Just as terrestrial atmospheres can be obscured by atmospheric pollutants and dense cloud cover, marine environments are likewise susceptible to periods of profound obscurity.
These extended durations of diminished light penetration are not mere transient shadows; they possess the capacity to engulf entire oceanic sectors for months on end, inflicting considerable ecological detriment upon the benthic realms.
In a notable scientific advancement, researchers have established a conceptual structure for comprehending a phenomenon they have termed ‘marine darkwaves’ – transient, yet potentially calamitous occurrences that can exert severe pressure on photic-dependent marine organisms.
“Light serves as a fundamental impetus for marine biological activity, influencing trophic dynamics all the way to the apex predators. However, until this juncture, a standardized methodology for quantifying significant reductions in subaquatic illumination was absent, and this phenomenon lacked even a definitive nomenclature,” stated marine biologist François Thoral, affiliated with Waikato and Canterbury Universities in New Zealand.
“The introduction of the ‘marine darkwave’ concept facilitates the precise identification of the temporal and spatial dimensions of these events, thereby illuminating a critical yet frequently disregarded ecological process.”
For a considerable period, marine scientists have been monitoring a trend known as oceanic dimming – a sustained, incremental decline in water transparency that impedes the penetration of solar radiation into the water column. This phenomenon has been linked to diminishing kelp forests, delayed initiation of phytoplankton blooms, stressed coral reef structures, and contracting seagrass beds.
However, this represents a gradual, progressive alteration that has been unfolding over many decades. It does not encompass the acute, episodic periods of profound darkness precipitated by meteorological events, algal proliferations, and sediment resuspension, frequently occurring in the aftermath of natural disturbances such as wildfires, cyclonic systems, and landslides.
These intensified phases of light reduction – the marine darkwaves – can be as detrimental as the more protracted, slow-acting dimming process, according to the research findings published by the investigators.
The recently developed framework provides researchers with an analytical tool for identifying these shorter-term events by adapting methodologies employed for the detection of other episodic oceanic phenomena, such as marine heatwaves and cold snaps. This adaptation allowed for the establishment of defining parameters for a marine darkwave, including minimum temporal duration, the magnitude of light attenuation relative to a seasonal norm, and the specific depth at which this reduction occurs.
Subsequently, the research team applied this derived framework to a dataset comprising 16 years of subaquatic illumination measurements previously acquired from the Californian coastline, and 10 years of data from coastal monitoring sites within New Zealand’s Hauraki Gulf (Tikapa Moana). These measurements were systematically recorded at depths of 7 and 20 meters. Furthermore, the developed framework was utilized to analyze 21 years of satellite-derived data pertaining to seabed light levels in the maritime regions adjacent to New Zealand’s East Cape.
Over the period spanning 2002 to 2023, an aggregate of 25 to 80 marine darkwave events were identified off the East Cape, with typical durations ranging from 5 to 15 days. The most prolonged occurrence extended for a continuous period of 64 days.
A significant proportion of these identified events were correlated with severe weather patterns, including the impact of Cyclone Gabrielle in 2023. Coastal mooring instruments situated in the Firth of Thames, a large bay in the northern sector of New Zealand, also registered distinct darkwave episodes attributable to storm activity. Additional causal factors identified included topsoil runoff originating from deforestation activities, sediment discharge from wildfire events, and plankton blooms, with potential contributions from dredging operations and coastal infrastructure development.
In specific extreme instances, at the zenith of certain darkwave events, the intensity of light reduction can create conditions that are among the darkest experienced by these oceanic segments at any given point in the annual cycle.
While the published research did not provide a quantitative assessment of the direct consequences on marine biota, it referenced prior scientific investigations that demonstrate profound impacts of diminished light availability on entire ecosystems, affecting organisms ranging from kelp communities and macroalgal populations to cnidarians like jellyfish.
“Even abbreviated intervals of reduced light intensity can impede photosynthetic processes within kelp forests, seagrasses, and coral colonies,” observed Thoral. “These events can also exert an influence on the behavioral patterns of fish, sharks, and marine mammals. When prolonged periods of darkness ensue, the resultant ecological ramifications can be substantial.”
Further investigative efforts will be requisite to meticulously differentiate between various categories of darkwave events – as phytoplankton blooms and sediment deposition may affect light quality through distinct mechanisms – and to establish a quantifiable measure of habitat degradation attributable to these marine darkwave phenomena.
Nevertheless, with the foundational framework now firmly established, subsequent research endeavors are poised to advance from a robust theoretical and methodological platform.
“Coastal ecosystems are increasingly encountering heightened exposure to storm-induced sedimentation and escalating climatic variability,” commented coastal scientist Chris Battershill from the University of Waikato.
“Marine darkwaves furnish us with a crucial insight into periods when these ecological systems are subjected to acute stress. This established framework will prove invaluable for Māori iwi and hapū, coastal communities, and marine conservation practitioners who necessitate precise data to inform their strategic decision-making processes.”
