The Northeast Greenland Sirius Water Polynya dynamics and by pengxiuhui

VIEWS: 25 PAGES: 12

									      AL
         OF GEO
              GR          The Northeast Greenland Sirius Water Polynya
    JOURN




                          dynamics and variability inferred from satellite
                APHY 20



                          imagery
ISH




             10
       DAN




Jørn Bjarke Torp Pedersen, Laura Hauch Kaufmann, Aart Kroon & Bjarne Holm Jakobsen

Abstract                                                                with locations where significant concentrations of spring and summer
One of the most prominent polynyas in Northeast Greenland, already      settlements from the Thule Inuit culture (AD 1400-1850) are ob-
noted by the early expeditions in the area, is located around Shan-     served, indicating a connection between the presence of the polynya
non Ø and Pendulum Øer between 75° and 74°N in the transition           and the Thule Inuit living in the area in prehistoric times.
zone between the fast ice and pack ice. This study names the polynya
the ‘Sirius Water Polynya’, and examines its spatial and temporal       Keywords
dynamics by analysis of recent satellite imagery, modelled meteo-       Northeast Greenland, polynya, sea ice cover, satellite remote sens-
rological data and historical data covering the last decade. The        ing, Sirius Water Polynya.
dominating mechanisms to form and sustain the polynya are inferred
and the persistence and inter-annual variability of the phenomenon      Jørn Bjarke Torp Pedersen (Corresponding author)
are estimated. The polynya formation is predominantly governed by       Laura Hauch Kaufmann
mechanical forcing caused by northerly gales, and it is classified      Aart Kroon
as a wind-driven shelf water polynya. A marked seasonal difference      Bjarne Holm Jakobsen
in the surface wind field, together with the obvious seasonal cycle     Department of Geography and Geology, University of Copenhagen,
in insolation, creates distinct winter and summer regimes in the        Denmark
seasonal evolution of the polynya. During the winter regime, both       E-mail: jtp@geo.ku.dk
the size of and the ice cover within the polynya varies significantly
on a temporal and spatial scale. Intermittent wind-driven openings      Geografisk Tidsskrift
of the polynya alternate with periods of increasing ice cover. Some     Danish Journal of Geography 110(2):131-142, 2010
of the most persistent areas of open water in the polynya coincide




Introduction                                                            seal at specific sites. The open water areas were presum-
                                                                        ably preconditioning this culture and strictly determined the
The distribution of recurring areas of open water in an oth-            spatial variation of the density and location of settlements
erwise ice covered ocean (i.e., polynyas) is closely related            in the region over the seasons (Jakobsen et al., 2008; Sø-
to archaeological sites of prehistoric settlements in the high          rensen et al., 2008; Grønnow et al., in press). Throughout
Arctic area (e.g., Stirling, 1997). Prehistoric settlements             this paper, we name the open water areas collectively as the
close to recent olynyas have in turn served as indicators of            ‘Sirius Water Polynya’, as it is situated close to Daneborg,
the existence of these specific polynyas in past times (e.g.,           the headquarter of sledge patrol Sirius, in the middle of
the Northeast Water Polynya in Hjort, 1997). The presence               what to some people is known as ‘Siriusland’.
of and the access to a polynya with its marine-based life                   The relation between polynyas and an increased bio-
has been of vital importance to sustain human populations               logical productivity is well documented (Stirling, 1997;
for long periods of time (Stirling, 1997). The Thule Inuit              Morales Maqueda et al., 2004). Recurring polynyas are
culture inhabiting the Northeast Greenland area around                  ‘oases’ in a polar ocean desert, as they support a diverse
1400-1850 AD used a specialized subsistence strategy that               range of marine life forms on all trophic levels from ben-
included seasonal gatherings and large scale hunting of,                thic communities through spring and summer blooming
e.g., walrus, narwhale, ringed seal, harp seal and bearded              phytoplankton and zooplankton to migrating or overwin-


