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Along Greenland's coastline, the magnitude and timing of primary production in fjords is influenced by meltwater release from marine-terminating glaciers. How local ecosystems will adapt as these glaciers retreat onto land, forcing fundamental changes in hydrography, remains an open question. To further our understanding of this transition, we examine how marine- and land-terminating glaciers respectively influence fjord bloom phenology. Between spring and autumn 2019, we conducted along-fjord transects of hydrographic variables, biogeochemical properties and pico- and nanophytoplankton counts to illustrate the contrasting seasonal bloom dynamics in the fjords Nuup Kangerlua and Ameralik. These fjords are in the same climatic region of west Greenland but influenced by different glacial structures. Nuup Kangerlua, a predominantly marine-terminating system, was differentiated by its sustained second summer bloom and high Chl a fluorescence in summer and autumn. In Ameralik, influenced by a land-terminating glacier, we found higher abundances of pico- and nanophytoplankton, and high cyanobacteria growth in autumn. The summer bloom in Nuup Kangerlua is known to be coincident with subglacial freshwater discharge sustaining renewed nutrient supply to the fjord. We observe here that the intermediate baroclinic circulation, which creates an inflow at subsurface depths, also plays an important role in increasing nutrient availability at shallower depths and potentially explains the distribution of primary producers. Our observations suggest that the retreat of marine-terminating glaciers onto land, with consequent increases in surface water temperature and stratification, and reduced light availability, may alter the magnitude, composition, and distribution of summer productivity.

Highlights: • Higher representation of picophytoplankton in land-terminating glacier fjord. • Smaller phytoplankton cells associated with glacial retreat. • Intermediate baroclinic circulation influences phytoplankton distribution. • Glacial retreat likely to have major implications for summer productivity. Abstract: Along Greenland's coastline, the magnitude and timing of primary production in fjords is influenced by meltwater release from marine-terminating glaciers. How local ecosystems will adapt as these glaciers retreat onto land, forcing fundamental changes in hydrography, remains an open question. To further our understanding of this transition, we examine how marine- and land-terminating glaciers respectively influence fjord bloom phenology. Between spring and autumn 2019, we conducted along-fjord transects of hydrographic variables, biogeochemical properties and pico- and nanophytoplankton counts to illustrate the contrasting seasonal bloom dynamics in the fjords Nuup Kangerlua and Ameralik. These fjords are in the same climatic region of west Greenland but influenced by different glacial structures. Nuup Kangerlua, a predominantly marine-terminating system, was differentiated by its sustained second summer bloom and high Chl a fluorescence in summer and autumn. In Ameralik, influenced by a land-terminating glacier, we found higher abundances of pico- and nanophytoplankton, and high cyanobacteria growth in autumn. The summer bloom in Nuup Kangerlua is known to be coincident with subglacial freshwater discharge sustaining renewed nutrient supply to the fjord. We observe here that the intermediate baroclinic circulation, which creates an inflow at subsurface depths, also plays an important role in increasing nutrient availability at shallower depths and potentially explains the distribution of primary producers. Our observations suggest that the retreat of marine-terminating glaciers onto land, with consequent increases in surface water temperature and strat

Changes in the distribution of coastal macrophytes in Greenland, and elsewhere in the Arctic are difficult to quantify as the region remains challenging to access and monitor. Satellite imagery, in particular Sentinel-2 (S2), may enable large-scale monitoring of coastal areas in Greenland but its use is impacted by the optically complex environments and the scarcity of supporting data in the region. Additionally, the canopies of the dominant macrophyte species in Greenland do not extend to the sea surface, limiting the use of indices that exploit the reflection of near-infrared radiation by vegetation due to its absorption by seawater. Three hypotheses are tested: I) 10-m S2 imagery and commonly used detection methods can identify intertidal macrophytes that are exposed at low tide in an optically complex fjord system in Greenland impacted by marine and land terminating glaciers; II) detached and floating macrophytes accumulate in patches that are sufficiently large to be detected by 10-m S2 images; III) iceberg scour and/or turbid meltwater runoff shape the spatial distribution of intertidal macroalgae in fjord systems with marine-terminating glaciers. The NDVI produced the best results in optically complex fjord systems in Greenland. 12 km2 of exposed intertidal macrophytes were identified in the study area at low tide. Floating mats of macrophytes ranged in area from 400 m2 to 326,800 m2 and were most common at the mouth of the fjord. Icebergs and turbidity appear to play a role in structuring the distribution of intertidal macrophytes and the retreat of marine terminating glaciers could allow macrophytes cover to expand. The challenges and solutions presented here apply to most fjords in Greenland and, therefore, the methodology may be extended to produce a Greenland-wide estimate of intertidal macrophytes.

