Holocene permafrost from ice wedge polygons in the vicinity of
large seabird breeding colonies in the Thule District, NW Greenland, was
drilled to explore the relation between permafrost aggradation and seabird
presence. The latter is reliant on the presence of the North Water Polynya (NOW)
in the northern Baffin Bay. The onset of peat accumulation
associated with the arrival of little auks (
The Thule District of Northwest Greenland (Fig. 1) is notable for its
large seabird colonies along the coast, especially the little auk,
The study area in the Thule District, NW Greenland, including the location of coring sites on Saunders Island (SI1) and at Annikitisoq (GL3) and the distribution of breeding colonies of little auk and thick-billed murre after Boertmann and Mosbech (1998) and The Greenland Seabird Colony Register, maintained by the Danish Centre for Environment and Energy, Aarhus University, and the Greenland Institute of Natural Resources.
The seabirds transport large quantities of marine-derived nutrients (MDNs) from their foraging areas at sea to the terrestrial coastal environments surrounding their breeding sites. By doing so, they act as ecosystem engineers transforming the areas around the colonies, and leaving explicit signatures of their presence (González-Bergonzoni et al., 2017). The input of MDNs around large breeding sites facilitates vegetation growth and peat accumulation at high latitudes (e.g., Zwolicki et al., 2013), completely altering the prevailing ice-free coastal area that is otherwise dominated by bedrock. Hence, areas around bird colonies are hotspots of floral and faunal biodiversity and productivity (Mosbech et al., 2018), and the onset of peat formation and syngenetic permafrost aggradation coincides with the establishment of seabird colonies.
High-latitude soils affected by avian MDN input are enriched in limiting plant nutrients such as nitrogen and phosphorus (e.g., Zwolicki et al., 2013), leading to increased diversity, biomass, and coverage of vegetation. Soil-inhabiting protist communities such as testate amoebae (testaceans) show altered species richness and composition if their habitats are influenced by seabird colonies (Mazei et al., 2018; Vincke et al., 2007).
Vegetation fertilized by MDNs and the subsequent peat formation over millennia enable permafrost aggradation. Syngenetic (concurrent with accumulation) freezing of the peat and ice wedge polygon formation shape the topography when ice wedges grow in polygonal patterns owing to thermal contraction (frost) cracking of the frozen ground in winter and filling of the cracks mostly by snowmelt in spring (Leffingwell, 1915). The melt water entering the frost cracks refreezes immediately due to the subzero ground temperatures and forms vertical ice veins. Ice wedges widen by repetition of these processes and grow upwards with ongoing organic or mineralic accumulation on top. The stable isotope composition of water from wedge ice serves as a proxy of winter climate conditions since the ice derives mainly from winter precipitation (e.g., Opel et al., 2018).
Previous studies have examined the current relation between the NOW and little auk populations (Mosbech et al., 2018), including the availability of their preferred zooplankton prey (e.g., Møller et al., 2018). The onset of seabird colonies in the study area was previously explored using lake sediments and frozen peat by Davidson et al. (2018), whose data are partly employed in the present study that focuses on resulting peat growth and permafrost aggradation in connection with seabird breeding sites. By using for the first time Holocene permafrost and testacean records from the Thule District the study, aims at deciphering (1) the relation between the seabird colony presence and syngenetic permafrost aggradation onset over time and (2) the alternation and preservation of bird presence signals in OM properties of frozen peat.
The climate conditions in Pituffik (Thule Air Base, TAB, 1948–2013, WMO
station 4202) display mean annual air temperatures of
The sample material was retrieved at two locations, at Annikitisoq (informal
name Great Lake; 76.03288
High-center polygons at Annikitisoq
Fieldwork was undertaken between 21 July and 14 August 2015 in the Thule District, NW Greenland. The centers of high-center polygons were chosen for coring. The uppermost active layer was excavated using spades and sampled. The active layer depth reached 20 cm at Annikitisoq and 10 cm on Appat. Below the permafrost table, the peat deposits were extracted using a SIPRE corer driven by a two-stroke engine (Hughes and Terasmae, 1963). The diameter of the coring barrel was 48 mm and its length 1 m. Extensions were used to reach deeper deposits until the corer hit boulders, larger than the drill tube diameter, whose density increased at the transition between the peat and the underlying bedrock. The drilling at Annikitisoq (core GL3) reached a depth of 320 cm b.s. and on Appat (core SI1) 195 cm b.s. (Table 1). After drilling, cryostructures of intrasedimental ice were described following French and Shur (2010), and the cores were kept frozen until subsampling and analyses. At Annikitisoq, wedge ice was exposed in a trench between two high polygon centers at the cored GL3 polygon. Neither a distinct frost crack nor rejuvenation stages were observed in the ice wedge. Thus, no traces of modern ice wedge growth were seen and the ice represents the buried remains of a degrading ice wedge network. Clearly expressed shoulders confirm the syngenetic formation of the wedge ice. The wedge ice exposure was about 1.7 m wide, about 1 m high above the trench bottom, and about 1.2 m below the GL3 polygon surface (Fig. 3). Using an axe and hammer, the ice was split into 35 subsamples across a horizontal transect between 30 and 50 cm above the trench bottom (at 50 to 80 cm b.s.).
