Arctic Science
Interactions between climate and landscape drive Holocene ecological change in a High Arctic lake on Somerset Island, Nunavut, Canada
Journal: Arctic Science
Manuscript ID AS-2016-0013.R1
Manuscript Type: Article
Date Submitted by the Author: 14-Sep-2016
Complete List of Authors: Paull, Tara; University of Ottawa, Geography, Environment and Geomatics Finkelstein,Draft Sarah; University of Toronto, Office, 3129 Earth Sciences Centre Gajewski, Konrad; University of Ottawa, Geography, Environment and Geomatics
Keyword: paleoclimate, lake sediments, diatom dissolution, pollen, paleolimnology
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Interactions between climate and landscape drive Holocene ecological change in a High Arctic lake on Somerset Island, Nunavut, Canada
Tara M Paull 1, Sarah A. Finkelstein 2, Konrad Gajewski 1*
1Department of Geography, Environment and Geomatics, University of Ottawa, Ottawa, ON, Canada K1N 6N5
2Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, Canada M5S 3B1
Draft * Corresponding author ([email protected]) T: 1 613 562 5800x1057 F: 1 613 562 5145
Sept 2016
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Abstract
This study presents a diatom based analysis of the postglacial Holocene environmental history at
Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post glacial diatom assemblages (10,200 – 10,000 cal yr BP) consisted mainly of small, benthic Fragilarioid taxa.
Poor diatom preservation in the early Holocene (~10,000 6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediments records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of
Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid Holocene.
During this time period, cooling causingDraft changes in lake ice phenology was likely a major driver of the reconstructed mid Holocene pH decline. Watershed processes, including reduced fluxes of base cations as the rate of sediment accumulation slowed, may also be contributors to long term shifts in lake water pH and associated changes in diatom assemblages. The uppermost sediments in the Lake RS29 record were characterized by abrupt declines in Aulacoseira alpigena , and increases in benthic diatom taxa Cyclotella sensu lato , suggesting an increase in lake water pH and longer ice free seasons.
Keywords: paleoclimate, Holocene, Canadian Arctic Archipelago, lake sediments, diatoms, paleolimnology, pollen, diatom dissolution
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Introduction
Understanding long term climate impacts on the aquatic communities of Arctic lakes requires
separating the effects of climate variations from changes within the lake and in the watershed, as
well as from the processes associated with lake ontogeny over the long time span of the
Holocene (Fritz and Anderson 2013; Rühland et al. 2015). Numerous non climate factors have
been shown to influence diatom assemblages and production including limnological variables,
bedrock geology and other watershed characteristics (e.g., Lim et al. 2001; Bouchard et al. 2004;
Fortin and Gajewski 2009; Finkelstein et al. 2014). Changes through time of alkalinity, for
example due to vegetation development or climate, alter the lake environment and aquatic
communities (Anderson et al. 2008). However, comparative analyses have shown that diatom
communities differ greatly between nearbyDraft sites due to factors of lake morphometry, dispersal
and watershed characteristics (Smith 2002; Finkelstein and Gajewski 2007, 2008; Rühland et al.
2015).
Diatom responses to pH are well documented, and in many cases, quantitatively
reconstructed. Changes in pH through time in Arctic sediment cores may be inferred through
transfer functions based on a modern calibration set and fossil diatom assemblages (Finkelstein
et al. 2014). Changes in pH can also be reconstructed using indices of past production and lake
chemistry (loss on ignition, LOI, and biogenic silia, BSi) (Fortin and Gajewski 2009). Bedrock
lithology is the strongest predictor of lake water pH in Arctic systems; lakes with lower pH and
poor buffering capacity are found on crystalline rocks whereas the large parts of the Canadian
Arctic underlain by carbonate rocks support more alkaline lakes with significant buffering
capacity (Fortin and Gajewski 2009). Superimposed on the primary control imposed by bedrock,
variability in lake water pH over time may be in part influenced by climate, via fluctuations in
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dissolved inorganic carbon (DIC) mediated by lake ice phenology, in the more poorly buffered sites (Koinig et al. 1998; Wolfe 2002). Since a primary control of diatom communities in Arctic lakes is pH (Finkelstein et al. 2014), this mechanism likely affects diatom communities in poorly buffered lakes, particularly during cold periods when the ice cover persists over much or all of the summer. On millennial time scales, diatom inferred pH and climate have been shown to be tightly coupled in poorly buffered High Arctic lakes (Wolfe 1996, 2002; Michelutti et al. 2007).
Other long term controls on the pH of Arctic lakes may relate to watershed processes, and landscape development (Law et al. 2015).
Autecological studies in the Canadian Arctic Archipelago have determined habitat preferences of individual diatom species based on their distribution and abundances in different habitats (e.g., Bouchard et al. 2004; CremerDraft et al. 2005; Karst Riddoch et al. 2009). Planktonic diatoms, in Arctic lakes Cyclotella sensu lato , often increase in both relative and absolute abundances in response to availability of open water habitat during warm climate intervals
(Douglas and Smol 1999; Rühland et al. 2008; Devlin and Finkelstein 2011; Rühland et al.
2015). Conversely, relative abundance of benthic and epiphytic diatoms often increase when open water habitats are less available during longer ice covered seasons, or when suitable littoral and periphytic habitats develop (Smol et al. 2005). Further, diatom production and diversity are often highest during warm intervals when ice cover is reduced and the growing season lengthens
(Douglas and Smol 1999), although the diatom temperature relation is complex (Anderson
2000). Changes in habitat availability and growing season length may result in increased diatom diversity and production. Although most of these responses are observed in post 19 th century records, these patterns of community response are not always consistent in records that span several millennia (LeBlanc et al. 2004; Michelutti et al. 2007; Finkelstein and Gajewski 2007).
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In order for diatom communities to provide a reliable record of environmental change,
the assemblages must be well preserved in lake sediment records. Some studies have shown
diatom free zones in Holocene cores from the Canadian Arctic, which could either reflect
dissolution of diatom frustules after deposition, dissolution between the death of the diatom and
deposition in the core or absence of living diatoms during the time of sediment deposition (e.g.,
Smith 2002; Podritske and Gajewski 2007; Peros et al. 2010; Courtney Mustaphi and Gajewski
2013). Some species are more susceptible to dissolution than others (Ryves et al. 2001); diatom
records in which differential dissolution has taken place therefore contain non representative
assemblages and will yield poor estimates of overall diversity or production. Although potential
causes of dissolution are well known (Battarbee et al. 2001; Ryves et al. 2006), the importance
of these factors is not well documented Draftin Arctic freshwater ecosystems.
This study presents a diatom stratigraphy from Lake RS29 on Somerset Island in the
Canadian Arctic. Diatom autecological information and community composition, as well as
ecosystem parameters such as diatom production and diversity are used to infer Holocene
environmental changes in the lake. The diatom record is compared to several independent proxy
climate records from the Canadian Arctic, including a pollen record from the same core
(Gajewski 1995) and a reconstruction of Holocene climate variability of the region (Gajewski
2015a). The potential causes of low diatom production, especially relating to possible
dissolution, are examined. Finally, the merit of autecological information and diatom community
indices in providing reliable inferences that are consistent with other independent proxies is
assessed.
