Long-term monitoring of O2 and pH in Alaska waters; a sentinel for global climate change and ocean acidification

Background and Objectives: The effects of global climate change and ocean acidification are expected to be more extreme at higher latitudes, such as in Alaska. Deep- coral and some sponge communities are especially susceptible to ocean acidification through reductions in calcification rates due to reduction in the available carbonate ions. Thus it is important to determine the rates of ocean acidification through monitoring pH and to determine shoaling and expansion of O2 minimum zones in order to predict and understand the effects of climate change on deep coral and sponge ecosystems.

Approach: The AFSC RACE Division annually conducts stock assessment surveys in Alaska ecosystems aboard chartered fishing vessels. These platforms provide an opportunity for low cost monitoring by instrumenting the bottom trawl survey nets to collect additional environmental data. We purchased two Aanderra oceanographic units that have sensors that collect depth, temperature, salinity, turbidity, pH and O2.

Significant Results to Date: Beginning in 2012, protocols for data collection were developed and the oceanographic equipment was deployed on bottom trawls in the eastern Bering Sea slope survey. Environmental variables were collected during 168 trawl hauls from Bering slope to the US-Russian border. In 2013, the environmental data was collected on 218 trawl hauls in the Gulf of Alaska and in 2014 data was collected on 300 trawl hauls in the Aleutian Islands.

Oxygen concentrations were higher in shallow areas of the eastern Bering Sea slope, but there were also some areas of low oxygen concentration in the middle of Pribilof and Zhemchug canyons (Figure 32). pH distribution followed oxygen very closely. Oxygen concentration in the Gulf of Alaska was highest in areas to the west of the Shumagin Islands the on the middle and inner shelf and was uniformly low in SE Alaska (Figure 32). pH was low in a band across the shelf near the Shumagin Islands and generally was low on the outer shelf elsewhere in the Gulf of Alaska (Figure 32). pH and oxygen varied spatially in the Aleutian Islands and also changed with depth. Both variables exhibited lower values on underwater banks (such as Petral Bank) and generally the two values appeared to be correlated. The highest concentrations of oxygen and the highest values of pH occurred in the central Aleutian Islands.

Environmental variables continued to be collected in 2015 and beyond. The on bottom environmental data is summarized annually and included in the Ecosystem Considerations Chapter of the Stock Assessment and Fisheries Evaluation documents provided to stock assessment authors and fisheries managers each year. In the future we plan to use these data to document changes in distribution of environmental conditions and model the effects on the distribution of deep-sea coral and sponge ecosystems.

Funding: Funding was provided by the DSCRTP to purchase two CTDs ($58,816) in FY12 and for calibration and modification in FY14 ($12,140).

Point of contact: Chris Rooper, AFSC-RACE Division, chris.rooper(at)noaa.gov

Rooper C., Stone R., Etnoyer P., Conrath C., Reynolds J., Greene H. G., Williams B., Salgado E., Morrison C., Waller R. & Demopoulos A.. 2017. Long-term monitoring of O2 and pH in Alaska waters; a sentinel for global climate change and ocean acidification. In “Deep-Sea Coral Research and Technology Program: Alaska Deep-Sea Coral and Sponge Initiative Final Report”, NOAA Tech. Memo. NMFS-OHC-2, pp. 46-47. Report.

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