value of 14C’s half-life than its mean-life. The currently accepted value for the half-life of 14C is 5,730 ± 40 years. This means that after 5,730 years, only half of the initial 14C will remain; a quarter will remain after 11,460 years; an eighth after 17,190 years; and so on.
Light sediments can record changes in the ecosystem such as the advent of farming.
Recording environmental signals – changes in the ecosystem
Human settlers would arrive at the shores of the lake at some point in history.
Archaeologists think the first humans settled around Swiss lakes between 5000 and 4000BC.
Structures were discovered in the winter of 1853/54 at Lake Zurich, which at the time had an unusually low water level.
The discovery of this shore settlement marked a significant moment in archaeological research. Sealed off from the atmospheric oxygen by the water and remarkably well preserved – a range of household items, woodworking, forestry and agricultural tools, weapons, hunting and fishing equipment, jewellery and clothing; finished products, semi-finished products and processing wastes from everyday village life that had been lost, discarded or burnt in a fire disaster. These cultural deposits yielded entire layers of cultivated and foraged plants and the bones of domestic and wild animals, giving an insight into the eating habits and economy of the inhabitants.
The settlers built their houses on stilts along the lakesides in order not to waste valuable agricultural land. However, the residents had to be flexible – at high water they were often forced to leave their homes temporarily or even forever. Despite these risks, people were living in such pile dwellings for around 3,000 years.
Th domesticating of animals would have resulted in biomarkers such as faeces and urine (and other biological components) being transported into the lake sediments. These sediments can be “read” using different geochemical and biogeochemical analysis methods.
Sediments can even record which animals were in the area at a given time
Reading the sediments – laminated and homogenous
Researchers like to work with lakes that are anoxic because when the water column is poorly ventilated there isn’t much oxygen at the bottom layers meaning the sediments will be nicely preserved. There will be no biodegradation and the layers will be very well pronounced. Sometimes the layers can be counted and this gives a floating chronology. Counting the layers gives some idea of the number of summers and winters it took to lay down the sediments.
Of course researchers don’t live in a perfect world and anoxic layers don’t happen very often. So most sediments are quite well oxygenated. This happens because the bottom of the lake is oxygenated (there is oxygen present). This makes it more likely that burrowing animals (such as some types of worm) will live there and they can cause the layers to mix, as shown in the above image and the snapshots below.
The sediments aren’t completely homogenised but not nicely laminated. One of the thick layers (a sort of couplet) is more likely an event layer relating to flooding and an increased supply of detrital material from the catchment area.
Questions and answers 1
1) When all the sediments start sinking to the bottom of the lakes does pressure and gravity play an important role in how well defined, they become.
Well gravity is always important because it is something that makes the sediments sink. Pressure is important but not in the early stages of formation.
It really depends on the lake and the sediment load but pressure starts to be important way beyond the point that the researchers are interested in.
Back to the talk
Lake sediment recovery in Brandenburg, Germany
Brandenburg is a state in the northeast of Germany. With an area of 29,478 square kilometres and a population of 2.5 million residents, it is the fifth-largest German state by area and the tenth-most populous. Potsdam is the state capital and largest city, while other major towns include Cottbus, Brandenburg an der Havel and Frankfurt (Oder).
The images above show a researcher holding a gravity corer (sitting in a little boat)
The gravity corer allows researchers to sample and study sediment layers at the bottom of lakes or oceans. It got its name because gravity carries it to the bottom of the water body. Recovering sediment cores allows scientists to see the presence or absence of specific fossils in the mud that may indicate climate patterns at times in the past, such as during the ice ages. Scientists can then use this information to improve understanding of the climate system and predict patterns and events in the future. Cores capture a time capsule that, in some cases, can span the past hundreds of thousands and even millions of years. Because sedimentation rates in some areas are quite slow, even a smaller corer a few meters in length may represent thousands of years of particles. These particles are a historical record of condition in the water column and in the atmosphere and can be used to reconstruct past conditions on Earth.
