During the time in between large earthquakes, smaller seismic events, or microseismicity events have been detected along the Cascadia plate boundary. This microseismicity represents the accommodation of small stresses along the margin, and may provide information on the location of high stresses or zones of weakness in the crust and upper mantle, or along the plate boundary. Studying the distribution of microseismicity and comparing it to known structural models based on seismic reflection profiles may help us to better understand the overall faulting process at subduction zones. In this research, I compared the spatial distribution of microseismicity along different parts of the subduction zone with structural features from seismic reflection images. I used earthquakes dataset that are recently compiled using regional seismometer located within the subduction zone as part of the Cascadia Initiative. I presented a depth profile of Cascadia subduction zone forearc, a margin between the oceanic trench and the continental plate, to investigate whether current depth estimates for recent earthquakes are more consistent with upper plate seismicity within the North America Plate, along the plate boundary, or within the down going oceanic plate. The results of this study will help us to better visualize the spatial distribution of microseismic events and draw its relation with the damage zone or other fault structures along Cascadia subduction zone.

Ocean acidification is projected to put coral reefs in a state of net dissolution by the end of the century. Coral reef ecosystems are important habitats, supporting 25% of marine biodiversity in less than 0.1% of its surface area. As humans continue to burn fossil fuels, adding CO2 to the atmosphere and oceans, local mitigation approaches become increasingly important to consider for preserving these vital ecosystems. Bubble stripping is a geoengineering approach to ocean acidification that has been modeled and tested in the laboratory as an effective means of enhancing air-sea gas exchange in coastal ecosystems. Bubbling of CO2-deplete air through the water column allows dissolved CO2 to diffuse into the bubbles and, ultimately, the atmosphere. Bubbling is strategically timed to occur at night, when organisms are respiring and CO2 is not removed by photosynthesis. By increasing the rate of air-sea gas exchange, the ocean and atmosphere equilibrate such that concentrations of CO2 do not reach the extremes that would otherwise occur in the water column. In this study, we used airstones (bubble diffusers) and a test tank to confirm the results of an earlier bubble stripping experiment. Bubbling increased pH and decreased dissolved inorganic carbon (DIC). Its effectiveness could be optimized by testing parameters like bubble size, air flow rate, and water column height. However, obtaining and expelling compressed air is an energetically expensive process, so bubble stripping would likely be useful only for stabilizing seawater chemistry in specific, small sections of reef.

As general circulation models (GCMs) increase in complexity, the number of physical processes representing the climate system increases. A central goal of climate science is to understand how uncertainty in these physical processes, translates into uncertainty in the system response. But the very complexity of the GCMs generates a troublesome question: how do you properly define a stable and unchanging reference system with which to compare constituent elements and characterize their uncertainties? To navigate around this, we introduce a simple energy balance model (EBM) that accounts for the transport of both sensible and latent heat in the atmosphere. We demonstrate that the EBM accounts for approximately 90% of the inter-model spread in the temperature response for an ensemble of GCMs subjected to increasing CO2. We then calculate the unique model patterns of ocean heat uptake, radiative forcing, and radiative feedbacks and demonstrate that 100-years after an abrupt quadrupling of CO2 above preindustrial values, the largest source of uncertainty is the pattern and amplitude of radiative feedbacks. Using this, we identify regions of high feedback uncertainty and show how this can bias temperature responses in other regions.

Diatoms are small photosynthetic organisms that are important in global carbon fixation and help provide a base to the oceanic food web. Viruses are known to play a role in the overall life and death of diatoms but the extent of this role is not fully understood. A previous member of the Rocap laboratory has isolated a virus (PmDNAv) known to infect diatoms of the species Thalassiosira pseudonana. This virus is infectious in six out of the seven cultured strains kept in the lab; a seventh, CCMP 1012, is resistant. Each of the seven strains has a microbial community that propagates with the diatom cells as they are kept in culture. I hypothesized that the T. pseudonana CCMP 1012 was able to survive the viral inoculation because a beneficial microbe absent in the other strains was able to confer viral resistance. To test this hypothesis, I confirmed the previous results that showed viral resistance in the CCMP 1012 strain and susceptibility in another cultured strain. I then treated the diatoms with antibiotics to remove the microbial community. With the newly microbe free CCMP 1012 culture I performed infection experiments to test if the axenic strain would behave similar to the nonresistant strains and die, or if it would remain resistant to the virus. When the microbial community was removed from the previously resistant CCMP 1012, the strain was susceptible to viral infection. The most likely explanation was that the microbes were conferring resistance to the diatom strain. This implies that microbial interactions can lead to drastic changes in the dynamics at the base of the food web. Future work includes experiments questioning if the microbial community from the resistant strain can confer viral resistance to other strains and analyzing how the microbial communities differ genetically among resistant and susceptible strains.

