# Dynamics of dissolved carbohydrates during the spring sea ice melt season in the Canadian Arctic

Christos Panagiotopoulos, Remi Amiraux, Kevin Crampond, Richard Sempéré

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Christos Panagiotopoulos, Remi Amiraux, Kevin Crampond, Richard Sempéré. Dynamics of dissolved carbohydrates during the spring sea ice melt season in the Canadian Arctic. Arctic Science, 2025, 10.1139/as-2024-0054. hal-05023831

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# Dynamics of dissolved carbohydrates during the spring sea ice melt season in the Canadian Arctic

Christos Panagiotopoulos<sup>a,†</sup>, Remi Amiraux<sup>a,b</sup>, Kevin Crampond<sup>a,c</sup>, and Richard Sempéré<sup>b,d</sup>

<sup>a</sup>Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO, Marseille, France; <sup>b</sup>Takuvik International Research Laboratory, Université Laval and CNRS (France), Québec, QC G1V 0A6, Canada; <sup>c</sup>Institut des Sciences de la Mer de Rimouski, Université du Québec à Rimouski, Rimouski, QC G5L 3A1, Canada; <sup>d</sup>Aix-Marseille Univ., CNRS, LCE, UMR 7376, Ocean Sciences Institute, Marseille, France

Corresponding author: Christos Panagiotopoulos (email: christos.panagiotopoulos@mio.osupytheas.fr)

## Abstract

In spring 2016, the temporal evolution of organic carbon and carbohydrate concentrations was monitored in and under the sea ice during the microalgal-ice algae and subsequent phytoplankton-productive periods in western Baffin Bay (Canadian Arctic). The results showed that total carbohydrates (TCHO) closely followed total organic carbon, with the highest concentrations observed in the bottom-most few centimeters of sea ice (mean 186 µM C, n = 22). Such organic matter accumulation likely comprises labile organic matter, reflecting the presence of a concentrated algal biomass, as suggested by the significant correlation between TCHO and chlorophyll *a* (*r* = 0.625, *p* < 0.05). Compositionally, the bottom-most ice core was dominated by monosaccharides, which accounted for 38%-90% of TCHO, and were probably the result of an important in situ exoenzymatic activity of polysaccharides. Conversely, total dissolved carbohydrates in the underlying water did not follow dissolved organic carbon patterns and were dominated by dissolved polysaccharides, indicating that carbohydrates may have multiple sources, not solely from microalgae in either pelagic or sympagic (ice-associated) environments. Overall, our results suggest significant differences in carbohydrate dynamics between sea ice and the under-ice water, despite the strong coupling of these systems during ice melt, highlighting the complexity of the processes occurring within these ecosystems.

**Key words:** organic matter, bottom ice core, carbohydrates, temporal variability, seawater

## 1. Introduction

The Arctic environment currently experiences an increase of 2.7 °C in air temperature (Box et al. 2019; IPCC 2022) due to global warming, effectively reducing the thickness and extent of sea ice. This, in turn, impacts the entire Arctic system, including ice light penetration (Frey et al. 2011; Vancoppenolle et al. 2013), phytoplankton blooms beneath the ice (Assmy et al. 2017; Massicotte et al. 2020), nutrients distribution once the sea ice melts (Hawkings et al. 2015; Zhang et al. 2015), and the environmental distribution of ice-associated (sympagic) biota (Arrigo 2017; Findlay et al. 2017). These biota are mainly composed of diatoms, which, according to conservative estimates, contribute 4%-20% of the total annual primary production in ice-covered regions (Arrigo et al. 2010; van Leeuwe et al. 2018).

Recent investigations using lipid biomarkers (highly branched isoprenoid alkenes and palmitoleic acid) have supported earlier findings regarding the release of ice-associated microalgae during the melting season (Amiraux et al. 2019), including bacteria associated with sympagic algae (Amiraux et al. 2020). These results highlight the significance of these organisms in the changing Arctic environment and their implication for biogeochemical cycling and carbon transfer (Duncan and Petrou 2022). Notably, most of the microalgal

biomass is concentrated in the lower section of sea ice, further demonstrating the direct interaction of this ice biota with the underlying seawater (Boetius et al. 2013; Galindo et al. 2014). Furthermore, studies have indicated that ice-associated microalgae and bacteria can also produce enormous amounts of exopolymeric organic matter within the ice (Krembs et al. 2002), often in response to environmental stress such as changes in brine salinity, pH, or strong irradiance (Thomas et al. 2010; Thornton 2014; Aslam et al. 2018). However, very little is known about the dynamics of this organic matter in the ice and the associated water column in the changing Arctic environment.