Study Area
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Lake RS29 (unofficial name) is located on western Somerset Island in the Canadian Arctic
Archipelago at 73.140°N, 95.278°W, 160 m.a.s.l. (Fig. 1). Lake RS29 has a surface area of ~12 ha and the depth at the coring location was 14.5 m. The catchment area is small and the lake is closely surrounded by hills that are 30 to 40 m above the level of the basin. Water chemistry data are not available from the site, however, three lakes from the general area of RS29 on Somerset
Island had average pH of 7.4 (+/ 0.2), specific conductance of 40 (+/ 7) S cm 1 and total
Phosphorus and total Nitrogen concentrations near or below detection limit (sites CI02 04;
Bouchard et al. 2004). The regional vegetation is a polar desert, located in the High Arctic bioclimatic zone, where plant cover is sparse (~covering 2 to 40% of the landscape) (CAVM
2003).
Mean annual temperature at theDraft nearest weather station in Resolute (176 km to the north of RS29) is 15.9°C and this area receives approximately 170 mm of precipitation annually
(Environment Canada 2002). The bedrock is composed of relatively unweathered gneiss and granite with discontinuous overlying till veneer (Dyke 1983). The substrate has a pH between 5.5 and 7.2 (CAVM 2003). Dated whalebone from northwestern Somerset indicate that deglaciation began ca . 10,900 cal yr BP and the island was fully deglaciated ca. 10,000 cal yr BP (Dyke
1983).
Methods
Lake RS29 was cored in the summer of 1991 from a 2.4 m thick ice surface using a 5 cm diameter Livingstone corer. The coring hole was cased, and a driver was used to push the corer into the sediment. The uppermost sediments, including the sediment interface, were collected in a clear plastic tube fitted with a piston. The top 20 cm of the core were extruded at 1 cm intervals
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while the remaining sediment cores were wrapped in cellophane and aluminum foil and placed
into PVC tubing. The core was stored at 4°C.
The core had been previously used for a pollen study (Gajewski, 1995). A total of eight
samples were sent for radiocarbon analysis; see Gajewski (1995) for additional information
(Table 1, Fig. 2). The R program BACON (Blaauw and Christen 2011) was used to derive a new
chronology for this study, and this included calibrating the ages to calendar years (cal yr BP).
For this study, the core was sampled at contiguous 1 cm intervals to estimate organic
matter, carbonate, and biogenic silica content. Organic and carbonate content were estimated
using loss on ignition (Dean 1974; Heiri et al. 2001). Samples of 0.5 cm 3 were placed into
crucibles and dried at 105°C in order to remove moisture and were subsequently ignited at 550°C
for 4 hours and 950°C for 2 hours to Draftestimate organic (LOI 550 ) and inorganic (LOI 950 ) carbon
content. Biogenic Silica (BSi) concentration was determined using the wet alkali digestion
method (DeMaster 1979; Conley and Schelske 2001). Aliquots were withdrawn at 2, 3, 4, and 5
hours from a sodium carbonate (Na 2CO 3) solution heated at 80°C. The molybdosilicic acid
spectrophotometric method (Parsons et al. 1984) was used to determine BSi concentration of the
aliquots and the weight percent BSi calculated by regression analysis.
A total of 62 samples were processed for identification and enumeration of diatoms.
Samples were processed at 1 cm intervals for the top 40 cm of the core, at 2 cm intervals for
depths 40 60 cm and at 5 10 cm intervals thereafter. Sediment was processed using standard
acid digestion methods (Battarbee 1986). Standard dilutions of the initial diatom slurry were
prepared so that concentrations could be calculated. Diatom solutions were dried onto 18x18 mm
coverslips and mounted onto slides with Naphrax®. Valves were enumerated at 1000x
magnification using a Nikon Eclipse 90i light microscope with DIC optics. A minimum of 600
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valves were identified in samples with high valve concentrations. In samples below 75 cm depth in the core, where valve concentrations were very low, slides were prepared from the most concentrated dilution and diatoms were enumerated in at least 30 transects to reach a minimum count of 100 valves. Diatoms were identified using image collections kept in the laboratory, taxon lists for Arctic lakes (Joynt and Wolfe 2001; Bouchard et al. 2004; Finkelstein et al. 2014) as well as standard taxonomic references (Krammer and Lange Bertalot 1986–91; Patrick and
Reimer 1996; Fallu et al. 2000; Moser et al. 2004). All diatom nomenclature was updated to reflect up to date conventions, and was verified using Algaebase (Guiry and Guiry 2016). A list of taxa recorded and taxonomic authorities are given in Table 2.
As discussed below, several studies of Arctic sediment cores have reported zones with no diatoms or very low concentrations, asDraft was found in RS29. The literature was searched for studies reporting diatom assemblages in lake sediment cores from the Canadian Arctic and
Greenland; records consisting of more than ~3000 years were considered (Table 3). For the subset of these cores where diatom free zones were reported by the authors, the depths and ages of the diatom free zones were recorded.
The statistical language R (R Core Development Team 2006) was used for data analyses.
Species richness was calculated using rarefaction analysis (Tipper 1979), based on a total count of 612 and 104 individuals to represent samples with both high and low valve concentrations.
The Shannon index was calculated as a measure of diversity, although we acknowledge the limitations of this metric in sediment cores (Peros and Gajewski 2008a). Changes in the diatom community were summarized using detrended correspondence analysis (DCA). The vegan package for R (Oksanen et al. 2006) was used to calculate the community indices and for diatom ordination; C2 was used to plot stratigraphic diagrams (Juggins 2008). Fossil diatom data were
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used in conjunction with the diatom calibration set and pH model of Finkelstein et al (2014) to
produce a Holocene pH reconstruction for the RS29 record; model details are given in
Finkelstein et al (2014).
Results
Core chronology
The RS29 core measured 150 cm; its chronology is based on a total of 8 radiocarbon dates (2 on
mosses, 2 on macrofossil fragments and 4 bulk sediment dates; Table 1), as well as the interface
assigned as modern (1991 AD)(Gajewski 1995). Although the age of the sample from 53 55 cm
was unusually old, it is essentially ignored in the model fitting process; in terms of model
parameters, the memory was set to 0.7Draft and priors at 50 (Fig. 2). The model used in this paper
was developed using Bayesian age depth modeling (Bacon: Blaauw and Christen 2011), which
uses an iterative curve fitting process which is more robust to outliers than the polynomial fit
used previously. The new age model differs from that of Gajewski (1995) mostly in late
Holocene sediments where the Bayesian model estimates the age of samples as younger than the
cubic polynomial used in Gajewski (1995). Sedimentation rates are highest in the middle portion
of the record (~ 7800 – 5800 cal yr BP). A basal age of 10,020 cal yr BP confirms that lake
sediments began to accumulate immediately following deglaciation of Somerset Island (Dyke
1983).
