This study examines the process of water-column stratification breakdown in Antarctic coastal polynyas adjacent to an ice shelf with a cavity underneath. This first part of a two-part sequence seeks to quantify the influence of offshore katabatic winds, alongshore winds, air temperature, and initial ambient stratification on the time scales of polynya destratification through combining process-oriented numerical simulations and analytical scaling. In particular, the often-neglected influence of wind-driven circulation on the lateral transport of the water formed at the polynya surface—which we call Polynya Source Water (PSW)—is systematically examined here. First, an ice shelf–sea ice–ocean coupled numerical model is adapted to simulate the process of PSW formation in polynyas of various configurations. The simulations highlight that (i) before reaching the bottom, majority of the PSW is actually carried away from the polynya by katabatic wind–induced offshore outflow, diminishing water-column mixing in the polynya and intrusion of the PSW into the neighboring ice shelf cavity, and (ii) alongshore coastal easterly winds, through inducing onshore Ekman transport, reduce offshore loss of the PSW and enhance polynya mixing and PSW intrusion into the cavity. Second, an analytical scaling of the destratification time scale is derived based on fundamental physical principles to quantitatively synthesize the influence of the physical factors, which is then verified by independent numerical sensitivity simulations. This work provides insights into the mechanisms that drive temporal and cross-polynya variations in stratification and PSW formation in Antarctic coastal polynyas, and establishes a framework for studying differences among the polynyas in the ocean.
Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater‐induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high‐resolution coupled ice‐shelf/sea‐ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near‐surface restratification, particularly in the outer‐polynya region where chlorophyll concentration tends to be high. Downwelling‐favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near‐surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near‐surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas.
more » « less- NSF-PAR ID:
- 10497069
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 129
- Issue:
- 3
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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