From a chemical perspective, this organic matter (mainly in its dissolved form) comprises carbohydrates, including extracellular polymeric substances (EPS), which could be released into to the marine environment when the ice melts (Krembs et al. 2002; Underwood et al. 2013; Aslam et al. 2016). In under ice seawater, these carbohydrates/EPS eventually enrich the dissolved organic matter (DOM) pool with labile or semi-labile components stimulating the microbial food web (Aslam et al. 2012a; Niemi et al. 2014; Piontek et al. 2020; Tisserand et al. 2020); affecting aggregation processes and, thus carbon flux (Riebesell et al. 1991; Riedel et al. 2006; Rontani et al. 2016); and/or participating in the formation of
**Fig. 1.** Map of the study area in Baffin Bay. The white circle in Fig. 1A indicates the sampling station of the ice camp. The sea ice core sections (0–3, 3–6, and 6–10 cm) and the underlying seawater sampled in this study are shown in Fig. 1B. doi:10.1525/elementa.076.f1

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sea-spray aerosols (Wilson et al. 2015; Decho and Gutierrez 2017). Other studies indicated significant relationships between dissolved/particulate carbohydrate concentrations and chlorophyll *a* (Chl *a*) or bacterial abundance (BA) (Underwood et al. 2013; Aslam et al. 2016); however, these studies were limited to the sea ice environment. To the best of our knowledge, an integrated study tracking carbohydrates from the sea ice to the underlying seawater column (i.e., a continuum of carbohydrates) has not yet been conducted.

In the frame of the Green Edge project (http://greenedge-expeditions.com/), which aimed to shed light on the processes controlling the microalgal spring blooms in the Arctic (Massicotte et al. 2020), we investigated carbohydrate dynamics in the sea ice and the underlying water column. Specific objectives included monitoring the distribution of carbohydrates to the environment during the spring bloom, across habitat (i.e., sympagic or pelagic) and correlating this chemical parameter with other chemical data (lipid tracers) or well-known environmental variables such as nutrients, BA, and Chl *a*.

# 2. Materials and methods

## 2.1. Sampling

The sampling period spanned approximately 2 months (16 May–6 July 2016) and was undertaken within the framework of the Green Edge project at the ice camp located south of Qikiqtarjuaq Island in Baffin Bay (Canadian Arctic; 67.48°N,

63.79°W; Fig. 1A) (Massicotte et al. 2020). Seawater samples were collected every 48 h at depths of 0, 1.5, 5, 10, 20, and 40 m using a Niskin bottle passing through a 1 m × 1 m hole in the ice sea, which was covered by a tent. The samples were transferred into 500 mL Schott bottles precombusted at 450 °C for 6 h. At the shore-site laboratory, seawater samples were filtered through 0.7 µm GF/F filters (47 mm, Whatman; pre-combusted at 450 °C for 6 h) to retain most of the phytodetritus and algal cells. Prior to filtration, 50–100 mL of the collected seawater was dispensed to wash the filtration system and filter. Duplicate seawater samples were collected for both dissolved organic carbon (DOC) and dissolved carbohydrates in pre-combusted (450 °C for 6 h) glass vials and Falcon tubes (previously washed with 5% HCl, Milli-Q water and 4–5 mL of the filtrate), respectively. For DOC analysis, the samples were acidified (pH = 2) with 20 µL of H₃PO₄ (85%) and stored in the dark at 4 °C, whereas those for sugars were frozen at –20 °C until analysis.