                                                                          Geografisk Tidsskrift-Danish Journal of Geography 110(2) 131
tering marine mammals and birds (e.g., Boertmann et al.,         hopefully lead towards a better understanding of the role
2009). These migrating or overwintering birds and mam-           it played for prehistoric settlements in the area. The study
mals depend on the existence of recurring polynyas during        is focused on the period 2007-2008 with special emphasis
the critical part of the year when the coastal sea is largely    on the late winter and spring condition, and supplemented
ice-covered. The ice-water interface supports an increased       with historic data. The late winter and spring seasons prob-
primary production and a general higher biomass of in-           ably had the strongest influence on the survival strategies
vertebrates and fish on which seabirds and mammals feed          of the Thule Inuit in the high arctic environment.
upon. Besides, the polynyas are surrounded by heavily
ice covered areas that constitutes important habitats for a
number of top predators depending on areas of open water         Physiographic setting of the study area
to breathe and feed. Finally, polynyas can lend protection
from predators, navigational aid to migrating species as         The study area is located in Northeast Greenland, between
well as areas of calmer water, which makes resting and           74°-75°N, around the peninsula Wollaston Forland and
diving for food easier than at open sea (Stirling, 1997).        the islands Shannon Ø, Pendulum Øer and Clavering Ø
    The biological resources and their accessibility in a        (Figure 1). The majority of the glacier-free coastal area
high Arctic ecosystem are to a great extent controlled by        of Northeast Greenland is a mountainous landscape, cut
environmental factors like the snow and ice coverage. The        by numerous fjord-systems, with a number of large bays,
snow coverage determines the length and quality of the           peninsulas and islands more or less exposed to the sea. The
growing season. The ice coverage and recurrent polynyas          coastal landscape is dominated by sedimentary features,
will steer the presence of and the access to the marine game     interrupted by features of glacial and periglacial origin as
animals over seasons, and has played a key role in the evo-      well as a mountainous relief of eroded bedrock, mainly
lution of the Thule Inuit culture in Northeast Greenland.        granite, gneiss and basalt (Jakobsen et al., 2008; Kroon et
The land-fast ice in the coastal waters may have constituted     al., 2009). The study area is located in a high arctic climate
an important route of transport in an otherwise not easily       zone with continuous permafrost. The complex topography
passable landscape during winter, and may have given             of the coast creates large contrasts in local weather condi-
passage to areas of open water during spring.                    tions and makes the climate vary considerably even over
    Estimates of the extent of the sea ice in the Greenland      short distances (Cappelen et al., 2000; Hinkler, 2005).
Sea prior to the satellite era were primarily derived from            The large scale circulation of the North Atlantic Ocean
ship- and ground-based observations. Lassen (1997, 1998)         plays a dominant role in the overall energy exchange of the
reported the deduced variation of the sea ice area from          entire region, and thus in determining the marine environ-
1877-1997 in the Greenland Sea showing large oscilla-            ment and ocean circulation in the Greenland Waters. In
tions superimposed on a general decreasing trend of sea          the Nordic Seas, the large scale circulation is dominated
ice coverage. Lassen & Thejll (2005) indicated that the          by the warm northward flowing Atlantic water on the east-
recently reported retreat of the ice in the Greenland Sea        ern side and the cold southward flowing East Greenland
may be related to the termination of the so-called Little
Ice Age in the early twentieth century.
    Since the 1970s, the extent of the sea ice coverage in
the Polar regions has been frequently measured with the
use of satellite-borne instruments. Multiple studies have
reported a general decreasing trend during the last decades
(e.g., Parkinson et al., 1999; Vinje, 2001; Johannesen et al.,
2004; Parkinson & Cavalieri, 2008). More detailed research
from a specific area in Northeast Greenland also indicates a
trend towards a prolonged open water period in the Young
Sound fjord during the last decade (Glud et al., 2007).
    The main aim of this study is to examine the spatial
and temporal extent and variability of the Sirius Water
Polynya by means of satellite imagery and historical data.
Explaining the extent and variability of the polynya will        Figure 1: Study area in Northeast Greenland.



132 Geografisk Tidsskrift-Danish Journal of Geography 110(2)
Current (EGC) on the western side (Foldvik et al., 1988;        Methods
Dickson et al., 2000; Buch, 2007). The EGC constitutes
a major coastal-shelf current, transporting relatively fresh    Satellite remote sensing images form the primary basis for
water from the Arctic Ocean together with ‘re-circulating’      the present analysis. The images are supported by meteo-
Atlantic water southward along the east coast of Greenland.     rological model data and historical ice charts and observa-
The near-shore areas and fjord systems are greatly affected     tions. There are no in situ measurements available from
by local conditions like bathymetry and shoreline exposure,     the polynya area (see Table 1 for data description). The
waves and freshwater input from river runoff during sum-        remote sensing method is based on visual interpretation of
mer (Kroon et al., 2009) and ice formation during winter        different types of satellite images, and is a widely used and
(Buch, 2002).                                                   internationally acknowledged method in ice-charting. The
    The EGC transports large amounts of polar ice from          method allows for a large amount of different information
the Arctic Ocean southward along the coast in a band that       to be considered and processed in each analysis.
may be up to several hundred kilometres wide (Woodgate              The sea ice classifications are carried out in accordance
et al., 1999; Rigor et al., 2002). This transport is ongoing    with the World Meteorological Organization (WMO) sea
throughout the year, although dampened during the sum-          ice nomenclature, including the Ice Egg Symbol (WMO,
mer (Schmith & Hansen, 2003). In the winter, additional         1970), as it offers an internationally standardized system
sea ice is formed within the entire coldwater area as new       and terminology and hence, a uniform method of classify-
ice and young ice is continuously formed in the pack ice        ing sea ice. In short, the Ice Egg Symbol states the total
in open leads between floes and in polynyas. In addition to     ice concentration, the concentration of the three thickest
oceanographic currents, wind has a major impact on the sea      ice types, the stage of development (ice thickness) and the
ice drift. As the pack ice drifts southward along the coast,    floe size. The total ice concentration is the most important
the floes are broken into continuously smaller pieces by        for the purpose of polynya demarcation.
wind, currents, sea swells and collision with other floes.          A detailed analysis of the evolution and dynamics of the
Turbulence causes churning and meandering and mixing            Sirius Water Polynya was carried out for the late winter/
of all ice types (Buch, 2007).                                  spring period of 2008 with the use of the available satellite
    The sea ice cover along the east coast of Greenland can     data sources (Table 1). This period was chosen because it
be divided into four different zones from land to sea, each     had sufficient and frequent satellite data coverage of good
with their own characteristic features and dynamics (Wad-       quality and resolution with many days of more or less cloud
hams, 1981; Buch, 2007): the land-fast ice zone, a transition   free conditions in the study area, and because this was the
zone, the pack ice zone and the marginal ice zone. The          time of year when the Thule Inuit left their winter houses
land-fast ice, or simply coastal fast ice, forms and grows      in the inner fjords and moved to the outer coast in search
seaward from the coast and remains stationary throughout        for mainly marine mammal game. The result of the analy-
the winter. The transition zone lies between coastal fast ice   sis was a time series of 19 consistent ice charts covering
and the main body of pack ice. Here, a very characteristic      a period of approximately 10 weeks, starting on the 29th
phenomenon is the intermittent presence of open water           of February 2008. The 19 ice charts were synthesized to
seaward of the fast ice edge, either as well-defined polynyas   one ice chart that showed the average ice coverage during
or as a more or less continuous strip of open water (i.e.,      the period. To this purpose, we used the Ice Egg Symbol
landwater). In many other places within the arctic region,      and classified a total ice concentration of 6 tenth to equal
the transition zone is an actual shear zone. The pack ice       60% ice cover, a total ice concentration of 9-10 tenth to
zone is composed of polar ice originating mainly from the       equal 95% ice cover, and so on. Thereafter, we weighted
Arctic Ocean and is in a state of almost free drift under the   the successive ice charts with the length of the period they
influence of wind and surface currents. The marginal ice        represented.
zone, finally, is defined as the area between the pack ice          Observational metrological data was available from the
and the open sea.                                               meteorological stations of Danmarkshavn and Daneborg,
    The ice cover of Northeast Greenland can be divided         but after careful consideration, it was chosen to use model
into a summer (June-August) and a winter (October-April)        derived data of temperatures, wind speed and direction
regime, with May and September being the transition pe-         instead. One reason for this choice was the obvious source
riods with the onset of respectively melting and freezing.      of error introduced by the different local topographic and
                                                                climatic conditions caused by the geographical distance


