Abstract

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 [2σ] cal yr B.P. to present) to be ∼4200–4400 ± 670 m3/yr, with a decrease in the offshore sand flux to ∼920–970 ± 270 m3/yr during the latter part of the Holocene (ca. 2730–2610 [2σ] cal yr B.P. to present). The tidal delta initially formed ca. 2100 (1σ 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 (1σ median) cal yr B.P. to 200 yr ago to be ∼4700 m3/yr. Evidence from navigational charts and sediment cores suggests this flux has increased to ∼10,000 m3/yr over the past ∼200 yr. Coupling these data with recently published long-term sand fluxes to the shoreface of Galveston Island yields a total of only ∼130,000 ± 28,000 m3/yr, i.e., significantly less than the ∼240,000 ± 49,000 m3/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.

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