Climate Change

Corals in the Persian/Arabian Gulf are the most thermally tolerant in the world, but live very near the thresholds of their thermal tolerance. Warming sea temperatures associated with climate change have resulted in numerous coral bleaching events regionally since the mid-1990s, but it has been unclear why unusually warm sea temperatures occur some years but not others. Using a combination of 5 years of observed sea-bottom temperatures at three reef sites and a meteorologically linked hydrodynamic model that extends through the past decade, we show that summer sea-bottom temperatures are tightly linked to regional wind regimes, and that strong 'shamal' wind events control the occurrence and severity of bleaching. Sea bottom temperatures were primarily controlled by latent heat flux from wind-driven surface evaporation which exceeded 300 W m −2 during shamal winds, double that of typical breeze conditions. Daily temperature change was highly correlated with wind speed, with breeze winds (<4 m s −1) resulting in increased warming, while faster winds caused cooling, with the magnitude of temperature decline increasing with wind speed. Using observed and simulated data from 2012 to 2017, we show that years with reported bleaching events (2012, 2017) were characterized by low winds speeds that resulted in temperatures persisting above coral bleaching threshold temperatures for >5 weeks, while the cooler intervening years (2013-2016) had summers with more frequent and/or strong shamal events which repeatedly cooled temperatures below bleaching thresholds for days to weeks, providing corals temporary respite from thermal stress. Using observed data from 2012 onward and simulated data from 2008 to 2011, we show that the severity of bleaching events over the past decade was linked to both the number of cumulative days above bleaching thresholds (rather than total days, which obfuscates the cooling effects of occasional brief shamal events), as well as to maxima. We show that winds of 4 m s −1 represents a critical threshold for whether or not corals cross bleaching threshold temperatures, and provide simulations to forecast sea-bottom temperature change and recovery times under a range of wind conditions. The role that wind-driven cooling may play on coral reefs globally is discussed.

New Kingdom royal cult temples in Thebes (Luxor, Egypt) are all located on the lower desert edge. Kom el-Hettân (Amenhotep III: reign 1391-1353 BCE, 18th Dynasty) is an exception, as it is located in the present Nile floodplain. Its anomalous position has puzzled Egyptologists, as has the termination of its use, which traditionally has been attributed to natural hazards such as flooding or earthquakes. Geoarchaeological analyses of the subsurface shows that Amenhotep III's temple was initially founded on a wadi fan that stood several metres above the contemporary surrounding floodplain landscape. The temple was fronted by a minor branch of the Nile, which connected the temple to the wider region, but the temple itself was relatively safe from the annual flood of the Nile. This geoarchaeological study comprised a coring programme to determine the c. 4000-yr landscape history of the local area. Chronological control was provided by the analysis of ceramic fragments recovered from within the sediments. This study shows that the New Kingdom period was, at least locally, characterised by extremely high sedimentation rates that caused a rapid rise of the floodplain and gradual submergence of the pre-existing high temple grounds. This is, however, not a plausible reason for the destruction of the temple, as frequent inundation did not begin until the temple was already out of use and largely dismantled .