                                                                  Geografisk Tidsskrift-Danish Journal of Geography 110(2) 133
Table 1: Data description.

 Data type               Spatial        Temporal      Temporal      Number              Data description            Source/citation
                        resolution      resolution     coverage     of scenes/
                                                     (this study)     charts
                                                                                 RGB-composite where spectral
 Visible and
                                                                                 bands 1, 2, and 3, respectively,
 thermal infra-
                                                                                 are assigned to the red, green,
 red satellite
                                                                                 and blue channels of a digital
 images                                                                                                             The National
                                                                                 image. Applications: cloud and
                                                                                                                    Oceanic and
                                                                    approx.      surface mapping, land-water
 NOAA               1090 m x 1090 m     Daily        2004-2008                                                      Atmospheric
                                                                    100          boundaries, snow and sea ice
 AVHRR                                                                                                              Administration
                                                                                 detection.
 (Advanced                                                                                                          (NOAA)
                                                                                 Infrared channel 4. Applica-
 Very High
                                                                                 tions: Night cloud mapping
 Resolution Ra-
                                                                                 and sea surface temperature.
 diometer)
                                                                                 Satellite: AVHRR/3
                                                                                 True-colour composites where
                                    Daily                                        spectral bands 1, 4, and 3, re-
 Visible satellite
                                    (but only                                    spectively corresponding to the
 images
                   500 m x 500 m in used during                                  red, green, and blue range of      The National
                   years 2001-2005; February-                       approx.      the light spectrum are assigned    Aeronautics and
 MODIS (Mod-                                    2002-2008
                   250 m x 250 m in October, as                     250          to the red, green, and blue        Space Adminis-
 erate Resolution
                   years 2007-2009 this is the                                   channels of a digital image.       tration (NASA)
 Imaging Spec-
                                    period with                                  Applications: land/cloud/aero-
 troradiometer)
                                    daylight)                                    sols boundaries
                                                                                 Satellite: MODIS Terra
                    Radarsat-1;
                                                                                 Recorded surface reflections of
                    ScanSAR wide
 Active micro-                                                                   transmitted microwave energy.      Canadian Space
                    mode: 100 m
 wave                                                                            Applications: Day and night        Agency (CSA)
                    x100 m              Sporadic                    approx.
                                                     1998-2008                   surface structure (ocean cur-      & European
                    Envisat ASAR:       coverage                    200
 Radarsat-1 &                                                                    rents and topography, land-        Space Agency
                    app. 150 m x
 Envisat ASAR                                                                    scape topography, snow and         (ESA)
                    150 m. (Wide
                                                                                 ice).
                    Swath mode)
                                                                                 Ice charts for navigational use
 Ice charts                                                                      (typically from the summer
                                        Sporadic                    approx.                                         DMI Ice Ser-
 of northeast       -                                1982-2008                   period) and winter ice charts
                                        coverage                    200                                             vice
 Greenland                                                                       for the military Sledge patrol
                                                                                 Sirius.
 Model derived
 meteorological     Single grid-point                                            ECMWF deterministic atmo-
 data               extraction                                                   spheric model.
                    (74°30N             12-hour                                  Wind and temperature param-        Persson &
                                                     2003-2008      -
 ECMWF              18°30W) of a        time-step                                eters (as 2 m temperature, 10      Grazzini (2007)
 global atmo-       0.5° resolution                                              m wind U-velocity and 10 m
 spheric model      grid                                                         wind V-velocity).
 TL799L91




134 Geografisk Tidsskrift-Danish Journal of Geography 110(2)
between the observational stations and the phenomena
under consideration. The station Danmarkshavn was much
farther north than the study area and the station Daneborg
was more inland. Besides, the observational data series
from Daneborg suffered from long periods of no data and
lots of errors during the last decade because it used an
old and run-down automatic weather station (Cappelen,
2008, pers. comm.). The model data was extracted from
the ECMWF deterministic atmospheric model, the pres-
ently valid ECMWF global atmospheric model TL799L91
(Table 1), and offered a consistent data series, for the pe-
riod 2003 to the present, extracted from a single grid-point
localized within the area of polynya formation (74°30N
18°30W).


