ocean – Ukko Elhob's World

Spices, Power and Rock – The Pacific Ocean

23. Juli 201525. Juli 2015 Martin BohleHinterlasse einen Kommentar

Western Boundary Currents – what?

Western Boundary Currents are a common marine agent with manifold impacts on the global ocean circulation and climate. The warming of the western coast of all continents is the best-known feature that these currents trigger. However, there are many more features as the examples of Pacific Ocean show. Anyhow, how are these boundary currents set-up? That is the story to tell here, because the impacts of the western boundary currents on the global ocean circulation and climate variability are manifold.

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Dirty sea-bottom, litter everywhere

14. Juli 201529. Juli 2015 Martin BohleHinterlasse einen Kommentar

Summary of: Dirty sea-bottom, litter everywhere – and: bon appetit !

To recall, sea-birds confuse small bits of plastic with food. They swallow the bits of plastic and it kills them. To recall, abandoned fishing gear entangles fish, turtles and marine mammals, and its kills them. Floating plastic bags do the same. That is not the end of the story

Each year some 6.4 million tonnes of litter are entering the oceans, or about one kilogram for each human being. Most litter stems from cities. “The world’s cities currently generate around 1.3 billion tonnes of municipal solid waste a year, or 1.2 kilogram per city-dweller per day” (Economist 7th June 2012). The litter discharged into the sea corresponds to about 4-5% of the municipal solid waste produced in the cities of the world. In that sense its a small part of waste produced by the nine billion humans, but as any dumping it causes problems.

Persistent littering the sea likely has started with disposing “clinker” from steamships and currently has found its peak with “plastic”. Clinker, the residue of burnt coal, was commonly dumped from steamships well into the 20th century. Currently, the most abundant marine litter is plastic. Plastic accumulation on the seabed is more abundant than in the open sea. On the global scale, the ocean currents sweep the litter to the centre of the ocean-gyres where it accumulates, called the big garbage patch. On the local scale, litter is washed upon the beach. On the hidden scale, litters is channelled to the deep sea. Marine litters accumulates in particular high densities in submarine canyons. Submarine canyons act as passages for litter transport from continental shelves into deeper waters. A survey [1] of European seas published in April 2014, confirmed again that marine litter is found everywhere, from the beach down to the deep sea. Litter density in submarine canyons reached an average of 12.2 – 6,4 items per ten-thousand square meters, or the double of the litter density found elsewhere. A litter density of 12.2 – 6,4 items per ten-thousand square meters means to find about 10 items of litter on a surface wide as a football field!

Litter is a serious risk for the marine environment. The degradation of plastics generates micro-plastics that are ingested by organisms, leading to contaminants across trophic levels up to the fish [2] that we may eat. So plastic debris may return to their source, finally.

[1] Christopher K. Pham et. Al, 2014. Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins. PLOS ONE, 9(4), pp. 1-13.

[2] Chelsea M. Rochman et al. 2013, Ingested plastic transfers hazardous chemicals to fish and induces hepatic stress, Nature, doi:10.1038/srep03263;

A dramatic story of global change

12. Juli 201525. Juli 2015 Martin BohleHinterlasse einen Kommentar

Summary of : Marine Heavens on Snowball Earth ?

Time has passed, admittedly, since the Proterozoic eon – meaning the „eon of early life“ – had reached its last phase 635 Million years ago, the Neoproterozoic era. This „recent era of early life“ – was a dramatic time of global change. Twice Earth was ice-covered and was looking more like a ball of slush or snow. Twice Earth was sweating in run-away greenhouse. Life, only found in the sea went through big swings.

The kilometre-thick layer of ice of the Neoproterozoic ice-age made Earth looking like Jupiter’s icy moon Europa. „Snowball Earth“ looked far different from the blue ball that fascinated so much the first astronauts. However the global ocean kept active under the global ice cover. How would life survive when the entire planet, land and seas, are covered by ice?

The ocean of „Snowball Earth“ was not frozen to the bottom. Salinity of seawater, high pressure and geothermal heat-flux from the bottom prevented that. The ocean was covered by a thick ice cover that is a very good thermal isolator preventing heat loss from the ocean. Water flows were driven by heat-flux from the sea-bottom and freezing at the surface. Water warmed at the sea-bottom by geothermal heat and rose towards the surface. Salt leaked out of the freezing water at the bottom of the marine glaciers. Adding salt to the cooled water is making it heavier so that it sinks towards the bottom. In the Neoproterozoic ocean, close to the equator warmer and less-salty water rose to the surface, moved poleward and sunk down again.

Temperature, salinity and density of Neoproterozoic ocean was fairly uniform in the vertical direction but showed lateral differences. These lateral differences of density sustained, because of the rotation of earth, jet-currents along the Equator. These currents were unstable and were shedding off eddies. These eddies transported warm water away from the Equator to the ice-margin. There the water was melting ice, was cooled, partly frozen to the ice, partly enriched in salt so that it sunk downward. A compensating upward flow of warm water occurred at the Equator to close the circulation cell. Ridges at the sea-bottom or continental margins brought the source of heat closer to the surface and were interacting with the equatorial jet-currents. This interaction caused local jets, eddies, coastal up-welling and down-welling as well as convective mixing . The weak stratification of the Neoproterozoic ocean made up-welling and down-welling far easier to happen than today in our well stratified ocean. Thus „Snowball Earth“ ocean was not a stagnant pool of cold water, it was highly dynamic; at least to the eye of the oceanographer.

And marine life? It survived „Snowball Earth“. Both, the chemotrophic life that is using sulphur as source of energy and the phototrophic life that is using light as source of energy. Chemotrophic life would have survived in the depth of ocean under total ice-cover. Phototrophic life would have needed patches open surface water or thin ice; at least temporarily. The physics of ocean dynamics make it likely that these patches, „marine heavens“ existed regularly in the ice-covered Neoproterozoic equatorial seas close to ridges and continental margins.

The end of Snowball Earth likely was caused by volcanism blowing carbon-dioxide into the very dry and cold atmosphere of that time. Rain must have been seldom, and without rain little carbon-acid weathering of rocks occurs and no carbonates are flushed into the sea. Thus carbon-dioxide accumulates in the atmosphere building up a greenhouse effect that finally caused Earth to warm again.

Earth was saved from staying frozen in snowball stage by its active geophysical processes. To note the difference, Jupiter’s moon Europa is frozen in snowball stage; likely the moon is too small for having an active geophysical evolution as planet Earth. However, researchers are quite certain that under the icy surface of moon Europa an ocean is alive. If it bears life we don’t now. But if, then it will be of a chemotrophic form. Luckily survival of phototophic life on Earth in the global glaciations of the Neoproterozoic era has happened. The causes were: ocean dynamics on a geophysical active planet with continents moving, plate-tectonics and a robust geothermal heat-flux to create some „marine heavens“.