Current structures and topographic Rossby waves in the Levantine basin south of Crete revealed by snapshot and time series current measurements.

Abstract

The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time in April 2016 with a combination of direct current measurements comprised by CTD-LADCP (Lowered Acoustic Doppler Current Profiler) grid casts and ship-track ADCP measurements in the upper 500 m, while a mooring was launched at the end of the continental slope and provided yearly current records at 700 m and 30 m off the bottom depth of 4300 m. Horizontal flow structures are mapped in the upper 1000 m via objective analysis of the direct current measurements depicting the Cretan Cyclone at the west, the Rhodes Gyre at the east and anticyclonic circulation in the middle due to Modified Atlantic Water in the upper 80 m and a thick, saline, warm mass extending from ~100 m to ~1500 m, possibly of Cretan origin. The bottom kinetic energy spectra have higher density values than those at 700 m. In the two-month energetic period of end/Jan.-to-end/Mar. 2017, topographic Rossby waves (TRW) with wavelength of ~42 km exist in the window of ~34-19 days with significant coherence between the near-bottom and the 700-m records. At the TRW spectral window, the motions are transverse and the direction of maximum velocity variance veers from nearly along isobaths ~20° (north-northeast) to ~45° (northeast) with decreasing period. The presence of TRWs in the specific time period within 2017 appears to be related to the lateral shifts of the Ierapetra Anticyclone over the sloping bottom of the continental margin.