[DOI: 10.1038/s41598-019-43466-2]
Abstract
This elaborate news article delves into the complex nature of open-ocean polynyas, focusing on the Maud Rise Polynya in the Southern Ocean. It highlights recent research and its implications for understanding deep convection processes that drive critical oceanic circulation.
Keywords
1. Maud Rise Polynya
2. Southern Ocean
3. Deep convection
4. Weddell Polynya
5. Southern Annular Mode
In the desolate and frigid expanse of the Southern Ocean, mysterious events periodically disturb the vast sheets of ice. One such phenomenon is the spontaneous appearance of open-ocean polynyas – vast, ice-free areas that stand in stark contrast to the surrounding sea ice. The re-emergence of the Maud Rise Polynya, situated near the Greenwich Meridian, has captured the attention of oceanographers and climatologists alike. A new study, published in Scientific Reports, meticulously unravels the intricate set of circumstances that led to this anomaly during the austral winters of the past, specifically focusing on the strong appearance in 2017 [1].
The study in question, spearheaded by Cheon Woo Geun from the Maritime Technology Research Institute, Agency for Defense Development, Changwon, Republic of Korea, alongside Arnold L. Gordon from the Lamont-Doherty Earth Observatory of Columbia University, leans on an amalgamation of historical data and ocean models to propose a systematic account of the conditions conducive to the formation of the Maud Rise Polynya [1].
Maud Rise Polynya: A Window to the Ocean’s Depths
The phenomenon of a polynya, commonly associated with coastal regions, occurs in the central expanses of the Southern Ocean. Its mechanism extends beyond just atmospheric conditions; it is deeply intertwined with oceanic processes. The Maud Rise Polynya has been scrutinized since its notable occurrence in the mid-1970s when it served as a precursor to the more persistent and larger Weddell Polynya, which became the subject of intensive study due to its role in stimulating open-ocean deep convection [2].
Deep convection is an aspect of ocean dynamics where surface water becomes denser than the underlying layers, commonly due to cooling and increased salinity, and subsequently sinks, instigating a vertical movement of water. This mixing process is a crucial component of global thermohaline circulation, which significantly affects climate patterns [3].
The 2017 Occurrence: Triggers and Drivers
The 2017 Maud Rise Polynya appeared without warning during the austral winter months. This caught scientists’ attention as the polynya events had been relatively dormant in the preceding decades. The study’s analysis points to a multitude of factors including the underlying topography, ocean stratification, and atmospheric conditions [1].
A combination of a weakly stratified ocean column near Maud Rise, and a wind-induced increase in the speed of the cyclonic Weddell Gyre – the circular flow of water around the Weddell Sea – played a pivotal role. Elevated flow over the southwestern flank of Maud Rise intensified eddy activity, which, in turn, disturbed the pycnocline – the layer within the ocean that separates different water densities [1].
The Interplay with Southern Annular Mode
A crucial aspect that differentiates the events of the 1970s from more recent occurrences is the phase of the Southern Annular Mode (SAM). This climatological term refers to the non-stationary belt of westerly winds that encircle Antarctica. A positive SAM index describes a situation where these winds are confined closer to the Antarctic, while a negative index points to a more equatorward location [4].
During the 1970s, a prolonged, negative phase of the SAM was tied to a saltier surface layer above the pycnocline, which favored deeper convection. In stark contrast, the 2017 event coincided with a positive SAM, which, while not leading to an event of the magnitude of the 1970s’ Weddell Polynya, resulted in considerable convective activity [1].
The Significance of Polynyas in the Climate System
The emergent research on polynyas touches on a wider spectrum of climate-related inquiries. As these events can lead to substantial exchanges of heat, gases, and momentum between the ocean and the atmosphere, they contribute to our understanding of polar processes that regulate global climate [5].
Furthermore, the open-ocean polynyas potentially affect sea ice formation and local weather systems. The deep convection associated with these areas alters the ocean’s heat content, influencing the stability of ice shelves and impacting the reproductive habitat of Antarctic fauna [6].
This research is closely aligned with previous works that have underscored the importance of ocean dynamics. A wealth of literature emphasizes the gravity of deep water convection and its relevance to the Southern Ocean’s capacity to absorb and redistribute heat and carbon dioxide [7-10].
Future Implications
These findings regarding the Maud Rise Polynya reverberate beyond the confines of academic circles; they are of immense significance in the era of climate change. The study predicts that anthropogenic influences may alter the frequency and intensity of these phenomena [11].
As part of an intricate climate system, the Southern Ocean’s behavioral changes have extensive implications. Predictive models incorporating the dynamics of polynyas could enhance our capability to forecast long-term changes and initiate timely climate strategies.
Conclusion
The research on the Maud Rise Polynya illuminates the interconnected nature of oceanic and atmospheric phenomena. The combined effects of wind patterns, ocean stratification, and seabed topography coalesce to shape the scenarios that lead to these insightful windows into the ocean’s deep convection processes. The reverberations of these findings underscore the importance of continued monitoring of the Southern Ocean as a key player in the global climate system.
References
[1] Cheon Woo Geun, Gordon Arnold L. (2020). Open-ocean polynyas and deep convection in the Southern Ocean. Scientific Reports. DOI: 10.1038/s41598-019-43466-2.
[2] Gordon AL. (1978). Deep Antarctic convection west of Maud Rise. J. Phys. Oceanogr.
[3] Wadhams, P. (2000). Ice in the Ocean. Gordon and Breach Sci. Publ.
[4] Holland, D. M. (2001). Explaining the Weddell Polynya – a Large Ocean Eddy Shed at Maud Rise. Science.
[5] de Lavergne C., et al. (2014). Cessation of deep convection in the open Southern Ocean under anthropogenic climate change. Nature Climate Change.
[6] Wang Z., et al. (2017). Impacts of open-ocean deep convection in the Weddell Sea on coastal and bottom water temperature. Clim. Dyn.
[7] Ou HW, Gordon AL. (1986). Spin-down of baroclinic eddies under sea ice. J. Geophys. Res.
[8] Zanowski H., et al. (2017). Weddell Polynya transport mechanisms in the abyssal ocean. J. Phys. Oceanogr.
[9] Killworth PD. (1983). Deep convection in the world ocean. Rev. Geophys.
[10] Swart S., et al. (2018). Return of the Maud Rise polynya: climate litmus or sea ice anomaly? [in State of the Climate in 2017] Bull. Amer. Meteor. Soc.
[11] Martinson DG., et al. (1981). A convective model for the Weddell Polynya. J. Phys. Oceanogr.