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The Northeast Greenland shelf is a broad Arctic shelf located between Greenland and Fram Strait. It is the principal gateway for sea ice export and sea ice-associated freshwater from the Arctic Ocean. Sea ice thickness has decreased by 15% per decade since the early 1990s and meteoric freshwater discharge has increased. The consequence of changing sea-ice and freshwater conditions in the region on ocean dynamics and the biological system remains unknown. Determining the source(s) of freshwater is important to be able to understand how the area will react to future upstream change. Here we present a synoptic survey of the Northeast Greenland shelf and slope with observations of hydrography, the nutrients nitrate, phosphate and silicate, and conservative tracers δ18O, δ2H and total alkalinity during late summer 2017. We compare these to previously published values, including those which identify Pacific and Atlantic water, the Siberian shelf seas, and the 6 largest Arctic rivers. We show that a major source of freshwater on the Northeast Greenland shelf during late summer 2017 is the Laptev Sea and find no conclusive evidence of Pacific Water. Our observations provide a direct link between Northeast Greenland hydrology and processes occurring on Eurasian shelves.

Glacial rock flour (GRF) is a felsic, silicate sediment that originates below the Greenland Ice Sheet, where the ice abrades basement rocks to a very fine powder. This is then transported by meltwater rivers or subglacial discharge into fjords and coastal waters. Thus, GRF is a naturally occurring component of the oceans around Greenland. The grain size of GRF typically ranges

Greenland's fjords and coastal waters are highly productive and sustain important fisheries. However, retreating glaciers and increasing meltwater are changing fjord circulation and biogeochemistry , which may threaten future productivity. The freshening of Greenland fjords caused by unprecedented melting of the Greenland Ice Sheet may alter carbonate chemistry in coastal waters, influencing CO2 uptake and causing biological consequences from acidification . However, few studies to date explore the current acidification state in Greenland coastal waters. Here we present the first-ever large-scale measurements of carbonate system parameters in 16 Greenlandic fjords and seek to identify the drivers of acidification state in these freshening ecosystems. Aragonite saturation state (Ω), a proxy for ocean acidification , was calculated from dissolved inorganic carbon (DIC) and total alkalinity from fjords along the east and west coast of Greenland spanning 68–75°N. Aragonite saturation was primarily >1 in the surface mixed layer. However, undersaturated—or corrosive––conditions (Ω < 1) were observed on both coasts (west: Ω = 0.28–3.11, east: Ω = 0.70–3.07), albeit at different depths. West Greenland fjords were largely corrosive at depth while undersaturation in East Greenland fjords was only observed in surface waters. This reflects a difference in the coastal boundary conditions and mechanisms driving acidification state. We suggest that advection of Sub Polar Mode Water and accumulation of DIC from organic matter decomposition drive corrosive conditions in the West, while freshwater alkalinity dilution drives acidification in the East. The presence of marine terminating glaciers also impacted local acidification states by influencing fjord circulation: upwelling driven by subglacial discharge brought corrosive bottom waters to shallower depths. Meanwhile, discharge from land terminating glaciers strengthened stratification and diluted alkalinity. Regardless of the drivers in each system, increasing freshwater discharge will likely lower carbonate saturation states and impact biotic and abiotic carbon uptake in the future.

Highlights • Lab-test showed efficient entrainment of bottom water and moderate oxygenation • In salt-stratified basin ventilation oxidized and removed H2S and nutrients • Induced stratification erosion promoted inflow oxidation in salt-stratified basin only • In temperature-stratified basin ventilation not successful; nutrient release occurred • Artificial ventilation is option to improve status of salt-stratified coastal basins We studied the effects of pumping surface water down through the pycnocline (i.e. artificial ventilation) on hydrodynamics, oxygen concentrations, hydrogen sulfide, and nutrients in two anoxic coastal basins (Lännerstasundet and Sandöfjärden). In addition, in a corresponding laboratory aquarium experiment, pumping of less saline surface water entrained dense bottom water with a mixing ratio of 6.8 and illustrated dispersal below the pycnocline. Oxygen saturation increased from 0 to 20%; oxygen penetrated poorly into the sediment of the aquarium. In the salinity-stratified Lännerstasundet basin, ventilation also oxidized the anoxic bottom water. The ventilation removed hydrogen sulfide and decreased the sub-pycnocline water pools of phosphorus and ammonium, which was not observed in a neighboring reference basin. The summertime ventilation warmed and made the sub-pycnocline water less saline. In the autumn, the inflows of cooled water from the surroundings with equal or higher salinity promoted its sinking in the relatively warm ventilated basin. The inflows maintained oxygen concentrations between 4 and 8 mg L−1 for months after the ventilation ended. In contrast to Lännerstasundet, ventilation did not prevent formation of anoxia and release of nutrients in the temperature-stratified Sandöfjärden. Here, the ventilation capacity was less than that in Lännerstasundet and ventilation expanded the sub-thermocline bottom area, warmed the bottom sediments, and probably displaced oxic water from the experimental area. The ventilation did not promote density conditions for inflows and no marked inflow-induced oxidation was observed after midsummer. We conclude that a significant amount of anoxic water was entrained into the ascending plume which reduced the oxygen content below the pycnocline ventilation in aquarium experiment. Additionally, summertime ventilation may improve the status of the salinity-stratified basins for further oxidation. The improvement occurs due to autumn cooling and favorable basin topography, which promote inflows of oxic water with larger density and thereby, renewal of bottom water in the pumped basin. The semi-enclosed and temperature-stratified basin cannot form such favorable density conditions for inflows and thus ventilation is less efficient.