Sea-ice samples without duplicates were collected using a Kovacs Mark V 14 cm diameter corer. During the period investigated, snow and ice thicknesses decreased from 33.4 to 0.3 cm and from 149 to 107 cm, respectively (Fig. 2). A total of 10 cm of the sample was recovered from the bulk ice core and further split into 0–3, 3–6, and 6–10 cm sections (Fig. 1B). These ice sections were sub-sampled using a 19 mm hole saw to obtain finer samples, which were then directly placed in glass and Falcon tubes (duplicates included) as previously indicated for DOC and dissolved carbohydrates. Similarly,
**Fig. 2.** Temporal evolution of snow, ice core thickness beneath the snow, sea-ice total organic carbon (TOC) stocks (integrated values from 0–10 cm), and seawater dissolved organic carbon (DOC) stocks (integrated values from 0.5 to 40 m) at the sampling location in Baffin Bay (Figs. 1A and 1B).

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samples for total organic carbon (TOC) were acidified with H₃PO₄ (85%) and stored in the dark at 4 °C, whereas those for sugars were frozen at -20 °C until further analysis. Only TOC and total sugars (TCHO) were estimated in sea ice, as the samples were not filtered before analysis.

## 2.2. TOC and DOC analysis

TOC and DOC concentrations were measured by high-temperature combustion using a Shimadzu TOC 5000 analyzer according to Sohrin and Sempéré (2005) and Para et al. (2013). A four-point calibration curve was performed daily using standards prepared by diluting a stock solution of potassium hydrogen phthalate in Milli-Q water. To avoid random errors associated with day-to-day instrument variability, all samples from the same day of sampling were analyzed in a single day. Owing to the relatively high TOC content of ice samples (generally >200 µM C), procedural blanks (i.e., runs with Milli-Q water) were run between each sample. Blank values ranged from 1 to 2 µM C and were subtracted from the values presented here. Deep seawater reference samples (provided by D. Hansell, University of Miami; https://hansell-lab.rsmas.miami.edu/consensus-refence-material/index.html) were run daily (42.7 µM C, n = 4) to ascertain the accuracy of the organic carbon analysis.

## 2.3. Carbohydrate analysis

Carbohydrates were determined in ice and filtered seawater samples using the TPTZ method (Myklestad et al. 1997; Panagiotopoulos and Wurl 2009). This method detects the following monosaccharides (MCHO): hexoses (fructose, galactose, glucose, and mannose), pentoses (ribose, arabinose, and xylose), deoxy sugars (fucose and rhamnose), and uronic acids (glucuronic, galacturonic, and mannuronic acids). In filtered seawater samples, dissolved monosaccharides (DMCHO) were determined without acid hydrolysis, whereas total dissolved monosaccharides (TDCHO) were determined after acid hydrolysis using 1 M HCl (final concentration) at 100 °C for 20 h (Panagiotopoulos et al. 2014). Hydrolysis was stopped by placing the tubes in an ice bath for 5 min. Thereafter, dissolved polysaccharides (i.e., combined monosaccharides or DPCHO) were then calculated as the difference between TDCHO and DMCHO. For ice samples, which were not filtered, monosaccharides present in the dissolved and particulate phase (MCHO), and total monosaccharides (TCHO, after hydrolysis) were measured. Similarly, as above mentioned, polysaccharides were calculated as the difference between TCHO and MCHO. A standard calibration curve was obtained by analyzing five glucose standards spanning a concentration range of 0.2–2 mg L⁻¹. The response was linear across this concentration range (R² = 0.999), and MCHO concentrations
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Temporal evolution of total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations in sea ice core sections (0–3, 3–6, and 6–10 cm) and the underlying seawater, from 18 May–6 July 2016, at the sampling location in Baffin Bay (Fig. 1B).</figcaption></figure>

were converted to carbon-equivalents by using a molar conversion factor of 6.

# 3. Results and discussion

## 3.1. Distribution and stocks of organic carbon in sea ice and underlying water

During the sampling period, TOC concentrations were found to be highest in the first few centimeters of the sea ice (0–3 cm; 519 ± 338 µM C, *n* = 23) and decreased in the upper layers (3–6 cm; 205 ± 172 µM C, *n* = 22; 6–10 cm; 153 ± 147 µM C, *n* = 23), which is consistent with previous studies (Underwood et al. 2013; Aslam et al. 2016). TOC concentrations exhibited the highest values during May–June 2016 with a peak on 13 June and significantly decreased during July (Fig. 3). The high TOC concentrations (ranging from 485 to 773 µM C), recorded during the period from 25 May to 8 June 2016, corresponded to the initial peak in ice algal biomass, which developed in the 0–3 cm section of sea ice (Amiraux et al. 2019). This first biomass peak, which ended on 8 June 2016, coincided with the start of snowmelt, leading to reduced snow thickness and increased light exposure (Amiraux et al. 2020). This light-induced stress likely con-

tributed to the release of some ice algal material into the underlying water column, as observed by Amiraux et al. (2019).

