Award: OCE-1220412

The impact of the increased absorption by the ocean of fossil fuel derived atmospheric carbon dioxide is one of the major present-day challenges in the ocean sciences. The steady absorption of carbon dioxide has led to a slow decrease in ocean pH with uncertain consequences to marine biota. This project supported a consortium, OMEGAS (Ocean Margin Ecosystem Group for Acidification Studies), of 13 Principal Investigators associated with six academic/research institutions along the California Current Large Marine Ecosystem (CCLME). The CCLME is subject to the phenomena of coastal upwelling where northwesterly winds act to draw water from depth, rich in the nutrients that drive photosynthesis, but also high in carbon dioxide and low in oxygen and pH. Coastal topography strongly modifies the coastal upwelling processes; coastline irregularities such as capes and bays produce variations in coastal wind, ocean currents, chemistry and biology. Strong upwelling at wind-exposed capes results in "upwelling centers", while in their lee, in bays or behind headlands, winds, upwelling and ocean currents are weaker creating "upwelling shadows". Strong gradients form between the freshly upwelled waters, low in pH, off a cape and the protected shadow waters behind the cape where photosynthesis is able to consume carbon dioxide and increase pH. The consortium research had two broad goals: 1) To understand the oceanographic drivers of the striking time-space variability in coastal pH documented previously in the CCLME and; 2) To link this pH seascape to the physiological and ecological performance of a key member of the coastal rocky intertidal ecosystem of the California Current System, the mussel Mytilus californianus. To address these goals the consortium: 1) Created a network of pH sensors from Oregon to Santa Barbara; 2) Tested the effects of varying pH on the growth, shell accretion, and resistance to predation of juvenile mussels collected from 10 sites spanning 1400 km of coastline; 3) Determined the physiological and genetic responses of field-deployed juvenile mussels that were subsequently exposed to varying pH conditions in a common garden experiment and; 4) Evaluated the linkage between basin-scale oceanography and local-scale variation in inner shelf oceanography to determine the relative influences of variation at these two scales on intertidal pH. As part of consortium MBARI (Monterey Bay Aquarium Research Institute): 1) Developed and built low cost autonomous pH sensors for deployment in intertidal locations from Oregon to Santa Barbara, 2) developed small, low cost moorings to measure pH, the partial pressure of carbon dioxide at the sea surface and in the atmosphere together with other standard oceanographic variables such as temperature, salinity, oxygen, chlorophyll fluorescence, and wind speed and direction; 3) Deployed these moorings and collected ancillary ocean acidity data from the intertidal to the California Current in the Monterey Bay region; 4) used a coupled ecosystem model to understand the processes driving variations in ocean pH along the US West Coast. Significant results from the MBARI work were: 1) Document large variations in pH along the US West Coast; 2) Determine that these variations were driven by both by the location of the site relative to upwelling centers and the CO2 but also by the content of the local upwelling source waters; 3) Determining that the CO2 content (and the pH) of upwelling source waters was strongly modulated by the decay of material at depth and its associated respiration; 4) Uncovering a strong and pervasive diel cycle in intertidal pH from Oregon to California; 5) Determining that this cycle was driven by photosynthesis (increase in day) and respiration (decrease at night) and; 6) Determining an exponential decay in the amplitude of the diel pH cycle with distance from shore in the Monterey Bay region. As part of the project we were able to demonstrate: 1) That it is possible to...