Marine eutrophication and hypoxia caused by excess nutrient availability is a growing environmental problem. In this study, we explore marine nitrogen enrichment in the context of Absolute Environmental Sustainability Assessment (AESA), a method combining life cycle assessment (LCA) with environmental boundaries aiming to compare environmental impacts from an activity (product or system) with the safe operating space (SOS) for the activity. Specifically, we aim to increase the spatial resolution and improve life cycle impact assessment (LCIA) models for marine eutrophication for use in AESAs. By estimating a proxy of the areal extent of eutrophication and hypoxia in coastal large marine ecosystems (LME), we increased model resolution from 66 LMEs in the original LCIA method to 289 coastal LME subsegments and updated relevant LME parameters to the new scale (residence time, bottom water volume, reference O2 concentration, primary production rates and depths). The new method was tested and validated by comparing the global and spatially differentiated occupation of SOS by global nitrogen emissions with observations and it showed an improved ability to identify critical areas where the SOS is exceeded, in accordance with observations of hypoxic events. Despite limitations such as the estimation of benthic zone volume and low spatial differentiation of environmental boundaries, the method can be used by AESA and LCA practitioners wishing to assess the impact of nitrogen release on marine eutrophication with a higher and more relevant spatial resolution.

Vertical mixing of upper water masses in Arctic fjords is important for circulation and transport of nutrients and heat. However, the distribution of turbulent mixing is poorly known. Here we present hydrographic and microscale turbulence measurements from six fjords in Northwestern (69°N–75°N) Greenland. Water mass distributions showed the presence of warm bottom water of Atlantic origin in all fjord transects and a significant modification of upper water masses in fjords with tidewater outlet glaciers. Spatial and temporal distribution of turbulence in the fjordsshowed, in general, low rates of turbulent kinetic energy, ε (∼10 −9 W kg−1), and strong stratification implies that vertical exchange in the upper ∼200 m was relatively weak. However, measurements within 2 km of the terminus of a tidewater outlet glaciershowed values of ε and inferred turbulent diffusion coefficients >10 −4 m2 s−1 that were about two orders of magnitude larger than elsewhere in the deep fjords. This elevated mixing corresponded to comparatively large heat and salt fluxes. These observations suggest that vertical mixing near tidewater outlet glaciers results in localized mixing hot spots, likely due to subglacial discharge and near-glacial current shear, that contribute significantly to vertical exchange in the deep fjords.

The study is based on a very extensive data-set of physical, biological, and optical parameters from below the sea ice in the western Amundsen Basin, central Arctic Ocean, in August–September 2012 during the record low sea ice extent. The water column was strongly stratified at all stations related to salinity differences between a surface layer of reduced salinities (34). A nitrate utilization-based budget in the surface layer gave a primary production of 67.5 mg C m− 2 d− 1, which reduced to 3.9 mg C m− 2 d− 1 in August 2012. Amundsen Basin primary production rates are lower than rates determined for other Arctic Ocean deep-water basins, and also lower compared to rates on the shelf. Below ice phytoplankton was well adapted to low light conditions in the Amundsen Basin and the photosynthetic potential was high, but limited by the low nutrient fluxes induced by the strong stratification. Amundsen Basin is foreseen to be ice-free in summer in 3–4 decades, and the question whether primary production will increase when ice-free was resolved with a coupled physical-biogeochemical model. Results showed that production will increase 10 to 14 times from the present 3.9 mg C m− 2 d− 1 to 37.4 and 55.2 mg C m− 2 d− 1 for an ice-free August and July–August, respectively. The study substantiates that both present and future ice-free low production rates were related to the strong stratification, reduced nutrient fluxes, and deep lying nutrient rich waters. Low production rates and strong stratification are discussed in the view of parameters that increase this stratification as higher freshwater run off or reduce stratification as wind.

The accelerated melt of the Greenland Ice Sheet has been linked to a sudden increase in the presence of warm subsurface coastal water in west Greenland. Yet pathways of warm coastal water along the entire west Greenland coast have remained largely unstudied. Here we present the first, near‐synoptic hydrographic observations at both the continental slope and fjord entrances of the west Greenland coastal system from Cape Farewell (59°N) to Melville Bay (75°N) in summer 2016. We observed a distinct north‐south division in the water mass distribution in west Greenland, approximately partitioned by the northern part of Davis Strait, and a division between the continental slope and fjord entrances. Waters from the regional southern freshwater source with origin in the East Greenland Current that rounds Cape Farewell are not observed to enter Baffin Bay. The regional heat source transported by the West Greenland Current is blocked by Southwest Greenland Coastal Water in the south but the deep connections in the north allow warm deep Subpolar Mode Water to enter fjords. Furthermore, we observed cold and relative saline Baffin Bay Polar Water over the inner part of the banks, periodically reaching as far south as 64°N, suggesting the presence of an undescribed southward current at the Southwest Greenland continental shelf.

