Wind-driven upwelling of iron sustains dense blooms and food webs in the eastern Weddell Gyre

The Southern Ocean is a major sink of anthropogenic CO2 and an important foraging area for top trophic level consumers. However, iron limitation sets an upper limit to primary productivity. Here we report on a considerably dense late summer phytoplankton bloom spanning 9000 km(2) in the open ocean of the eastern Weddell Gyre. Over its 2.5 months duration, the bloom accumulated up to 20 g C m(-2) of organic matter, which is unusually high for Southern Ocean open waters. We show that, over 1997-2019, this open ocean bloom was likely driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of Warm Deep Water enriched in hydrothermal iron and, possibly, other iron sources. This recurring open ocean bloom likely facilitates enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hot spots for marine birds and baleen whales. This study reports a dense, late summer phytoplankton bloom in the Southern Ocean that accumulated unusually high levels of organic matter and supported feeding hot spots for birds and whales. The authors show that this recurring open ocean bloom is driven by anomalies in easterly winds that push sea ice southwards and favour the upwelling of deep waters enriched in hydrothermal iron.

Automated summary

This study reports on a dense late summer phytoplankton bloom in the Southern Ocean that accumulated unusually high amounts of organic matter and supported feeding hot spots for birds and whales. The authors show that this recurring open ocean bloom is driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of deep waters enriched in hydrothermal iron.