Diatom biostratigraphy
Of the 110 diatom taxa identified in samples from Lake RS29, 62 species were considered
common, occurring at abundance of over 1% in at least 3 samples (Table 2; Fig. 3). The diatom
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record was divided into three zones on the basis of diatom preservation and valve concentration
(Fig. 4). Zone 1 (6200 10,200 cal yr BP) was characterized by very low diatom concentrations and few taxa. Slides of undiluted diatom slurry had very low concentrations and reaching counts of 100 valves was difficult in most samples from this period. Many valves appeared poorly preserved; for example, highly silicified central areas and raphe ends of Naviculoid and
Pinnularioid diatoms were abundant relative to intact diatom valves. This evidence for dissolution indicates that the diatom assemblages through Zone 1 are biased to the better preserved types, and assemblages must be interpreted with caution. Of the taxa that are present in
Zone 1, the assemblage is co dominated by a mixture of epiphytic or epilithic diatoms ( Eunotia praerupta, Neidium affine and Pinnularia nodosa ), and Tabellaria flocculosa , documented in benthic habitats in Arctic lakes (AntoniadesDraft et al. 2008). The small, benthic, often alkalophilous
Fragilarioids Staurosira venter, S. lapponica, Staurosirella pinnata and in particular,
Stauroforma exiguiformis, were present in this zone as well; these taxa especially predominate in the assemblages of the oldest two samples of the zone (10,000 – 10,200 cal yr BP). These two basal samples were characterized by higher valve counts and concentrations. Overall, these assemblages yielded circum neutral to slightly acidic values for reconstructed lake water pH in
Zone 1 (mean = 6.5; standard deviation (std) = 0.1; Fig. 4).
At the onset of Zone 2 (6200 cal yr BP), diatom preservation improved markedly as diatom valve concentration and species richness increased, reaching values typical for High
Arctic lakes with good diatom preservation through the Holocene (Finkelstein and Gajewski
2007, 2008). Tychoplanktonic taxa Aulacoseira alpigena, A. nivalis and A. perglabra increased in abundance in Zone 2, along with epiphytic Pinnularia microstauron , a suite of benthic
Naviculoid (e.g., Humidophila schmassmannii, Navicula digitulus ) and Achnanthoid
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(Achnanthidium kriegeri, Nupela impexiformis, Psammothidium levanderi ) taxa, and acidophilic
Frustulia rhomboides (Fig. 3). Diatom inferred pH declined in Zone 2 to 6.3 6.5 (mean 6.4; std
0.1), and diatom to Chrysophyte cyst ratios reached maximum values in the middle of the zone.
Zone 3 began approximately 1400 cal yr BP according to the age model, and is
characterized by an abrupt decrease in Aulacoseira alpigena , increases in benthic taxa such as
Brachysira brebissonii , several species of acidophilic Eunotia and Psammothidium , and in the
planktonic diatoms Cyclotella rossii and Discostella pseudostelligera (Fig. 3). Diatom and
Chrysophyte cyst concentrations increased at the onset of Zone 3, and diatom diversity measures
also showed further increases. Reconstructed pH increased through Zone 3 (mean 6.5, std 0.1)
(Fig. 4).
Biogenic silica (BSi) increasedDraft over the Holocene. In this core, diatom assemblage
diversity and richness is significantly correlated with total concentration (p<.001), but not with
pH or temperature.
Detrended Correspondence Analysis (DCA) was used to summarize the trends in diatom
assemblages through the Holocene (Fig 4). DCA axis one is highly correlated with total diatom
concentration (r=0.94, p<0.001), suggesting that a major source of variation in diatom
assemblages is the differential preservation of valves through Zone 1. The second DCA axis
reflects the high variability of some of the more abundant diatoms in Zone 2. The third and
fourth axes again illustrate that variability of the diatom assemblage is associated with changes in
the diatom concentrations. Diatom concentration is negatively correlated equally with pH and
July temperature ( 0.3; p=0.04), suggesting that at least through the zone of poor diatom
preservation, reconstructed pH is biased. These results underline the importance of considering
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the impact of differential preservation on the results of diatom inferred pH reconstructions
(Ryves et al. 2009).
Comparisons with available pollen data
Transitions in the diatom assemblages, as illustrated by the DCA scores (Fig 4) occurred at approximately the same time as marked changes in pollen assemblages and concentrations
(Gajewski 1995). Diatom Zone 1 (10,200 – 6200 cal yr BP) corresponds to higher pollen reconstructed air temperatures, higher percentages of low Arctic pollen taxa, mainly Salix , and maximum values for pollen concentration (Fig. 4) . However, this time period also corresponds to minimum abundances of siliceous microfossils, suggesting high terrestrial but low aquatic production, or dissolution of the diatomDraft assemblages. At ~6000 cal yr BP when pollen concentrations decreased and high Arctic pollen taxa such as Oxyria , Ranunculaceae and
Saxifraga increased, suggesting cooling, the concentration of diatom valves in the sediment record increased. There was a further decrease in pollen concentration at ~1500 cal yr BP concurrent with an increase in both diatom and cyst concentrations as well as BSi, demonstrating divergent responses in terms of production proxies (pollen and diatom concentrations) for watershed vegetation vs. aquatic communities.
Discussion
The sediments of Lake RS29 yielded a complex siliceous microfossil record. Analyses of diatom concentrations indicate two major transitions; according to the proposed age model, these take place at 6200 and 1400 cal yr BP. These transitions also coincide with changes in diatom assemblages and vegetation changes recorded in a previously published pollen diagram from the
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same core (Gajewski 1995). Other transitions in the diatom assemblages, such as at 8200 and
~5200 cal yr BP, coincide with major climate transitions in the Arctic (Gajewski, 2015a). The
marked shifts in diatom communities recorded an interaction between taphonomy (diatom
preservation), climate and ontogeny of the lake.
Early to mid-Holocene paleoenvironments
The basal two samples in this record (10,000 – 10,200 cal yr BP) record higher diatom
concentrations in an otherwise low concentration zone. They are dominated by small, colonial
Fragilarioid diatom taxa ( Staurosira venter, Staurosirella pinnata and Stauroforma exiguiformis )
which typically occupy benthic habitats and are generally associated with early post glacial
paleoenvironments where glacial run offDraft supplies some mineral nutrients to sustain diatom
communities in recently established ultra oligotrophic lakes. These taxa have been widely
reported in those conditions in early post glacial sediments of Arctic lakes for the Holocene
(Smol 1983; Cremer et al. 2001; Finkelstein and Gajewski 2007; Rouillard et al. 2012) and for
earlier interglacials (Wilson et al. 2012). At Lake RS29, this early post glacial assemblage was
quickly replaced by a more unusual assemblage dominated by Eunotia praerupta, Neidium
affine, Pinnularia nodosa and Tabellaria flocculosa . In Arctic lakes, these taxa occupy benthic
and periphytic habitats, and are associated with higher dissolved organic carbon (DOC)
concentrations (Antoniades et al. 2005, 2008; Fallu et al. 2000). Taken as a whole, the diatom
assemblages in Zone 1 suggest some supply of base cations from the watershed to the lake, and a
warm and wet enough climate to support the development of the littoral zone vegetation,
providing periphytic diatom habitats and releasing DOC to the lake. Further, given the warmer
climate at this time (see below), the thicker active layer may have increased particulate and DOC
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fluxes from the watershed to lakes, influencing diatom assemblages (Fritz and Anderson 2013); high DOC concentrations have been inferred spectroscopically from other High Arctic lakes during early Holocene thermal maxima (Rouillard et al. 2012). Indications of significant dissolution of diatom valves further characterized diatom Zone 1. These indications include low concentrations and valve counts, the preservation of more heavily silicified central areas without surrounding frustules, and the assemblage composition itself suggests important bias. For example, maximum abundance of Neidium species in ~150 lakes and ponds in the Canadian
Arctic (Bouchard et al. 2004; Antoniades et al. 2008) are an order of magnitude lower than the maximum abundances observed in Lake RS29.
