The Earth Story

The Sea of Marmara Nestled in between the Asian and European locales of Turkey, the Sea of Marmara is large inland body of water that links the Black Sea to the Aegean Sea. The narrow Bosphorus Strait, which separates Istanbul into its Asian and European territories, connects the Marmara to the Black Sea, while the Dardenelles Strait flows from the Marmara into the Aegean Sea. Its strategic location makes the Sea of Marmara an important port for trade and shipping between the Black Sea and the Mediterranean — an economic feature that has lasted since the days of Constantinople and the Byzantine Empire.

The not so Black Sea.

This image taken by NASA's Aqua MODIS, shows a phytoplankton bloom in the Black Sea on July 15th 2012.

Phytoplankton, derived from the Greek words phyto (plant) and plankton (made to wander or drift), are microscopic organisms that live in watery environments, both salty and fresh. Some phytoplankton are bacteria, some are protists, and most are single-celled. Among the common kinds are: cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.

The colours of the blooms are typically derived from the pigments in the phytoplankton, which use chlorophyll for photosynthesis. Some of the colour is also attributable to the minerals in the fine shells of these organisms. Coccolithophores, for example, produce a calcite shell that can give the water a milky appearance as in this image.

-Jean.

Photo courtesy of NASA (good to have them back)

THE BLACK SEA

The Black Sea is a unique body of water situated between Asia and Europe, and has a surface area of roughly 436,400 square kilometers. Originally dubbed Pontus Axeinos (The Inhospitable Sea) as it was difficult to navigate, the name was changed to Pontus Euxinos (The Hospitable Sea) soon after the Ancient Greeks arrived on its shores.

It was once a part of the ancient Sarmatic Sea -- which also included the Caspian Sea and Aral Lake -- until a collapse created the Bosphor Strait, resulting in the Pontic Lake becoming the Black Sea. The Black Sea communicates with the Atlantic Ocean via the Mediterranean Sea (basically, the Black Sea- Bosphor Strait- Marmara Sea- Dardanele Strait- Mediterranean Sea). Surrounded by six countries (Bulgaria, Romania, Ukraine, Russia, Georgia, Turkey), the Black Sea -- continuously supplied by several major rivers including the Danube, Dnieper, Dniester, and Don -- hosts several busy ports, fishing fleets, and is a popular tourist destination.

What makes the Black Sea unique is a layering effect, known as stratification. The surface layers (0-200 m) are oxygenated, and teeming with light and life (plants and animals). The deeper layers (200-2211 m) are anoxic -- aka deprived of oxygen -- with no light or life due to the presence of a toxic gas (hydrogen sulfide), which forms from the decomposition of dead plants and animals. Thanks to the major rivers that flow into it, the surface layers have an average salinity (17-18%), while the deeper layers have a higher salinity (21-22%) due to a hydrological exchange with the salty Mediterranean Sea.

The large volume of freshwater delivers many nutrients, which support large blooms of phytoplankton (algae and bacteria). In 2012, NASA captured a satellite image in which the Black Sea was turned light blue because of the phytoplankton bloom (aka coccolithophores).

FUN FACT: The Black Sea lacks tides (because of its continental character), which has contributed to the formation of the Danube Delta in Romania -- arguably one of the most amazing places to visit in Europe.

Sources: Personal knowledge and materials, www.blackseascene.net http://www.marineinsight.com/know-more/8-amazing-facts-about-the-black-sea/ https://apod.nasa.gov/apod/ap170424.html https://earthobservatory.nasa.gov/IOTD//view.php?id=78705 http://oceanservice.noaa.gov/facts/phyto.html

Image: NASA/Aqua/MODIS https://apod.nasa.gov/apod/ap170424.html

This one is pretty amazing. Black Sea coast, Eastern Turkey.

Shells

With the exception of one small outlet, the Black Sea is closed to the ocean. A few major rivers like the Danube carry large amounts of sediment into the black sea, but away from those river deltas there is little continental, siliciclastic sediment carried around the black sea. If a portion of the edge of this sea is an environment where shell-growing organisms can live, a beach made of this pile of slightly broken shells is a likely end result. If these shells were buried, dissolution and reprecipitation of the carbonate minerals that make up the shells would likely turn these rapidly into a rock, a limestone made almost entirely of shells called a coquina (https://tmblr.co/Zyv2Js1H6xogw).

-JBB

Image credit: EGU Open Access photos https://imaggeo.egu.eu/view/4684/

Black Sea not site of Noah's flood.

In recent years the controversial hypothesis that the biblical event was a transmitted oral memory of the catastrophic flooding of the Black Sea by post ice age rising sea levels has been advanced, notably by Robert Ballard of Titanic fame. While it is clear that the freshwater lake did fill with salt water around 12000 years ago, and that people had lived around it and moved away, new geochemical evidence published in Geology implies that this rise was gradual rather than sudden. The lake's chemistry changed from oxygenated to anoxic during this transition, as the sea spilled over the Bosporus sill (a natural dam of intruded igneous rock). Currently the chemocline between oxygenated surface fresh water and deeper salt anoxic water is at 150M, and the surface water from rivers is exchanged for salt water from the Aegean.

