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by Lisa Robbins

Scientists from the U.S. Geological Survey (USGS) and the University of South Florida (USF) are working on an icebreaker in the Arctic Ocean during August and September 2011, continuing studies begun last year on Arctic Ocean acidification. Their findings will provide an important baseline of information about Arctic Ocean chemistry, which is likely to change in response to projected declines in summer sea ice.

Ocean acidification is the result of elevated atmospheric CO2 that has been mixed with oceanic surface water, resulting in lower (more acidic) oceanic pH. The lower pH, and a concomitant decrease in carbonate in the ocean, can lead to problems for biota such as calcifying phytoplankton and shellfish and, in turn, can affect the oceanic food chain. One of the most vulnerable and little known areas for ocean acidification on our planet is the Arctic Ocean.

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USGS scientists from the St. Petersburg Coastal and Marine Science Center in St. Petersburg, Florida, and their colleagues from USF in Tampa departed on August 15 from Barrow, Alaska, on the U.S. Coast Guard Cutter Healy for a 7-week expedition to the western Canada Basin and the northern Arctic Ocean. They are working side-by-side with other scientists on the Healy who are gathering data for the Extended Continental Shelf Project, a multiagency program to determine the extent of the United States' "extended continental shelf," where the nation can exercise sovereign rights over resources on and beneath the seabed according to the provisions of the Convention on the Law of the Sea.

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This is the second year in which scientists from the USGS and USF have conducted research on ocean acidification in the Arctic. In summer 2010, three geochemists were aboard the Healy in the Arctic Ocean for 5 weeks. During that cruise, water samples were collected continuously every 2 minutes by the Multiparameter Inorganic Carbon Analyzer (MICA), resulting in a remarkable +25,000 records of data on pCO2 (partial pressure of CO2), pH, and total dissolved inorganic carbon along ship's paths totaling more than 9,450 km. Such an extensive high-resolution dataset had never before been collected in the Arctic Ocean. Discrete water samples were taken every 2 hours throughout the cruise and analyzed onboard for pH, alkalinity, and carbonate (CO3-2). An additional 240 discrete samples were collected and subsequently analyzed in laboratories on land for carbon and oxygen isotopes, nutrients, and metals. Ten vertical casts (during which a sampling instrument is lowered from the ship to near the seafloor) using a rosette sampler were also performed, allowing collection of water from as deep as 3,500 m. This sampling device—a frame holding a circle, or rosette, of water-sampling bottles triggered remotely from the ship—collects water at prescribed depths throughout the water column.

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Data from the 2010 cruise in the Arctic Ocean are being processed for quality assurance and analyzed for trends and will be published in the USGS Data Series. Preliminary data were presented at poster sessions at the Alaska Marine Science Symposium in Anchorage on January 18 and at the American Society of Limnology and Oceanography (ASLO) Aquatic Sciences Meeting in Puerto Rico on February 15, 2011. The presentations met with enthusiastic responses as 3-D views of the Canada Basin carbon parameters were shown on an iPad mounted to the posters, enabling symposium participants to interact with the data. In particular, the data show the quality and high-resolution spatial information that this unique dataset provides. A synoptic view of the plotted data shows a continuous line more than 9,400 km long; zooming into an area reveals data points that were taken every 2 minutes and, consequently, the details of specific areas. These data show the overall trends and comprehensive structure of the carbon chemistry of seawater in the Canada Basin and, significantly, can be used for modeling the carbonate saturation state of this part of the Arctic Ocean. (Carbonate saturation state is a measure of the potential for a solution—such as seawater—to precipitate or dissolve calcium carbonate. The greater the saturation state, the more the precipitation of calcium carbonate is favored, and the easier it is for calcifying organisms to build their shells and skeletons.)

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In August and September 2011, USGS senior scientist Lisa Robbins, Chris DuFore (USGS), Brian Buczkowski (USGS), Paul Knorr (USGS), and Jonathan Wynn (USF-Geology) will be on the Healy, while Kim Yates (USGS), John Lisle (USGS), and Bob Byrne (USF-Marine Science) remain on land. The onboard Arctic team is using the same data-collection techniques as in 2010: running the MICA continuously to collect and analyze seawater every 2 minutes, collecting discrete water samples every 2 hours from the Healy's flow-through seawater system for onboard analysis, and using a rosette sampler to collect samples throughout the water column when the ship is stopped "on station." This summer, the Healy added a new pCO2 analyzer that is built into the flow-through sampling system, and the ocean-acidification team added an AFT (autonomous flow-thru) system (Sunburst, LLC) that also monitors pCO2. Because the 7-week cruise does not include scheduled "port calls" where broken parts could be fixed, the scientists are using these robust and redundant data streams as insurance against any system failing, with the added benefit of enabling inter-calibration and comparison of techniques. Using this sampling strategy, the scientists aboard the Healy are obtaining carbonate parameters, as well as pH, dissolved oxygen, fluorescence, salinity, temperature, and depth information, to gain a better understanding of the regional ocean chemistry in this rapidly changing environment. Equally important, a team back at the USGS center in St. Petersburg is working with the onboard team to monitor and analyze the Arctic data feeds and to analyze samples collected on the Healy when the scientists return from the field. This year, the ship is expected to reach more northerly latitudes than last year, which will provide the opportunity to collect data inside and outside of the Canada Basin—potentially as far north as the Lomonosov Ridge.

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For the first time, the ocean-acidification research-cruise team has an educational outreach blog on the USGS St. Petersburg Web site and is also posting information on Twitter and Facebook. Many local public and private elementary, high-school, and college students are following the cruise information feeds from home as well as from the classroom, allowing students and teachers a unique educational opportunity to see day-by-day how scientists live on a research vessel and collect samples and data in the field. Scientists at sea and at the USGS center are providing the information to the students by posting pictures and blog entries sent from the field. Student visits to the USGS office are planned for later in the year as an additional "meet the scientists" educational opportunity.