Monday, November 29, 2010

Getting you're hot

Curator Chad Broyles (IODP-USIO/TAMU; back to camera), Expedition Project Manager and Staff Scientist Jörg Geldmacher (IODP-USIO/TAMU), Co-Chief Scientist Takashi Sano (National Museum of Nature and Science, Japan), and Co-Chief Scientist Will Sager (TAMU) discuss a core recovered from Shatsky Rise. (Credit: John Beck, IODP/TAMU)

Will Sager is a professor at Texas Agricultural and Mechanical University (TAMU) in College Station. When I invited him to speak he was bobbing about in a small boat in the Indian Ocean doing seismic surveys - and didn't seem quite as enthused about the experience as he expresses on his web page.

'Dr. Sager’s research is broadly about Earth history, plate tectonics, and the evolution of ocean basins. He is a marine geophysicist who loves to explore the ocean and has been on 38 research cruises and was chief scientist on 17 of them. He has participated on seven Ocean Drilling Program cruises and was co-chief scientist for two. His expeditions have taken him and his students to each of the big three oceans.'

Sager will be discussing the results from a recent cruise to the Shatsky Rise in the northwest Pacific where they were examining hot spot volcanism. Hot spots are taught in entry level plate tectonics classes as an important piece of evidence to support the global theory of plate tectonics. In geology, a hot spot is a portion of the Earth's surface that is far from tectonic plate boundaries where volcanism occurs due to a rising mantle plume or some other cause.

Figure showing the three basic types of volcanism on the planet and the mantle behaviour beneath those volcanoes.

Plumes were once thought to have formed most seamount chains, but today it is thought that classic, deep-rooted mantle plumes are rare. The 145 million-year-old Shatsky Rise seamount chain has some characteristics that fit the plume-head hypothesis however other scientists suggest its formation is linked to spreading ridges (B in the figure above - creation of new ocean floor) and a triple junction. Located ~1500 kilometers (930 miles) east of Japan, Shatsky Rise measures roughly the size of California. This underwater mountain chain is one of the largest supervolcanoes in the world: the top of Shatsky Rise lies three and a half kilometers below the sea surface, while its base plunges to nearly six kilometers below the surface. Shatsky Rise is composed of layers of basalt, with individual lava flows (now hardened) that are up to 23 meters thick.

Map of the North Pacific showing the hotpot track of the Hawaiian and Emperor sea mount chains. To the west of the Emperor Chain is the Shatsky Rise (SR on the map). The map also shows trenches to the north and west of the chains.

According to Sager, Shatsky Rise is unique in that
'it is the only supervolcano to have formed during a time when Earth’s magnetic field reversed frequently.” This process creates “magnetic stripe” patterns in the seafloor. We can use these magnetic stripes to decipher the timing of the eruption and the spatial relationship of Shatsky Rise to the surrounding tectonic plates and triple junctions.'

On Friday Sager will discuss the expedition results, seamounts and plateaus of the Pacific, and his changing views on hotspots.

Tuesday, November 16, 2010

Sharpening the tools in the carbon dioxide garden shed

This weeks Smith Lecturer is Barbel Honisch, a tenure-track geochemist at Lamont-Doherty Earth Observatory (Columbia University). Lamont is center for research on Earth and ocean processes with a strong emphasis on climate. Like last weeks speaker Honisch is both German (which is irrelevant) and interested in reconstructing past ocean pH and atmospheric CO2 levels. Honisch was initially trained as a marine biologist, so she approaches ocean history questions with biological in mind. She is specifically interested in using boron isotopes as an indicator of past seawater pH. To check if calcium carbonate organisms are recording the pH of the seawater they float in correctly, Honisch has grown these organisms (foraminifera) in the lab.

Boron isotopes in marine carbonates have the potential to provide us with information about past ocean carbonate chemistry, as the boron isotopic composition of marine carbonates is primarily controlled by the pH of seawater. The boron isotope paleoacidity indicator is that the uncharged species B(OH)3 is enriched in 11B by 20% over the charged species B(OH)4-. As the fraction of boron changes with pH, so must the isotope.

11B(OH)3 + 10B(OH)4- double arrow 10B(OH)3 + 11B(OH)4-

Boron isotopes alone provide us with only one parameter (i.e. pH) of the marine carbonate system. For accurately translating boron isotope data into pH values and subsequently for calculating other parameters of the carbonate system such as aqueous PCO2, we need additional information on temperature, salinity and a second carbonate parameter such as carbonate ion concentration or alkalinity (the amount of carbonate ion).

