The Ecology of a Subarctic Intertidal Fiat Pangnirtung Fiord, Baffin Island, N.W.T. and the Paleoecology of Quaternary Molluscan Assemblages

Abstract

<p>Marine terraces and intertidal flats in Pangnirtung Fiord have developed in response to fluctuating Holocene sea level. The presence of subarctic molluscs in the macrofauna of Holocene marine terraces record an amelioration of marine climate associated with the incursion of subarctic waters into Cumberland Sound about 8700 a BP. The present intertidal biota of Pangnirtung Fiord is composed of a distinctly subarctic biota consisting of a bivalve, Macoma balthica, a polychaete, Arenicola marina, a gastropod, Littorina, saxatilis, a barnacle, Balanus balanoides and algae of the genus Fucus that cohabit with panarctic shallow water species such as Mya truncata and Hiatella arctica.</p> <p>A distinct morphological and faunal zonation occurs on Pangnirtung Fiord intertidal flats. Six sedimentary environments are defined on the basis of sediment texture, primary sedimentary structures and their associated macrofaunas and ichnofaunas: proceeding seaward, beaches, sand bars, mixed flats, Macoma sand-flats, Arenicola sandflats and boulder barricades.</p> <p>Bioturbation by deposit-feeding macrofauna, in combination with ice turbation, actively modify intertidal sediments. Field experiments have demonstrated that Macoma balthica and Arenicola marina are capable of reworking large volumes of sediment in a short period of time. Sea ice actively erodes and redistributes sediments and their associated biota within and beyond the intertidal zone. Observations at Pangnirtung suggest that bioturbation and ice turbation contribute to the destruction of physical sedimentary structures in intertidal deposits. The low preservation potential of physical sedimentary structures enhances the value of biogenic structures in environmental interpretation of Arctic marginal marine sediments.</p> <p>Sea ice-related processes influence the population dynamics of the intertidal biota. Intertidal populations of Macoma balthica and Mya truncata from southeastern Baffin Island exhibit low annual growth rates and great longevity. At Pangnirtung, Macoma may live more than 13 years and Mya may attain ages of 15 to 20 years. The short growth season for these bivalves contributes to the slow rate of growth at Pangnirtung.</p>