Results

The Sirius Water Polynya is situated in the transition zone
between the coastal fast ice and the main body of pack ice
between latitudes 74°-75°N. The coastward extent of the
Sirius Water Polynya is alternately bounded by the coast
and the fast ice, depending on the exact location of the edge
of the fast ice. This is not entirely stationary throughout the
winter as the most seaward areas of the fast ice repeatedly
breaks off and refreezes. The seaward extent of the Sirius
Water Polynya is limited by the constantly moving pack
ice and therefore varies continuously.
    Figure 2 shows the ice conditions in the study area
                                                                  Figure 2: Satellite image of the study area during the freeze-up in
in mid September just around the onset of freezing. The           autumn 2007. Datasource image: MODIS (Table 1).
inner parts of the fjords are still ice-free after the summer
melt and local ice formation has not begun. Remnants of
previous winter’s fast ice have survived north of Shannon
Ø and pack ice is present in high concentrations off the          consistent time series of ice charts with an underlay of the
coast. At this time of the year, the pack ice consists of         satellite images on which they are based.
mainly multi-year ice that has been broken into relatively            Figure 3a shows the first cloud free satellite image
small floe sizes. The predominant small floe sizes allows         where distinct polynya formation is observed just south
for the distinction of pronounced meanders and eddies             of Shannon Ø on the 9th October 2007. The fast ice in
caused by turbulence, which in turn causes the ice floes          the coastal areas is still not entirely consolidated, but the
to break into continuously smaller pieces (Figure 2). The         polynya is delimited where a relatively marked fast ice
sea ice is sometimes advected into the area of polynya            edge forms the northern and western extent, and where the
formation south of Shannon Ø and Pendulum Øer in rela-            polynya forms a distinct area of lower ice concentrations
tively high concentrations during the late summer season          and thickness compared to its surroundings. Five days later
(see also Figure 2). These ice floes become trapped in the        (Figure 3b), the polynya has opened up significantly and
freeze-up of the coastal waters when it occurs late in the        now extents all the way down to the southern corner of
season.                                                           Wollaston Forland, where the fast ice has broken off at
    The continuous freeze-up of the coastal waters and the        the most eastern capes of Clavering Ø. The entire polynya
subsequent opening of the Sirius Water Polynya after the          is characterized by very small ice concentrations. After
late summer season is presented in Figure 3 as a small            this, the polynya gradually refreezes and the fast ice edge


                                                                    Geografisk Tidsskrift-Danish Journal of Geography 110(2) 135
                                                                                             Figure 3: Ice charts of the Siri-
                                                                                             us Water Polynya in early win-
                                                                                             ter 2007. The Ice Egg Symbol
                                                                                             states (from top): a) total ice
                                                                                             concentration (in tenth parts);
                                                                                             b) partial concentration of the
                                                                                             three thickest ice types (in tenth
                                                                                             parts); c) stage of development
                                                                                             (ice thickness); and d) floe size.
                                                                                             Datasource images: MODIS
                                                                                             (Table 1).




advanced on to 21st October, when the polynya is only di-         The sequence of polynya opening followed by refreezing
rectly in contact with the coast at Hvalros Ø and Wollaston    shown in Figure 3 illustrates how new ice is continuously
Forland (Figure 3c-d).                                         generated in the polynya. The new ice was only actively


136 Geografisk Tidsskrift-Danish Journal of Geography 110(2)
Figure 4: Examples of special ice
chart (left) and annotated NOAA
AVHRR image (right), respec-
tively, showing the Sirius Water
Polynya. Both are from the period
during winter when no visible data
can be obtained due to the lack of
daylight. The NOAA image depicts
one of the thermal infrared bands
(band 4) measuring the heat emit-
ted from the surface objects. As sea
ice is generally much colder than
the surrounding ocean, the bright
areas represent high ice concen-
trations and thickness, while the
dark areas (especially observed in
the polynya), represent relatively
thin ice and possibly also lower ice
concentrations.




advected away from the polynya at a rate sufficiently high     because data coverage, quality and resolution are too poor
to generate a large area of distinctive open water around      to allow for any exact sea ice classification of the study
14th October. Over the following dates, the advection rate     area. An inspection of NOAA AVHRR data and old ice
is so small that new ice formed in the polynya is allowed      charts from this period reveals nonetheless that the Sirius
to form sheets of young ice, although these thin ice sheets    Water Polynya exist throughout the year as an area of
are prone to the action of wind, currents and waves and        markedly thinner ice cover than the surrounding areas of
therefore frequently broken into floes of varying size and     fast ice and pack ice (Figure 4). The staff from the Danish
thickness.                                                     Military sledge patrol Sirius, the only persons travelling in
    The only available regular data coverage of the study      this remote area during winter, confirms the presence of a
area during the following months (November 2007 –              polynya with no or thin ice cover. They always travel over
February 2008) is from satellite-borne infrared sensors.       land when they go north from Daneborg on their winter
Visible sensors cannot be used at this time of year at         sledge journeys.
these latitudes because of the lack of daylight. No detailed       The total polynya area with ice concentration less than
analysis of the polynya has been carried out for this period   6/10 is plotted in Figure 5, together with modelled data of




Figure 5: Total polynya area of
<6/10 ice (bars) plotted with mod-
elled temperature (punctuated
line), wind speed (full line) and
direction (top).



