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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. Wildfires are expected to increase in frequency and severity. Here the authors use geochemical paleo-reconstructions to show that over decadal timescales in Earth history wildfires are positively correlated with phytoplankton production off the coast of Australia. [ABSTRACT FROM AUTHOR]

Seagrass ecosystems rank amongst the most efficient natural carbon sinks on earth, sequestering CO2 through photosynthesis and storing organic carbon (Corg) underneath their soils for millennia and thereby, mitigating climate change. However, estimates of Corg stocks and accumulation rates in seagrass meadows (blue carbon) are restricted to few regions, and further information on spatial variability is required to derive robust global estimates. Here we studied soil Corg stocks and accumulation rates in seagrass meadows across the Colombian Caribbean. We estimated that Thalassia testudinum meadows store 241 ± 118 Mg Corg ha−1 (mean ± SD) in the top 1 m-thick soils, accumulated at rates of 122 ± 62 and 15 ± 7 g Corg m−2 year−1 over the last ~ 70 years and up to 2000 years, respectively. The tropical climate of the Caribbean Sea and associated sediment run-off, together with the relatively high primary production of T. testudinum, influencing biotic and abiotic drivers of Corg storage linked to seagrass and soil respiration rates, explains their relatively high Corg stocks and accumulation rates when compared to other meadows globally. Differences in soil Corg storage among Colombian Caribbean regions are largely linked to differences in the relative contribution of Corg sources to the soil Corg pool (seagrass, algae Halimeda tuna, mangrove and seston) and the content of soil particles < 0.016 mm binding Corg and enhancing its preservation. Despite the moderate areal extent of T. testudinum in the Colombian Caribbean (661 km2), it sequesters around 0.3 Tg CO2 year−1, which is equivalent to ~ 0.4% of CO2 emissions from fossil fuels in Colombia. This study adds data from a new region to a growing dataset on seagrass blue carbon and further explores differences in meadow Corg storage based on biotic and abiotic environmental factors, while providing the basis for the implementation of seagrass blue carbon strategies in Colombia. [ABSTRACT FROM AUTHOR]

Tidal marshes rank among the ecosystems with the highest capacity to sequester and store organic carbon (Corg) on earth. To inform conservation of coastal vegetated ecosystems for climate change mitigation, this study investigated the factors driving variability in carbon storage. We estimated soil Corg stocks in tidal marshes across temperate Western Australia and assessed differences among geomorphic settings (marine and fluvial deltas, and mid-estuary) and vegetation type (Sarcocornia quinqueflora and Juncus kraussii) linked to soil biogeochemistry. Soil Corg stocks within fluvial and mid-estuary settings were significantly higher (209 ± 14 and 211 ± 20 Mg Corg ha−1, respectively; 1-m-thick soils) than in marine counterparts (156 ± 12 Mg Corg ha−1), which can be partially explained by higher preservation of soil Corg in fluvial and mid-estuary settings rich in fine-grained (< 0.063 mm) sediments (49 ± 3% and 47 ± 4%, respectively) compared to marine settings (23 ± 4%). Soil Corg stocks were not significantly different between S. quinqueflora and J. kraussii marshes (185 ± 13 and 202 ± 13 Mg Corg ha−1, respectively). The higher contribution of tidal marsh plus supratidal vegetation in fluvial (80%) and intermediate (76%) compared to marine (57%) settings further explains differences in soil Corg stocks. The estimated soil Corg stocks in temperate Western Australia's tidal marshes (57 Tg Corg within ~ 3000 km2 extent) correspond to about 2% of worldwide tidal marsh soil Corg stocks. The results obtained identify global drivers of soil Corg storage in tidal marshes and can be used to target hot spots for climate change mitigation based on tidal marsh conservation. [ABSTRACT FROM AUTHOR]

Seagrass meadows form valuable ecosystems, but are considered to have low cultural value due to limited research efforts in this field. We provide evidence that seagrass deposits play a hitherto unrealized central role in preserving valuable submerged archaeological and historical heritage across the world, while also providing an historical archive of human cultural development over time. We highlight three case studies showing the significance of seagrass in protecting underwater cultural heritage in Denmark, the Mediterranean and Australia. Moreover, we present an overview of additional evidence compiled from the literature. We emphasize that this important role of seagrasses is linked to their capacity to form thick sedimentary deposits, accumulating over time, thereby covering and sealing submerged archaeological heritage. Seagrass conservation and restoration are key to protecting this buried heritage while also supporting the role of seagrass deposits as carbon sinks as well as the many other important ecosystem functions of seagrasses. [ABSTRACT FROM AUTHOR]

Policies aiming to preserve vegetated coastal ecosystems (VCE; tidal marshes, mangroves and seagrasses) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here, we present organic carbon (C) storage in VCE across Australian climate regions and estimate potential annual CO2 emission benefits of VCE conservation and restoration. Australia contributes 5–11% of the C stored in VCE globally (70–185 Tg C in aboveground biomass, and 1,055–1,540 Tg C in the upper 1 m of soils). Potential CO2 emissions from current VCE losses are estimated at 2.1–3.1 Tg CO2-e yr-1, increasing annual CO2 emissions from land use change in Australia by 12–21%. This assessment, the most comprehensive for any nation to-date, demonstrates the potential of conservation and restoration of VCE to underpin national policy development for reducing greenhouse gas emissions. Policies aiming to preserve vegetated coastal ecosystems (VCE) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here the authors assessed organic carbon storage in VCE across Australian and the potential annual CO2 emission benefits of VCE conservation and find that Australia contributes substantially the carbon stored in VCE globally. [ABSTRACT FROM AUTHOR]