Oceanographic and ice-mass-balance records are presented from two moorings deployed on landfast multiyear ice in the Wandel Sea (North Greenland) during June-August 2015. Here we show that the melting and drainage of > 1 m of snow from June 14 to July 14 created a double-diffusive vertical stratification which resulted in supercooling of water and enabled the formation of platelet crystals below the sea ice. Although the effect of supercooling, with temperatures up to 0.58 degrees C below the freezing point, might be overestimated considerably in our records, this process led to the formation of similar to 1.1-1.2 m-thick subice platelet layer. While warm water temperatures lead to the complete loss of this layer at one mooring site, the layer persisted through summer and became incorporated into the congelation ice at the second site. The warm water that melted out the platelet layer can be ascribed to two different sources: (1) in situ heating from solar radiation resulting in a temperature increase up to 0.8 degrees C in late July and (2) advection of warm surface water (with temperatures up to 3-4 degrees C) from the ice-free coastal regions in mid-August. The combination of processes causing the seasonal growth of a platelet layer and either its subsequent ablation or incorporation into congelation ice is discussed with respect to the ice-mass balance and stability of the landfast ice cover in the Wandel Sea. Furthermore, this study provides evidence for the formation of a platelet layer in the Arctic, a phenomenon that historically has only been observed in the Antarctic.

The current downturn of the arctic cryosphere, such as the strong loss of sea ice, melting of ice sheets and glaciers, and permafrost thaw, affects the marine and terrestrial carbon cycles in numerous interconnected ways. Nonetheless, processes in the ocean and on land have been too often considered in isolation while it has become increasingly clear that the two environments are strongly connected: Sea ice decline is one of the main causes of the rapid warming of the Arctic, and the flow of carbon from rivers into the Arctic Ocean affects marine processes and the air–sea exchange of CO2. This review, therefore, provides an overview of the current state of knowledge of the arctic terrestrial and marine carbon cycle, connections in between, and how this complex system is affected by climate change and a declining cryosphere. Ultimately, better knowledge of biogeochemical processes combined with improved model representations of ocean–land interactions are essential to accurately predict the development of arctic ecosystems and associated climate feedbacks.

Buoyant freshwater released at depth from under Greenland's marine-terminating glaciers gives rise to vigorous buoyant discharge plumes adjacent to the termini. The water mass found down fjord formed by mixing of buoyant subglacial freshwater and ambient fjord water and subsequent modification by glacial ice melt in the ice mélange is referred to as subglacial water. It substantially affects both the physical and chemical properties of the fjords' marine environment. Despite the importance of this freshwater source, many uncertainties remain regarding its transformation and detection. Here we present observations close to a marine-terminating glacier in a fjord with substantial ice mélange and follow the down-fjord changes of the subglacial discharge plume. Heat brought to the surface by entrainment of warm ambient fjord water into the rising plume causes intense melting of the ice mélange close to the plume pool. This results in an increase of glacial ice melt fraction to total glacial meltwater from 1–2% in the plume pool to ~18% eleven kilometers down-fjord, with the largest increase being observed within the first few kilometers. Down-fjord of the ice mélange two temperature minima bound the layer containing subglacial water. The upper bound is linked to the adjacent ice mélange and down-fjord runoff sources, whereas the lower bound is linked to the stratification of the ambient water. We show that similar bounds can be observed in other marine-terminating glacier fjords along West Greenland that contain an ice mélange, suggesting that similar processes work in other fjords.

In high-latitude fjord ecosystems, the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web. However, the environmental factors that control the timing and intensity of these spring blooms remain uncertain. In 2013, we studied the spring bloom dynamics in Godthabsfjord, a large fjord system adjacent to the Greenland Ice Sheet. Our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers. A combination of out-fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring (April–May), which supplied nutrient-rich water to the surface layer. This surface water was subsequently transported out-fjord, and due to this circulation regime, the biomass accumulation of phytoplankton was displaced away from the glaciers. In late May, the upwelling weakened and the dominant wind direction changed, thus reversing the direction of the surface water transport. Warmer water was now transported toward the inner fjord, and a bloom was observed close to the glacier terminus. Overall, our findings imply that the timing, intensity, and location of the spring blooms in Godthabsfjord are controlled by a combination of upwelling strength and wind forcing. Together with sea ice cover, the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem.

New production of organic matter from photosynthesis based on “new” nitrate transported into the illuminated surface layer fuels temperate ecosystems during periods of stratification when surface waters are nutrient limited. Published observations from the northeastern North Sea show a large spatial heterogeneity in vertical nitrate fluxes and suggest shelf edge mixing may be the major source for new production here during the stratified summer season. In the current study, we further investigate these empirical findings with a numerical model, where physical transports and mixing are evaluated against observations of temperature, salinity, nutrients and dissipation of turbulent kinetic energy. The relatively shallow central North Sea is separated from the deep Norwegian trench by a strong shelf edge current. This shelf edge frontal zone is characterized by a vertical separation of the surface and benthic boundary layers by an intermediate layer exhibiting low turbulence. A new nitrate assimilation model, driven by light and nitrate availability, is developed and applied for quantifying the potential for, and distribution of, new production in the area. New production in the frontal zone above the shelf edge is located in a narrow high productive (~100 mg C m−2 day−1) band. This is in qualitative accordance with observations. The model results also suggest, however, that new production of similar magnitude occurs above the deep Norwegian trench, where a shallow nutricline in combination with mesoscale eddy activity leads to increased transport of nitrate to the surface layer. Increased new production along the shelf edge could potentially impact ecosystem structure and may explain the relatively high species richness and fishing activity recorded in this part of the North Sea.

