Seaward-dipping prograding successions of beachrock of the shoreline of the rift valley of the Gulf of Aqaba, a steep-sided tectonic valley that forms the northern segment of the Red Sea, reflect progressive stages of cementation, which unravel a geologic history of the shoreline. The oxygen isotopic composition of Gulf of Aqaba beachrock, recorded by carbonate cement, reflects a temperature decrease of ambient seawater for approximately half of the Holocene. The computed temperature excursion of the Red Sea beachrock cement implies a temperature decrease between the ages 7.07 +/- 0.380 and 2.62 +/- 0.23 ka, an interval of approximately 4500 yr, during which the average Red Sea seawater temperature fell from 33 to 17 degrees C. This discovery is at variance with the climate-change debate that involves increasing temperatures.