What is the significance of the ginger smell in Song of Solomon?

In Toni Morrison's Song of Solomon, the ginger smell is carried off the lake and drifts toward certain party of the city. It's described as, "[a]n odor like crystallized ginger, or sweet iced tea with a dark clove floating in it." This is a strange phenomenon since the lake was ruined by the dumping of mill refuse and chemical waste from a nearby plastics manufacturer. This makes in an inhospitable ecosystem for humans, flora, and fauna alike; "[c]arp floated belly up onto the beach," "the hair of the willows that stood near the shore was thin and pale," and "ear infections were a certainty for those who swam in those waters." 

Despite the disgusting makeup of the lake, it mysteriously emanate that "heavy spice-sweet smell" that makes those who encounter it think of the Far East. Nonetheless, many people in its vicinity have not noticed it due to the presence of air conditioning units in their homes; they no longer have to keep their windows open to keep cool at night.

In Southside, however, the smell is able to drift through the open windows, and the ginger odor seems to have a powerful impact on the waking and dreaming thoughts of those who dwell there. If someone asleep detects the ginger, he or she will believe that his or her deepest desires had already manifested, believing, "the things he hungered for were right at hand." Those who smelled the ginger waft while awake felt that their behaviors and thoughts were "both intimate and far away." When Milkman and Guitar smell the ginger while loitering on Darling Street, it makes them think of freedom, justice, luxury, and/or vengeance. The impact of this scent is that it seems to give everything a surreal, dream-like quality; reality is illusory when the ginger odor is present, and it brings out the hidden cravings and traits of those who encounter it.  

On a more symbolic level, ginger has an association with the presence of the dead in African cultures and folklore. Note that the ginger scent appears before Milkman breaks into Pilate's house to steal the bag of "gold" (which is actually just a bag of human bones); when he visits the almost impossibly old former slave and midwife, Circe; and when Pilate and Milkman are shot at by Guitar in the final scene of the book. This scent may, thus, foretell what is to come--some encounter with death or the nearly dead--or remind us of the thin veil between the living and the dead. It may also speak to Milkman's ties to his family (as complicated or unpleasant as they may be) and the long history of strange and wonderful powers that they possess as descendants of  Solomon, the slave who could fly.