No . 32 2006 Report of the 2005 Workshop on Oceanic

• In situ indices of iron limitation in phytoplankton • Phytoplankton biomass and systematics with flowcytometry and microscopy North American scientists discussed the fundamental questions and observational details of proposed comparative studies of ecological processes in the upper waters of the oceanic subarctic Pacific. The physical setting of the subarctic Pacific was well described by Favorite et al. (1976). North of the latitude where the 33 pss salinity isocline turns vertically and surfaces, about 43°N, the water column is characterized by a 1 pss halocline at about 100 m depth, a density gradient which supports substantial internal waves. It is also a barrier to vertical mixing throughout the year that prevents (1) full replenishment of surface nutrients to deep concentrations and (2) complete removal of euphotic zone biota during winter mixing. From spring through autumn, there is also a seasonal thermocline, usually at about 35 m, which divides the euphotic zone into two distinct habitats. The region is a current gyre with slow, disperse flow along the southern side, slow flow east of the dateline, and stronger flow with rapid central cores (the Alaska 'stream') along the northern side. Flow is northward along the British Columbia–Alaska coast (the Alaska Current) and southward past Kamchatka, the Okhotsk Sea entrance and northern Japan (the Oyashio). There is also evidence, although not particularly clear evidence, that this gyre divides into two south of the central Aleutians, resulting in partially closed western and eastern subarctic gyres. Oceanic sectors of the seas are defined as being far from the influence of land. The cores of both western and eastern gyres (whether or not they are indeed separate) definitely qualify as oceanic. In the Gulf of Alaska, at sufficient distance from shore, the oceanic character includes HNLC conditions, that is, high nitrate (HN) and low chlorophyll (LC), throughout the year. Despite the presence of high concentrations of major nutrients (e.g., nitrate always greater than 6 μM), phytoplankton never bloom. The bulk of phytoplankton are always nanoplankton, with cells smaller than about 5 μm, and chlorophyll levels rarely exceeding 0.5 μg l –1. It has been established that the HNLC character of subarctic Pacific waters far from land is attributable to limited availability of iron in the euphotic zone (suggested by Martin and Fitzwater, (1988)). Several mesoscale iron-addition experiments, the Japanese SEEDS project (Tsuda et al., 2005b) and the Canadian–Japanese SERIES experiment (Boyd and Harrison, 2006), have …