Arctic Ice Shelves: An Introduction

Abstract

Ice shelves are relatively thick ice masses that are afloat but attached to coastal land rather than adrift. They form by the seaward extension of glaciers or ice sheets or by build up of multiyear landfast sea ice. They thicken further by surface accumulation of snow and superimposed ice and by accretion of ice from water beneath. Composite ice shelves are composed of sea ice and glacier ice. Glacier tongues are floating ice margins that are narrow relative to their length. Ice shelves comprise 55% or 18,000 km of the Antarctic coast. ‘Classical’ Antarctic ice shelves are fed from glaciers or ice streams and are dynamically part of the parent ice sheet; the largest, the Ross and Ronne, are 105 km2 and hundreds of metres thick. Where they ground on isolated bedrock peaks, ‘ice rises’ are formed. Arctic ice shelves are restricted to several archipelagos fringing the Arctic Ocean and to a few Greenland fjords. The Ward Hunt Ice Shelf is the largest at about 400 km2. Arctic and Antarctic ice shelves have expanded and contracted during the Holocene. The Ellesmere Ice Shelf developed about 5500 years ago in response to Holocene cooling. In the warmer Twentieth century, calving events have broken this continuous ice-shelf into several remnants. Floating glacier tongues of the Greenland Ice Sheet have also broken up recently. The entire Arctic Ocean may have been covered by a huge ice shelf during the coldest Late Cenozoic glacial periods. Large, often tabular icebergs calve from ice shelves. Ice islands are a form of tabular iceberg in the Arctic Ocean which have a characteristic undulating surface. Icebergs drift mainly under the influence of currents and Arctic Ocean ice islands have been used occasionally as research stations.

Full text

3© Springer Science+Business Media B.V. 2017
L. Copland, D. Mueller (eds.), Arctic Ice Shelves and Ice Islands, Springer Polar
Sciences, DOI10.1007/978-94-024-1101-0_1
Chapter 1
Arctic Ice Shelves: AnIntroduction
JulianA.Dowdeswell andMartinO.Jeffries
Abstract Ice shelves are relatively thick ice masses that are aoat but attached to
coastal land rather than adrift. They form by the seaward extension of glaciers or ice
sheets or by build up of multiyear landfast sea ice. They thicken further by surface
accumulation of snow and superimposed ice and by accretion of ice from water
beneath. Composite ice shelves are composed of sea ice and glacier ice. Glacier
tongues are oating ice margins that are narrow relative to their length. Ice shelves
comprise 55% or 18,000km of the Antarctic coast. ‘Classical’ Antarctic ice shelves
are fed from glaciers or ice streams and are dynamically part of the parent ice sheet;
the largest, the Ross and Ronne, are 105 km2 and hundreds of metres thick. Where
they ground on isolated bedrock peaks, ‘ice rises’ are formed. Arctic ice shelves are
restricted to several archipelagos fringing the Arctic Ocean and to a fewGreenland
fjords. The Ward Hunt Ice Shelf is the largest at about 400km2. Arctic and Antarctic
ice shelves have expanded and contracted during the Holocene. The Ellesmere Ice
Shelf developed about 5500 years ago in response to Holocene cooling. In the
warmer Twentieth century, calving events have broken this continuous ice-shelf into
several remnants. Floating glacier tongues of the Greenland Ice Sheet have also
broken up recently. The entire Arctic Ocean may have been covered by a huge ice
shelf during the coldest Late Cenozoic glacial periods. Large, often tabular icebergs
calve from ice shelves. Ice islands are a form of tabular iceberg in the Arctic Ocean
which have a characteristic undulating surface. Icebergs drift mainly under the
inuence of currents and Arctic Ocean ice islands have been used occasionally as
research stations.
Keywords Ice shelf • Glacier • Sea ice • Sikussak • Surface accumulation • Bottom
accretion • Iceberg • Ice Island • Ellesmere Island • Greenland • Severnaya Zemlya
• Franz Josef Land
J.A. Dowdeswell (*)
Scott Polar Research Institute, University of Cambridge, Cambridge, UK
e-mail: jd16@cam.ac.uk
M.O. Jeffries
Ofce of Naval Research, Arctic and Global Prediction Program, Arlington, VA, USA
e-mail: martin.jeffries@navy.mil
derek.mueller@carleton.ca

4
1.1 Introduction
The cryosphere, all those parts of the Earth that are frozen, has a number of compo-
nents: permafrost; snow; freshwater ice on lakes and rivers; sea ice and icebergs on
the ocean; glaciers and ice sheets; and ice shelves. Among the ice categories, the
thickness ranges from a few millimetres to metres (freshwater and sea ice), to hun-
dreds to thousands of metres (glaciers and ice sheets). Ice shelves, ranging in thick-
ness from tens to hundreds of metres, fall between the two extremes. Simply dened,
an ice shelf is a relatively thick ice mass that is aoat on the ocean but attached to
coastal land rather than free to drift under the inuence of winds and currents, as
happens to sea ice and icebergs.
