Melting sea ice represents the beginning of SML formation.

Climate change and in turn rising sea temperatures is one of the most prominent stressors the marine environment is facing today, making it a highly studied topic in marine biology. Sea ice is at an increasing risk from the record temperatures the Arctic environment is facing, sea ice harbours large amounts of polymeric substances produced by the microorganisms, which is released during sea ice retreat which can cause drastic changes in the cloud formation.  

Galgani et al., 2016 aimed to understand how retreating Arctic sea ice affects the organic composition of the sea surface microlayer (SML), and to determine the implications for marine primary organic aerosol (POA) release. 

Sampling took place on a research cruise in 2012 in the Arctic ocean 21 sites were sampled which were categorised into 3 types of sample site, t1=freshwater melt ponds, created from melting sea ice, t2= open melt ponds, created when the freshwater ponds become deeper and begin to mix with more saline waters, and t3= open sea samples. After sampling dissolved organic carbon (DOC), dissolved amino acids (DHAA), dissolved uronic acids (DURA), bacteria abundance and marine gel particles (TEP and CSP) levels were all measured from all 21 sites. 

This study showed that the open ocean SML had an enrichment of DOC but no enrichment of bacteria compared to the freshwater melt ponds, although no enrichment the bacteria concentrations were significantly related to DOC, TEP abundance and TEP size. TEP abundance, volume concentrations and total area in the SML increased in the transition from fresh water melt ponds to the open sea samples. 

Interestingly the melt ponds (t1 and t2) had higher percentages of liable DOC compared to more saline water, the open ocean SML had more refractory DOC which is formed from the continuous working of DOC from bacteria and viruses.

In both the SML and the underlying water (ULW) the average TEP size increased with increasing salinity, supporting the idea that TEP formation is enhanced when divalent cations become increasing abundant at higher salinity. 

Melt pond SMLs represent dynamic exchange interfaces between the sea ice and the atmosphere, organic polymers in the SML of recently formed shallow melt ponds may be incorporated as gel into frost flowers and brine skim, potentially representing an important source for Arctic POA during melting periods, and contributing to the exchange of carbon dioxide during both melting and freezing. 

The authors observed DHAA in similar concentrations in all stages of ice melting and coomassie stainable particles (CSP) dominating gel abundances, they indicated that the transition towards first year ice (FYI) in the central Arctic ocean and the increasing number of melt ponds during the summer supports proteinaceous compounds in the SML and their contribution to Arctic aerosols. 

This paper nicely shows that melting sea ice releases trapped DOC, as well as creating enriched SMs in DHAA and proteinaceous gels, there is a nice story being told in this paper with the clear transition from melting sea ice, a SML forming and developing in the an appropiate SML for the open ocean. 

In the Arctic ocean, low wind speed and the absence of breaking waves, suggest that the transfer of organic compounds from the SML to the atmosphere may be mediated by bubble rising and bursting, which releases POA's, and diatom and phytoplankton exudes which nucleates ice under the cold Arctic conditions, forming high altitude ice clouds which can alter precipitation (Wilson et al., 2015).

Reviewed paper: Galgani, L., Piontek, J., & Engel, A. (2016). Biopolymers form a gelatinous microlayer at the air-sea interface when arctic sea ice melts. Scientific Reports, 6, 29465. doi:10.1038/srep29465, http://www.nature.com/articles/srep29465

Wilson, T. W., Ladino, L. A., Alpert, P. A., Breckels, M. N., Brooks, I. M., Browse, J., … Murray, B. J. (2015). A marine biogenic source of atmospheric ice-nucleating particles. Nature, 525(7568), 234–238. doi:10.1038/nature14986, http://www.nature.com.plymouth.idm.oclc.org/nature/journal/v525/n7568/full/nature14986.html