Oil spill attenuation in Arctic marine environments depends on oil-degrading bacteria. However, the seasonally harsh conditions in the Arctic such as nutrient limitations and sub-zero temperatures limit the activity even for bacteria capable of hydrocarbon metabolism at low temperatures. Here, we investigated whether the variance between epipelagic (seasonal temperature and inorganic nutrient variations) and mesopelagic zone (stable environmental conditions) could limit the growth of oil-degrading bacteria and lead to lower oil biodegradation rates in the epipelagic than in the mesopelagic zone. Therefore, we deployed absorbents coated with three oil types in a SW-Greenland fjord system at 10–20 m (epipelagic) and 615–650 m (mesopelagic) water depth for one year. During this period we monitored the development and succession of the bacterial biofilms colonizing the oil films by 16S rRNA gene amplicon quantification and sequencing, and the progression of oil biodegradation by gas chromatography – mass spectrometry oil fingerprinting analysis. The removal of hydrocarbons was significantly different, with several polycyclic aromatic hydrocarbons showing longer half-life times in the epipelagic than in the mesopelagic zone. Bacterial community composition and density (16S rRNA genes/ cm2) significantly differed between the two zones, with total bacteria reaching to log-fold higher densities (16S rRNA genes/cm2) in the mesopelagic than epipelagic oil-coated absorbents. Consequently, the environmental conditions in the epipelagic zone limited oil biodegradation performance by limiting bacterial growth.

Meltwater runoff from glaciers carries particles, so-called glacial flour that may affect planktonic organisms and the functioning of marine ecosystems. Protist microplankton is at the base of marine food webs and thus plays an important role in sustaining important ecosystem services. To assess the effect of glacial flour on photoautotrophic, heterotrophic and mixotrophic microplankton, the spatial distribution of these trophic groups was studied in four Greenlandic fjords during summer. The results suggest that the abundance of the autotrophic microplankton was affected by the glacier meltwater due to reduced light penetration and nutrient availability. The abundance of heterotrophic and mixotrophic microplankton were not apparently affected by the glacier meltwater. Incubation experiments were conducted on the natural population and in laboratory cultures of two mixoplanktonic ciliate species. The experiments on the natural population revealed that none of the trophic groups were affected by the suspended material at concentrations up to 50 mg L−1. The experiments on cultures gave no indication that glacial flour was ingested by the mixoplanktonic ciliates. Growth rates of cultured ciliates were not affected by the glacial flour addition. These results suggest that heterotrophic and mixotrophic microplankton are not affected by glacial flour as much as autotrophic microplankton.

The melting of the Greenland Ice Sheet is accelerating, with glaciers shifting from marine to land termination and potential consequences for fjord ecosystems downstream. Monthly samples in 2016 in two fjords in southwest Greenland show that subglacial discharge from marine-terminating glaciers sustains high phytoplankton productivity that is dominated by diatoms and grazed by larger mesozooplankton throughout summer. In contrast, melting of land-terminating glaciers results in a fjord ecosystem dominated by bacteria, picophytoplankton and smaller zooplankton, which has only one-third of the annual productivity and half the CO2 uptake compared to the fjord downstream from marine-terminating glaciers.

Glaciers and ice sheets are experiencing rapid warming under current climatic change and there is increasing evidence that glacial meltwaters provide key dissolved and dissolvable amorphous nutrients to downstream ecosystems. However, large debate exists around the fate of these nutrients within complex and heterogenous fjord environments, where biogeochemical cycling is still often poorly understood. We combine silicon (Si) concentration data with isotopic compositions to better understand silicon cycling and export in two contrasting fjordic environments in south-west Greenland. We show that both fjords have isotopically light dissolved silicon (DSi) within surface waters, despite an apparently rapid biological drawdown of DSi with increasing salinity. We hypothesize that such observations cannot be explained by simple water mass mixing processes, and postulate that an isotopically light source of Si, most likely glacially derived amorphous silica (ASi), is responsible for further modifying these coastal waters within the fjords and beyond. Fjord to coastal exchange is likely a relatively slow process (several months), and thus is less impacted by short-term (

