Wildfires enhance phytoplankton production in tropical oceans

Dongyan Liu,Oscar Serrano,Janine Kinloch,Aleksey Sadekov,Axel Werner,Yan Du,Pere Masque,Yingjun Chen,Chongran Zhou,Yin Fang,John K Keesing

doi:10.1038/s41467-022-29013-0

Abstract

Wildfire magnitude and frequency have greatly escalated on a global scale. Wildfire products rich in biogenic elements can enter the ocean through atmospheric and river inputs, but their contribution to marine phytoplankton production is poorly understood. Here, using geochemical paleo-reconstructions, a century-long relationship between wildfire magnitude and marine phytoplankton production is established in a fire-prone region of Kimberley coast, Australia. A positive correlation is identified between wildfire and phytoplankton production on a decadal scale. The importance of wildfire on marine phytoplankton production is statistically higher than that of tropical cyclones and rainfall, when strong El Niño Southern Oscillation coincides with the positive phase of Indian Ocean Dipole. Interdecadal chlorophyll-a variation along the Kimberley coast validates the spatial connection of this phenomenon. Findings from this study suggest that the role of additional nutrients from wildfires has to be considered when projecting impacts of global warming on marine phytoplankton production.

Highlights

Wildfire magnitude and frequency have greatly escalated on a global scale
There are two common characteristics in the three cores: (1) biogenic silicate (BSi) and black carbon (BC) displayed a strongly positive correlation in the three cores during the phase of positive Indian Ocean Dipole (pIOD) dominance (Table 1). (2) The frequency and magnitude of regime shift index (RSI) increased in the three cores during the phase of pIOD dominance (Fig. 2b–g); a common increase for Total organic carbon (TOC), total nitrogen (TN), BSi, and BC appeared after 2010s when strong El Niño Southern Oscillation (ENSO) conditions coincide with pIOD phase (Fig. 2)
During the phase of negative IOD (nIOD) dominance (1926–1990), no positive correlation was found between TOC, TN, BSi, and BC in Core 185 and KGR, but BC displayed positive correlations with TOC (r = 0.56, p < 0.01) and TN (r = 0.56, p < 0.05) in Core 200 (Table 1)

Summary

Introduction

Wildfire magnitude and frequency have greatly escalated on a global scale. Wildfire products rich in biogenic elements can enter the ocean through atmospheric and river inputs, but their contribution to marine phytoplankton production is poorly understood. Hypothetical conjecture, when strong ENSO occurs during the pIOD phase, escalating wildfires can increase the flux of biogenic elements into the ocean via the pathways of atmospheric deposition and riverine input and lead to higher MPP. To prove their connection in the context of climate modes, it is necessary to examine a decadal relationship between wildfire magnitude and MPP. In high-temperature fossil fuel combustion (e.g. vehicle emissions and industrial coal combustion) the ratio of char/soot ratio is less than one, while for the relatively low-temperature biomass burning (e.g. wildfire), the ratio of char/soot is much higher than one[24]

Methods

Results

Conclusion