Ice shelves are common at the seaward margins of the modern Antarctic Ice
Sheet, where about 55% of the coast is made up of these oating ice features
(Fig.1.1) (e.g. Drewry etal. 1983; Griggs and Bamber 2011; Pritchard etal. 2012).
The largest of the Antarctic ice shelves, the Ross and Ronne, are 105 km2 in area and
hundreds of metres thick. In the Arctic, ice shelves are much smaller and fewer than
in the Antarctic. For example, the most extensive individual ice shelf in the Arctic,
the Ward Hunt Ice Shelf, Nunavut, Canada, is, at about 224km2, three orders of
magnitude smaller than the large Antarctic ice shelves. Geographically, the Arctic
Fig. 1.1 Map of the Antarctic, with the locations of the major ice shelves shown
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ice shelves are restricted to several of the high-Arctic archipelagos that fringe the
Arctic Ocean (Dowdeswell 2017; Jeffries 2017) and to the fjords of Greenland,
where a number of fast-owing glaciers drain the Greenland Ice Sheet to the sea
(Fig.1.2) (Reeh 2017).
This book is concerned primarily with the Ellesmere Island ice shelves of the
Canadian High Arctic, but it also describes Eurasian and Greenlandic ice shelves
(Dowdeswell 2017; Reeh 2017). The aims of this chapter are to introduce the gen-
eral characteristics and signicance of modern Arctic ice shelves. We begin by
developing a general denition of an Arctic ice shelf and describe the three main
types of Arctic ice shelf and how they differ from ‘classical’ Antarctic ice shelves.
The chapter continues with sections on the types and distribution of ice shelves,
their physics and mass balance, ice shelves and environmental change, and the ice-
bergs and ice islands that are produced by calving from them.
1.2 Dening anArctic Ice Shelf
In the rst paragraph we dened an ice shelf simply as a relatively thick ice mass
that is aoat on the ocean but attached to the land (coast) rather than free to drift
under the inuence of winds and currents. This basic picture quickly becomes more
complex when factors such as the morphology, thickness, mass balance, ice sources
and composition of ice shelves are considered.
This complexity was recognized by Barkov (1985), who proposed a sixteen-
category genetic classication for Antarctic ice shelves, each category being dened
by the type of ice that formed the main mass at the time of initial ice-shelf forma-
tion, and the direction of subsequent mass transfer at the top and bottom surfaces.
Vaughan (1998) proposed a simpler nine-category classication for both Antarctic
and Arctic ice shelves, each category being dened by the dominant source of input
(from glacier ow, in situ surface accumulation or basal accretion) and the dominant
route for ablation (by iceberg calving, surface melting/sublimation or basal melt-
ing). According to Vaughan, there are well-documented contemporary examples of
ice shelves for six of the nine possible categories. Thus, in the Canadian Arctic, the
Ward Hunt Ice Shelf falls within Vaughan’s Type E; that is, build up through basal
accretion and mass loss mainly by surface melting/sublimation. The continuing dis-
integration of part of this ice shelf, however, would also put it in Vaughan’s Type C,
with iceberg calving being the dominant mechanism of mass loss. In the Eurasian
Arctic, the Matusevich Ice Shelf on Severnaya Zemlya, which largely disintegrated
in 2012 (Willis etal. 2015), would be Vaughan’s Type A, with glacier input and
calving loss (Williams and Dowdeswell 2001).
To dene an Arctic ice shelf, we return to one of the earliest, and most simple,
denitions of an ice shelf (Armstrong etal. 1966):
A oating ice sheet of considerable thickness attached to the coast. Ice shelves are usually
of great horizontal extent and have a level or undulating surface. They are nourished by
accumulation of snow and often by seaward extension of land glaciers. Limited areas may
be aground
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6
Fig. 1.2 Maps of the Arctic with the locations of several major ice shelves, oating ice tongues
and glaciers indicated. (a) Greenland and the Canadian Arctic. DJG is Daugaard Jensen Gletscher,
East Greenland. KF is Kangerlussuaq Fjord, East Greenland. NEIS refers to the northern Ellesmere
Island ice shelves, including Ward Hunt, Milne and Serson ice shelves. NHFG is Niohalvfjerdsfjorden
Gletscher, East Greenland. NS is Nares Strait. RG is Ryder Gletscher, NW Greenland. (b) Eurasian
Arctic, MIS is Matusevich Ice Shelf on Severnaya Zemlya
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7
However, there are also ice shelves that are nourished, or originate, from other
sources. This is indeed the case in the Arctic, where sea ice is a signicant compo-
nent of some ice shelves (Jeffries 2017), as indicated by the denition of fast ice
(Armstrong etal. 1966):
Sea ice which remains fast along the coast, where it is attached to the shore, to an ice wall,
to an ice front, or over shoals, or between grounded icebergs. Fast ice may extend a few m
or several km from the shore. Fast ice may be more than a year old. When its surface level
becomes higher than about 2m above sea level, it is called an ice shelf
Combining the essential genetic elements of these two denitions, an ice shelf is
an ice mass that forms by the seaward extension of glaciers or the formation of
multiyear sea ice, or both, and thickens further by the accumulation of snow.