Current studies have shown that changing climate is responsible for methane releases from the seafloor, making it important to understand how methane plumes can impact the ocean. Methane plumes impact the stratification and circulation within the water column which can influence primary productivity and seawater chemistry and potentially atmospheric greenhouse gas levels if the methane from the plume undergoes exchange with the atmosphere. Along the Washington margin there has been over 1772 individual bubble plumes located and identified in depths ranging from 40 meters to 1988 meters water depth. Compilation of archived CTD (conductivity, temperature, depth) data at active methane plume sites including Southern Hydrate Ridge, Grays Harbor, and Vancouver Island, can provide estimates of the plume fluids temperature and salinity. Using these estimates, the point where buoyancy reaches zero determines the possible depth of horizontal plume fluid intrusion into the water column and the entrainment coefficient to quantify the fluid that’s entrained by the plume can be calculated., I can determine the plumes’ ability to penetrate through sea water density interfaces such as the thermocline by calculating the Richardson number for the plumes. Using pre-established bubble models, I will also quantify sea water entrainment by the plumes. Through these methods, I will be able to determine how methane plumes impact water column stratification on the Washington Margin.

The ARGO float program consists of over 3,000 profiling floats that are free drifting and take temperature and salinity measurements of the upper 2000 meters of the ocean. Understanding why these floats are failing prematurely in the field is important to ensure the longevity of floats in the future and the overall effectiveness of the ARGO array. In this investigation I looked primarily at floats deployed by the University of Washington since 2005 to determine the success rate and identify problems in the floats deployed by our lab. This was accomplished using engineering data communicated back from the floats which includes the piston position, which is used to control the density of the float, battery levels, pressure sensor readings, as well as temperature and salinity readings. Each float also has an associated energy budget model which was used to calculate the number of expected profiles based on the batteries powering the float. Preliminary results have uncovered a significant number of floats having a gain in buoyancy, followed by a sudden and catastrophic buoyancy loss, and soon afterwards, float failure. Based on what we observed on a shoaled float with corrosion around the endcaps, we believe this loss in buoyancy is due to corrosion. A float which showed similar buoyancy trends was recovered and also had significant corrosion around the endcaps, confirming that we are able to identify corrosion using engineering data. Energy budget models have identified that most floats will achieve approximately 80% of their expected lifespan, which is considered a successful float lifecycle. Having reliable methods to identify failure modes using only engineering data will enable us to remotely diagnose problems with a deployed float and correct those issues for floats we deploy in the future, extending the life expectancies of floats in the future.

The California Current region encompasses a gradient between coastal upwelling and oligotrophic offshore zones, where the phytoplankton biomass is dominated by species of large and small celled phytoplankton, respectively. Mesoscale eddies are ubiquitous in the mixed region between the coastal and offshore zones, and they mediate the offshore transport of coastal waters. Mesoscale eddies are known to trap and transport water masses and their associated biogeochemical signatures, acting much like traveling mesocosms. It is unclear to what extent phytoplankton communities are trapped by the eddies, and how much they mingle with the communities found in the surrounding waters. In this study we characterized the phytoplankton community structure found within three mesoscale eddies, two cyclones and one anticyclone, using flow cytometry and 16S and 18S tag sequencing. We tracked the age and region of formation of the eddies from sea surface height. The two cyclonic eddies were formed in the same region, but at different times, C1 was 22 days old and C2 was 214 days old at the time of sampling. The anticyclonic eddy, A1, was formed further to the south and was 19 days old at the time of sampling. We assess to what extent the phytoplankton communities within each of the eddies are distinct from their surrounding waters, differ from each other, and how much the phytoplankton communities vary within each of the eddies with distance and depth. Our results show that the phytoplankton community is structured, to first order, by the physical environment, such that the phytoplankton metacommunities differ between eddies. However, we also see finer scale features with community changes within and across the eddies. These deviations reveal patchiness in the communities likely driven by corresponding local patchiness in nutrient and trace metal concentrations.