Coasts

Coastal regions are disproportionately affected by the impacts of climate change. Preserving the ecological, economic and societal benefits of these environments will rely on synergy across disciplines.

Coastal systems are hotspots of ecological, geochemical and economic activity, yet their dynamics are not accurately represented in global models. In this Review, Ward and colleagues assess the current state of coastal science and recommend approaches for including the coastal interface in predictive models.

Accounting guidelines exist for carbon flows in terrestrial and coastal ecosystems, but not shelf sea sediments. In this Review, the authors explore whether effective management of carbon stocks accumulating in shelf seas could contribute to a nation’s greenhouse gas emissions reduction targets.

The role of Blue Carbon in climate change mitigation and adaptation has now reached international prominence. Here the authors identified the top-ten unresolved questions in the field and find that most questions relate to the precise role blue carbon can play in mitigating climate change and the most effective management actions in maximising this.

Understudied in the Antarctic system are the subsurface interfaces between ice-sheet, ocean and geological substrate. Here, the authors review our understanding of these components and propose new avenues of holistic dynamic modeling to achieve a unified understanding of past, present and future polar climate.

Mangroves and the carbon they store are threatened by deforestation, but the efficacy of policies to protect them is unknown. Here the authors assess changes in mangrove carbon stocks between 1996 and 2016 and show less loss than previous methods estimated, indicating conservation has had a positive effect.

Anthropogenic CO₂ is acidifying the ocean, but knowledge of the carbonate properties underlying these dynamics in coastal oceans is lacking. Here, the authors reveal spatial distribution patterns and variability in carbonate chemistry along North America’s coasts.

Wetlands are global hotspots of carbon storage, but errors exist with current estimates of the extent of their carbon density. Here the authors show that mangrove sediment organic carbon stock has previously been overestimated, while ecosystem carbon stock has been underestimated.

In this study, the authors show that water flowing through thawed soils below the tundra surface (supra-permafrost groundwater) can be a major source of dissolved organic matter (DOM) to Arctic coastal waters during the summer. This DOM contains leachates from old soil carbon stocks, including potential contributions from thawing permafrost.

The authors here present the global entry of nutrients into marine systems through fresh submarine groundwater discharge to be below 1%. However, they also identify hotspots and argue that about 25% of world’s estuaries are at danger of eutrophication.

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.

The California Current System is characterized by wind-driven upwelling and by rich mesoscale eddy activity, resulting in a highly productive ecosystem. Here the authors show that offshore cyclonic eddies which were generated near the coast contain higher carbon concentrations in their interior than eddies of the same amplitude generated locally offshore.

The presence and activity of sulfide-oxidizing denitrifying bacteria in sulfide-poor offshore oxygen minimum zone waters remains unclear. Here, the authors combine oceanography, molecular, biogeochemical and single-cell techniques to examine their distribution, metabolic capacity, and origins.

It remains unclear whether surface water partial pressure of CO₂ (pCO₂) in continental shelves tracks with increasing atmospheric pCO₂. Here, the authors show that pCO₂ in shelf waters lags behind rising atmospheric CO₂ in a number of shelf regions, suggesting shelf uptake of atmospheric CO₂.

Coastal river delta regions are particularly impacted by the effects of climate change, yet though these regions are densely inhabited, robust estimates of population are lacking. Here the authors use global datasets to predict the number of people and regions most threatened by flooding and extreme weather.

The degree of flooding in a particular location depends sensitively on local topography and bathymetry. Here the authors used the remarkability of flood events to estimate county-specific flood thresholds for shoreline counties along the Atlantic and Gulf coasts of the United States and found that several areas experience noticeable flooding at a height lower than existing thresholds.

The authors here combine a range of geophysical data, numerical modelling and borehole data to present a high resolution map of an offshore freshened groundwater system in the Canterbury Bight, New Zealand. The study shows the extensions of the offshore freshened groundwater system to be controlled by high permeability shelf sediments, buried paleochannels and onshore rivers.

The authors here investigate in the susceptibility of coastal aquifers to seawater intrusion. Based on 20 years’ worth of observational data, the study finds that 15% of the US coastline is affected by landward hydraulic gradients conducive to seawater intrusion.

