The central Red Sea (CRS) has been characterized by significant eddy activity throughout the year. Weakened wintertime stratification contributes to enhanced vertical exchange. In winter 2014-2015, an extended glider time series in the CRS captured this variability. Surface cooling and stronger winds resulted in deepening of the mixed layer (ML) to nearly 90 m. The vertical distributions of density and oxygen suggest that the ML did not penetrate into the nutricline. However, mixing events dispersed phytoplankton from the deep CHL maximum (DCM) throughout the ML increasing nearsurface chlorophyll. Following the mixing events a mesoscale cyclonic eddy (CE) grew and intensified causing weakening of stratification and a decrease in the ML depth within the eddy. Where the CE interfaced with an adjacent anticyclonic eddy (AE), the CE DCM subducted beneath the shallower AE DCM leading to a local integrated chlorophyll maximum. Low salinity water containing relative high chlorophyll and CDOM concentrations, originating from the Gulf of Aden, appeared in late winter. Mesoscale eddy activity resulted in an 160 m upward displacement of the nutricline to ∼60 m, well within the euphotic layer. Remote sensing imagery indicates that these eddies contribute to horizontal dispersion, including exchange between the open sea and coastal coral reefs. When the phytoplankton is distributed through the ML, clear diel variability was evident in the temporal CHL distribution. Because not all of the biogeochemical responses were apparent at the surface, sustained glider observations were essential to understand the temporal and spatial scales and their impact on these processes.
Bibliographical noteKAUST Repository Item: Exported on 2021-02-16
Acknowledgements: The authors gratefully acknowledge the NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group for remote sensing data and the Copernicus website for the SLA data used in this study. Datasets from ocean color and SLA are freely accessible online on their official websites (https://oceancolor.gsfc.nasa.gov/) and (https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=SEALEVEL_GLO_PHY_L4_REP_OBSERVATIONS_008_047). The glider data that support the study are available at 10.6084/m9.figshare.13670125. The authors are grateful to the KAUST Coastal Marine Resources Core Lab (CMRCL) for their engineering and field support during the glider operations. Particular thanks go to Sebastian Steinke, Brian Hession, Samer Mahmoud and Lloyd Smith for their help with the glider deployments. We thank Ian Walsh and an anonymous reviewer for evaluating the paper and providing insightful suggestions. Funding from King Abdullah University of Science and Technology (KAUST) supported the research in this publication