The breathing sand

An Eddy Correlation Lander analyzes the strength of the oxygen fluxes at the bottom of the North Sea. -  Photo: ROV-Team, GEOMAR
An Eddy Correlation Lander analyzes the strength of the oxygen fluxes at the bottom of the North Sea. – Photo: ROV-Team, GEOMAR

A desert at the bottom of the sea? Although the waters of the North Sea exchange about every two to three years, there is evidence of decreasing oxygen content. If lower amounts of this gas are dissolved in seawater, organisms on and in the seabed produce less energy – with implications for larger creatures and the biogeochemical cycling in the marine ecosystem. Since nutrients, carbon and oxygen circulate very well and are processed quickly in the permeable, sandy sediments that make up two-thirds of the North Sea, measurements of metabolic rates are especially difficult here. Using the new Aquatic Eddy Correlation technique, scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel, Leibniz Institute of Freshwater Ecology and Inland Fisheries, the University of Southern Denmark, the University of Koblenz-Landau, the Scottish Marine Institute and Aarhus University were able to demonstrate how oxygen flows at the ground of the North Sea. Their methods and results are presented in the Journal of Geophysical Research: Oceans.

“The so-called ‘Eddy Correlation’ technique detects the flow of oxygen through these small turbulences over an area of several square meters. It considers both the mixing of sediments by organisms living in it and the hydrodynamics of the water above the rough sea floor”, Dr. Peter Linke, a marine biologist at GEOMAR, explains. “Previous methods overlooked only short periods or disregarded important parameters. Now we can create a more realistic picture.” The new method also takes into account the fact that even small objects such as shells or ripples shaped by wave action or currents are able to impact the oxygen exchange in permeable sediments.

On the expedition CE0913 with the Irish research vessel CELTIC EXPLORER, scientists used the underwater robot ROV KIEL 6000 to place three different instruments within the “Tommeliten” area belonging to Norway: Two “Eddy Correlation Landers” recorded the strength of oxygen fluxes over three tidal cycles. Information about the distribution of oxygen in the sediment was collected with a “Profiler Lander”, a seafloor observatory with oxygen sensors and flow meters. A “Benthic chamber” isolated 314 square centimetres of sediment and took samples from the overlying water over a period of 24 hours to determine the oxygen consumption of the sediment.

“The combination of traditional tools with the ‘Eddy Correlation’ technique has given us new insights into the dynamics of the exchange of substances between the sea water and the underlying sediment. A variety of factors determine the timing and amount of oxygen available. Currents that provide the sandy sediment with oxygen, but also the small-scale morphology of the seafloor, ensure that small benthic organisms are able to process carbon or other nutrients. The dependencies are so complex that they can be decrypted only by using special methods”, Dr. Linke summarizes. Therefore, detailed measurements in the water column and at the boundary to the seafloor as well as model calculations are absolutely necessary to understand basic functions and better estimate future changes in the cycle of materials. “With conventional methods, for example, we would never have been able to find that the loose sandy sediment stores oxygen brought in by the currents for periods of less water movement and less oxygen introduction.”

Original publication:
McGinnis, D. F., S. Sommer, A. Lorke, R. N. Glud, P. Linke (2014): Quantifying tidally driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study. Journal of Geophysical Research: Oceans, doi:10.1002/2014JC010303.

Links:

GEOMAR Helmholtz Centre for Ocean Research Kiel

Eddy correlation information page

Leibniz Institute of Freshwater Ecology and Inland Fisheries, IGB

University of Southern Denmark

University of Koblenz-Landau

Scottish Marine Institute

Aarhus University

Images:
High resolution images can be downloaded at http://www.geomar.de/n2110-e.

Video footage is available on request.

Contact:
Dr. Peter Linke (GEOMAR FB2-MG), Tel. 0431 600-2115, plinke@geomar.de

Maike Nicolai (GEOMAR, Kommunikation & Medien), Tel. 0431 600-2807, mnicolai@geomar.de

The causes and consequences of global climate warming that took place 56 million years ago studied

This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). -  UPV/EHU-University of the Basque Country
This image shows continental sediments in the Esplugafreda ravine, a small tributary of the Noguera Ribagorzana river, in the extreme west of the province of Lleida and close to the village of Aren (Huesca). – UPV/EHU-University of the Basque Country

The growing and justified concern about the current global warming process has kindled the interest of the scientific community in geological records as an archive of crucial information to understand the physical and ecological effects of ancient climate changes. A study by the UPV/EHU’s Palaeogene Study Group deals with the behaviour of the sea level during the Palaeocene-Eocene Thermal Maximum (PETM) 56 million years ago and has ruled out any connection. The study has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

“The fall in sea level did not unleash the emission of greenhouse gases during the Palaeocene-Eocene Thermal Maximum (PETM),” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher of the study.

