Ocean 'Dead Zones' Are Releasing One of The Worst Greenhouse Gases

I set sail in October 2019 with a group of scientists aboard the Canadian Coast Guard vessel John P. Tully, just off the coast from Vancouver Island.We struggled with rough seas, lack of sleep, and spent the better part a week shoulder-to-shoulder working in a small refrigerator. We analyzed seafloor sediments to find out more about the impact of low oxygen conditions on deep-sea environments.As organisms die they sink through the water column and consume oxygen from the sub-surface ocean. This results in oxygen-depleted water known as "dead zones" or oxygen minimum zones.These extreme environments are not suitable for most organisms. These dead zones can occur naturally in certain areas. However, they often form when fertilizer or sewage is washed downstream to coastal areas. This causes algal blooms that then die off.One of the studies we did on that expedition showed that sediments below oxygen-depleted water are a significant source for nitrous oxide (N2 O). This gas is released into atmosphere when deep water rises above the surface, a process called upwelling.Nitrous oxide is also known as "laughing gas" and is 300 times more potent than carbon dioxide.Human activities that increase its production are increasing global N2O emissions.Science article on decreasing oxygen levels in the oceans and coastal waters as a result of climate change. More than 500 dead zones near coastlines have been identified in the oceans. This is a significant increase from 50 in 1950 https://t.co/NBohXhtkaI Pic.twitter.com/VLKA4PbHmO Manolis Kogevinas. January 5, 2018, @KogevinasMHotspots N 2 OScientists are currently working to increase estimates of the marine contribution to global N2O emissions.Research has mainly focused on oxygen minimum zones, also known as hotspots for N 2 O emissions.Globally, the expansion of marine oxygen minimal zones is being driven by the warming of the oceans due to climate change. It is now believed that N 2O emissions from the oceans could continue to rise and accelerate climate change.Our research suggests that these low-oxygen waters may produce more N 2 O than expected.The environment contains a variety of forms of nitrogen, which is essential for life on Earth. For energy, cellular functions to be driven, specialized groups of single-celled microbes rely on nitrogen-containing compounds such as ammonium or nitrate.These metabolic reactions mediate nitrogen's transformation between its different states in the environment. N2 O can also leak out of the environment during these reactions.N 2 O, in addition to its greenhouse effects, is the most important ozone-depleting chemical emitted into the atmosphere.Experiments in sediment incubation underway in a cold room aboard the Tully. (Brett Jameson).Mangroves are N 2 O banksIn collaboration with the Bermuda Institute of Ocean Sciences, our team went to Bermuda in 2020 to measure N2O emissions from a mangrove forest.These sediments were more accessible to snorkelers and were therefore easier to study in detail.The Bermuda mangroves' seabed sediments actually consumed N 2 O from the seawater. Similar N2O "sinks", have previously been described in other pristine systems such as estuaries and mangroves, as well terrestrial soils.These areas' ability to absorb N 2 O from the air is dependent on the environmental nitrogen-containing nutrients. When these nutrients are not available, nitrogen oxide production will be inhibited.If the nutrient level is sufficiently low, marine habitats may act as net consumers for N 2 O.When exposed to higher nitrogen loads from urban runoff or agricultural waste water, sediments that act as N2 O sinks may also act as net sources.Mangroves and other nearshore ecosystems that receive a steady input of dissolved nitrogen are large N 2O emitters.It is not clear whether pristine environments can act as buffers against rising atmospheric N2 O concentrations. The majority of studies have been conducted in densely populated, highly disturbed areas of Europe and Asia. These regions are known to be sources of N2 O.There is still much to learn about the role of pristine marine ecosystems as N2O sinks, and their overall impact on global N2O budgets.Targeting fertilizerWhile reducing future marine N 2O emissions is dependent on the more complicated problem of slowing growth and spread marine oxygen minimum zones, there are simple interventions that can be made to preserve and restore beautiful coastal environments.Currently, more than two-thirds global N2 O emissions are caused by human agricultural practices. Much attention has been paid to reducing nitrogen additions to agricultural soils by fertilizer.Policies that reduce overuse of fertilizers can also be beneficial to adjacent aquatic ecosystems, as nutrients that aren't taken up by plants often end-up in watersheds that run into the ocean.To further reduce marine emissions, a multifaceted approach will be required that addresses both coastal development and waste-water disposal in highly impacted areas.The United Nations declared 2021 the beginning of a Decade of Ocean Science for Sustainable Development. It has never been more important to highlight the crucial link between oceans & climate change than now.Brett Jameson, PhD Candidate, University of Victoria, Biological OceanographyThis article was republished by The Conversation under Creative Commons. You can read the original article.