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Geosciences Column: Adapting to acidification, scientists add another piece to the puzzle

12 Sep

In the latest Geosciences Column Sara Mynott sheds light on recent research into how ocean acidification is affecting the California Current Large Marine Ecosystem. The findings, published in Biogeosciences, reveal large differences between the abilities of different animals to adapt and highlight the urgent need to understand the way a greater suite of species are responding…

Large Marine Ecosystems (LMEs) are highly productive ocean areas that border the continents. To give you a flavour of just how productive we’re talking, together the world’s LMEs account for 80% of the global marine fisheries catch, making them incredibly important regions both socially and economically. The California Current Large Marine Ecosystem (CCLME) is one such system and covers the length of the US Pacific coast. But, like other ocean ecosystems, the CCLME is under threat from climate change.

Major changes in the carbonate chemistry of the oceans are expected over the next few decades, and changes in the California Current system are to be some of the most rapid. Determining how this system, and indeed other ecosystems, will respond is a significant challenge for biologists, ecologists and climate scientists alike.

In 2010, an interdisciplinary research group known as OMEGAS (Ocean Margin Ecosystems Group for Acidification Studies) set out to find answers by monitoring a ~1300 km stretch of the CCLME that runs from central Oregon to southern California. Because this stretch of ocean can be divided into distinct areas with differing pH and carbonate chemistry, the researchers could compare the characteristics of animals living in more acidic conditions with those living in a less acidic environment and assess their ability to adapt.

Like other LMEs, the California Current system is characterised by upwelling – a process that brings nutrient-rich deep water to the surface. Upwelling waters bring with them a change in pH. In the southern CCLME, there is regular upwelling but in the north it is intermittent. This means animals living off the Oregon coast experience more variable pH, and are exposed to lower pH water more often. By comparing animals in the north with those in the south of the study area, the OMEGAS scientists could effectively peer into the ecosystem’s future. The scientists were substituting space for time.

The California Current Large Marine Ecosystem, showing the sites monitored by OMEGAS for changes in the region’s biology and chemistry. Seawater is coloured according to temperature and land is shown in grey. (Credit: Hoffman et al., 2014)

The California Current Large Marine Ecosystem, showing the sites monitored by OMEGAS for changes in the region’s biology and chemistry. Seawater is coloured according to temperature and land is shown in grey. (Credit: Hoffman et al., 2014)

By matching measurements of ocean properties, including pH, temperature and the amount of CO2 in the water, with information about the way different animals are responding to acidity (e.g. growth rate, shell thickness) and their genetic variation, the team are putting together a picture of how acidification is likely to affect the ecosystem in the future. One such animal is the purple sea urchin, a conspicuously bright spiny mass found throughout the CCLME, and an important control on the amount of algae carpeting the coast.

Purple sea urchin, Strongylocentrotus purpuratus. (Credit: Wikimedia Commons user Taollan83)

Purple sea urchin, Strongylocentrotus purpuratus. (Credit: Wikimedia Commons user Taollan83)

When peering at their skeletons for signs of acidification-related stress, the OMEGAS team found that the urchins differed little between sites – they were all tolerant of the pH range experienced across the CCLME. Urchin larvae travel large distances, rendering populations relatively homogeneous, so it isn’t too surprising. Taking a look at another ecologically important species, the Californian mussel, the team found that they were also made of hardy stuff, as growth in adult mussels was not reduced in low pH regions.

The news wasn’t all good though. A series of complementary experiments revealed that mussel larvae exposed to low pH water showed a decline in both growth and shell strength, similar to that seen in other young marine bivalves. Such a weakness would leave them more susceptible to attack from predators and, as ocean acidification continues, means they will become yet more vulnerable to predation in the future. Purple sea urchin larvae, on the other hand, could tolerate present day CO2 conditions, and higher levels had little influence on their growth and development. What’s more, studies of the sea urchin’s genetics revealed high genetic variation in the purple sea urchin population – a good indicator that they’d be able to adapt to future change.

California mussels, Mytilus californianus. (Credit: Stephen Bentsen)

California mussels, Mytilus californianus. (Credit: Stephen Bentsen)

The study highlights that the impact of acidification varies widely between species and a greater understanding of how ocean acidification will affect a variety of marine organisms is urgently needed. The OMEGAS team are now figuring out the capacity of other organisms in the CCLME to adapt, including coralline algae, a widely distributed algae with a calcium carbonate skeleton, making it highly vulnerable to ocean acidification.

The team are continuing their work in an effort to find refuges that may be relatively safe from future acidification, populations and life stages that are particularly vulnerable and those that are able to adapt to the rate of change our oceans are currently experiencing. Understanding how multiple species can adapt is critical to creating a coherent picture of how acidification will affect regions such as the CCLME in the future.

