Scientists from British Antarctic Survey have analysed sea-bed colonies of bryozoans *) from coastal and deep sea regions around the continent and from further afield. They found striking similarities in particular species of bryozoans living on the continental shelves of two seas ' the Ross and Weddell ' that are around 2400 km apart and separated by the West Antarctic Ice Sheet. These bryozoans must have survived glaciations(s) during subsequent ice ages in refuges, whereas they were wiped out in most other regions of the Antarctic shelf.
Because the larvae of these bryozoans sink and this stage of their life is short ' and the adult form anchors itself to the seabed ' it's very unlikely that they would have dispersed the long distances carried by ocean currents.
The new finding, published in the journal Global Change Biology, therefore leads the team to conclude that these bryozoans could have spread across both seas only by means of a trans-Antarctic seaway through what is now a 2 km solid layer of ice. They suggest also that this seaway opened up during a recent interglacial perhaps as recently as 125,000 years ago, when In a brief warm period world sea levels were about five m higher than today and temperatures probably at least 4??C warmer.
A schematic of partial collapse of the West Antarctic Ice Sheet showing a seaway between the Weddell and Ross seas. Such a collapse would enable mixing of faunas but would also generate significant sea level rise.
For comparison a map of Antarctic bedrock:
As I have no access to the journal Global Change Biology this post is mainly based on a press release from the British Arctic Survey.
*) Bryozoans
I mainly know fossil bryozoans (with exoskeletons made of the mineral calcium carbonate) from Maastrichtian 'bryozoan chalk' . I will however here show you an image of similar bryozoan fossil colonies of Ordovician age in an Estonian oil shale, where they contrast better with the host rock sediment (white on brown instead of white on white).
Bryozoans are aquatic animals, sometimes referred to as moss animals, and feed on microorganisms suspended in the water column. They are filter feeders that sieve food particles out of the water. Their larvae are benthic (i.e.living on the sea bottom) and short-lived but this is the dispersal stage ' as adults they anchor themselves to the seabed. Many of the 500 species around Antarctica are restricted to shallows and particular continental shelves.
One genus of modern bryozoans is solitary, but the rest colonial. Bryozoans take many different forms, some of which are shown in the image below. All of these occur on Southern Ocean continental shelves.
One of my readers has asked a few questions about the jet stream. As I intended to reply with a few general basic principles rather than going into too much detail, and as my posts are generally about simplified general basic principles, I thought that I might as well make a post of my reply.
Jet streams are waves (Rossby waves to be more exact) that form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and the warmer air nearer to the equator. The jet stream is characterised by large undulations or meanders, typically three to six in numbers.
Heat is transported to polar regions by the atmosphere. Any mechanism that transfers heat from the surface of the Earth to the atmosphere also contributes to the poleward transport of heat.
The following diagram shows a cross section of the subtropical and polar jet streams by latitude.
I hope the figure (taken from Wikipedia) shows that motion in the upper troposphere is generally polewards. The Earth's surface is uneven heated. The Hadley, Ferrel, and Polar cells plus the lows and highs are a manifestation of the need for heat to be moved polewards, to compensate for the imbalance between low and high latitudes.
My reader asks:
'Why does the jet stream on the northern hemisphere come "down" to 30??N, whereas the antarctic jet stream seems content to stay closer to the south pole'?
The short, and maybe oversimplistic, answer is the presence of smaller landmasses in the Southern Hemisphere.
Sea water has a high thermal coefficient compared with ground and increase less in temperature from solar radiation, furthermore the water will spread the radiation to a depth that is not possible on land. The ocean water temperature will therefore show less variability than land masses. As a result the southern polar jet stream exhibit less day-to-day, and month-to-month, variability due to the presence of much smaller landmasses.
Indeed the southern hemisphere polar jet tends to mostly circle the Antarctic. I have tried to illustrate 4 things in the figure above. 1. The larger landmasses on the Northern Hemisphere as compared to the Southern Hemisphere. 2. The southern polar jet stream exhibit less variability. 3. The Antarctic polar jet stream does indeed constantly stay closer to the South Pole. 4. May I also point out that the Jet Streams are nearer to their poles in the summer than in the winter. (When you compare, please note that summer in Antarctica means January - as opposed to the North pole, where summer means July).
It was, however, not my intention to show any exact latitudes for the possible extension of the jet stream's operation area.
The weather in Antarctica is really special because of the Antarctic Circumpolar Current, which is the only ocean current that flows completely around the globe. This cold current isolates Antartica from any warm current transporting heat southwards. Antarctica with its ice sheet is therefor extremely cold, and this has of course implications for the atmospheric heat transfer.
