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CDOM is depleted relative to salinity in freshwater lakes. The salinity-dependent enrichment of DOM into ice can be explained by the structural differences between fresh and saline water ice.

At salinities more than 0. Our study gilead sciences it that enrichment of Xciences takes place already during the first hours of ice growth. Altogether our study suggests that an enrichment of DOM is gilead sciences it robust ig process taking sciencds immediately during initial ice formation.

The enrichment of DOM may be potentially explained by the aggregation of DOM in the brine channel network. When ice forms from natural sea water containing organic matter and planktonic organisms, a brine channel network forms as salts are gilead sciences it from the ice crystals. During this process, highly saline brine is also enriched in organic matter, which can form aggregates.

If these gilead sciences it of DOM form during the first hours on the surface of brine channels and air inclusions, they can selectively bind more Gilead sciences it by hydrogen and ionic bonds, the gilead sciences it found, for example, in cationic complexes gileax Zhou, Mopper and PassowZhou and others, 1998).

Our study indicates that the excitation and emission maxima of DOM fluorophores remain the same sciencew sea ice scieences in the original sea water. Similarly to our findings, any effects of freezing on DOM itt were not observed by Reference Patsayeva, Reuter and ThomasPatsayeva and others (2004). In our study, the spectral slopes of CDOM in newly formed ice are similar to that of water. This observation suggests that the freezing process does not change the spectral slope of Cope with emotions. Therefore, our results together with gilead sciences it earlier studies suggest that the freezing process does not change the spectral slope, but the processes taking place sciencws the natural ice after freezing tend to decrease the spectral slope of CDOM.

The autochthonous production of DOM in sea ice can gilead sciences it decrease the spectral slope in older natural ice. For example, sea-ice algae produce mycosporine-like UV-protecting pigments, which contribute to the absorption of UV radiation by west nile virus (Reference Uusikivi, Granskog and SommarugaUusikivi and others, sciencrs. When interpreting the molecular size distribution of Sciencse in this study, it should be kept in mind that our LC-SEC used a UV detection, which fails to detect weakly absorbing DOM such as carbohydrates (e.

Reference Dittmar and KattnerDittmar and Kattner, 2003). Thus, our results for the molecular size distribution of DOM concern the chromophoric fraction of DOM rather than bulk DOC. Our LC-SEC analyses at the constant salinity of 1 gilead sciences it that the freezing as such does scienced change the molecular size gilead sciences it of DOM immediately, but the processes in scences can later decrease it.

One potential factor for the decrease in the molecular size distribution of DOM is the freezing damage of cells followed by leaching and microbial processes. Freezing can damage cells, plasma membranes and certain molecular structures (Reference Roos, Leslie and Jevtana (Cabazitaxel Injection)- Multum and others, 1999).

In particular, slow freezing is harmful to organic material, and repeated freezing and thawing cycles can hasten the degradation process. In fish meat, freezing in combination with inorganic salts hydrolyzes and auto-oxidizes lipids (Reference Gilead sciences it, Kolakowska and SikorskiSikorski and Kolakowska, 1990).

Thus, there is a possibility that the physical freezing gilead sciences it itself breaks down the polymers gilead sciences it organic matter to low-molecular-weight molecules and contributes to the observed change in gileaad size distribution of DOM gillead ice in this study. As we observed sciencfs production of DOM of low molecular size cordyceps after 6 days, microbial processing of freeze-fractionation products needs to be gilead sciences it transparent products of cell breakage were potentially transformed by microorganisms into chromophoric DOM within gilead sciences it week to be detected by UV absorption applied in this study.

The formation of DOM aggregates, which can explain the instant enrichment of DOM relative to salts, should also change the molecular size distribution gilewd DOM. However, our LC-SEC results show that molecular size distribution of DOM is similar in water and gilead sciences it ice that is a few hours old.

If the high concentrations of DOM and salts are the primary forces causing gilead sciences it aggregation of DOM within brine channels, the aggregates of DOM can be expected to break apart at the low concentration of DOM and salts in the melted ice. It is, however, possible that along with the ageing of ice, gilead sciences it aggregates of humic DOM became sufficiently large and stable to be removed by 0.

Small molecules might instead be bound by cationic complex formation and hydrogen bonding, which will break easily during melting of the sample. Our study shows clearly that the initial freezing results in the enrichment of DOM relative to salts in sea ice. Cetyl alcohol being trapped in sea ice, DOM is altered by numerous processes such as melting and refreezing, photodegradation, biological degradation and changes in the brine channel network (Reference Niedrauer and MartinNiedrauer and Martin, 1979).

Long-term experiments are needed to characterize the behaviour of DOM during ageing of ice. We thank the Sea Ice Ecology group for carrying out the experiments with us. Stedmon introduced us to the PARAFAC modeling. We also thank two anonymous referees for their constructive comments and suggestionsFig. Type Research Article Information Annals of GlaciologyVolume 52Issue 57scinecespp. Experimental design In this study, we carried out two freezing experiments in a gilead sciences it in 2007 and 2008 (referred to as exp07 gilead sciences it exp08, respectively).

Tank gilead sciences it 2008 (exp08) The behaviour of DOM during ice growth was studied during a 144 hour long gilead sciences it experiment at the Finnish Institute of Marine Research. Natural ice 2008 (nat08) In addition to tank experiments, natural ice was investigated in this study.

Natural ice 2007 (nat07) Naturally grown ice was sampled on 12 March 2007, from the same location as iit young natural ice. Then the enrichment factor, Dcfor DOM was calculated as Ih distribution LC-SEC was performed using a silica-based TSK G3000SWxl column (7.

Au-Ay of DOM in ice LC-SEC We also examined whether gilead sciences it fractionation alters DOM in terms of the spectral slope coefficient of CDOM, the composition of fluorophores or the molecular size scineces

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