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by James

Exploring Antarctica: How there is a potential layer of meteorites beneath the ice

March 11, 2016 in Articles 2015-16

Antarctica is one of the harshest environments in the world covered in ice and remaining in sub-zero temperatures all year round but it is one of the most productive regions in the world for meteorite collection due to large numbers of meteorites congregating in zones called meteorite stranding zones (MSZs) due to upward flowing ice and high ablation rates causing clusters of meteorites to be found in zones on the surface of the ice. However, research has shown that meteorites that fall to the ice could possibly melt further down due to a phenomenon known as englacial solar warming.

A study published recently on Nature Communications explores the potential of such a layer of meteorites beneath the ice of Antarctica.

Due meteorites being guided to MSZs via ice flows it leads to the efficient recovery of many meteorites on the Antarctic continent. Up to December 2015 34,927 meteorites were recovered, currently awaiting names from the Meteoritical Nomenclature Committee (MNC), accounting for 66.3% of the worlds collected meteorite specimens. This shows the importance that Antarctica has to meteorologists due to the sheer number of meteorites collected and the data can be gained from the specimens collected.

However, research has shown that meteorites, especially meteorites with high thermal conductivity, have the potential to be heated up and consequently melt the surrounding ice causing them to sink further beneath the ice forming a potential layer of meteorites beneath the ice of Antarctica. This process is known as englacial solar warming.

Englacial solar warming will cause meteorites to be warmed up as they rise through the ice via MSZs. As a meteor gets closer to the surface there is more solar energy available to the meteorite, this will result in surrounding ice melting and the temperature of the meteorite to increase- causing the meteorite to sink further as its warmer temperature will cause further melting of the ice enabling it to sink further.

However not every type of meteorite will sink further beneath the ice due to englacial solar warming. Only meteorites that have high thermal conductivity will be able to sustain warm enough temperatures enabling them to melt further beneath the ice. These meteorites are generally iron or stony iron meteorites. Due to the lack of iron meteorites and stony-iron meteorites found in MSZs it has lead researchers to believe that a layer of these types of meteorite have sank further beneath the ice than normal stony asteroids, due to their high thermal conductivity.

There are three main types of meteorite: Iron meteorites, Stone meteorites and Stony-iron meteorites. Iron meteorites have a 90-95% iron concentration and the other 5-10% is made up of trace elements and nickel. Due to the very high metal concentration these types of meteorite have high thermal conductivity enabling them to sink further beneath the ice after being heated up via englacial solar warming. Iron meteorites are said to originate from the core of a planet. The next type of meteorite is the stony meteorites. The stony meteorites are the most commonly found of the meteorites and are comprised of mainly rock but the do contain enough iron to be drawn to a magnet. Stony meteorites are said to originate from the outer crust of a planet or from a meteor. The last type of meteorite is the Stony-iron meteorite. The stony-iron meteorites are the least abundant of all the meteorites, accounting for less than 2% of all found meteorites on earth. Stony-iron meteorites are made up of equal parts nickel/iron and stone and are said to have originated from the mantle/core region of the planet they were from.

The results calculated from the recent research carried out show that iron meteorites on average sink lower and are not brought up to the surface of the ice through MSZs. Scientists devised a model that calculated the rate that iron rich meteorites would sink in comparison to non-iron rich meteorites. The results found support the theory of a potential layer of iron rich meteorites further beneath the ice of Antarctica. These meteorites are believed to be trapped 50-100cm beneath the ice and are believed they will never reach the surface as they have sunk too deep to be affected by MSZs.

This has opened up a world of potential for many meteorologists as they can potentially find out more about many early planetary/asteroid bodies from all over the universe by analyzing the data from these iron meteorites that originate from the core of planetary bodies. This could result in many new discoveries about the geology of planets across the universe.

The three different types of meteorite: stony, iron and stony-iron

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by Tanya

The lasting effects of PCBs on two isolated populations of Atlantic and Pacific Orca.

March 11, 2016 in Uncategorized

The Orca

The orca (Orcinus Orca) is easily the most recognisable of all cetaceans (whales, dolphins and porpoises) in the world. Its striking black and white colouration has captured the hearts of many, both young and old, over recent decades.

The now rare sight of an orca calf, unlikely to be seen in Eurpoean waters again.

Figure 1 – The now rare sight of an orca calf, unlikely to be seen in European waters again.

The orca is widely distributed throughout the world’s oceans. In the Pacific Ocean, the orca is an important natural symbol for the people of British Colombia. It is here that two harmonious populations with differing diets live. These populations consist of the transient orcas that are mostly marine mammal eating and the resident population which feed on fish. Over in the Atlantic Ocean the orca is less numerous and only a small resident population is found in industrialized regions of Europe around the Mediterranean Sea. This resident population is primarily tuna-feeding. Also, a small group of marine mammal eating orca is regularly seen around western Ireland and North West Scotland. These four populations of orca are all heavily monitored for research purposes.

However, in a recent paper in Nature Communications it has been proposed that these populations are under threat from an almost silent enemy, PCB pollution.

What is PCB?

Polychlorinated biphenyls (PCBs) are a major toxic industrial chemical that was produced during the twentieth century. PCB is well known for its environmental toxicity and its classification as a persistent organic pollutant. It was in the 1960s that PCBs where first identified as a problem. They were then subsequently banned in America in 1979 and in Europe in 1981. More recently they were banned by the Stockholm Convention on Persistent Organic Pollutants in 2001.

PCB is known to have numerous effects on humans including being carcinogenic. Not only can PCBs and other persistent toxins affect humans but they are having increasing and lasting effects on other organisms, especially those that are top predators in marine food chains.

Marine mammals that inhabit coastal waters of Europe, the Mediterranean Sea and the waters around Vancouver Island have been found to be highly contaminated with not only PCBs but also other toxic pollutants like dichlorodiphenyltrichloroethane (DDT). These chemicals accumulate in the fatty tissues of these animals.

The evidence is increasingly supportive that the increased concentration of PCBs in the ocean is leading to an increase in abnormalities seen in numerous marine species. Such abnormalities include: skeletal deformities, hormone disruption, immunotoxicity, and reproductive failure.

One majestic marine organism that is feeling the increasing effects of PCB in the world’s oceans in very different ways is the orca.

Effects of PCBs

Both the Pacific and Atlantic populations of orca are being affected by PCBs. It has been found that the PCB concentrations in individual male Pacific resident orca increases with age. This is due to them gaining PCB from their prey, which are also contaminated with this toxin. Contrastingly, the PCB concentrations of females in resident populations is greatly reduced with reproductive activity. The females pass on PCB to their offspring when in the womb and during lactation thus, reducing their own levels of PCB contamination. This is evident in many populations of orca where females are reproducing normally, and the concentrations of PCB is seen to decrease significantly with each successful pregnancy. The transient Pacific orca are particularly contaminated with PCBs due to their dietary preference of marine mammals, which themselves are high in PCB contamination. These two Pacific populations are considered to be among the most contaminated cetaceans in the world.

The two monitored populations of orca in European waters are split into almost identical categories as the Pacific orca, the Scottish population been marine mammal eating like the transients, and the southern population been predominantly fish-eating. This allows for good comparison between the Pacific and Atlantic populations.

Over the last 19 years that the Scottish population has been studied there has not been a single report of a calf seen within the group. Similarly for the resident Atlantic population between 1998-2011 only 5 calves were successfully produced and survived beyond a year. This means that over a 13 year period the southern population had a reproductive success rate of only 6.4%. This is one of the lowest recorded reproductive rates for orcas across the globe.

Adult females in the Atlantic consistently have substantially great concentrations of PCBs in their bodies than any individual Pacific orca. The adult males in the Atlantic also have higher PCB concentrations than the resident Pacific orcas and only slightly lower concentrations than the Pacific transients. The high concentrations of PCB in the adult females in the Atlantic is consistent with the reproductive failure seen in the Atlantic populations.

It is evident that the Atlantic females are either having trouble offloading PCBs to their calves during pregnancy or that they may be reaccumulating PCBs in their diets.

What now?

It is clearly evident that whilst the use of PCBs has been banned since the early 1980s, orcas are still continuing to being found heavily contaminated with this deadly toxin. Over the years the concentrations found in orca has decreased. Nevertheless this is a painstakingly slow process. The current levels of PCB in the Pacific orca has allowed them to be classified as among the most contaminated cetaceans in the world.

It is obvious that PCB levels represent an increasing toxicological risk to the Atlantic orcas. They are more heavily affected through the lack of reproduction which is having an increasingly dramatic effect on their population numbers and the future survival of these populations. It is nearing the point where if action is not taken to ascertain why PCB levels are not falling in the Atlantic Ocean that they will become under threat of extinction due to reproductive failure.

The levels of PCB in the Pacific has been declining over recent decades, however this trend has not been duplicated in the Atlantic, we must look into why this is or we may lose the Atlantic orca forever.