Traditional tagging techniques are simple and cost-effective, but inferences require recaptures and data on movement/migration are limited to a start and end position at unpredictable intervals. Pop-up satellite archival tags (PSATs) offer other opportunities, as they provide positions at pre-programmed times and collect on-route data, which can be used to describe position, behavior, and habitat preferences. Species suitability should, however, be documented prior to large-scale studies using PSATs. We deployed PSATs on six relatively large (total length 84-125 cm) Atlantic cod (Gadus morhua) in inshore West Greenland waters. Three tags were physically recovered, providing high-resolution data on depth and temperature (readings every 3 s), while three tags did not report (recovery rate = 50 %). To evaluate the tag’s applicability on Atlantic cod, we made a detailed behavioral analysis by defining swimming behavior, occupied water types and depth phases, which were cross-evaluated in relation to depth, temperature and water stratification to identify behavioral patterns. Distinct and shared patterns in swimming behavior were evident and we found no signs of impaired swimming behavior except for an adaptation period lasting up to 39h after release. Generally, the three cod were pelagic and preferred waters ranging 2-5 °C. When encountering colder water masses these were avoided. During late summer/early autumn, increased vertical activity could in some cases be linked to darkness and a high-activity event could be linked to possible predator avoidance. All combined, we conclude that PSATs are suitable to monitor natural behavior on large specimens of Atlantic cod for periods of at least four months.

Water mass composition and transit times of outflowing waters from the Arctic Ocean can reflect changes of polar climate and ocean circulation upstream. In this study we apply a novel approach using anthropogenic uranium tracers (233U and 236U), combined with salinity , and nutrients (nitrate and phosphate) to estimate transit times of waters from the Atlantic passing through the Arctic and into East Greenland fjords . In Polar Surface Water (PSW, typically found in surface ~150 m of the fjords) the dominant source of 236U is European reprocessing plants (63%) while in Arctic Atlantic Water (AAW, typically directly below PSW in these fjords) it is much less (26%) and the 236U signalis dominated by the global fallout contribution. Here we isolate the236U signal from reprocessing plants using 236U/ 233U ratios and use the temporal development in 236U discharges to estimate transit times for Atlantic Water entering the Arctic Ocean and exiting as either PSW or AAW on the Greenland Shelf. PSW, which flows into the fjords from the shelf, has a transit time of between 6 and 14 years from the Arctic entrance (Barents Sea Opening, 74°N, 19°E). The transit time of AAW, which is entrained into upwelling subglacial discharge in the inner parts of the fjords, is in the order of 24–25 years since entrance in the Barents Sea. The findings indicate the potential of this novel 233U-236U approach to trace Atlantic

The waters on the West Greenland continental shelf and slope play an important role in the global climate system with their link to the subpolar North Atlantic Ocean circulation system and the Greenland Ice Sheet. Lately, low temperature waters on the West Greenland shelf have been observed as far south as ∼64°N and associated with a cold and relatively saline water mass originating north of Davis Strait in Baffin Bay referred to as Baffin Bay Polar Water (BBPW). Here we use long, seasonal hydrographic time series from West Greenland at ∼64°N to study how frequently BBPW is reaching this far south. The analysis covers the period 1950–2018 with a data gap between 1988 and 2005. BBPW was observed frequently and was responsible for the temperature changes observed in the late 1960s–1980s and more intermittently post-2008. Some of the large temperature changes we observe in the time series have previously been ascribed to “Great Salinity Anomalies” (GSAs) propagating around the subpolar North Atlantic Ocean circulation system. The prevailing view of the propagation of GSAs has been ascribed to advection of anomalies along the large-scale circulation system. Our study shows that BBPW may play an important role in the interpretation of GSAs and melt of the Greenland Ice Sheet. Large temporal temperature changes at ∼64°N are associated with arrival of BBPW from the north and not advection of anomalies with the large-scale current system from the south. This advocates for a shift in water masses caused by changes in the position and/or strength of oceanic currents.

