Using the delta O-18 composition in landfast ice as a record of arctic estuarine processes

Estuaries that produce substantial amounts of ice differ from those that do not. First, ice formation and melting make important contributions to salt and freshwater budgets and thereby influence water circulation. Second, ic e cover provides a physical barrier which severely restricts the air-sea ex change of properties and energy. Unfortunately, the logistical problems of oceanographic sampling in the Arctic during winter have resulted in sparse data sets. Here, we show how the oxygen isotope composition (delta(18)O) in landfast ice at the end of winter provides a record of surface water prope rties throughout winter. Two arctic estuaries are contrasted: the Mackenzie estuary which faces directly onto a broad, open shelf and the Husky Lakes estuary which comprises a series of basins that exchange with one another a nd the shelf through narrow channels. The method of converting records of d elta(18)O in ice cores to surface water salinity as a function of time thro ughout winter is outlined. The Mackenzie estuary has a large winter inflow which spreads beneath the ice as a plume overwhelming brine production by s ea-ice formation and thereby shutting down convection. Using only ice recor ds, confident estimates can be made of the rate and direction of plume spre ading. In contrast, the Husky Lakes estuary is supported only by a local, t ruly Arctic drainage basin which becomes frown in winter. The landfast ice in this system records a large. and relatively static, horizontal gradient in surface salinity. Small variations in delta(18)O with time evident in al l ice cores are found to correlate between adjacent sites suggesting cohere nt displacements of surface water by 10-15 km as might be produced by seich ing. (C) 1999 Elsevier Science B.V. All rights reserved.