Despite the low abundance and probable dissolution of diatoms in Zone 1, this time period (10,200 6200 cal yr BP) is associatedDraft with maximum Holocene temperatures for this region of the Canadian Arctic (Fig. 4). The maximum abundance of Salix in the pollen record from the RS29 core, as well higher pollen concentrations and influx (Gajewski 1995; 2015b) suggest warmer conditions, and possibly a longer growing season prior to ~6000 cal yr BP. A diatom record from Russell Island adjacent to nearby Prince of Wales Island (Finkelstein and
Gajewski 2008) was also interpreted as signaling warmer temperatures prior to 6500 cal yr BP.
The spatio temporal pattern of postglacial climates in the Canadian Arctic and Greenland has been summarized in several recent studies (Kauffman et al. 2005; Briner et al. 2016;
Gajewski 2015a). The general conclusion is that warmest temperatures occurred earlier in the
Holocene, and this is based on multi proxy records from dozens of sites and is consistent between proxies. Maximum temperatures were identified in the early to mid Holocene prior to
5200 cal yr BP, with the timing depending on region and this is documented in lake sediment records (Bradley 1990; Gajewski and Atkinson 2003; Kaufman et al. 2004; Gajewski, 2015a;
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Briner et al. 2016), ice cores (Devon Ice Cap, Koerner and Fisher 1985; Agassiz Ice Cap, Fisher
et al. 1995; Vinter et al. 2009), fossil whalebone distributions (Dyke et al. 1996) and pollen
diagrams (Gajewski 1995; Gajewski and Frappier 2001; Gajewski et al. 2000; Gajewski 2015a,
b; Peros et al. 2010; Peros and Gajewski 2008b, Zabenskie and Gajewski 2007). Gajewski
(2015a) provided a quantitative summary of the climates of the Canadian Arctic and Greenland,
and found warmest temperatures before 8000 cal yr BP in the western and central Arctic,
between 8000 and 5000 cal yr BP in the eastern Arctic and most of Greenland, and later in South
Greenland. All regions showed Neoglacial cooling, intensifying around 3700 cal yr BP (Fig 5).
Thus, a variety of independent paleoclimate estimates suggest that diatom Zone 1 in the RS29
record corresponds to a period of maximal warmth, with a higher vegetation density and
terrestrial production on the landscape (GajewskiDraft 2015b).
Diatom-free zones in Arctic lake sediments
The presence of a zone of very low diatom concentrations and influx, at a time that independent
paleoclimate records show was the warmest period has been identified in several sites from the
Canadian Arctic and Greenland. Cores reporting Holocene diatom analyses were obtained from
the literature (Table 3). Of the 49 sites located (Table 3), 21 reported diatom free zones (Fig. 5).
Of course, this is not a complete dataset as many sites with no diatoms would simply not be
reported, since the site would be abandoned for study (Smith 2002). Lakes where the author had
reported diatom free zones fall into two broad groups.
The first group includes records where diatoms are completely lacking or only present in
the uppermost samples (e.g., DV09, WB02, Sawtooth, Ward Hunt, RS36; see Table 3 for
citations). Several authors have proposed that the absence of diatoms from these kinds of records
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was due to continuous ice cover (e.g., Smith 2002; Perren et al. 2003; 2012a; Antoniades et al
2007, but see Gajewski 2008; Rühland et al. 2015) and the presence of diatoms in the uppermost sediments is due to recent climate warming. However, our results from RS29 show that at least at this site, diatoms were missing during both warm and cold periods prior to the 20 th century, and indeed, they were missing in the sediments deposited earlier in the Holocene, when conditions were warmer than the 20 th century (Gajewski 2015a). A monotonically decreasing concentration of diatoms with depth in the sediment suggests post depositional dissolution (e.g., Florian et al.
2015), as does the presence of diatoms only in the uppermost few cm. However, in some cases, authors report lack of evidence of dissolution in the diatom valves (e.g., Perren et al. 2003;
Antoniades et al. 2007), although Ryves et al (2013) suggest that dissolution may not always be noticed. Dissolution may be inferred byDraft the presence of only the more heavily silicified taxa, morphological criteria (Ryves et al. 2009), or concentration data (Ryves et al. 2002; Florian et al.
2015). For example, at Lake DV09, diatoms were only present in sediments of the past 150 years, but concentrations decreased from the surface downwards in the uppermost 15 cm
(Gajewski et al. 1997). The presence of varves for at least the past 1000 years at Lake DV09 demonstrates that the lake was ice free seasonally through this period, making it unlikely that diatoms were completely absent. Thus, any diatoms deposited on the sediment surface were possibly being dissolved over time in the carbonate rich sediment (Courtney Mustaphi and
Gajewski 2013; Outridge et al. subm).
Several factors are known to enhance dissolution of diatom valves in the water column or in surface sediments, including elevated lake water pH, temperature and silica depletion (Flower
1993; Ryves et al. 2001), elevated conductivity, salinity or alkalinity (Ryves et al 2002; 2006;
2013), grazing and bioturbation (Battarbee et al. 2001; Gibson et al. 2000), bacterial activity
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(Bidle and Farooq 1999; Ryves et al. 2006), fragmentation (Ryves et al. 2006) or reduced
sedimentation rate (Ryves et al. 2013). Further, post depositional changes in pore water
chemistry creating micro environments of elevated pH can promote dissolution of diatom valves
down core (Florian et al. 2015).
The modern pH and specific conductance were reported in several of the studies (Table
3). The mean pH of sites with a diatom free layer at some point in time (i.e., those shown in
Figure 5) was 7.7 (standard deviation 0.8), whereas it was 6.7 (std 0.7) at sites without a diatom
free zone reported. Average specific conductance was 144 µS cm 1 (std 205) for sites with
missing diatoms and 74 µS cm 1 (std 141) for sites not reporting such levels. The pH and specific
conductance are higher in the sites with diatom free zones, although these values should be too
low to cause dissolution (Ryves et Draft al. 2002). However Ryves et al. (2002) also found
preservation decreased in fresh waters as conductivity increased and Ryves et al (2006) report
“substantial dissolution” at the pH values found in the lakes in our study. Fragmentation of
diatoms, presumably due to more turbulence in the lake, may increase destruction of diatoms,
even in lakes with low alkalinity (Ryves et al. 2006). Sites on Baffin Island, which is underlain
by Precambrian Shield, rarely reported diatom free layers, whereas sites in the northern, western
and central Arctic, which are underlain by carbonates or other sedimentary deposits, have a
higher tendency to contain these zones. Of course, the values of temperature, pH and alkalinity
have changed over the course of the Holocene. Given these values of the water chemistry,
however, a simple biogeochemical explanation for dissolution cannot be sufficient to explain all
of these records. Due to some particular characteristic of the lake, diatoms are not preserved in
these sites.
