Interannual variability of chemical parameters at the western end of a South Atlantic Ocean section (34.5°S)

Ana Beatriz Leite Cavalcante1, Vitor Gonsalez Chiozzini2, Henrique José Rodrigues Dias2, Edmo Jose Dias Campos2 and Elisabete de Santis Braga3, (1)University of Sao Paulo, Oceanographic Institute, Sao Paulo, United States, (2)University of Sao Paulo, Oceanographic Institute, Sao Paulo, Brazil, (3)University of Sao Paulo, Oceanographic Institute, São Paulo, Brazil
Abstract:
The Atlantic Meridional Overturning Circulation (AMOC) is responsible for major of the heat transport between hemispheres, with a strong role on climate regulation. Considering the climate changes and its reflex on the circulation, the chemical properties of the water masses constitute important complements to monitor the AMOC. In the context of the SAMBAR project, water samples were collected during Fall 2018 and Winter 2019 along the western end of the parallel 34.5°S aiming the use of chemical properties (dissolved oxygen and nutrients) to indicate possible changes in AMOC circulation model. Until now, the greatest interannual differences were observed on the continental shelf stations due to La Plata river influence, promoting high nutrient values (silicate ~ 23.54 µmol L-1; phosphate ~ 1.08 µmol L-1; nitrate ~ 2.68 µmol L-1) and lower salinities (min. 27.709) in 2019, in relation to 2018 (min. salinity: 32.358; silicate ~ 6.13 µmol L-1; phosphate ~ 0.64 µmol L-1; nitrate ~ 0.09 µmol L-1). In both campaigns, Tropical Water presented low nutrient concentrations (nitrate ~ 0.03 µmol L-1 in 2018 and ~ 0.12 µmol L-1 in 2019). Below the euphotic zone, the dissolved oxygen and nutrient vertical distribution presented similar profile in both years. In 2019, the South Atlantic Central Water (~ 299 m) was marked by a nitrate increase (2.38-20.01 µmol L-1) as well as in 2018 (2.23 - 22.35 µmol L-1). Antarctic Intermediate Water presented high dissolved oxygen values in both years (> 6.7 mg L-1) and the North Atlantic Deep Water showed a decrease in nutrient concentrations in relation to water masses immediately above and below (phosphate ranged 1.25 - 1.90 µmol L-1 in 2018 and 1.42 - 1.96 µmol L-1 in 2019). Antarctic Bottom Water presented a silicate maximum evidenced in both years (> 140 µmol L-1). Long term studies are required to observe significant modifications in water mass properties assisted by chemical parameters.
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