BEIJING, July 10 (Xinhua) -- The lake ice in northeast China froze later and melted earlier with shortened frozen duration from 2003 to 2016, according to a recent study.

Researchers from the Chinese Academy of Sciences and American universities used satellite data to establish a time series for the extent of lake ice and extracted lake ice freezing and thawing cycle dates and durations for eight large typical lakes in northeast China.

They found that the investigated lakes were tending to freeze later and melt earlier, implying a decrease in frozen duration of 0.84 days per year.

The lake ice duration was also found to increase with latitude, and the lakes with a relatively small area had a higher yearly rate of change and were more variable compared with the larger ones, according to the study published in the International Journal of Remote Sensing.

The freezing process was more dependent on the lake size, while the melting process was more dependent on changes in climate, particularly air temperature.

Besides, the variations of both dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations in lake ice, underlying waters were also examined in 40 shallow lakes across the Songnen Plain of northeast China. The lakes, frozen annually during winter, included freshwater and brackish systems.

The results showed that lake ice contained lower DOC and DIC concentration in comparison with underlying waters, according to a paper published in the Journal of Hydrology.

The two types of carbon concentrations of underlying waters were also different between freshwater and brackish lakes.

The researchers proposed that water salinity increases due to climate change and human activity, and significant changes can occur in dissolved carbon in shallow lakes.

Optical remote sensing images with high temporal resolution can be used to monitor periodic freezing and thawing cycles of lake ice resulting from seasonal and inter-annual climate variations.