Travel, Science, Mountains and Oceans

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Oceans in a changing world

The Earth is a dynamic planet and the relationships between its oceans, atmosphere and land masses are incredibly complex. Disentangling them is not just interesting science; it might well be crucial to our future survival.

The oceans, which cover 70% of the Earth's surface, are a central component of the environment. Water circulation patterns in and between the different oceans strongly influence the climate of many parts of the world. Northern Europe for example, is at the same latitude as Alaska, but it has a much milder climate because of the Gulf Streamthat brings warm tropical water from the Gulf of Mexico

All the oceans of the world are linked and events in one ocean can have widespread effects in other oceans, on the land and in the atmosphere. Today, we know that some water circulation patterns are changing, but we have two problems. Not only is it virtually impossible to separate the changes due to natural phenomena from changes caused by human activities, it is also difficult to say what the eventual consequences might be.

Models that predict how the global environment might change in the future do give a lot of good information - many are now incredibly sophisticated. However, any model is only ever as good as the data fed into it. European researchers recognise that to improve our models, we need to learn a lot more about how water moves in the oceans.

In deep water

Deep water circulation patterns form the very deep, cold water in the vreenland Sea, deep water formation in this area is important for the climate of Europebecause it encourages the northward flow of the Gulf Stream Drift. The process of deep water formation in the Greenland Sea is also relevant to the global environment since it takes carbon from the atmosphere into the deep ocean, preventing it from contributing to the greenhouse effect.

Despite its importance, the physical processes involved in deep water formation are not well understood.

Investigators were surprised to find that strong currents rapidly transported the tracer-labelled water from the 300 m level down to a depth of more than 3 km, causing storms on the seabed. In addition to this large-scale movement of water, the team also discovered a localised chimney effect - thin currents, which take water from the surface straight down to the bottom. One chimney, detected in May 1997, takes surface water down to a depth of 2 km.

Lessons from the past

Studying the past is also important for predicting the future. Measurements over the last 100 years tell us that the global environment is changing: we have released large amounts of carbon dioxide and other gases into the atmosphere and these seem to be causing a slight global warming. However, although average temperatures might rise, some parts of the world could become very much hotter whilst others could actually cool.

To predict the future, we need to know the past. Researchers are studying ice and sediment cores to chart previous climate changes and gain important information to understand the global environmental variations that we are seeing today.

Events that took place more than a hundred thousand years ago. During the warm period just before the last ice age, some of the ice sheets in the Atlantic broke up and formed icebergs that floated south and melted when they met warm water. The large amounts of freshwater released into the ocean blocked the normal water circulation patterns and stopped currents like the Gulf Stream bringing warm water northwards. This led to a strong cooling effect over Northern Europe which lasted for 1-2 thousand years and which was then followed by a rapid warming.

This warming, however, was only temporary and within a few hundred years there was another period of cooling, although not large enough to cause a real ice age. This time the change to a colder climate cannot be explained by melting icebergs. What seems to have been more important is that, at the time (115-127 thousand years ago), the North Pole was tilted further away from the Sun than it is today and so less heat was able to enter the top of the atmosphere in the Northern Hemisphere. This resulted in less heat at the higher latitudes and cooler, less salty water in the North Atlantic, which again prevented the Gulf Stream reaching Northern Europe.

The oceans and the atmosphere

                 The oceans play an important role in the cycling of carbon between the atmosphere, the physical environment and living organisms. Carbon dioxide from the atmosphere dissolves in water and is transported around the globe by currents in the deep oceans. Plankton which can photosynthesise (make organic matter by combining carbon dioxide and water and using energy from sunlight) use some of this carbon. If they are plentiful, the ocean becomes a net sink for carbon, taking it out of the atmosphere and locking it up in organic debris that eventually become trapped in sediments on the seabed.

If the CO2 in the atmosphere goes up, as it has during the last 200 years, it pushes more CO2 into the oceans. Unfortunately, this increase does not mean more growth of living organisms because the carbon they need is already present in great excess. So more carbon in the atmosphere generally means more carbon in the sea.

The oceans play an important role in the cycling of carbon between the atmosphere, the physical environment and living organisms. Three large European projects - ESCOBA, CARUSO and ASGAMAGE - are investigating these complex processes using experimental techniques and specially developed computer models.
Carbon dioxide from the atmosphere dissolves in water and is transported around the globe by currents in the deep oceans. Plankton which can photosynthesise (make organic matter by combining carbon dioxide and water and using energy from sunlight) use some of this carbon. If they are plentiful, the ocean becomes a net sink for carbon, taking it out of the atmosphere and locking it up in organic debris that eventually become trapped in sediments on the seabed.

