No, writing "are a" in a sentence is not correct because ''are '' is used for plural objects or things such these are boys, footballs are big etc while n the other hand, ''a'' is used for singular objects such as a ball, a boy etc so these two words which are used in separate sentences not in a single sentence with each other. so we can say that we can't write "are a" in a single sentence.
They are brought from colder regions e.g. the North and South poles where ice caps are melting to give cold water. Currents are due to the effect of wind on the water.
