# Spatiotemporal patterns and implications of suspended Alexandrium catenella cysts in the Pacific Arctic region

## TL;DR

This study explores how warming and wind patterns in the Pacific Arctic may increase harmful algal blooms by suspending and transporting toxic cysts of Alexandrium catenella.

## Contribution

The study introduces a novel approach combining field observations and simulations to assess how wind-driven mixing and warming could enhance cyst germination and bloom initiation.

## Key findings

- Suspended cysts of Alexandrium catenella were found in near-bottom waters overlying benthic accumulations.
- Cyst suspension and export pulses were observed seasonally, with wind-driven resuspension peaking in the fall.
- Simulations suggest stormy conditions enhance cyst access to surface waters, potentially increasing future bloom risks.

## Abstract

The persistent presence of a massive accumulation of resting cysts of the toxic dinoflagellate Alexandrium catenella on the Chukchi shelf represents a significant risk to Pacific Arctic ecosystems, as warming conditions are likely to promote harmful algal blooms of this species. While the majority of cysts are found in the benthos, cysts can also be suspended through the water column, allowing them to be transported by currents or to experience elevated temperature and light conditions that may accelerate germination. Spatial patterns of cyst suspension were investigated during a Fall 2020 survey, revealing broad presence of suspended cysts in near-bottom waters overlying benthic cyst accumulations. Enhanced suspension was observed at shallow, well-mixed stations – in some places extending beyond the bottom boundary layer into surface waters. Sinking particles collected continuously from 2017 to 2019 showed seasonal patterns of cyst flux, with export pulses during the late summer and wind-driven resuspension peaking during the fall. To evaluate the potential contribution of resuspension to bloom initiation, a hydrographic climatology of the southern Chukchi Sea was used to estimate cyst germination rates through the water column during the summer (June–September). This analysis was paired with wind-driven 1-D mixing simulations, demonstrating that cyst access to surface waters is enhanced under stormy conditions. While storm events are not currently common during the summer bloom season, a trend towards increasingly windy conditions points towards future potential for resuspended cysts to contribute to blooms in the shallow and warming waters of the Pacific Arctic region.