Michael Krom - Research Interests
Present and Past Oceanography of the Eastern Mediterranean: Importance of the P CycleThe Eastern Mediterranean is the largest body of water in the world which is unequivocally phosphorus limited. In 2002 I co-ordinated an international project (EU-CYCLOPS) in which we carried out the first Lagrangian nutrient addition experiment that did not involve iron. We showed that the Eastern Mediterranean is phosphorus starved, with no nutrient reservoir in DOM, POM, surface or deep water. In winter the system is P-limited in the conventional sense. By contrast in summer when the Lagrangian experiment was carried out, to our surprise, the chlorophyll content in the surface water decreased when phosphate fertilizer was added. We explained this observation by noting that surface water was P-limited for bacteria for the entire year, because they had access to the large DON reservoir, but N and P co-limited for phytoplankton in summer. After phosphate was added, both bacteria and phytoplankton were grazed. We showed that there was also a considerable excess of grazing potential that resulted in a new process called 'trophic tunnelling', which transferred primary productivity rapidly to zooplankton grazers. |
Satellite image of the Eastern Mediterranean showing the transition between winter ‘bloom’ conditions and summer nutrient starved conditions |
We have been able to explain why the basin is P limited. There is an excess of N over P in the nutrient supply, particularly the atmospheric supply. However, unlike other bodies of water where the N:P input is greater than 16:1, in the Eastern Mediterranean there is very limited denitrification and thus no biological process available to reduce the N:P ratio to Redfieldian numbers. The reason for low denitrification and the reason why excess anthropogenic nutrients seem not to accumulate in the system is the unusual anti-estuarine circulation. N fixation is unlikely to be an important process in this system.
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Paleoenvironmental StudiesWe have carried out studies to look at rapid global climate change in Africa using 87Sr/86Sr to examine the paleoclimate record of the Nile flood over the past 7000years. We found that between 7ka BP and 4.2ka BP, there was a systematic decrease in Nile water flow at the same time as a systematic increase in Blue Nile sediment. This process, which is known as the drying of the Sahel, reached its climax with a long period of drought that caused the end of the Old Kingdom in Egypt. We are planning to examine cores in detail to determine if we have evidence of the specific horizon that represents the complete drying of the delta. |
Sr isotopic ratios in sediment provide evidence for reduction of rainfall in the Nile catchment compatible with the theory that a prolonged drought caused the collapse of the Old Kingdom in Egypt |
Loch Duich has been used as the field site to study anoxic nitrification and other sedimentary geochemical processes |
Sedimentary GeochemistryThe research group has a major interest in understanding natural processes in recent sediments and in using sediments as a historical record of past environmental change. We have developed a gel probe to sample sediment pore waters at high resolution. This technology has been used to study biogeochemical processes in a variety of different environments, including determining the present active front in Mediterranean sapropels, nutrient recycling in estuarine sediments in the Humber estuary and Loch Duich, Scotland, in peat bogs and in wetlands. We have also used the gel probes to quantify the rate of groundwater seepage into Lake Kinneret (Sea of Galilee), Israel. |
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Water Quality Processes in MaricultureMariculture is the last untapped food resource on earth. We are involved in developing intensive mariculture systems that are both commercially viable and environmentally friendly. Recently a fishpond-seaweed-abalone system developed from our work has been put into commercial operation in Israel.A new system that works entirely on bacterial biofilters has been developed. Fish excrete ammonia which is toxic to the fish. The ammonia is oxidized to nitrate in an oxidizing nitrification filter and then converted to nitrogen gas in an anaerobic denitrifying filter. This system, which has operated successfully for more than three years, runs without any exchange of water, enabling mariculture to be carried far from the sea if necessary. |
Research Interests
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