The Palaeocene-Eocene Thermal Maximum (PETM) was a brief interval (in geological terms, it “only” lasted about 200,000 years) of extremely high temperatures that took place 56 million years ago as a result of a massive emission of greenhouse gases into the atmosphere. The global temperature increase is reckoned to have been between 5º C and 9º C. It was recorded in geological successions worldwide and was responsible for a great ecological impact: the most striking from an anthropological point of view was its impact on mammals, but it also affected other organisms, including foraminifera and nannofossils (marine microorganisms that are at the base of the trophic chain) and plants.

However, what actually caused this warming remains a controversial issue. The most widely accepted hypothesis suggests that it was due to the destabilising of methane hydrates that remained frozen on ocean floors. “Some authors, like Higgins and Schrag (2006), for example, proposed that a fall in sea level could have caused or co-contributed towards the unleashing of the emission of methane or CO2,” pointed out Victoriano Pujalte, lecturer in the UPV/EHU’s Department of Stratigraphy and Palaeontology, and lead researcher in the study. According to this hypothesis, “the marine sediments that were submerged in the sea were exposed when the sea level fell, and were responsible for the CO2 emissions,” he added. That is what, to a certain extent, prompted this study. Others not only reject that possibility but also the fall in sea level itself. “We set out to try and establish the behaviour of the sea level during that time interval, the PETM,” said Pujalte.

There is no cause-effect relationship

The studies were carried out mainly in the Pyrenees between Huesca and Lérida, specifically in the Tremp-Graus Basin, and also in Zumaia (Gipuzkoa, Basque Country). The Palaeocene-Eocene rocks have outcropped extensively in both areas, in other words, exposed on the surface, and they represent a whole range of ancient atmospheres, both continental and marine. “They provide a unique opportunity to explore the effects of changes in sea level and to analyse their effects,” added Pujalte.

The most useful indicators are the stable oxygen and carbon isotopes. The oxygen ones provide information on palaeotemperatures, but any sign of them can only be retrieved in deep-sea sample cores. The carbon isotopes provide data on variations in CO2 content in the atmosphere and in the oceans, and they can also be retrieved in ancient rocks that have outcropped in above-ground plots of land. In general, the variations of both isotopes run parallel, given that an increase in the proportion of CO2 is coupled with an increase in temperature.

The results obtained indicate that the PETM was in fact preceded by a fall in sea level, the size of which is estimated to have been about 20 metres and the maximum descent of which probably occurred about 75 million years before the start of the PETM. “However, it is doubtful that the descent was the cause of the PETM, although it could have contributed towards it,” pointed out Victoriano Pujalte. “They occurred at the same time, but there is no cause-effect relationship.”

Furthermore, the researchers observed that the rise in the sea level continued after the PETM, when the global temperature returned to normal levels. “Its origin was not only caused, therefore, by the thermal expansion of the oceans linked to the warming,” said Pujalte. “It is suggested that the most likely cause of it was the volcanic activity documented in the North Sea during the end of the Palaeocene and start of the Eocene; this activity was related to the expansion of the oceanic ridge in the North Atlantic,” he concluded.

3D model reveals new information about iconic volcano

The volcano on the Scottish peninsula Ardnamurchan is a popular place for the study of rocks and structures in the core of a volcano. Geology students read about it in text books and geologists have been certain that the Ardnamurchan volcano have three successive magma chambers. However, an international group of researchers, lead from Uppsala University, Sweden, has now showed that the volcano only has one single magma chamber.

The new study is published in Scientific Reports, the new open access journal of the Nature Publishing Group.

The 58 million year old Ardnamurchan volcano is an iconic site for the study of rocks and structures in the core of a volcano, which is why thousands of geology students from all over the world visit Ardnamurchan every year. Since the early days of modern geology the Ardnamurchan volcano is believed to have had three successive magma chambers (or centres) that fed hundreds of thin arcuate basalt intrusions, so-called cone sheets, that are exposed all over the peninsula.

The researchers from the universities of Uppsala (Sweden), Quebec (Canada), Durham and St. Andrews (UK), challenges the 3-centre concept using a 3D model of the subsurface beneath today’s land surface. According to this model, the Ardnamurchan volcano was underlain by a single but elongate magma chamber.

Studying extinct volcanoes is a way for geologists to understand the interior of volcanic edifices and to gain knowledge on the processes that occur within active volcanoes today. It is therefore that the volcanic centres of western Scotland and northeastern Ireland were intensely studied by British geologists in the late 19th and early 20th century. It was in these eroded volcanoes that the foundation for modern volcanology was laid. Ardnamurchan in particular has an iconic status among geologists everywhere in the world. Geology students read about it in text books and visit it during field excursions.

“It came as a bit of a surprise to us that there is still so much to learn from a place that has received so much attention by geologists, in particular since we used the original data collected in 1930 by Richey and Thomas.” said Dr Steffi Burchardt, senior lecturer at Uppsala University.

“Modern software allows visualizing field measurements in 3D and opens up a range of new perspectives. After projecting hundreds of cone sheets in the computer model, we were unable to identify three separate centres. The cone sheets instead appear to originate from a single, large, and elongate magma chamber about 1.5 km below today’s land surface.”

