Friday, July 31, 2015

Burkolator on the Brown: Part II

We’ve completed our CTD operations for the 2015 Gulf of Alaska OA cruise, but the Burkolator is still running and will collect data all the way to the dock in Kodiak. With this truly groundbreaking system, we have been able to highly resolve the marine carbonate system over the course of this project. The figure below shows the saturation index for aragonite (a form of calcium carbonate; Ωarag) and the pH (pHT) of surface water measured as we traveled during our survey (July 14 – July 31, 2015). Blue shades in the saturation index are values where some juvenile shellfish may begin to feel stress from the ocean conditions. We’ve seen these conditions associated with freshwater input at various locations as well as possibly upwelling in areas around southeast Alaska and Kodiak. What is particularly interesting to me are the areas where these conditions caused by freshwater input differ in terms of  pH. In other words, freshwater decreases the saturation index for aragonite, but pH does not always follow this decrease. In the area around Icy Bay (marked on saturation index map), where there is a huge freshwater signal from the largest marine-terminating glacier on North America, the pH actually goes up! We refer to this as a decoupling between saturation index and pH, which is caused in this setting by glacial melt. This is a situation very unique to Alaska in comparison to other US coastal states, and is an important reason not to rely on pH measurements alone to track the occurrence of seawater conditions that may be harmful to marine life such as shellfish. 
2015 Gulf of Alaska OA cruise (July 14 – Jul 31) track maps of the saturation index for aragonite (top; Ωarag) and pH (bottom; pHT). For reference, Icy Bay and the Seward Line are marked in the saturation state map. Note that these data are preliminary and should be treated as such. For questions regarding these data, please email
Keeping our fingers on the pulse of changing chemical conditions in the Gulf of Alaska is a central goal for the UAF Ocean Acidification Research Center, for the Alaska Ocean Observing System and for NOAA’s Ocean Acidification Program. This trip has been the most extensive OA survey ever conducted in Alaskan waters, and was incredibly important for providing a broad description of conditions that allow us to add context to our long-term efforts on the Seward Line (marked in the saturation index map), in hatchery settings, and from our moorings.  These long-term efforts are incredibly important to resolve the pace of change in Alaskan coastal waters, and cruises such as this provide the broad brushstroke of measurements allowing us to compare and contrast well-resolved regions (Seward Line) with areas less-frequently sampled (Icy Bay). This cruise will hit the dock and the scientists on board will disembark, but the Burkolator will stay on board for the next leg up to the Arctic and then back to Seattle, providing an even broader snap shot of OA conditions around the state of Alaska. 

 - Wiley Evans

No comments:

Post a Comment