The corer is basically a type of piston and a PVC core tube. The equipment is slowly lowered down into the lake and when it hits the lake bed it is carefully lifted up. This is a good way of investigating smaller thicknesses of sediment (they can never be deeper than the length of the corer tube), This is a good way of obtaining a sediment-water interface but it isn’t a good way of getting old records.
Above left: Schematic drawing of a gravity corer. (Diagram by Caleb McClennen, Sea Education Association). Above right: an arrow pointing to the water bit of the column (the sediment-water interface can be seen).
Lake sediment recovery in Greenland, the Alps and lake Van in Turkey
Greenland is the world’s largest island, located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago.
A better method of obtaining sediment cores is to use a platform although the arrangement above left isn’t as stable as the arrangement on the right.
The tube is lowered down into the sediment from the tripod using a small piston. With this method the researchers could get 6m of sediment with a well-preserved water-sediment interface.
Below is the more sophisticated method used on Lake Van
Lake Van the largest lake in Turkey and the Armenian Highlands, lies in the far east of Turkey in the provinces of Van and Bitlis. It is a saline soda lake, receiving water from many small streams that descend from the surrounding mountains. It is one of the world’s few endorheic lakes (a lake having no outlet) of greater size than 3,000 square kilometres and has 38% of the country’s surface water (including rivers). A volcanic eruption blocked its original outlet in prehistoric times. It sits at 1,640 m which makes for several weeks each year usually below zero degrees Celsius. High salinity mainly prevents it from freezing at such times. Specifically, the shallow northern section can freeze, but rarely
Above left: From space, September 1996 (top of image is roughly northwest)
The International Continental Scientific Drilling Program is a multinational program to further and fund geosciences in the field of Continental Scientific Drilling. Scientific drilling is a critical tool in understanding of Earth processes and structure. It provides direct insight into Earth processes and critically tests geological models. Results obtained from drilling projects at critical sites can be applied to other areas worldwide. It is, therefore, believed that international cooperation in continental scientific drilling is an essential component for a responsible management strategy for the Earth’s natural resources and environment.
The ICDP was founded in February 1996 in the German Embassy in Tokyo as a result of the German Continental Deep Drilling Program (KTB; 1987-1995). The GFZ German Research Centre for Geosciences serves as the headquarters for both the current ICDP and the former KTB project.
Lake Van in Turkey is an excellent paleoclimate archive comprising long high resolution annually laminated sediment records covering several glacial-interglacial cycles. The lake is situated on the high plateau of eastern Anatolia and has a surface area of 3,522 km2. Its maximum depth is 451 m and its length is 130 km. It is the fourth largest of all terminal lakes in the world and contains highly alkaline waters.
The Lake Van research used a platform that was far more stable and was similar to those used for shipping goods. There is a rig which is able to recover cores from very deep lakes. The 2010 Turkey campaign recovered more than 600m cores, drilling at a water depth of 400m.
The ICDP Turkey campaign was huge in relation to others. It took several years of preparation and lots of different scientists from many different countries were involved.
Once the cores were collected, they were shipped to Bremen in Germany
The City Municipality of Bremen is the capital of the German federal state Free Hanseatic City of Bremen (also called just “Bremen” for short), a two-city-state consisting of the cities of Bremen and Bremerhaven. With around 570,000 inhabitants, the Hanseatic city is the 11th largest city of Germany as well as the second largest city in Northern Germany after Hamburg.
The Lake Van cores were cut half and analysed.
So, what can be found in the sediment?
A random “slice” of sediment
Every slice (the thickness can be varied but is usually 1cm) may contain the sort of things seen in the above image.
SEM analysis of a random “slice” of sediment
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector (Everhart-Thornley detector). The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometre.
Specimens are observed in high vacuum in a conventional SEM, or in low vacuum or wet conditions in a variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments.
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as “calcite”.
Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite is even less stable.
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3 (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
The crystal lattice of aragonite differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal. Repeated twinning results in pseudo-hexagonal forms. Aragonite may be columnar or fibrous, occasionally in branching helictitic forms called flos-ferri (“flowers of iron”) from their association with the ores at the Carinthian iron mines.