TOC concentrations further increased during the period from 13 to 22 June 2016. This was likely due to the second peak in ice algal biomass on 13 June 2016 (Amiraux et al. 2019) and the enrichment of carbon in all ice core sections after snowmelt water was flushed out (Eicken et al. 2002) through the entire ice core (Fig. 3). Although we did not measure TOC in the snow in the overlying ice core layer, previous investigations undertaken in Arctic and Antarctic continental shelves suggest that surface snow can contain as much as 50–60 µM C, which may be transferred to the sea ice and possibly to the under-ice seawater, thereby increasing their respective organic carbon content (Grannas et al. 2004; Antony et al. 2011; Zhang et al. 2020). Alternatively, these high TOC concentrations may result from the selective incorporation of DOM from the underlying ice seawater, as shown experimentally by other studies (Müller et al. 2013). The results of this study showed that TOC stocks (integrated values from 0 to 10 cm of the ice core) during the period from 13 to 22 June 2016 were twice as high as those during the period from 25 May to 8 June 2016, with values ranging from 37 to 75 mmol m⁻² highlighting the extent of the second ice algal bloom in terms of carbon (Fig. 2).
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Temporal evolution of TCHO and TDCHO concentrations in the sea ice core (0–3, 3–6, and 6–10 cm) and the underlying seawater, respectively, from 18 May to 6 July 2016, at the sampling location in Baffin Bay (see Fig. 1B).</figcaption></figure>

Recent research in the same sampling area and period suggests that the snow melt onset marked the end of the ice algal bloom and the initiation of the phytoplankton bloom beneath the ice (approximate initiation date: 13 June 2016), which was related to the increasing light availability and water column stratification (Oziel et al. 2019; Massicotte et al. 2020). Nevertheless, this under-ice phytoplanktonic bloom became significant only after 29 June 2016, as revealed by Chl *a* (>10 mg m⁻²) and primary productivity (>10 mmol C m⁻² day⁻¹), suggesting that our sampling missed the biomass peak of the phytoplanktonic bloom (Fig. 3). During the period from 18 to 25 May 2016, DOC concentrations were relatively high (80–90 µM C), at all depths, due to the low stratification of seawater. After 25 June 2016, DOC values remained relatively constant, ranging from 63 to 67 µM C. The elevated DOC values observed during the period from 1 to 10 June (80–90 µM C) and again at the end of June 2016 (75 µM C) were most likely related to organic carbon patches released from the above-ice algae (Amiraux et al. 2019) (Fig. 3). Overall, DOC concentrations did not exhibit dramatic changes over the sampling period, which is also reflected in DOC stocks that remained fairly constant (~2500–3000 mol m⁻²) (Fig. 2).

## 3.2. Distribution of carbohydrates in sea ice and underlying water

TCHO concentrations exhibited similar patterns to TOC, being high in the first few bottom-most centimeters (0–3 cm) of sea ice (mean 186 µM C, *n* = 22), indicating the presence of concentrated algal biomass (Underwood et al. 2013; Cimoli et al. 2020). Afterward, TCHO concentrations progressively decreased across the ice core (3–6 cm; 36 µM C, *n* = 22; 6–10 cm; 19 µM C, *n* = 22). TCHO concentrations peaked most of the time in June 2016, with values ranging from 292 to 413 µM C, before decreasing considerably in July 2016, attaining values <10 µM C (Fig. 4). TCHO concentrations in the sea ice showed a significant correlation with TOC in the first 0–3 cm section of the core (*n* = 18, *p* < 0.01, R² = 0.68), whereas moderate relationships were observed in 3–6 cm (*n* = 21, *p* < 0.05, R² = 0.27) and 6–10 cm (*n* = 22, *p* < 0.05, R² = 0.29). These results suggest that TCHO constitutes 36% and 42% of TOC in 3–6 and 0–3 cm sections, respectively, in the ice core (similar slopes of TOC vs. TCHO for 0–3 and 3–6 cm; Fig. 5), further reflecting the presence of algal biomass as revealed by the substantial carbohydrate content.

