Publication Date:
2021-12-09
Description:
Mixing processes in the upper equatorial Atlantic at 23°W on the basis of direct microstructure measurements from June 2006, March 2008, and November 2009 have been studied. These measurements indicate large differences in mixing intensities below the mixed layer. In March 2008 vertical shear and mixing levels were comparatively low. At similar stratification in June 2006, enhanced mixing well below the mixed layer was observed. During this time a tropical instability wave passed by which was connected with strong vertical shear in upper 60 m of the water column. Throughout these two cruises, nocturnal mixing rates exceeded daily values, associated with the known deep diurnal cycle. The averaged diapycnal heat flux between 2°S and 2°N across the base of the mixed layer was 55 W/m² in June 2006. The Equatorial Undercurrent changed its position significantly over one week in November 2009. During the southward cruise, weak nocturnal mixing rates below the mixed layer were found. The deep position of the undercurrent core with its high shear zone above may explain this observation. Nocturnal measurements during the northward cruise at the equator reveal much higher vertical shear directly under the base of the mixed layer in connection with significantly increased turbulence. These results suggest that the variability of mixing processes in the investigated area might be determined to a large portion by the strength and position of the vertical shear above the undercurrent core.
Keywords:
Course of study: BSc Physics of the Earth System
Type:
Thesis
,
NonPeerReviewed
Format:
text
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