It remains challenging to estimate carbon accumulation rates in tidal wetlands on a scale as large as the conterminous US. Here, the authors find that mean C accumulation rates vary greatly among watershed regions but not among vegetation types, and that tidal wetlands’ C sequestration capability will remain or increase by 2100, suggesting a resilience to sea level rise.

The variations in overbank flow from rivers onto floodplains from regional to continental scales are understudied. Here, the authors investigate this variation as a function of hydroclimatic parameters and channel size in the conterminous U.S. and find that the timing of floodplain inundation is largely controlled by regional factors, while the frequency, duration and magnitude of these inundations vary consistently with channel size.

Assessments of sea level rise risks depend on elevation data. Here, the authors present a new dataset on the Mekong Delta which shows it to have a much lower elevation (0.82 m above sea level) than previously thought – underlying principles may also imply major elevation uncertainties in other deltas.

Tropical cyclone-induced coastal flooding will increase under climate change. Here the authors estimate the effects of sea level rise and tropical cyclone climatology change on late–21st–century flood hazards along the US Atlantic and Gulf Coasts and find that the effect of tropical cyclone change could surpass the effect of sea level rise at some areas in the Gulf of Mexico.

Sea-level rise threatens coastal mangroves, with global consequences for these important blue carbon sinks. Here the authors analyse four Holocene sediment cores from islands in Florida Bay and find that mangroves that comprised the South Florida coastline 4–3000 years ago rapidly transitioned to estuarine conditions, despite low rates of sea-level rise, and propose that their demise was driven by high climate variability.

Accurate estimates of global mean sea-level rise are important. Here the authors employ a new digital elevation model (DEM) utilizing neural networks and show that the new DEM more than triples the NASA SRTM-based estimates of current global population occupying land below projected sea levels in 2100, with more than 200 million people could be affected based on RCP4.5 and 2 degC of warming.

UNESCO World Heritage located in low-lying coastal areas is increasingly at risk from flooding and erosion due to sea-level rise. This study shows that up to 82% of cultural World Heritage sites located in the Mediterranean will be at risk from coastal flooding and over 93% from coastal erosion by 2100 under high-end sea-level rise.

Extreme sea levels are a flood risk along the world’s coastlines. Here the authors carry out probabilistic projections of extreme sea levels and show that for the present century coastal flood hazards will increase significantly along most of the global coastlines.

River networks worldwide follow the emblematic Hack’s Law, which expresses the length of a stream as a function of its watershed area. Here the authors show this law does not depend on lithology or rainfall, but on the shape of watersheds and confirms the self-similarity of river networks.

Increasingly, eDNA is being used to infer ecological interactions. Here the authors sample eDNA over 18 months in a marine environment and use co-occurrence network analyses to infer potential interactions among organisms from microbes to mammals, testing how they change over time in response to oceanographic factors.

Seagrass meadows are important but one of the most threatened ecosystems globally. Here the authors analyse data about extent and density of seagrasses in Europe from 1869 to 2016, and find evidence of recent trend reversal for declining European seagrass meadows.

Random walk movement patterns with specific step size distributions are commonly associated with resource search optimization strategies in mobile organisms. Here, the authors show that clonal expansion of beach grasses follows a Lévy-type step size strategy that optimizes early dune building.

Artisanal fish fences are used for fishing along many tropical coastlines. Here, Exton et al. examine the impact footprint of artisanal fish fences, showing that they are highly non-selective, cause direct harm across the tropical seascape, disrupt ecological connectivity and create social conflict.

Quantifying the vulnerability of tidal marsh ecosystems to relative sea-level rise (RSLR) is essential if the threat is to be mitigated. Here, the authors analyze the response of Great Britain’s tidal marshes to RSLR during the Holocene and predict an almost inevitable loss of this ecosystem by 2100 under rapid RSLR scenarios.

Coral reefs provide significant coastal protection from storms but they have experienced significant losses. Here the authors show that the annual damages from flooding would double globally without reefs and they quantify where reefs provide the most protection to people and property.

Whether marine microbes form strongly differentiated communities over time remains unknown. Here, Martin-Platero and colleagues develop a time series analysis to characterize marine bacteria and Eukarya communities at a fine temporal grain, revealing cohesive but rapidly changing communities.