However, from a genetic perspective, this denition remains incomplete, as it does
not include ice accretion at the bottom surface, which is now known to be a relatively
common process (e.g. Jenkins and Doake 1991; Jeffries 1992a; Wen etal. 2010).
We now have the essential genetic elements (glaciers, sea ice, snow accumula-
tion, bottom accretion) for a denition of an Arctic ice shelf, but the morphology or
appearance, particularly of the top surface, is also an important element, as recog-
nized by the denition of an ice island (Armstrong etal. 1966):
A form of tabular berg found in the Arctic Ocean, with a thickness of 30-50m and from a
few thousand square m to 500 square km in area. Ice islands often have an undulating sur-
face, which gives them a ribbed appearance from the air.
The ribbed appearance of the original ice islands that were discovered in the late
1940s is inherited from their source; the ice shelves of northernmost Ellesmere
Island (Koenig etal. 1952). While the Ellesmere ice shelves are generally consid-
ered to be the main source of ice islands, Higgins (1989) drew attention to the fact
that large tabular icebergs with an undulating surface also calve from the long oat-
ing glacier tongues in the fjords of northernmost Greenland.
Finally, we note a minor contradiction between the minimum thickness of an ice
shelf originating from sea ice (20 m, as inferred from a surface elevation of 2m
above sea level) and the minimum thickness of an ice island (30 m). Given that sea-
ice formation is an essential element of the Ellesmere ice shelves, the source of the
original ice islands, we choose 20m as a minimum thickness for an Arctic ice shelf
or, by implication, an ice island.
Now we are in a position to propose a general denition of an Arctic ice shelf that
includes morphological and genetic elements, and thickness:
An ice mass of considerable thickness (≥20 m) that is aoat on the ocean but attached to the
coast. It is often of great horizontal extent (many km) and has, typically but not exclusively,
a regularly undulating surface. An ice shelf can form by the seaward extension of a glacier
or glaciers, or by the formation of multiyear sea ice, or both, and thicken further by the
accumulation of snow at the top surface and the accretion of ice from water at the bottom
surface.
In the next section, we begin with a description of the ‘classical’ type of ice shelf
that is typically associated with Antarctica, and then describe the three types of
Arctic ice shelf that are the subject of this book; each is sufciently different from
the ‘classical’ ice shelf to warrant separate description.
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8
1.3 Types andDistribution ofIce Shelves
1.3.1 ‘Classical’ Ice Shelf
The ‘classical’ ice shelves comprise most of the oating margins of the Antarctic
Ice Sheet (Fig.1.1). They extend up to hundreds of kilometres seaward of a ‘ground-
ing zone’ where glaciers and ice sheets become decoupled from the bed and reach
hydrostatic equilibrium with the underlying water. Often originating from many
glaciers and/or ice streams that coalesce in very large embayments, these ‘classical’
ice shelves, such as the Ross, Ronne and Amery, are dynamically a part of the parent
ice sheet. The largest Antarctic ice shelves are over a thousand metres thick at the
grounding zone, thinning to roughly 200–300m at their seaward fronts (Dowdeswell
and Bamber 2007; Griggs and Bamber 2011; Fretwell etal. 2013), which can be
several hundred kilometres long and a similar distance from the grounding zone.
These ice shelves form extensive areas of low-gradient ice (Fretwell etal. 2013),
with water hundreds of metres deep beneath them. Where their beds come into con-
tact with isolated bedrock peaks, basal shear stress and ice-surface-gradient increase,
forming domes known as ‘ice rises’. Ice rises are easily identied on otherwise at
ice-shelf surfaces (Fig.1.3a).
About 18,000km of the seaward margin of the Antarctic Ice Sheet is aoat, with
about 14,000km of the coastline being made up of ‘classical’ ice shelves and a
further 4000km being outlet glaciers and ice streams with oating tongues (Fig.1.1)
(Drewry etal. 1983). The huge Ross, Ronne and Amery ice shelves extend up to
450km from grounding zone to terminus and are about 300m thick at their margins
(Dowdeswell and Bamber 2007; Griggs and Bamber 2011). A large number of
smaller fringing ice shelves, often only about 200m thick at their margins and with
ow lines of tens of kilometres, are located around both West and East Antarctica,
and the Antarctic Peninsula (e.g. Getz, Shackleton, Larsen C ice shelves; Fig.1.1).