In contrast to seawater, where the carbohydrate pool was dominated by polysaccharides (Fig. S1), MCHO were the
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Relationships between TCHO concentrations and total organic carbon (TOC) in the different sections of the ice core (0–3, 3–6, and 6–10 cm).</figcaption></figure>

dominant carbohydrate species in bottom-most sea ice sec-
tion (0–3 cm), with concentrations >100 µM C, representing
38%–90% of TCHO (Fig. S2). Previous investigations of sea ice
samples from several Arctic sites have reported carbohydrate
concentrations for polysaccharides or low molecular weight
carbohydrate fractions (Aslam et al. 2016). To the best of
our knowledge, data on MCHO concentrations in sea ice are
scarce. The only study that reported monosaccharide occur-
rence in sea ice was conducted in Antarctica and showed that
these compounds may account for as much as 70% of TCHO,
which aligns with the findings of the present study (Herborg
et al. 2001). Considering that MCHO are primarily present in
the dissolved phase, these results suggest that enzymatic ac-
tivity associated with sympagic bacteria plays a crucial role
in hydrolyzing dissolved/particulate polysaccharides (PCHO
concentrations <80 µM C in most cases; Fig. S1), thereby re-
leasing DMCHO. Conversely, in the upper sea ice layer (3–
6 cm section), PCHO concentrations were higher than those
of MCHO with values 19 ± 11 µM C (n = 22) and 12 ± 11 µM
C (n = 21), respectively. A similar pattern was recorded at 6–
10 cm (PCHO = 12 ± 6 µM C vs. MCHO = 7 ± 5 µM C), indi-
cating the predominance of PCHO over MCHO suggesting a
lower bacterial activity in these sections.

In contrast to sea ice, TDCHO concentrations did not cor-
relate with DOC (n = 68, p > 0.1, R² = 0.027) and increased
considerably after 1 June 2016, attaining values of 26–39 and
23–31 µM C in the surface waters and deep waters, respec-
tively (Fig. 4). As indicated above between 1 and 10 June 2016,
and by the end of June 2016, some ice algal biomass had en-
tered the under-ice seawater (increasing of DOC concentra-
tions) through the formation of fast-sinking particles, a fea-

ture commonly observed in many marine environments, in-
cluding the Arctic (Trudnowska et al. 2021; Gal et al. 2022).
Previous studies have shown that fast-sinking particles con-
tain significant amounts of EPS, predominantly polysaccha-
rides, originating from diatoms or bacteria, which contribute
to mucilage structures (Verdugo 2012; Underwood et al. 2013;
Decho and Gutierrez 2017; Aslam et al. 2018). Therefore, the
high concentrations of TDCHO observed in seawater after 8
June 2016 were most likely due to enriched organic matter
in EPS derived from fast-sinking particles produced by the
release of ice algae (1–10 June 2016 and end of June 2016)
because of light stress and the subsequent downward per-
colation of meltwater. This is further supported by the high
concentration of DPCHO in the under-ice seawater ranging
from 12 to 32 µM C, which in most cases represented >60%
TDCHO (Fig. S1). The persistence of the DPCHO in seawater
indicates an accumulation of semi-labile DOM in the under-
ice seawater, which is characteristic of freshly produced dis-
solved carbohydrates in the oceanic environments (Sempéré
et al. 2008; Goldberg et al. 2011; Carlson and Hansell 2015;
Panagiotopoulos et al. 2019).

