Estimates of ikaite export from sea ice to the underlying seawater in a sea ice-seawater mesocosm

The precipitation of ikaite and its fate within sea ice is still poorly understood.We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice.seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO2), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO2 to the atmosphere during the growth phase, taking up CO2 as it melted and exporting both ikaite and TCO2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 μmolkg-1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64.66 μmolkg-1 in the water column. The export of TCO2 from sea ice to the water column increased the underlying seawater TCO2 by 43.5 μmolkg-1, suggesting that almost all of the TCO2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper the effect of oceanic acidification on the aragonite saturation state (ωaragonite) in fall and in winter in ice-covered areas, at the time when ωaragonite is smallest

Sivetrafik

Vejdirektoratet har foretaget en undersøgelse af mængden af sivetrafik i et område vest for København. Resultatet viste, at mange trafikanter søger at undgå bl.a. Frederikssundsvej i myldretiden og i stedet kører ad mindre lokale veje, som slet ikke er beregnet til denne trafik. En konsekvensberegning har vist at mer-trafikken faktisk påfører lokalsamfundene gener for 2,8 mio. kr. årligt mere, end hvis denne sivetrafik var kørt ad de overordnede veje

Storm-induced water dynamics and thermohaline structure at the tidewater Flade Isblink Glacier outlet to theWandel Sea (NE Greenland)

In April 2015, an ice-tethered conductivity&ndash;temperature&ndash;depth (CTD) profiler and a down-looking acoustic Doppler current profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The 3-week time series showed that water dynamics and the thermohaline structure were modified considerably during a storm event on 22&ndash;24 April, when northerly winds exceeded 15 m s⁻¹. The storm initiated downwelling-like water dynamics characterized by on-shore water transport in the surface (0&ndash;40 m) layer and compensating offshore flow at intermediate depths. After the storm, currents reversed in both layers, and the relaxation phase of downwelling lasted ∼&thinsp;4 days. Although current velocities did not exceed 5 cm s⁻¹, the enhanced circulation during the storm caused cold turbid intrusions at 75&ndash;95 m depth, which are likely attributable to subglacial water from the Flade Isblink Ice Cap. It was also found that the semidiurnal periodicities in the temperature and salinity time series were associated with the lunar semidiurnal tidal flow. The vertical structure of tidal currents corresponded to the first baroclinic mode of the internal tide with a velocity minimum at ∼&thinsp;40 m. The tidal ellipses rotate in opposite directions above and below this depth and cause a divergence of tidal flow, which was observed to induce semidiurnal internal waves of about 3 m height at the front of the glacier terminus. <br><br> Our findings provide evidence that shelf&ndash;basin interaction and tidal forcing can potentially modify coastal Wandel Sea waters even though they are isolated from the atmosphere by landfast sea ice almost year-round. The northerly storms over the continental slope cause an enhanced circulation facilitating a release of cold and turbid subglacial water to the shelf. The tidal flow may contribute to the removal of such water from the glacial terminus

Seasonal rates of benthic primary production in a Greenland fjord measured by aquatic eddy correlation

We present the first year-round estimates of benthic primary production at four contrasting shallow (3–22 m depth) benthic habitats in a southwest Greenland fjord. In situ measurements were performed using the noninvasive aquatic eddy-correlation (EC) oxygen (O2) flux method. A series of high-quality multiple-day EC data sets document the presence of a year-round productive benthic phototrophic community. The shallow-water sites were on average autotrophic during the spring and summer months, up to 43.6 mmol O2 m22 d21, and heterotrophic or close to metabolic balance during the autumn and winter. Substantial benthic gross primary production (GPP) was measured year-round. The highest GPP rates were measured during the spring, up to 5.7 mmol O2 m22 h21 (136.8 mmol O2 m22 d21), and even at low light levels (, 80 mmol quanta m22 s21) during late autumn and winter we measured rates of up to 1.8 mmol O2 m22 h21 (43.2 mmol O2 m22 d21) during peak irradiance. The benthic phototrophic communities responded seasonally to ambient light levels and exhibited year-round high photosynthetic efficiency. In situ downwelling irradiances as low as , 2 mmol quanta m22 s21 induced an autotrophic response and light saturation indices (Ik) were as low as 11 mmol quanta m22 s21 in the winter. On an annual timescale, the average areal rate of benthic GPP was 11.5 mol O2 m22 yr21, which is , 1.4 times higher than the integrated gross pelagic primary production of the , 30–50 m deep photic zone of the fjord. These results document the importance of benthic photosynthesis on an ecosystem level and indicate that the benthic phototrophic compartment should be accounted for when assessing carbon and nutrient budgets as well as responses of coastal Arctic ecosystems to climate change

A fast numerical solution to the general mass-conservation equation for solutes and solids in aquatic sediments

Mathematical modeling of species transformations in aquatic sediments is usually based on numerical solutions to the same general one-dimensional mass-conservation equation and is likely to require substantial computation time. In this paper we present a fast numerical solution to this equation. The solution is suited for both single and multi-component models and it is based on an implicit control volume discretization of the general mass-conservation equation. The solution consists of two algorithms, one that decomposes the discretization matrix once and one that subsequently produces multiple solutions with minimal computational effort. A unique feature of these algorithms is that values of boundary conditions can vary as a simulation progresses without requiring new decompositions of the discretization matrix. This feature can reduce computation time significantly relative to commonly used procedures for modeling dynamic systems. Finally, we present four examples in which the numerical solution is applied to specific problems. From these examples guidelines are derived for the discretization in space and time required to obtain precise solutions of the general mass-conservation equation

