The 2011 Fridtjof Nansen Medal is awarded to Bert Rudels for his leadership in developing ocean observing systems for climate research and forecasting and for fundamental contributions to our understanding of the ocean’s role in climate.
The ice-covered Arctic Ocean is one of the least systematically investigated oceans to date. By a combination of dedicated field work, thorough analysis of observations and using these as inspiration for the development of theoretical concepts, Bert Rudels formulated many of the basic mechanisms that shape our modern picture of the Arctic Ocean. His preferred method has been the use of conventional temperature and salinity observations and their use for the critical development of conceptual models of the Arctic Ocean’s role in climate system. Examples of the features and processes where he brought first or new insight are (1) the basic circulation scheme of Atlantic water in the Arctic Ocean as a series of cyclonic boundary current loops in all basins. The related papers include description and basic quantification of the eminent role of the Barents Sea branch which had been ignored more or less completely in the literature to that date. (2) The role and strength of entrainment of Atlantic water to shelf water plumes in shaping the Arctic Intermediate and Deep Water properties. These waters form the Arctic contribution to the thermohaline circulation. (3) A concept for the formation of the cold halocline water in the Atlantic Water boundary current which is alternative to previous assumptions that the halocline is exclusively formed in the shelf seas. (4) The constraints of ocean heat loss below sea ice. (5) The prominent role of double diffusion and its quantification as the mixing agent in the Arctic Ocean interior where the turbulence level is low. (6) The role of external forcing (such as increasing Greenland melt or warmer Atlantic inflow) vs the internal Arctic Ocean dynamics of a double estuary in setting the exchange between Arctic and subarctic oceans. Rudels’ aim was never conducting academic exercises but to focus on explaining essential and basic mechanisms and to develop models as simple as possible to quantify the major processes and thereby to explain observed structures. He instructed and inspired many students and colleagues in physical oceanography as well as in other disciplines with his findings through an abundance of lectures, classes and field courses. Through his outstanding achievements in the development and distribution of knowledge Bert Rudels serves as example that quiet but thorough thinking remains one of the basic ways to decipher the puzzles of the Earth system.