The 2022 Fridtjof Nansen Medal is awarded to Monika Rhein for pioneering measurements and analysis of physical and chemical tracers furthering the understanding of ventilation and circulation in the Atlantic subpolar gyre and Deep Western Boundary Current.
Monika Rhein’s oceanographic research manifests the power of a wide-horizon vision coupled with leadership and expertise in driving forward with the collection and analysis of key measurements, thus leading to the unraveling of mysteries of ocean circulation and its longer term variability. Her observational toolkit and deep experience combines both physical and chemical tracer measurements in a way that remains powerful and rare, thus exemplifying the best of integrative oceanography.
Rhein was an early pioneer in the use of chemical tracers for inferring water mass ventilation and spreading. This innovative work greatly enhanced fundamental understanding of circulation and dynamics of the North Atlantic subpolar gyre, including Labrador Sea Water formation and its spread. The subpolar gyre plays a key role in the Atlantic Meridional Overturning Circulation (AMOC), which is one of the most important and complex components of the ocean’s role in climate. Rhein and the group she leads employed a diverse and state-of-the-science suite of observational measurements, including hydrography, Argo floats, physical and chemical tracers, and direct current measurements, all involving extensive seagoing and laboratory work. In analyzing these measurements, Rhein constructed extensive regional full-depth inventories of anthropogenic chemicals such as CFCs and in turn, used these inventories to help reveal the net effect of deep convection on ventilation of Atlantic intermediate and deep waters. This research also led Rhein and her group to identify a significant positive correlation between Labrador Sea Water formation variability and the uptake of anthropogenic carbon in the Atlantic.
Rhein’s longstanding authoritative observational toolkit has garnered major insights into the North Atlantic circulation and variability from time-series of tracer inventories and circulation measures along a repeat section at 47N. These measurements, now extending over 25 years, have shown a significant decline in equatorward transport at 47N, which their analysis finds is likely due to climate warming. Furthermore, Rhein’s group firmly established the role of the Deep Western Boundary Current as the major export pathway from the Atlantic subpolar gyre to the rest of the World Ocean, with this work resolving a longstanding scientific controversy.
Rhein’s tireless leading-edge research and generous mentoring of future generations of scientists have established her as a trusted leader in the field of integrative observational oceanography. Indeed, her influence has been instrumental in shaping 21st century physical and chemical oceanography. In addition, Rhein has provided visionary leadership across the international community by serving as president of the EGU Ocean Sciences division, as well as with heroic contributions to the IPCC as coordinating lead author for the AR5 ocean observations chapter (2013), and as review editor for the special report on the ocean and cryosphere in a changing climate (2019).