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In the context of global climate change, ocean iron fertilization (OIF) has been suggested as a potential geoengineering strategy to enhance the growth of marine phytoplankton, subsequently promote the ocean carbon sink, and ultimately regulate atmospheric carbon dioxide (CO2) and mitigate climate change. However, in past artificial OIF experiments, the elevation of both net primary production and carbon export to the deep ocean is far less than anticipated. This discrepancy can be attributed to several key factors that strongly influence the efficiency of OIF and biological carbon pump (BCP) including iron bioavailability and retention time, the sensitivity of phytoplankton to iron limitation, the influence of viruses and other microorganisms comprising the microbial carbon pump (MCP), and non-biological carbon cycles. Although previous reviews have extensively summarized the outcomes of the past OIF experiments, the mechanisms and key factors that influence climate regulation mediated by OIF have not been elucidated. In this review, we analyze these mechanisms throughout the whole process from OIF, to phytoplankton physiological responses, to carbon dioxide removal (CDR) and sequestration in the ocean, and ultimately to CDR in the atmosphere and its impact on climate change. By examining both natural and artificial OIF cases, as well as recent advancements in phytoplankton physiological ecology and carbon pump theory, possible reasons leading to the inconsistencies between OIF and carbon export are explored. These comprehensive analyses are helpful to identify the key issues in regulating climate change by providing a reference and scientific approach to guide potential OIF attempts in the future. © 2023

An unprecedented devastating forest fire occurred in Australia from September 2019 to March 2020. Satellite observations revealed that this rare fire event in Australia destroyed a record amount of more than 202,387 km2 of forest, including 56,471 km2 in eastern Australia, which is mostly composed of evergreen forest. The released aerosols contained essential nutrients for the growth of marine phytoplankton and were transported by westerly winds over the Southern Ocean, with rainfall-induced deposition to the ocean beneath. Here, we show that a prominent oceanic bloom, indicated by the rapid growth of phytoplankton, took place in the Southern Ocean along the trajectory of fire-born aerosols in response to atmospheric deposition. Calculations of carbon released during the fire versus carbon absorbed by the oceanic phytoplankton bloom suggest that they were nearly equal. This finding illustrates the critical role of the oceans in mitigating natural and anthropogenic carbon dioxide releases to the atmosphere, which are a primary driver of climate change. © 2021 The Authors

Dataset: Coastal Maine CTD Data, This dataset includes vessel CTD profiles from the outer reaches of the Damariscotta River Estuary in the mid-coast region of Maine collected from June 2017 to July 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/809309, NSF Division of Ocean Sciences (NSF OCE) OCE-1435021

Typhoons are assumed to stimulate ocean primary production through the upward mixing of nutrients into the surface ocean, based largely on observations of increased surface chlorophyll concentrations following the passage of typhoons. This surface chlorophyll enhancement, seen on occasion by satellites, more often is undetected due to intense cloud coverage. Daily data from a BGC-Argo profiling float revealed the upper-ocean response to Typhoon Trami in the Northwest Pacific Ocean. Temperature and chlorophyll changed rapidly, with a significant drop in sea surface temperature and surge in surface chlorophyll associated with strong vertical mixing, which was only partially captured by satellite observations. However, no net increase in vertically integrated chlorophyll was observed during Typhoon Trami or in its wake. Contrary to the prevailing dogma, the results show that typhoons likely have limited effect on net ocean primary production. Observed surface chlorophyll enhancements during and immediately following typhoons in tropical and subtropical waters are more likely associated with surface entrainment of deep chlorophyll maxima. Moreover, the findings demonstrate that remote sensing data alone can overestimate the impact of storms on primary production in all oceans. Full understanding of the impact of storms on upper ocean productivity can only be achieved with ocean observing robots dedicated to high-resolution temporal sampling in the path of storms.

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chen, S., Wells, M. L., Huang, R. X., Xue, H., Xi, J., & Chai, F. Episodic subduction patches in the western North Pacific identified from BGC-Argo float data. Biogeosciences, 18(19), (2021): 5539–5554, https://doi.org/10.5194/bg-18-5539-2021., Subduction associated with mesoscale eddies is an important but difficult-to-observe process that can efficiently export carbon and oxygen to the mesopelagic zone (100–1000 dbar). Using a novel BGC-Argo dataset covering the western North Pacific (20–50∘ N, 120–180∘ E), we identified imprints of episodic subduction using anomalies in dissolved oxygen and spicity, a water mass marker. These subduction patches were present in 4.0 % (288) of the total profiles (7120) between 2008 and 2019, situated mainly in the Kuroshio Extension region between March and August (70.6 %). Roughly 31 % and 42 % of the subduction patches were identified below the annual permanent pycnocline depth (300 m vs. 450 m) in the subpolar and subtropical regions, respectively. Around half (52 %) of these episodic events injected oxygen-enriched waters below the maximum annual permanent thermocline depth (450 dbar), with >20 % occurring deeper than 600 dbar. Subduction patches were detected during winter and spring when mixed layers are deep. The oxygen inventory within these subductions is estimated to be on the order of 64 to 152 g O2/m2. These mesoscale events would markedly increase oxygen ventilation as well as carbon removal in the region, both processes helping to support the nutritional and metabolic demands of mesopelagic organisms. Climate-driven patterns of increasing eddy kinetic energies in this region imply that the magnitude of these processes will grow in the future, meaning that these unexpectedly effective small-scale subduction processes need to be better constrained in global climate and biogeochemical models., This work was supported by the National Natural Science Foundation of China (NSFC) projects (grant nos. 41906159, 42030708, and 41730536), the Scientific Research Fund of the Second Institute of Oceanography MNR (grant no. 14283), and the Marine S&T Fund of Shandong Province for the Pilot National Laboratory for Marine Science and Technology (Qingdao) (grant no. 2018SDKJ0206).

With the nexus of climate change, globalization, and dwindling marine fishes, more attention is being paid to the increasing global burden of ciguatera fish poisoning (CFP) and the development of appropriate strategies for intervention, especially in endemic areas such as the South Pacific Islands and the Caribbean Sea. CFP is a non-bacterial food poisoning event with outbreaks around the world in which fish concentrate a potent neurotoxin (ciguatoxin) in their organs and tissues from inadvertent feeding on toxic benthic algal species. Outbreaks are frequent in endemic areas in the tropics and semi-tropics with developed corals and benthic fish fisheries. Occurrences are also present in non-endemic areas where contaminated fish are exported for consumption. Local populations on tropical or semi-tropical islands are particularly vulnerable to this poisoning through the consumption of ciguatoxin-contaminated fish. Here, we consider the pecuniary costs of population exposure to CFP using two published studies as a template for developing a case study of the eco-socio-economic cost model in island nations