The natural history of the Hardangerfjord

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Abstract
Transport of phytoplankton from the outer coastal waters into the more than 100 km long Hardangerfjord is considered with the use of records published by Braarud, Föyn Hofsvang, Hjelmfoss & Överland (1974). A major water exchange in August/September affected hydrography, phytoplankton composition and distribution, and phosphate distribution. Spectacular changes in coccolithophorids involved an increase of the populations and an inconsistent vertical and horizontal distribution of the various species. The phosphate content of the layers immediately underlying the euphotic zone became strongly reduced during the exchange. It was restored during the following months until in late summer a similar exchange brought about a new reduction. Vertical and possibly advective admixture of water with higher salinity and presumably higher phosphate content was active in the restoration. In the course of June, an influx to the inner fjord carried inwards remains of a rich diatom society recorded offshore at the 20 m level in early June. Transport within the fjord proper is also considered. Transport processes of the kind described may be of significance in studies of pollution in fjords.