A portion of the freshwater transport through Fram Strait consists of low‐salinity Pacific‐derived Arctic water flowing southward along the east coast of Greenland. The pathways of this water are currently unclear. An Ice Tethered Profiler deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected a profile every 3 hr for a year recording conductivity‐temperature‐depth (CTD) and Colored Dissolved Organic Matter (CDOM) fluorescence.This was accompanied by velocity observations. The CTD data revealed that the subsurface water (~15–85 m depth) characterized by high CDOM resembles the “cold Halostad” in the Canada Basin formed by the injection of Pacific water. A coastal branch of the Pacific water outflow from the Arctic Ocean supplies the Wandel Sea halostad, which shows a clear seasonal pattern.From July to October–November, the halostad is shallow, more saline, warmer, and with less CDOM. Conversely, from November to April, the halostad deepens, cools, freshens and CDOM increases, likely indicating a higher fraction of Pacific winter water. The CTD surveys, wind and current data, and numerical simulations show that the seasonal variation of wind over the continental slope likely controls seasonal changes of this intermediate water layer.Over northeast Greenland, winter winds have a northerly component from November to April, favoring Ekman transport of the Pacific‐derived water to the Wandel Sea shelf. In contrast, the prevailing southerly summer winds result in retreat of the Pacific‐derived water off the shelf. The landfast ice off‐slope extension modifies wind‐forcing disrupting seasonal patterns

The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers. Currently, there is a large disagreement between observed and simulated ice flow, which may arise from inaccurate parameterization of basal motion, subglacial hydrology or geothermal heat sources. Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth’s interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature and salinity time series (2005–2015) in the deep stagnant basin water are used to quantify a GHF of 93 ± 21 mW m−2 which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream.

Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these fjords are limited making it difficult to assess linkages between the fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade-long monthly hydrographic time series from a southwest Greenland fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the fjord. In general, the fjord's seasonal circulation system damps the seasonal variation in temperature in the fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the fjord that is half the observed range at the fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.

Organic carbon (OC) synthesised by plankton is exported out of the surface layer as particulate (POC) and dissolved (DOC) organic carbon. This “biological pump” constitutes a major pathway in the global marine carbon cycle, each year exporting about 10 Pg C into the ocean interior, where it is subsequently remineralised via biological decomposition. Remineralised inorganic nutrients and carbon are, ultimately, again brought to the surface by advection and turbulent mixing which closes the OC-cycle in the upper ocean. Thus, remineralisation rates of OC are a critical component of the biological pump. These rates are regulated by the lability of the material and the environmental conditions in the ambient water. Temperature is particularly important in regulating the rate of microbial respiration and, thus, remineralisation rates. A significant temperature dependence of the microbial metabolic activity in the ocean interior is expected, as this is a feature observed elsewhere in the biosphere. Such temperature dependence of microbial remineralisation of POC and DOC will alter the amount of material available for transport by the biological pump to the deep ocean. Very few studies on the lability of OC and temperature sensitivity of microbial degradation processes in the mesopelagic zone (∼100–1000 m) have, to date, been carried out. Here, we present a comprehensive new experimental data set from all major ocean basins and quantify remineralisation rates of OC and their temperature sensitivity in long-term incubations of water from the upper 350 m. Microbial respiration was measured by non-invasive oxygen optodes and oxygen consumption was used as a constraint for determining the remineralisation rates and temperature sensitivity by two complementary methods. First, we analysed the oxygen consumption from a multi-component OC-model where the concentration, remineralisation rates and temperature sensitivity of two bio-available (labile) pools of organic carbon were fitted to the data via a non-linear fitting procedure. Thereafter, a continuous OC-model was fitted to the data through an inverse method and information about lability, temperature sensitivity and structural composition of the OC-pool was analysed together with the results from the two-pool solutions. Median values of remineralisation rates from all experiments on material characterising sinking POC were found to be 0.6 and 0.05 days −1 for the two decomposable pools corresponding to turnover times of 2 and 21 days, respectively. Accordingly, solutions from the continuous model resulted in median turnover times between 6 and 11 days. Similar analyses were carried out for the OC-pool characterising DOC. A significant bio-available OC-pool was found to be present in the surface layer with a median value from all experiments of 30 μM TOC. The median values of all remineralisation rates from the two bio-available OC-pools were found to be 0.2 and 0.02 days −1 , corresponding to turnover times of 5 and 56 days, respectively, in good agreement with previous studies. The corresponding temperature sensitivities, characterised by a Q 10 -value, were found to be about 1.9 for the POC-fraction whereas the DOC fraction was characterised with values above 2.8 for the continuous OC-models. The analysis of the structural composition indicated that the TOC distribution in the surface layer was characterised by more heterogeneous material in terms of lability compared with the POC material sampled from the upper 350 m. Finally, we analyse the potential impact of the calculated temperature sensitivity on the general OC-cycling in the upper ocean and show that the implied reduction in OC-flux in a warmer ocean may have significant impact on nutrient cycling in general and also tends to reduce future ocean carbon uptake significantly.

We present bathymetry and hydrological observations collected in the summer of 2014 from two fjord systems in Southeast Greenland, using SS Activ with a multibeam system temporally installed over the side of the ship. Our results provide a detailed bathymetric map of the fjord complex around Skjoldungen Island and the outer part of Timmiarmiut Fjord and show far greater depths compared to the International Bathymetric Chart of the Arctic Ocean. The hydrography collected show different properties in the fjords with the bottom water masses below 240 m in Timmiarmiut Fjord being 1–2 °C warmer than in the two fjords around Skjoldungen Island, but data also illustrate the influence of sills on the exchange of deeper water masses within fjords. Moreover, evidence of subglacial discharge in Timmiarmiut Fjord, consistent with satellite observations of ice mélange set into motion, adds to our increasing understanding of the distribution of subglacial meltwater. Data is available through the PANGAEA website https://doi.pangaea.de/10.1594/PANGAEA.860627.