This magma chamber beneath Ardnamurchan was up to 6 km long and has the shape of an elongate saucer.

“These types of magma chambers are known to exist for example within volcanoes in Iceland have have been detected in the North Sea bedrock. Ardnamurchan’s new magma chamber is hence much more realistic considering everything we have learned about Ardnamurchan and other extinct and active volcanoes since the time of Richey and Thomas” said Prof. Valentin Troll, chair in petrology at Uppsala University.

Oil boom possible but time is running out

There is potential for CO2 transfer from the industrial centers on the UK's eastern seaboard to the oilfields and saline aquifers of the North Sea. -  Professor Jon Gluyas, Durham University
There is potential for CO2 transfer from the industrial centers on the UK’s eastern seaboard to the oilfields and saline aquifers of the North Sea. – Professor Jon Gluyas, Durham University

Oil recovery using carbon dioxide could lead to a North Sea oil bonanza worth £150 billion ($ 240 billion) – but only if the current infrastructure is enhanced now, according to a new study published today by a world-leading energy expert.

A new calculation by Durham University of the net worth of the UK oil field shows that using carbon dioxide (CO2) to enhance the recovery from our existing North Sea oil fields could yield an extra three billion barrels of oil over the next 20 years. Three billion barrels of oil could power, heat and transport the UK for two years with every other form of energy switched off.

Importantly, at a time of rising CO2 emissions, the enhanced oil recovery process is just about carbon neutral with as much carbon being put back in the ground as will be taken out.

The technique could yield an enormous amount of oil revenue at a time of public service cuts and developing the infrastructure would put the UK in the driving seat for developing enhanced recovery off-shore oil production around the world. It would also allow the UK to develop its carbon storage techniques in line with the UK government’s commitments on emissions reductions.

The study, funded by DONG Energy (UK) Ltd. and Ikon Science Ltd., will be presented today, October 14th 2010, at a conference on Carbon Capture and Storage (CCS), at the Institution of Mechanical Engineers, London. The new figures are conservative estimates and extend a previous calculation that predicted a 2.7 billion barrel yield from selected fields in the North Sea.

The UK Government’s Energy Statement, published in April 2010, outlines the continued role that fossil fuels will have to play in the UK energy mix. CO2 enhanced oil recovery in the UK would secure supplies for the next 20 years.

Jon Gluyas, a Professor in CCS & Geo-Energy, Department of Earth Sciences, Durham University, who has calculated the new figures, said: “Time is running out to make best use of our precious remaining oil reserves because we’re losing vital infrastructure as the oil fields decline and are abandoned. Once the infrastructure is removed, we will never go back and the opportunity will be wasted.

“We need to act now to develop the capture and transportation infrastructure to take the CO2 to where it is needed. This would be a world-leading industry using new technology to deliver carbon dioxide to the North Sea oil fields. We must begin to do this as soon as possible before it becomes too expensive to do so.

“My figures are at the low end of expectations but they show that developing this technology could lead to a huge rejuvenation of the North Sea. The industrial CO2 output from Aberdeen to Hull is all you need to deliver this enhanced oil recovery.”

Carbon dioxide is emitted into the atmosphere when fossil fuels are burnt and the UK Government plans to collect it from power stations in the UK. Capturing and storing carbon dioxide is seen as a way to prevent global warming and ocean acidification. Old oil and gas fields, such as those in the North Sea, are considered to be likely stores.

Enhanced oil recovery using carbon dioxide (CO2 EOR) adds further value to the potential merits of CCS.

Oil is usually recovered by flushing oil wells through with water at pressure. Since the 1970s oil fields in West Texas, USA, have been successfully exploited using carbon dioxide. CO2 is pumped as a fluid into oil fields at elevated pressure and helps sweep the oil to the production wells by contacting parts of the reservoirs not accessed by water injection; the result is much greater oil production.

Experience from the USA shows that an extra four to twelve per cent of the oil in place can be extracted using CO2-EOR. Professor Gluyas calculated the total oil in place in the UK fields and the potential UK gain in barrels and revenue from existing reserves using the American model.

David Hanstock, a founding director of Progressive Energy and director of COOTS Ltd, which is developing an offshore CO2 transport and storage infrastructure in the North Sea, said: “The UK has significant storage capacity potential for captured carbon dioxide in North sea oil and gas fields.

“There is a unique opportunity to develop a new offshore industry using our considerable experience in offshore engineering. This would give us a technical lead on injecting and monitoring CO2 that we could then export to the wider world to establish the UK as a world leader in carbon capture and storage technology.”

Professor Gluyas added: “Enhanced recovery of oil in the North Sea oil fields can secure our energy supplies for the next fifty years. The extra 3 billion barrels of oil that could be produced by enhanced CO2 recovery would make us self sufficient and would add around £60bn in revenue to the Treasury.

“Priming the system now would mean we have 10-15 years to develop CO2 recycling and sufficient time to help us bridge to a future serviced by renewable energy.”