Seasonal and spatial variations in the RNA:DNA ratio and its relation to growth in sub-Arctic scallops

We examined the RNA and DNA concentration of field-caught scallops Chlamys islandica, maintained in suspended cultures at 15 and 30 m depth, and scallops from a wild population at 50 to 60 m in Kobbefjord, southwest Greenland. General relations between RNA and DNA concentrations and individual shell height were established, and we found that the RNA:DNA ratio (RD) worked well as a standardisation of the RNA concentration independent of size and sex. During an experimental period of 14 mo, we observed a pronounced seasonal pattern in RD and mass growth, and differences between depths. Even though the period with high levels of RD reflected the growth season relatively well, RD was a poor predictor of individual mass growth rates of C. islandica. However, we found a non-linear response in RD to increased food concentrations resulting in RD being up- and down-regulated at the beginning and end of the productive summer season, respectively. These results indicate that short-term dynamics in the actual mass growth rate might be controlled through regulation of ribosome activity rather than ribosome number (RNA concentration). This adaption would allow scallops to up-regulate protein synthesis more rapidly, thereby ensuring efficient utilisation of the intense peaks in food availability in coastal areas in the Arctic. Therefore, we suggest that RD in C. islandica reflects the growth potential rather than the actual growth rate. Still, the amount of unexplained variance in RD is considerable and not independent over time, suggesting the existence of unresolved mechanisms or relationships

Inorganic carbon system dynamics in landfast Arctic sea ice during the early-melt period

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 3542-3566, doi:10.1002/2014JC010620.We present the results of a 6 week time series of carbonate system and stable isotope measurements investigating the effects of sea ice on air-sea CO2 exchange during the early melt period in the Canadian Arctic Archipelago. Our observations revealed significant changes in sea ice and sackhole brine carbonate system parameters that were associated with increasing temperatures and the buildup of chlorophyll a in bottom ice. The warming sea-ice column could be separated into distinct geochemical zones where biotic and abiotic processes exerted different influences on inorganic carbon and pCO2 distributions. In the bottom ice, biological carbon uptake maintained undersaturated pCO2 conditions throughout the time series, while pCO2 was supersaturated in the upper ice. Low CO2 permeability of the sea ice matrix and snow cover effectively impeded CO2 efflux to the atmosphere, despite a strong pCO2 gradient. Throughout the middle of the ice column, brine pCO2 decreased significantly with time and was tightly controlled by solubility, as sea ice temperature and in situ melt dilution increased. Once the influence of melt dilution was accounted for, both CaCO3 dissolution and seawater mixing were found to contribute alkalinity and dissolved inorganic carbon to brines, with the CaCO3 contribution driving brine pCO2 to values lower than predicted from melt-water dilution alone. This field study reveals a dynamic carbon system within the rapidly warming sea ice, prior to snow melt. We suggest that the early spring period drives the ice column toward pCO2 undersaturation, contributing to a weak atmospheric CO2 sink as the melt period advances.We acknowledge support from the Polar Continental Shelf Program (PCSP) of Natural Resources Canada, the Natural Sciences and Engineering Research Council of Canada, the Northern Scientific Training Program, Canada Economic Development, and Fisheries and Oceans Canada.2015-11-1

Benthic microalgal production in the Arctic: Applied methods and status of the current database

The current database on benthic microalgal production in Arctic waters comprises 10 peer-reviewed and three unpublished studies. Here, we compile and discuss these datasets, along with the applied measurement approaches used. The latter is essential for robust comparative analysis and to clarify the often very confusing terminology in the existing literature. Our compilation demonstrates that i) benthic microalgae contribute significantly to coastal ecosystem production in the Arctic, and ii) benthic microalgal production on average exceeds pelagic productivity by a factor of 1.5 for water depths down to 30 m. We have established relationships between irradiance, water depth and benthic microalgal productivity that can be used to extrapolate results from quantitative experimental studies to the entire Arctic region. Two different approaches estimated that current benthic microalgal production in the Arctic is between 1.1 and 1.6×107 tons C year-1. Climate change is expected to increase the overall primary production and affect the balance between pelagic and benthic productivity in the Arctic. It is therefore imperative to get better quantitative understanding of the relationship between increased freshwater run-off, shrinking sea-ice cover, light availability and benthic primary production to assess future impact on the Arctic food web and trophic coupling. © 2009 by Walter de Gruyter

KAFKA - revurdering af vejregler for kapacitet og trafikafvikling i Danmark.

Trafikafviklingen på det danske vejsystem bliver mere og mere træg, på grund af den stadigt stigende trafik. Vejdirektoratet har bl.a. derfor taget initiativ til en revurdering af det danske regelsæt, der omhandler kapacitet og trafikafvikling, indenfor et projekt kaldet KAFKA. Formålet med et revurderet regelsæt er gennem et større kendskab til trafikale sammenhænge at forbedre trafikafviklingen på alle typer vejanlæg, både i byer og i åbent land. I sin endelige form skal det udarbejdede regelsæt bl.a. indgå i de danske vejregler. I dette notat beskrives projektets formål og baggrund samt en gennemgang af de påtænkte forsknings- og udviklingsprojekter, hvor der sammenlignes med relevante internationale kilder