I hope I have also made clear that the meridional exchange of air is not an effect of the jet stream, but that it is the other way round - the jet stream is an effect of the atmospheric meridional heat transfer or, if you wish, exchange of air. And that the temperature at the Earth's surface has a more or less direct influence on the jet streams (remembering that the jet streams flow at interfaces between cold and warm air, albeit miles above our head).
I also ought to mention that when the polar-front jet penetrates to subtropical latitudes (as was the case to the north of Pakistan during the extraordinary rains in Pakistan this year), it may merge with the subtropical jet to form a single band (until they split again).
Of course all these atmospheric phenomena are interactive (the jet stream may indeed have a large influence on the local weather), but I hope it helps to see them all as parts of a global heat transfer system (complementary to ocean circulation).
Once again events have made me post something else than originally planned. The eruption of mount Sinabung on Sumatra is certainly an event worth writing about. The blogs 'The Volcanism Blog' and 'Eruptions' are of course as usual doing a great job on keeping us informed about a volcanic event as this, and there is not much that I can add.
First a YouTube video (from AlJazeera)
Sumatra's volcanism is caused by the northeastward subduction of the Indian Ocean plate under the continental Sunda plate.
I have added a Google map showing the position of Sinabung (Red S marker) to the north of Lake Toba (See my post on Toba Super-Eruption). (Location 3??10'12'N 98??23'31'E - Elevation 2,460 m)
Mount Sinabung, which had been dormant for more than 400 years, began erupting 15 minutes past midnight, Sunday 29 August 2010) after rumbling for several days, now followed by a new eruption today Monday 30 August 2010 at 06:30.
At least a couple of people have died, and thousand have flied or been evacuated. Yesterday (Sunday) the authorities estimated the number of refugees fleeing their homes at 16,800 but the number might have grown today. (Latest: According to Red Cross workers more than 18,000 people are now living in camps and government shelters.)
I find the NOAA image below an excellent starting point for a discussion of the two weather events that became hot news this summer.
The Great Russian Heat Wave of 2010 brought temperatures of 37??C or more to Moscow, and smog and smoke from wildfires blanketed the city for many days. Air pollution levels were 2 - 3 times the maximum safe level. The death toll from fires, heat and air pollution in Russia has been estimated to 15,000.
The heaviest monsoon downpours in Pakistan's history has caused floods that have displaced more than 10 million people. The humanitarian situation in Pakistan is described as worse than what we have seen in the world in the last decade, or in other words 'ever'.
The NOAA map shows world temperature anomalies for July 2010. I have enlarged the part showing Russia and Pakistan, and drawn in a couple of features I think you can implicitly read from the map.
The jet stream was blocked for a long period. Such a blocking event happens when an area of high pressure air forms that is strong enough to stop the normal flow of the west-to-east jet stream, and stays in one spot. I have tentatively drawn a black line where the jet stream approximately must have been for a very long period (leading to extreme temperature anomalies).
Before I go on just a few words about the jet stream. Actually there are two jet streams in both hemispheres, a subtropical and a polar jet stream. To keep things simple I shall here concentrate on the polar jet stream. In the Northern Hemisphere the polar jet stream is today most commonly found between latitudes 30??N and 70??N. The jet stream is in fact a wave (at around 7'12 km above sea level) at the interface of the colder polar air and warmer southern air at the so-called polar front. These atmospheric waves propagate westward with respect to the flow in which they are embedded, but relative to the ground, they migrate eastward across the globe. In general, winds are strongest just under the tropopause. If two air masses of different temperatures meet, the resulting pressure difference (which causes wind) is highest along the interface. The wind does not flow directly from the hot to the cold area, but is deflected by the Coriolis effect and flows along the boundary of the two air masses. The paths taken by mid-latitude depressions (also known as cyclones or lows) and anticyclones (highs) are determined by the path taken by the jet stream.
The high pressure resulting in the heat wave over Moscow was thus a result of the (over a prolonged period stationary) position of the jet stream. This high 'froze' over Moscow because the jet stream got blocked. Why. is open for discussion. Such blocking events happen regularly, but usually in the winter, not the summer. So in this aspect the block over Russia was an impressive, rather unusual, and particularly strong and persistent event, and at 34 days the longest blocking on record.
The same blocking event was probably also responsible for the exceptional heavy rains in Pakistan. (Here the subtropical jet stream probably also played its role, but as I said I will leave this out to keep things simple). In the summer the land areas are warmed up, the air rises, and the pressure at the surface becomes low, resulting in winds from the sea where the pressure is higher, bringing moisture over land, in other words it rains. In Pakistan this happens every year in the monsoon months of July, August and September. The long time blocking of a low pressure to the north of Pakistan in connection with the blocking of the jet stream, strengthened the winds blowing from the high pressure areas over the Indian ocean towards the low pressure areas above the Tibetan Plateau and lead to the heaviest monsoon downpours in Pakistan's history. Actually the strongest period of blocking, at the end of July, was during the strongest period of rain.
