What it means to be marine: Sulfur isotope variability in the historical Chesapeake Bay ecosystem

Stable sulfur isotope (δ³⁴S) analysis is an important tool for addressing archaeological and ecological questions about diet and mobility. A growing body of work has underscored the value of δ³⁴S for tracing food sources linked to specific kinds of aquatic primary production, including saltmarshes, freshwater wetlands, seagrass beds, and benthic microalgal communities. Comparatively little work has investigated δ³⁴S variation in other marine vertebrate food webs. This may reflect prevailing assumptions that isotopically homogenous marine sulfates will be the main contributor to consumer δ³⁴S in all marine ecosystems. We explore this assumption through δ³⁴S, δ¹³C, and δ¹⁵N analyses of bone collagen from a taxonomically and ecologically broad cross-section of marine fauna from preindustrial contexts at the archaeological site of Jamestown, near the Chesapeake Bay in present-day Virginia. Results for most taxa show δ³⁴S values that diverge from those expected based on species’ marine ecologies. Benthic primary production, serving as a vector for sulfide-influenced, low-δ³⁴S sulfur entering aquatic food webs, offers the most parsimonious explanation. The ecological diversity represented in these findings, covering a wide range of marine and estuarine habitats, suggests that this phenomenon could be common where benthic algae form an important part of primary production in estuarine and other coastal habitats across the globe. Implications for archaeological and ecological δ³⁴S interpretive frameworks are discussed.