The Columbia River is particularly important to unraveling the dynamics of coastal ocean acidification in the Pacific Northwest because it brings waters with elevated temperatures and oxygen concentrations and lower salinities, pH values, and aragonite saturation states compared to open ocean waters into the coastal environment. The Columbia River flows into coastal waters in a near-surface plume that acts as a source of corrosive waters to marine organisms that live in the upper reaches of the water column. The plume also serves as a barrier to the upward movement of the denser, more CO2-rich water upwelling from below. In late spring and early summer, the Columbia River plume waters are at their maximum volume and flow southward along the mid-shelf waters, forced by local winds from the northwest. In the wintertime the plume flows northward toward the Strait of Juan de Fuca due to the influence of winds from the south.
On Sunday, May 29, we begin our sampling run up the Columbia River near Astoria, Oregon. It is a warm, sunny afternoon when we start upriver during an ebb tide. Winds are light and variable, and the river flows briskly to the sea, as the sun glints off the waves. As we travel up the river, we watch sea lions jump on the navigation buoys to sun themselves in the warm air. A sea lion in the water barks at its compatriots on the buoy, as if to say to them, “Move over, I’m coming aboard!” The sea lions on top of the buoys eventually – almost reluctantly – adjust their position, and the sea lion in the water jumps up onto the buoy. Of course the buoy naturally tilts far to one side until all the sea lions are forced to move ever so slightly on their perch, just enough to rebalance it, and they return to basking in the sun with not a care in the world. Ahh, such a life!
The Brown finally reaches its first station just west of the Astoria Bridge, and we all begin our work. The survey technician on the deck tells the winch operator to lift the CTD/rosette package off the deck, position it over the water, and drop it just below the surface. Next, the CTD operator directs the winch operator to lower the package to a predetermined depth just above the bottom. This is a very tense time for us, as we cannot allow the CTD package to touch the bottom for fear that the delicate instruments measuring temperature, salinity, and pressure would be ruined. The CTD operator waits for about 30 seconds to let the water in the rosette bottles settle and triggers the firing mechanism, which automatically closes the bottles and captures a water sample. The CTD operator then tells the winch operator to raise the CTD/rosette package to the next shallower depth. This process of “tripping” the bottles at pre-selected depths is repeated again and again until all of the bottles have been closed, and we have a complete set of water samples to measure the distribution of physical, chemical, and biological properties throughout the water column. We repeat this process at several stations along the river in order to determine how the river chemistry is changing along our path. We will track the path of the Columbia River plume into the nearshore estuary and along the coast, studying its changing chemistry and biology along the way and conducting experiments with the animals and plankton that we collect there. We complete our work in the Columbia River right around dinnertime and go to the galley to eat a delicious meal of seafood while sharing our experiences of the day.