Ground ice exposed in a trench at the GL3 polygon
Cryolithological description of peat core GL3 and wedge ice from Annikitisoq and peat core SI1 from Appat in the Thule District (NW Greenland).
The frozen cores were sectioned at 2–4 cm increments by a band saw for further analytical work and then freeze-dried. The GL3 core totalled 75 samples (including four unfrozen active-layer samples) and the SI1 core 49 samples (including 1 unfrozen active-layer sample). The gravimetric ice content was measured as the weight difference between fresh and freeze-dried bulk sediment samples and is expressed as ice content in weight percentage (wt %).
The oxygen (
In total, 11 samples from the GL3 core and 6 samples from the SI1 core
were radiocarbon-dated at the Aarhus AMS Centre (AARAMS). The dates are
published by Davidson et al. (2018), wherein more details on lab procedures are
given. The radiocarbon ages were transformed into calendar years using the
IntCal13 calibration curve (Reimer et al., 2013). Age models for the cores
were fitted using the R routine BACON, a Bayesian age–depth modeling
approach (Blaauw and Christen, 2011). Ages reported and used in the figures
are median modeled ages with
Total nitrogen (TN) and total organic carbon (TOC) contents of the peat
samples were measured with elemental analyzers (Elementar Vario EL III for TN
and Elementar Vario MAX C for TOC; analytical accuracy
Modern reference and core data from Annikitisoq and Appat showing the core zonation by depth and time intervals, the accumulation rates as well as the mean values and standard deviation of organic matter properties per zone and per entire core.
Samples of about 1 g (dry weight) for testacean analysis were suspended in
purified water and wet-sieved through a 500
The polygon development at Annikitisoq covers the period from 4400 to 540 cal BP over the total core length of 320 cm and the succession was divided into three zones as follows: GL3-I (4400 to 3520 cal BP, 320 to 129 cm b.s.), GL3-II (3520 to 2620 cal BP, 129 to 58 cm b.s.), and GL3-III (2620 to 540 cal BP, 58 to 0 cm b.s.) (Table 2).
Zone GL3-I is composed of reddish light-brown partly stratified peat with
nonparallel, wavy lenticular and irregular reticulated cryostructures.
Single ice lenses were
OM data and age information according to Davidson et al. (2018) as
well as testacean ecological groups and zonation of core GL3 from
Annikitisoq. TN data are given as black diamonds and refer to the upper
The testacean record of core GL3 comprises 39 taxa (Table 3). Of those, 20
belong to the moss-inhabiting hygrophilic group, including mainly the genera
Presence of testacean species and their ecological indication in core GL3 from Annikitisoq and core SI1 from Appat (Saunders Island).
In zone GL3-I, varying soil moisture at the rim and the center of the developing low-center polygon is mirrored by xerophilic and hygrophilic species, while the episodical presence of hydrophilic species indicates open water conditions (Fig. 4). Constant wet conditions continue in zone GL3-II where hygrophilic species dominate. In zone GL3-III, xerophilic and eurybiontic species reoccur with the continued presence of hygrophilic species, indicating moisture changes and occasional dry out.
The wedge ice sampled in a trench at the GL3 polygon exhibited visible
vertical ice veins and numerous air bubbles
The SI1 core covers the period from 5650 to
The entire SI1 core is rather homogeneous and is composed of clayish
gray-brown peat including single pebbles. The cryostructures are not visible
except for vertical ice veins about 10 cm long and
As in the GL3 core, core SI1 shows a stepwise decrease in accumulation rates
over time from SI1-I to SI1-III, while the uppermost zone, SI1-IV, returned
to higher accumulation rates at
OM data and age information according to Davidson et al. (2018) as
well as testacean ecological groups and zonation of core SI1 from Appat. TN
data are given as black diamonds and refer to the upper
Both TN and TOC contents exhibit an overall slight decrease over time in
mean values per zone. The
Testaceans are rare and not diverse in core SI1 with only 12 species present
(Table 3). Nine of these belong to the eurybiontic group. The wet onset of
polygon evolution is reflected by hydrophilic
The abrupt warming at the Younger Dryas–Holocene transition promoted intense deglaciation in the Canadian Arctic and Greenland (Briner et al., 2016) and left large parts of the northern Baffin Bay coastlines free of glacial ice from the Early Holocene (Bennike and Björck, 2002). Early Holocene deglaciation of the Wolstenholme Fjord area was dated to 11.2 and 10.6 ka cal BP (Bennike and Björck, 2002). Radiocarbon-dated marine bivalves in raised marine deposits on Appat, although at a different location as our study site, show ages between about 9.9 and 9.2 ka cal BP (Farnsworth et al., 2018) in agreement with modeled deglaciation data for the Greenland ice sheet according to which both Appat and Annikitisoq became ice free around 10 to 9 ka cal BP (Lecavalier et al., 2014). Epigenetic freezing of the areas newly exposed by ice sheet retreat and glacio-isostatic rebound is assumed, while the setup of syngenetic permafrost aggradation as recorded in the lowermost peat zones above bedrock is dated to 5.7 ka cal BP on Appat and to 4.4 ka cal BP at Annikitisoq (Davidson et al., 2018). Thus, the deglaciation preceded the formation of peat and ice wedge polygon development by several thousands of years. The syngenetic permafrost onset falls into the neoglacial cooling period with declining summer insolation after about 7.8 ka cal BP (e.g., Briner et al., 2016; Lecavalier et al., 2017). However, the formation of ice wedge polygons is closely related to the presence of seabird colonies, which provide MDNs that fertilize the vegetation and initiate peat accumulation, and the presence of breeding seabirds is in turn dependent on the formation of the NOW (Davidson et al., 2018). The polynya formation results from the development of an ice arch during winter in the southern part of Kane Basin in Nares Strait (Barber et al., 2001; Barber and Massom, 2007). The ice arch blocks the inflow of drift ice from the north and the prevailing northerly winds and currents sweep the area south of the ice arch free from the new ice that continuously forms on the sea surface, keeping the polynya open. Wind-driven upwelling in the eastern part of the polynya provides heat and nutrients from deeper waters, and the combination of open water (light) and a steady supply of nutrients to the photic zone creates the conditions for the exceptional productivity of the NOW (Stirling, 1980), and in turn the basis for the large seabird breeding populations (Møller et al., 2018).
