Sea Ice Changes in the Pacific Sector of the Southern Ocean in Austral Autumn Closely Associated With the Negative Polarity of the South Pacific Oscillation

Abstract

We present an explanation for the sea ice concentration trends in the Pacific sector of the Southern Ocean (PSSO) in austral autumn (April‐June) during 1979–2018. Sea ice has decreased in the Bellingshausen Sea and increased in the Ross Sea, concurrently with a negative trend in the South Pacific Oscillation (SPO). SPO statistically explains 43% of the sea ice concentration trend averaged over PSSO. Convective activities over East Africa and the southwestern Indian Ocean, the Interdecadal Pacific Oscillation (IPO), and extratropical processes excite a wavetrain that propagates from the Indian Ocean to the Southern Ocean and South America. The wavetrain contributes to the decrease of the autumn SPO index, which influences sea ice changes over PSSO. During the negative phase of SPO, an anomalous surface anticyclonic wind field over high‐latitude South Pacific Ocean generates anomalous sea ice concentrations via heat advection and wind forcing on ice drift.

The Impact of the Indian Ocean Basin Mode on Antarctic Sea Ice Concentration in Interannual Time Scales

“…Positive surface air temperature anomalies related to anomalous southward heat transport and increasing downward longwave radiation anomaly also favor negative sea ice concentration anomalies. Such a response of Antarctic sea ice to the changes in the atmospheric circulations is in agreement with previous studies (Yu et al, 2018;Yu, Zhong, Vihma, et al, 2021).…”

A regional and seasonal approach to explain the observed trends in the Antarctic sea ice in recent decades

“…Daily Antarctic sea ice concentration data from the U.S. National Snow & Ice Data Center (NSIDC) (http://nsidc.org/data/NSIDC-0051) are used in the current analysis. The daily sea ice data is utilized, instead of monthly data as in most previous studies, because synoptic scale variability plays an important role in the interannual and decadal variability of sea ice concentration (Yu et al ., 2021a; 2021b). The sea ice concentration data, which are on a 25‐km resolution Equal Area Scalable Earth (EASE) grid from October 1978 to the present, are derived from brightness temperatures of passive microwave radiometers on board of Nimbus‐7 SMMR and DMSP SSM/I‐SSMIS using the NASA Team algorithm (Cavalieri et al ., 1996).…”

“…The decades‐long overall increasing trend in the Antarctic sea ice has been attributed to internal variability of the climate system. In particularly, the trends have been linked to changes in surface winds (Holland and Kwok, 2012; Holland et al ., 2017a) to various ocean processes including Southern Ocean convection (Zhang et al ., 2019), ice shelf melt (Bintanja et al ., 2013; 2015), and ice–ocean feedbacks (Zhang, 2007; Goosse and Zunz, 2014), and to well‐known modes of climate system variability (Raphael and Hobbs, 2014) related to ocean–atmosphere interactions including the El Niño–Southern Oscillation (ENSO) (Stammerjohn et al ., 2008), the Southern Annular Mode (SAM) (Holland et al ., 2017b), the Amundsen Sea Low (ASL) (Fogt et al ., 2012; Turner et al ., 2015; 2016; Holland et al ., 2018), the Zonal Wave Three (ZW3) (Raphael, 2007), the Interdecadal Pacific Oscillation (IPO) (Lopez et al ., 2016; Meehl et al ., 2016), the Atlantic Multidecadal Oscillation (AMO) (Yu et al ., 2017), and the South Pacific Oscillation (Yu et al ., 2021a). External factors, such as increases in the greenhouse gas emissions and ozone depletion, have also been found to influence Antarctic sea ice trends by modifying high‐latitude climate variability modes, particularly the SAM (Thompson and Solomon, 2002; Gillett et al ., 2013; Fogt and Zbacnik, 2014; Christidis and Stott, 2015).…”

The seasonal Antarctic sea ice concentration anomalies related to the Atlantic Niño index

“…The Amundsen Sea Low anomaly is also related to the dipole variability of sea ice in the Ross Sea and the Antarctic Peninsula/Bellingshausen Sea (Turner et al 2016). Moreover, the South Pacific Oscillation is linked to opposite austral autumn Antarctic sea ice variability in areas to the west and east of 150 • W longitude in the Pacific sector of the Southern Ocean (Yu et al 2021).…”