Calcite and aragonite are polymorphs of the same mineral
Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typically around 1 mm in size, but varying from 0.2 to 30 mm in the case of Gigantocypris. Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or “shell”. The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic; and early molecular phylogeny was ambiguous on this front, recent combined analyses of molecular and morphological data found support for monophyly in analyses with broadest taxon sampling
Dolomite is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO3)2. The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomitic rock type is dolostone.
Diatoms are a major group of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth’s biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile deep on the ocean floor, and the entire Amazon basin is fertilised annually by 27 million tonnes of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.
Diatoms are unicellular: they occur either as solitary cells or in colonies, which can take the shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 200 micrometres.
In the above slice of sediment there were two types of diatom, made up of biogenic silica.
It was surprising to find dolomite in the sample, not just because of where it was found but because it was nicely crystallised.
The ostrocod shell seen above looked quite normal under a binocular optical microscope but under a low resolution (above left) SEM there were patterns of lines that Dr Kwiecien hadn’t seen before. Zooming in further showed grazing traces. It looked like something had been munching on the carbonate that makes up the shell. Researchers are still working on what could have been the cause. Could it have been a microparasite? Without the SEM they wouldn’t have noticed the traces.
The above images show dolomite and diatoms together. This is a very rare occurrence
Above left: Dolomite crystals (carbonate material). Above right: Silica from diatoms
Normally these two minerals are precipitated differently and are preserved in water of different PH
In chemistry, pH is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions. PH 7 is neutral.
Test tubes containing solutions of pH 1–10 (left to right; acid to alkali) coloured with an indicator.
Silica requires a slightly more acidic environment than carbonates (they need a more basic environment). So, it is very rare to see them in the same sediment.
Sometimes it takes practice and time to identify the objects found in the sediment.
NASA/Goddard Space Flight Centere https://svs.gsfc.nasa.gov/10394
Above left: Scanning Electron Microscopic image of pollen grains from sunflower, morning glory, prairie hollyhock, oriental lily, evening primrose, and castor bean. Above right: Diatoms
The above items are only visible with an electron microscope.
Combining “slices” or “snapshots” to produce a chronological timeseries
Each point on each of the graphs would represent one sample taken from the sediment. The researchers would systematically work through the samples and count, for example, how many ostracods are present, how many grass and tree pollens are present in each sample sediment. They would then look how the numbers of each have changed in each layer and construct a chronological timescale.
Chronological timescales with the help of XRF line scanning and elemental ratios
X-ray fluorescence (XRF) is the emission of characteristic “secondary” (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science, archaeology and art objects such as paintings.
When materials are exposed to short-wavelength X-rays or to gamma rays, ionisation of their component atoms may take place. Ionisation consists of the ejection of one or more electrons from the atom, and may occur if the atom is exposed to radiation with an energy greater than its ionisation energy. X-rays and gamma rays can be energetic enough to expel tightly held electrons from the inner orbitals of the atom. The removal of an electron in this way makes the electronic structure of the atom unstable, and electrons in higher orbitals “fall” into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon, the energy of which is equal to the energy difference of the two orbitals involved. Thus, the material emits radiation, which has energy characteristic of the atoms present. The term fluorescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy (generally lower).
Each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen. The main transitions are given names: An L→K transition is traditionally called Ka, an M→K transition is called Kβ, an M→L transition is called La, and so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital. The wavelength of this fluorescent radiation can be calculated from Planck’s Law:
λ = hc/E where h is Planck’s constant, c is the speed of the electromagnetic wave and E is the energy of the emitted photon
The fluorescent radiation can be analysed either by sorting the energies of the photons (energy-dispersive analysis) or by separating the wavelengths of the radiation (wavelength-dispersive analysis). Once sorted, the intensity of each characteristic radiation is directly related to the amount of each element in the material. This is the basis of a powerful technique in analytical chemistry.