 

By Sara Mynott, PhD Student, University of Exeter

 

Reference:

Hofmann, G. E., Evans, T. G., Kelly, M. W., Padilla-Gamiño, J. L., Blanchette, C. A., Washburn, L., Chan, F., McManus, M. A., Menge, B. A., Gaylord, B., Hill, T. M., Sanford, E., LaVigne, M., Rose, J. M., Kapsenberg, L., and Dutton, J. M.: Exploring local adaptation and the ocean acidification seascape – studies in the California Current Large Marine Ecosystem, Biogeosciences, 11, 1053-1064, doi:10.5194/bg-11-1053-2014, 2014.

Geosciences Column: From the desolate to the diverse, a story of volcanic succession

18 Jul

When a volcano erupts and spews lava onto the surrounding terrain, it is merciless in its destruction. All that is green on the land is engulfed in flame, or buried by an insurmountable mass of molten rock. Whatever charred remains of what lies beneath it will not see the light of day once the lava cools, turning the landscape into a barren black mass of solid basalt.

But volcanoes around the world are not barren basaltic masses. On the contrary, many volcanic slopes are teeming with life. Much of the Hawaiian archipelago is a tropical paradise, its older lava fields thick with forest and foliage. Likewise, Iceland’s flotilla of fiery peaks hasn’t rendered the land completely barren. So how does life return to the scene after an eruption?

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

The answer lies in a process known as succession. One by one, starting with the hardiest life forms, the lava is recolonised by wind-blown spores and seeds that have managed to make it from areas unharmed by the latest eruption. Over time, the growing community of plants attracts animals that bring further seeds to the site, either clinging desperately to their fur, or deployed stealthily in their droppings.

A long-term investigation of two very different volcanoes has revealed what allows the earliest arrivals to take hold: Surtsey, an isolated volcanic island in the North Atlantic, and Mount St. Helens, a once towering and peak in Washington State. The findings are published in Biogeosciences, an open access journal of the European Geosciences Union.

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey emerged off the Icelandic coast in 1963 amid billowing plumes of ash and steam. Erupting from underwater, Surtsey created its own island – a fresh field of lava that has been consistently monitored since 1990. Mount St Helens erupted violently in 1980, after a catastrophic landslide triggered a volcanic blast so large that the volcano’s entire north flank, together with 370 square kilometres of forest, were obliterated. The resulting fields of pumice, tephra and lava provided a blank canvas for life to start afresh in the area.

Surtsey and Mout St Helens differ in terms of their age, the way they’re isolated, their climate and their size. But, despite these differences, scientists Roger del Moral and Borgþór Magnússon found the way vegetation first established itself followed the same fundamental principles, regardless of where it set up camp.

It’s all down to two different filters: isolation and stress. Isolation creates the biggest filter; meaning only the most well-travelled species can take hold. Then stress further sorts the species that can survive – well-travelled weaklings wouldn’t stand a chance in a place with incredibly poor fertility.

Birds make life a little easier for all involved, particularly in coastal areas, where an entire colony of birds can become established. These birds import nutrients from the surrounding sea by consuming fish from and depositing their waste on land. On Surtsey, these nutrient imports have meant the richest plant life has developed where the bird colonies are.

On Mount St Helens, winds carrying nutrient-laden dust created the first fertile material. This let a group of flowering plants known as lupines take hold and, after several cycles of lupine blooms, the ground became much more fertile. The areas where lupines bloom are now the most species rich.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

In a world where environments are rapidly changing and species are having to move into new territories to adapt, these findings can help shed light on how plants could keep pace with the change as they shift from one site to the next.

By Sara Mynott, EGU Communications Officer

Reference:

del Moral, R. and Magnússon, B.: Surtsey and Mount St. Helens: a comparison of early succession rates, Biogeosciences, 11, 2099-2111, doi:10.5194/bg-11-2099-2014, 2014.

 

Geosciences Column: Meshing models with the small-scale ocean

12 Jun

The latest Geosciences Column is brought to you by Nikita Marwaha, who explains how a new generation of marine models is letting scientists open up the oceans. The new technique, described in Ocean Science, reveals what’s happening to ocean chemistry and biology at scales that are often hard to model…

Diving into the depths of the ocean without getting your feet wet is possible through biogeochemical modelling – a method used by scientists in order to study the ocean’s living systems. These simulated oceans are a means of understanding the role of underwater habitats and how they evolve over time. Covering nutrients, chlorophyll concentrations, marine plants, acidification, sea-ice coverage and flows, such modelling is an important tool used to explore the diverse field of marine biogeochemistry.

Barents Sea plankton bloom: sub-mesoscale flows may be responsible for the twisted, turquoise contours of this bloom (Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC)

Barents Sea plankton bloom: sub-mesoscale flows may be responsible for the twisted, turquoise contours of this bloom (Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC)

There is one outstanding problem with this technique though, as the very-small scale or sub-mesoscale marine processes are not well represented in global ocean models. Sub-mesoscale interactions take place on a scale so small, that computational models are unable to resolve them. Short for sub-medium (or ‘sub- meso’) length flows – the smaller flows in question are on the scale of 1-10 km. They are difficult to measure and observe, but their effects are seen in satellite imagery as they twist and turn beautiful blooms of marine algae.

