Peter M. Walz

The annual cycle of iron and the biological response in central California coastal waters

Iron has been measured for 16 months with ∼21 day resolution at three stations in the upwelling ecosystem of central California, providing the first detailed assessment of the annual iron cycle in the coastal zone. A large pulse of iron occurs during the first spring upwelling event of the year. Iron concentrations then decay up to 100-fold over several months, although upwelling continues. Excess surface nitrate and low iron are the result during the summer and fall at the two stations furthest offshore (20 and 45 km), while nitrate is depleted and iron high nearshore (5 km). Phytoplankton biomass, primary production and community structure appear to be controlled by iron concentrations in offshore waters during this period.

Influence of Rossby waves on nutrient dynamics and the plankton community structure in the North Pacific subtropical gyre

Ocean Time-Series (HOT) Program’s Station ALOHA (22� 45 0 N; 158� W). Nitrate concentrations were determined with OsmoAnalyzers deployed at depths of 120 and 180 m. Deployments in 1997 and 1999 captured monthlong events that brought relatively cold high-nitrate seawater up into the euphotic zone. These events were correlated with negative sea surface height (SSH) anomalies measured by the TOPEX/Poseidon satellite altimeter. These nutrient injections at the Hawaii site were predominantly associated with first baroclinic mode Rossby waves. Elevated nitrate concentrations resulted in increased Chl a concentrations, increased primary productivity, and shifts in the phytoplankton community structure, as determined by HPLC analysis of pigment concentrations. The relative increase in pigments associated with phytoplankton that can grow rapidly and exploit nitrate (e.g., haptophytes and pelagophytes) coincided with the passage of Rossby waves in 1997–1999. A long-term combination of satellite remote sensing, moored instrumentation or remote vehicles and periodic ship-based sampling is needed to fully characterize the spatial and temporal variability due to the passage of Rossby waves and their associated biological responses. INDEX TERMS: 4556 Oceanography: Physical: Sea level variations; 4572 Oceanography: Physical: Upper ocean processes; 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling; 4815 Oceanography: Biological and Chemical: Ecosystems, structure and dynamics; 4894 Oceanography: Biological and Chemical: Instruments and techniques; KEYWORDS: nitrate, mooring, Rossby waves, phytoplankton, nutrient

In situ Raman‐based measurements of high dissolved methane concentrations in hydrate‐rich ocean sediments

Ocean sediment dissolved CH4 concentrations are of interest for possible climate-driven venting from sea floor hydrate decomposition, for supporting the large-scale microbial anaerobic oxidation of CH4 that holds the oceanic CH4 budget in balance, and for environmental issues of the oil and gas industry. Analyses of CH4 from recovered cores near vent locations typically show a maximum of similar to 1 mM, close to the 1 atmosphere equilibrium value. We show from novel in situ measurement with a Raman-based probe that geochemically coherent profiles of dissolved CH4 occur rising to 30 mM (pCH(4) = 3 MPa) or an excess pressure similar to 3x greater than CO2 in a bottle of champagne. Normalization of the CH4 Raman nu(1) peak to the ubiquitous water nu(2) bending peak provides a fundamental internal calibration. Very large losses of CH4 and fractions of other gases (CO2, H2S) must typically occur from recovered cores at gas rich sites. The new data are consistent with observations of microbial biomass and observed CH4 oxidation rates at hydrate rich sites and support estimates of a greatly expanded near surface oceanic pore water CH4 reservoir. Citation: Zhang, X., K. C. Hester, W. Ussler, P. M. Walz, E. T. Peltzer, and P. G. Brewer (2011), In situ Raman-based measurements of high dissolved methane concentrations in hydrate-rich ocean sediments, Geophys. Res. Lett., 38, L08605, doi: 10.1029/2011GL047141.

Deep ocean experiments with fossil fuel carbon dioxide: Creation and sensing of a controlled plume at 4 km depth

The rapidly rising levels of atmospheric and oceanic CO2 from the burning of fossil fuels has lead to well-established international concerns over dangerous anthropogenic interference with climate. Disposal of captured fossil fuel CO2 either underground, or in the deep ocean, has been suggested as one means of ameliorating this problem. While the basic thermodynamic properties of both CO2 and seawater are well known, the problem of interaction of the two fluids in motion to create a plume of high CO2/low pH seawater has been modeled, but not tested. We describe here a novel experiment designed to initiate study of this problem. We constructed a small flume, which was deployed on the sea floor at 4 km depth by a remotely operated vehicle, and filled with liquid CO2. Seawater flow was forced across the surface by means of a controllable thruster. Obtaining quantitative data on the plume created proved to be challenging. We observed and sensed the interface and boundary layers, the formation of a solid hydrate, and the low pH/high CO2 plume created, with both pH and conductivity sensors placed downstream. Local disequilibrium in the CO2 system components was observed due to the finite hydration reaction rate, so that the pH sensors closest to the source only detected a fraction of the CO2 emitted. The free CO2 molecules were detected through the decrease in conductivity observed, and the disequilibrium was confirmed through trapping a sample in a flow cell and observing an unusually rapid drop in pH to an equilibrium value.

