Archive for the ‘Ocean acidification’ Category

Mapping the Bottom of the Seas

Wednesday, August 26th, 2015

We are a map loving species – from our local streets and highways to the whole universe. Now we have a new map of the bottom of the world’s oceans, and it is wonderful.

It is digitized, built from 14,400 data points pulled from data gathered by research cruises over the past half century and now converted to a continuous map by Big Data experts at the University of Sydney. Thirteen types of bottom sediments are color coded, and the whole globe is there on your screen to rotate in any direction and explore.

Take it for a spin: it is irresistible.

One view of the digitized seafloor (geologyin.com)

One view of the digitized seafloor (geologyin.com)

Seafloor sediments distinguished by source and nature of particles, and are coded by color (geologyin.com)

Seafloor sediments distinguished by source and nature of particles, and are coded by color (geologyin.com)

Published in the current issue of Geology, this is really the first new view of the ocean floor in 40 years, and not surprisingly, it is full of surprises.

First, it is a much more complex patchwork of the microfossil remains of diatoms, radiolarians, sponge spicules, shell and coral fragments, along with sand, silt, clay, mud and vulcaniclastics than all previous maps had led us to expect.

Radiolarian ooze is made up of the skeletons of protistan radiolarians which are microscopic single celled animals that secrete silicon skeletons and feed with pseudopods that stick out through the holes in skeleton (micro.magnet.fsu.edu)

Radiolarian ooze is made up of the skeletons of protistan radiolarians which are microscopic single celled animals that secrete silicon skeletons and feed with pseudopods that stick out through the holes in skeleton (micro.magnet.fsu.edu)

And then, also unexpected, surface productivity of phytoplankton diatoms (a major carbon source) is not reflected by the abundance of seafloor abundance of diatom ooze (a carbon sink) – we understand less than we thought we did.

Diatom ooze is made up of the silicon skeletons of phytoplankton diatoms, each species with its own unique architecture, which are so abundant in the  surface waters (ucmp.berekely.edu)

Diatom ooze is made up of the silicon skeletons of phytoplankton diatoms, each species with its own unique architecture, which are so abundant in the surface waters (ucmp.berekely.edu)

Calcareous ooze contains the calcareous skeletons of other single celled protistans like coccolithophores (serc .carleton.edu)

Calcareous ooze contains the calcareous skeletons of other single celled protistans like coccolithophores (serc .carleton.edu)

The chalky cliffs of Dover were once coccolithophore sediments (wordsinmocean.com)

The chalky cliffs of Dover were once coccolithophore sediments (wordsinmocean.com)

In fact, at stake is our much broader understanding of the deep ocean’s response to climate change. We need to understand the global geochemical cycles, the behavior of deep-water currents, and the transport of ocean sediments, and this map provides a framework for asking – and answering – more detailed questions.

What we see now is a more complicated, less predictable picture of the global seafloor. If we understand why sediments on the seafloor are where they are, we have another window into reconstructing the past environments of our planet, a valuable key to understanding what is now occurring.

Perhaps most of all, we are reminded once again by a new and global map like this new one that in our local piece of our galaxy our planet is a small, isolated biological and physical oasis where change in any one component may radically influence all the others in ways we can increasingly monitor and struggle to understand, with a history we can increasingly explore.

And of course with a near-future that is so uncertain yet we must still plan for.

This map can only help.

Signal from Sea Butterflies

Sunday, June 8th, 2014

Sea butterflies are in the news, stressed by ocean acidification.

What do we now know about the decline in pH of ocean waters?

Well, we know that the pH has dropped from 8.2, where it was at the start of the Industrial Revolution, to its current level of about 8.1, and that the rate of change has increased in the past several decades. This may not sound like much, but in fact it indicates a 30% increase in the concentration of H+ ions in sea water. That is plenty to stress species that depend on carbonate ions in the water to build the calcium carbonate shells and skeletons that they depend on.

pH of ocean water in 1850 was about 8.2, with lower levels occurring in a few areas of coastal upwelling (igbp.net)

pH of ocean water in 1850 was about 8.2, with lower levels occurring in a few areas of coastal upwelling (igbp.net)

At current rates of global atmospheric CO2 emissions, ocean pH will drop further to 7.8 by the end of the century.

By 2100 ocean pH will have dropped to about 7.8, with extensive coastal areas particularly affected (igbp.net)

By 2100 ocean pH will have dropped to about 7.8, with extensive coastal areas particularly affected (igbp.net)

Ocean acidification has occurred before on the planet, but this event is different: it is happening 100 times more rapidly than any previous events we know of. Geochemists are looking 300 million years into the past, and there is nothing like it.

As CO2 levels in the atmosphere have risen, about 30% has dissolved in ocean water, where pH has dropped (igbp.net)

As CO2 levels in the atmosphere have risen, about 30% has dissolved in ocean water, where pH has dropped (igbp.net)

And it matters. Anything with an exposed calcium carbonate shell or skeleton will be affected – think mollusks, corals, and shellfish like crabs, shrimp and lobsters. With more CO2 dissolved in the water, there are more more bicarbonate ions along with the greater levels of H+ ions, and as a result less carbonate is available to make calcium carbonate. The shells are vulnerable to dissolution unless the surrounding water is saturated with carbonate ions, for they then lose calcium back into the water. As the shells erode and weaken, the animals become stressed, misshapen and potentially dead.

