An Ocean in Transition - Climate Change and Ocean Change
A major focus of our laboratory is the response of marine animals and ecosystems to anthropogenic changes in ocean conditions - particularly ocean acidification. Carbon dioxide emissions to the atmosphere have raised atmospheric CO2 levels far beyond the range of variation known to occur for the past million years, and perhaps as much as 30 million years. In addition to greenhouse warming due to these emissions, the oceans have absorbed much (~41%) of our fossil fuel carbon dioxide. This excess CO2 in the ocean reacts with seawater to form carbonic acid, which reaches an equilibrium under existing ocean conditions to make increase the acidity of the oceans and reduce carbonate ion concentrations, a key mineral used for the formation of shells and skeletons of marine organisms. Will ocean life tolerate this massive and rapid change in ocean chemistry, in addition to warming and increasing hypoxia in deep waters?
In addition to the unintentional changes in ocean conditions listed above, society is also considering methods to avoid atmospheric emissions and its associated climate impacts, including the capture of waste carbon dioxide at power generating plants, followed by the injection of carbon dioxide (as a liquid) into deep-sea waters. This carbon storage notion, known as direct deep-sea carbon dioxide sequestration, could be effective in avoiding some climate warming owing to a reduction in atmospheric emissions, but could also cause potentially important changes in the chemistry of deep-sea waters. Another idea for reducing atmospheric CO2 levels is the fertilization of surface waters in the oceans where the major nutrients used for phytoplankton growth (e.g. nitrate and phosphate - just likely your plants at home) are abundant, but a key micronutrient (iron) is present in only low levels. Spraying an iron-rich solution on these surface waters has been shown in many areas to stimulate a phytoplankton bloom, which will ultimately lead to higher rates of organic debris sinking toward the bottom. As it sinks, it will be remineralized (consumed and metabolized) by organisms in the water column. If enough extra organic material makes it all the way to the deep-sea, it will bring with it more carbon than normally sinks, thereby 'sequestering' carbon that was drawn from surface waters by phytoplankton growth into deep waters. This leads to more carbon dioxide entering surface waters from the atmosphere, ultimately reducing the amount of extra CO2 in the atmosphere. This idea, 'iron fertilization' may or may not work, but if it does, it will increase the carbon dioxide levels in deep waters, as well as reducing oxygen levels, due to the remineralization of the extra organic material sinking to depth.
Will deep-sea ecosystems be affected by changes in ocean chemistry - either direct ocean CO2 injection or iron fertilization? Changes in ocean chemistry by the passive influx of carbon dioxide at the surface or through direct efforts to sequester carbon in the deep sea both have similar effects on ocean chemistry - increased carbon dioxide levels leading to greater acidity and lower concentrations of minerals important for shell and skeletal formation for a variety of organisms. Unlike surface waters, environmental conditions in the deep-sea are typically stable over large scales in space and time. Thus, organisms that inhabit the deep-sea have experienced only mild changes in conditions from day to day, and through much of their recent evolutionary history. In addition, the deep-ocean is a food poor environment compared to surface waters, and most species in these low food, mostly invariant conditions are expected to be far less tolerant of environmental change than related species in shallow waters.
Our laboratory uses a variety of experiments in the laboratory and in the ocean to examine how changing ocean conditions, mainly related to ocean acidification, affect the physiology and survival of marine animals. We use MBARI's remotely operated vehicles (ROVs) to collect animals live and bring them to the laboratory where we perform experiments to examine their physiological responses to higher carbon dioxide levels, or lower oxygen levels, or both. In addition, we develop in situ methods to study deep sea animals in the deep sea and measure their response to changing ocean conditions.
Simulated Deep-Sea CO2 Injection
The image above shows an experiment where we released liquid CO2 into small 'corrals' at a depth of 3600 m off the California coast to examine how nearby organisms would respond as the liquid CO2 slowly dissolved into seawater and drifted over the animals and seabed, bathing the organisms (like the deep sea eels and the octopus in the adjacent cage) in a CO2-rich, acidic plume. This experiment simulated direct deep-sea CO2 injection. Click here to see a short movie showing the corrals filled with clear liquid CO2, filling the corrals, and a variety of sensors and cages with animals scattered around at different distances from the CO2 pools. We also show the ROV collecting a sediment sample with a coring device, from which we examine the smaller organisms living in the surficial sediments.
In Situ Benthic Respiration System
In collaboration with the engineering group at MBARI, we have developed a 'Benthic Respiration System', used to measure rates of oxygen consumption of various marine animals. Oxygen consumption, or respiration, is related directly to the metabolic rates of organisms. Higher oxygen consumption indicates a higher metabolism. All of the activities of organisms are linked to their metabolism. Our system has 8 chambers into which we place individual animals collected using the ROV robotic arms and a small 'slurp gun'.
The image above right shows the BRS at 650 meters off the central California coast, and if you click the image or here, you'll see a movie of the BRS in action, so to speak, as we visit it using the ROV, collecting individual urchins (Strongylocentrotus fragilis - see below), and placing them in chambers. Once in the chambers, we close the lids and the experiment has begun. There is a stirring pump and an oxygen sensor in each chamber. We record oxygen levels every 5 minutes, which drops as the urchins consume oxygen (just think about being closed in a jar!). After a pre-programmed period (8 hours in this case), a flushing pump starts and refreshes the water in the jar with ambient water outside to avoid suffocating the urchins. We calculate the oxygen consumption rate by how fast the oxygen concentration drops, and correct it for the size of the animal. The flushing pump then stops and we begin another incubation period. This can continue for nearly a month, giving us many incubation periods for each animals. After a number of incubations to determine a 'baseline' respiration rate, we inject CO2 or O2 rich fluid into some chambers to alter the conditions and measure how their respiration rates change, if at all. In this way, we combine laboratory and field experiments to evaluate how deep and shallow living animals may respond to future changes in ocean conditions
Deep-sea "Fragile Urchin", Strongylocentrotus fragilis