Unprecedented erosion of the upper Texas coast: Response to accelerated sea-level rise and hurricane impacts

The upper Texas coast is an ideal location to examine coastal response to global change over geologic and historic time. Here we quantify the long-term sequestration for sand eroded from an island into two main sinks, offshore Galveston Island and San Luis Pass Tidal Delta, in order to compare long-term and short-term erosion. We determine the average storm-related offshore sand flux for the middle part of the Holocene (ca. 5240-5040 [2 sigma] cal yr B.P. to present) to be similar to 4200-4400 +/- 670 m(3)/yr, with a decrease in the offshore sand flux to similar to 920-970 +/- 270 m(3)/yr during the latter part of the Holocene (ca. 2730-2610 [2 sigma] cal yr B.P. to present). The tidal delta initially formed ca. 2100 (1 sigma median) cal yr B.P., when the rate of sea-level rise slowed from 2.0 mm/yr to 0.60 mm/yr. We calculate the sand flux from Galveston Island into San Luis Pass from ca. 2100 ( 1s median) cal yr B. P. to 200 yr ago to be similar to 4700 m(3)/yr. Evidence from navigational charts and sediment cores suggests this flux has increased to similar to 10,000 m(3)/yr over the past similar to 200 yr. Coupling these data with recently published long-term sand fluxes to the shoreface of Galveston Island yields a total of only similar to 130,000 +/- 28,000 m(3)/yr, i.e., significantly less than the similar to 240,000 +/- 49,000 m(3)/yr estimated to have been eroded during historic time using the measured erosion rates. While some of this increased erosion can be attributed to anthropogenic influences, the magnitude of change requires additional forcing, specifically, the recent acceleration in relative sea-level rise punctuated by storm impacts during historic time.