Many tidewater outlet glacier fjords surround the coast of Greenland, and their dynamics and circulation are of great importance for understanding the heat transport toward glaciers from the ice sheet. Thus, fjord circulation is a critical aspect for assessing the threat of global sea level rise due to melting of the ice sheet. However, very few observational studies describe the seasonal dynamics of fjord circulation. Here we present the first continuous current measurements (April–November) from a deep mooring deployed in a west Greenland tidewater outlet glacier fjord. Four distinct circulation phases are identified during the period, and they are related to exchange processes with coastal waters, tidal mixing, and melt processes on the Greenland Ice Sheet. During early summer, warm intermediate water is transported toward the glacier at an average velocity of about 7 cm s−1. In late summer, the average velocity decreases to 3 cm s−1 during a period with significant subglacial freshwater discharges. During this period, a large variability in current velocities is also observed. The associated average heat transport in an intermediate-depth range corresponds to 568 GW in early summer and is reduced to 287 GW in late summer. These heat fluxes are at the higher end of previously reported fluxes. Our measurements show that the intermediate heat transport varies over time and during summer provides a major contribution to the heat budget and, thereby, potentially to glacial melt. We suggest that intermediate heat transport may play a similar important role in other fjords around Greenland.

Runoff from the Greenland Ice Sheet, local glaciers, and snowmelt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south toward Denmark Strait. Very few direct measurements of runoff currently exist in this large area, and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/Tyrolerfjord in northeast Greenland (74°N), provide some of the few observations of hydrographic, hydrologic, and atmospheric parameters from this remote area. Here we analyze measurements from the fjord and also measurements in the ambient water masses, which are found in the outer fjord and between the fjord and the East Greenland Current and validate and apply a numerical model of the fjord. A model sensitivity study allows us to constrain runoff estimates for the area. We also show that a total runoff between 0.9 and 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low-saline coastal water mass formed by runoff from fjords north of the Young Sound/Tyrolerfjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the fjord.

The drainage of ice-dammed lakes in the form of outburst floods in Greenland is detected regularly by remote sensing, and these events are expected to occur more frequently in a warmer climate. However, their impact on ice sheet stability and neighboring water bodies is still unknown. In this interdisciplinary study, we investigate lake drainages from the Greenland Ice Sheet into a west Greenland fjord by analyzing simultaneous time series of satellite observations and direct hydrographic measurements of temperature and salinity in the fjord. Satellite images show that, in general, lake drainages have occurred quasiperiodically during the last decade. A particular sequence of drainage events was observed by satellite in 2009 and was analyzed together with the first direct hydrographic observations. Signs of ice-dammed lake drainages were observed by a downstream mooring located just below the intertidal zone. The release of freshwater occurred at the fjord subsurface at a tidewater outlet glacier. The downstream in-water sequence of property changes in relation to these drainage events was observed as an almost immediate decrease in surface layer temperature (~2°C) followed within a week by the arrival of a high-saline pulse (~ +5 units) with elevated salinity lasting for several days during the passage. During lake drainages, large amounts of relatively warm and saline intermediate water are brought to the near-surface layers by entrainment processes near the glacier front, and this influences the hydrography of the fjord but also impacts the ecosystem through upwelling of nutrient-rich intermediate water.

Previous studies have demonstrated that patches of eel larvae are found in the frontal region of the Subtropical Convergence Zone (STCZ), but to date no clear evidence of why this region might confer advantage to the larvae has been presented. This study demonstrates that there may be localized patches within a frontal region in the STCZ in the Sargasso Sea that experience elevated vertical mixing and an associated vertical flux of nutrients. This localized vertical mixing was suggested by a group of stations within the frontal region that exhibited a greater similarity (Jaccard index) between the diatom communities at 10 m and >100 m (in the deep chlorophyll maximum, DCM) than in other parts of the frontal region. Thorpe displacements supported the hypothesis of elevated mixing intensities around these stations, as did vertical mixing rates inferred from stratification and vertical current shear calculated from acoustic Doppler current profiler (ADCP) measurements. Combining these mixing estimates with vertical nutrient gradients suggests that nutrient fluxes to the euphotic zone at these mixing sites may be an order of magnitude greater than elsewhere in the frontal region. This mixing may influence the plankton food web, as indicated by elevated values/concentrations of (1) primary production, (2) variable fluorescence (Fv/Fm) and (3) total seston. In addition, the fraction of the total biomass of both copepods and nauplii found closest to the DCM in the frontal region correlated with the stratification (Brunt-Vaisala frequency), with the greatest fractions found below 75 m at the most weakly stratified stations. While this study cannot directly link these observations to eel larvae ecology, Munk et al. (2010; Proc R Soc B 277:3593-3599) reported that eel larvae were most abundant at locations where we found evidence for elevated vertical mixing. © Inter-Research 2014.

