Small-scale vertical and horizontal variability of physico-biogeochemical properties across the Equatorial Undercurrent in the Atlantic Ocean


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Volker.Strass [ at ] awi.de

Abstract

In May 2018 we towed a new vertical undulator across the equator from 2°S to 2°N along 25°W in the central Atlantic Ocean. Towing the vehicle along a sawtooth path between 5 and 300 m depth a horizontal resolution (wavelength) of 2.5 km was achieved. The vehicle was instrumented in order to bring together marine physics, chemistry and biology. The oceanographic measurements comprised the variables of state (temperature, salinity, pressure, density), and currents as well as solar irradiance. The chemical data collected were dissolved oxygen, nitrate, pH and (indirectly) particulate organic carbon. Biological information on phytoplankton concentration and composition was obtained from fluorometry and hyperspectral radiometry. The major hydrographic feature crossed was the Equatorial Undercurrent (EUC) between roughly 1.8°S and 1.5°N in the depth range 50 to 250 m flowing mainly ENE with maximum velocities of 1 m/s, whereas the slow flow of the nitrate-deplete surface layer was westward. The chlorophyll (phytoplankton) was found concentrated subsurface in the depth range 60 to 90 m on top of the nitracline and within the vertical shear zone of the upper EUC. Horizontally the deep Chl maximum displayed patchiness at scales down to the resolution achieved, hypothetically stimulated by the variable shear-driven vertical supply of nitrate. Below the euphotic zone and both at the southern and northern flank of the EUC patches of increased oxygen concentration were found, which correlate with decreased nitrate concentration and elevated pH.



Item Type
Conference (Talk)
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Primary Division
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Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
ASLO 2019 Aquatic Sciences Meeting, 23 Feb 2019 - 02 Mar 2019, San Juan, Puerto Rico.
Eprint ID
49233
Cite as
Strass, V. , von Appen, W. J. , Bracher, A. , Xi, H. , Spahic, S. , Mathieu, L. , Haake, H. , Waite, A. and Leach, H. (2019): Small-scale vertical and horizontal variability of physico-biogeochemical properties across the Equatorial Undercurrent in the Atlantic Ocean , ASLO 2019 Aquatic Sciences Meeting, San Juan, Puerto Rico, 23 February 2019 - 2 March 2019 .


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