                                                                 Geografisk Tidsskrift-Danish Journal of Geography 110(2) 137
Figure 6: Windroses for summer (June-August 2008) and winter
(October-May 2007-2008), respectively. Based on modelled wind
data from the ECMWF-model by extraction of single grid-point
located at lat-long 74°30N 18°30W.



temperature, wind speed and wind direction for the period       Figure 7: Average ice cover during the period 29th February to 10th
29th February 2008 to 10th May 2008.                            May 2008. The average ice cover ranges from 100% (white) over
    The fluctuating nature of the polynya area extent is        90% (lightest blue) to 35% (darkest blue).
apparent and the events of strong winds play a major role
in opening up the polynya (Figure 5). These events are
typically characterized by northerly wind directions and        current patterns at the mouth of the fjords and the local
relatively high (up to -5°C) temperatures. These wind           bathymetry may also stimulate the polynya occurrence.
conditions are characteristic for winter conditions (Figure
6). Winter winds are generally stronger and more persis-
tent with a predominant northerly component, and sum-           Discussion
mer winds are generally weak and more frequently from
southerly directions, except for an occasional summer           The Sirius Water Polynya exists throughout the winter as
storm (Hansen et al., 2008). Generally, the area of open        an area of markedly thinner ice cover intermittently opened
water increases as the thin and fragile ice cover of the        up by the advection of sea ice caused by strong northerly
polynya area are advected downwind to the polynya edge          winds. Relationships between strong wind events and po-
in the wake of strong northerly winds. The advection rate       lynya opening are also known from the Storfjorden Polynya
decreases again when the wind speed drops and a thin ice        near Svalbard (Geyer et al., 2010) and from the Northeast
cover gradually builds up in the polynya. The area of open      Water Polynya (Minnett et al., 1997). Though the dominant
water thus reduces until strong wind occurs again.              mechanism for the Sirius Water Polynyas maintenance
    The polynya formation may extend from Shannon Ø             during the winter is evidently the wind, there are several
in the north to Gael Hamkes Bugt in the south (Figure 1).       other factors contributing to the polynya formation and
However, the extent of open water areas varies greatly. The     also some important seasonal differences. In addition to
average ice cover in the period from 29th February – 10th       the obvious seasonal cycle in insolation, there is a marked
May 2008 is presented in Figure 7.                              difference in the surface wind field between winter and
    The most stable areas of open water and the thinnest ice    summer. Winter winds are generally stronger and more
cover is generally found at the mouth of Hochstetter Bugt       persistent with a predominant northerly component and
just south of Shannon Ø as well as south of Hvalros Ø, Lille    summer winds are generally weak and more frequently
Pendulum and Sabine Ø and east of Clavering Ø. The loca-        from southerly directions.
tion of the polynya may be caused by the northerly winds            The summer regime typically begins during May with
that are channelled and strengthened by the topography          the springtime increase in insolation gradually decreasing
in these particular places and increases the advection rate     the new ice formation (Hansen et al., 2008). The amount of
of sea ice. However, additional local forcing by specific       open water between the floes increases with the decrease


138 Geografisk Tidsskrift-Danish Journal of Geography 110(2)
of new ice formation, and the low albedo of the open water          ening the prevailing northerly winds and thus in certain
allows the insolation to heat the surface layer of water.           areas inhibiting or even preventing fast ice formation. Koch
This results in an increased rate of sea ice melt causing a         (1945) observed gale events that were connected to kata-
general opening of the polynya. The eastern and southern            batic winds or foehns and that were funnelled through Ar-
polynya-edge gradually becomes more disintegrated with              dencaple Fjord (extending NW-SE from the northwestern
the general opening of the pack ice and more frequent oc-           part of Hochstetter Bugt) to the mouth of Hochstetter Bugt
currence of land water. The northerly winds have become             and the straits surrounding Pendulum Øer.
less prevalent during the spring and the dominant mecha-                The presence of fjord entrances and the location of both
nism of polynya formation at this time of year is rather the        the Sirius Water Polynya and the Scorebys Sund polynya
absorption of solar radiation in the surface water layers           is striking. Specific current patterns related to the tides at
producing sea ice melt in and around the polynya. The               the mouth of the fjords may influence the position of the
absorption of solar radiation plays an increasing role in re-       polynyas (Morales Maqueda et al., 2004). Tidal activity
ducing the ice cover through melting as summer progresses           over shallow waters may inhibit fast ice formation and
and the albedo of the ice cover decreases.                          surface currents in general are likely to contribute to the
    The growth of the summer polynya until a point where            more or less constant fracturing of thin ice sheets and floes
it disintegrates, typically associated with the break-up and        and possibly also to the advection of sea ice.
retreat of fast ice, is mainly the result of ice melt and an epi-       The significance of the offshore bathymetry and the
sodic export of ice from the area by winds and surface cur-         offshore ocean currents on the polynya formation in the
rents. The summertime disintegration of the Sirius Water            area are difficult to estimate because detailed observa-
Polynya is obvious in years where the pack ice retreats             tions of hydrographic conditions are lacking. However,
north of the study area, like in the summer of 2008. How-           the strong halocline of the East Greenland Current probably
ever, there are also years of continuous heavy ice conditions       prevents any significant vertical mixing or upwelling from
in the area throughout the summer, like in 2007. The main           the deeper strata of warmer, more saline water.
reason for ice-free waters in the area during such condi-               Regarding a classification of the Sirius Water Polynya,
tions with low winds is the protection by islands against           the argumentation can be summarized as follows: Sensible
the inflow of ice from the north. However, stormy wind              heat polynyas are defined as areas of low ice production
events during summer can radically redistribute the ice             and preferably occurs in regions of upwelling or strong
cover, by advecting ice from the EGC into the area that was         vertical mixing associated with tidal activity, typically in
previously open water. A packing of sea ice is frequently           bays, straits and channels or in areas of interaction be-
observed at the southern coasts of Shannon and Pendulum             tween currents and topographic features, e.g., seamounts
Øer. Furthermore, surface currents become more dominant             (Morales Maqueda et al., 2004). The present analysis on
in the summer and frequently contribute to the advection of         the contrary illustrates how the Sirius Water Polynya is an
sea ice into the area. An interesting observation in relation       area of significant and continuous ice production during the
to this is the episodic occurrence of high concentrations of        freezing period, where the polynya formation is predomi-
pack ice in the polynya during summer, where sea ice is             nantly mechanically forced. During the episodes of active
advected into the area by winds and surface currents (Fig-          advection of sea ice from the polynya, the Sirius Water
ure 2). A clear distinction of turbulent eddies in the area         Polynya can be classified as a latent heat polynya using the
is sometimes possible when small floe sizes occur. This             most widespread definition (e.g., Morales Maqueda et al.,
indicates that the specific factors forcing polynya formation       2004). In a more exact terminology though, as argued by
in the winter are not so dominant in summer.                        Morales Maqueda et al. (2004), the winter polynya could
    A prerequisite for polynya formation in the Sirius Water        be classified as a wind-driven shelf water polynya.
Polynya is probably the location of the islands Shannon Ø,              A total freezeover of the Sirius Water Polynya has not
Sabine Ø, and Lille Pendulum. They protect the polynya              been observed in the data, but it cannot be excluded that
area against the inflow of ice from the north. A similar            it periodically occurs under the proper climatic condi-
phenomenon has been observed at the Northeast Water                 tions, for example a periodic change in the general wind
Polynya, where the fast ice features Norske Øer and Ob’             field with less frequent storm events and/or a periodic
Bank Ice Shelves prevents the inflow of ice (Minnett et             temperature drop that increases the freezing-rate might
al., 1997). The coastal orography also plays an important           allow the formation of a wide belt of fast ice in the area
role in the polynya formation by channelling and strength-          of the previous polynya. However, the Sirius Water Po-