To reconstruct Holocene temperature changes, Lasher et al. (2017) employed
The exceptional setting of climate and oceanographic conditions maintained
the polynya that attracted seabirds to colonize the shores of the northern
Baffin Bay and controlled, by doing so, the onset of peat accumulation and
syngenetic ice wedge polygon growth. The spatial distribution of the
polygonal peat development is related to seabird colonies. Peat records
published by Malaurie et al. (1972) from a little auk colony site at Iita at
the northern edge of the NOW indicate continuous peat growth since
1795 cal BP (Delibrias et al., 1972; calibrated using INTCAL, CALIB
REV7.1.0; Stuiver and Reimer, 1993; Reimer et al., 2013) at a mean
accumulation rate of 37 yr cm
An ice wedge remnant was sampled at Annikitisoq (Fig. 3) at about 1.2 m
depth below the GL3 polygon surface. This position suggests that the wedge
ice formed mainly during accumulation of the GL3-II core zone, i.e., after
3520 cal BP although direct dating of the ice is not available. The wedge
ice shows low variation in
In summary, the Holocene NOW dynamics controlled by oceanographic and climate variation enabled bird colonization of shores of the Thule District. The recorded onset of bird presence and thus of ice wedge polygon development at about 4400 cal BP at Annikitisoq and at about 5650 cal BP on Appat (Davidson et al., 2018) falls within the period of decreasing temperatures and decreasing SIC, and SST and SSS maxima and the deduced establishment of the NOW (Levac et al., 2011). Thus, the syngenetic permafrost formation directly depending on peat deposition (controlled by bird activity) indirectly follows the Holocene climate trends.
A study by Zwolicki et al. (2013) compared the impact of a little auk and a
mixed thick-billed murre and kittiwake (
The OM input from bird colonies with
When comparing the
This pattern reflects the temporal dimension of OM decomposition when high
accumulation rates as observed in the GL3 core (
Nitrogen distribution and turnover influenced by little auk have been
studied at the northern shore of Hornsund Fjord in Spitsbergen (Skrzypek et
al., 2015). There, the major N sources have been examined by means of
The microbial-biased fractionation from bird faeces to plant-available
substrate amounts to about 5 ‰ (Fig. 7) and is seen in
the isotopic composition of the uppermost sample (
Comparable stable isotope data of piscivorous thick-billed murre food have
not yet been obtained. The information presented here shows no shift
between faeces (
In summary, the impact of seabird colony presence is evidenced for both studied
species and these results are comparable with previous studies (e.g.,
González-Bergonzoni et al., 2017; Skrzypek et al., 2015; Zwolicki et
al., 2013). The
The impact of seabird colonies on High Arctic terrestrial environments is
seen in the input of marine-derived nutrients that is traceable by
geochemical signatures of organic matter in
Original data are available at
The supplement related to this article is available online at:
AM and TAD initiated and designed the present study. SW, TAD, and IGB drilled and documented the cores supported by KLJ and AM. TW and IGB carried out stable isotope and OM analyses. AB carried out testacean analysis and interpretation. TO and EJ supported the overall data analysis and interpretation. SW and TAD wrote the paper with contributions from the other co-authors, who contributed equally to the final discussion of the results and interpretations.
The authors declare that they have no conflict of interest.
This study is part of The NOW Project (
Thomas Opel and Sebastian Wetterich acknowledge funding from the German Research Foundation (grant nos. OP217/4-1 and WE4390/7-1, respectively).The article processing charges for this open-access publication were covered by a Research Centre of the Helmholtz Association.
This paper was edited by Anja Rammig and reviewed by two anonymous referees.