In the Arctic, the Milne Ice Shelf of northernmost Ellesmere Island, conned
within the steep-sided Milne Fiord, is composed of a number of small coalesced
glacier tongues (Jeffries 1986, 2017). As such, it is probably the closest of all the
Ellesmere ice shelves to being a classical ice shelf.
1.3.2 Glacier Tongue
By contrast with ‘classical’ ice shelves, a glacier tongue (sometimes also referred to
as an ice tongue) is a oating ice margin that is narrow relative to its length (Hambrey
1994). Glacier tongues are usually fed from fast-owing outlet glaciers or ice
streams, which are constrained by valley sides or are bounded laterally by shear
zones between fast- and slow-owing ice, respectively. In either case, fast-owing
ice is conned to linear or curvilinear laments within the ice sheet (Bamber etal.
2000) and the oating tongues represent the terminus regions of these ice masses.
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9
In the Antarctic, a number of glacier tongues extend well beyond constraining
mountains and into the open ocean beyond (Fig.1.3b); examples include the Erebus,
Drygalski and Mertz glacier tongues (e.g. McIntyre 1985). Some of these ice
tongues, usually less than 100km long, are sources for among the thickest oating
ice around Antarctica, with termini of 400 to 600 m in thickness (Fig. 1.3b)
(Dowdeswell and Bamber 2007).
In the Arctic, glacier tongues are often conned to fjords, with the mountainous
rock walls of a number of Greenland glacier tongues providing clear examples
(Fig.1.3c) (e.g. Higgins 1989, 1990; Mayer etal. 2000; Enderlin and Howat 2013).
The very large (104 km2 in area) interior basins of the Greenland Ice Sheet are
drained by about fteen fast-owing outlet glaciers that have eroded deep valleys
and troughs through the fringing mountains (e.g. Rignot and Kanagaratnam 2006;
Reeh 2017). The margins of a number of these outlet glaciers form oating ice
tongues in fjords which can exceed 1000m in water depth (e.g. Nick etal. 2012).
The ice tongues are often less than 10km long, but can be as much as a few tens of
kilometres in length, with a marginal thickness of about 400–600m. The largest
example is Niohalvfjerdsfjorden Gletscher, at 79°N in NE Greenland (Fig.1.2a),
which has a 60 km-long oating terminus (Mayer etal. 2000). The Greenland gla-
cier tongues are described in more detail by Reeh (2017).
Fig. 1.3 Photographs of Antarctic and Arctic ice shelves. (a) Larsen C Ice Shelf and Gipps Ice
Rise, eastern Antarctic Peninsula (Photo: C.W.M.Swithinbank). The ice rise is about 18km long.
(b) A oating glacier tongue, 2–4km wide, embedded in sea ice immediately north of the larger
Aviator Glacier Tongue, Victoria Land Coast, Antarctica (Photo: J.A.Dowdeswell). (c) The oat-
ing margin of Daugaard Jensen Gletscher, East Greenland (Photo: J.A.Dowdeswell). (d) The Ward
Hunt Ice Shelf, northern Ellesmere Island, Arctic Canada (Photo: D.R.Mueller)
1 Arctic Ice Shelves: AnIntroduction
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10
Finally, it should be noted that glacier tongues and tidewater glaciers are not
synonymous. Whereas an ice tongue is aoat, tidewater glaciers are grounded; that
is, resting entirely on the sea oor (but still able to calve icebergs). In principle, a
tidewater glacier could become an ice tongue if thinning and/or sea-level rise made
it sufciently buoyant to oat.
1.3.3 Sea-Ice Ice Shelf
Unlike classical ice shelves and glacier tongues, which are both composed mainly
of glacier ice, some ice shelves owe their origin to sea-ice growth and remain com-
posed predominantly of sea ice. Lemmen etal. (1988) coined the term ‘sea-ice ice
shelf’ for these ice shelves. The best-known example of a sea-ice ice shelf, the
40–50m thick and ~224km2 Ward Hunt Ice Shelf (Fig.1.3d), is the largest remnant
of the former Ellesmere Ice Shelf. Extending tens of kilometres offshore and hun-
dreds of kilometres alongshore in the early years of the twentieth century (Koenig
etal. 1952), the Ellesmere Ice Shelf was, in all likelihood, predominantly a sea-ice
ice shelf. Sea-ice ice shelves form initially from multiyear fast ice (also known as
multiyear landfast sea ice, MLSI; Jeffries etal. (1989)), often in sheltered inlets and
embayments, but also along more exposed stretches of coast where multiyear pack
ice provides protection from the inuence of the open ocean. The multiyear landfast
sea ice acts as a platform, or basement, for further thickening by both snow and
superimposed ice accumulation at the top surface and accretion of ice from the
water at the bottom surface. As indicated by the denition of fast ice in the previous
section, sea-ice ice shelves are at least 20m thick.
