FORAMINIFERAL ANALYSIS OF HOLOCENE SEA LEVEL RISE WITHIN TRINITY RIVER INCISED PALEO-VALLEY, OFFSHORE GALVESTON BAY, TEXAS

Sea-level is expected to continue to rise throughout the next century, and as society prepares to deal with this hazard it is critically important to understand how coastal systems will respond, especially in sediment-poor, subsiding regions like the Texas coast. Tide gauge records in Galveston Bay, Texas indicate that local sea level rise rates are more than twice the global average, raising important questions about the long-term stability of the barrier islands protecting the bay and how the estuary and coastline will respond to sea-level rise. However, tide gauge records are limited to the last century, and longer records are needed to provide insight into dynamic coastal response to sea-level fluctuations. Here, we combine geophysical (chirp seismic) surveys and sediment cores (providing sedimentological and micropaleontological data constrained by radiocarbon dating) to characterize ~10 kyr paleoenvironmental change in the buried Holocene estuary system offshore modern Galveston Bay. Our foraminiferal analysis provides ecological context on the stability of these paleoenvironments and the timing of coastal change including during a 4 kyr period of rapid sea level rise more than twice the modern rate. We provide a model of Holocene shoreline change challenging published models of rapid landward shifts with asymmetric coastal geometry to more gradual transitions matching modern coastal geometry and maintaining a largely stable paleoestuarine environment throughout the middle Holocene (~6.9 ka – 8.8 ka). Subsequent shoreline shifts occurred after global sea level rise slowed below modern rates, indicating hydroclimate impacts on sediment flux likely had a greater influence on the earlier stability of the estuarine system and later shoreline retreat.

Keywords: Sea level rise, Foraminifera, Holocene, Galveston Bay