We’ve known about the increasing threat of ocean acidification for some years, but perhaps it has seemed a more distant threat than others associated with our increased CO2 emissions. But we know there already has been an impact on shell growth of oysters and mussels, and we know that coral reefs are particularly vulnerable as pH continues to decline. We have certainly been warned.

Sea butterflies are planktonic snails abundant over the world's continental shelves (realmonstrosities.com)

Sea butterflies are planktonic snails abundant over the world’s continental shelves (realmonstrosities.com)

Now we are warned once again, this time by sea butterflies. Also known as pteropods, these actually are pea-sized snails that live in the plankton where they are predators of other plankton and the common prey of fish. They are very beautiful to us – translucent, graceful, with the snail foot modified into what look like flapping wings. The shell is much reduced, though still very present, and the shells of species living in the California Current along the west coast of the US are showing signs of unusual erosion from exposure to the lower pH.

Electron micrographs of the shell of a healthy sea butterfly on the left, and the eroded shell of one stressed by lower pH on the right (arstecnhica.com)

Electron micrographs of the shell of a healthy sea butterfly on the left, and the eroded shell of one stressed by lower pH on the right (arstecnhica.com)

There are several key issues here. The rate of ocean acidification is unprecedented, and we don’t really know what lies ahead. We also know that vulnerable organisms will have insufficent time to adapt even if adaptation were possible. Eliminating vulnerable species like pteropods – or brittle stars, corals, mollusks or crustacesns – from ecosystems where they play a critical role as prey or predator will change the communities in ways that may also effect the top predators we want to catch. We are not short of discouraging examples of such community restructuring.

Do poster species help? Though the looming loss of coral reefs has not galvanized us to action, effective conservation campaigns have been built on the images of a variety of mammals, from whales and polar bears to koalas and pandas.

But sea butterflies as poster species? Because of their beauty, perhaps that isn’t impossible. It can’t hurt.

Tatoosh and Ocean Acidification

Wednesday, October 31st, 2012

Long-term studies are rare – the costs in time, effort, enthusiasm, persistence and funding are all formidable. But they are as valuable as they are rare.

One such study, stretching back five decades, is the research on the intertidal community of Tatoosh island, off the northwestern-most point of Washington State, at the mouth of the Strait of Juan de Fuca. Like other long-term studies it has depended on the initial and long-term research of a particular scientist and then his graduate students, and then theirs. In this case Robert Paine started the work, Timothy Wootton and Catherine Pfister are among his graduates students, and their graduate students continue to work with them on the island.

Tatoosh Island from the air – an old lighthouse, some steep cliffs, a few trees, and an extensive and accessible intertidal studied intensely since the 1960s (pbase.com)

The research on Tatoosh has given us insights into how predation and competition structure a community of species, including the concept of keystone species. Recently it has also provided critical evidence of current ocean acidification and correlated changes in the intertidal community.

Because the community has been so well studied for so long, changes in distribution, occurrence and sizes of individuals within populations are possible to recognize when they occur. For more than a decade now Pfister and Wootton have also measured ocean pH levels in great detail. What they are seeing is very troubling.

The intertidal of Tatoosh Island. Cape Flaherty on the Washington mainland is in the background (esa.org)

Concerning ocean pH, they have found that there is considerable diurnal and seasonal variation, a result of variation in sunlight (photosynthesis), darkness (respiration), temperature, phytoplankton abundance, and upwelling of the coastal waters, all of which modify CO2 levels, and hence pH, of the water. This in itself is really interesting, for the extent of the variation is certainly unexpected.

But they also have found a declining trend in ocean pH levels over the eight years of the initial study – 2000-2007. Allowing for the various sources of CO2 variation, and applying some sophisticated statistical tests, they have concluded that the decline in pH is correlated only with increased levels of atmospheric CO2.

In fact, pH dropped 0.045 units over the 8 years, 2.5 times faster than simulation models had predicted. Not good news, but good data, and the first of its kind outside of the tropics.

Species with calcareous shells or skeletons are particularly vulnerable to erosion as ocean pH drops. Over the same time period, several well-studied intertidal species with calcareous shells or skeletons – two species of mussels, and goose barnacles – declined in abundance and mean size, while non-calcareous algae increased in abundance.

Blue mussels Mytilus californianus have declined in abundance and size in the past decade, correlated with the decline in ocean pH (eeb.ucsc.edu)

Why the drop in pH is so great remains unexplained, but further research has addressed the question of whether such a drop in pH is just natural variation, or whether it is new. Mussel shells can last a long time after the animal inside dies, and their age can be determined. They also carry in them a record of the pH of the water they formed in. They provide an extraordinary record to compare with the present changes, dating back not just to the 1960s but as much as 1340 years ago to the middens left by the Makah who fished from the island in summer.

Shells of the intertidal shield limpet, Lottia pelta, though more difficult to analyse, confirm what the mussel shells have shown (wsu.edu)

And the conclusions? For the past decade the ocean waters around Tatoosh are acidifying at a rate faster than predicted. Nothing like this has occurred in the past 1300 years. We clearly don’t know enough yet about the causes, but the only strong correlation is with increased atmospheric CO2.

With the long-term studies of Tatoosh, we have a chance to detect such changes in water chemistry and community structure, and predict their occurrence elsewhere. That’s good science.

Meanwhile, we are warned once again. The emerging new world is going to look a lot different.

Populations of sea birds – murres and gulls – nesting on the cliffs of Tatoosh have also declined by 50% over the past decade (nytimes.com)