Scientists find widespread ocean anoxia as cause for past mass extinction

For decades, scientists have conducted research centered around the five major mass extinctions that have shaped the world we live in. The extinctions date back more than 450 million years with the Late Ordovician Mass Extinction to the deadliest extinction, the Late Permian extinction 250 million years ago that wiped out over 90 percent of species.

UNM Researcher Maya Elrick gathers samples on Anticosti Island [Credit: University of New Mexico]

Over the years, scientists have figured out the main causes of the mass extinctions, which include massive volcanic eruptions, global warming, asteroid collisions, and acidic oceans as likely culprits. Other factors sure to play part include methane eruptions and marine anoxic events - when oceans lose life-supporting oxygen.

The events that triggered the Late Ordovician Mass Extinction or LOME of marine animals and plants has largely remained a mystery until now. The Ordovician was a dynamic time interval in Earth history that recorded a major increase in marine biologic diversity and a greenhouse-to-icehouse climatic transition. Researchers believe this cooling period, which culminated in the first Phanerozoic glaciation led to the Late Ordovician Mass Extinction.

Now a team of researchers, including Maya Elrick at The University of New Mexico, Elrick's former master's student Rick Bartlett, now earning his doctorate at Louisiana State University, James Wheeley from the University of Birmingham (England) and the University of Ottawa's Andre Desrochers, have deciphered geochemical evidence left behind in marine limestone sediment that suggests this extinction was caused by a period of global cooling that created a global marine anoxic event.

The research, "Abrupt global-ocean anoxia during Late Ordovician-early Silurian detected using uranium isotopes of marine carbonates," was published in Proceedings of the National Academy of Sciences. It was supported, in part, through a three-year, $680,000 National Science Foundation grant.

"This extinction is the first of the 'big five' extinctions that hit the Earth and our research indicates that it was coincident with the abrupt development of widespread ocean anoxia that lasted for at least 1 million years," said Elrick.

Working with an international crew, Elrick and her team travelled to Anticosti Island in the St. Lawrence seaway of Quebec, Canada where they collected limestone rock samples. The returned samples were analyzed for uranium isotopes using a mass spectrometer housed in the UNM Department of Earth and Planetary Sciences. Results from the study indicate that abrupt and widespread marine anoxia occurred at the same time 85 percent of marine life went extinct.

Researchers gather samples on Anticosti Island [Credit: University of New Mexico]

"These results provided the first evidence for abrupt global ocean anoxia initiating and continuing through peak and waning glacial conditions," Elrick said. "We suggest that the anoxia was driven by global cooling which reorganized large-scale ocean circulation and led to decreased deep-ocean oxygenation and, enhanced nutrient fluxes, which caused phytoplankton blooms and expanded the areas of low oxygen concentrations. These results also provide the first evidence for widespread ocean anoxia initiating and continuing during glacial conditions."

Elrick and Bartlett's research is the first study of this type that uses a geochemical proxy (uranium isotopes) which integrates the entire ocean oxygen concentration. The results agree with what other scientists had been saying before, although the earlier studies were assessing only local oxygen concentrations rather than globally integrated concentrations. Further, Elrick and her team are modeling global ocean oxygen concentrations to evaluate how much of the seafloor went anoxic during the Late Ordovician extinction.

The team compared conditions 450 million years ago to those of today and determined that about there was about a 15 percent increase in anoxic seafloor during the Late Ordovician mass extinction. The modern ocean has less than a half a percent of seafloor that is anoxic (mainly the Black Sea), so a 15 percent increase in seafloor anoxia is quite significant.

"Anticosti Island is the best natural laboratory in the World for studying fossils and sedimentary strata dating from the first mass extinction nearly 445 million years ago. The island is now awaiting recognition at the UNESCO World Heritage program because of its exceptional geology and paleontology," said the University of Ottawa's Andre Desrochers.

Elrick is also studying three of the other 'big five' mass extinctions using uranium isotopes as oxygenation proxy.

"So far each of them have widespread anoxia associated with them, so we are finding that low seawater oxygen concentrations is a major killer," Elrick said

These results for the past 'big five' mass extinctions have implications for the modern extinction our planet is presently experiencing.

"We are warming and acidifying the oceans today and warmer oceans hold less and less oxygen. Some marine organisms can handle the heat and the acidity, but not the lack of oxygen" Elrick said. "All these things are happening today and the results from the Late Ordovician study indicate the potential severity of marine anoxia as an extinction driver for many of the past and ongoing biologic extinction events."

Source: University of New Mexico [May 21, 2018]

Major shift in marine life occurred 33 million years later in the South

A new study of marine fossils from Antarctica, Australia, New Zealand and South America reveals that one of the greatest changes to the evolution of life in our oceans occurred more recently in the Southern Hemisphere than previously thought. The results are published in the journal Communications Biology.

