Outflow from under the Pine Island Bay Ice Shelf: finescale structure and its temporal variability

Abstract

The water column structure of the ice shelf cavity outflow from under Pine Island Glacier and its temporal variability were investigated using a hourly time series of yo-yo CTD and LADCP data collected over ~24 h at the southern end of the ice shelf front. The primary water types present over the continental shelf off Pine Island Bay were Circumpolar Deep Water (CDW), modified Circumpolar Deep Water (mCDW), Shelf Water (SW), and Ice Shelf Water (ISW). As CDW transited the shelf, it transitioned into cooler, mCDW. In the upper 200 m, ISW dominated within 100 km of the ice shelf and SW further offshore. Within Pine Island Bay, the water column was partitioned into two primary layers based on their behavior: an upper outflowing layer from 100 m to 450 m composed of ISW with a significant meltwater component, 1%–2%, over an inflowing layer from ~550 m to the sea bed composed of mCDW. Due to the small cavity extent, the outflowing water was warmer than the seawater freezing point. The upper ISW layer was further split into upper ISW layer #1 (100–300 m) and upper ISW layer #2 (320–450 m) with the transition coinciding with the ice shelf draft. Small step-like features with heights from 1–50 m existed within both the ISW layers and were more prominent in upper ISW layer #1. A baroclinic signal at the semidiurnal frequency existed within both primary layers with the strongest signal, ~ 10 cm·s -1 , propagating vertically in the upper ISW layer. Citation: Robertson R. Outflow from under the Pine Island Bay Ice Shelf: finescale structure and its temporal variability. Adv Polar Sci, 2016, 27: 245-263, doi:10.13679/j.advps.2016.4.00245