Inter-annual and Seasonal Hydrographic Characteristics in Northern Red Sea

The purpose of this study is to understand the inter-annual and seasonal buoyancy fluxes and its associated processes in the northern Red Sea with latitudinal variability. Four cruises were conducted in March 2010, September 2011, August 2014 and April 2015. CTD, bio-optical and nutrient data were collected from over 80 stations; some sites are duplicated to provide both seasonal and interannual comparisons. Modeling results and observations indicate that deep water formation in the Red Sea comes from three sources: Gulf of Aqaba, Gulf of Suez and open basin convection. This study will focus on the open basin convection process. Northern Red Sea convection is driven by the strong evaporation throughout the year and wintertime cooling. The intensity will vary dependent on the upper layer salinity and the extent of wintertime cooling. Results from different cruises show that high chlorophyll concentrations result when low oxygen water rises from below, indicative of available nutrients. Weak stratification during late winter and winter convection to more than 150 m depth appear to contribute to the available nutrients in the upper layer. Weak stratification during late winter/early spring enables vertical transport from a cyclonic eddy to bring nutrients closer to the surface. During spring the difference between the surface temperature and bottom temperature is only 0.8 (°C), an indication that little cooling is required to destabilize the water column. During late summer shoaling of isopycnals toward offshore is consistent with a cyclonic gyre indicated by satellite images of SSH. However, the water column is highly stratified due to upper ocean heating, contributing to the evaporation in this region.