Zambia is a major copper exporter, and copper dominates the economy. In 2008, half of Zambia's copper exports were consigned to Switzerland as they left the country's customs, but according to Swiss import data most of this never arrived at the other end, so where does Zambia's copper actually go to?
The pricing is another mystery. Switzerland's copper exports have much higher declared prices than those of Zambia. While Zambia's prices are close to world averages (which is now a Zambian legal requirement, as they attempt to combat abuse), the Swiss prices are much higher. Were Zambia to receive Swiss export prices for its exports to Switzerland, the total value received would in 2008 have been almost six times higher than it was.
I would, of course, not dare to suggest that anything illegal is going on. Those sort of allegations are dangerous, with all the lawyers around, but the Zambian authorities are, helped by Norwegian auditors, apparently investigating the case - 'probably' involving places like the British Virgin Islands (a tax haven), a.o. wondering, 'where has all the money gone'?
Is that what they call globalisation?
Zambia is an extreme case of over dependence on the production and export of a single product, namely copper mined in the Zambian 'copperbelt'.
According to the Guardian the oil company Cairn Energy has confirmed that it has discovered gas and oil-bearing sands off the coast of Greenland. The discovery may lead to a change in the relationship between Greenland and Denmark. It is a Greenlandic dream to become economically independent from Denmark, and maybe even on long term a completely independent state, but to reach that goal they need an incredible lot of money.
Greenpeace, WWF and other environmental organisations, however, want the drilling to stop in the fragile arctic environment.
In 2008 USGS estimated the Greenland oil potential to be between 10 and 20 billion barrels of oil - for comparison Denmark's oil fields in the North sea held around 3 to 4 billion barrels before production began.
REDD stands for 'Reducing Emissions from Deforestation and Forest Degradation'. It is an instrument agreed at the 2007 Bali UNFCCC (United Nations Framework Convention on Climate Change) meeting consisting of a set of steps designed to use market/financial incentives in order to reduce the emissions of greenhouse gases. The reason is that estimates for deforestation and forest degradation in recent years were shown to account for 20-25% of greenhouse gas emissions, which is higher than the transportation sector.
This leads me to mangroves, once again. Mangroves and the people that depend upon them could really benefit from Redd-related carbon payments. OK, mangroves only account for around 0.4% of all forests, but their functions as coastal protection, nursery habitat for fish and filtration of pollution and sediments make them a conservation priority, particularly as they are also highly effective natural sinks for carbon, capturing up to six times more carbon per ha than undisturbed rainforests.
Dr Mark Huxham, an Earthwatch researcher based at Napier University, Scotland, came up with some very good points in BBC's 'Green Room' in a piece called 'Mangroves offer win-win opportunity' [http://news.bbc.co.uk/2/hi/science/nature/8893767.stm], where he argues that schemes such as Redd offer a vital lifeline to the important ecosystems. I would highly recommend you to read the article.
All I can add is, 'beware of crocodiles'. (If you want my opinion it looks like a Nile Crocodile, they are by the way 'holy' in several African communities - feeding allowed).
Have you ever thought that (South-American) anteaters and (African) aardvarks look a bit alike with their huge snout ? They are in fact related, but a long way back (more than 100 million years), which leads us to a bit of plate tectonics.
In the early Cretaceous, around 120 million years ago, Africa was connected to South America, with the two continents separating about 105 million years ago. Africa was relatively isolated between 105 and 40 million years ago. Around 30 million years ago, Africa began to collide with Europe and Asia, and since then these areas have been closely associated. This plate tectonic history had far reaching consequences for the evolution of mammals still visible today.
The rifting between Africa and South America more than 100 million years ago appears to coincide with the division of two of the four major groups of placental mammals. Placental mammals are mammals having a placenta (also known as afterbirth) and are currently the dominant form of terrestrial life on Earth. The division in four groups is based on DNA studies.
A common ancestral forefather of anteaters, aardvarks and elephants probably lived on the supercontinent Gondwana, and notably in the southern hemisphere. About 103 million years ago they differentiated into two main groups the Xenarthra (e.g., anteaters, armadillos, sloths) found in South America, and Afrotheria, which as the name suggests evolved from an African ancestor. Afrotheria are e.g. elephants, aardvarks, manatees (see cows), elephant shrews and a funny creature I met some years ago in Africa, the Rock Hyrax. Much to my surprise it tried to convince me that hyraxes are the closest living relatives to the elephant, but this honour, again according to DNA studies, probably goes to dugongs and manatees.