In order to excite the atoms, a source of radiation is required, with sufficient energy to expel tightly held inner electrons. Conventional X-ray generators are most commonly used, because their output can readily be “tuned” for the application, and because higher power can be deployed relative to other techniques. X-ray generators in the range 20–60 kV are used, which allow excitation of a broad range of atoms. The continuous spectrum consists of “bremsstrahlung” radiation: radiation produced when high-energy electrons passing through the tube are progressively decelerated by the material of the tube anode (the “target”).
Bremsstrahlung radiation is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into radiation (i.e., a photon), thus satisfying the law of conservation of energy. The term is also used to refer to the process of producing the radiation. Bremsstrahlung has a continuous spectrum, which becomes more intense and whose peak intensity shifts toward higher frequencies as the change of the energy of the decelerated particles increases.
Each element will radiate photons with a unique energy which is how they are identified and the most common elements found in the sediment samples would be calcium (Ca), Silicon (Si), Iron (Fe)Titanium (Ti), Potassium (K) and Aluminium (Al).
The strength of the energy signal will indicate how much of the element is present in each sample layer
Typical wavelength dispersive XRF spectrum
At the moment it is still a theoretical approach
Above left: Schematic of Itrax micro-XRF sediment core scanner showing the main components and the moveable SDD. Above right: Scanning the laminated sediment, which shows variations between summer and winter. The white object contains the detector.
Above left: The Itrax with sample and measuring turret doors open. Above right: core loaded on the Itrax being prepared prior to a run.
The above images show the equipment for XRF line scanning. The equipment creates plots that show the changes in the different elements in the profile
Plots showing the Itrax elemental data and X-ray radiographic image
ITRAX: description and evaluation of a new multi-function X-ray core scanner
Croudace et al, 2006
A new automated multi-function core scanning instrument, named ITRAX, has been developed that records optical, radiographic and elemental variations from sediment half cores up to 1.8 m long at a resolution as fine as 200 μm. An intense micro-X-ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both X-radiography and X-ray fluorescence (XRF) analysis.
BOSCORF is the UK national deep sea core repository, set up by the Natural Environment Research Council (NERC) to store marine sediment cores collected by NERC ships and NERC-funded researchers.
XRF core scanning yields reliable semiquantitative data on the elemental composition of highly organic-rich sediments: Evidence from the Füramoos peat bog (Southern Germany)
Kern et al 2019
A sample is taken from a relatively shallow lake – the coastal zone. Different elements in each region of sediment, either detrital or from the lake water itself, is due to the minerals precipitated.
The sample is carefully put in the XRF core scanner. The results aren’t quite quantitative but give qualitative changes in the elemental ratios.
How palaeoenvironmental (an environment at a period in the geological past) data is produced.
It is important to link the type of element to the process. Iron and aluminium come from the catchment area. They don’t normally come from any organisms in the water. They definitely come from outside the lake. However, calcium and silicon can come from diatoms as well as clastic sediment and drainage. Calcium is related to the precipitates in the lake water.
Looking at the different elements in a sediment allows the identification of the environmental process that caused them to be present. This information can be linked back to changes in the environment.
Questions and answers 2
1) How long does it take to form metamorphic rocks?
They don’t occur in lakes. High pressure and temperature are necessary for their formation. Pressure is a geological process and it might take millions of years to create something that is metamorphic. Temperatures can be linked to processes such as volcanism.
Volcanism (or volcanicity) is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface.
Lava or folding, which releases extremes of temperature in a very short time, can cause contact metamorphism very quickly.
In structural geology, a fold is a stack of originally planar surfaces, such as sedimentary strata, that are bent or curved during permanent deformation. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur as single isolated folds or in periodic sets (known as fold trains). Synsedimentary folds are those formed during sedimentary deposition.
The scale of the metamorphic bodies can be different depending on whether it is created by more pressure or temperature if you are thinking about the processes that are happening deep down in the Earth.
Sediments might be deposited in water e.g. an ocean, and with subduction they will be exposed to increasing temperature and pressure causing large quantities of metamorphic rock to be formed.
