Wildfire aerosol deposition likely amplified a summertime Arctic phytoplankton bloom

Abstract

Summertime wildfire activity is increasing in boreal forest and tundra ecosystems in the Northern Hemisphere. However, the impact of long range transport and deposition of wildfire aerosols on biogeochemical cycles in the Arctic Ocean is unknown. Here, we use satellite-based ocean color data, atmospheric modeling and back trajectory analysis to investigate the transport and fate of aerosols emitted from Siberian wildfires in summer 2014 and their potential impact on phytoplankton dynamics in the Arctic Ocean. We detect large phytoplankton blooms near the North Pole (up to 82°N in the eastern Eurasian Basin). Our analysis indicates that these blooms were induced by the northward plume transport and deposition of nutrient-bearing wildfire aerosols. We estimate that these highly stratified surface waters received large amounts of wildfire-derived nitrogen, which alleviated nutrient stress in the phytoplankton community and triggered an unusually large bloom event. Our findings suggest that changes in wildfire activity may strongly influence summertime productivity in the Arctic Ocean.

What data are needed to detect wildfire effects on coastal ecosystems? A case study during the Thomas Fire

“…In this study, in situ measurements of 𝑅 𝑟𝑠 (𝜆), IOPs, and chlorophyll-a allowed for a system-wide consideration of the impacts of wildfire smoke and ash on ocean ecology and optics. In many recent studies examining wildfire impacts on the ocean, particularly in more remote or open ocean environments, in situ samples are not available (Ardyna et al, 2022;Wang et al, 2022;Weis et al, 2022). Inversion modeling and derived products are essential in these cases: all three studies used chlorophyll-a from remote sensing to consider the possibility of a phytoplankton bloom occurring in the wake of a wildfire smoke plume.…”

“…In the coastal ocean, increased CDOM from ash leaching may impact both remotely sensed AOPs (as seen in the shape and magnitude of the MODIS-Aqua 𝑅 𝑟𝑠 (𝜆) spectra) and in situ IOPs and AOPs (as seen in the GIOP retrievals from C-OPS reflectances; Figure 5B-C). In situ measurements will also allow for an evaluation of the impact of these other optically significant materials on the estimation of chlorophyll-a from remote sensing, particularly if further conclusions about ecosystem impacts will be drawn from an enhanced chlorophyll signal (e.g., Ardyna et al, 2022;Wang et al, 2022;Weis et al, 2022).…”

“…Increasingly, satellite remote sensing provides a (near) real-time tool to monitor the impacts of these sporadic wildfire events on the open ocean, as has been done with volcanic impacts on the ocean (Westberry et al, 2019;Bisson et al, in review). Both ocean color remote sensing and autonomous profiling floats (e.g., Argo) have been used as tools to identify phytoplankton blooms following a wildfire, particularly in inaccessible, open ocean and/or highlatitude regions (Ardyna et al, 2022;Wang et al, 2022;Weis et al, 2022). All three of these studies examined the changes in chlorophyll-a concentration and phytoplankton carbon from optical proxies and determined that wildfire smoke and ash is potentially fertilizing the Southern and Arctic Oceans, similarly to the effects observed after volcanic eruptions.…”

“…There are no studies comparing in situ optical observations to satellite or in situ ocean color measurements during or immediately after wildfires, when smoke and ash inevitably influence the atmospheric correction via absorbing aerosols and also may impact the typical balance of colored dissolved organic matter (CDOM) and particulate ash (included as non-algal particles, or NAP) in the water. Furthermore, existing studies (e.g., Ardyna et al, 2022;Wang et al, 2022;Weis et al, 2022) use business-as-usual satellite products and assume those aerosol models and atmospheric corrections are appropriate, which may not be true during a wildfire.…”

Wildfires in the western United States are mobilizing PM2.5-associated nutrients and may be contributing to downwind cyanobacteria blooms

“…11,12 PM mobilizes chemical species with potential impacts on downwind ecosystems. 13–15 Altogether, fires can lead to negative impacts on air quality and wildlife. 16…”