Spatial and temporal variability of water masses in the Southern Ross Sea

Relatively warm modified Circumpolar Deep Water accesses the southern Ross Sea steered by bathymetric troughs. There it provides nutrients to support phytoplankton blooms in spring, and heat to melt the Ross Ice Shelf.  Here we present new observations collected by two ocean gliders during December 2022 and January 2023, in the Ross Sea polynya adjacent to the Ross Ice Shelf.  The gliders surveyed the full depth of the water column (about 700 m depth) carrying sensors measuring temperature, salinity, dissolved oxygen, chlorophyll fluorescence and optical backscatter, and also yielded estimates of the dive-average-current which we use to reference geostrophic shear.  Repeated quasi-meridional high resolution (profiles approximately every 1.5 km) sections along the sea ice edge allow analysis of the spatial and temporal variability, as well capturing the dynamic field of eddies, tides and coastal current. We discuss the influence of the sea ice and the atmospheric forcing on the water properties. One glider made an unauthorised foray beneath the Ross Ice Shelf, surveying the upper 200 m of the water column in high resolution beneath an ice shelf base at about 80 m depth. We observe solar-warmed water penetrating beneath the ice shelf with significant signatures of elevated chlorophyll fluorescence and optical backscatter, and low oxygen and salinity. We discuss the likely mechanisms involved in advecting this water beneath the ice shelf and its importance for physical and biogeochemical processes of ocean-ice interaction.