About: 2015 Expedition

The U.S. GEOTRACES Arctic Expedition

aboard the USCGC Healy (HLY1502)

August 9-October 12, 2015

Over the past few years prior to the expedition, members of the scientific community have planned the U.S GEOTRACES Arctic Expedition (Figure 1), and it is finally scheduled to begin on August 9, 2015. The research vessel/icebreaker that will be used to complete the expedition is the U.S. Coast Guard Cutter Healy, having the cruise number 'HLY1502'. When the Healy is not breaking ice in the Arctic, it has the homeport of the U.S. Coast Guard base in Seattle, Washington. During one week in June, cruise participants flew to Seattle to load the Healy with scientific equipment and secure lab spaces (see Resting Easier), while the Coast Guard loaded the ship with food and other essential items. Since June, the Healy has embarked on its first research cruise of 2015 (cruise number HLY1501) that ends in Dutch Harbor, Unalaska, Alaska in late July, prior the arrival of HLY1502 cruise participants. During the first few days of August, approximately 50 scientists, students and technicians will fly to Dutch Harbor to finish preparations before the Healy embarks on the 65-day cruise.

Figure 1. The intended (see A turn in the left direction) northbound and southbound routes of HLY1502. The cruise begins and ends at Dutch Harbor on the island of Unalaska, Alaska, and will reach the North Pole sometime in the middle of September.

The objectives of the different scientific groups involved in HLY1502 are to collect and analyze seawater, ice, snow and air samples along the cruise path (Figure 1), in accordance with the goals of the GEOTRACES program, while also including some Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) stations. GEOTRACES is an international program that focuses on understanding the marine biogeochemical cycles of traces elements and their isotopes. GO-SHIP is also an international program, however, its goals are to investigate ocean circulation and the oceanic carbon cycle. In essence, both programs study marine biogeochemistry, with the overarching goal of understanding and addressing the ocean's sensitivity to change. In the Arctic, where warming and environmental change are apparent (see Arctic News), research such as that conducted during HLY1502 is necessary for understanding the Arctic climate and Earth's sensitivity to change.

To accomplish GEOTRACES and GO-SHIP scientific objectives, sampling will be carried out in the Bering Strait, Chukchi Sea, the Canada Basin and the Makarov Basin (see Figure 1 and About the Arctic Ocean). The majority of samples to be collected are seawater samples, which will be collected using Niskin bottles, pictured around a rosette in Figure 2. Niskin bottles are essentially plastic tubes with caps on both ends and a sampling nozzle, which are held open by spring-loaded lanyards, triggered to close (collecting seawater) at desired depths throughout the water column. For the most part, depths are determined prior to arriving on station locations, but sometimes depths are determined based on features identified in the water column. These features are identified by using Conductivity (how salinity is measured), Temperature and pressure (or Depth) sensors that relay CTD data back to the ship.

Figure 2. A rosette being deployed on station in the Ross Sea, Antarctic on February 19, 2013, about to do a vertical cast.

At typically stations, rosettes equipped with a CTD sensor package and 24-36 Niskin open bottles are lowered to the bottom of the ocean by a conductive wire (pictured in Figure 2), which is connected to a CTD display screen and control panel onboard the ship. Once the rosette reaches the bottom of the ocean, it is raised to the desired depths, and the Niskin bottles are closed as it moves upward on its way back to the ship. The reason why bottles are closed on the rosette's way up—rather than on its way down—is because there is enough pressure at the bottom of the ocean to destroy closed bottles by crushing them! Lowering and raising a rosette on station is illustrated in Animation 1.

Animation 1. A research vessel stopping on station, lowering and raising the rosette to sample the water column (and smoke plume), before moving to the next station to repeat the process (animation from NOAA). This routine (other than sampling smoke plumes) will be carried out many times during HLY1502.

Some of the measurements that will be made include full-depth vertical profiles of salinity, temperature, oxygen, nutrients (nitrate, phosphate and silicate), currents, pH, total alkalinity, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and nitrogen (DON), and chlorofluorocarbons (CFCs), iron (Fe), zinc (Zn), cobalt (Co), arsenic (As), selenium (Se), copper (Cu), and mercury (Hg) and many other elements, while autonomous measurements will also be made as the ship is underway, measuring surface temperature, salinity, partial pressure of carbon dioxide (pCO2), air-sea fluxes, bathymetry, navigation). Sounds like a lot, doesn't it!