This is the 13364th most frequent Turkish word.
kirlenmesinin
"The act of becoming dirty" or "its contamination/pollution."
Here, 'kirlenmesinin' is the genitive form referring to 'pollution' (as the modifying noun) of 'deniz suyu' (sea water). It shows possession or relation, and is used in a phrase to indicate what the pollution pertains to.
Deniz suyunun kirlenmesinin nedenlerini araştırıyoruz.
We are investigating the causes of the pollution of the sea water.
In this sentence, 'kirlenmesinin' describes 'havanın' (air), establishing a relationship where the pollution is specifically associated with the air. It is used to convey a broader environmental concept in a possessive structure.
Havanın kirlenmesinin sağlık üzerindeki etkileri önemlidir.
The effects of air pollution on health are significant.
The usage of 'kirlenmesinin' here specifies the pollution pertaining to 'göl' (lake), pointing to its influence on 'doğal hayat' (wildlife). It expresses a similarity to other possessive and causative contexts in Turkish.