Abstract
An open-ocean polynya is a large ice-free area surrounded by sea ice. The Maud Rise Polynya in the Southern Ocean occasionally occurs during the austral winter and spring seasons in the vicinity of Maud Rise near the Greenwich Meridian. In the mid-1970s the Maud Rise Polynya served as a precursor to the more persistent, larger Weddell Polynya associated with intensive open-ocean deep convection. However, the Maud Rise Polynya generally does not lead to a Weddell Polynya, as was the situation in the September to November of 2017 occurrence of a strong Maud Rise Polynya. Using diverse, long-term observation and reanalysis data, we found that a combination of weakly stratified ocean near Maud Rise and a wind induced spin-up of the cyclonic Weddell Gyre played a crucial role in generating the 2017 Maud Rise Polynya. More specifically, the enhanced flow over the southwestern flank of Maud Rise intensified eddy activity, weakening and raising the pycnocline. However, in 2018 the formation of a Weddell Polynya was hindered by relatively low surface salinity associated with the positive Southern Annular Mode, in contrast to the 1970s’ condition of a prolonged, negative Southern Annular Mode that induced a saltier surface layer and weaker pycnocline.
Highlights
An open-ocean polynya is a large ice-free area surrounded by sea ice
We focus on 4 questions: 1- how has been the thermohaline stratification of the upper ocean weakened within the Weddell Gyre before the occurrence of MRP2017? 2- how did the basin-scale atmosphere circulation over the Weddell Sea intensify the underlying cyclonic Weddell Gyre circulation? 3- what events occurred in the vicinity of Maud Rise and led to the MRP2017? and 4- why didn’t the MRP2017 lead to a larger-scale, more persistent Weddell Polynya (WP) event, as materialized in the 1970s?
A series of STD (Salinity-Temperature-Depth recorder) hydrographic station data were obtained by Glacier in January-February of 1973, showing the oceanic state before the occurrence of the 1970s’ WP, and the CTD (Conductivity-Temperature-Depth recorder) hydrographic station data were obtained by Islas Orcadas (IO) in February of 19775,6, depicting the ocean stratification after the WP
Summary
An open-ocean polynya is a large ice-free area surrounded by sea ice. The Maud Rise Polynya in the Southern Ocean occasionally occurs during the austral winter and spring seasons in the vicinity of Maud Rise near the Greenwich Meridian. In the mid-1970s the Maud Rise Polynya served as a precursor to the more persistent, larger Weddell Polynya associated with intensive open-ocean deep convection. Less persistent open-ocean polynyas are observed in the vicinity of Maud Rise located in the Weddell Sea during late winter or early spring[10]. Measurements of the thermohaline stratification within the Weddell Gyre before and after the WP reveal active winter open-ocean deep convection, cooling the WDW and by injecting warm water into the surface layer, acting to prevent overlying sea ice cover, inducing the WP4
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