Researchers used a combination of iron isotopes (to trace the changes in oxygen levels) and molybdenum (to trace changes in salinity) in sediment cores to reconstruct the history of the lake's evolution and gradual conversion to anoxic conditions. The results showed that the change had happened over thousands of years, between 12,000 and 3,000 BCE.

On another note, the image shows phytoplankton blooms in the Black Sea, due to fertiliser runoff flowing down the Danube, Don and Kuban rivers. Following the current flooding in Central Europe, another large bloom is a near certainty, which will temporarily change the level of the chemocline.

Loz

Image credit: MODIS/AQUA/NASA

http://geology.gsapubs.org/content/41/4/523.full#ref-7 http://geology.gsapubs.org/content/41/4/431 Tag Photo

Neat, waves in the black sea shot from Drone’s eye.

Sail Rock, Russia

This sandstone monolith located in the Russian region of Krasnodar Krai obtained its name for its both peculiar and stunning appearance. This sheer cliff resembles a ship's sail.

Lying on the coast of the Black Sea, this sheer cliff is 25 meters tall, yet only a mere meter thick! Contributing to its image lies the fact that this rock is perpendicular to the coastline. The reason behind this, as with many geological features, is erosion. Behind this thin cliff lies another sandstone cliff, but far greater in height, width, and pure quantity of rock. Natural erosion forces of the water slowly removed thousands of cubic meters of rock over millions of years, which reversed the lithification process and turned sandstone into gravel, sand, and clay. Only the strongest sections of rock remained, which today can be seen as the picturesque image of Sail Rock. Lithification produces different densities and strengths of deposited rock, and Sail Rock is composed of the strongest rock that was able to remain.

Effects of the continuous and ongoing erosion can be seen today on the rock. The "lacerations" that appear to cover this cliff from head to toe are long lasting effects of this strong, dense, monolith's enduring of erosion.

The very visible hole in the cliff is of unknown origin, yet it is predicted to be a result of projectile weapons during the Caucasian War. Sail Rock has been a protected Russian National Monument since 1971.

--Sam J.

Image Credit: The World Geography

References:

http://www.theworldgeography.com/2012/05/10-famous-sea-stacks-from-around-world.html

http://www.praskoveevka.ru/okrestnost/skala_parus.php

http://www.parus-bo.ru/parus.shtml

The meaning of black

Unless they are volcanic basalts, black rocks tend to mean one thing to a geologist: an absence of rotting, and quite often a hard time for life. It denotes a period where the ground or sea bottom was poor in oxygen, as happens in the current day in peat bogs, some deltas where sediments bury the organic matter quickly or in stratified lakes or basins such as the Black Sea. When organic matter does not rot, it leaves a black carbon rich residue behind, giving a colour to the surrounding rocks. When metamorphosed during a continental collision the carbon turns into graphite, often woven through the texture of the rock.

The most common black rocks are mudstones, sometimes extremely localised, that are born in lakes or seas. Oil shales are the most organic rich examples and provde the source material for the oil trapped elsewhere in the sedimentary stack, or even directly from the shale itself these days. The vast oil deposits in the limestones of the Middle East come from a series of Cretaceous events (145-65 million years ago) when the Tethys Ocean became stratified and the sea bottom was anoxic. The dark strata in the photo are coal seams from the Alaska range. Coal often forms in deltas and peat bogs, where organic matter is either buried away from oxygen by rapid sedimentation or does not rot due to the anoxic and acidic conditions in the bog.

Loz

Image credit: Liyamu

The Sea of Marmara

Nestled in between the Asian and European locales of Turkey, the Sea of Marmara is large inland body of water that links the Black Sea to the Aegean Sea. The narrow Bosphorus Strait, which separates Istanbul into its Asian and European territories, connects the Marmara to the Black Sea, while the Dardenelles Strait flows from the Marmara into the Aegean Sea. Its strategic location makes the Sea of Marmara an important port for trade and shipping between the Black Sea and the Mediterranean — an economic feature that has lasted since the days of Constantinople and the Byzantine Empire.

Similar to the Black Sea, the Sea of Marmara possesses a unique layered structure with denser, saltier water at its bottom and fresher water at the surface. With rivers and waterways that contribute organic-rich runoff from the continental interior and the surrounding cities and villages, the top freshwater layer is a natural breeding ground for microscopic algae, also known as phytoplankton. This image, captured by the Operational Land Imager on the Landsat 8 satellite in May of this year, shows the swirling blooms of phytoplankton in the Sea of Marmara. The most concentrated swirls reveal the currents and eddies in the Sea of Marmara — a complicated mix of patterns compounded from the inflow and outflow of water from the Bosphorus and Dardenelle Straits, as well as interference from the rugged Turkish shores and the disjointed, tectonically active seafloor.

