Abstract
Abstract. Maud Rise polynyas (MRPs) form due to deep convection, which is caused by static instabilities of the water column. Recent studies with the Community Earth System Model (CESM) have indicated that a multidecadal varying heat accumulation in the subsurface layer occurs prior to MRP formation due to the heat transport over the Weddell Gyre. In this study, a conceptual MRP box model, forced with CESM data, is used to investigate the role of this subsurface heat accumulation in MRP formation. Cases excluding and including multidecadal varying subsurface heat and salt fluxes are considered, and multiple polynya events are only simulated in the cases where subsurface fluxes are included. The dominant frequency for MRP events in these results, approximately the frequency of the subsurface heat and salt accumulation, is still visible in cases where white noise is added to the freshwater flux. This indicates the importance and dominance of the subsurface heat accumulation in MRP formation.
Highlights
The Weddell Sea is a region where open-ocean polynyas occasionally form
Formation of the Maud Rise polynyas (MRPs) is clearly related to bathymetry, i.e., Maud Rise, an underwater seamount, whereas this clear relation is absent for Weddell Sea polynyas (WSPs)
The MRP box model is forced by a monthly varying heat flux (Qoa or Qia) and a monthly varying freshwater flux (F ) that are repeated for each model year (Fig. 3c, d; Table 3)
Summary
The Weddell Sea is a region where open-ocean polynyas occasionally form. A distinction is made between the larger Weddell Sea polynyas (WSPs) and the smaller Maud Rise polynyas (MRPs). In the KCM, for example, a stronger stratification results in a longer period for deep convection, because more buoyancy gain is necessary to overcome the more stable stratification (Latif et al, 2017; Reintges et al, 2017) Another important feature is model resolution, as shown by Weijer et al (2017): MRPs were found in a high-resolution (0.1◦) version of the CESM, whereas no MRPs were simulated in the low-resolution (1◦) version of the same model. A recent model study by van Westen and Dijkstra (2020a) showed a multidecadal occurrence of MRPs and suggested that the timescale of MRP formation is affected by intrinsic ocean variability through subsurface preconditioning.
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