Logic diagram shows how seawater pH (on the left) influences the ratio of stable isotopes of boron in corals that grew in that water (on the right). From Chacko (2009)
Application of the boron isotope pH proxy to the late Pleistocene ice ages has led to a convincing estimation of surface ocean pH that can be compared to atmospheric pCO2 as recorded in ice cores. Now Honisch is in the process of extending the pH and pCO2 reconstructions beyond the reach of ice records, into the Cenozoic era. The first application beyond the reach of ice core CO2 measurements focused on the mid-Pleistocene transition when the ice ages became significantly longer in length and duration. Her results suggest that although CO2 and climate were tightly coupled, the climate transition was not driven by an overall decrease in atmospheric CO2 that could have cooled the planet.

Video about growing 'pets' that will tell you about climate change through time.

Monday, November 8, 2010

'Look what you've done!! I'm melting, melting....'

Danni Schmidt is a Royal Society University Research Fellow at the University of Bristol is this weeks Smith lecturer. She writes
'I have always been deeply in love with the ocean (though I grew up in a rather land locked part of Germany) and hence studied Marine Geology at the University of Bremen and the Alfred Wegener Institute for Marine and Polar Research. During my time at AWI, I went to the Southern Ocean and knew that I want to continue studying the Ocean, its environments and how climate change is affecting life. During my PhD at ETH Zurich I studied the effect of biotic interaction and climate change on plankton evolution. Currently, my work is focussing on calcification and ocean acidification – past and future”. I am trying to inform policy decisons by contributing to the Marine Climate Change Impact Plan (UK) and by being a Lead author for the Working Group II of IPCC on the open ocean chapter. '

Schmidt will be talking about a hot new topic in Earth system science - ocean acidification. Another impact of raising atmospheric CO2 levels is the diffusion of atmospheric CO2 into water. About 1/3 of the CO2 we pump into the atmosphere dissolves in sea water (pCO2) where it dissociates into bicarbonate (HCO3) and carbonate (CO3) releasing H ions as it does so. Acidity or pH measures the number of H ions in water, as the number goes up, pH goes down (pH =-log10(H+) ). It is estimated that since the start of the industrial revolution (1750) ocean pH has dropped from 8.179 to 8.104.

Estimated change in annual mean sea surface pH between the pre-industrial period (1700s) and the present day (1990s). Δ pH here is in standard pH units.

The problem with this is that many marine organisms make their skeletons out of calcium carbonate (CaCO3). Different arrangements of CaCO3 molecules produce different minerals of calcium carbonate. For example aragonite is an arrangement that is physically strong and is favored by corals, but is chemically weak (dissolves easily), while calcite is chemically stronger and is favored by foraminifera and coccolithosphores. As pH drops these organisms will need to use more energy to build and prevent their shell from dissolving. The stress this causes can be seen in the misshapen shells/skeletons of these organisms.

Schmidt will be talking about other time periods in the past when CO2 levels were high. These intervals are perfect laboratories to examine the response of the ocean to higher pHs. Her research has shown that the change in ocean pH is happening faster than previous time intervals. Schmidt and her collaborators applied a model that compared current rates of ocean acidification with the greenhouse event at the Paleocene-Eocene boundary, about 55 million years ago when surface ocean temperatures rose by around 5-6°C over a few thousand years. During this event, no catastrophe is seen in surface ecosystems, such as plankton (the planktonic foraminifera and coccolithosphorids), yet bottom-dwelling organisms in the deep ocean experienced a major extinction. This is because the cold deep waters of the ocean can dissolve far more CO2 than the surface waters, making the deep ocean realm susceptible to rapid and extreme acidification. The occurrence of widespread extinction of these organisms during the Paleocene-Eocenegreenhouse warming and acidification event raises the possibility of a similar extinction in the future.

Monday, November 1, 2010

The Critical Zone - need I say more

This weeks Smith Lecturer is Suzanne Anderson from the University of Colorado, Boulder. Anderson's research uses field work to understand the mechanisms by which chemical and physical processes shape the Earth's surface and control chemical weathering and erosion. She will be focusing on the Critical Zone - a term that is coming into wide use to describe the layer of loose, heterogeneous material covering solid rock, and includes vegetation, the water table and water bodies. Within this zone a number of physical, chemical, and biological processes and reactions occur that impact mass and energy exchange necessary for biomass productivity, chemical recycling, and water storage. The concept of the Critical Zone unifies many complex biogeochemical and physical geologic processes in an attempt to create a numeric value from which predictions can be made. Why might this be important? You might want to make predictions based on the Critical Zone if you were interested in understanding how contaminants (heavy metals, radioactive material and other pollutents) might spread through the environment for example. This weeks reading is a review paper Anderson wrote for the magazine 'Elements'. This magazine is produced for a number of minerological and gechemical societies, with each issue exploring broad and current themes in the mineral sciences.