Abstract. To study the influence of basal melting of the Ross Ice Shelf (BMRIS) on the
Southern Ocean (ocean southward of 35∘ S) in quasi-equilibrium,
numerical experiments with and without the BMRIS effect were performed using
a global ocean–sea ice–ice shelf coupled model. In both experiments, the
model started from a state of quasi-equilibrium ocean and was integrated for
500 years forced by CORE (Coordinated Ocean-ice Reference Experiment)
normal-year atmospheric fields. The simulation results of the last 100 years
were analyzed. The melt rate averaged over the entire Ross Ice Shelf is
0.25 m a−1, which is associated with a freshwater flux of 3.15 mSv
(1 mSv = 103 m3 s−1). The extra freshwater flux
decreases the salinity in the region from 1500 m depth to the sea floor in
the southern Pacific and Indian oceans, with a maximum difference of nearly
0.005 PSU in the Pacific Ocean. Conversely, the effect of concurrent heat
flux is mainly confined to the middle depth layer (approximately 1500 to
3000 m). The decreased density due to the BMRIS effect, together with the
influence of ocean topography, creates local differences in circulation in
the Ross Sea and nearby waters. Through advection by the Antarctic
Circumpolar Current, the flux difference from BMRIS gives rise to an increase
of sea ice thickness and sea ice concentration in the Ross Sea adjacent to
the coast and ocean water to the east. Warm advection and accumulation of
warm water associated with differences in local circulation decrease sea ice
concentration on the margins of sea ice cover adjacent to open water in the
Ross Sea in September. The decreased water density weakens the subpolar cell
as well as the lower cell in the global residual meridional overturning
circulation (MOC). Moreover, we observe accompanying reduced southward
meridional heat transport at most latitudes of the Southern Ocean.
DASSO: a data assimilation system for the Southern Ocean that utilizes both sea-ice concentration and thickness observations