A Review of Advances in Deep-Ocean Raman Spectroscopy

We review the rapid progress made in the applications of Raman spectroscopy to deep-ocean science. This is made possible by deployment of instrumentation on remotely operated vehicles used for providing power and data flow and for precise positioning on targets of interest. Early prototype systems have now been replaced by compact and robust units that have been deployed well over 100 times on an expeditionary basis over a very wide range of ocean depths without failure. Real-time access to the spectra obtained in the vehicle control room allows for expedition decision making. Quantification of some of the solutes in seawater or pore waters observed in the spectra is made possible by self-referencing to the ubiquitous m2 water bending peak. The applications include detection of the structure and composition of complex thermogenic gas hydrates both occurring naturally on the sea floor and in controlled sea floor experiments designed to simulate the growth of such natural systems. New developments in the ability to probe the chemistry of sediment pore waters in situ, long thought impossible candidates for Raman study due to fluorescence observed in recovered samples, have occurred. This permits accurate measurement of the abundance of dissolved methane and sulfide in sediment pore waters. In areas where a high gas flux is observed coming out of the sediments a difference of about ×30 between in situ Raman measurement and the quantity observed in recovered cores has been found. New applications under development include the ability to address deep-sea biological processes and the ability to survey the sea floor chemical conditions associated with potential sub-sea geologic CO2 disposal in abandoned oil and gas fields.

Use of a Free Ocean CO2 Enrichment (FOCE) System to Evaluate the Effects of Ocean Acidification on the Foraging Behavior of a Deep-Sea Urchin

The influence of ocean acidification in deep-sea ecosystems is poorly understood but is expected to be large because of the presumed low tolerance of deep-sea taxa to environmental change. We used a newly developed deep-sea free ocean CO2 enrichment (dp-FOCE) system to evaluate the potential consequences of future ocean acidification on the feeding behavior of a deep-sea echinoid, the sea urchin, Strongylocentrotus fragilis. The dp-FOCE system simulated future ocean acidification inside an experimental enclosure where observations of feeding behavior were performed. We measured the average movement (speed) of urchins as well as the time required (foraging time) for S. fragilis to approach its preferred food (giant kelp) in the dp-FOCE chamber (-0.46 pH units) and a control chamber (ambient pH). Measurements were performed during each of 4 trials (days -2, 2, 24, 27 after CO2 injection) during the month-long period when groups of urchins were continuously exposed to low pH or control conditions. Although urchin speed did not vary significantly in relation to pH or time exposed, foraging time was significantly longer for urchins in the low-pH treatment. This first deep-sea FOCE experiment demonstrated the utility of the FOCE system approach and suggests that the chemosensory behavior of a deep-sea urchin may be impaired by ocean acidification.

Microstructure characteristics during hydrate formation and dissociation revealed by X-ray tomographic microscopy

AbstractDespite much progress over the past years in fundamental gas hydrate research, frontiers to the unknown are the early beginning and early decomposition of gas hydrates in their natural, submarine environment: gas bubbles meeting ocean water and forming hydrate, and gas starting to escape from the surface of a hydrate grain. In this paper we report on both of these topics, and present three-dimensional microstructure results obtained by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM). Hydrates can precipitate when hydrate-forming molecules such as methane exceed solubility, and combine with water within the gas hydrate stability zone. Here we show hydrate formation on surfaces of bubbles from different gas mixtures and seawater, based on underwater robotic in situ experiments in the deep Monterey Canyon, offshore California. Hydrate begins to form from the surrounding water on the bubble surfaces, and subsequently grows inward into the bubble, evidenced by distinct edges. Over time, the bubbles become smaller while gas is being incorporated into newly formed hydrate. In contrast, current understanding has been that hydrate decomposition starts on the outer surface of hydrate aggregates and grains. It is shown that in an early stage of decomposition, newly found tube structures connect well-preserved gas hydrate patches to areas that are dissociating, demonstrating how dissociating areas in a hydrate grain are linked through hydrate that is still intact and will likely decompose at a later stage. FigureThe boundaries of a gas hydrate grain: excepting for the matrix (transparent, not shown), one can see tubular structures, pores from decomposition, and bubbles.