An example of a fossilised sea lily [Credit: British Antarctic Survey]

The Marine Mesozoic Revolution (MMR) is a key theory in evolutionary history. While dinosaurs ruled the land, profound changes occurred in the shallow seas that covered the Earth.

During the Mesozoic, around 200 million years ago, marine predators evolved that could drill holes and crush the shells of their prey. And although small in comparison to dinosaurs, these new predators, including crustacea and some types of modern fish, had a dramatic impact on marine life.

Among the species most heavily affected were sea lilies or isocrinids - invertebrates tethered to the seafloor by graceful stalks. Side on, these stalks resemble a vertebral column; in cross section, they are shaped like a five-pointed star - because sea lilies are related to starfish, sea urchins, and sand dollars. At their height during the Paleozoic, forests of sea lilies carpeted seafloors the world over.

Their restricted ability to move made sea lilies vulnerable to the new predators, so during the MMR they were forced into deeper waters in order to survive. Because it marked such a radical change in marine communities, scientists have long sought to understand this shift. They believed it occurred around 66 million years ago, but this new study shows that in the Southern Hemisphere, sea lilies remained in shallow waters until much more recently - around 33 million years ago.

A team from British Antarctic Survey, the University of Cambridge, the University of Western Australia, and the Royal Botanic Gardens, Victoria, made the discovery when they brought together field samples from Antarctica and Australia, with fossils from museum collections for the first time. The study provides conclusive evidence that this change happened at different times in different parts of the globe, and in the Antarctic and Australia, sea lilies hung on in shallow waters until the end of the Eocene, around 33 million years ago and it is unknown exactly why.

A modern feather star, a species which took over following the decline of the sea lillies
[Credit: British Antarctic Survey]

The study shows that knowing more about the Antarctic can reshape - or overturn - existing scientific theories.

According to lead author Dr Rowan Whittle from British Antarctic Survey: "It is surprising to see such a difference in what was happening at either end of the world. In the Northern Hemisphere these changes happened whilst the dinosaurs ruled the land, but by the time these sea lilies moved into the deep ocean in the Southern Hemisphere the dinosaurs had been extinct for over 30 million years.

"Given how the ocean is changing and projected to change in the future it is vital that we understand how different parts of the world could be affected in different ways and at a range of timescales."

To get this richer picture of how sea lilies responded to the changing oceans of the Southern Hemisphere over millions of years, the team travelled to some of the remotest regions of Western Australia and Antarctica. Their hunt for fossil sea lilies was rewarded by the discovery of nine new species.

Co-author Dr Aaron Hunter from the University of Cambridge says: "We have documented how these sea lilies evolved as Australia split away from Antarctica moving north and becoming the arid outback we know today, while ice formed over the South Polar Region.

"The sea lilies survived in the shallow waters for millions of years longer than their Northern Hemisphere cousins, but as the continents moved further apart, they eventually had nowhere to go but the deep ocean depths where they have clung on to existence to this day".

Source: British Antarctic Survey [May 17, 2018]

Marine animals have been following their preferred climate for millions of years

Current global warming has far-reaching ecological consequences, also for the Earth's oceans. Many marine organisms are reacting by migrating towards the poles. Researchers at Geozentrum Nordbayern at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have now discovered that marine animals have been migrating for millions of years when the temperature on Earth increases or decreases.

Using a model, they determined how the tectonic plates have moved since the time when the animals were living and
combined the results with the current coordinates of the location where the fossil samples were discovered. This
enabled them to retrace changes in fossil species composition over long time periods. The researchers used
 a global database that they helped to set up that contains records of all fossils ever found
[Credit: University of Manchester]

Marine animals follow changed temperature zones to the poles or equator

Most living organisms on Earth have settled into ecological niches and one of the decisive factors in their choice of habitat is a certain temperature. Marine animals either need warmer water for their metabolism, such as tropical species, or colder water, such as animals that depend on a higher oxygen content in the water. They therefore migrate either towards the poles or the equator as soon as the temperature changes, and have been doing so for millions of years. 'Whilst the climate appears to be changing more rapidly today than ever before, the climate also changed rapidly in the past, forcing organisms to migrate in order to survive. Adaptation tended to be the exception,' emphasises Prof. Wolfgang Kießling, Chair of Palaeoenviromental Research.

By investigating fossils, Prof. Kießling and Dr. Carl Reddin, who is also at GeoZentrum Nordbayern, have shown that coral, molluscs, and sponges have been following their preferred cold and warm zones for half a billion years. Isotherms (geographic lines denoting the same temperature, for example 20°C) shift towards the poles or the equator as soon as the global temperature rises or decreases. Isotherms have been shifting towards the poles for several years due to global warming.

