Observed winter salinity fields in the surface layer of the Arctic Ocean and statistical approaches to predicting large-scale anomalies and patterns

Ekaterina A Cherniavskaia,Leonid A Timokhov,Ivan Sudakov,Kenneth M Golden,Courtenay Strong

doi:10.1017/aog.2018.10

Abstract

AbstractSignificant salinity anomalies have been observed in the Arctic Ocean surface layer during the last decade. Our study is based on an extensive gridded dataset of winter salinity in the upper 50 m layer of the Arctic Ocean for the periods 1950–1993 and 2007–2012, obtained from ~20 000 profiles. We investigate the interannual variability of the salinity fields, identify predominant patterns of anomalous behavior and leading modes of variability, and develop a statistical model for the prediction of surface-layer salinity. The statistical model is based on linear regression equations linking the principal components of surface-layer salinity obtained through empirical orthogonal function decomposition with environmental factors, such as atmospheric circulation, river runoff, ice processes and water exchange with neighboring oceans. Using this model, we obtain prognostic fields of the surface-layer salinity for the winter period 2013–2014. The prognostic fields generated by the model show tendencies of surface-layer salinification, which were also observed in previous years. Although the used data are proprietary and have gaps, they provide the most spatiotemporally detailed observational resource for studying multidecadal variations in basin-wide Arctic salinity. Thus, there is community value in the identification, dissemination and modeling of the principal modes of variability in this salinity record.

Highlights

The Arctic Ocean is very sensitive to changing environmental conditions
Observations show that increases in Arctic Ocean salinity have accompanied this warming as it was associated with significant shoaling of the upper Atlantic waters (AW) boundary and weakening of the upper ocean stratification in the Eurasian Basin as well
This is complemented by the data made available over the period 2007–2012 from the expeditions of the International Polar Year (IPY) and afterward, which consist of Conductivity Temperature Depth (CTD) and eXpendable Conductivity Temperature Depth (XCTD) data, as well as data from the Ice-Tethered Profiler (ITP)-buoys

Summary

Introduction

The Arctic Ocean is very sensitive to changing environmental conditions. Its surface layer is a key component of the Arctic climate system, which serves as the dynamic and thermodynamic link between the atmosphere and the underlying waters (Carmack, 2000). The rejection of salt during seaice formation strongly impacts upper ocean salinity, so that the stability and development of the ice cover are closely associated with the thermohaline properties of the upper ocean, such as the depth of the mixed layer and halocline In this context, the Arctic Ocean surface layer is a critical indicator of climate change (Toole and others, 2010). Of particular interest is the great salinification of the surface layer of the Eurasian and Makarov Basins in the early 1990s – a phenomenon unprecedented in the record back to 1950 (Fig. 1) One hypothesis for this is that the increase of Arctic atmospheric cyclone activity in the 1990s led to a large change in the salinity in the Eurasian Basin through changes in river inflow, and increased brine formation due to changes in Arctic sea-ice formation (Dickson, 1999; Polyakov and others, 2008). Recent observations show that the upper ocean of the Eurasian Basin was appreciably fresher in 2010 than it was in 2007 and 2008 (Timmermans and others, 2011)

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