                                                                      Geografisk Tidsskrift-Danish Journal of Geography 110(2) 139
lynya is one of the most stable polynyas on the northeast        Conversely, knowledge of the spatial and temporal dynam-
coast of Greenland in sense of both its recurrence and its       ics of a particular polynya in recent times may contribute
persistence, as the Sirius Water Polynya appears to be           to a more qualified interpretation and understanding of
characterized by episodic openings throughout the winter         observed patterns of Inuit settlements, past migrations and
as argued above.                                                 environmental conditions. The observed pattern of prehis-
    A review of older satellite data and ice chart available     toric settlements in the area is to some degree determined
at the Danish Meteorological Institute (DMI), mainly from        by access to marine resources and thus to the location of
the last 5-13 years, strongly supports the findings of the       polynyas as described in this study (see the archaeological
present analysis. The Sirius Water Polynya is recognized         findings of the GeoArk project in Sørensen et al., 2008,
in the vast majority of both satellite data and ice charts       2009). The archaeological investigations of Inuit Thule
from the freezing period. In the few ice charts where the        culture settlements during summer and winter shows that
polynya has not been mapped, the location of the fast ice        summer tents are concentrated along the outermost coastal
edge indicates that it is more likely a matter of lacking        areas, in particular Hvalros Ø, Sabine Ø and the eastern
depiction than an actual absence of the Sirius Water Po-         capes of Clavering Ø and winter houses are concentrated
lynya. The review furthermore confirms the existence of          around the southern coast of Clavering Ø. The concen-
the Sirius Water Polynya throughout the winter as an area        tration of the winter houses is observed on south facing
of markedly thinner ice cover as well as the locations of        shores in places with a stable coastal geomorphology with
more persistent open water or low ice concentrations south       access to building materials and shelter against the prevail-
of Shannon Ø and in the vicinity of Pendulum Øer. Over-          ing northerly gales of this season. The spring and summer
all, the dynamic nature of the Sirius Water Polynya in the       settlements are more exposed and further seaward located,
winter, with intermittent openings of the polynya by gale        close to the open water areas (Kroon et al., 2010).
winds alternating with periods of more calm weather al-
lowing an advancement of the fast ice edge and growing
ice cover in the polynya area, seems to apply throughout         Conclusions
the reviewed period.
    On an inter-annual scale, the fast ice formation and         The Sirius Water Polynya is a wind-driven shelf water
break-up in different areas varies with regard to the exact      polynya located in the transition zone between the fast
timing, presumably caused by inter-annual variations in          ice/the coast and the pack ice in Northeast Greenland. The
the onset of freezing and melting as well as the effect of       polynya formation is predominantly governed by mechani-
occasional gales in these transition periods. Furthermore,       cal forcing caused by northerly gales. A marked seasonal
the maximum extent of fast ice is observed to vary be-           difference in the surface wind field, together with the obvi-
tween years. In some years, calm periods allow the fast          ous seasonal cycle in insolation, creates distinct winter and
ice to advance in places that are normally characterized         summer regimes in the seasonal evolution of the polynya.
by frequent break-up of ice due to their exposed location.       While the winter regime is characterized by intermittent
Such advances of fast ice are typically associated with the      openings of the polynya by gale winds alternating with
climatic transition periods in early winter and spring, where    periods of more calm weather allowing an advancement
the temperature favours freezing and northerly gales are         of the fast ice edge and growing ice cover in the polynya,
not as strong and frequent as during winter. This pattern is     the summer regime is rather characterized by winds being
particularly pronounced in the northern part of Gael Hamke       generally light and more frequently from southerly direc-
Bugt extending to the eastern capes of Clavering Ø and           tions as well as a gradual increase in net surface radiation
Pendulum Øer, where it can be observed in most years. In         and decrease in new ice formation, eventually leading to
these situations, Hvalros Ø appears to be the only island        a positive surface heat budget and as melt-off proceeds, a
in more or less direct contact with open water. In years         disintegration of the polynya.
where such a periodical advancement of the fast ice edge             During the winter regime, spatial variability is observed
is extreme, a strip of fast ice may even be formed along         as both size of and ice cover within the polynya varies
the eastern coast of Wollaston Forland connecting the fast       significantly. Intermittently winds are sufficiently strong
ice of Gael Hamke Bugt and Hochstetter Bugt.                     to create a large coherent area of open water along the
    The presence of prehistoric settlements may serve as an      coast/fast ice edge. However, most often the polynya is
indicator of the existence of specific polynyas in past times.   characterized by relatively high ice concentration. As an