Rudyard Kipling told a beautiful story about how the elephant got its trunk, but as you see it may have got it because of its relation with other nosy animals. Please let me repeat that the basal split between Afrotheria and other placentals at about 103 million years may be accounted for by the separation of South America and Africa in the Cretaceous.
Now that I have mentioned all four superordinal groups of placental mammals, namely Afrotheria, Xenarrthra, Laurasiatheria, and Euarchontoglires, I might as well use a few words on the two remaining groups, groups that evolved on the northern hemisphere. As the name suggests Laurasiatheria have their origin in Laurasia (the protocontinent of the Northern Hemisphere). It is possible that populations of the ancestors of Laurasiatheria, and Euarchontoglires became divided by the opening of the North Atlantic Ocean between Europe and North America - it would be nice to see some sort of proof for this hypothesis. As for Afrotheria increasing amounts of molecular and anatomical data have since the 1990s been applied that support the idea that afrotherian mammals are descended from a single common ancestor to the exclusion of other mammals.
Finally below a palaeomap from Late Cretaceous, demonstrating that Africa was isolated from other continents at that time. later Afrotheria got a chance to invade the northern hemisphere, and after the formation of the Isthmus of Panama South America became open for migration from the northern hemisphere.
First let me state that it is not unusual for tectonic plates to rotate. Our Earth is not flat, it is a globe. So airplanes fly in circles ('great circles') and tectonic plates rotate. With which velocity is another matter.
Based on the history of plate motions, and simple dynamical considerations, a 'speed limit' for tectonic plates has been suggested at around 20 cm/year. According to new evidence uncovered by a team of Yale University geologists the Gondwana supercontinent underwent a 60-degree rotation across Earth's surface during the Early Cambrian period. Based on the directions of the ancient rock's magnetization, they discovered that the entire Gondwana landmass underwent a rapid 60?? rotational shift, with some regions attaining a speed of at least 16 cm/year, about 525 million years ago. By comparison, the fastest shifts we see today are at speeds of about 4 cm/year.
The star to the right in the image marks the paleomagnetic record from the Amadeus Basin in Australia.
The study, which appears in the August issue of the journal Geology, has implications for the environmental conditions that existed at a crucial period in Earth's evolutionary history, namely the Cambrian explosion, when most of the major groups of complex animals rapidly appeared. The observations suggest that either nonuniformitarian plate tectonics or an episode of rapid true polar wander occurred during the Cambrian 'explosion' of animal life.
"True polar wander" is when the Earth's solid land mass (down to the liquid outer core almost 3,000 km deep) rotates together with respect to the planet's rotational axis, changing the location of the geographic poles. If, however, the shift was due to plate tectonics, the speed is astonishing. Whatever the cause, the massive shift had some major consequences. As a result of the rotation, the area that is now Brazil would have rapidly moved from close to the southern pole toward the tropics. Such large movements of landmass would have affected environmental factors such as carbon concentrations and ocean levels. This could, indeed, have had huge implications for the Cambrian explosion of animal life at that time.
It has become popular to look for impact craters in Google Maps. Physicist Amelia Sparavigna of Politecnico di Torino in Italy found a crater in the Bayuda desert in Sudan using Google Maps, a free astronomical image processing program she helped develop called AstroFracTool, and open source image processing tool GIMP.
Source: Google Earth
But is it an impact crater? Maybe or maybe not. Actually no one has gone to the Bayuda crater site to confirm that it was formed by a meteor impact - and there are many (confirmed) volcanic craters in the Bayuda desert, like this 'salt crater'. Field work is always a must!
The Bayuda desert is an arid region in Sudan outlined by a huge bend of the river Nile, from the fourth to the sixth cataract. It is thus located north of Khartoum, west of Kadabas, and south of the Nubian Desert, together making up part of the Sahara's eastern flank. The Bayuda Desert is mainly stony, characterised from the basaltic rocks of ancient volcanoes, with various volcanic ancient black eruption cone-shaped formations that are in the central area. There are a cluster of well preserved volcanoes in the northern part of Bayuda Desert. These volcanoes are creating a more or less continuous field, with isolated centres of eruption. The distribution of volcanoes was partly controlled by large granitic ring-intrusions belonging to the Younger Granite association of Late Precambrian or Lower Palaeozoic age and representing one of the volcanic-intrusive episodes widespread in northern Africa.
What is now the Bayuda desert was possibly a part of the Gondwanaland, where it may have hosted the position of the North Pole.
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