Mechanisms Modulating the Ocean Forcing of Pine Island Glacier
Benjamin Webber1, Karen J. Heywood2, David P Stevens3, Pierre Dutrieux4, Stan Jacobs5, Einar Povl Abrahamsen6, Adrian Jenkins6, Ho Kyung Ha7, Sang Hoon Lee8, Tae-Wan Kim8, Satoshi Kimura6, Karen Assmann9 and Anna Wahlin9, (1)University of East Anglia, Norwich, United Kingdom, (2)University of East Anglia, Norwich, NR4, United Kingdom, (3)University of East Anglia, School of Environmental Sciences, Norwich, United Kingdom, (4)Applied Physics Laboratory University of Washington, Seattle, WA, United States, (5)Columbia Univ, Palisades, NY, United States, (6)British Antarctic Survey, Cambridge, United Kingdom, (7)Inha University, Ocean Sciences, Incheon, South Korea, (8)Korea Polar Research Institute, Incheon, South Korea, (9)University of Gothenburg, Gothenburg, Sweden
Abstract:
Pine Island Glacier terminates in a rapidly melting ice shelf, where ocean forcing of the melt rate has been implicated in the acceleration and retreat of the glacier. A set of mooring records close to the Pine Island ice shelf were recovered in 2014, two of which are combined to provide an unprecedented five-year time series of temperature, salinity and current velocity. These data reveal considerable seasonal and interannual variability in intermediate to deep ocean temperatures, of sufficient magnitude to make a substantial impact on the melt rate of Pine Island ice shelf. The seasonal cycle in ocean temperature is correlated with surface wind speed over the continental shelf, suggesting a role for local surface heat fluxes and convection in influencing the observed temperatures down to 600 m depth. Meanwhile, the interannual variability is associated with Ekman upwelling near the easternmost shelf-edge depression that feeds into Pine Island Bay. Observations of ocean currents suggest this cold period was accompanied by a reversal in the circulation pattern around the bay, and the concurrent increase in salinity implies increased sea ice formation.
Numerical modelling simulations conducted in a high-resolution regional configuration of the MITgcm are used to further investigate the dynamical links between surface forcing and ocean forcing of the glacial melt rates. Heat fluxes into the cavity beneath the Pine Island Ice shelf exhibit large variability on interannual and decadal time scales. At the decadal time scale, these variations are closely linked to heat fluxes onto the continental shelf driven by surface winds at the shelf break and surface-driven upwelling across the continental shelf. The barotropic circulation around the Pine Island Trough region spins up and down in response to this forcing. In addition, there is an overturning cell within Pine Island Trough that strengthens (weakens) during periods of strong (weak) heat fluxes towards Pine Island Bay.