Global warming accelerates melting of glaciers and increases the supply of meltwater and associated inorganic particles, nutrients, and organic matter to adjacent coastal seas, but the ecosystem impact is poorly resolved and quantified. When meltwater is delivered by glacial rivers, the potential impact could be a reduction in light and nutrient availability for primary producers while supplying allochthonous carbon for heterotrophic processes, thereby tipping the net community metabolism toward heterotrophy. To test this hypothesis, we determined physical and biogeochemical parameters along a 110-km fjord transect in NE Greenland fjord, impacted by glacial meltwater from the Greenland Ice Sheet. The meltwater is delivered from glacier-fed river outlets in the inner parts of the fjord, creating a gradient in salinity and turbidity. The planktonic primary production was low, 20–45 mg C m−2 d−1, in the more turbid innerhalf of the fjord, increasing 10-fold to around 350 mg C m−2 d −1 in the shelf waters outside the fjord. Plankton community metabolism was measured at three stations, which displayed a transition from net heterotrophy in the inner fjord to net autotrophy in the coastal shelf waters. Respiration was significantly correlated to turbidity, with a 10-fold increase in the inner turbid part of the fjord. We estimated the changes in meltwater input and sea ice coverage in the area for the last 60 y. The long-term trend and the observed effects demonstrated the importance of freshwater runoff as a key driver of coastal ecosystem change in the Arctic with potential negative consequences for coastal productivity.

Greenland’s coastal margins are influenced by the confluence of Arctic and Atlantic waters, sea ice, icebergs, and meltwater from the ice sheet. Hundreds of spectacular glacial fjords cut through the coastline and support thriving marine ecosystems and, in some places, adjacent Greenlandic communities. Rising air and ocean temperatures, as well as glacier and sea-ice retreat, are impacting the conditions that support these systems. Projecting how these regions and their communities will evolve requires understanding both the large-scale climate variability and the regional-scale web of physical, biological, and social interactions. Here, we describe pan-Greenland physical, biological, and social settings and show how they are shaped by the ocean, the atmosphere, and the ice sheet. Next, we focus on two communities, Qaanaaq in Northwest Greenland, exposed to Arctic variability, and Ammassalik in Southeast Greenland, exposed to Atlantic variability. We show that while their climates today are similar to those of the warm 1930s­–1940s, temperatures are projected to soon exceed those of the last 100 years at both locations. Existing biological records, including fisheries, provide some insight on ecosystem variability, but they are too short to discern robust patterns. To determine how these systems will evolve in the future requires an improved understanding of the linkages and external factors shaping the ecosystem and community response. This interdisciplinary study exemplifies a first step in a systems approach to investigating the evolution of Greenland’s coastal margins.

Manganese (Mn) is an essential micro-nutrient that can limit or, along with iron (Fe), co-limit phytoplankton growth in the ocean. Glacier meltwater is thought to be a key source of trace metals to high latitude coastal systems, but little is known about the nature of Mn delivered to glacially-influenced fjords and adjacent coastal waters. In this work, we combine in-situ dissolved Mn (dMn) measurements of surface waters with Mn K-edge X-ray absorption spectroscopy (XAS) data of suspended particles in four fjords of West Greenland. Data were collected from transects of up to 100 km in fjords with different underlying bedrock geology from 64 to 70°N. We found that dMn concentrations generally decreased conservatively with increasing salinity (from 80 to 120 nM at salinity < 8 to < 40 nM at salinities > 25). Dissolved Fe (dFe) trends in these fjords similarly declined with increasing distance from glacier outflows (declining from > 20 nM to < 8 nM). However, the dMn/dFe ratio increased rapidly likely due to the greater stability of dMn at intermediate salinities (i.e. 10–20) compared to rapid precipitation of dFe across the salinity gradient. The XAS data indicated a widespread presence of Mn(II)-rich suspended particles near fjord surfaces, with structures akin to Mn(II)-bearing phyllosilicates. However, a distinct increase in Mn oxidation state with depth and the predominance of birnessite-like Mn(IV) oxides was observed for suspended particles in a fjord with tertiary basalt geology. The similar dMn behaviour in fjords with different suspended particle Mn speciation (i.e., Mn(II)-bearing phyllosilicates and Mn(IV)-rich birnessite) is consistent with the decoupling of dissolved and particulate Mn and suggests that dMn concentrations on the scale of these fjords are controlled primarily by dilution of a freshwater dMn source rather than exchange between dissolved and particle phases. This work provides new insights into the Mn cycle in high latitude