Transport, preservation and accumulation of organic carbon in the North Sea

Abstract

This thesis contains the results of the research on the burial of organic carbon in the North Sea as it was carried out at the Netherlands Institute for Sea Research in the period 1993-1997. Carbon in the form of carbon dioxide (C02 ) is one of the major contributors to the natural greenhouse effect. As a result of the increase in the combustion of fossil fuels by man, the amount of CO2 in the atmosphere and therefore the greenhouse effect increases. In order to be able to forecast a reliable scenario of the possible future consequences of an increased greenhouse effect (climate change, melting ice caps, rising sea level, etc.) it is essential to understand the natural cycle of carbon in the geosphere and biosphere. In the marine environment CO2 is incorporated into organic matter by algae during photosynthesis. Organic matter containing organic carbon (Corg) is largely mineralized in the water column and at the sea floor, during this process CO2 is produced. A small part however is buried in marine deposits, attached to fine grained sediments. In this manner a part of the carbon is withdrawn from the carbon cycle for a long period of time. Although shelf seas, like the North Sea, occupy only 8% of the total seas and oceans surface area they acount for about one third to one fifth of the primary production, this makes them important possible sinks for Corg. In literature their is a strong disagreement on the importance of shelf seas as Corg sinks. Some researchers state that 90% of the Corg that is stored in marine deposits, is buried on the shelves. Others say that the largest amount of the organic matter is transported over the shelf edge and stored in the continental slope and abyssal plain sediments. The goal of the research described in this thesis is to investigate the role of the North Sea as a storage for organic matter, possible variations in storage in time, and the causes of these possible variations.