Creating Controlled CO 2 Perturbation Experiments on the Seafloor - Development of FOCE Techniques

Experimental recent progress on the design and testing of systems for carrying out controlled CO₂ perturbation experiments on the sea floor with the goal of simulating the conditions of a future high CO₂ world. Controlled CO₂ enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO₂ levels on vegetation, but only limited work on CO₂ enrichment on enclosed systems has yet been carried out in the ocean. With rising concern over the impacts of ocean acidification on marine life there is a need for greatly improved techniques for carrying out in situ experiments, which can create a DeltapH of 0.3 to 0.5 by addition of CO₂, on natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. This is no easy task. Unlike land based experiments where simple mixing in air is all that is required, CO₂ has complex chemistry in seawater with significantly slow reaction kinetics. Scientists must design systems to take this into account. The net result of adding a small quantity of CO₂ to sea water is to reduce the concentration of dissolved carbonate ion, and increase bicarbonate ion through the following reaction:CO₂+H₂O+CO₃^2- -> 2HCO₃ In practice the reaction between CO₂ and H₂O is slow and is a complex function of temperature, pH, and TCO₂, with the reaction proceeding more rapidly at lower pH and higher temperatures. Marine animals in the natural ocean will typically experience only small and temporary shifts from environmental CO₂ equilibrium. Valid perturbation experiments must try to expose an experimental region to a stable lower pH condition, and avoid large and rapid pH variability. The most common sensor used for experimental control is the pH electrode, and this detects only H+ ion, not any of the dissolved CO₂ species. We first explored the reaction kinetics of a CO₂ perturbation in a series of closed loop pH cell experiments carried out at various depths under ROV control. These were found to be well matched to the Zeebe & Wolf-Gladrow [1] model. From these results, functions for the delay time required for equilibrium were devised and a design for a delay loop to achieve at least 2 e-folding times between CO₂ injection and animal exposure was developed. We tested this prototype system in October 2007 in a series of ROV controlled experiments at a depth of 1000 meters. The working fluid used for enrichment was surface sea water saturated at one atmosphere with pure CO₂ gas to create a solution of about pH 4.8 and 56 mM total CO₂. This was carried to depth in a 56 liter piston accumulator, and dispensed as needed into a flexible polyethylene bag for subsequent addition into the experimental unit. The design consisted of a 4 meter delay loop leading to a control volume (square box, 25 cm per side) outfitted with three pH electrodes and a CTD. To determine the uniformity of the pH, two pH electrodes were positioned in the control volume and a third electrode was positioned just beyond the control volume in the flow stream. Ambient seawater, pumped at a desired rate with a modified thruster, was mixed at the beginning of the delay loop with controlled continuous injection of the CO₂-rich working fluid in a ratio typically of about 2001 depending on the pH perturbation desired. For these initial tests, a feed-forward system was used where flow rates of both the ambient seawater and CO₂-rich seawater were varied to produce a desired pH change. Future designs will incorporate a feedback loop to allow for automated precision pH control. These field tests were successful in showing that a plume of lower pH seawater could be accurately created and maintained in the deep ocean. The pH was reduced by up to 0.9 pH units from the ambient value of 7.8 covering well beyond the range of projected ocean pH scenarios for the next century. Near future goals will involve use of the MARS undersea cable recently deployed in Monterey Bay, California for power, communication and control, and a long-term experiment will be performed to demonstrate the operational feasibility of this technology for ocean acidification studies worldwide.pH electrodes and a CTD. To determine the uniformity of the pH, two pH electrodes were positioned in the control volume and a third electrode was positioned just beyond the control volume in the flow stream. Ambient seawater, pumped at a desired rate with a modified thruster, was mixed at the beginning of the delay loop with controlled continuous injection of the CO2-rich working fluid in a ratio typically of about 200:1 depending on the pH perturbation desired. For these initial tests, a feed-forward system was used where flow rates of both the ambient seawater and CO2-rich seawater were varied to produce a desired pH change. Future designs will incorporate a feedback loop to allow for automated precision pH control. These field tests were successful in showing that a plume of lower pH seawater could be accurately created and maintained in the deep ocean. The pH was reduced by up to 0.9 pH units from the ambient value of 7.8 covering well beyond the range of projected ocean pH scenarios for the next century. Near future goals will involve use of the MARS undersea cable recently deployed in Monterey Bay, California for power, communication and control, and a long-term experiment will be performed to demonstrate the operational feasibility of this technology for ocean acidification studies worldwide.