1.3.4 Composite Ice Shelf
A composite ice shelf is composed of both sea ice and glacier ice (Lemmen etal.
1988). The Serson Ice Shelf on Ellesmere Island was a good example of a compos-
ite ice shelf until summer 2008, when much of the sea ice unit and two glacier
tongues calved and drifted away. The Serson Ice Shelf is now composed largely of
just two remaining glacier tongues. The original glacier tongues that owed off-
shore to form the glacier component of the ice shelf were clearly visible as ‘la-
ments’ of glacier ice (Jeffries 2017), as were the glacier tongues that formed part of
Ice Island ARLIS II (Smith 1964), which calved from the Serson Ice Shelf in the
mid-1950s (Jeffries 1992b).
In Greenland, the Inuit use the term ‘sikussak’ to describe the mélange of multi-
year landfast sea ice and icebergs that is typically found in protected High Arctic
fjords (Fig.1.4). The many icebergs trapped in multiyear sea ice at the southern end
of Yelverton Fiord, and in Disraeli Fiord to the south of the disintegrating Ward
Hunt Ice Shelf, are examples of sikussak on Ellesmere Island. Extensive areas of
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11
sikussak have also been reported in North and North-East Greenland (Koch 1945),
including that in Sherard Osborne Fjord, into which Ryder Gletscher drains, where
icebergs up to about 10km in length have been observed trapped in the multiyear
landfast sea ice (Higgins 1989). Recently, the term ‘ice mélange’ has been adopted
by many workers to describe the mix of sea-ice oes and icebergs found in Greenland
fjords with calving glaciers at their heads (e.g. Amundson etal. 2010; Cassotto
etal. 2015).
In principle, continued thickening of sikussak, by accumulation of snow and ice
at the top surface and accretion of ice at the bottom surface, could produce a form
of composite ice shelf; the glacier component being icebergs that have calved from
glaciers, rather than being glacier tongues that have owed seaward from the ice
sheet. More normally, sikussak or ice mélange breaks up at timescales that range
from seasonal to decadal, with the release of trapped icebergs and a series of large
multiyear ice oes (e.g. Reeh etal. 1999; Dowdeswell etal. 2000; Cassotto etal.
2015).
Sikussak-like ice is also found in the Eurasian Arctic, where calving outlet gla-
ciers mix with multiyear landfast sea ice. In Matusevich Fjord, Severnaya Zemlya
(Fig.1.2b), for example, where sea ice has persisted for many years, it contains
icebergs from outlet glaciers which enter the fjord from the surrounding ice caps
(Williams and Dowdeswell 2001). However, the few ice shelves that do exist in the
Eurasian Arctic, in Severnaya Zemlya and Franz Josef Land, are formed mainly
from glacier ice rather than the build up of old sea ice (Dowdeswell 2017).
Fig. 1.4 Sikussak; a frozen ice mélange of multiyear sea ice and icebergs, Kangerlussuaq Fjord,
East Greenland. Landsat ETM+ image, path 229 row 012, 16 August 2002
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1.4 Physics andMass Balance ofIce Shelves
Ice shelves are, for the most part, fully buoyant, in hydrostatic equilibrium with the
underlying water (Robin 1979). Close to the grounding zone, at their lateral margins
and at any pinning points where they ground on bedrock pinnacles as ‘ice rises’
(Fig.1.3a), a part of their mass may be supported by the bed and side walls. Ice
shelves have very low-gradient surfaces because, at the almost frictionless contact
with the water beneath, the basal shear stress approaches zero. Ice shelves thin
under their own weight by internal deformation, a process that is most rapid in
unbounded ice shelves without side walls or pinning points where they touch the sea
oor. Creep thinning is responsible, in part, for the systematic reduction in ice thick-
ness with distance from the grounding zone. In an unbounded ice shelf, creep or
deformation thinning is approximately proportional to the fourth power of ice thick-
ness (Weertman 1957; Robin 1979; Thomas 1979).
The mass balance of ice shelves is the sum of gains and losses of mass to the
system, usually measured over a balance year (from one late-summer to the next).
An ice shelf is in equilibrium when these gains and losses are approximately equal.
Classical ice shelves and ice tongues that are fed from a parent glacier or ice-sheet
drainage basin gain mass in several ways; by advection of ice across the grounding
zone owing from an ice-sheet interior, by accumulation of snow on the ice shelf
surface and by adfreezing of sea water at the bottom surface. Mass is lost by iceberg
production, known as calving, by surface melting (and sometimes sublimation), and
by basal melting at the ice-ocean interface.
