HSB Workshop Oceanography
Estimates of global sea level rising during the 21st century vary from 9 to 88 cm, with latest results in fact pointing to the lower values (Intergovernmental Panel on Climate Change, IPCC 2005). In the opening lecture of the September HSB workshop on Oceanography, Gerrit Burgers from the Royal Dutch Meteorological Institute (KNMI) discussed influences of deep ocean processes on the Benelux area. Although scientists remain opposed with regard to the human influence on increased carbon dioxide, observations lead to the above prediction. The largest proportion of sea level changes (75%) is undoub-tedly caused by temperature variations leading to compression or expansion of the water volume. In addition to the thermohaline circulation – the ocean conveyor belt – as a main mechanism to distribute heat across the Earth’s surface, the mixing of water masses is also considered critical. Recent results show that the level of mixing varies with ocean floor topography. The effect of mixing on the main circulation is considered significant.
The workshop addressed three main aspects of oceanography: modelling, satellite observation and local (in situ) measurement. As in any science, oceanographic modelling efforts can only be validated by measurements. Han Wensink is director of ARGOSS, who provide operational guidance for offshore operations using satellite observations and models. Satellites are most effective when looking at surface conditions. Environmental parameters such as wind, waves, current and sea level need to be accurately known to support design, planning and operations at sea to reduce risk. Optimal data (clean, complete, unambiguous and accurate) are used for statistics, hindcasting and forecasting. In addition to making these data available to the industry, the large database with satellite observations provides crucial material to validate models in oceanography, climatology and meteorology.
In situ data collection was the main focus of the remaining two lectures. Frans van
Dongen of the Oceanographic Company of the Netherlands showed a number of in situ monitoring systems. International co-operation is required to obtain and manage in situ data systematically. Oceanographic monitoring and information systems contribute to the Global Ocean Observing System (GOOS). The objective of the complex organisation of GOOS is to apply the scientific approach mentioned above to sustainable development. With regard to in situ measurements of mooring systems, an important financial aspect is to reduce the number of times a system is serviced. If this number is halved, costs may be reduced by 25%. Prevention of biofouling of oceanographic instruments is an important issue.
In the final lecture, Herman Ridderinkhof of the Netherlands Institute for Sea Research (NIOZ) showed a number of examples of long observation series. If one regards in situ measurements with vertical sensor strings as the starting point for obtaining accurate oceanographic data, these data need to be expanded in time and space to improve their value in validating models. Satellites provide spatial expansion. However, to assess variability in time there is no alternative to long measurement series. Especially for models such as the ocean conveyor belt, it is essential to have such extended data series. NIOZ contributes to global change research by monitoring the main conveyor belt at three locations: Indonesian through-flow, inter-ocean exchange near Madagascar and the heat losses in the North Atlantic. Every 2 years, NIOZ’s research vessel Pelagia conducts oceanographic measurements at some 40 locations between Ireland and Greenland. The CP is a very valuable tool for these long-term sessions, both for oceanic and near-shore campaigns. Not only the two-way travel time, but also the intensity of the back-scattering content is used.
Another fine CP application is an accumulation of 5-year data across the Marsdiep with the instrument deployed from the Texel ferry. This data set provided much improved knowledge about the flow of water and sediment to and from the sensitive Waddenzee.
Oceanography and hydrography are closely related in many ways. This was clearly shown by the inspired presentations. Although the number of members attending was slightly less than average during workshops, the afternoon – as witnessed by involved discussion – was satisfying to those who were there.
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