-DC

Photo credit: http://1.usa.gov/1SVeAa7

More reading: http://1.usa.gov/1T8mNSV http://bit.ly/1KTWeBK http://1.usa.gov/1DtLckv

Geology of Sochi III: the Black Sea

In my previous posts on the geology of Sochi, I covered the mountains (http://tinyurl.com/l6upzzm) and the rivers and basins of the area (http://tinyurl.com/n3om8bh). The Black Sea is the final ingredient of the Sochi area, and it is a geologically fascinating area, directly linked to the history discussed in my previous posts.

The Black Sea was formed during the late Cretaceous period when part of Asia was torn away from the continent. That sounds sort of exciting to me, and yeah it was.

The Tethys seaway was made of old oceanic crust. The older oceanic crust gets, the colder and denser it gets and the more rapidly it sinks into the mantle. Old oceanic crust wants to sink like crazy. To understand this property, let’s consider the opposite case. If we look at areas like the west coast of North or South America, we see mountain ranges being built. The rocks are being squeezed and pushed together…but in those areas, the ocean crust being subducted is young and warm. Young, warm oceanic crust doesn’t subduct easily; pushing it down requires the continent to do a lot of work, and can cause the continent above to be squeezed and deformed into mountains. Old oceanic crust doesn’t do this, it really wants to sink. In fact, it wants to sink so much that it can even start pulling on the continent. We see this effect today in the western Pacific Ocean where old oceanic crust is subducting; the island arcs in the western Pacific are being pulled away from the continent, creating basins behind them. This process created the Black Sea. The Tethys Ocean was subducting beneath Asia and creating a volcanic arc, but the oceanic plate wanted to sink so badly that it literally ripped the volcanic arc away from Asia. Several basins, including the Caspian Sea and the Black Sea, formed in these back-arc environments as the volcanic arcs were torn away. Today, the Black Sea sits as a unique environment. Its base is made of Cretaceous and Paleocene aged igneous rocks, formed as the continent was ripped apart. On top of that, 75 million years of sediments have been deposited, leading to the setup we find today. -JBB Image credit: Florin Mogos http://www.flickr.com/photos/florin_mogos/1133732053 Read more: http://dare.ubvu.vu.nl/bitstream/handle/1871/8349/6785.pdf?sequence=1 http://www.deepseadrilling.org/42_2/volume/dsdp42pt2_51.pdf http://geology.gsapubs.org/content/22/3/267.short

Geology of Sochi II: the basin In my last post, I covered the geology of the mountains which tower over Sochi, Russia, and discussed how the mountains are built by a series of faults (see here: http://tinyurl.com/l6upzzm). Another major feature of the area is the Mzymta River, seen here where it enters the Black Sea. All of the Olympic venues are located within this valley. The river is sourced in the high peaks of the Caucasus and winds its way to the coast, crossing several waterfalls and the Dzykhra and Akhshtyr rivers. The river’s flow is regulated by hydro-power stations and is a popular tourist site for rafting. Many of the Sochi venues sit on sediments deposited by this river. Sochi itself sits in a tectonic lowland, south of the thrust faults in the mountains, known as the Rioni basin. A basin sitting at the base of thrust faults is a very common setup caused by gravity. As a mountain range builds, its weight pushes nearby rocks downwards, creating a basin that will commonly be filled by sediments derived from erosion of the mountains. Typically, as mountain ranges grow, their faults will penetrate into these basins and they will be incorporated into the growing range. The Rioni basin sits between the Caucasus and the Black Sea in this area and it is filled in part with sediments brought down from the mountains along the river. For construction of large facilities like the Olympics, this setup creates enormous potential problems due to the combination of active faults and sediments. When an earthquake happens near a sediment-filled basin, the sediments tend to focus the energy. As they shake, the fine-grained sediments mix with water and undergo “liquefaction” – basically losing all strength and flowing like a mudflow. If a building is sitting on top of sediments that are shaken in an earthquake, it will be very difficult for the building to survive. The area around Sochi is a mix of sandy beaches, bogs, and wetlands. The ground remains waterlogged and the area gets heavy rains and floods often. Constructing an Olympic village in this area required developing drainages to move the water, pouring foundations stable enough to survive earthquakes and liquefaction, and then building the facilities on top. The geology of the area made the construction of these facilities a difficult, expensive proposition regardless of whatever else went on. -JBB Image credit: http://en.wikipedia.org/wiki/File:Mzymta_River.JPG Read more: http://blogs.scientificamerican.com/rosetta-stones/2014/02/03/building-sochis-olympic-village-an-olympic-task-in-a-geologically-risky-area/