3.3. Carbohydrate yields and relationships
between carbohydrates and environmental
variables in sea ice and under-ice water

The contribution of carbohydrates to the organic carbon
pool, referred to here as TCHO or TDCHO yields, is presented
as a percentage of TOC or DOC (i.e., TCHO × TOC⁻¹%, TD-
CHO × DOC⁻¹%). TCHO yields were higher in the bottom
ice core (0–3 cm, mean 36%, *n* = 22) and progressively de-
creased in the upper layers (3–6 cm, 22%, *n* = 21; 6–10 cm, 17%, *n* = 21). These elevated TCHO yields were likely due to the release of fresh ice algae by-products, including freshly derived DOM present in the ice (Amon and Benner 2003; Aslam et al. 2012b; Cimoli et al. 2020). Previous investigations using microscope analysis and imaging FlowCytobot data from the same 2016 campaign showed that the bottom-most sea ice (0–3 cm) mainly comprised pennate diatoms, particularly *Nitzschia frigida*, *Navicula* sp., and *Nitzschia closterium*. These taxa, which dominate sea ice algal communities (Leu et al. 2015; Szymanski and Gradinger 2016; Amiraux et al. 2019), are critical contributors to under-ice blooms (Dezutter et al. 2019). Previous studies have shown that carbohydrates represent 10%–25% of the particulate organic weight of these species (Ben-Amotz et al. 1985; Brown et al. 1997), aligning with the present TCHO yields, even though our data refer to the total (not particulate) carbohydrate fraction in the sea ice. These observations are supported by the high correlation of TCHO (*r* = 0.63, *p* < 0.05) and TOC (*r* = 0.63, *p* < 0.05) with the microalgae biomass proxy Chl *a*, indicating that these carbohydrates and associated organic matter (i.e., TOC) in sea ice are linked to ice algae (Table S1).

BA (bact. mL⁻¹) showed no significant correlation with any
carbohydrate species but correlated positively with Chl *a*
(*r* = 0.85, *p* < 0.05) implying an important degree of coupling
between bacteria biomass and sea ice algae in bottom sea ice,
as well as in the under-ice water (*r* = 0.97, *p* < 0.05; Table S2).
The coupling between resources and bacterial activities has
already been reported during diel cycle, which might be con-
nected to the variable intensity of bacterial predatory activity
by ciliates or other organisms, as well as to the variations in
enzymatic activity (Van Wambeke et al. 2001). BA also corre-
lated with TOC and nutrients, particularly NO₃⁻ and PO₄³⁻,
in the bottom sea ice, aligning with previous studies (Zhou
et al. 2014; Kaikkonen et al. 2020), which suggests that these
environmental parameters control BA dynamics.

Carbohydrate species in the bottom sea ice (0–3 cm) showed no significant correlation with ice algae biomarkers (i.e., IP25) or certain nutrients (NO3- or SiO2), indicating a decoupling of carbohydrates from these environmental variables (Table S1). Conversely, MCHO showed a significant correlation with PO4 3- (*r* = 0.75, *p* < 0.05) possibly indicating a common origin of these species. Sugars and phosphorus are found together in intracellular organic compounds such as nucleic acids, ATP, and sugar phosphates, which are involved in several biological processes (energy transactions via ATP and nucleic acid synthesis) (Karl and Björkmann 2015 and references therein). Therefore, the strong correlation between MCHO and phosphorus explicitly suggests the presence of these compounds in samples, highlighting the involvement of biologically active organisms like phytoplankton and prokaryotic bacteria as well as other biological activities like assimilation of extracellular nucleic acids and ATP utilization in the bottom sea ice. An equally significant correlation was observed between DMCHO and PO4 3- (*r* = 0.66, *p* < 0.05) in under-ice water (Table S2), probably indicating the presence of the similar compounds near the ice edge.

TDCHO yields in the under-ice ranged from 20% to 39% be-
tween the mid-May and early 2016, progressively increasing

attaining 62% by 13 June 2016 (Fig. 4). TDCHO yields remained between 35% and 43% for the rest of June but decreased considerably to 13% in July 2016. Unlike sea ice carbohydrates, TDCHO in under-ice water did not correlate with Chl *a* (negative and insignificant; Table S2), implying that carbohydrates may have multiple sources, apart from phytoplankton. Overall, our results suggest significant differences in carbohydrate dynamics between sea ice (dominated by MCHO), and under-ice seawater (dominated by PCHO), despite the strong coupling of these systems, before and after ice melt. This further implies that carbohydrate composition varies as organic carbon dramatically differs between under-ice and sea ice. Further research is warranted to elucidate the composition of organic matter with respect to other components such as proteins and lipids within these ecosystems.

