Abstract. Freshwater discharge from glaciers is increasing across the Arctic in response to anthropogenic climate change, which raises questions about the potential downstream effects in the marine environment. Whilst a combination of long-term monitoring programmes and intensive Arctic field campaigns have improved our knowledge of glacier–ocean interactions in recent years, especially with respect to fjord/ocean circulation, there are extensive knowledge gaps concerning how glaciers affect marine biogeochemistry and productivity. Following two cross-cutting disciplinary International Arctic Science Committee (IASC) workshops addressing the importance of glaciers for the marine ecosystem, here we review the state of the art concerning how freshwater discharge affects the marine environment with a specific focus on marine biogeochemistry and biological productivity. Using a series of Arctic case studies (Nuup Kangerlua/Godthåbsfjord, Kongsfjorden, Kangerluarsuup Sermia/Bowdoin Fjord, Young Sound and Sermilik Fjord), the interconnected effects of freshwater discharge on fjord–shelf exchange, nutrient availability, the carbonate system, the carbon cycle and the microbial food web are investigated. Key findings are that whether the effect of glacier discharge on marine primary production is positive or negative is highly dependent on a combination of factors. These include glacier type (marine- or land-terminating), fjord–glacier geometry and the limiting resource(s) for phytoplankton growth in a specific spatio-temporal region (light, macronutrients or micronutrients). Arctic glacier fjords therefore often exhibit distinct discharge–productivity relationships, and multiple case-studies must be considered in order to understand the net effects of glacier discharge on Arctic marine ecosystems.

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Antarctic pack ice is inhabited by a diverse and active microbial community reliant on nutrients for growth. Seeking patterns and overlooked processes, we performed a large-scale compilation of macro-nutrient data (hereafter termed nutrients) in Antarctic pack ice (306 ice-cores collected from 19 research cruises). Dissolved inorganic nitrogen and silicic acid concentrations change with time, as expected from a seasonally productive ecosystem. In winter, salinity-normalized nitrate and silicic acid concentrations (C*) in sea ice are close to seawater concentrations (C w ), indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C* < C w ), commensurate with the seasonal build-up of ice microalgae promoted by increased insolation. Stronger and earlier nitrate than silicic acid consumption suggests that a significant fraction of the primary productivity in sea ice is sustained by flagellates. By both consuming and producing ammonium and nitrite, the microbial community maintains these nutrients at relatively low concentrations in spring. With the decrease in insolation beginning in late summer, dissolved inorganic nitrogen and silicic acid concentrations increase, indicating imbalance between their production (increasing or unchanged) and consumption (decreasing) in sea ice. Unlike the depleted concentrations of both nitrate and silicic acid from spring to summer, phosphate accumulates in sea ice (C* > C w ). The phosphate excess could be explained by a greater allocation to phosphorus-rich biomolecules during ice algal blooms coupled with convective loss of excess dissolved nitrogen, preferential remineralization of phosphorus, and/or phosphate adsorption onto metal-organic complexes. Ammonium also appears to be efficiently adsorbed onto organic matter, with likely consequences to nitrogen mobility and availability. This dataset supports the view that the sea ice microbial community is highly efficient at processing nutrients but with a dynamic quite different from that in oceanic surface waters calling for focused future investigations.

The Mediterranean Sea presents several biogeochemical anomalies compared to the global ocean. An unbalanced N budget, high nitrate/phosphate ratios in subsurface waters and low 15N/14N ratios in particulate and dissolved nitrogen suggest a significant occurrence of N2 fixation. This study presents, for the first time, a basin‐wide overview of direct measurements of N2 fixation, with values in the North Atlantic for comparison, during late spring 2007. Very low N2 fixation rates (0.052 ± 0.031 nmols N l−1d−1) were observed in all sub‐regions of the Mediterranean, in contrast to the higher values measured in the North Atlantic (0.300 ± 0.115 nmols N l−1d−1). Higher phosphorus (inorganic or organic) concentrations were not associated with higher N2 fixation rates. Low 15N/14N ratios in particulate organic nitrogen (from −2.10 to +4.11‰), associated with low N2 fixation rates, suggest that other N sources, such as atmospheric inputs, fuel the Mediterranean ecosystem.

