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Variability and trends of drifter pathways near the Antarctic Peninsula and potential ecological impacts

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Near-surface currents near Antarctic Peninsula (AP) are strongly affected by complex frontal features and atmospheric forcings. They transport material from the tip of the peninsula along the western shelf and into the Scotia Sea and are therefore important for the ecosystem of the region. The trajectories of modelled drifters, deployed in the northwestern Weddell Sea over 43 model years, show distinct pathways tied to topography and fronts of the Antarctic Circumpolar Current. From the shelf of the eastern AP, drifters tend to enter Bransfield Strait and are advected towards the Bellingshausen Sea. From the deeper Weddell Sea, drifters are more likely to cross the South Scotia Ridge into the Scotia Sea and reach South Georgia. Over the 43-year timeseries of modelled drifters, there is a significant decrease of drifters going west into the Bellingshausen Sea and travel times to South Georgia become shorter. The changes are partly due to changes in the atmospheric circulation. High (low) transports and short (long) travel times to South Georgia, and low (high) transports to the west can be linked to strong (weak) westerlies, signature of the positive (negative) phase of the Southern Annular Mode. The key region determining the fate of the drifters is east and southeast of Elephant Island. There, a southward shift of ocean fronts during years of strong westerlies restricts the connection from the Weddell Sea to the western AP, and drifters follow the open paths to South Georgia and the east. The eastern AP shelf is a potential source region for Antarctic krill communities around South Georgia. Drifter simulations and observations suggest connections between communities on both sides of the AP. Changes in transports and travel times of material, forced by atmospheric circulation changes, are likely to influence the ecosystem structure in the Scotia and Bellingshausen Seas.

This talk is part of the British Antarctic Survey series.

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