High-resolution hydrographic and biological observations in the Arctic frontal regime were made in February 1989 along 74¿45'N. The frontal zone was found to contain four individual frontal interfaces. These fronts were a result of the large-scale convergence of the currents around the Greenland Sea gyre, bringing together Arctic and Polar surface waters and two modes of Atlantic Surface Water. The distribution of Arctic and Atlantic copepod species as well as the composition of their developmental stages showed a strong correlation with the distribution of water masses whereby the frontal interfaces acted as biogeographic boundaries. Whereas the fronts bounding the Polar Water reached only to a depth of about 100 m, the fronts bordering the Atlantic water masses could be observed to depths of 600 m. At subsurface levels a core of Atlantic Intermediate Water from the Jan Mayen Current was observed. The properties of this water type can be explained quantitatively from double-diffusive exchange with the overlying water. The mixing across the fronts was found to be dominated by fluxes of heat, salt, and copepods toward the central Greenland Sea gyre. ¿1991 American Geophysical Union