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Journal Article

Red Sea gravity currents cascade near-reef phytoplankton to the twilight zone

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Niemann,  H.
HGF MPG Joint Research Group for Deep Sea Ecology & Technology, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Jonkers,  H. M.
Permanent Research Group Microsensor, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Citation

Niemann, H., Richter, C., Jonkers, H. M., & Badran, M. I. (2004). Red Sea gravity currents cascade near-reef phytoplankton to the twilight zone. Marine Ecology-Progress Series, 269, 91-99.


Cite as: https://hdl.handle.net/21.11116/0000-0001-D191-E
Abstract
Cross-reef variations of sea water density, currents and phytoplankton pigments were investigated in the northern Gulf of Aqaba, Red Sea. Differential cooling of near- and offshore surface water during cold winter nights results in cross-shore gradients of density (sigma-t) triggering gravity currents which cascade downslope along sandy valleys. Two 4-wk deployments of 3-D acoustic current meters showed that cross-shore currents near the sea bed (35 and 90 m) were 2- to 5-fold higher than long-shore currents, inversely related to surface flow and highly correlated with seasonally detrended diel variations in seawater temperature. Cross-shore flow varied during the course of the night, with offshore pulses of up to 15 cm s(-1) associated with sudden temperature drops of similar to0.15degreesC. Spatial distribution of chl a pigments shows that phytoplankton enriched nearshore waters are entrained in the gravity currents to depths < 300 m. Gravity currents may therefore provide an important and previously overlooked pathway of reef-borne material to the food-impoverished deeper strata of the Red Sea.