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A second group includes sites where diatoms are lacking for a portion of the core (Fig 5) and these tend to be found in the older sections. The RS29 record is an example; essentially no diatoms were found in the sediments dated to greater 6,200 cal yr BP, low values from 6,200 –
1,400 cal yr BP, and high values in the past 1,400 years. The inverse correlation between aquatic and terrestrial production, where pollen concentrations were high when temperatures are warm, as expected, but diatom concentrations were not, suggests the possibility that the diatoms were being dissolved at some point between the living diatom assemblage and the burial at depth in the sediment. Similarly, at site BC01 from Melville Island, diatoms only appeared in the sediments at ~5000 cal yr BP, at precisely the time where a pollen based July temperature reconstruction from the same core began to show a decrease from high values reconstructed for the previous 8000 years, and when pollenDraft concentrations decreased (Peros et al. 2010). At site
KR02, diatoms were missing in the sediments between 8500 8200, 7600 7000 and 5600 5000 cal yr BP. In all three periods, both a pollen based and chironomid based July temperature reconstruction were above the long term mean, and reconstructed pH (using the method of Fortin and Gajewski 2009), was above the mean (Fortin and Gajewski 2010). Smith (2002) found very low concentrations of diatoms at all of his sites in the older sediments. In several sites in southern Greenland and the eastern Arctic, zones with low concentrations of diatoms were found in the older sections as well, with diatom concentrations subsequently increasing at various times
(Adams and Finkelstein 2010; Perren et al. 2112a; Florian et al. 2015; Law et al. 2015).
Most of these sites had well preserved diatoms in sediments of the past 3000 4000 years, which corresponds, across the entire North America Arctic except for South Greenland, to the
Neoglacial cooling (Gajewski 2015a). Diatoms were absent during the time that coincides broadly with the warmest part the Holocene. However, Law et al (2015) attributed increased
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dissolution of diatoms at two sites in Greenland to increased alkalinity in the early stages of the
lake ontogeny. They suggested that time since deglaciation determined the alkalinity levels of the
lake more than climate. In the western and central Arctic, the early stages of the lake history
coincide with the warmest period, so untangling these two potential causes may be difficult.
Potential factors causing the lack of diatoms in the sediments, such as pH or alkalinity,
nutrient or Si limitation in the water, temperature and ice cover, may vary over the course of the
Holocene, but the changes are relatively small, so it would seem surprising that the
disappearance of diatoms was caused by dissolution due to temperature or alkalinity changes, for
example. In several cases where multi proxy records are available, the continuous deposition of
other proxies, during a time when diatoms were not found in the sediments, demonstrates that a
continuous ice cover cannot be the explanationDraft for the absence of diatoms (Lake KR02: pollen
and chironomids Podritske and Gajewski 2007; Peros and Gajewski 2008b; Fortin and
Gajewski 2010a; Lake BC01: pollen – Peros et al. 2010; Lake WB02: chironomids – Fortin and
Gajewski 2010b; Lake DV09: varves – Courtney Mustaphi and Gajewski 2013). Dilution of
diatoms due to rapid sedimentation is a possibility, but the diatom free layers are not always
associated with clear evidence of sedimentation rate changes (op cit).
In these oligotrophic, dilute and low alkalinity lakes, it is possible that when the climate
warmed, the diatom production increased over the course of the lengthened growing season. As
the diatoms died and were removed from the water column or surface sediments, the Si was
recycled, leading to few remains in the sediment. Extensive dissolution and Si recycling has been
observed in more productive temperate systems (e.g., Conley et al. 1988; Nriagu 1978; Parker et
al. 1977a, b; Ryves et al. 2013) and in Alaska (Cornwall and Banahan 1992). The increased
terrestrial vegetation production, along with the continual presence of permafrost may have
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reduced input of Si to the lake. Changes in precipitation over the Holocene, which could have affected runoff are not well known for the Arctic. If this is the case, the inverse relation between terrestrial production (ie the pollen concentration) and diatom concentration in the sediments may be the result of a more productive lake, with high diatom production, but that the silica was recycled before the sediment was buried.
While further study is needed to determine the relationship between absence of diatoms in the sediments and warmer temperatures in records from Arctic lakes, our literature survey and results from Lake RS29 suggests the possibility of warm temperatures exacerbating diatom dissolution, given the right chemical environment and lake production. Increases in diatom production, as inferred by increases in biogenic silica, in diatom valve concentrations or in fluxes of photosynthetic pigments, in Arctic lakeDraft sediment records are often interpreted as indicative of warmer temperatures (e.g., Cremer et al. 2001; LeBlanc et al. 2004; Michelutti et al 2005;
Rühland et al. 2015 and references therein). Other studies indicate that in some lakes, diatom production and community composition is more closely related to nutrient availability and light penetration (Baier et al. 2004; Malik and Saros 2016) or lake catchment hydrochemistry and only indirectly controlled by climate (Anderson 2000, Anderson et al. 2008, 2012; Law et al. 2015).
Our results suggest that this relationship may be further modified by dissolution in warm periods, and out of phase relations would appear between independent temperature proxies and the diatom production proxies (e.g., Michelutti et al. 2007; Wagner et al. 2008).
Mid- to late Holocene paleoenvironments
Biogenic silica continued to increase and diatom valves appeared much better preserved at the onset of Zone 2 (6200 cal yr BP), as major taxonomic shifts took place. More alkalophilic taxa
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that are important in Zone 1, such as Neidium affine, Staurosirella pinnata and Tabellaria
flocculosa decreased, as a variety of acidophiles in the genera Aulacoseira, Eunotia and
Pinnularia increase. Aulacoseira alpigena and Pinnularia microstauron were most abundant in
this zone (Fig. 3). The high abundances of A. alpigena indicate an adequate supply of nutrients,
in particular silica, and open water conditions with high enough energy to maintain the position
of this heavier, more silicified (tycho)planktonic diatom in the upper part of the water column
(Wolfe and Härtling 1996; Miller et al. 1999). Further, the assemblage suggests the development
of a mossy littoral zone, providing habitat for epiphytic Pinnularia populations. Diatom inferred
pH (Fig. 4) indicates increasing acidity between 5500 and 2000 cal yr BP. A post glacial
succession from small benthic Fragilarioids, recorded in the initial two samples of the record, to
assemblages dominated by Aulacoseira Draft spp. and other more acidophilic diatoms has been widely
recorded in Arctic lakes (Smol 1983; Miller et al. 1999; Wilson et al. 2012).
The increasing acidity evidenced by these changes may be driven by a variety of
processes. Natural acidification has been documented for many temperate lakes in forested
catchments due to gradual leaching of base cations through weathering processes and export of
humic acids with progressive pedogenesis and plant succession. These processes have been
invoked as an important mechanism in southern Greenland (Anderson et al. 2008), but they are
less applicable to Lake RS29, located in the High Arctic polar desert. The short snow free
season, thin active layer, cold temperatures through the summer, prevailing aridity, and low plant
biomass means there is little pedogenesis and slow rates of chemical weathering (Gajewski
2015b). In the Arctic, lack of extensive vegetation or soil development suggests climate may be a
more important factor than catchment processes in determining ecological communities (Wilson
et al. 2012). Despite the potential for acidic weathering products in areas of the Arctic underlain
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by granitic rocks, it is not well established that these processes promote acidification of fresh waters in the Arctic. The presence of moss remains in the RS29 core (Table 1) indicates the establishment of a shallow littoral zone suited to mosses and other aquatic plants. Other pollen taxa increased at that time, including Artemisia , Polypodiaceae, Rosaceae and Ranunculaceae
(Gajewski 1995). While the taxonomic resolution of the pollen record does not allow species to be identified, the flora of Somerset Island contains a variety of species within these groups that are found in aquatic or littoral habitats (Porsild 1964). Bryophyte rich wetland plant communities typically yield acidic runoff, potentially contributing to the development of the acidophilic diatom community recorded in Zone 2.
