Earth scientists and oceanographers at the King Abdullah University of Science and Technology (KAUST) have discovered that deep water in the Red Sea is replenished much faster than previously thought. Its deep circulation was also found to be directly affected by major climatic events, including volcanic eruptions, around the world.
Dr. Ibrahim Hoteit, professor of earth science and engineering at KAUST, said "the researchers have gained further insight into the circulation of the Red Sea's deep waters by using temperature and salinity data gathered by six cruises from along the central axis of the Red Sea and an ocean circulation simulator."
The team also found that the depths of the Red Sea have experienced rather rapid water renewals, which is against the conventional idea that it is mostly stagnant.
Waters at depths of 300 to 2,000 meters in the Red Sea are recognized as the warmest and saltiest deep-water environments in the world. To date, research suggested that the Red Sea's deep water is relatively stagnant, taking about 36 to 90 years to renew, and that its main source of renewal is water flowing from the northern gulfs of Suez and Aqaba into the sea's main basin.
In KAUST, the scientists linked the Red Sea deep-water renewals to the global climate variability associated with remote volcanic eruptions and the North Atlantic oscillation, an inherent atmospheric variability mostly affecting Europe. Volcanic eruptions tend to warm the middle atmosphere of the tropics by releasing large amounts of sulfate aerosols, which absorb the sun rays for periods of up to two years. The westerly jet across the Atlantic Ocean becomes stronger as the atmospheric circulation adjusts to this warming. This, in turn, increases dry, cold northwesterly winds above the Red Sea: Heat is lost from the sea's waters to the air, and the surface temperature becomes cold enough to trigger surface colder waters to sink. This is known as open-ocean deep convection. In contrast with previous studies, the KAUST scientists found that it was this open-ocean deep convection caused by volcanic eruptions that formed the primary source of the replenishment of the Red Sea's deep water, while the flows of water originating in the gulfs of Suez and Aqaba represented secondary sources.
Understanding the deep-water ocean currents of the Red Sea enables researchers to better gauge its health, since organic matter from surface waters falls into the ocean depths, where it decomposes into its basic mineral components. The movements of these mineral-rich waters carry oxygen and important nutrients that support ecosystems and sea life.
Another study by the KAUST's scientists has revealed that surface temperatures in the Red Sea do not rise.
Analysis of long term data sets shows that the current high warming rates of the Red Sea appears to be a combined effect of global warming and natural long-duration changes in sea surface temperature.
Hoteit said the study revealed a sequence of alternating positive and negative trends in Red Sea surface temperatures. Over the next decades, the trends indicate a cooling phase that may counter the effects of global warming.
Hoteit and colleagues in the Red Sea Modelling and Forecasting Group analyzed over a hundred years of satellite data that reveals how the Atlantic Multidecadal Oscillation (AMO) strongly influences surface temperatures in the Red Sea. Counter to global trends related to climate change, the research points to a cooling phase over the next few decades.
The research team drew upon satellite and historical data from the US National Oceanic and Atmospheric Administration (NOAA), The National Aeronautics and Space Administration (NASA) and the UK Met Office.
Collaborating institutions involved in the research, published in Geophysical Research Letters, included colleagues from the University of Athens as well as the Hellenic Centre for Marine Research. NOAA describes the AMO as "an ongoing series of long-duration changes in the sea surface temperature of the North Atlantic Ocean."
According to NOAA, the changes are "natural and have been occurring for at least the last 1,000 years."
KAUST team's work shows that the long-term oscillation related to AMO has modulated the warming of the Red Sea over the past three decades, and is projected to enter a negative phase in the following years.
"The AMO is a permanent feature of the Earth's climate system and is primarily associated with variations in the Atlantic conveyor belt. The AMO has also been linked to important global climate impacts, such as the variation of mean surface temperatures in the northern hemisphere over several decades," explained Hoteit.