At the base of large Antarctic ice shelves, basal melting generally occurs close to
the grounding zone and towards the ice margin. Basal melting can reach more than
10m year−1 near the grounding zone (e.g. Jenkins etal. 1997; Rignot etal. 2013).
Dense (cold and saline) ocean water, often formed by sea-ice production beyond the
ice-shelf edge, usually ows in towards the grounding zone along the sea oor,
which typically slopes inshore due to ice-sheet loading and isostatic depression. The
water becomes less dense as it mixes with meltwater close to the grounding line
and, thus, ows up the ice-shelf basal boundary as it become more buoyant. As it
rises, pressure decreases, the melting point is raised, and supercooled water may
freeze to the ice-ocean interface (Jenkins and Doake 1991). This process can lead to
the accretion of tens of metres of sea-water derived ice at the ice shelf base. Ice core
and radar studies of Antarctic ice shelves have shown a three-part structure; glacier
ice derived by ow from continental drainage basins is sandwiched between densi-
ed snow from accumulation on the ice-shelf surface, and sea-water derived ice
frozen on at the oating ice-shelf base (Jenkins and Doake 1991; Fricker et al.
2001).
While their dimensions are certainly smaller, the Arctic ice shelves are similar, in
many respects, to the Antarctic ice shelves in terms of mass balance and physics.
Glaciers nourish part or all of some Arctic ice shelves, for example those of
Greenland and the Russian Arctic. In the case of the Ellesmere ice shelves, there
has been in situ surface accumulation of snow and superimposed ice, in addition to
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13
sea- ice thickening, although superimposed ice is currently being lost during a
prolonged period of surface melting and negative surface mass balance in summer
(Braun 2017; Jeffries 2017). The Arctic ice shelves also lose mass by iceberg (ice
island) calving and bottom melting. Basal melting close to the grounding zones of
Greenland ice tongues is often several metres to tens of metres per year (Rignot and
Kanagaratnam 2006; Enderlin and Howat 2013). Unlike most of their Antarctic
counterparts, however, surface melting is also important on Arctic ice shelves.
Bottom accretion is also known to occur on the Ellesmere ice shelves (Jeffries
2017). It is the nature of bottom accretion that perhaps distinguishes the Ellesmere
ice shelves from their larger Antarctic counterparts; that is, bottom accretion com-
monly involves the freezing of fresh and brackish waters as well as seawater (Jeffries
2017). The primary source of fresh and brackish waters is drainage from epishelf
lakes, which form behind the dam-like ice shelves. An epishelf lake is a tidal body
of low-salinity water which, because of its lower density, “oats” on seawater. The
epishelf lake in Disraeli Fiord to the south of the Ward Hunt Ice Shelf, and the role
of the positive feedback that occurs between them in the mass balance of the ice
shelf, are discussed in Jeffries (1991).
1.5 Ice Shelves andEnvironmental Change
In both the Arctic and the Antarctic there is evidence that ice shelves have expanded
and contracted during the Holocene. The Ellesmere Ice Shelf appears to have devel-
oped about 5500 years ago as a response to cooling after the Early Holocene cli-
matic optimum (Koerner and Fisher 1990; England etal. 2008; England etal. 2017).
At the beginning of the Twentieth century, at the end of the centuries-long cold
interval known as the ‘Little Ice Age’, the ice shelf extended unbroken for about
500 km with an area of 8900 km2 along the coast of northern Ellesmere Island
(Vincent etal. 2001). Since then, a series of calving events has broken the once
single, continuous ice-shelf fringe into a number of small and isolated remnants
(Mueller etal. 2017).
The oating tongues of several fast-owing outlet glaciers of the Greenland Ice
Sheet have also broken up in recent years; a consequence, in part at least, of the
northward penetration of relatively warm Atlantic water into Greenland fjords,
enhancing basal melting and thinning of the oating ice tongues (Holland et al.
2008; Christoffersen etal. 2011). Conversely, in periods of climatic cooling, such as
the Little Ice Age or the Younger Dryas stadial, colder conditions would apply to
more parts of the Arctic coastline and multiyear landfast sea ice and sikussak would
be expected to spread southward, especially into fjords and protected inlets (Reeh
etal. 1999; Dowdeswell etal. 2000). The presence of sikussak is also thought to
help stabilize and protect oating glacier tongues from mass loss by iceberg calving
(Reeh etal. 2001; Amundson etal. 2010; Cassotto etal. 2015).