140 Geografisk Tidsskrift-Danish Journal of Geography 110(2)
exception to this, a few specific areas within the polynya         the North Atlantic Oscillation. Journal of Climate 13
are rather predominated by conditions of more or less open         (15): 2671-2696.
water caused by sea ice advection and frequent break off of     Foldvik, A., Aagaard, K. & Tørresen, T. (1988). On the
fast ice due to the exposed nature of these locations. The         velocity field of the East Greenland Current. Deep-Sea
most distinct areas are located south of Shannon Ø and             Research 35(8): 1335-1354.
Pendulum Øer, a third less distinctive area is located at the   Glud, R.N., Rysgaard, S., Kühl, M. & Hansen, J.W. (2007):
easternmost capes of Clavering Ø. The two latter locations         The sea ice in Young Sound: Implications for carbon
coincide with areas of significant findings of spring and          cycling. Pp. 62-85 in: Rysgaard, S. & Glud, R.N.
summer settlements from the Thule culture, indicating a            (eds.): Carbon Cycling in Arctic marine ecosystems:
connection between the presence of the polynya and Inuit           Case study Young Sound. Meddelelser om Grønland,
living in the area in prehistoric times.                           Bioscience 58.
                                                                Geyer, F., Fer, I. & Smedsrud, L.H. (2010): Structure and
                                                                   forcing of the overflow at the Storfjorden sill and its
Acknowledgements                                                   connection to the Arctic coastal polynya in Storfjorden.
                                                                   Ocean Science 6(1): 401-411.
The Danish Meteorological Institute (DMI) provided data,        Grønnow, B., Gulløv, H.C., Jakobsen, B.H., Gotfredsen,
technical facilities and practical experience to carry out         A.B., Kaufmann, L.H., Kroon, A., Pedersen, J.B.T. &
this study. We like to thank Centre of Ocean and Ice, and          Sørensen, M. (in press): At the Edge: High Arctic Walrus
in particular the staff in the Ice Service, for their advice,      Hunters during the Little Ice Age. Antiquity.
comments, help and support. A special thanks to Leif Tou-       Hansen, B.U., Sigsgaard, C., Rasmussen, L., Cappelan, J.,
dal Pedersen, Keld Qvistgaard, Gorm Dybkjær, Mikkel                Hinkler, J., Mernild, S.H., Petersen, D., Tamstorf, M.P.,
Sørensen, John Cappelen and Søren Rysgaard for their               Rasch, M. & Hasholt, B. (2008): Present-Day Climate
contributions in form of personal comments, fruitful dis-          at Zackenberg. Advances in Ecological Research 40:
cussions and/or assistance.                                        111-149.
                                                                Hinkler, J. (2005): From digital cameras to large-scale sea-
                                                                   ice dynamics. A snow-ecosystem perspective. PhD the-
References                                                         sis. University of Copenhagen, Institute of Geography
                                                                   and National Environmental Research Institute (NERI).
Boertmann, D., Olsen, K. & Nielsen, R.D. (2009): Seabirds          Department of Arctic Environment.
  and marine mammals in Northeast Greenland. Aerial             Hjort, C. (1997): Glaciation, climate history, changing
  surveys in spring and summer 2008. NERI Technical                marine levels and the evolution of the Northeast Water
  Report 721. Aarhus University, Aarhus, National Envi-            Polynya. Journal of Marine Systems 10: 23-33.
  ronmental Research Institute.                                 Jakobsen, B.H., Kroon, A., Pedersen, J.B.T., Andersen,
Buch, E. (2002): Present oceanographic conditions in               T.J., Grønnow, B., Sørensen, M., Gulløv, H.C., Jensen,
  Greenland Waters. DMI Scientific Report 02-02. Co-               J.F., Gotfredsen, A.B. & Meldgaard, M. (2008): Geo-
  penhagen, Danish Meteorological Institute.                       Ark 2007, Kyst mennesker og miljø i Nordøstgrønland.
Buch, E. (2007): Physical oceanography of the Greenland            Geografi 2007. Årsskrift om selskabets aktiviteter og
  Sea. Pp. 14-21 in: Rysgaard, S. & Glud, R.N. (eds.):             geografien ved de danske universiteter. [in Danish]
  Carbon Cycling in Arctic marine ecosystems: Case              Johannesen, O.M., Bengtson, L., Miles, M.W., Kuzmina,
  study Young Sound. Meddelelser om Grønland, Bio-                 S.I., Semenov, V.A., Alekseev, G.V., Nagurny, A.P.,
  science 58.                                                      Zakharov, V.F., Bobylev, L.P., Pettersson, L.H., Hassel-
Cappelen, J., Jørgensen, B.V., Laursen, E.V., Stannius,            mann, K. & Cattle, H.P. (2004): Arctic climate change:
  L.S. & Thomsen, R.S. (2000): The Observed Climate                observed and modelled temperature and sea-ice vari-
  of Greenland, 1958-99 – with Climatological Standard             ability. Tellus 56A: 328-341.
  Normals, 1961-90. DMI Technical Report No. 00-18.             Koch, L. (1945): The East Greenland Ice. Meddelelser
  Copenhagen, Danish Meteorological Institute.                     om Grønland 130(3). Kommisionen for Videnskabelige
Dickson, R.R., Osborn, T.J., Hurrell, J.W., Meincke, J.,           Undersøgelser i Grønland. København, C.A. Reitzels
  Blindheim, J., Adlandsvik, B., Vinje, T., Alekseev, G.,          Forlag.
  Maslowski, W. (2000). The Arctic Ocean Response to


