Recent Decrease of Summer Sea Ice in the Weddell Sea, Antarctica

John Turner,Babula Jena,C C Bajish,Tom Andersson,Eugene J Murphy,Gareth J Marshall,Kyle Clem,Jack Arnatt,Rachel Cavanagh,Zhaomin Wang,Tony Phillips,Maria Vittoria Guarino

doi:10.1029/2020gl087127

Abstract

AbstractIn Austral summer 2016/2017, the sea ice extent (SIE) in the Weddell Sea dropped to a near‐record value in the satellite era (1.88 × 106 km2), a large negative seasonal anomaly that persisted in an unprecedented fashion for the following three summers. Various atmospheric and oceanic factors played a part in the change. Ice loss started in September 2016 when the northern Weddell Sea experienced westerly winds of record strength, advecting multiyear sea ice from the region. In late 2016, a polynya over Maud Rise contributed to low SIE over the eastern Weddell Sea. With extensive areas of open water early in the summer, upper ocean temperatures increased by ~0.5°C, with the anomalies persisting in subsequent years. The reappearance of the Maud Rise polynya in 2017, high ocean temperatures, and storms of record depth kept the summer SIE low.

Highlights

Variability and change in the Weddell Sea sea ice cover is important for many atmospheric (Turner et al, 2017), oceanographic (Ohshima et al, 2013), biological (Meyer et al, 2017), and chemical processes (Zemmelink et al, 2008), as well as logistical activities (Turner et al, 2002)
In Austral summer 2016/2017, the sea ice extent (SIE) in the Weddell Sea dropped to a near‐record value in the satellite era (1.88 × 106 km2), a large negative seasonal anomaly that persisted in an unprecedented fashion for the following three summers
The Southern Annular Mode (SAM) index for November 2016 was −3.12, the fifth lowest November value on record, with new record high November mean sea level pressure (MSLP) values set at five continental staffed and automated weather stations. This pattern marked a dramatic switch from the strong positive SAM index in September to the strong negative SAM index in November, favoring warm, northerly flow toward much of the continent resulting in an ~3°C positive surface air temperature (SAT) anomaly (2 standard deviations) over the Weddell Sea, new record high November mean SATs at four coastal East Antarctic staffed stations, and the overall Antarctic‐wide SIE dropped to more than 5 standard deviations below the November climatological average (Scambos & Stammerjohn, 2018)

Summary

Introduction

Variability and change in the Weddell Sea sea ice cover is important for many atmospheric (Turner et al, 2017), oceanographic (Ohshima et al, 2013), biological (Meyer et al, 2017), and chemical processes (Zemmelink et al, 2008), as well as logistical activities (Turner et al, 2002). Sea ice can survive the summer (December–February) melt over the western Weddell Sea east of the Antarctic Peninsula (Comiso & Nishio, 2008) since it is a frigid region remote from relatively warm airmasses found west of the peninsula and in other sectors of the Southern Ocean. Between 2015/2016 and 2016/2017, there was the largest decrease in summer SIE in the 40‐year record (0.89 × 106 km2) This came after the major Antarctic‐wide decrease of sea ice in spring 2016 (Meehl et al, 2019; Purich & England, 2019; Turner et al, 2017; Wang et al, 2019; Wang et al, 2019), in which the Weddell Sea sector made the largest contribution (34%) to the total Southern Ocean sea ice decrease. We examine the conditions that led to the low summer Weddell Sea SIE in 2016/2017 and consider how the anomalies could persist for the following three summers

Data and Methods

Variability of Summer Sea Ice in the Weddell Sea

Persistence of the Sea Ice Anomaly Over the Following Summers

Discussion and Conclusions

Findings

Data Availability Statement