Temporal and spatial patterns of sedimentation in the subarctic fjord malangen, Northern Norway

Abstract

Abstract Sedimentation processes in Malangen, a relatively wide and deep North-Norwegian fjord, are dependent on seasonal patterns in the biological production of auto- and heterotrophic plankton, different modes of advective transport and erosion of particulate materials, and freshwater discharge due to precipitation and snow-melting. Sedimentation rates of total particulates (TPM), chlorophyll a (Chl a), phaeopigments and particulate organic carbon (POC) and nitrogen were measured from March to October 1991 at five moored arrays covering the entire fjord area. On an average during the period studied, sedimentation pulses of TPM from the euphotic zone were in the range 2-7 g m·2 day-1. Secondary sedimentation due to resuspension and advection of bottom sediments was considerable at all trap moorings. Maximum contributions of inorganic matter were obtained at a mooring in the Miilselv Estuary, especially during the spring freshet peak in the second half of June. The highest pulses in Chl ·a sedimentation occurred in the first half of April (maximum values), the end of May and the beginning of July at all moorings, ranging between 0.2 and 1.4 mg m·2 day-1 at 30 m depth. A similar pattern is true for the settling of POC, however, high contributions of detrital carbon not coinciding with Chl · fluxes complicate the picture. Seasonal POC sedimentation ranged between 60 and 770 mg ·2 day-1 throughout the period studied, apart from two massive sedimentation pulses where resuspension caused exceptional rates of 1.3 and 1.8 g m·2 day-1, respectively, at the two outermost locations.