Subduction is a geological process that takes place at convergent boundaries between tectonic plates. One plate dives under another and sinks into the mantle. Regions where this process occurs are known as subduction zones. Rates of subduction are typically measured in centimetres per year, with the average rate of convergence being approximately two to eight centimetres per year along most plate boundaries.
The timescale for the formation of metamorphic rocks can be short or long. It depends on the processes and conditions whether the sedimentary rocks become metamorphic.
2) How is the information gathered on sediments used?
Imagine analysing pollen e.g. grasses and trees and you notice there are cyclical changes in them. This means there must have been changes in terms of temperature or precipitation. So, the vegetation on land changes from grassland to woods.
One of the common ways of interpreting pollen allows them to identify how the environment around a lake has changed, how the vegetation has changed, however vegetation doesn’t usually change immediately. There is always a driver and this is usually atmospheric circulation.
Timescales could be dictated by glacial changes or, during the last 10000 years, by human activity. A latter example would be humans chopping down forests for farming. In Britain, it is believed that most of the island was covered in forests before Neolithic people took up agriculture.
Research being done now is very relevant considering the recent fires in Australia and the Amazon.
Sediment investigations don’t always just find pollen. Charcoal can be present and depending on where it was found researchers can count back and work out how often wildfires were happening. Based on the material found in the sediment a researcher can say how large the fire was and what kind of temperature it reached.
3) Which of the methods is the most common when extracting sediment cores from lakes?
It depends on the lake. Big, deep lakes are sampled using large platforms. There are organisations that provide logistical support for these operations but they are very expensive and needs a lot of planning. There needs to be a specific scientific idea and a well thought out project.
The smaller platforms can be moved by helicopter or car from one lake to another. This isn’t cheap but can be done on a smaller scale with university departments rather than it being a huge international effort.
The platform used will be determined by the lake and whether the science to be found is relevant enough.
Back to talk
Lake Van PALEOVAN 2010 goals
The main objectives of the PALEOVAN project were the recovery and analysis of a long continental paleoclimate record in a sensitive, semiarid region. This included exploration of the dynamics of lake level fluctuations and hydrogeological development and analysing organic matter content and composition (biomarkers). Further scientific goals were the temporal, spatial and compositional evolution of explosive volcanism as reflected in the succession of tephra deposits, as well as the reconstruction of earthquake activities. In addition, the sediments may host key pathways for migration of continental and mantle-derived noble gases to be analysed in pore waters.
This was an expedition that Dr Kwiecien was involved with.
It was important to have a scientific goal for the research. The area they were looking at was volcanic and techtonically active. They wanted to reconstruct the volcanic and tectonic history of the region.
The geology of Turkey is the product of a wide variety of tectonic processes that have shaped Anatolia over millions of years, a process which continues today as evidenced by frequent earthquakes and occasional volcanic eruptions.
Plate tectonics in Turkey: there are geologic faults around the Anatolian Plate, the African Plate, the Arabian Plate, and the Eurasian Plate.
The researchers had a lot of trouble with the ash layers. The layer in the above right picture was from several metres down and completely clogged the coring device and messed up the recording equipment. The project had to be stopped for a few days whilst all the equipment was cleaned. However, the project was successful as the group managed to partly reconstruct the volcanic history.
Lake Van is on the route of human movement, almost the equivalent of the “Silk Road”, which isn’t actually a road.
The Silk Road was a network of trade routes which connected the East and West, and was central to the economic, cultural, political, and religious interactions between these regions from the 2nd century BCE to the 18th century. The Silk Road primarily refers to the land routes connecting East Asia and Southeast Asia with South Asia, Persia, the Arabian Peninsula, East Africa and Southern Europe.
The aim of the project was to provide a climatic narrative for human history for at least several thousand years
Dynamics of the last four glacial terminations recorded in Lake Van, Turkey
Kwiecien et al 2014
Lake Van deep drilling project PALEOVAN Litt et al 2014
A 600,000 yearlong continental pollen record from Lake Van, eastern Anatolia (Turkey) Litt et al 2014
The black line in the above image is showing glacial-interglacial changes. The grey regions are showing warmer times and the white regions are showing colder regions.