The tendency towards climate-related migration is most apparent in tropical species. This may be due to the fact that several of these species live near the thermal maximum for complex organisms of 35-45°C . Current global warming trends are driving marine animals towards the poles, provided there is a suitable habitat they can migrate to.

Tracing climate change by investigating shifts in species distribution

How did the palaeobiologists discover this prehistoric migration pattern? Firstly, they determined the geographic coordinates of the area in which the fossils were found when they were alive. Using a model, they determined how the tectonic plates have moved since the time when the animals were living and combined the results with the current coordinates of the location where the fossil samples were discovered. This enabled them to retrace changes in fossil species composition over long time periods. The researchers used a global database that they helped to set up that contains records of all fossils ever found.

The results are also significant for the present. Wolfgang Kießling and Carl Reddin expect that the current shifts will affect mostly tropical species, and it is thought that there will be a significant reduction of such species in the long run. Research up to now has largely been limited to central latitudes, where migration is already occurring on a large scale.

The study is published in Global Ecology and Biogeography.

Source: University of Erlangen-Nuremberg [May 17, 2018]

The Baltic Sea as a time machine

At first glance, the Baltic Sea seems to be rather uninteresting for scientists working on global ocean topics. It is comparatively shallow, has a low salinity and only a very narrow connection to the North Atlantic. This impression is, however, deceiving. In the current issue of the international journal Science Advances, 26 authors from 21 scientific institutions in seven countries appeal to the greater scientific community and policy makers to use the Baltic Sea Region as a model for coming changes in the World Ocean. "This unique sea of brackish water can serve as a kind of time machine that allows us to better estimate future global changes," says Prof. Thorsten Reusch from the GEOMAR Helmholtz Center for Ocean Research Kiel, one of the lead authors of the article.

The Baltic Sea can be regarded as a model area for changes in the world ocean
[Credit: Christoph Kersten, GEOMAR]

The scientists argue that changes that are only expected for the future in the global ocean can already be observed in the Baltic today. "This is because the small volume of water and slow water exchange with the open ocean, behaves like an amplifier, allowing many processes and interactions to occur at a faster pace", emphasizes Dr. Jan Dierking from GEOMAR, who initiated the study together with Prof. Reusch.

As examples, the oceans have warmed by an average of 0.5°C over the past 30 years, while in the same period, time-series measurements in the Baltic Sea have recorded warming of around 1.5°C. Likewise, there are large oxygen-free zones in the deep areas of the Baltic Sea, which have increased tenfold over the past century; and the pH--a measure of ocean acidification--of Baltic waters regularly reaches values that are expected in other ocean areas only in the next century.

Water sampler on RV LITTORINA in the Baltic [Credit: GEOMAR]

On the one hand, these extremes are caused by the particular basin topography of the Baltic Sea. On the other hand, intensive use by humans continues to accelerate negative changes. Nine countries border on the Baltic Sea directly and all are highly industrialized, with densely populated coastal regions. Moreover, intensive agriculture in the interior ensures high nutrient runoff, while equally intensive fisheries puts pressure on the pelagic food-web.

But it's not all doom and gloom. The Baltic Sea is one of the best-surveyed seas on Earth. Scientific observation and monitoring of physical and biological processes began around 1900. There is a strong tradition in scientific co-operation among many countries surrounding the Baltic, culminating in the implementation of the joint Baltic Sea research and development programme BONUS of the European Union, a dedicated macro-regional research agenda and funding scheme that also enabled the present study. These data provide a sound basis for science-based resource management--"on a level accomplished in only a few regions of the world," emphasizes Professor Reusch.

Collection of water samples on RV LITTORINA [Credit: GEOMAR]

Among the management success stories: the bordering countries have managed to significantly reduce nutrient inputs since the 1980s, to reverse the decline of large predators, and to curb overfishing. This has been achieved through the binding agreements within the framework of the European Union, but also thanks to the ambitious goals of the Baltic Sea Action Plan (BSAP), which included Russia, even before the end of the Cold War. In fisheries, the protection of capture fisheries, marine mammals and bird populations among the perimeter countries have led to measurable improvements of existing stocks.

"Overfishing, warming, acidification, pollution, eutrophication, loss of oxygen, intensive use of coasts--all these are phenomena that we observe around the globe. Because they have been particularly drastic in the Baltic, but also because some key problems were successfully addressed, the region can, for good and for bad, tell us what to expect and how to respond to the challenges of the future," Prof. Reusch concludes, "The Baltic Sea, as a model region, can contribute to achieving the United Nation's Sustainable Development Goal 14--the conservation and sustainable use of the oceans, seas and marine resources."

Source: Helmholtz Association of German Research Centres [May 09, 2018]