Engineering Development of the Free Ocean CO 2 Enrichment (FOCE) Experiment

Globally, the burning of fossil fuels for energy production produces over 25 gigatons of CO2 per year and this material is released directly into the atmosphere. While approximately half of the CO2 has remained in the atmosphere long-term, most of the rest has been absorbed by the surface ocean. This has resulted in a lowering of the surface ocean pH by about 0.1 units since the beginning of the industrial revolution and if society is able to stabilize atmospheric CO2 levels at twice their pre-industrial concentrations will result in a lowering of surface ocean pH by 0.25 units. While many are asking the question of whether we should pursue direct ocean CO2 sequestration, the FOCE experiment is asking what will be the impact of the pH change on the ocean. In order to address this question, MBARI science and engineering have designed a small-scale in situ CO2 enrichment experiment to assess the chemical and biological impacts in a manner analogous to the land-based Free Air CO2 Enrichment (FACE) experiments. This prototype design is testing the ability to control pH within a fixed but freely exchanging volume of sea water. The technology concept for the experiment is based on a small ring structure using a central valve to direct the flow of pH altering fluid. The initial phase of the project uses concentrated HCl mixed with sea water and includes directional and volume control to achieve a desired pH offset. Control feedback is obtained by using pH sensors in the center of the control volume. Other aspects of the design that address the inherent time delays and noise of the associated pH signal are also discussed. Test results will show the capability of the system to maintain close loop control of pH in a given volume. Sea trials then demonstrate the ability of this initial system at a selected site to control pH to specified average level over a given amount of time. Further discussion includes systems in-situ results analysis, corrective actions, upgrades, and the anticipated next phase for FOCE including the use of CO2 addition to change the local chemistry

Cabled observatory technology for ocean acidification research

The burning of fossil fuels for energy production has produced cumulative emissions on the order of 1 trillion tons since the beginning of the industrial revolution. While approximately half of the CO2 has remained in the atmosphere, the ocean is the predominant repository for the remainder of these emissions. This has resulted in a lowering of the surface ocean pH by about 0.1 units and, if society is able to stabilize atmospheric CO2 levels at twice the pre-industrial concentration, will result in a lowering of surface ocean pH by 0.25 units. While some researchers are asking the question of whether we should pursue direct ocean CO2 sequestration, FOCE technology enables scientists to ask what the impact of this pH change will be on ocean biogeochemistry and ecology. In order to address this question, MBARI scientists and engineers have designed apparatus that enable small-scale in situ CO2 enrichment experiments to be carried out, in a manner analogous to the land-based Free Air CO2 Enrichment (FACE) experiments. FOCE is a system that is configured around the science question(s) and is implemented to control pH within a fixed but freely exchanging volume of seawater. The technology uses control feedback and pH sensors to inject CO2 and create the future environment per science requirements. Other aspects of the FOCE design address the inherent time delays and natural background noise of the associated oceanic pH signal. We report recent progress on the design and testing of systems for carrying out controlled CO2 perturbation experiments on the sea floor with the goal of simulating the conditions of our future high CO2 world. Controlled CO2 enrichment (FACE) experiments have long been carried out on land to investigate the effects of elevated atmospheric CO2 levels on vegetation, but only limited work on CO2 enrichment on enclosed systems has yet been carried out in the ocean. With rising concern over the impacts of ocean acidification on marine life there is a need for greatly improved techniques for carrying out in situ experiments, which can create a ΔpH of 0.3 to 0.5 by addition of CO2, on natural ecosystems such as coral reefs, cold water corals, and other sensitive benthic habitats. The FOCE system is now full scale and installed in deep waters in the Monterey Bay Canyon. FOCE is connected to the Monterey Accelerated Research System (MARS) and enables scientists to control a variety of parameters while monitoring in situ ocean acidification experiments. This paper describes the enabling technologies for in situ ocean acidification experimentation. FOCE was originally designed for observatory science and cabled observatories in particular. This paper will discuss the technologies that enable observatory efforts in ocean acidification research. We also discuss the associated technologies that are useful to the greater science community in general. Furthermore the paper will conclude with the next phase of FOCE development and the exportation of the technology to a variety of ocean observatory systems. Details will outlined for a new FOCE system currently in concept design for installation on Heron Island as part of long term studies of the Great Barrier Reef.