Alternate explanations for acidification in poorly buffered Arctic lakes relate to climate, which determines the duration of ice Draft cover, and in turn regulates dissolved inorganic carbon speciation through pCO 2, and hence lake water pH (Koinig et al. 1998). The inferred acidification of Lake RS29 coincided temporally with cooling climates as inferred by pollen and a variety of other proxies across this region (Gajewski 1995, 2015a), although the correlation of pH and July temperature is low (0.15, p=0.2). Thus, the declining pH through diatom Zone 2 in the RS29 record may also be an effect of climatic cooling and prolonged ice cover, as has been suggested for other Arctic lakes with dilute waters in the middle and late Holocene (Wolfe 2002;
Michelutti et al. 2007).
The uppermost diatom Zone 3 was characterized by an abrupt decrease in Aulacoseira alpigena , and an increase in numerous epiphytic (e.g., Eunotia exigua and Psammothidium marginulatum ), and plankontic taxa ( Cylotella rossii and Discostella pseodostelligera ). Overall, diatom diversity continued to increase through Zone 3. The assemblages in this zone indicate a well developed littoral zone with diverse periphytic diatom habitats, as well as longer open water
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seasons, facilitating the increase in relative abundance of diatoms in the Cyclotella sensu lato
complex. The decline in Aulacoseira spp. may relate to enhanced thermal stratification, and less
of the turbulence required to keep these heavy taxa afloat in the upper part of the water column
(Rühland et al. 2008). This suite of changes is often associated with the onset of anthropogenic
climate warming in the late 19 th or early 20 th century (Douglas et al. 1994; Smol et al. 2005;
Rühland et al. 2008), although the situation may be more complex (Saros and Anderson 2015).
According to the age depth model developed for Lake RS29 these shifts are occurring
considerably earlier, as has been found elsewhere (e.g., Finkelstein and Gajewski 2007; Perren et
al. 2009, 2012a; Saros and Anderson 2015). Given the uncertainties of radiocarbon (Gajewski et
al. 1995) and 210 Pb (e.g., Hadley et al. 2010) chronologies in Arctic lakes, the timing of these
changes should be interpreted with caution.Draft
Summary
At Lake RS29, the major diatom assemblages in the early Holocene included mostly benthic taxa
reflecting circumneutral to slightly acidic conditions, more mineral nutrients and a warmer
climate but with significant dissolution taking place. A shift to more acidophilic taxa,
tychoplanktonics and large benthics began around 6200 cal yr BP, when diatom concentrations
increased significantly as dissolution rates declined. A further shift took place around 1400 cal yr
BP; at this time, the acidophilic taxon Aulacoseira alpigena declined abruptly, as diverse benthic
and periphytic taxa, as well as planktonic diatoms in the Cyclotella sensu lato group increased,
indicating a return to somewhat less acidic conditions, further development of littoral
macrophyte communities, and increased duration of ice free seasons. This record shows the
importance of both climate and local habitat controls in explaining the changes in Arctic diatom
23 https://mc06.manuscriptcentral.com/asopen-pubs Arctic Science Page 24 of 49
records, as well as the need to consider taphonomic processes which affect diatom abundance.
The availability of pollen data from the same site allowed for an independent paleoclimate record to better evaluate the relative importance of climatic and watershed driven controls on diatom assemblages.
Acknowledgments
This research was funded by a Discovery Grant from the Natural Sciences and Engineering
Research Council of Canada (NSERC) and a grant from the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) to K. Gajewski as well as a Discovery Grant to S.
Finkelstein. Further funding was provided by the Northern Science Training Program (NSTP) and an Ontario Graduate Scholarship (OGS)Draft to T. Paull. Logistic support was provided by the
Polar Continental Shelf Project (PCSP), contribution number 04708. Thanks to Brett O’Neill for help with lab work and Marie Claude Fortin for help with BSi analyses. Diatom data from the
RS29 core will be archived at the Neotoma Paleoecology Database, and at the University of
Ottawa Laboratory for Paleoclimatology and Climatology website (www.lpc.uottawa.ca).
24 https://mc06.manuscriptcentral.com/asopen-pubs Page 25 of 49 Arctic Science
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List of figures
Figure 1. Location of Lake RS29 and other records mentioned in text.
Figure 2. Age depth curve of RS29. See text for details.
Figure 3. Relative abundances of common diatoms identified in Lake RS29. Species authorities are given in Table 2. Grey lines in lowermost panels are 5x exaggerations.
Figure 4. Diatom community indices including diatom and chrysophyte cyst concentrations and rarefaction diversity measures, pH reconstructed from the diatom assemblages, sample scores from detrended correspondence analysis, sediment parameters and biogenic silica estimates, pollen concentrations, and July mean temperatures estimated from pollen assemblages for the central Arctic. See text for details.
Figure 5: Sites where diatom free zones or dissolution were reported. See Table 3 for site information. Grey bar means diatoms present and white means absent; if low concentrations were reported the bar is half filled. Also shown are the July temperatures for the regions from Gajewski (2015a). Draft
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Table 1. Conventional radiocarbon ages and calibrated age BP (where year zero is AD1950) from lake RS29.
Depth Material Dated Conventional Error Calibrated age, Lab code (cm) 14 C age (+/ ) 2σ range 13 14 Dichelyma 1020 60 790 1060 CAMS 17391 capillaceum 26 27 bulk sediment 2490 60 2360 2740 TO 3033 27 31 macrofossil 4410 120 4650 5450 CAMS 18043 fragments 53 55 macrofossil 8640 150 9330 10170 CAMS 18047 fragments 58 59 bulk sediment 5510 70 6130 6450 TO 3034 84 85 Drepanocladus cf 5380 60 6000 6290 CAMS 17404 vernucosus 118 119 bulk sediment 6490 70 7270 7560 TO 3035 148 149 bulk sediment 9870 250 10570 12340 TO 3036
Draft
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Table 2. Maximum abundances and number of occurrences of the common diatom taxa identified from Lake RS29; taxa are listed in order of decreasing maximum abundance.
