Arctic Ocean Surface Energy Flux and the Cold Halocline in Future Climate Projections

Abstract

Ocean 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.

Spatial Complexity in Dissolved Organic Matter and Trace Elements Driven by Hydrography and Freshwater Input Across the Arctic Ocean During 2015 Arctic GEOTRACES Expeditions

“…All rights reserved. (Middag et al, 2011;Jensen et al, 2020). The correlations of dMn with in situ CDOM fluorescence, DOC, and lignin phenols were positive but statistically insignificant.…”

“…The buoyant, low-salinity fluvial discharge mixed with the Atlantic water creates an upper ocean flow from the shelves to the central Arctic Ocean (Rennermalm et al, 2006). Arctic shelf waters are diverted by the Coriolis force to form a circumpolar anti-clockwise current shaped by coastal geometry resulting in multiple branches (Carmack et al, 2016;Horner-Devine et al, 2015).Below these upper waters is the lower halocline, which is believed to be formed via two mechanisms: a convective formation implying salinification of cold and fresh surface water and melting of sea ice as Atlantic water enters the ice-covered Arctic shelves, and an advective formation involving the cold and saline shelf water spreading into the deep Arctic basins (Kikuchi et al, 2004;Metzner et al, 2020).…”

Divergence in Climate Model Projections of Future Arctic Atlantification

“…In observations, the lower boundary of the halocline is usually determined using a density ratio algorithm following the method proposed by Bourgain and Gascard (2011), which was also used by e.g. Polyakov et al (2018) and Metzner et al (2020). Following Bourgain and Gascard (2011), such density ratio is defined as…”

Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)3 Project

“…The pressure gradients cause southerly winds that are comparable to the prescribed forcing anomalies, suggesting a positive feedback. In another study within (AC) 3 , Metzner et al (2020) investigated the role of changes in the Arctic Ocean cold halocline for ocean heat transfer from the ocean to the atmosphere. The cold halocline is a stable layer that separates warm Atlantic water from the overlying cold mixed layer.…”