Looking at the pollen record extracted from the lake there was a similar pattern to the glacial-interglacial changes.
The resolution of the record was not always great. The last 150 thousand years is probably the best.
The “blue” record shows the ratio between calcium and potassium. These came from outside the lake.
The graphs show that during the interglacial warmer times there was much more pollen and less detrital input.
During warmer wetter times there are better developed soils, which are keeping the detrital and cplastic material on the land.
As soon as there are drier times with less trees but more grassy vegetation, with poorer soils, more detrital material will be washed into the lake. So there would be a greater detrital input to the sediment.
Several hundred metres of sediment covered about 600000 years. The blank region between 400 thousand and 500 thousand years was because there were problems with recovery. It turned out there was a huge slump in the sediment and the researchers weren’t able to say how the sediment was laid down in that section.
A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope. Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope.
Gravitational slumps are quite common with light sediments.
In 2014, when the reports were published, they represented the longest and most detailed set of records of the Mediterranean region. The results showed that this region followed the glacial-interglacial cycle pattern.
Other groups of researchers have published longer records for other lakes.
Lake El’gygytgyn is an impact crater lake located in the Chukotka Autonomous Okrug in northeast Siberia, about 150 km southeast of Chaunskaya Bay.
The word “Elgygytgyn” means “white lake” in the Chukchi language.
The lake is of particular interest to scientists because it has never been covered by glaciers. This has allowed the uninterrupted build-up of 400 m of sediment at the bottom of the lake, recording information on prehistoric climate change.
Most of the time this lake is near frozen but the ground near it is soft. This makes it difficult to bring in the equipment for drilling.
The researchers drilled through the ice during the winter and actually lived on the ice during the process.
Questions and answers 3
1) Could large amounts of carbon dioxide stored in sediments be released into the atmosphere?
If the water is well ventilated then very little carbon (in the form of organic material) will be stored (unless it is converted to carbonates). It will become mineralised, i.e. oxidised to carbon dioxide and released into the atmosphere.
Recent studies have pointed out that eutrophic environments tend to have high rates of mineralization, resulting in higher carbon emissions into the atmosphere and less accumulation of this element in the sediments (Bastviken et al., 2011; Pacheco et al., 2013).
Eutrophication is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae. This process may result in oxygen depletion of the water body after the bacterial degradation of the algae. One example is an “algal bloom” or great increase of phytoplankton in a pond, lake, river or coastal zone as a response to increased levels of nutrients.
High carbon emissions have also been found in hydroelectric reservoirs, especially during the first years after flooding, when the mineralization of soil and flooded vegetation causes significant CO2 and CH4 emissions (Roland et al., 2010; Barros et al., 2011; Mendonça et al., 2012b). It is also estimated that elevations in global temperatures predicted for the next few years (2°C to 4°C, IPCC, 2007, 2013) could cause a significant increase in the carbon mineralization rates in the sediments, resulting in higher carbon emissions to the atmosphere, and contributing to the worsening of the greenhouse effect (Gudasz et al., 2010; Regnier et al., 2013; Raymond et al., 2013). In general, knowledge about CO2 and CH4 emissions from sediments becomes more and more essential for an accurate carbon cycle balance in aquatic environments, and also to support strategic planning for the management and conservation of these environments (natural and artificial) at local, regional and global scales.
If the lakes are stratified with an anoxic layer then most of the organic matter will be stored and the only way to release any trapped gases is to disturb the sediment and mix it up in the water.
Mixing up the water releases the trapped gases, not just carbon dioxide, which is how organic carbon is released from the lakes.
Lakes are not necessarily great stores of residual carbon. Peak lands and bog are huge stores of carbon. Lakes are so-so in comparison.
2) Dr Kwiecien outlined her career path.
She always like science but didn’t want to dissect animals so she opted for geology and not biology. She didn’t want to be stuck in a lab which is why she didn’t want to do physics or chemistry (although I would agree with Ernest Rutherford “Anything of importance is physics, everything else is just stamp collecting”). She is an out-door person