The life cycle of many benthic macro-invertebrates is characterised by a planktonic life stage where larvae are transported by ocean currents and mixing and after some time they reach a stage where they settle onto the ocean bottom and, provided a suitable habitat is available, initiate their benthic life stage as juvenile organisms and complete their life cycle when they mature and spawn as adults. Such age-specific behaviour is in general difficult to include in large scale ocean models unless dispersal is considered on an individual basis, i.e. individual based model coupled with a Lagrangian description of the flow field. However, here we address this issue in an Eulerian framework and develop and apply a new life cycle and population dynamical model of benthic fauna and implement the model in a high-resolution three-dimensional circulation model of the North Sea/Baltic Sea transition zone. The model explicitly describes specific life stages of the population and considers the different processes affecting the organisms during their life cycle, e.g. spawning, dispersion and settling. The model considers different life stages of an idealised marine organism, representing a typical benthic macro-invertebrate species in the area. Populations of juvenile and adult benthic organisms are maintained by spawning, occurring regularly every spring, and subsequent settling of larvae. The pelagic larval stages are simulated by a larval concentration distribution function, i.e. discrete age-classes of the total larval concentration, and age-specific physiological processes, as the onset of their settling behaviour, is explicitly accounted for in the model. Model simulations show, in general, a large connectivity between habitats in the northern and southern part of the area but also that self-recruitment is sufficient to sustain the two populations independently. A sensitivity study were carried out with the spawning rate as a control parameter and two non-trivial quasi-stationary steady states of benthic biomass distributions were identified, characterised by a high and low distribution of organisms in the area, respectively. A stability diagram identifies a bifurcation point when the spawning rate is reduced by 65% and where lower spawning rates implies two different stable equilibria. The existence of multiple quasi-stationary steady states can be explained by the general circulation in the area: when spawning into the surface layer takes place from recruitment areas close to the North Sea where the out-flowing Baltic Sea surface water hinder the southward transport of pelagic larvae. The existence of multiple equilibria support the hypothesis of regime shifts in coupled physical-biological systems where modest changes in critical processes causes rapid and extensive structural changes in the ecosystem. Such changes could occur if a system is close to a bifurcation point such that small changes in critical internal biotic dynamics or in environmental conditions force the system into a new equilibria, for example due to hypoxia or changes in temperature or salinity. Finally, it is shown that model simulations of periods with hypoxic bottom water masses reduces the total benthic biomass distribution in the area significantly.

Hypoxic conditions (O 2 −1 ) are frequently observed in the relatively shallow and stratified North Sea–Baltic Sea transition zone. Inter-annual variability with more extensive hypoxia has been observed in years with calm weather conditions during late summer. A future warmer climate may increase hypoxia in the area due to combined effects from decreased oxygen solubility and increased respiration rates. Feedbacks from climate change can, therefore, amplify negative effects from eutrophication, such as hypoxia. Here we apply a high resolution three-dimensional ocean circulation model with a simple pelagic and benthic oxygen consumption model (OXYCON), based on the seasonal organic carbon budget in the area, and demonstrate that the model is able to simulate the temporal and spatial variability of the observed oxygen concentration in the bottom waters during a three-year period. The potential impact from a warmer climate was analysed in a sensitivity study with a 3 °C warmer climate, and showed a significant increase of hypoxic bottom areas compared to present day conditions. The relative role of increased respiration and decreased oxygen solubility in the inflowing bottom water and at the surface was analysed and it was found that decreased solubility accounted for about 25% of the simulated decrease in bottom water oxygen concentration in the centre of the area in the early fall. A sensitivity study showed that the simulated effect from a 3 °C temperature increase on the bottom water oxygen concentration could be compensated by a 30% reduction in the export production. The model simulations of the North Sea–Baltic Sea transition zone indicate a significant expansion of the hypoxic areas and a lengthening of the hypoxic period under a warmer climate.

[1] The Greenland Ice Sheet releases large amounts of freshwater into the fjords around Greenland and many fjords are in direct contact with the ice sheet through tidewater outlet glaciers. Here we present the first seasonal hydrographic observations from the inner part of a sub-Arctic fjord, relatively close to and within 4–50 km of a fast-flowing tidewater outlet glacier. This region is characterized by a dense glacial and sea ice cover. Freshwater from runoff, subglacial freshwater (SgFW) discharge, glacial, and sea ice melt are observed above 50–90 m depth. During summer, SgFW and subsurface glacial melt mixed with ambient water are observed as a layered structure in the temperature profiles below the low-saline summer surface layer ( 1°C) intermediate water mass is a significant subsurface heat source for ice melt. We analyze the temperature and salinity profiles observed in late summer with a thermodynamic mixing model and determine the total freshwater content in the layer below the summer surface layer to be between 5% and 11%. The total freshwater contribution in this layer from melted glacial ice was estimated to be 1–2%, while the corresponding SgFW was estimated to be 3–10%. The winter measurements in the subsurface halocline layer showed a total freshwater content of about 1% and no significant contribution from SgFW.

The marine Arctic is considered a net carbon sink, withlarge regional differences in uptake rates. More regionalmodelling and observational studies are required toreduce the uncertainty among current estimates.Robust projections for how the Arctic Ocean carbonsink may evolve in the future are currently lacking.Direct connections have been documented betweensea-ice dynamics and carbon cycling in marineecosystems and on land. Projections suggest furthersea-ice decline may accelerate changes in carboncycling dynamics at sea and on land. Although rivertransportedorganic and inorganic carbon plays a majorrole in the marine Arctic carbon cycle this is not wellstudied. Changes in terrestrial ecosystems may alsoaffect sea-ice decline – at least in the long term.Permafrost underlies ~75% of the area draining into theArctic Ocean but its hydrology is poorly understood,especially under global warming. Arctic tundra is anet sink for atmospheric carbon dioxide (CO2) in thegrowing season and the sink strength has more thandoubled since 2000 in Eurasia. In contrast, the fewwinter data available show tundra ecosystems are anet source of atmospheric CO2 in winter. Small featuresbelow the resolution of current lake and wetlanddatabases may be important controls on carbontransfer from permafrost soils to the atmosphere.Earth System Models (ESMs) are not yet able to reliablysimulate the full dynamics of the Arctic carbon cycle.This is mainly because such models still addressterrestrial and marine systems separately and becausethey vary widely in their representation of permafrost.Further development of ESMs should include a focuson improving the connections between ocean and land,especially in the representation of lateral fluxes.

