13-years of sea ice draft observations in the Laptev Sea from moored ADCPS and ULSs: changes, variability and comparison to Earth Observation data

Moored upward-looking Acoustic Doppler Current Profilers (ADCPs) can be used to observe sea ice draft. While previous studies relied on the availability of auxiliary pressure sensors to measure the instrument depth of the ADCP, we present an adaptive approach that infers instrument depth from the ADCPs default bottom track (BT) mode measurements of error velocity and range. We demonstrate that this method can be used to obtain daily mean sea ice draft time series with an estimated uncertainty of 0.1 m. The ADCP-derived ice draft time series are validated with data from adjacent Upward-Looking Sonar (ULS) moorings in the Laptev Sea. This new approach provides a low-cost opportunity to derive daily mean ice draft time series accessing existing ADCP data. Applying this method to ADCP data from the sparsely-sampled Laptev Sea allows an extension of mooring-based in situ ice draft measurements from 2 to about 13 years. The Laptev Sea is an important region for net ice production and a major contributor to the Transpolar Drift System. Recent studies show that sea ice area and volume exports from the Laptev Sea are increasing. This increased export accelerates summer sea ice retreat in the Laptev Sea and has far-reaching consequences for the entire Arctic sea ice balance. The newly acquired Laptev Sea ice draft data archive is used to analyse seasonal and interannual changes in sea ice thickness from 2003 to 2016. In addition, it provides unique data for the comparison with sea ice thickness data records derived from ENVISAT, CryoSat-2 and SMOS satellite measurements in an area where large-scale validation data sets are currently unavailable.