At longer time scales, it has been suggested that the entire Arctic Ocean may
have been covered by a huge ice shelf in one or more of the longest and coldest
1 Arctic Ice Shelves: AnIntroduction
derek.mueller@carleton.ca

14
full- glacial periods in the Late Cenozoic (Mercer 1970). Sea-oor morphological
features, interpreted by some to represent regions of ice-shelf grounding, have been
observed on, for example, the Lomonosov Ridge and the Yermak Plateau in the
Arctic Ocean (e.g. Vogt etal. 1994; Polyak etal. 2001; Jakobsson 2016). The dating
of such events is still uncertain, but it appears that a major ice shelf may have occu-
pied the whole Arctic Basin at about 660,000 years ago (e.g. Vogt etal. 1994; Flower
1997), and that ice shelves may also have developed around at least the fringes of
the deep-water basin during Marine Isotope Stage 6 about 140–160,000 years ago
(Jakobsson etal. 2010, 2014, 2016).
In the Antarctic, too, considerable variability in Holocene ice-shelf extent has
been demonstrated. Although the relatively large Larsen B Ice Shelf appears not to
have disintegrated in the Holocene prior to its collapse in 2002 (Domack etal.
2005), smaller ice shelves on the Antarctic Peninsula disappeared in the mid-
Holocene and reformed about 2000 years ago (Pudsey and Evans 2001). More
recent, dramatic retreat or disintegration of a number of ice shelves on the Antarctic
Peninsula has been observed from satellite imagery over the past two decades and
linked with climate warming (e.g. Doake and Vaughan 1991; Vaughan and Doake
1996; Scambos etal. 2003; Cook and Vaughan 2010). The rapid ice-shelf disinte-
gration in the Antarctic Peninsula has been ascribed to surface meltwater penetra-
tion into crevasses, which then deepen to the ice-shelf base to cause break-up (e.g.
Scambos etal. 2003; Banwell etal. 2013), although enhanced basal melting and
thinning due to warming ocean waters has also been implicated (Shepherd etal.
2003). A mean summer air temperature of about 0°C is thought to represent an
empirical upper climatic limit for the viability of Antarctic ice shelves (Robin and
Adie 1964), and Vaughan and Doake (1996) make a similar suggestion concerning
the −5°C mean annual isotherm. It has been proposed that, because of this empirical
air temperature threshold, ice shelves may represent a particularly sensitive indica-
tor of climate change (Mercer 1978; Vaughan and Doake 1996).
1.6 Icebergs andIce Islands
Relatively large, often tabular icebergs calve from ice shelves (e.g. Dowdeswell
etal. 1992; Dowdeswell and Bamber 2007). They are known as ‘tabular’ for their
characteristically steep sides and low-gradient, regular surface, and are often kilo-
metres to tens of kilometres in length (Fig.1.5a, b). They contrast with the smaller
and more irregular icebergs typically produced from grounded tidewater- glacier
margins (Fig.1.5c), where the relatively close spacing of marginal crevasses means
that few large icebergs are produced (Dowdeswell and Forsberg 1992). The oating
tongues at the margins of the outlet glaciers of the Greenland and Antarctic ice
sheets produce the deepest-keeled icebergs at about 400–600 m (Dowdeswell
etal. 1992; Dowdeswell and Bamber 2007). The Ross and Ronne ice shelves in
Antarctica produce thinner icebergs, characteristically about 300m thick, because
J.A. Dowdeswell and M.O. Jeffries
derek.mueller@carleton.ca

15
creep thinning and basal melting reduce ice-shelf thickness along owlines that
extend several hundred kilometres beyond the grounding zone.
The tabular icebergs, more commonly known as ice islands (Fig.1.5d), that calve
from the Ellesmere ice shelves have typically been up to 50m thick (e.g. Copland
etal. 2007; Jeffries 2017). Jeffries (1992a) dened an ice island as ‘a tabular iceberg
which has broken away or calved from an Arctic ice shelf. They have a gently undu-
lating surface which gives them a ribbed appearance from the air’. A fuller descrip-
tion of the morphology and characteristics of the Ellesmere ice islands is provided
by Jeffries (2017) and Van Wychen and Copland (2017). Although Higgins (1989)
also used the term ‘ice island’ to describe the tabular icebergs that calve from the
glacier tongues of North Greenland, many of the icebergs produced from fast-
owing outlet glaciers of the Greenland Ice Sheet have a surface dominated by
heavy crevassing rather than being gently undulating (Fig.1.5b); they are also an
order of magnitude thicker than the Ellesmere ice islands (Dowdeswell etal. 1992).
Thus, the term ‘ice island’ is usually restricted to icebergs derived from the Ellesmere
ice shelves.
