Scientists identify key factor that controls ocean nitrogen availability

Feb 24, 2013
Oceanic oxygen minimum zones. Depicted is the oxygen concentration at 300 meter water depth. Around 30- 50% of global marine N-loss takes place in these areas, which represent only ca. 0.1% of the ocean´ s volume. Credit: Image is modified after World Ocean Atlas 2009 nodc.noaa.gov

(Phys.org)—During an expedition to the South Pacific Ocean, scientists from the Max Planck Institute for Marine Microbiology in Bremen, along with their colleagues from the GEOMAR and Christian-Albrechts University in Kiel, discovered that organic matter derived from decaying algae regulates nitrogen loss from the Ocean's oxygen minimum zones. They published their discovery in the renowned scientific journal Nature Geoscience.

One of the central aims of today's marine research is to better predict the response of our Ocean to global warming and human activity in general. Understanding of the oceanic is of key importance in this effort as nitrogen is the limiting nutrient for life in the Ocean. Its bio-available form (so-called fixed nitrogen, such as ammonium) is produced biologically from nitrogen gas by bacteria or is transported to the ocean as dust or river run-off. However, due to the activity of marine microorganisms growing in virtually oxygen free conditions, this fixed nitrogen is rapidly converted back to , which escapes from the Ocean to the atmosphere. There are two processes, which are mainly responsible for this nitrogen loss: denitrification and anammox ( of ammonium with nitrite), both performed by .

Up to 40% of global oceanic nitrogen loss occurs in so-called oxygen minimum zones (OMZ), which are areas with low to non-measurable oxygen concentrations. "The eastern tropical OMZ is one of the largest OMZs in the world," explains Tim Kalvelage from the Max Planck Institute for , the first author of this study. "We assumed that if we could identify and constrain the parameters that regulate N loss from this OMZ, we could better predict the N loss from all OMZs, and possibly from the Ocean, as well." Professor Andreas Oschlies of GEOMAR Kiel and speaker of the Collaborative Research Centre SFB 754 adds: "This research is fundamental for improving our current biogeochemical models that, so far, cannot reliably reproduce the patterns of N loss that we measure."

As a part of the German National Research Foundation (DFG) funded SFB 754 a series of expeditions onboard of the research ship Meteor in 2008/2009 were specifically dedicated to collect samples from the South Pacific OMZ. Further analyses and measurements followed in the laboratories of the Max Planck Institute for Marine Microbiology in Bremen, GEOMAR Helmholtz Centre for Ocean Research and Institute for General Microbiology in Kiel. The results provide a detailed overview of nutrient distributions, rates of N loss processes and abundances and identity of bacteria in the South Pacific OMZ. Furthermore, models were employed to calculate the amount of algal biomass that is exported from the surface to the deeper OMZ waters. This large-scale study resulted in the so far most comprehensive nitrogen budget for an oceanic OMZ. The results were surprising: "We saw that the rates of nitrogen loss, mainly due to anammox, strongly correlated with the export of organic matter," explains Tim Kalvelage. "This was unexpected because anammox bacteria do not grow on organic matter but use ammonium and CO2." The scientists found out that the N-rich most likely serves as a key source of for the anammox reaction.

Professor Marcel Kuypers concludes: "Our results will help to more realistically estimate the short- and long-term impacts of human-induced ocean de-oxygenation and changing productivity on cycling in the OMZs, as well as the rest of the Ocean. This is critical to estimate how much CO2 can be taken up by the Ocean in the future."

Explore further: Magnitude-7.2 earthquake shakes Mexican capital

More information: Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone, Tim Kalvelage, Gaute Lavik, Phyllis Lam, Sergio Contreras, Lionel Arteaga, Carolin R. Löscher, Andreas Oschlies, Aurélien Paulmier, Lothar Stramma and Marcel M. M. Kuypers, Nature Geoscience (2013) doi:10.1038/NGEO1739

Related Stories

How much nitrogen is fixed in the ocean?

Aug 10, 2012

In order to predict how the Earth's climate develops scientists have to know which gases and trace elements are naturally bound and released by the ocean and in which quantities. For nitrogen, an essential element for the ...

Nitrous oxide from ocean microbes

Dec 10, 2007

A large amount of the greenhouse gas nitrous oxide is produced by bacteria in the oxygen poor parts of the ocean using nitrites, Dr Mark Trimmer told journalists at a Science Media Centre press briefing today.

Recommended for you

Magnitude-7.2 earthquake shakes Mexican capital

Apr 18, 2014

A powerful magnitude-7.2 earthquake shook central and southern Mexico on Friday, sending panicked people into the streets. Some walls cracked and fell, but there were no reports of major damage or casualties.

User comments : 0

More news stories

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

UN weather agency warns of 'El Nino' this year

The UN weather agency Tuesday warned there was a good chance of an "El Nino" climate phenomenon in the Pacific Ocean this year, bringing droughts and heavy rainfall to the rest of the world.

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...