The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study

This paper with attached PDF is an important advance in how to understand a changing environment directed by humans use of fossil fuels, and to more appropriately deal with interactions of different material phases in our World through modeling a fully coupled global climate TraCE-21ka model, specifically directed at appreciating the Southern Ocean and Antarctic de-glaciation with concomitant rise in sea level.

SUSTAINABILITY

Gagan Mandal 1,2,3 , Shih-Yu Lee 3,* and Jia-Yuh Yu

1 Taiwan International Graduate Program, Earth System Science Program, Academia Sinica, Taipei 11529, Taiwan; gagan.iitroorkee@gmail.com

2 Department of Atmospheric Sciences, National Central University, Taoyuan 32001, Taiwan; jiayuh@atm.ncu.edu.tw

3 Research Center for Environmental Changes, Academia Sinica, Taipei 11529, Taiwan * Correspondence: shihyu@gate.sinica.edu.tw

Citation: Mandal, G.; Lee, S.-Y.; Yu, J.-Y. The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study. Sustainability 2021, 13,353. https://doi.org/ 10.3390/su13010353

Received: 11 November 2020 Accepted: 26 December 2020 Published: 2 January 2021

Abstract: The Southern Ocean (SO) played a fundamental role in the deglacial climate system by exchanging carbon-rich deep ocean water with the surface. The contribution of the SO’s physical mechanisms toward improving our understanding of SO upwelling’s dynamical changes is devel- oping. Here, we investigated the simulated transient SO atmosphere, ocean, and sea ice evolution during the last deglaciation in a fully coupled Earth system model. Our results showed that decreases in SO upwelling followed the weakening of the Southern Hemisphere surface westerlies, wind stress forcing, and Antarctic sea ice coverage from the Last Glacial Maximum to the Heinrich Stadial 1 and the Younger Dryas. Our results support the idea that the SO upwelling is primarily driven by wind stress forcing. However, during the onset of the Holocene, SO upwelling increased while the strength of the wind stress decreased. The Antarctic sea ice change controlled the salt and freshwater fluxes, ocean density, and buoyancy flux, thereby influencing the SO’s dynamics. Our study highlighted the dynamic linkage of the Southern Hemisphere westerlies, ocean, and sea ice in the SO’s latitudes. Furthermore, it emphasized that zonal wind stress forcing and buoyancy forcing control by sea ice together regulate the change in the SO upwelling.

1. Introduction

The last deglaciation from 21 to 9 kyr BP (before present) offers a case study for the most recent natural global warming process. This period involved a transient climate evolution from a colder to a warmer world. It was interrupted by Northern Hemisphere millennial events with a simultaneous CO2 rise that is comparable to anthropogenic emission since the industrial revolution [1]. The Southern Ocean (SO) plays a pivotal role in controlling the variation in atmospheric CO2 concentrations over glacial–interglacial cycles [2]. It ventilates a significant part of the global ocean and acts as a window for the return of carbon-rich deep ocean water to the surface. The dynamical theory of the SO dy- namics is developing. Thus, understanding the physical mechanisms that determined the temporal and spatial change in SO upwelling throughout the Earth’s history will improve our comprehension of the response of the SO’s dynamics in future climate projections and the associated difference in atmospheric CO2 concentrations.

During the northern Atlantic millennial events, studies show a correlation between the change in the atmospheric CO2 concentrations and Antarctic temperatures involving a poleward shift in the Southern Hemisphere mid-latitude westerlies and an increase in the SO overturning [3]. Northern Atlantic cooling during the Heinrich Stadial 1 and the Younger Dryas overlapped with the Southern Hemisphere deglacial warming, with a rise in wind-driven SO upwelling [4–9]. Thus, Northern Hemisphere stadial millennial events,

The PDF from this Sustainability: An Open Access Journal is provided below…

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