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Greenland's glacial fjords modulate the exchange between the ice sheet and ocean. Subglacial‐discharge‐driven plumes adjacent to glaciers may exert an important influence on fjord water properties, submarine glacier melting and the export of glacially‐modified waters to the shelf. Here we use a numerical plume model in conjunction with observations from proximal to 14 glaciers in northwest Greenland to assess the impact of these plumes on near‐glacier water properties. We find that in late summer, waters emanating from glacial plumes often make up >50% of the fjord water composition at intermediate depths. These plume waters are comprised largely of upwelled Atlantic Water, warming the near‐glacier water profile and likely increasing submarine melting. Our findings demonstrate the key role played by plumes in driving water modification in Greenland's fjords, and the potential for simple models to capture these impacts across a range of settings. Plain Language Summary Fjords form an important point of contact between the Greenland Ice Sheet and surrounding ocean. Warm ocean waters in these fjords melt the submerged sections of marine‐terminating glaciers, whilst freshwater draining from the ice sheet modifies coastal water properties, impacting ocean circulation. In this study, we use observations of fjord temperature and salinity in combination with numerical modeling to evaluate the mechanisms through which glaciers modify fjord circulation and water properties. Across 14 glaciers in northwest Greenland, we find that the input of glacial meltwater drives the upwelling of warm, deep Atlantic‐origin waters, which mix with the cooler Arctic‐origin waters typically found above ∼250 m depth. These glacially modified waters thus cause a substantial warming of fjord waters relative to those off the coast, a feedback that will amplify the oceanic melting of these glaciers. Key Points We assess the impact of subglacial‐discharge plumes on water properties proximal to 14 tidewater glaciers in northwest Greenland In late summer, waters emanating from glacial plumes often make up >50% of the fjord water composition at intermediate depths These plume waters are comprised largely of upwelled Atlantic Water, warming the near‐glacier water profile and likely increasing submarine melting

We investigated the relative contributions of various factors that influence seasonal changes in sea surface partial pressure of CO 2 ( pCO 2 , calculated from the measured pH and total alkalinity) in four regions of northwestern Greenland: Nares Strait, Lincoln Sea, Sherard Osborn and Petermann fjords. Using the temperature minimum layer as a proxy for winter conditions, we examined pCO 2 dynamics from the onset of sea-ice melt to summer. Our findings revealed significant spatial variability in pCO 2 , driven by differences in temperature, freshwater inputs, and biological activity. In particular, in Sherard Osborn Fjord substantial freshwater inputs and strong stratification were found to enhance pCO 2 accumulation, while in Petermann Fjord biological CO 2 uptake was the main driver. This study, conducted in summer 2019, underscores the critical role of northwest Greenland’s coastal waters as a summer CO 2 sink. It highlights the complex interplay of physical and biogeochemical processes in modulating pCO 2 , suggesting significant regional differences in CO 2 dynamics between two neighboring fjords.

The discharge of nutrient-rich meltwater from the Greenland Ice Sheet has emerged as a potentially important contributor to regional marine primary production and nutrient cycling. While significant, this direct nutrient input by the ice sheet may be secondary to the upwelling of deep-ocean-sourced nutrients driven by the release of meltwater at depth in glacial fjords. Here, we present a comprehensive suite of micro- and macronutrient observations collected in Sermilik Fjord at the margin of Helheim, one of Greenland’s largest glaciers, and quantitatively decompose glacial and ocean contributions to fjord dissolved nutrient inventories. We show that the substantial enrichment in nitrate, phosphate and silicate observed in the upper 250 m of the glacial fjord is the result of upwelling of warm subtropical waters present at depth throughout the fjord. These nutrient-enriched fjord waters are subsequently exported subsurface to the continental shelf. The upwelled nutrient transport within Sermilik rivals exports by the largest Arctic rivers and the ice sheet as a whole, suggesting that glacier-induced pumping of deep nutrients may constitute a major source of macronutrients to the surrounding coastal ocean. The importance of this mechanism is likely to grow given projected increases in surface melt of the ice sheet.

