Description: A detailed survey of a high Arctic fjord (Kongsfjorden, Svalbard),subjected to a large glacier discharge, was carried out from 24 July to 13 August 2016. Field activities addressed the identification ofthe effects of glacier and iceberg melting on the evolution of nutrient, dissolved organic matter and carbonate systems in this coastal marine environment. Complete CTD profiles were collected in 60 marine stations in theinner area of Kongsfjorden, during six oceanographic surveys, by means of CTD downcasts. CTD profiles were acquired with a Seabird 19plus SeaCATprofiler, equipped with a TURNER Cyclops turbidimeter.

Description: Oceanographic data were collected in 60 marine stationsinthe inner area ofKongsfjorden, during six oceanographic surveys (24 July -10 August 2016),by means ofCTD downcastsandbottle sampling.CTD profileswere acquired with a Seabird 19plus SeaCATprofiler,equipped with a TURNER Cyclops turbidimeter. Potential temperature (Θ, ITS-90; °C), salinity (Practical Salinity Scale, PSS-78) and potential density anomaly (σΘ, sigma-theta) were calculated according to McDougall et al. (2010).Seawater samples for chemical analyses were collected using 10 L Niskin bottles at 1-7 depths per station, depending on the depth of the station (9-304 m), withamore intensive sampling of upper layer. Samples for the determination of Dissolved Oxygen (DO;μmol L-1) were drawnin 60 mL borosilicate glass bottles and spiked with Winkler reagents.Samples forthe determination ofmacronutrients (nitrate, NO3-; nitrite, NO2-; reactive silicate, Si(OH)4; orthophosphate, PO43-; μmol L-1), Dissolved Organic Carbon (DOC, μmol L-1) and Nitrogen (DON, μmol L-1) were syringe filtered withprecombusted (450 °C, 4 h) GF/F filters, placed in acid-washed HDPE vials and stored at -20 °C until analysis.Seawater samples for the determination of pH, dissolved inorganic carbon (DIC; μmol kgSW-1) and total alkalinity (TA; μmol kgSW-1) were collected in borosilicate glass bottles. Sample lids were immediately greased (Apiezon L), sealed with positive pressure on the lid, and stored refrigerated (4 °C) in the dark until analysis. The samples were poisoned with 100 μL HgCl2soln. only if they could not be analysed within 24 hour of the collection (Dickson et al., 2007).

Description: Ice samples (1-2 kg) from small icebergs floating in the fjord were collected and returned to the laboratoryin insulated plastic boxes, rinsed with ultra-pure laboratory water and melted in low-density polyethylene bags. The first melt water was discarded, whereas the remaining freshwater was subsampled for the determination of chemical parameters.

Description: Freshwater samples and physical parameterswere also collectedin theglacial drainages surrounding the fjordin 55 sampling points. This included supraglacial streams and proglacial watercourses from the moraines to the coast (0-5 km in length). Temperature and conductivityin freshwaterwere measured with a portable Conductivity-Meter (LF325, WTW). For chemical parameters, a 10 L carboy was submerged in streams until the bubbles were removed. Subsamples were then collected using a silicone tube for the determination of nutrients, DOC, DON, DIC, pH and TA.

Description: A detailed survey of a high Arctic fjord (Kongsfjorden, Svalbard), subjected to a large glacier discharge, was carried out from 24 July to 13 August 2016. Field activities addressed the identification of the effects of glacier and iceberg melting on the evolution of nutrient, dissolved organic matter and carbonate systems in this coastal marine environment. Hydrological (CTD downcasts) and biogeochemical (bottle sampling) data were collected during six oceanographic surveys in the inner area of the fjord, in concomitance to the annual phase of maximum air warming. An extensive sampling was also carried out in all glacier drainage systems located around the fjord and from several iceberg samples, in order to characterize all freshwater loads. The dataset includes hydrological data (T, Sal., density) carbonate chemistry data (pH, DIC, TA) and the concentrations of dissolved oxygen (DO), inorganic nutrients (NO3-, NO2-, NH4+, PO43-, SiO2), dissolved organic matter (DOC, DON) and some micronutrients (Fe, Mn).

Description: Key Points In Kongsfjorden, an Arctic glacier fjord, freshwater from glacier runoff and ice meltwater decreases phosphate, alkalinity and DOM concentrations Estuarine mixing is the major driver of summer CO2 undersaturation in glacially modified waters and near‐corrosive conditions were observed Future changes will amplify ocean acidification in the inner‐fjord surface waters Abstract A detailed survey of a high Arctic glacier fjord (Kongsfjorden, Svalbard) was carried out in summer 2016, close to the peak of the meltwater season, in order to identify the effects of glacier runoff on nutrient distributions and the carbonate system. Short‐term weather patterns were found to exert a strong influence on freshwater content within the fjord. Freshwater inputs from glacier runoff and ice meltwater averaged (±SD) low nitrate (1.85±0.47 μM; 0.41±0.99 μM), orthophosphate (0.07±0.27 μM; 0.02 ±0.03 μM), dissolved organic carbon (27 ±14 μM in glacier runoff), total alkalinity (708±251 μmol kg‐1; 173±121 μmol kg‐1) and dissolved inorganic carbon (622±108 μmol kg‐1; 41±88 μmol kg‐1), as well as a modest silicate concentration (3.71±0.02 μM; 3.16±5.41 μM). pCO2 showed a non‐conservative behavior across the estuarine salinity gradient with a pronounced under‐saturation in the inner‐fjord, leading to strong CO2 uptake from the atmosphere. The combined effect of freshwater dilution and atmospheric CO2 absorption was the lowering of aragonite saturation state, to values that are known to negatively affect marine calcifiers (ΩAr, 1.07). Glacier discharge was therefore a strong local amplifier of ocean acidification. Future increases in discharge volume and the loss of marine productivity following the retreat of marine‐terminating glaciers inland are both anticipated to further lower ΩAr within inner‐fjord surface waters. This shift may be partially buffered by an increase in the mean freshwater total alkalinity as the fractional importance of iceberg melt to freshwater fjord inputs declines and runoff increases.