![]() |
||||||||||||||
Australia: The Land Where Time Began |
||||||||||||||
Southern Ocean Overturn Upper Branch – Water-Mass transformation
by Sea Ice
A continuous thermodynamic transformation of the buoyancy of seawater is
required by ocean overturning circulation. In the Southern Ocean a
pathway for the upwelling of Circumpolar Deep Water from mid depth
without strong Diapycnal mixing is provided by the steeply sloping
isopycnals (Toggweiler & Samuels, 1995; Wolfe & Cessi, 2011; Nikurashin
& Vallis, 2012), where it is transformed directly by surface fluxes of
heat and freshwater and splits into an upper and lower branch (Speer,
Rintoul & Sloyan, 2000; Marshall & Speer, 2012; Talley, 2013). The role
of sea ice in the upper branch is less well understood, in part due to a
paucity of observations of the thickness and transport of sea ice (Ren,
Speer & Chassingnet, 2011; Tamura et al., 2011), while it is believed
that brine rejection from sea ice contributes to the lower branch
(Jacobs, 2004). In this paper Abernathy et
al., present the results of
their study in which they quantified the sea ice freshwater flux by use
the Southern Ocean State Estimate, which is a state-of-the-art
assimilation of data incorporating millions of ocean and ice
observations. They then compared the relative roles of atmosphere, sea
ice, and glacial freshwater fluxes, heat fluxes, and mixing of the upper
ocean in transforming buoyancy within the upper branch, by use of the
water-mass transformation framework (Walin, 1982). They found that sea
ice is a dominant term, with differential brine rejection and the
melting of ice transforming upwelled Circumpolar Deep Water at a rate of
~22 x 106 m3 s-1. It is implied by
these results that there is a prominent role for Antarctic sea ice in
the upper branch and suggest that there is a tight coupling between
residual overturning and sea ice transport that is wind-driven.
|
|
|||||||||||||
|
||||||||||||||
Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |