Amundsen Science

Abstract Heavy ice conditions along Canada's east coast during spring 2017 presented hazardous conditions for the maritime industry and required the Canadian Coast Guard to pull its research icebreaker, CCGS Amundsen , off its scientific cruise to provide ice escort services and conduct search and rescue operations along Newfoundland's northeast coast. Greater ice concentrations and a thicker ice pack than are typical of this area created the anomalous ice cover. Within this paper we present in situ observations of the ice cover, confirming that pieces of multiyear sea ice from the high Arctic were present within the ice cover, and subsequently examine the transport pathway that connects the export of thick multiyear sea ice from the Lincoln Sea and Canadian Arctic Archipelago to coastal communities in Newfoundland. We conclude with a discussion on how an increasingly mobile Arctic sea ice cover may increase these ice hazards in the south.

An assessment of the production, distribution and fate of highly branched isoprenoid (HBI) biomarkers produced by sea ice and pelagic diatoms is necessary to interpret their detection and proportions in the northern Bering and Chukchi Seas. HBIs measured in surface sediments collected from 2012 to 2017 were used to determine the distribution and seasonality of the biomarkers relative to sea ice patterns. A northward gradient of increasing ice algae deposition was observed with localized occurrences of elevated IP25 (sympagic HBI) concentrations from 68-70°N and consistently strong sympagic signatures from 71-72.5°N. A declining sympagic signature was observed from 2012 to 2017 in the northeast Chukchi Sea, coincident with declining sea ice concentrations. HBI fluxes were investigated on the northeast Chukchi shelf with a moored sediment trap deployed from August 2015 to July 2016. Fluxes of sea ice exclusive diatoms (Nitzschia frigida and Melosira arctica) and HBI-producing taxa (Pleurosigma, Haslea and Rhizosolenia spp.) were measured to confirm HBI sources and ice associations. IP25 was detected year-round, increasing in March 2016 (10 ng m-2 d-1) and reaching a maximum in July 2016 (1331 ng m-2 d-1). Snowmelt triggered the release of sea ice algae into the water column in May 2016, while under-ice pelagic production contributed to the diatom export in June and July 2016. Sea ice diatom fluxes were strongly correlated with the IP25 flux, however associations between pelagic diatoms and HBI fluxes were inconclusive. Bioturbation likely facilitates sustained burial of sympagic organic matter on the shelf despite the occurrence of pelagic diatom blooms. These results suggest that sympagic diatoms may sustain the food web through winter on the northeast Chukchi shelf. The reduced relative proportions of sympagic HBIs in the northern Bering Sea are likely driven by sea ice persistence in the region.

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797 ∘ N, 63.7895 ∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies. The dataset is available at https://doi.org/10.17882/59892 (Massicotte et al., 2019a).

Sea ice in the Arctic Ocean has been undergoing dramatic changes during the last two decades. In addition, the water temperature of the inflow of Atlantic water masses at the gateway Fram Strait has recently increased. Long-term data may help to evaluate the impact of these physical changes on the biological processes in surface waters. Over a 25-year period, and mostly in summer, water samples were collected at discrete depths within the uppermost 100 m of the Fram Strait and other regions of the Arctic Ocean (AO) to investigate chlorophyll a (Chl a) and particulate organic carbon (POC) standing stocks. Stations sampled from 1991 to 2015 were located in the Fram Strait, Barents Sea, on the Eurasian shelf, and over the Nansen, Amundsen, and parts of the Amerasian basins. Discrete Chl a and POC measurements obtained during 33 and 24 expeditions, respectively, were integrated over the upper 100 m of the water column to monitor spatial and interannual variations in distribution patterns of standing stocks. In general, the highest Chl a and POC standing stocks were observed in the eastern Fram Strait and in the Barents Sea, while the lowest biomasses were observed in the heavily ice-covered regions of the central AO, mainly in the Amundsen and Amerasian basins. Whereas summertime Chl a stocks sharply decreased northwards from the Fram Strait and Barents Sea towards high latitudes, the decline in POC standing stocks was less pronounced. Over the sampling period, summertime Chl a stocks slightly increased in the eastern Fram Strait but remained more or less constant in the central AO. In contrast to Chl a, standing stocks of POC eventually increased over the last 25 years in the central AO, possibly as an effect of increasing air temperatures, decreasing sea ice extent and thickness, and increasing light availability. Moreover, variations in riverine discharge and in sea ice export within the Transpolar Drift may have contributed to the enhanced POC stock in the central AO surface waters.

Ascophyllum nodosum is a foundation macroalgae of the intertidal zone that distributes across latitude 41.3–69.7°N. We tested the hypothesis that growth of A. nodosum near the northern distribution edge increases with warming. We retrospectively quantified the growth of eight A. nodosum populations at West Greenland and North Norway (from 64°N to 69°N). For seven populations, we measured growth rates since 1997–2002 and for one of them we extended the time series back to 1956 using published estimates. Individuals at northern populations elongated between 2.0 and 9.1 cm year−1 and this variability correlated with temperature and annual ice-free days. A spatial comparison of A. nodosum growth across the species distribution range showed that Northern (and coldest) populations grew at the slowest rates. Our results demonstrate that arctic climate change enhances the growth of A. nodosum populations and suggest that their productivity may increase in response to projected global warming.

Unusually warm conditions recently observed in the Pacific Arctic region included a dramatic loss of sea ice cover and an enhanced inflow of warmer Pacific-derived waters. Moored sediment traps deployed at three biological hotspots of the Distributed Biological Observatory (DBO) during this anomalously warm period collected sinking particles nearly continuously from June 2017 to July 2019 in the northern Bering Sea (DBO2) and in the southern Chukchi Sea (DBO3), and from August 2018 to July 2019 in the northern Chukchi Sea (DBO4). Fluxes of living algal cells, chlorophyll a (chl a), total particulate matter (TPM), particulate organic carbon (POC), and zooplankton fecal pellets, along with zooplankton and meroplankton collected in the traps, were used to evaluate spatial and temporal variations in the development and composition of the phytoplankton and zooplankton communities in relation to sea ice cover and water temperature. The unprecedented sea ice loss of 2018 in the northern Bering Sea led to the export of a large bloom dominated by the exclusively pelagic diatoms Chaetoceros spp. at DBO2. Despite this intense bloom, early sea ice breakup resulted in shorter periods of enhanced chl a and diatom fluxes at all DBO sites, suggesting a weaker biological pump under reduced ice cover in the Pacific Arctic region, while the coincident increase or decrease in TPM and POC fluxes likely reflected variations in resuspension events. Meanwhile, the highest transport of warm Pacific waters during 2017-2018 led to a dominance of the small copepods Pseudocalanus at all sites. Whereas the export of ice-associated diatoms during 2019 suggested a return to more typical conditions in the northern Bering Sea, the impact on copepods persisted under the continuously enhanced transport of warm Pacific waters. Regardless, the biological pump remained strong on the shallow Pacific Arctic shelves.

Icebergs and ice islands (large, tabular icebergs) are challenging targets to survey due to their size, mobility, remote locations, and potentially difficult environmental conditions. Here, we assess the precision and utility of aerial photography surveying with structure-from-motion multi-view stereo photogrammetry processing (SfM) and vessel-based terrestrial laser scanning (TLS) for iceberg deterioration detection and mass estimation. For both techniques, we determine the minimum amount of change required to reliably resolve iceberg deterioration, the deterioration detection threshold (DDT), using triplicate surveys of two iceberg survey targets. We also calculate their relative uncertainties for iceberg mass estimation. The quality of deployed Global Positioning System (GPS) units that were used for drift correction and scale assignment was a major determinant of point cloud precision. When dual-frequency GPS receivers were deployed, DDT values of 2.5 and 0.40 m were calculated for the TLS and SfM point clouds, respectively. In contrast, values of 6.6 and 3.4 m were calculated when tracking beacons with lower-quality GPS were used. The SfM dataset was also more precise when used for iceberg mass estimation, and we recommend further development of this technique for iceberg-related end-uses.

The shallow Pacific Arctic shelf has historically acted as an effective carbon sink, characterized by tight benthic pelagic coupling. However, the strength of the biological carbon pump in the Arctic has been predicted to weaken with climate change due to increased duration of the open-water period for primary production, enhanced nutrient limitation, and increased pelagic heterotrophy. In order and gain insights into how the biological carbon pump is functioning under the recent conditions of extreme warming and sea ice loss on the Pacific Arctic shelf, we measured sinking particulate organic carbon (POC) fluxes from drifting and moored sediment traps, as well as rates of primary production and particle-associated microbial respiration in June 2018. We measured high sinking POC fluxes similar to and/or higher than previous measurements from this region (up to 2.3 g C m-2 d-1), reaching flux levels among the highest ever documented in the global oceans. Furthermore, high export ratios averaging 82% and low rates of particle-associated microbial respiration also indicated negligible recycling of sinking POC in the water column during spring of 2018. These results highlight the extraordinary strength of biological carbon pump on the Pacific Arctic shelf during an unusually warm and low-sea ice year. While additional measurements and time are needed to confirm the ultimate trajectory of these fluxes in response to ongoing climate change, these results call into question the prevailing hypothesis that the strength of the biological carbon pump in the Pacific Arctic will weaken under these conditions.

Abstract Sea ice is a critical component of the Earth’s Climate System and a unique habitat. Sea-ice changes prior to the satellite era are poorly documented, and proxy methods are needed to constrain its past variability. Here, we demonstrate the potential of sedimentary DNA from Polarella glacialis , a sea-ice microalga, for tracing past sea-ice conditions. We quantified P. glacialis DNA (targeting the nuclear ribosomal ITS1 region) in Arctic marine and fjord surface sediments and a sediment core from northern Baffin Bay spanning 12,000 years. Sea ice and sediment trap samples confirmed that cysts of P. glacialis are common in first-year sea ice and sinking particulate matter following sea-ice melt. Its detection is more efficient with our molecular approach than standard micropaleontological methods. Given that the species inhabits coastal and marine environments in the Arctic and Antarctic, P. glacialis DNA has the potential to become a useful tool for circum-polar sea-ice reconstructions.

Two mooring arrays carrying sediment traps were deployed from September 2011 to August 2012 at ∼83°N on each side of the Gakkel Ridge in the Nansen and Amundsen Basins to measure downward particle flux below the euphotic zone (approx. 250 m) and approximately 150 m above seafloor at approximately 3500 and 4000 m depth, respectively. In a region that still experiences nearly complete ice cover throughout the year, export fluxes of total particulate matter (TPM), particulate organic carbon (POC), particulate nitrogen (PN), biogenic matter, lithogenic matter, biogenic particulate silica (bPSi), calcium carbonate (CaCO 3 ), protists and biomarkers only slightly decreased with depth. Seasonal variations of particulate matter fluxes were similar on both sides of the Gakkel Ridge. Somewhat higher export rates in the Amundsen Basin and differences in the composition of the sinking TPM and bPSi on each side of the Gakkel Ridge probably reflected the influence of the Lena River/Transpolar Drift in the Amundsen Basin and the influence of Atlantic water in the Nansen Basin. Low variations in particle export with depth revealed a limited influence of lateral advection in the deep barren Eurasian Basin. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.

This paper proposes institutional innovations to advance a transparent monitoring system for the environmental impacts from mineral development on the deep seabed beyond national jurisdictions managed by the International Seabed Authority (ISA). Using a literature review, ISA’s regulations, and five cases of other environmental monitoring of the deep sea, this study observes that ISA's environmental monitoring system for exploration and exploitation currently lacks critical elements to facilitate transparency. Insufficient compliance reporting and review systems, as well as limited access to information by stakeholders, lower the system's effectiveness. ISA has not developed adequate mechanisms to support effective multinational collaboration in monitoring. The ISA monitoring system without these characteristics may not be sufficiently adaptive to allow detection and management of environmental changes in the deep seabed. This study suggests 15 institutional recommendations to ISA in order to enhance transparency for monitoring nodule mining in the Central Pacific deep seabed. Principal recommendations include establishing compliance review committees independent of ISA governing bodies, implementing collective monitoring and reporting by adjacent contractors, and reconsidering the centralized decision-making authority by the Secretary-General to improve confidentiality.

Abstract The Arctic Ocean north of Svalbard has recently experienced large sea ice losses and the increasing prominence of Atlantic water (AW) advection. To investigate the impact of these ongoing changes on annual particle export, two moorings with sequential sediment traps were deployed in ice‐free and seasonally ice‐covered waters on the shelf north (NSv) and east (ESv) of Svalbard, collecting sinking particles nearly continuously from October 2017 to October 2018. Vertical export of particulate organic carbon (POC), total particulate matter (TPM), planktonic protists, chlorophyll a , and zooplankton fecal pellets were measured, and swimmers were quantified and identified. Combined with sensor data from the moorings, these time‐series measurements provided a first assessment of the factors influencing particle export in this region of the Arctic Ocean. Higher annual TPM and POC fluxes at the ice‐free NSv site were primarily driven by the advection of AW, higher grazing by large copepods, and a wind‐induced mixing event during winter. Higher diatom fluxes were observed during spring in the presence of sea ice at the ESv site. Along with sea ice cover, regional differences in AW advection and the seasonal presence of grazers played a prominent role in the biological carbon pump along the continental shelf off Svalbard.

The characteristics of the CISE-LOCEAN seawater isotope dataset ( δ 18 O, δ 2 H, referred to as δ D) are presented (https://doi.org/10.17882/71186; Waterisotopes-CISE-LOCEAN, 2021). This dataset covers the time period from 1998 to 2021 and currently includes close to 8000 data entries, all with δ 18 O, three-quarters of them also with δ D, associated with a date stamp, space stamp, and usually a salinity measurement. Until 2010, samples were analyzed by isotopic ratio mass spectrometry and since then mostly by cavity ring-down spectroscopy (CRDS). Instrumental uncertainty in this dataset is usually as low as 0.03 ‰ for δ 18 O and 0.15 ‰ for δ D. An additional uncertainty is related to the isotopic composition of the in-house standards that are used to convert data to the Vienna Standard Mean Ocean Water (VSMOW) scale. Different comparisons suggest that since 2010 the latter have remained within at most 0.03 ‰ for δ 18 O and 0.20 ‰ for δ D. Therefore, combining the two uncertainties suggests a standard deviation of at most 0.05 ‰ for δ 18 O and 0.25 ‰ for δ D. For some samples, we find that there has been evaporation during collection and storage, requiring adjustment of the isotopic data produced by CRDS, based on d -excess ( δ D − 8× δ 18 O). This adjustment adds an uncertainty in the respective data of roughly 0.05 ‰ for δ 18 O and 0.10 ‰ for δ D. This issue of conservation of samples is certainly a strong source of quality loss for parts of the database, and “small” effects may have remained undetected. The internal consistency of the database can be tested for subsets of the dataset when time series can be obtained (such as in the southern Indian Ocean or North Atlantic subpolar gyre). These comparisons suggest that the overall uncertainty of the spatially (for a cruise) or temporally (over a year) averaged data is less than 0.03 ‰ for δ 18 O and 0.15 ‰ for δ D. However, 18 comparisons with duplicate seawater data analyzed in other laboratories or with other datasets in the intermediate and deep ocean suggest a larger scatter. When averaging the 18 comparisons done for δ 18 O, we find a difference of 0.082 ‰ with a standard error of 0.016 ‰. Such an average difference is expected due to the adjustments applied at LOCEAN to saline water data produced either by CRDS or isotope ratio mass spectrometry (IRMS), but the scatter found suggests that care is needed when merging datasets from different laboratories. Examples of time series in the surface North Atlantic subpolar gyre illustrate the temporal changes in water isotope composition that can be detected with a carefully validated dataset.

Abstract Recent research highlighted significant marine biological activity during the Arctic winter, with poorly known implications for the biological carbon pump. We used moored instruments to (1) track the development of the pelagic food web of a high‐Arctic marine ecosystem from winter to spring, and (2) assess the role of zooplankton‐mediated processes in the sinking export of particulate organic carbon (POC). Zooplankton collected by a sediment trap at 40 m depth in Kongsfjorden showed a shift in species composition in February coinciding with an inflow of Atlantic water and the return of sunlight. The Atlantic copepod Calanus finmarchicus and the Arctic Calanus glacialis became dominant in the post‐inflow assemblage of large mesozooplankton. However, large copepods were never abundant (0.3–4.6 ind m−3) in January–April in the upper 40 m. Despite the low chlorophyll fluorescence, POC export increased substantially, from 2–13 mg C m−2 d−1 in January–February to 13–35 mg C m−2 d−1 in March–April 2014. By late March, zooplankton fecal pellets contributed largely (23–100%) to this significant POC export before the phytoplankton bloom. The lack of change in copepod and euphausiid population sizes suggests that enhanced feeding activity in the surface layer supported the increasing fecal pellet export. Our results revealed the swift response of active zooplankton in winter, evidenced by increased carbon export, to improved food availability.

The Fram Strait connects the Atlantic and Arctic Oceans and is a key conduit for sea ice advected southward by the Transpolar Drift and northward inflow of warm Atlantic Waters. Continued sea ice decline and “Atlantification” are expected to influence pelagic–benthic coupling in the Fram Strait and Arctic as a whole. However, interannual variability and the impact of changing ice conditions on deepwater particle fluxes in the Arctic remain poorly characterized. Here, we present long-term sediment trap records (2000–2013) from mesopelagic (200 m) and bathypelagic (2,300 m) depths at two locations (HGIV and HGN) in the Fram Strait subjected to variable ice conditions. Sediment trap catchment areas were estimated and combined with remote sensing data and a high-resolution model to determine the ice cover, chlorophyll concentration, and prevailing stratification regimes. Surface chlorophyll increased between 2000 and 2013, but there was no corresponding increase in POC flux, suggesting a shift in the efficiency of the biological carbon pump. A decrease in particulate biogenic Si flux, %opal, Si:POC, and Si:PIC at mesopelagic depths indicates a shift away from diatom-dominated export as a feasible explanation. Biogenic components accounted for 72% ± 16% of mass flux at 200 m, but were reduced to 34% ± 11% at 2,300 m, substituted by a residual (lithogenic) material. Total mass fluxes of biogenic components, including POC, were higher in the bathypelagic. Biomarkers and ∂13C values suggest both lateral advection and ice-rafted material contribute to benthic carbon input, although constraining their precise contribution remains challenging. The decadal time series was used to describe two end-members of catchment area conditions representing the maximum temperatures of Atlantic inflow water in 2005 at HGIV and high ice coverage and a meltwater stratification regime at HGN in 2007. Despite similar chlorophyll concentrations, bathypelagic POC flux, Si flux, Si:POC, and Si:PIC were higher and POC:PIC was lower in the high-ice/meltwater regime. Our findings suggest that ice concentration and associated meltwater regimes cause higher diatom flux. It is possible this will increase in the future Arctic as meltwater regimes increase, but it is likely to be a transient feature that will disappear when no ice remains.

The Green Edge project was designed to investigate the onset, life, and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in Arctic Ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the Arctic environment will affect it. Green Edge was a large multidisciplinary, collaborative project bringing researchers and technicians from 28 different institutions in seven countries together, aiming at understanding these changes and their impacts on the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice camp and a research vessel in Baffin Bay, in the Canadian Arctic. This paper describes the sampling strategy and the dataset obtained from the research cruise, which took place aboard the Canadian Coast Guard ship (CCGS) Amundsen in late spring and early summer 2016. The sampling strategy was designed around the repetitive, perpendicular crossing of the marginal ice zone (MIZ), using not only ship-based station discrete sampling but also high-resolution measurements from autonomous platforms (Gliders, BGC-Argo floats …) and under-way monitoring systems. The dataset is available at https://doi.org/10.17882/86417 (Bruyant et al., 2022).

Abstract. Submarine canyons enhance shelf–slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring (PDMc) was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an acoustic Doppler current profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system (PDM-154, PDM-224) and offshore Baie-Comeau (BC-133). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in sediment traps PDM-154 and PDM-224 located > 2.6 km further offshore by enhancing lateral dispersion of resuspended sediments. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred 2 weeks earlier (in mid-April) at the PDM site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. Annual diatom and dinoflagellate fluxes were almost 2 times lower at the PDM site than at the BC site, possibly due to differences in riverine input and the structure of the water column, as well as increased sediment input and resuspension at the PDM site, leading to limited light availability. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the ecosystem offshore PDM. The study period further covered an anomalously nearly ice-free winter, and thus, in the context of climate change, it provides valuable insight into future trends of biogenic matter export in the LSLE.

Dead zooplankton, including crustaceans, are increasingly recognized as important agents of vertical carbon export from surface waters and in marine food webs. Quantifying the contribution of passively sinking copepods (PSCs) to vertical fluxes of total particulate organic carbon (POC) is important for understanding marine ecosystem carbon budgets. Information on this is limited because identifying PSCs in sediment trap samples is difficult. Generally, swimmers (undecomposed metazoans, including PSCs, caught in sediment traps) are removed from a trap sample before the POC content is measured, although ignoring PSCs causes the total POC flux to be significantly underestimated. We quantified temporal and regional variability in PSC flux and contribution of PSCs to total POC flux (PSCs + detrital sinking particles, generally analyzed to estimate detrital POC flux) at the Mackenzie Shelf margins in the Beaufort Sea. Six datasets were used to examine PSC flux variability at ~100 m depth, which is deeper than the winter pycnocline depth (30-50 m), at the continental margin. The average (±SD) annual PSC flux (1378 ± 662 mg C m -2 yr -1 , n = 6 [datasets]) and PSC contribution to the total POC flux (21 ± 10%, n = 6) suggested that PSCs, especially Pareuchaeta glacialis , were important agents of POC export from the surface layer (~100 m) to deeper water at the inter-regional and multiyear scales. We propose a hypothesis that processes controlling PSC flux variability may vary seasonally, perhaps relating to life cycle (reproduction) in winter (February) and osmotic stress in July-October when the PSC flux is relatively high.

Abstract. The Green Edge initiative was developed to investigate the processes controlling the primary productivity and the fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797N, 63.7895W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea ice cover from the surface to the bottom at 360 m depth to better understand the factors driving the PSB. Key variables such as temperature, salinity, radiance, irradiance, nutrient concentrations, chlorophyll-a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, carbon stocks and fluxes were routinely measured at the ice camp. Here, we present the results of a joint effort to tidy and standardize the collected data sets that will facilitate their reuse in other Arctic studies. The dataset is available at http://www.seanoe.org/data/00487/59892/ (Massicotte et al., 2019a).

Ocean warming and Arctic sea-ice decline are expected to affect the biological pump efficiency by altering the timing, quantity, quality, and composition of export production. However, the origins and composition of sinking organic matter are still generally understudied for the oceans, especially in ice-covered areas. Here, we use the compound-specific isotope analysis (CSIA) of amino acids (AAs) to investigate the sources and composition of exported organic matter from a sediment-trap-derived time series of sinking particles collected at depths of 469 and 915 m at the edge of Saglek Bank in the northwestern Labrador Sea from October 2017 to July 2019. The outer edge of Saglek Bank is located at the confluence of cold and fresh Arctic outflow and relatively warmer Atlantic waters. The area is subject to seasonal sea-ice cover and is a biological hotspot for benthic organisms, including deep-sea corals and sponges. Sea ice was present for ∼ 50 % to 60 % of the deployment days in both cycles. Phytoplankton blooms at our study site co-occurred with the onset of sea-ice melt. Microalgal taxonomy indicated the presence of ice-associated diatoms in the sinking particles during the spring bloom in 2018, confirming that sea-ice algae contributed to the organic particle export at our study site. The presence of abundant copepods and copepod nauplii caught in the sediment traps was consistent with a high abundance of copepods in overlying epipelagic waters. Stable carbon isotopes ( δ 13 C) of essential amino acids (EAAs) of the sinking particles revealed a potentially important contribution of sea-ice algae as a carbon source at the base of the food web to sinking particles, with only minor modification by microbial resynthesis. Stable nitrogen isotopes ( δ 15 N) of AAs of sinking particles provided independent evidence of the minor bacterial degradation, and Bayesian mixing models based on normalized δ 15 N-AA values revealed the dominant contribution of fecal pellets (76 %–96 %) to the sinking particles. Our study demonstrates the importance of sea-ice algae and fecal pellets to the biological pump in the seasonally ice-covered northwestern Labrador Sea, with sea-ice algae exported either directly via passive sinking or indirectly via zooplankton grazing and with fecal pellets dominating the organic particle fluxes.