Once calved, and providing they do not become trapped by the shallow sills
found in many fjords (Syvitski etal. 1987), icebergs drift in the ocean mainly under
Fig. 1.5 Photographs of icebergs from the Antarctic and Arctic seas. (a) A tabular iceberg about
1km long in Pine Island Bay, West Antarctica (Photo: J.A.Dowdeswell). (b) Heavily crevassed
tabular iceberg (about 1km long) calved from the oating tongue of the fast-owing Daugaard
Jensen Gletscher, East Greenland (Photo: J.A.Dowdeswell). (c) Relatively small icebergs (<100m
long) of irregular shape calved from a grounded tidewater glacier margin, Austfonna, eastern
Svalbard (Photo: J.A.Dowdeswell). (d) Hobson’s Choice Ice Island, calved from the Ward Hunt
Ice Shelf, northern Ellesmere Island (Photo: M.O.Jeffries)
1 Arctic Ice Shelves: AnIntroduction
derek.mueller@carleton.ca

16
the inuence of currents. Icebergs gradually deteriorate by fragmentation due to
exure in ocean-swell waves (Kristensen etal. 1982) and by melting as they oat
into warmer waters (e.g. Weeks and Campbell 1973; Enderlin and Hamilton 2014).
In the Arctic Ocean, several ice islands are known to have circulated for many years
in the Beaufort Gyre before becoming entrained in the Transpolar Drift and drifting
south via Fram Strait into the North Atlantic Ocean along the east coast of Greenland
(e.g., Jeffries 1992a; Van Wychen and Copland 2017). Icebergs calving from East
Greenland outlet glaciers take a similar path. Ice islands also drift into the inter-
island channels of the Canadian Arctic Archipelago (Koenig etal. 1952; Jeffries and
Shaw 1993; Copland etal. 2007), and into Bafn Bay via Nares Strait (Nutt 1966),
the channel separating Ellesmere Island from Greenland (Fig.1.2a). Icebergs pro-
duced from north-west Greenland outlet glaciers follow a similar route, and those
which calve directly into Bafn Bay from West Greenland can circle the bay anti-
clockwise before reaching the waters off Labrador and Newfoundland (Robe 1980;
Van Wychen and Copland 2017).
Because of their large size and relative stability, ice islands that have entered the
Arctic Ocean have been used occasionally as platforms for drifting research stations
by the USA, Canada and the Soviet Union/Russia (Althoff 2017; Belkin and Kessel
2017). In addition to supporting scientic investigations of the atmosphere, sea ice,
ocean and seaoor, the ice islands themselves have revealed much about the ice
shelves from which they calved (e.g. Jeffries 1992a, 2017).
1.7 Summary
The interface between ice sheets and the ocean can be made up of either oating ice
shelves or grounded tidewater glaciers. Antarctic ice shelves, and some in the Arctic,
are fed from fast-owing ice streams and outlet glaciers advecting mass from inte-
rior ice-sheet drainage basins to their termini to offset mass loss through iceberg
production and basal melting. The ice shelves of northern Ellesmere Island in the
Canadian High Arctic, although much smaller than they were only 100 years ago,
remain the largest in the circum-Arctic. They are distinguished by the role that mul-
tiyear landfast sea ice has often played in their expansion. Further bottom accretion
of fresh and brackish ice, as well as sea ice, and the inow of glacier tongues to form
composite ice shelves of glacier ice and sea ice, means that the crystallographic and
geochemical characteristics of the Ellesmere ice shelves differ from those ice
shelves located at ice-sheet margins. Tabular icebergs (known as ice islands when
they have calved from the Ellesmere ice shelves) are produced by calving from the
margins of both glacier-fed and sea-ice ice shelves, but icebergs from the two
sources can usually be differentiated by their internal structure and surface character
(Fig.1.5).
In dening and reviewing the different types of ice shelf and iceberg that occur in
the Arctic and Antarctic, our aim has been to provide a general context for the more
detailed chapters of this book (Copland and Mueller 2017) that focus, in particular,
J.A. Dowdeswell and M.O. Jeffries
derek.mueller@carleton.ca

17
on the characteristics, history and human use of the ice shelves and ice islands found
in northern Ellesmere Island and the Arctic Ocean to the north. The distribution and
character of ice shelves and icebergs in the Canadian Arctic, Greenland and the
archipelagos of the Eurasian Arctic are also considered briey here, and in more
detail in Jeffries (2017), Dowdeswell (2017) and Reeh (2017), to provide a wider
geographical and glaciological perspective.
Acknowledgments Grants from the John Ellerman Foundation and the Arctic Environmental
Program of ConocoPhillips supported JAD for parts of this work. MOJ contributed to this work
while he was on leave from the University of Alaska Fairbanks and working on secondment from
2006 to 2010 at the National Science Foundation (NSF) under the terms of the Inter-Governmental
Personnel Act; any opinion, ndings, and conclusions or recommendations expressed in this mate-
rial are his and do not necessarily reect the views of either NSF or the Ofce of Naval Research.
We thank Toby Benham for his work with the gures.
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1 Arctic Ice Shelves: AnIntroduction
derek.mueller@carleton.ca