Abstract
AbstractOcean heat transport is often thought to play a secondary role for Arctic surface warming in part because warm water which flows northward is prevented from reaching the surface by a cold and stable halocline layer. However, recent observations in various regions indicate that occasionally, warm water is found directly below the surface mixed layer. Here we investigate Arctic Ocean surface energy fluxes and the cold halocline layer in climate model simulations from the Coupled Model Intercomparison Project Phase 5. An ensemble of 15 models shows decreased sea ice formation and increased ocean energy release during fall, winter, and spring for a high‐emission future scenario. Along the main pathways for warm water advection, this increased energy release is not locally balanced by increased Arctic Ocean energy uptake in summer. Because during Arctic winter, the ocean mixed layer is mainly heated from below, we analyze changes of the cold halocline layer in the monthly mean Coupled Model Intercomparison Project Phase 5 data. Fresh water acts to stabilize the upper ocean as expected based on previous studies. We find that in spite of this stabilizing effect, periods in which warm water is found directly or almost directly below the mixed layer and which occur mainly in winter and spring become more frequent in high‐emission future scenario simulations, especially along the main pathways for warm water advection. This could reduce sea ice formation and surface albedo.
Highlights
Arctic surface warming currently proceeds at more than twice the global average rate (Cohen et al, 2014)
We find that in spite of this stabilizing effect, periods in which warm water is found directly or almost directly below the mixed layer and which occur mainly in winter and spring become more frequent in high-emission future scenario simulations, especially along the main pathways for warm water advection
Ocean processes are sometimes considered of secondary importance, climate models generally do not agree on the importance of meridional oceanic heat transport in driving Arctic Ocean warming, METZNER ET AL
Summary
Arctic surface warming currently proceeds at more than twice the global average rate (Cohen et al, 2014). In principle such an amplification of climate change in the northern polar latitudes is expected based on climate model simulations, paleodata records, and process understanding. Arctic climate change is modulated by atmospheric and oceanic heat transport on various timescales (Laîné et al, 2016; Nummelin et al, 2017; Salzmann, 2017; Spielhagen et al, 2011; Yang et al, 2010) and by increased surface fluxes from the warmer ocean to the atmosphere in the absence of sea ice (Screen & Simmonds, 2010a; Serreze et al, 2009). Sea ice loss in the Barents sea has previously been linked to heat transport from the Atlantic (Årthun et al, 2012), potentially providing a nonlocal contribution to the surface albedo feedback
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