Physical and ecological processes in the marginal ice zone of the northernBarents Sea during the summer melt period

The main physical and ecological processes associated with the summer melt period in the marginal ice zone (MIZ) were investigated in a multidisciplin ary research programme (ICE-BAR), which was carried out in the northern Bar ents Sea during June-August 1995-1996. This study provided simultaneous obs ervations of a wide range of physical and chemical factors of importance fo r the melting processes of sea ice, from its southernmost margins at about 77.5 degreesN to the consolidated Arctic pack ice at 81.5 degreesN. This pa per includes a description of the oceanographic processes, ice-density pack ing and structures in cores, optical properties of water masses and the ice , characteristics of the incident spectral radiation and chlorophyll - lead ing to primary production. Large seasonal and inter-annual variations in ice cover in the MIZ were evi dent from satellite images as well as ship observations. Even if the annual variation in ice extent may be large, the inter-annual variations may be e ven larger. The minimum observed ice extent in March, for example, can be s maller than the maximum observed ice extent in September. Oceanographic phe nomena such as the semi-permanent lee polynyas found west and south-west of Kvitoya and Franz Josef Land and the bay of open water, the "Whalers Bay", north of the Spitsbergen are structures which can change with time interva ls of hours to decades. For example, the polynya south of Franz Josef Land was clearly evident in 1995 but was only seen for a short period in 1996. The observed variability in physical conditions directly affects the primar y production in the MIZ. From early spring, solar radiation penetrates both leads and the ice itself, initiating algal production under the ice. Light measurements showed that the melt ponds act as windows, permitting the tra nsmission of incoming solar radiation through to the underlying sea ice, th us, accelerating the melting process and enhancing the under-ice primary pr oduction. In June 1995, the N-S transect went through a pre-bloom area well inside the ice-covered part of the Barents Sea to a post-bloom phase in th e open waters south of the ice edge. The biological conditions in the later season (August) of 1996 were considerably more variable. The longer N-S tr ansect in August 1996 passed through areas with variable ice and oceanograp hic conditions, and different developmental stages of phytoplankton blooms were encountered. The previously adapted picture of a plankton bloom follow ing the retreating ice edge northwards was not seen. (C) 2000 Elsevier Scie nce B.V. All rights reserved.