Johann R.E. Lutjeharms

The 2006 Fridtjof Nansen Medal is awarded to Johann R.E. Lutjeharms for his imaginative descriptions and analyses of the Greater Algulhas System.

Over the past decades Johann R.E. Lutjeharms has been the spider in the web the scientific description of the oceans around South Africa, coined by himself the ‘Greater Agulhas system’. His many contributions include the description of the regional oceanography of the Agulhas Current system, the southwest Indian Ocean gyre and its recirculation subgyre, the Agulhas Current Retroflection system and the shedding of rings from that retroflection. The Agulhas retroflection is a ‘choke point’ in the global ocean thermohaline (‘conveyor-belt’) circulation, connecting the warm and salty Indian Ocean with the southeast Atlantic. Johann was one of the first to investigate this system in a systematic and comprehensive way, using all the techniques available to characterise the mean and highly variable state of the retroflection system. He was one of the pioneers to use satellite remote sensing techniques in combination with in situ observations to describe such a complicated and variable western boundary current system.

Johann studied both the fate and impact of the Agulhas rings in the southeast Atlantic, the ‘Cape Couldron’, the upstream sources of the Agulhas and the controls on the retroflection and ring shedding. He pointed at the possible impact on the ring shedding frequency of variability originating in the Natal Bight and the varying inputs from the Mozambique Channel and East Madagascar Current. Here, again, analysis of satellite images was one of the ways of studying the variability of those upstream sources.

Being a descriptive physical oceanographer himself, Johann has inspired (and still does) quite a few theoreticians and modellers with his analyses and hypotheses. He collaborates in a very active and productive way with them, both in quantitative and qualitative studies. Collaboration is a key word in Johanns vocabulary. In spite of his small local group and limited resources he has been admirably successful in joining forces with observational groups from all over the world to establish relatively large programmes in his Agulhas ‘backyard’. Examples are the ARC-cruises in the 80’s, the Kapex experiment in the 90’s and the MARE and ACSEX experiments in the past years.

Johann’s investigations are not limited to the oceans. Together with his co-workers, he has contributed a series of studies on the air-sea interaction in the Agulhas region and its frontal systems, and over Agulhas rings. Large ocean to atmosphere fluxes were shown to result from the interaction of the warm Agulhas waters with the overlying cool atmosphere. He studied effects on regional climate variability and pointed at possible impacts on global climate.

Finally, he has also teamed up extensively with biologists to study the specific consequences of the unique Agulhas physics for the ecology of this part of the World Ocean.

In conclusion: Johann R.E. Lutjeharms is a very productive and original scientist, known and much cited for his seminal descriptions and analyses of the greater Agulhas System, inspiring many other ocean- and climate scientists, and collaborating with many of them.