Sub-mesoscale phenomena play a significant role in vertical nutrient supply – the vertical transfer of nutrients from nutrient-rich deep waters to light-rich surface waters where plankton photosynthesise. This is a major area of interest since the growth of marine plants is limited by this ‘two-layered ocean’ dilemma. But the ocean is partially able to overcome this, which is where sub-mesoscale flows come in. Sub-mesoscale flows are important in regions with large temperature differences over short distances – when colder, heavier water flows beneath warmer, lighter water. This movement brings nutrient-rich water up to the light-rich surface. Therefore, accurately modelling these important small-scale processes is vital to studying their effect on ocean life.

Global chlorophyll concentration: red and green areas indicate a high level or growth, whereas blue areas have much less phytoplankton. (Credit: University of Washington)

Global chlorophyll concentration: red and green areas indicate a high level or growth, whereas blue areas have much less phytoplankton. (Credit: SeaWiFS Project)

A group of scientists, led by Imperial College’s Jon Hill, probes the technique of biogeochemical ocean modelling and the issue of studying sub-mesoscale processes in a paper recently published in the EGU journal Ocean Science.  Rather than simply increasing the resolution of the models, the team suggests a novel method – utilising recent advances in adaptive mesh computational techniques. This simulates ocean biogeochemical behavior on a vertically adaptive computational mesh – a method of numerically analysing complex processes using a computer simulation.

What makes it adaptive? The mesh changes in response to the biogeochemical and physical state of the system throughout the simulation.

Their model is able to reproduce the general physical and biological behavior seen at three ocean stations (India, Papa and Bermuda), but two case studies really showcase this method’s potential: observing the dynamics of chlorophyll at Bermuda and assessing the sinking detritus at Papa. The team changed the adaptivity metric used to determine the varying mesh sizes and in both instances. The technique suitably determined the mesh sizes required to calculate these sub-mesoscale processes. This suggests that the use of adaptive mesh technology may offer future utility as a technique for simulating seasonal or transient biogeochemical behavior at high vertical resolution – whilst minimising the number of elements in the mesh. Further work will enable this to become a fully 3D simulation.

Comparison of different meshes produced by adaptive simulations: (a) Bermuda, taking the amount of chlorophyll into account (b) the original adaptive simulation at Bermuda, without taking chlorophyll into account (c) adaptive simulation at Papa, taking the amount of detritus into account (d) the original Papa simulation, without taking detritus into account. (Credit: Hill et al, 2014)

Comparison of different meshes produced by adaptive simulations: (a) Bermuda, taking the amount of chlorophyll into account (b) the original adaptive simulation at Bermuda, without taking chlorophyll into account (c) adaptive simulation at Papa, taking the amount of detritus into account (d) the original Papa simulation, without taking detritus into account. (Credit: Hill et al., 2014)

The fruits of this adaptive way of studying the small-scale ocean are already emerging as the secrets of the mysterious, sub-mesoscale ocean processes are probed. The ocean holds answers to questions about our planet, its future and the role of this complex, underwater world in the bigger, ecological picture – adapting to life and how we model it may just be the key we’ve been looking for.

By Nikita Marwaha

Reference:

Hill, J., Popova, E. E., Ham, D. A., Piggott, M. D. and Srokosz, M.: Adapting to life: ocean biogeochemical modelling and adaptive remeshing. Ocean Sci., 10, 323- 343, 2014

Imaggeo on Mondays: Long-lived lakes have a lot to tell

2 Jun

The world’s oldest, deepest freshwater lake lies in southeast Siberia: Lake Baikal. Stretching some 600 kilometres across the Russian landscape, Baikal marks what the very early stages of a new ocean – an ancient rift that cleaved the centre of Asia apart throughout the Palaeozoic, Mesozoic and Cenozoic. Today, there are still signs of tectonic activity and the rift continues to diverge 4 mm further apart each year. Much like the East African Rift, Baikal provides scientists with a window into the way oceans are formed.

Where the Selenga River meets Lake Baikal. (Credit: Galina Shinkareva via imaggeo.egu.eu)

Where the Selenga River meets Lake Baikal. (Credit: Galina Shinkareva via imaggeo.egu.eu)

The Selenga River, which snakes across Asia for over 900 km, brings 30 cubic kilometres of water and more than 3.5 million tonnes of sediment to the basin each year, feeding a rich wetland ecosystem at the northern end of the lake. What’s more, the lake’s age and isolation has led to the establishment of a unique world of underwater flora and fauna – 70% of the lake’s inhabitants are found nowhere else in the world. This combination has earned the lake the nickname ‘The Galapagos of Russia’ and its designation as a World Heritage Site, as well as providing a prime site for evolutionary studies.

Not only that, but the lake is a key spot for climate science too. Baikal’s high latitude location means that it’s particularly sensitive to comate change, leading to numerous investigations into how climate has varied over the last 250,000 years. No doubt we have a lot more to learn from this incredible environment.

By Sara Mynott, EGU Communications Officer

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

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