The Eastern Tropical Pacific Zonal Transect or ETPZ has 36 planned stations each sampling 12-36 depths – this puts the estimated sample total around 860. From each of these 860 sampling points, dozens of scientists collect water, some is analyzed in labs on board the ship and some is frozen in bottles that will be shipped back to the United States. Over the course of the next two months we will be collecting and analyzing thousands of samples! Team mercury will analyze 860 seawater samples for 4 different types of mercury on the ship and bring home some additional samples to work with back on land.
At each station there is a lot of activity, but in general there are three main sampling teams described below. Because we are collecting water for so many different scientists each team will deploy 2-3 casts at different depth ranges (shallow, mid-depth, deep), to collect enough water volume. I will add pictures throughout the cruise to help describe how each team operates.
1. GEOTRACES rosette
This team collects seawater for trace metal analysis. A trace metal is a metal dissolved in the ocean at concentrations less than 1 part per million (ppm). This means for every one million water molecules there is less than one metal molecule; it’s the aquatic version of finding a needle in a haystack. Because trace metal concentrations in seawater are so small, contamination becomes an issue. There is metal on the ship and in dust particles floating around in the air so this sampling teams takes many cautious measures to avoid contaminating seawater samples with metal from the surrounding environment. Mercury is a trace metal so my samples will be coming from this rosette; I will be busy analyzing samples throughout most of the cruise but will help out this sampling team whenever I have time.
2. Niskin rosette
Niskin bottles are used to collect seawater for nutrient analysis and other metals that are not prone to contamination. The deployment and recovery are similar to the GEOTRACES rosette but without the strict trace-metal clean procedures.
3. Particle pumps
Though often hard to see with the naked eye, seawater contains a lot of particles. These particles can be dust falling in from the air, sediment stirred up from below, or bits and pieces of biomass slowly decomposing as they sink to the ocean floor. Specialized pumps are deployed to collect these particles; 8 individual pumps are attached to a wire at intervals and lowered into the ocean. The pumps sit for about 4 hours and push seawater through filters that collect different particle size fractions. Each pump weighs about 100 lbs so this team does a lot of manual labor during their deployment and recovery.