Marine Heatwaves as a Catalyst for Disruption in Ocean Food Webs and Carbon Sequestration Dynamics
Marine ecosystems are undergoing profound transformations under the influence of climate change, with recent studies highlighting the disruptive role of marine heatwaves on oceanic biogeochemical cycles. A groundbreaking investigation, spearheaded by researchers at the Monterey Bay Aquarium Research Institute (MBARI) and collaborators across international institutions, has revealed that marine heatwaves fundamentally reshape ocean food webs. This reconfiguration significantly impedes the ocean’s biological carbon pump, a critical process responsible for sequestering atmospheric carbon dioxide in the deep sea over millennial timescales.
The study draws on an unprecedented synthesis of biological and chemical oceanographic data collected over more than a decade in the Gulf of Alaska, a region vulnerable to thermal anomalies. This area experienced two notable marine heatwave events, colloquially termed “The Blob” (2013–2015) and a subsequent episode during 2019–2020. These events provided a natural experimental framework to examine how sustained elevated temperatures perturb microscopic biota at the base of the trophic pyramid, and how these perturbations cascade through ecosystem functions related to carbon export.
Central to the ocean’s capacity to modulate global climate is the biological carbon pump, a conveyor mechanism wherein photosynthetic plankton capture dissolved carbon dioxide and convert it into organic matter. This material, upon ingestion by higher trophic levels or through sinking particulate organic carbon (POC), is transported from the sunlit surface waters into the mesopelagic twilight zone (ranging roughly 200 to 1,000 meters depth) and eventually the abyssal depths. The efficiency of this process dictates the proportion of atmospheric carbon dioxide that remains sequestered away from atmospheric reentry.
MBARI researchers employed cutting-edge technologies through the Global Ocean Biogeochemical (GO-BGC) Array, deploying autonomous biogeochemical Argo floats that collect high-frequency vertical profiles of variables including temperature, salinity, oxygen, nitrate, chlorophyll fluorescence, and particulate organic carbon concentration. These arrays offered a detailed temporal and spatial resolution of biogeochemical changes. Complementary data from ship-based plankton surveys and environmental DNA (eDNA) sequencing of water samples perfected the characterization of shifts in plankton community composition and functional dynamics during and after the heatwave phases.
The investigation uncovered that marine heatwaves induce marked alterations in planktonic populations and physiological processes that, in turn, modulate carbon cycling and export fluxes. During the 2013–2015 heatwave, despite heightened photosynthetic carbon fixation in the second year, the expected rapid sedimentation of organic carbon to deeper layers was impeded. Instead, carbon particles accumulated near the 200-meter depth mark, suggesting a bottleneck in vertical carbon transfer potentially linked to modifications in particle size distributions and fecal pellet production by zooplankton.
Contrastingly, the 2019–2020 heatwave displayed a distinct pattern: a significant buildup of particulate carbon occurred at the surface in the initial phase, not attributable solely to phytoplankton productivity. This phenomenon was likely propelled by intensified recycling of organic matter and detrital accumulation from heterotrophic activity. Although this carbon eventually descended into the twilight zone, it stalled at intermediate depths between 200 and 400 meters, further evidencing a disruption in the biological pump’s continuum toward abyssal carbon sequestration.
These divergences in carbon transport dynamics between the two heatwaves stem from shifts in planktonic community structure. Specifically, a proliferation of smaller grazer species during the later heatwave resulted in the production of slower-sinking or suspended organic particles, altering the vertical flux and retention of carbon. Such biological responses underscore the complexity and variability inherent in ecosystem responses to acute thermal stress, challenging conventional modeling approaches predicated on steady-state assumptions.
The implications of these findings are profound. The observed disruptions to the biological carbon pump manifest as a “conveyor belt jam,” whereby carbon is trapped in the upper ocean layers or twilight zone rather than being efficiently exported to the ocean interior. This bottleneck increases the likelihood of remineralization and subsequent release of carbon dioxide back into the atmosphere, potentially accelerating global warming through positive feedback mechanisms.
Moreover, the ecological repercussions extend beyond carbon fluxes. Since plankton form the base of marine food webs, changes in their abundance, diversity, and physiology cascade upward, potentially influencing higher trophic levels including commercially significant fish populations and broader biodiversity. The study advocates for the integration of long-term, multidisciplinary monitoring frameworks—combining autonomous float arrays, molecular tools, and traditional oceanographic surveys—to decode the complex interplay between climate extremes and ocean ecosystem function.
Importantly, the research highlights intrinsic variability among marine heatwaves. Not all heat events induce uniform ecological outcomes, as illustrated by differential planktonic responses and carbon flux patterns. This insight challenges the generalization of marine heatwave impacts and signals the necessity for high-resolution temporal and spatial data to inform predictive models on ecosystem resilience and carbon cycle feedbacks.
The data-driven approach presented exemplifies a paradigm shift in oceanographic science, where convergence of technologies offers unprecedented insight into the dynamic underpinnings of marine ecosystems. Autonomous platforms collecting biogeochemical parameters at fine scales enable near-real-time tracking of anomalous events, while eDNA and pigment analyses unravel community shifts invisible to traditional taxonomy, jointly enabling comprehensive ecological assessment.
As marine heatwaves escalate in frequency and magnitude under anthropogenic climate change, the urgency to understand their multifaceted impacts intensifies. Oceans currently absorb roughly one-quarter of anthropogenic carbon emissions, but the efficacy of this natural buffer hinges on the integrity of biological and physical processes vulnerable to warming. Disruptions to carbon transport mechanisms portend a weakening of this critical climate mitigation service, thereby exacerbating atmospheric CO2 accumulation.
This pioneering study, supported by the US National Science Foundation’s GO-BGC project alongside multiple international funding agencies, serves as a clarion call for sustained investment in ocean observing systems. Such efforts are imperative not only for advancing scientific understanding but also for informing policy and management strategies to safeguard ocean health, fisheries sustainability, and global climate stability amid escalating environmental pressures.
In summary, the insights gleaned from the Gulf of Alaska mark a keystone in marine climatology and biogeochemistry, elucidating the nuanced ways in which thermal extremes restructure ecosystems and modulate carbon fluxes. This knowledge equips the scientific community with critical perspectives to tackle the challenges poised by a rapidly changing oceanic environment.
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Subject of Research: Marine heatwaves’ impact on ocean food webs and carbon transport mechanisms.
Article Title: Marine heatwaves modulate food webs and carbon transport processes
News Publication Date: 6-Oct-2025
Web References: http://dx.doi.org/10.1038/s41467-025-63605-w
Image Credits: © 2022 MBARI
Keywords: Climate change, Plankton, Marine food webs, Ocean warming, Ocean surface temperature, Heat waves, Carbon flux, Carbon cycle
