News & Views

Iceberg calving from the Antarctic Nansen Ice Shelf in April 2016and its local impact

Tian Li • Yifan Ding • Tiancheng Zhao •

Xiao Cheng

Published online: 25 June 2016

� Science China Press and Springer-Verlag Berlin Heidelberg 2016

Owing to global warming, frequent ice shelf disintegration

and rapid acceleration of inland ice flow have occurred in

recent decades, which impacts the Antarctic mass balance

and the global sea level [1]. These events are closely linked

to atmospheric and oceanic processes. The prolonged melt

season and larger extent of melt ponds on the ice shelf

surface [2], as well as enhanced basal melting caused by

warmer sea water [3], will induce crevasses that expand

and enhance fracturing of Antarctic ice shelves. The calved

icebergs comprise a massive fresh water reserve, and ice-

berg evolution can affect ecological and oceanic environ-

ments, such as phytoplankton blooms, the fresh water

balance in the Southern Ocean and the growth and decay of

local sea ice, especially the alongshore fast ice [4].

Antarctic scientific research expeditions will also be

affected.

The Nansen Ice Shelf (NIS, 163�280E, 75�50S) is locatedon the west side of Terra Nova Bay (TNB) and abuts the

north side of the Drygalski Ice Tongue (DIT) in Victoria

Land, East Antarctica [5]. The NIS flows into TNB from

the grounding line at the flow branch of the Reeves Glacier

for approximately 45 km to the front and is approximately

35 km across between the southern boundary and Inex-

pressible Island, which is the potential site for the next

scientific station of China. On April 7, 2016, the front of

the NIS calved into two medium-sized icebergs—C33

(21 km 9 8 km, C33 is named by the National Ice Center,

which records icebergs with minimum lengths of 18.5 km)

and C33b (10 km 9 5 km, C33b is named based on the

National Ice Center principle for this paper) owing to the

large expanding crevasse. The calving area is approxi-

mately 203 km2 with an average thickness of 200 m, and

the mass loss is approximately 37 Gt, as calculated from

Sentinel-1A SAR data and Cryosat-2 radar altimetry pro-

files. After calving, the two icebergs drifted with melange

attached, which once filled the large crevasse.

Owing to the combined effect of basal melting and the

strain rate distribution, the crevasse in the calving event

initially formed in the central part of the NIS and was

approximately 6.5 km from the coastline. Its length sig-

nificantly expanded (north–south trending) from 2011 to

2013 at a rate of 6.6 km/year, as calculated from Envisat

ASAR, Landsat7 ETM? and Landsat8 OLI images; it

appeared as meandering threads in the north–south

direction. From 2013 to 2016, the width of the crevasse

expanded (east trending) owing to ocean current, wind

and hydraulic pressure [2]. The widest part prior to the

NIS calving was 1.7 km, according to Sentienl-1A SAR

data.

The drifting routes of the two icebergs are shown in the

Fig. 1a. The two icebergs C33 and C33b drifted along the

Antarctic coastline driven by ocean currents and winds

[6, 7]. They collided prior to April 9, 2016. Combined with

Coriolis forces, the iceberg C33b drifted towards the

coastline and became stranded on the east side of Abbott

Mount on April 14, 2014. This occurrence was caused by

the iceberg draft with respect to the ocean water depth. The

average thickness of iceberg C33b is approximately 200 m

as calculated from CryoSat-2 profiles, and the average draft

of the iceberg is estimated to be 178 m according to a

T. Li � Y. Ding � T. Zhao � X. Cheng (&)

State Key Laboratory of Remote Sensing Science, College of

Global Change and Earth System Science, Beijing Normal

University, Beijing 100875, China

e-mail: xcheng@bnu.edu.cn

T. Li � Y. Ding � T. Zhao � X. ChengJoint Center for Global Change Studies, Beijing 100875, China

123

Sci. Bull. (2016) 61(15):1157–1159 www.scibull.com

DOI 10.1007/s11434-016-1124-9 www.springer.com/scp

hydrostatic equilibrium equation; this draft is larger than

the water depth calculated from Bedmap-2 bed elevation

data near the coast of Abbott Mount (Fig. 1b). Abbott

Mount can serve as a natural barrier for the stranded ice-

berg as it can impede the strong katabatic wind from the

surrounding glaciers. Regarding iceberg C33, it freely

drifted to the Washington Cape on April 21, 2016. Iceberg

C33 has two inferred routes when it leaves the Ross Sea in

the future. The first route consists of drifting westwards

with the Antarctic Coastal Current, and the second route

entails drifting northwards away from the Antarctica owing

to the effect of Ross Gyre [6].

For the NIS calving event, the real risk is the

potential increase in the local fast ice extent owing to

the influence of the stranded iceberg C33b [8]. Fast ice

is a type of stationary sea ice that is attached to coastal

features, such as coastline, grounded icebergs, and an ice

wall or ice front, and forms in sheltered coastal

embayments [4]. Thus, the extent of fast ice is closely

related to terrain changes, and the stranded iceberg C33b

serves as an anchor site for fast ice growth. After iceberg

C33b was stranded on the Abbott Mount coast, fast ice

rapidly reformed by attaching to the iceberg’s sidewall

and coastline in less than 10 d (Fig. 1b). The fast ice

extent is expected to increase during this austral winter.

Compared with the maximum fast ice extent of this

region in 2015 (Fig. 1c), the possible fast ice extent this

year is expected to spread from the east of Campbell

Fig. 1 a Bathymetric map of the Ross Sea with the drift routes of icebergs C33 and C33b. The background is a Sentinel-1A SAR image that was

acquired on April 18, 2016 with a spatial resolution of 40 m. The bathymetric data are derived from Bedmap-2 bed elevation data with a

resolution of 1 km. The calving part of the Nansen Ice Shelf is delineated with a blue line. Iceberg C33 is delineated with a white line. Iceberg

C33b is delineated with an orange line. b Fast ice extent around iceberg C33b on April 21, 2016 with isobaths overlaid. c Maximum fast ice

extent observed in winter 2015

1158 Sci. Bull. (2016) 61(15):1157–1159

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Glacier Tongue to the east of Inexpressible Island and

extend approximately 3.5 km outward.

The worsening fast ice condition in this region can have

a severe impact on the research activities of nearby sci-

entific stations (Mario Zucchelli Station of Italy, Gond-

wana Station of Germany and Jang Bogo Station of Korea)

and the migration and foraging of penguins. If the fast ice

continues to grow southward, it will create new challenges

for site selection for construction of the new scientific

research station of China, which was planned on the

Inexpressible Island. The calving of the NIS may cause the

disintegration of melange that filled the north coast of the

DIT and decreases its support on the north side. Additional

crevasses are expected to appear on the southern side of the

DIT in the near future.

Our report can provide additional information for the

new scientific research station of China and early warnings

for nearby scientific research activities. In future studies,

we will monitor the local fast ice extent and iceberg

stranding state and analyze the potential impacts of this

calving event.

Acknowledgments This study is funded by the National Basic

Research Program of China (2012CB957704), the National Natural

Science Foundation of China (41176163), the Specialized Research

Fund for the Doctoral Program of Higher Education (201200031

10030), the Strategic Research Fund Program of Polar Science

(20140301), the Project of International Cooperation and Exchanges

CHINARE (IC201203).

Conflict of interest The authors declare that they have no conflict of

interest.

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