Ocean conditions in fjords play a key role in the accelerating ice mass loss of Greenland's marine-terminating glaciers. Ice mélange and icebergs have been shown to impact fjord circulation, heat and freshwater fluxes, and the submarine melting of glacier termini. Previous attempts to model icebergs largely fall into two camps: small-scale models that resolve icebergs and represent the impact of form drag and larger-scale models that parameterize sub-grid-scale icebergs but neglect iceberg drag. Here, we develop an extension of the large-scale-style iceberg package for the MIT general circulation model (MITgcm) to implement a novel, scalable parameterization to incorporate the impact of iceberg drag while also improving overall computational performance of the iceberg package by ∼ 90 %. To demonstrate our parameterization, we benchmark our method against existing iceberg-resolving models and compare it to the previous configuration of iceberg. With the inclusion of sub-grid-scale drag, our model skillfully reproduces ocean conditions and iceberg melt rates of iceberg-resolving models while reducing computational cost by orders of magnitude. When applied to a multi-month fjord-scale simulation, we find icebergs and iceberg drag have a significant impact on fjord and glacier-adjacent conditions, including cooling fjord waters and increasing circulation. We note that these effects are more moderate in the case of icebergs with drag, suggesting that studies without iceberg drag may overestimate the net impact of icebergs on the fjord system.

Interactions between ice masses and the ocean are key couplings in the global climate system. In many cases, these interactions occur through glacial fjords, which are long, deep, and narrow troughs connecting the open ocean to marine-terminating glaciers. By controlling the fluxes of ocean heat towards the ice sheet and ice sheet freshwater towards the ocean, glacial fjords play an important role in modulating ice sheet mass loss and the impacts of freshwater on ocean circulation. Yet, these dynamics occur at small scales that are challenging to resolve in earth system models and hence are often ignored, represented in an ad-hoc manner, or studied using expensive high-resolution models that are limited in scope. Here, we propose a means of capturing glacial fjord dynamics at negligible computational expense in the form of a “reduced-physics” model (FjordRPM) that resembles a “1.5-dimensional” or box model. We describe the design and physical parameterisations in the model and demonstrate its ability to capture important modes of glacial fjord circulation by comparing it against a general circulation model in idealised and realistic simulations. We suggest that the model is a useful tool for understanding fjord dynamics and a promising approach for representing glacial fjord processes within large-scale models or climate and sea level projection efforts.

Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet. Measurement(s) depth Technology Type(s) digital curation Factor Type(s) geographic location Sample Characteristic - Environment ocean floor Sample Characteristic - Location Arctic Ocean Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.12369314

We investigated the relative contributions of various factors that influence seasonal changes in sea surface partial pressure of ( , calculated from the measured pH and total alkalinity) in four regions of northwestern Greenland: Nares Strait, Lincoln Sea, Sherard Osborn and Petermann fjords. Using the temperature minimum layer as a proxy for winter conditions, we examined dynamics from the onset of sea-ice melt to summer. Our findings revealed significant spatial variability in , driven by differences in temperature, freshwater inputs, and biological activity. In particular, in Sherard Osborn Fjord substantial freshwater inputs and strong stratification were found to enhance accumulation, while in Petermann Fjord biological uptake was the main driver. This study, conducted in summer 2019, underscores the critical role of northwest Greenland's coastal waters as a summer sink. It highlights the complex interplay of physical and biogeochemical processes in modulating , suggesting significant regional differences in dynamics between two neighboring fjords.

Resource subsidies in the form of allochthonous primary production drive secondary production in many ecosystems, often sustaining diversity and overall productivity. Despite their importance in structuring marine communities, there is little understanding of how subsidies move through juxtaposed habitats and into recipient communities. We investigated the transport of detritus from kelp forests to a deep Arctic fjord (northern Norway). We quantified the seasonal abundance and size structure of kelp detritus in shallow subtidal (0‒12 m), deep subtidal (12‒85 m), and deep fjord (400‒450 m) habitats using a combination of camera surveys, dive observations, and detritus collections over 1 year. Detritus formed dense accumulations in habitats adjacent to kelp forests, and the timing of depositions coincided with the discrete loss of whole kelp blades during spring. We tracked these blades through the deep subtidal and into the deep fjord, and showed they act as a short-term resource pulse transported over several weeks. In deep subtidal regions, detritus consisted mostly of fragments and its depth distribution was similar across seasons (50% of total observations). Tagged pieces of detritus moved slowly out of kelp forests (displaced 4‒50 m (mean 11.8 m ± 8.5 SD) in 11‒17 days, based on minimum estimates from recovered pieces), and most (75%) variability in the rate of export was related to wave exposure and substrate. Tight resource coupling between kelp forests and deep fjords indicate that changes in kelp abundance would propagate through to deep fjord ecosystems, with likely consequences for the ecosystem functioning and services they provide.