If the CO2 in the atmosphere goes up, as it has during the last 200 years, it pushes more CO2 into the oceans. Unfortunately, this increase does not mean more growth of living organisms because the carbon they need is already present in great excess. So more carbon in the atmosphere generally means more carbon in the sea. At present, we do not know in detail how this is linked to ocean circulation patterns but ESCOBA has already developed several new computer models that should help us to do this in the future.

One of the biggest deficiencies in our knowledge of the ocean's role in the carbon cycle is our inability to accurately calculate the rate at which CO2 is exchanged between the air and the sea. This means that we cannot tell how much of the carbon dioxide produced by human activity goes into the ocean or if there is any chance that the oceans might save us from global warming by soaking up excess CO2.

A better sink in the South

The Southern Ocean is a larger carbon sink than the Northern Ocean. This is actually unexpected for two reasons. Firstly, the Antarctic has a very long winter with long nights and it also suffers very rough seas. Not only is light generally limited, plankton that can make use of it when they are floating on the surface are intermittently plunged to the depths where they get no light at all. Secondly, very cold and deep water tends to well up to the surface, releasing dissolved carbon dioxide into the atmosphere as it warms up.

The key seems to be that the water coming up from the deep Southern Ocean is not only high in carbon but also in major mineral nutrients such as nitrogen, phosphorus and silicon.

to show that horizontal currents coming from nearby continental margins enrich the surface water with iron: "Apart from light, iron could be the major limiting factor for photosynthesis. Its role is vital because one iron atom is at the heart of every single molecule of chlorophyll, the green pigment which enables the plankton to photosynthesise."

The fact that iron levels, not light, limit photosynthesis in the Southern Ocean in the summer months has led to the suggestion that adding more iron might enable larger plankton blooms to take more carbon out of the atmosphere. Some attempts at iron fertilisation have been made in various parts of the Pacific near to the Equator, with mixed results. In one experiment, a brief plankton bloom occurred but then the iron quickly disappeared. Hein de Baar and the rest of the CARUSO team are nevertheless considering some further iron-enrichment experiments. "Chemically-labelled iron will be added to the sea so that we can trace exactly where it goes."

At the edge of the ocean

Our interaction with the oceans is at its greatest along the world's 595 814 km of coastline: more than half the world's population - over 2.7 billion people - live within 100 km of the coast. The coastal zones are dynamic areas and most are of great economic and environmental importance. We use them for fishing, aquaculture, mineral extraction, industrial development, energy generation, tourism and recreation and for waste disposal.
It should come as no surprise that managing coastlines is very difficult.

At the moment we do not fully understand the natural physical, chemical, geological and biological processes that combine to form the many varied coastal environments. Particularly difficult is linking disturbances in coastal systems to their causes since events in the open sea and activities on the land all affect the coastal environment.

The 'Learning from the past' approach - tracing the development of tidal flats and salt marshes in different parts of Europe using sediment cores. As sedimentation is a slow process in such areas, the cores reveal changes that have occurred over short-term time scales (between one and 100 years) as well as over long-term time scales (centuries to millennia).

The natural patterns of flooding and storms that have been detected by analysing the cores provide important information for coastal management, especially in areas which are threatened by erosion. And, as Thomas de Groot, the project co-ordinator reports, one discovery was rather unexpected: "There are clear indications that human activities have been damaging the natural environment since long before the industrial revolution. Human use of land since Roman times and especially since the Middle Ages has influenced local erosion of the natural environment, particularly in coastal dune areas. We need to take this into account in our studies because local impacts, whether natural or human, overprint the signs of most large-scale climate changes in sediment cores.  

The balance of living organisms

Marine ecosystems in coastal areas can be strongly disturbed by human activity. One of the most serious problems is coastal eutrophication, an excess of nutrients in the water that can provoke uncontrolled growth of micro-organisms.
Regular blooms of a small organism called Phaeocystis plague a long stretch of European coast along the North Sea. Normally, this is a fairly harmless single-celled plankton, present in relatively small numbers. However, when it has an excess of nutrients Phaeocystis runs out of control, forming blooms which dominate the balance of organisms in the entire coastal ecosystem. And, when the bloom reaches a critical size, single cells clump together to form large gelatinous blobs that float on the surface of the water, releasing large amounts of protein as they die during the late spring.

The turbulence of the waves whips up the protein producing an effect similar to beating great volumes of egg white: lots of meringue. Although the froth is not toxic, it completely ruins the beach and areas badly affected by Phaeocystis blooms have experienced a large decrease in revenue from tourism.

on a global scale Phaeocystis-dominated phytoplankton blooms also have a serious impact on the environment since they are major sources of the volatile organic sulphur compound dimethylsulphide (DMS). DMS is the main natural sulphur gas emitted to the atmosphere and is thought to play a significant role in acid rain formation and in climate change. Clearly, something should be done to prevent Phaeocystis blooms and research is continuing to try and work out a cost-effective strategy.