                                                                  Geografisk Tidsskrift-Danish Journal of Geography 110(2) 141
Kroon, A., Jakobsen, B.H., Pedersen, J.B.T., Addington,        Stirling, I. (1997): The importance of polynyas, ice edges,
   L., Kaufmann, L., Grønnow, B., Jensen, J.F., Sørensen,         and leads to marine mammals and birds. Journal of Ma-
   M., Gulløv, H.C., Hardenberg, M., Gotfredsen, A.B.             rine Systems 10: 9-21
   & Meldgaard, M. (2009): Geographical Report of the          Sørensen, M., Grønnow, B., Jensen, J.F., Jakobsen, B.H.,
   GeoArk expeditions to North-East Greenland 2007 and            Pedersen, J.B.T., Gotfredsen, A.B., Kroon, A. & Gulløv,
   2008. Report 29. Copenhagen, SILA – The Greenland              H.C. (2008): Hvorfor forsvandt Thulekulturen fra Nor-
   Research Centre at the National Museum of Denmark.             døstgrønland? Geografisk Orientering 5: 694-703. [in
Kroon, A., Jakobsen, B.H. & Pedersen, J.B.T. (2010):              Danish]
   Coastal environments around Thule settlements in            Sørensen, M. Gotfredsen, A.B., Pedersen, J.T., Hardenberg,
   Northeast Greenland. Geografisk Tidsskrift-Danish              M., Gulløv, H.C., Grønnow, B., Jensen, J.F., Kroon, A.
   Journal of Geography 110(2).                                   & Jakobsen, B.H. (2009): GeoArk 2008. Archaeological
Lassen, K. (1997): Twentieth Century Retreat of Sea-Ice           and Zoo-archaeological Report on Investigations of the
   in the Greenland Sea. DMI Scientific Report 97-5. Co-          Southern Coast of Clavering Ø, the Revet area, Hvalros
   penhagen, Danish Meteorological Institute.                     Ø and the Estuary of Young Sund. Report 28. Copen-
Lassen, K. (1998): Extent of Sea-Ice in the Greenland Sea         hagen, SILA - The Greenland Research Centre at the
   1877-1997. DMI Scientific Report 98-12. Copenhagen,            National Museum of Denmark.
   Danish Meteorological Institute.                            Vinje, T. (2001): Fram Strait ice fluxes and atmospheric cir-
Lassen, K. & Thejll, P. (2005): Multi-decadal variation of        culation: 1950-2000, Journal of Climate 14: 3508-3517.
   the East Greenland Sea Ice extent: AD 1500-2000. DMI        Wadhams, P. (1981): The Ice Cover in the Greenland and
   Scientific Report 05-02. Copenhagen, Danish Meteo-             Norwegian Seas. Reviews of Geophysics and Space
   rological Institute.                                           Physics 19(3): 345-393.
Minnett, P.J., Bignami, F., Böhm, E., Budéus, G., Gal-         WMO (1970): WMO sea ice nomenclature, terminology,
   braith, P.S., Gudmandsen, P., Hopkins, T.S., Ingram,           codes and illustrated glossary. World Meteorological Or-
   R.G., Johnson, M.A., Niebauer, H.J., Ramseier, R.O. &          ganization, Geneva, Switzerland. WMO/OMM/BMO.
   Schneider, W. (1997): A summary of the formation and        Woodgate, R.A., Fahrbach, E. & Rohardt, G. (1999). Struc-
   seasonal progression of the Northeast Water Polynya.           ture and transports of the East Greenland Current at
   Journal of Marine Systems 10: 79-85.                           75°N from moored current meters. Journal of Geophysi-
Morales Maqueda, M.A., Willmott, A.J. & Biggs, N.R.T.             cal Research, 104(C8): 18,059-18,072.
   (2004): Polynya dynamics: A review of observations and      Pers. comm.: John Cappelen (2008), Danish Meteorologi-
   modelling. Reviews of Geophysics 42: 1-37.                     cal Institute-DMI.
Parkinson, C. L., Cavalieri, D. J., Gloersen, P., Zwally, H.
   J. & Comiso, J. C. (1999): Arctic sea ice extents, areas,
   and trends, 1978-1996. Journal of Geophysical Research
   104(C9): 20837-20856.
Parkinson, C. L., & Cavalieri, D. J. (2008): Arctic sea ice
   variability and trends, 1979-2006. Journal of Geophysi-
   cal Research 113: 1-19.
Persson, A. & Grazzini, F. (2007): Users Guide to ECMWF
   forecast products 4.0. Meteorological Bulletin M3.2,
   ECMWF. Website: http://www.ecmwf.int/products/fore-
   casts/guide/The_ECMWF_global_atmospheric_model.
   html (31-03-2007).
Rigor, I.G., Wallace, J.M. & Colony, R.L. (2002) Response
   of Sea Ice to the Arctic Oscillation. Journal of Climate
   15(18): 2648-2663.
Schmith, T. & Hansen, C. (2003): Fram Strait Ice Export
   during the Nineteenth and Twentieth Centuries Recon-
   structed from a Multiyear Sea Ice Index from South-
   western Greenland. Journal of Climate 16: 2782-2791


142 Geografisk Tidsskrift-Danish Journal of Geography 110(2)

								
To top