Phytoplankton diversity, whether defined on the basis of functional groups or on the basis of numbers of individual species, is known to be heterogeneous throughout the global ocean. The factors regulating this diversity are generally poorly understood, although access to limiting nutrients and light is known to influence distributions for certain groups of phytoplankton. Here, we develop a simple box model of biomasses and a limiting nutrient to describe the composition of phytoplankton communities in the euphotic zone. In addition to analyzing the relative importance of nutrient availability in generating and maintaining diversity, we apply the model to quantify the potential role of zooplankton grazing and ocean transport for the coexistence of competing species and phytoplankton diversity. We analyze the sensitivity of phytoplankton biomass distributions to different types of grazing functional responses and show that preferential grazing on abundant species, for example as formulated by the Holling type III grazing function, is a key factor for maintaining species’ coexistence. Mixing and large-scale advection are shown to potentially have a significant impact on the distribution of phytoplankton species and, in general, enhance phytoplankton diversity. Based on the model solutions, we argue that ocean transports of phytoplankton cells can have a significant influence on species composition and that even transports at horizontal spatial scales of up to at least 102 km and vertical scales of 102 m can be expected to be important for sustaining phytoplankton diversity. The model is applied in a multi-species simulation (n = 200) and model simulations suggest that global patterns of phytoplankton biodiversity are determined by a few dominating species within each group. This finding is shown to be in accordance with ecological observations.

Data collected at open water stations (depth>400m) in all major ocean basins in 2006-2008 are used to examine the relationship between the size structure of the phytoplankton community (determined by size fractionated chlorophyll filtration), temperature and inorganic nutrient availability. A significant relationship (p2 from the atmosphere. The reported results suggest that ocean warming may directly alter plankton community structure. This, in turn, may alter the structure of marine food webs and impact the performance of the open ocean as a natural carbon sink.

The transition zone between the North Sea and the Baltic Sea is a highly dynamic region where a general estuarine circulation forms a regional scale frontal system from northern Kattegat to the Arkona Sea. This system is characterized by an upper low saline outflowing Baltic water mass from the inflowing saline Skagerrak bottom water to the Kattegat and Belt Sea area. Large and rapid fluctuations of the frontal system are caused by barotropic transports, forced by changing sea level difference between northern Kattegat and the western Baltic Sea, and this results in high variability of the hydrographic conditions and also in frequent in- and outflow events to the Baltic. The dynamics in the region are here analyzed by a regional model of the transition zone, covering the area from the northern Kattegat to the Arkona Sea. The model is validated against water level, temperature and salinity measurements from the region, and the transports through the Danish straits are related to previous estimates and empirical relations. A sensitivity study quantify the role of bathymetry, the tidally induced mixing and the inflowing Skagerrak bottom water for ventilating the bottom water with Skagerrak water or surface water. Furthermore, the dynamics in the region is analyzed with tracers representing the age of the water. The distribution of age tracers with different boundary conditions are analyzed, and the role of advection and mixing for ventilating the bottom water is quantified in terms of the water age. It is shown that the Great Belt area is a very dynamical area where bottom water is ventilated with surface water. The interannual variation of the ventilation of bottom water in the period 2001–2003 is analyzed by various age tracers and related to observed oxygen conditions, and it is shown that the extreme hypoxic event in the autumn 2002 in the southern Kattegat, the Great Belt and in the western Baltic Sea coincide with an unusual low vertical ventilation rate in the Great Belt area, but normal advection rates of bottom water from the northern Kattegat. This indicates that during this particular event, and probably in general, ventilation of bottom water in the Great Belt has significant influence on oxygen conditions in the southern part of the region and for ventilation of bottom waters in the western Baltic Sea. In contrast, the central Kattegat is primarily ventilated by advection of bottom water from the Skagerrak. An age tracer representing the ventilation rate of bottom water with either Skagerrak water or surface water is shown to be inversely correlated to the observed oxygen distribution in the region.

Global and regional ocean primary production estimates are highly dependent on assumptions concerning the photosynthetic potential of the resident phytoplankton communities. Little is known, however, about global patterns in the distribution of photosynthetic potential and their causes. Here, we review existing literature reporting photosynthetic characteristics of natural populations. From this, we formulate hypotheses regarding abiotic and biotic factors of potential importance in determining photosynthetic performance. These hypotheses are then tested using data we have compiled from nearly all major ocean basins on the maximum rate of photosynthesis, PmaxB, and the slope of the photosynthesis vs. light curve, αB (both parameters normalized to chlorophyll) as well as standard environmental variables, size fractioned chlorophyll, taxonomic data (to group), size, and biovolume data for pico-, nano-, and micro-phytoplankton. In terms of abiotic variables, depth of sampling, temperature, and nutrient availability all can be related to photosynthetic parameters. The most important biotic variable influencing photosynthetic performance was found to be community size distribution and the small component (i.e., the proportion of the phytoplankton community passing through a 10 μm filter) is shown to have both higher PmaxB and αB than the larger phytoplankton component. A simple model was used to derive best fit values for PmaxB (1.53/2.50 μgC l−1 h−1) and αB (0.025/0.040) for the large/small groups in the subset of the data where taxonomic data were available (both surface and sub-surface samples) using fractioned chlorophyll data and bulk community photosynthetic parameters. Non-metric multidimensional scaling (NMDS) was used to relate the distribution of photosynthetic parameters and dominant (by biovolume) phytoplankton groups. High PmaxB was recorded in communities dominated by dinoflagellates, small flagellates and in warmer waters, picoeukaryotes, and Synecococcus. Diatom dominated communities exhibited lower PmaxB and were associated with high inorganic nutrients and colder temperatures. That photosynthetic parameters appear closely related to community size distributions and taxonomic group provides some hope for improving the parameterization of photosynthetic performance in global ocean primary production estimates as both of these parameters can be made from remotely sensed optical characteristics of surface waters.

