| Abstrakt: |
The Southwestern Atlantic Ocean (SWA), is considered one of the most productive areas of the world, with a high abundance of ecologically and economically important fish species. Yet, the biological responses of this complex region to climate variability are still uncertain. Here, using 24 years of satellite‐derived Chl‐a data, we classified the SWA into 9 spatially coherent regions based on the temporal variability of Chl‐a concentration, as revealed by SOM (Self‐Organizing Maps) analysis. These biogeographical regions were the basis of a regional trend analysis in phytoplankton biomass, phenological indices, and environmental forcing variations. A general positive trend in phytoplankton concentration was observed, especially in the highly productive areas of the northern shelf‐break, where phytoplankton biomass has increased at a rate of up to 0.42 ± 0.04 mg m−3 per decade. Significant positive trends in sea surface temperature were observed in 4 of the 9 regions (0.08–0.26 °C decade−1) and shoaling of the mixing layer depth in 5 of the 9 regions (−1.50 to −3.36 m decade−1). In addition to the generally positive trend in Chl‐a, the most conspicuous change in the phytoplankton temporal patterns in the SWA is a delay in the autumn bloom (between 15 ± 3 and 24 ± 6 days decade−1, depending on the region). The observed variations in phytoplankton phenology could be attributed to climate‐induced ocean warming and extended stratification period. Our results provided further evidence of the impact of climate change on these highly productive waters. Plain Language Summary: The Southwestern Atlantic Ocean (SWA), is one of the most biologically productive areas of the world, with a high abundance of fish species. This important area might be affected by the environmental consequences of climate change. In this study, we addressed the influence of the already observed changes in environmental conditions on phytoplankton, which are the base of the marine food web, over the last 24 years. There has been an increase in phytoplankton biomass as well as the timing and intensity of the autumn bloom in some specific areas of the SWA. We have found that these changes in phenology might be related to the increase in sea surface temperature and the shoaling of the mixed layer depth. Consistent with previous studies, our results provided further evidence of the impact of climate change on these highly productive waters. Key Points: Chlorophyll‐a concentration has increased over the last 24 years in most of the Southwestern AtlanticPhytoplankton phenological changes have been observed, mainly during the austral autumn bloomPhytoplankton biomass and phenology might be affected by the increasing sea surface temperature and mixing layer depth shoaling [ABSTRACT FROM AUTHOR] |
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