4. Conclusions

The results of this study showed that TCHO closely followed
TOC patterns, with the highest concentrations observed in
the first few bottom-most centimeters of sea ice (0–3 cm;
mean 186 µM C, *n* = 22), indicating the presence of labile
organic matter as a result of concentrated algal biomass. We
found that sea ice-TCHO concentrations peaked in June 2016,
with values ranging from 292 to 413 µM C when the ice
algal bloom occurred. In July, sea ice-TCHO concentrations
considerably decreased to values <10 µM C. Compositionally,
the bottom-most ice core (0–3 cm) was dominated by MCHO,
which exhibited concentrations >100 µM C, accounting for
38%–90% of TCHO, likely due to substantial in situ exoen-
zymatic activity of polysaccharides. Conversely, TDCHO in
the under-ice water followed neither DOC patterns nor cor-
related with Chl *a*, suggesting multiple sources of carbohy-
drates other than microalgae from pelagic or sympagic (ice-
associated) environments. TDCHO concentrations increased
after 1 June 2016, reaching values between 26 and 39 µM C,
most likely because of EPS released from fast-sinking par-
ticles derived from ice algae. This is further supported by
the high concentration of DPCHO in the under-ice seawater,
which ranged from 12 to 32 µM C and, in most cases, rep-
resented >60% TDCHO. Overall, our results suggest signifi-
cant differences in carbohydrate dynamics between sea ice
(dominated by MCHO) and under ice (dominated by PCHO),
despite the strong coupling between these systems during the
ice melt, highlighting complexity of the processes occurring
within these ecosystems.

Acknowledgements

The Green Edge project is funded by the following French and
Canadian programs and agencies: ANR (Contract #111112),
CNES (project #131425), IPEV (project #1164), CSA, Fonda-
tion Total, ArcticNet, LEFE, and the French Arctic Initiative
(Green Edge project). This project would not have been pos-
sible without the support of the Hamlet of Qikiqtarjuaq and
the members of the community as well as the Inuksuit School
and its Principal, Jacqueline Arsenault. The project was con-
ducted under the scientific coordination of the Canada Ex-
cellence Research Chair on Remote sensing of Canada's new
Arctic frontier and the CNRS & Université Laval Takuvik Joint
International laboratory (UMI3376). The field campaign was successful thanks to the contribution of J. Ferland, G. Bécu, C. Marec, J. Lagunas, F. Bruyant, J. Larivière, E. Rehm, S. Lambert-Girard, C. Aubry, C. Lalande, A. LeBaron, C. Marty, J. Sansoulet, D. Christiansen-Stowe, A. Wells, M. Benoît-Gagné, E. Devred, and M.-H. Forget from the Takuvik laboratory, C.J. Mundy and V. Galindo from University of Manitoba as well as F. Pinczon du Sel and E. Brossier from Vagabond. We also thank Michel Gosselin, Québec-Océan, the CCGS Amundsen, and the Polar Continental Shelf Program for their kind contributions in polar logistic and scientific equipment. Finally, the authors gratefully acknowledge M. Babin, leader of the Green Edge project.

## Article information

### History dates

Received: 22 July 2024

Accepted: 10 February 2025

Accepted manuscript online: 6 March 2025

Version of record online: 9 April 2025

### Copyright

©2025 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

### Data availability

All data can be accessed from the Green Edge database (http://www obs vlfr fr proof php GREENEDGE greenedge php) and will be made public after publication.

## Author information

### Author ORCIDs

Christos Panagiotopoulos https://orcid.org/0000-0001-6025-7703

Richard Sempéré https://orcid.org/0000-0002-2956-0998

### Author notes

Remi Amiraux served as Associate Editor at the time of manuscript review and acceptance; peer review and editorial decisions regarding this manuscript were handled by another editorial board member.

### Author contributions

Conceptualization: CP, RS

Formal analysis: CP, KC

Investigation: CP, RA, RS

Methodology: RA

Resources: RA

Software: KC

Supervision: CP

Validation: RS

Writing – original draft: CP

Writing – review & editing: CP, RA, KC, RS

## Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Supplementary material

Supplementary data are available with the article at https://doi.org/10.1139/as-2024-0054.

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