Patterns of distribution of inorganic nutrients in Red Sea and their implications to primary production

• Patterns of distribution of nutrients along the axis of Red Sea were of alternating highs and lows.
• These patterns are explainable in terms of zonal currents in three anticyclonic eddy circulations.
• Injection of nutrients by eddies could cause higher production over a substantial spread of Red Sea.
• Anticyclonic eddies in Red Sea may function as traps of nutrients.
• Peripheries and centers of the anticyclonic eddies may even function as independent mesocosms.

This paper presents data on inorganic nutrients obtained in several transects within Saudi Arabian waters of the Red Sea in 2012–2015. Increase in their concentrations from north to south is not monotonously linear but is punctuated by regions of high concentrations alternating with those of low concentrations, regardless of the type of nutrient (N, P or Si), season and location. Such a type of distribution could be only explained in terms of eddy circulations within the Red Sea basin. The enrichment with nutrients of the boundary currents of the eddies could be explained partly by entrainment of Gulf of Aden Intermediate Water in the eddies and the mixing of the latter with the underlying Red Sea Deep Water, and partly by a higher biological productivity in the peripheries of the eddies. These results have two major implications for our understanding of biogeochemical cycles in the Red Sea. The first is that the eddy-associated injection of nutrients into the euphotic zone could cause higher levels of production over a substantial spread of the Red Sea. The second is that the anticyclonic eddies may function as traps of nutrients and in that event, their peripheries and centers may function as independent mesocosms.