This paper examines the economic aspects of pumping of oxygen-rich water to anoxic bottoms of the Baltic Sea from two different angles. Drawing on the recent pumping experiments in the Swedish archipelago (Lännerstasundet) and in the Finnish archipelago (Sandofjärden), we generalize the findings to the anoxic coastal areas of the Gulf of Finland. For nutrient policies we find that under the current abatement levels and abatement costs in WWTPs, reduction of external loads produces higher annual net benefits and higher present value than oxygenating anoxic bottoms by pumping in the coastal areas of the Gulf of Finland. For pumping a means of speeding up the recovery after a hypothetical heavy reduction in nutrient loads we find that it might provide positive net benefits in the coastal anoxic bottoms in the Gulf of Finland but not in the open Gulf of Finland. This paper examines the economic aspects of pumping of oxygen-rich water to anoxic bottoms of the Baltic Sea from two different angles. Drawing on the recent pumping experiments in the Swedish archipelago (Lännerstasundet) and in the Finnish archipelago (Sandofjärden), we generalize the findings to the anoxic coastal areas of the Gulf of Finland. For nutrient policies we find that under the current abatement levels and abatement costs in WWTPs, reduction of external loads produces higher annual net benefits and higher present value than oxygenating anoxic bottoms by pumping in the coastal areas of the Gulf of Finland. For pumping a means of speeding up the recovery after a hypothetical heavy reduction in nutrient loads we find that it might provide positive net benefits in the coastal anoxic bottoms in the Gulf of Finland but not in the open Gulf of Finland.

The temporal evolution of biogeochemical state variables in shallow coastal seas and estuaries is tightly coupled to the turbulent mixing in the water column. In addition to the general regulation of nutrients for living organisms, vertical mixing in the surface boundary layer also strengthens the coupling between the pelagic and benthic communities in areas where the surface boundary layer reaches the bottom boundary layer. Here we analyse vertical mixing rates in the surface mixed layer with a one-dimensional model simulating the conditions in a shallow fjord during a 5-year period. The mixing rates are quantified by the distribution of an artificial water age tracer, where the age is related to the time elapsed since the water left the surface. A method is developed and applied taking into account the diffusive mixing of old water from deeper water, and the influence of upward diffusive mixing on the water age throughout the mixed layer is quantified. The resulting age of the water at different depth levels ranges from typically about 6 h at 2 m depth to 1–4 days at 8 m depth. Large interannual variability of the age tracer in the mixed layer is seen during the late spring and summer period, and this can be related to the variability of wind generated turbulence. The distribution of the water age in the mixed layer is relevant for analysing the coupling between the pelagic and benthic biomasses in shallow coastal systems on length and timescales corresponding to the mixed layer depth and about 1 week, respectively.

A new incoherent vibration–rotational Raman spectrum of 16 O 2 recorded by means of an interferometer is presented. The measured wavenumbers are analyzed together with a coherent Raman spectrum, six different microwave spectra from the vibrational ground state, and one microwave spectrum from the first vibrationally excited state in one fit. Due to the non-linear energy expression for oxygen, such an analysis requires the use of an iteration to find the minimum for the so-called merit function. A method has been developed to secure a stable iteration. The energy expression originally contains 21 constants. A systematic search leads to a reduction of this to 19 constants to make the fit possible. This results in two solutions, which are, however, only two different ways of indicating the one final energy function. The systematic use of iterations reduces the influence of the computational uncertainty on the final molecular constants to be orders of magnitude lower than the uncertainty due to the experimental errors.

The melting of tidewater outlet glaciers from the Greenland Ice Sheet contributes significantly to global sea level rise. Accelerated mass loss is related to melt-processes in front of calving glaciers, yet the role of ocean heat transports is poorly understood. Here we present the first direct measurements from a subglacial plume in front of a calving tidewater outlet glacier. Surface salinity in the plume corresponded to a meltwater content of 7 %, which is indicative of significant entrainment of warm bottom water and, according to plume model calculations, significant ice melt. Energy balance of the area near the glacier showed that ice melt was mainly due to ocean heat transport and that direct plume-associated melt was only important in periods with high meltwater discharge rates of ~100 m3 s−1. Ocean mixing outside of the plume area was thus the primary heat source for melting glacier ice.

[1] Estimates of changes in the global carbon budget are often based on the assumption that the terrestrial biosphere controls the isotopic composition of atmospheric CO2 since terrestrial plants discriminate against the 13C isotope during photosynthesis. However, this method disregards the influence of 13C fractionation by the marine biota. Here an interpretation of the glacial-interglacial shifts in the atmospheric CO2 concentration and δ13CO2 measured in the Taylor Dome ice core [Smith et al., 1999] is given by accounting for possible changes in the ocean biology based on sensitivity simulations undertaken with the intermediate complexity model CLIMBER-2. With a combined scenario of enhanced biological and solubility pumps, the model simulates glacial atmospheric CO2 and δ13CO2 similar to those inferred from the ice core. The simulations reveal that a strengthening of the oceanic biological carbon pump considerably affects the atmospheric δ13CO2.