Seasonality in the Trans-Atlantic Slave Trade

Introduction

The trans-Atlantic slave trade brings to mind images of haphazard, disorganized plunder that randomly scattered about eleven million African people throughout the Americas. When one examines information contained in the Voyages Database, however, one detects patterns in this forced diaspora. Many vessels sailing under Portuguese flag, for example, transported enslaved Africans from West-Central Africa to Brazil; many Dutch ships sailed from the Gold Coast to Surinam. Colonial power and mercantilism provide one reason to explain these trans-Atlantic routes made by slaving vessels. Portugal controlled coastal territories in Angola, such as the ports Luanda and Benguela, and shipped enslaved Africans from these sites across the South Atlantic to their colonial cities in Brazil. The Dutch controlled the Gold Coast fort Elmina and ordered their captains to proceed with slaves to their South American colony Surinam. Portuguese and Dutch laws restricted their slave trades to national carriers.

The Voyages Database also reveals that in all markets on the African coast, more slaves were embarked on board ship during some months than others. Similarly, in all markets in the Americas, more Africans, year after year, were disembarked during certain months. Why were there seasonal patterns? Focusing on the agricultural histories of African and American societies helps to explain monthly fluctuations in the supply of and demand for enslaved Africans. Whether soils supported subsistence or cash crops, each stage in the agricultural calendar—clearing land, planting, weeding, harvesting—requires different numbers of farmers, different “labor inputs.” On both sides of the Atlantic, seasonal crop cycles created seasonal demands for agriculturalists. The trans-Atlantic slave trade reconciled supply and demand for agricultural labor when captains transferred farmers from “in crop” seasons in Africa to “in crop” seasons in the Americas.

In shifting captives between Old and New World ecological zones, captains created systematic trans-Atlantic patterns when African and American crop cycles differed by the time needed to sail the Middle Passage. In Africa, the numbers of slaves embarked on board ships usually increased during the harvest and in the immediate post-harvest months. During these times fewer and fewer farmers were needed and food stocks began increasing. African merchants purchased slaves whose agricultural labor became temporarily redundant, and they bought seasonal provisions to keep their captives alive. In turn, New World plantation crop production required greater numbers of slaves to cut, gather, and process cane, berries, or leaves. Slaving captains attempted to trade “in season” in both Africa and the Americas by identifying American markets whose cash crop harvests seasons took place 1-3 months after harvest cycles in Africa. Those captains who linked Old and New World food-production cycles sailed along regular trans-Atlantic pathways and synchronized agricultural calendars.