Contributed by Wiley Evans of the Hakai Institute:
Data collection on the Alaska Marine Highway ferry Columbia has been ongoing since late October 2017. The ferry runs a weekly roundtrip from Bellingham, WA to Skagway, AK, and over 145,000 measurements of seawater carbon dioxide content, dissolved oxygen, temperature, and salinity have been collected so far.
Currently I’m onboard to collect discrete samples to help validate relationships we apply to the ferry data in order to calculate the seawater pH and carbonate mineral saturations. This is the second such ride-along cruise, the first was in winter to capture data during the storm season, and this second cruise is timed to target the season of peak glacial melt entering the coastal ocean. We have roughly 6 weeks left of data collection before the vessel goes in for annual service and this first year of observation is complete, and we’ve learned a significant amount regarding the time and space variability of the surface ocean CO2 system along the ferry’s near 1000 nm transit.
Below, I highlight pH measured in each of the communities serviced by the ferry. During wintertime, conditions are similar between these communities, but during spring and summer, the seasonal increase in pH differs across these sites. Some sites, like Juneau, reach high pH levels (near 8.4) that are fairly sustained over many weeks due to the high productivity that occurs in the water column there, while others do not reach the same peak in pH (i.e. Skagway or Ketchikan). Also, there is a timing offset between when pH seasonally increases across some communities by as much as a month (i.e. Wrangell and Petersburg) even though they may be in relatively close proximity. The project aboard the ferry is producing a wealth of new information, and we look forward to a data release this coming winter.
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