Quantifying Sea-Ice Volume Flux using Moored Instrumentation in the Bering Strait

Abstract

The Bering Strait is the sole pathway linking the Pacific and Arctic Oceans, and carries one-third of the freshwater entering the Arctic. Although the strait's throughflow dominates the hydrography of the highly productive Chukchi Sea and affects the freshwater budget and thermal structure of the Arctic Ocean, the contribution of sea ice to the freshwater flux has never been satisfactorily quantified. We use data from an array of subsurface moored Acoustic Doppler Current Profilers (ADCPs) and other instruments deployed in the Bering Strait from 2007–2008 to calculate the sea ice and corresponding freshwater volume fluxes through the strait. Data from remote-sensing systems such as the Advanced Microwave Scanning Radiometer (AMSR) and modeled sea level pressure data provide a check of ADCP-derived measurements. We correct the ADCP sea-ice thickness records for instrument-based errors (instrument pitch and roll, ridge shadowing, beam footprint, beam averaging, range outliers) and environment-based errors (sound speed variation, instrument depth, sea-ice freeboard and snow loading), and determine the uncertainty in our volume flux calculations. We estimate the total error in ADCP ice thickness measurements to be of order 0.5 m, with ∼ 46% of this error resulting from beam footprint effects that would remain even if a more precise sonar instrument had been used in our study. We compare our estimates of sea-ice volume flux (190 ± 50 km<super>3</super> yr<super>-1</super>) and corresponding freshwater transport (140 ± 40 km<super>3</super> yr<super>-1</super>) through the strait to values from previous surveys, commenting on differences in methodology between the studies. Our findings allow us to assess the utility of subsurface moored ADCPs in quantifying sea-ice presence, thickness, and velocity; the ADCP signal correlation parameter appears to provide a particularly good indication of sea-ice presence. In addition, we consider the use of similar methods to evaluate historical ADCP records and develop a more complete understanding of interannual sea-ice flux variability through the Bering Strait.