Maximum No. of Taxon Species authority abundance occurrences (%) Stauroforma exiguiformis (Lange Bertalot) Flower 83.2 59 Aulacoseira alpigena (Grunow) Krammer 71.0 55 Neidium affine (Ehrenberg) Pfitzer 56.8 20 Tabellaria flocculosa (Roth) Kützing 40.2 59 Eunotia praerupta Ehrenberg 26.4 46 Pinnularia nodosa (Ehrenberg) W. Smith 21.8 10 Pinnularia microstauron (Ehrenberg) Cleve 20.9 46 Psammothidium curtissimum (Carter) Aboal 20.3 47 Staurosirella pinnata (Ehrenberg) Williams and Round 18.6 28 Psammothidium marginulatum (Grunow) Bukhtiyarova and Round 16.3 54 Aulacoseira perglabra (Østrup) Haworth 15.6 47 Pinnularia microstauron (Ehrenberg) Cleve 14.1 46 Pseudostaurosira brevistriata (Grunow) Williams and Round 13.8 26 Eunotia rhomboidea Hustedt 12.0 24 Discostella pseudostelligera (Hustedt) Houk and Klee 10.4 30 Cavinula cocconeiformis (GregoryDraft ex Greville) Mann and Stickle 8.8 28 Aulacoseira undifferentiated N/A 8.2 44 Humidophila schmassmannii Hustedt (Buczkó and Wojtal) 7.3 51 Frustulia rhomboides (Ehrenberg) De Toni 7.2 46 Staurosira construens var. 7.1 13 venter (Ehrenberg) Hamilton Cyclotella rossii Håkansson 6.6 53 Aulacoseira nivalis (Smith) English and Potapova 6.2 44 (Krasske) Hamilton, Antoniades and Achnanthidium kriegeri 5.8 49 Siver Navicula digitulus Hustedt 5.3 50 Pinnularia septentrionalis Krammer 5.3 12 Encyonopsis naviculacea (Grunow) Krammer 4.7 34 Staurosirella lapponica (Grunow) Williams and Round 4.7 4 Brachysira brebissonii Ross in Hartley 4.6 52 Fragilaria berolinensis (Lemmermann) Lange Bertalot 4.2 16 Eunotia sudetica Otto Mueller 4.1 28 (Lange Bertalot) Lange Bertalot, Achnanthidium daonense 4.0 45 Monnier and Ector Eunotia implicata Nörpel, Lange Bertalot and Alles 3.6 38 Eunotia pseudopectinalis Hustedt 3.3 21 Eunotia septentrionalis Østrup 3.3 25 Psammothidium levanderi (Hustedt) Bukhtiyarova and Round 3.3 48 Pinnularia decrescens v. Krammer 3.1 45 ignorata Nupela impexiformis (Lange Bertalot) Lange Bertalot 2.9 48 Platessa conspicua (Mayer) Lange Bertalot 2.9 29 Cymbopleura incerta (Grunow) Krammer 2.6 36
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Eunotia bilunaris (Ehrenberg) Schaarschmidt 2.6 28 Aulacoseira lirata v. biseriata (Grunow) Haworth 2.5 6 Eunotia flexulosa (Brébisson ex Kützing) Kützing 2.4 25 Planothidium engelbrechtii (Cholnoky) Round and Bukhtiyarova 2.3 26 Encyonema minutum (Hilse ex Rabenhorst) Mann 2.1 39 Cavinula pseudoscutiformis (Hustedt) Mann and Stickle 1.9 40 Encyonema gaeumannii (Meister) Krammer 1.9 28 Eunotia arculus (Grunow) Lange Bertalot and Nörpel 1.9 20 Psammothidium helveticum (Hustedt) Bukhtiyarova and Round 1.9 22 Eunotia monodon Ehrenberg sensu lato 1.6 35 Fragilaria capucina var. (Kützing) Lange Bertalot 1.6 17 vaucheriae Nitzschia angustiforaminata Lange Bertalot 1.6 36 Psammothidium subatomoides (Hustedt) Bukhtiyarova and Round 1.6 14 Eunotia muscicola Krasske 1.4 20 Rossithidium pusillum (Grunow) Round and Bukhtiyarova 1.3 17 Stauroneis neohyalina Lange Bertalot and Krammer 1.3 38 Achnanthidium affine (Grunow) Czarnecki 1.2 22 Eunotia minor (Kützing) Grunow 1.2 9 Pinnularia rumrichae Krammer 1.2 26 Psammothidium bioretii (Germain) Bukhtiyarova and Round 1.2 23 Stauroneis anceps EhrenbergDraft 1.2 21 Planothidium holstii (Cleve) Lange Bertalot 1.1 14 Cavinula variostriata (Krasske) Mann and Stickle 1.0 30
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Table 3. Sites used to investigate diatom free zones in the Canadian Arctic and Greenland. All lakes in the table were considered, but only those where the authors report diatom free zones or dissolution are included in Fig. 5. The climate region is from Gajewski (2015a). The proxy column indicates which were available for each site: % = diatom percentages, C = diatom concentrations or influx, BSi = biogenic silica, P = pigments. Records had to be greater than ~3000 years in length to be included. Sp cond is specific conductance.
pH Sp Cond Lake Lat Long Elev Island / Climate Proxy (µS cm 1) Reference oN oW (m) Region Region KR02 71.34 113.7 229 Victoria West C, BSi 7.4 79 Podritske and Gajewski 2007 WB02 72.29 109.87 150 Victoria West BSi 8.0 88 Fortin and Gajewski. 2010b. BC01 75.18 111.9 225 Melville Isl West C, BSi 6.6 5 Peros et al. 2010 PW02 74.07 97.77 182 POW Cent C, BSi 7.9 50 Finkelstein and Gajewski 2008 PW03 73.12 96.68 243 POW Cent C, BSi 7.3 45 Finkelstein and Gajewski 2007 RS29 71.13 95.28 180 Somerset Cent C, BSi This paper RS36 72.58 94.93 160 Somerset Cent BSi Paull 2008 SL01 68.56 91.94 198 Boothia Cent BSi 6.5 10 Paull 2008 JR01 69.90 95.07 120 Draft Boothia Cent C, BSi 8.1 220 LeBlanc et al. 2004; Fortin and Gajewski 2016. SP02 68.56 83.29 220 Melville P East C, BSi 6.9 41 Adams and Finkelstein 2010 SP04 68.55 83.28 220 Melville P East C, BSi 6.9 39 Adams and Finkelstein 2010 DV09 75.57 88.68 35 Devon East C, BSi 8.4 100 Courtney, Mustaphi and Gajewski 2013 KHL 67.95 65.04 100 Baffin East %, BSi 6.4 14 Florian et al. 2015. CF8 70.51 68.95 195 Baffin East % 6.3 19 Wilson et al. 2012 Inqua 62.26 66.24 36 Baffin East C 6.6 15 Williams. 1990. Instaar 62.26 66.28 10 Baffin East C 6.5 13 Williams. 1990. Mercer 62.26 66.26 1 Baffin East C 6.6 14 Williams. 1990. CF3 70.50 68.30 Baffin East C, P 5.9 69 Michelutti et al. 2007 Amarok 66.27 65.70 848 Baffin East C 6.1 7 Wolfe and Hartling 1996 Tulugak 66.27 65.70 754 Baffin East C 6.1 7 Wolfe and Hartling 1996 Ukalik 66.27 65.70 545 Baffin East C 6.1 7 Wolfe and Hartling 1996 Kekerturnak 67.90 64.83 120 Baffin East C 6.3 10 Wolfe 2002 Fog 67.18 63.25 460 Baffin East C 6.3 10 Wolfe 2002 260 78.73 74.63 260 Pim N Gr %, P 6.5 36 Rouillard et al. 2012 West 78.73 74.50 260 Pim N Gr %, P 7.3 29 Rouillard et al. 2012 Elison 78.55 74.70 13 Ellesmere N Gr % Douglas et al. 1994 Camp 78.55 74.70 Ellesmere N Gr % Douglas et al. 1994 Col 78.55 74.70 135 Ellesmere N Gr % Douglas et al. 1994 Solstice 79.42 84.10 305 Ellesmere N Gr C 7.3 46 Wolfe 2000 Appleby 82.85 68.25 447 Ellesmere N Gr C 7.6 Smith 2002 Brainard 81.75 68.20 632 Ellesmere N Gr C 7.7 Smith 2002 Whisler 82.88 68.43 245 Ellesmere N Gr C 8.0 Smith 2002 Stygge 79.73 78.65 330 Ellesmere N Gr % 8.2 610 Paul et al. 2010
