Humboldtians in Focus

When the Sea Runs out of Air

By Jan Steffen

Could climate change lead to an expansion of low-oxygen ocean zones in which no life is possible? Oceanographer Victoria Bertics is literally trying to get to the bottom of this issue by examining the ocean floor.

Victoria Bertics, Humboldt Research Fellow at IFM-GEOMAR in Kiel since October 2010, evaluates the data and samples from an expedition.
Victoria Bertics, Humboldt Research
Fellow at IFM-GEOMAR in Kiel since
October 2010, evaluates the data
and samples from an expedition.

Photo: IFM-GEOMAR/Jan Steffen

Not always are humans to blame when hostile conditions occur in nature. In tropical oceans, nature itself creates huge, almost oxygen-free zones. Whether climate change is, however, causing these zones to expand, and how that might affect the rest of the world’s oceans, is a question oceanographers from Kiel have set out to answer. American biologist Victoria Bertics is a Humboldt Research Fellow and member of the team that spent more than four weeks on an expedition off the coast of Northwest Africa this spring collecting data in order to get to the bottom of this phenomenon.

It seems paradoxical: in the very areas of tropical oceans where large amounts of nutrients rise from the deep sea to the surface, creating heavenly conditions for oxygen-producing plants, that is precisely where the ocean is almost dead 100 metres below the surface because it lacks, of all things, oxygen. But the explanation is simple: where there is a lot of life, a lot of life also dies. As they break down dead plants and animals in the water, microorganisms use up the oxygen produced just below the surface. These natural minimum oxygen zones exist in all tropical seas. “The question is whether these natural low-oxygen zones are getting bigger, and whether climate change is contributing to that development,” says Victoria Bertics. That could lead to an overall imbalance between oxygen production and oxygen consumption which could influence ocean currents and ultimately affect all the world’s oceans.

Using autonomous underwater labs known as landers the IFM-GEOMAR scientists are tracking down biogeochemical processes in the deep sea.
Using autonomous underwater
labs known as landers the
IFM-GEOMAR scientists are tracking
down biogeochemical processes
in the deep sea. The equipment can
function at a depth of several
thousand metres for days, weeks or
months.

Photo: IFM-GEOMAR/M. Nielsen

The tools used by the researchers during the expedition include multibeam echosounders to map the previously barely surveyed ocean floor. Water sampling rosettes provide water samples taken at precisely defined depths, which can then be examined biologically, chemically and physically. Autonomous ocean-floor observation systems, known as benthic landers, are deposited on the ocean floor, take samples or collect biological, microbiological, biogeochemical and geochemical data over several days, and are then retrieved by the research vessel. In all, the work covers a depth range between 50 and 3,000 metres.

The measured data are worrying

The next step is to evaluate the results and answer the big question as to whether the low-oxygen zones really are expanding, as previously measured data and model calculations indicate.

Scenarios involving expanding minimum oxygen zones are not merely theoretical. Periods of drastically lower oxygen levels throughout the ocean are known to have occurred in the geological past, for example in the Permian or Cretaceous periods. This had extreme effects on the marine ecosystems of the time, all the way to mass extinctions. Events of this kind occurred in very warm climates and at very high atmospheric CO2 levels. The researchers are, therefore, also interested in finding out whether there are limit values beyond which changes in the ocean may be greatly accelerated.

In addition to this, Victoria Bertics is examining how oxygen levels are developing in the Baltic Sea, right in her own backyard at IFM-GEOMAR. Since last winter she has been undertaking regular dives in order to collect sediment samples from a depth of 30 metres, which she then examines in the lab. What she wants to know is which organisms in the sediment are able to bind nitrogen.

Distribution of low-oxygen zones in the world’s oceans (violet).
Distribution of low-oxygen zones
in the world’s oceans (violet). They
are most widespread in the tropical
oceans.

Photo: IFM-GEOMAR

The comparatively harsh Baltic climate doesn’t bother the American scientist, although she is normally more accustomed to the sunny Californian weather, having spent the previous years at the University of California in Berkeley and the University of Southern California in Los Angeles. That’s also where she met her host, Tina Treude, who finally also succeeded in convincing her to come to Kiel. Another argument in favour of coming to Germany was the fact that she has family roots in Kiel. After spending several years in large American cities, she relishes Kiel’s “intimate smalltown atmosphere” and its beautiful location by the sea. At IFM-GEOMAR she is pleased about the excellent and fairly easy access to research vessels. Getting day trips is much easier than at the two institutions in California where she previously studied and worked, she explains.

The 29-year-old currently has no thoughts of starting a family. But even if she did, she says, it would surely be possible to do so while maintaining her professional career. Her aim is a professorship, though where, she doesn’t yet know. Although she herself is ambitious, she feels there must be enough room left for other aspects of life. When she isn’t researching, she enjoys diving, hiking and travelling. “Here in Europe there’s so much to discover,” she says. Most recently she met other Humboldtians at a conference in Croatia. And of course, she headed for the sea there too – although for a change she just went swimming rather than conducting research.


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