Abstract:The analysis of the mixing processes involving water masses on the Ross Sea continental shelf is one of the goals of the CLIMA project (Climatic Long-term Interactions for the Mass balance in Antarctica). This paper uses extended Optimum MultiParameter analysis (OMP), which is applied to four datasets collected during the cruises of 1994/95, 1995/96, 1997/98 and 2000/01 in the Ross Sea (Antarctica). Data include both hydrological, (temperature, salinity, and pressure; T, S, and P, respectively) and chemical parameters (O 2 , Si(OH) 4 , PO 4 , and NO 3 +NO 2 ). The OMP analysis is based on the assumption that the mixing is a linear process which affects all parameters equally so that each sample shows physical/chemical properties that are the result of the mixing of some properly selected Source Water Types (SWTs). OMP thus evaluates the best set of contributions by all SWTs to each sample, and allows the spatial distribution and structure of the water masses in a basin to be evaluated. Ocean circulation may subsequently be inferred by means of a deeper analysis of the spreading of the water mass. In this study, the "real" Redfield ratios observed in the Ross Sea were used to correct the equations referring to the chemical parameters in accordance with the extended version of OMP. The solutions include some physically realistic constraints. The results allow a detailed description of the water mass distribution, validated through comparison with some "canonical" thermohaline characteristics of the Ross Sea hydrology. In particular our results verify the spreading of the HSSW over the entire continental shelf and emphasize the key role it plays in the ventilation of the deep waters outside the Ross Sea. In addition a description is given of the intrusion of relatively warm waters coming from the open ocean and flowing at some specific locations at the continental shelf break. isobath, runs NW-SE and links the area in front of Cape Adare to Cape Colbeck. Some depressions in the inner area are deeper than the continental shelf break, and therefore behave as reservoirs of the salty and dense waters.The Circumpolar Deep Water (CDW) is carried by the Antarctic Circumpolar Current (ACC) along the boundary of the Ross Sea, following the shelf slope from east to west. CDW strongly influences the thermohaline circulation of this basin, being the only water mass which provides heat to the shelf waters (Jacobs et al. 1985, Locarnini 1994, Jacobs & Giulivi 1998, Gouretsky 1999. In some specific locations it intrudes onto the Ross continental shelf forming, after the interaction with the shelf waters, the modified CDW (MCDW), which can be identified by a subsurface maximum temperature and minimum dissolved oxygen (Jacobs et al. 1985, Locarnini 1994, Budillon et al. 1999.On the western side of the Ross Sea, the physical features of the water column are also affected by the recurring presence of a substantial coastal ice free area, the Terra Nova Bay polynya (Bromwich & Kurtz 1984, Jacobs et al. 1985, Fusco et al. 2...

Abstract. Freshwater discharge from glaciers is increasing across the Artic in response to anthropogenic climate change, which raises questions about the potential downstream effects in the marine environment. Whilst a combination of long-term monitoring programmes and intensive Arctic field campaigns have improved our knowledge of glacier-ocean interactions in recent years, especially with respect to fjord/ocean circulation in the marine environment, there are extensive knowledge gaps concerning how glaciers affect marine biogeochemistry and productivity. Following two cross-cutting disciplinary International Arctic Science Committee (IASC) workshops addressing ‘The importance of glaciers for the marine ecosystem’, here we review the state of the art concerning how freshwater discharge affects the marine environment with a specific focus on marine biogeochemistry and biological productivity. Using a series of Arctic case studies (Nuup Kangerlua/Godthåbsfjord, Kongsfjorden, Bowdoin Fjord, Young Sound, and Sermilik Fjord), the interconnected effects of freshwater discharge on fjord-shelf exchange, nutrient availability, the carbonate system, and the microbial foodweb are investigated. Key findings are that whether the effect of glacier discharge on marine primary production is positive, or negative is highly dependent on a combination of factors. These include glacier type (marine- or land-terminating) and the limiting resource for phytoplankton growth in a specific spatiotemporal region (light, macronutrients or micronutrients). Glacier fjords therefore often exhibit distinct discharge-productivity relationships and multiple case-studies must be considered in order to understand the net effects of glacier discharge on Arctic marine ecosystems.

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