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RockBasin 78.50 76.73 295 Ellesmere N Gr %, BSi 6.0 12 Michelutti et al. 2006 Sawtooth 79.33 80.15 280 Ellesmere N Gr C 8.0 Perren et al. 2003. WardHunt 83.10 74.17 Ellesmere N Gr %, P Antoniades et al. 2007 Kaffeklubben 83.62 30.78 45 N Greenl N Gr C Perren et al. 2012b Raffles 70.60 21.53 40 E Greenl E Gr C, BSi Cremer et al 2001 Hjort 76.00 18.83 114 E Greenl E Gr C 9.2 16 Wagner et al. 2008 Igaliku 61.00 45.43 15 S Greenl S Gr % Massa et al. 2012 SS2 66.99 50.97 185 SW Greenl S Gr %, P 320 Anderson et al. 2008 FVL 65.61 37.70 73 SE Greenl S Gr C Balascio et al. 2013 AT1 66.97 53.40 475 S Greenl S Gr %, P 7.0 30 Law et al. 2015 AT4 66.97 53.42 200 S Greenl S Gr %, P 7.5 44 Law et al. 2015 SS1381 67.01 51.12 196 S Greenl S Gr %, P 8.8 605 Law et al. 2015 SS8 67.00 51.07 188 S Greenl S Gr %, P 8.1 362 Law et al. 2015 SS49 66.86 54.64 330 W Greenl S Gr % 6.6 26 Perren et al. 2012a. SS16 66.91 50.46 477 W Greenl S Gr % 7.2 107 Perren et al. 2012a. SS32 66.97 49.80 470 W Greenl S Gr % 7.3 51 Perren et al. 2012a.
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Kaffeklubben
Hjort
Appleby Whisler 80°N WardHunt Raffles Brainard Stygge Col Sawtooth Solstice Elison Camp RockBasin WestL260
BC01 DV09 FVL PW03 PW02 SS8 WB02 RS36 CF3 SS1381 SS2 CF8 AT4 SS16 70°N KR02 KHL SS49 RS29 Kekerturnak AT1 JR01 Fog SP02 AmarokUkalik Vegetation Zone SL01 Igaliku SP04 Tulugak Ice High Arctic Draft Mercer Inqua Middle Arctic Instaar 0125 250 500
Low Arctic Kilometers Boreal
100°W 80°W 60°W
Figure 1. Location of Lake RS29 and other records mentioned in text.
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10000
8000 Draft
6000
cal BP
4000
2000
0
0 50100 150 Depth
Figure 2. Age depth curve of RS29. See text for details.
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Depth (cm) cal BP Tabellaria flocculosaNeidium affineEunotia praeruptaPinnularia Staurosirellanodosa Stauroforma pinnata exiguiformisAulacoseira alpigenaPseudostaurosiraPinnularia brevistriataAulacoseira microstauronPsammothidium perglabraPsammothidium curtissimumEunotia marginulatum rhomboideaDiscostellaCyclotella peudostelligera rossiiCavinula cocconeiformis 0 III 1000
2000 20 3000 II 40 4000 60 5000 80 100 6000 120 7000
8000 140 I 9000
10000
25 50 25 50 25 50 25 50 25 50 25 50 75 25 50 75 25 50 25 50 25 50 25 50 25 50 25 50 25 50 25 50 10
Depth (cm) cal BP FragilariaPlanothidium berolinensisStaurosira Pinnulariaholstii construensStaurosirella septentrionalisFragilaria var. venterlapponicaNitzschia capucinaPinnularia Draftangustiforaminata var.Navicula vaucheriaedecrescensHumidophila digitulusAulacoseira v. ignorata Aulacoseiraschmassmanni undifferentiatedBrachysira nivalisFrustulia brebissoniiCavinula rhomboidesCavinula pseudoscutiformisCymbopleura variostriataEncyonopsis Encyonemaincerta naviculaceaEncyonema minutumStauroneis gaeumanniiStauroneis anceps neohyalina 0 1000 III 2000 20 3000 II 40 4000 60 5000 80 100 6000 120 7000 8000 140 I 9000 10000
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
Depth (cm) cal BP AchnanthidiumNupelaPsammothidium impexiformiskriegeriAchnanthidiumPlanothidium levanderiPlatessa daonense Achnanthidiumengelbrechtii conspicuaPsammothidiumPsammothidium affinePsammothidium helveticumRossithidium subatomoidesEunotia bioretii Eunotiapusillum septentrionalisEunotia pseudopectinalisEunotia sudeticaEunotia monodonEunotia implicataEunotia flexuosaEunotia bilunarisEunotia muscicola arculus 0 III 1000
2000 20 3000 II 40 4000 60 5000 80 100 6000 120 7000
8000 140 I 9000
10000
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 https://mc06.manuscriptcentral.com/asopen-pubs Figure 3. Relative abundances of common diatoms identified in Lake RS29. Species authorities are given in Table 2. Grey lines in lowermost panels are 5x exaggerations. Arctic Science Page 48 of 49
Valves Diatom Cyst Shannon DCA DCA DCA DCA LOI LOI Pollen Central Arctic counted Conc Conc Rarefaction H’ diatom/cyst pH 1 2 3 4 550o C 950o C BSi Conc T July 0 III 1000
2000
3000 Draft
4000 II
5000 cal BP 6000
7000
8000 I 9000
10000
1250 20 40 200 400 30 60 24 60 120 6.0 6.5 7.0 24 24 24 24 15 30 4 8 16 32 15 30 4 567 x108 x106 L: 104 WAPLS 2 % % Weight % x102 oC valves gdw-1 cysts gdw-1 R: 612 grains cm-3
Figure 4. Diatom community indices including diatom and chrysophyte cyst concentrations and rarefaction diversity measures, pH reconstructed from the diatom assemblages, sample scores from detrended correspondence analysis, sediment parameters and biogenic silica estimates, pollen concentrations, and July mean temperatures estimated from pollen assemblages for the central Arctic. See text for details.
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Western Central Eastern North East South Arctic Arctic Arctic Greenl Greenl Greenl
o o o o o o
Appleby
Kaffen So Kaffen
SS1381 SS8 SS16
Brainard Whisler Sawtooth
Hjort So
KHL
Ward Hunt Ward
KR02 DV09 WB02 BC01
PW02 PW03 RS29 RS36 SL01 C C SP02 C C C C 0 Draft 2000
4000
6000
cal BP
8000 ?
10000
12000 468 468 468 246 246 468
Figure 5: Sites where diatom-free zones or dissolution were reported. See Table 3 for site information. Grey bar means diatoms present and white means absent; if low concentrations were reported the bar is half-filled. Also shown are the July temperatures for the regions from Gajewski (2015a).
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