Science at sea

With 32 scientists onboard, there is always a lot of activity at any hour of the day. At each station we have sampling teams – there are two different water sampling teams and one particle sampling team. The first water sampling team collects seawater in Niskin bottles, which can collect a larger volume and are handled with more lenient procedures. The water from these bottles is analyzed for nutrients, salinity and radio-isotopes that are less prone to contamination. The second water sampling team collects seawater in Go-Flo bottles. Water from these bottles is analyzed for very low concentrations of different metals (like mercury) that are prone to contamination, so extra caution is exercised. Seawater from Go-Flo bottles is filtered in a Class-100 clean van filled with particle free air.

The particulate sampling team deploys pumps that sit at a certain depth and push over 1000 liters of seawater through a membrane filter. As phytoplankton and organic matter break down in surface waters, they sink to the ocean floor transporting metals and nutrients. These particles are trapped on the filters which are later subdivided to different groups for analysis.  Many of the metals and nutrients measured on this cruise are present at such a low concentration that a large volume of sample is needed to do the analysis. Because so much water is needed, each sampling team has two casts, one that collects deep samples and one that collects shallow samples, in order to collect enough for everyone to do their work.

Some of the samples collected are frozen and transported to labs for analysis, but many of the samples are analyzed at sea. Elements such as mercury and iron, for example, can change chemically when stored and must be analyzed immediately after collection. The ship has a laboratory and four different vans (portable labs) to do analysis of mercury, iron, lead, aluminum, copper and zinc. Analyzing at sea can also reveal contamination issues that otherwise would go uncorrected without on-board analysis.

Purging seawater samples for mercury

I should also mention that we have rainwater and aerosol samples being collected as we are underway. When the ship is not steaming (in order to prevent collecting any fuel fumes), air is pumped through filters that collect dust. Near the US, dust collected is usually from an anthropogenic source (man-made), but as we move towards the western side of the basin close to Africa we often see dust from the Sahara desert. Both desert dust and anthropogenic dust are a source of metals to the ocean.

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