Double‐Diffusive Layering in the Canada Basin: An Explanation of Along‐Layer Temperature and Salinity Gradients

Abstract

Double-diffusive mixing gives rise to layered structures in the Arctic Ocean: layers within a double-diffusive staircase overlying deeper layers associated with thermohaline intrusions. These layers exhibit well-defined lateral temperature and salinity gradients. Gradients in salinity along individual layers change sign with depth, while along-layer gradients in temperature remain the same sign with depth. A theoretical formalism is put forward to explain these features in terms of vertical divergences of double-diffusive fluxes; temperature and salinity gradients along layers are set by the depth-dependent ratio of double-diffusive heat to salt fluxes. Examination of fine structure in temperature and salinity profiles reveals how the net flux ratio depends upon whether the layer is part of an evolving thermohaline intrusion or a staircase. The physical framework in context with observations of varying along-layer gradients in temperature and salinity provides evidence for thermohaline intrusions evolving to a staircase and describes the parameters that dictate this process. Results bring new understanding to heat and salt transport in the Arctic Ocean as well as the physics of double-diffusive layering in the world's oceans.Plain Language Summary A type of ocean mixing process, double-diffusive convection, gives rise to layers in the Arctic Ocean that may be characterized by their differing temperature and salinity properties. The properties and physics of these layers are key to understanding how heat is transported vertically and laterally in the Arctic Ocean. A theoretical formalism is put forward to explain distinct features of the layers that are characterized in the observations. The physical framework in context with observations brings new understanding to how the layers evolve and how they relate to heat and salt transport in the Arctic Ocean.

Understanding Arctic Ocean Circulation: A Review of Ocean Dynamics in a Changing Climate

“…Walsh and Carmack () estimated lateral diffusivities associated with these thermohaline intrusions to be around 50 m 2 s −1 . In this way, diapycnal mixing can redistribute Atlantic Water heat laterally, with Atlantic Water intrusions taking around a decade to propagate across the Canada Basin (see, e.g., Bebieva & Timmermans, ).…”

Introduction to Special Collection on Arctic Ocean Modeling and Observational Synthesis (FAMOS) 2: Beaufort Gyre Phenomenon

“…Doddridge et al, ; Manucharyan & Isachsen, ; Proshutinsky, Krishfield, Toole, et al, ; Regan et al, ); identify the major sources of fresh water and the fresh water pathways from the sources to the Beaufort Gyre region (Kelly, Proshutinsky, Popova et al, ); explain the major patterns and regimes of the surface, Pacific, and Atlantic water layer circulation (e.g. Hu & Myers, ; Spall et al, ; Zhong et al, ); and reveal the physics of mechanical mixing and convection under the influence of wind, internal wave, and tidal forcing (e.g., Bebieva & Timmermans, ; Chanona et al, ; Shibley & Timmermans, ; Zhao et al, ). Other papers in the collection examine the role of sea ice conditions, major features of ice variability, and methods of sea ice prediction in the region (e.g.…”

“…Partitioning of kinetic energy into barotropic and baroclinic modes suggests that the halocline structure plays a specific role in limiting the capacity for frictional dissipation at the sea floor. Double-diffusive mixing and layers in the Beaufort Gyre region are studied by Bebieva and Timmermans (2019) and by Shibley and Timmermans (2019). These papers shed light on the origins of various layer types associated with heat and salt transport, as well as the role of turbulence in limiting double-diffusive heat fluxes.…”

Thermohaline interleaving induced by horizontal temperature and salinity gradients from above

“…Thermohaline intrusions are of great importance since they generate fine-scale thermohaline structures, drive lateral flux and mixing and affect the evolution of mesoscale vortices (Merryfield 2000; Lee & Richards 2004; Ruddick, Oakey & Hebert 2010; Sarkar et al. 2015; Bebieva & Timmermans 2019; Tang et al. 2019).…”