Zooplankton-based d13C and d15N isoscapes from the outer continental shelf and slope in the subtropical western South Atlantic
Troina, G.C.; Dehairs, F.; Botta, S.; Di Tullio, J.C.; Elskens, M.; Secchi, E.R. (2020). Zooplankton-based d13C and d15N isoscapes from the outer continental shelf and slope in the subtropical western South Atlantic. Deep-Sea Res., Part 1, Oceanogr. Res. Pap. 159: 103235. https://hdl.handle.net/10.1016/j.dsr.2020.103235
In: Deep-Sea Research, Part I. Oceanographic Research Papers. Elsevier: Oxford. ISSN 0967-0637; e-ISSN 1879-0119
Characterizing the patterns of stable carbon (d13C) and nitrogen (d15N) isotopes at the base of the food webs (baseline) is essential in ecological studies for assessing the feeding habits and migration patterns of marine predators. We analysed d13C and d15N in zooplankton samples collected in spring and autumn (2012–2015), along the south (SCM) and southeast (NCSM) Brazilian oceanic waters. An increase in d13C from the shelf break towards the offshore was associated with the influence of continental water input and upwellings along the shelf break, which introduce 13C-depleted inorganic carbon to the surface, where it will be incorporated into the biological system through phytoplankton growth. An opposite trend was observed in d15N, with higher values along the shelf break related to the intrusion of upwelled deep-water nutrients, contrasting with the oligotrophic offshore waters where N2 fixation takes place, resulting in primary and secondary production that is relatively more depleted in 15N. A latitudinal (north-south) decrease in d13C along the offshore area coincided with known isotopic patterns in inorganic carbon, which were more 13C-depleted towards higher latitudes. On the other hand, an increase in d15N was observed towards the south, reflecting the contrast between the N2 fixation in the more oligotrophic waters in the NCSM and the higher nutrient availability in the SCM. Additionally, d13C was significantly higher in autumn and d15N was higher in spring. Although inter-annual differences in d15N were non-significant, d13C was significantly lower in 2012 than in the later years. This study provides novel information regarding the patterns of baseline d13C and d15N in the southwestern Atlantic Ocean, which will be useful for future investigation of the ecology of higher trophic-level organisms occurring in this area.
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