Patterns of carbon supply and distribution and oxygen renewal in two Alaskan fjords

Abstract

The deep basin water of Resurrection Bay (a single-silled fjord at 60°N on the south-central Alaskan coast) is renewed each summer with water having a dissolved oxygen concentration > 4 ml l −1. Prior to 1976 > 90% of the allochthonous organic carbon supply to the basin was from fish-processing waste. Oxygen concentrations at the bottom were reduced to around 1 ml l 1 during the winter, and Heggie and Burrell (1981) have computed that a quantity of carbon > 50% of the annual phytoplankton production (19 moles C m −2 yr −1) was oxidized within the basin and near-surface sediments. Very little carbon (0.6 moles m −2 yr −1) is removed via sediment burial in this estuary. Boca de Quadra Fjord is located at approximately 55°N adjacent to the Alaska—British Columbia border. The annual summer flushing sequence of the deep (365 m) central basin is basically the same as in Resurrection Bay. Estimated benthic respiration (around 8 moles C m −2 yr −1) may be supported by the in-fjord annual primary production (> 12 moles C m −2 in 1980). The mean annual input of terrigenous particulate carbon is estimated to be of the same order of magnitude as the loss rate within the basin by sediment burial (9.0 moles C m −2 yr −1). The relatively high flux of allochthonous carbon into Boca de Quadra thus appears to consist predominantly of refractory material which does not create a significant oxygen demand within the basin.