The Main Players

When we get to stations, there is a 24 hour a day choreography of who can do their cast and when. Because we can only send 1 piece of equipment over the side at a time, it is important to be efficient in our work. Here on board, we have a large variety of equipment for the various types of samples we need to collect. There are 4 main players in this effort:

 

1. The GEOTRACES carousel (nickname Carlson): a frame equipped with a CTD (see post: 3 days in), transmissometer (water clarity sensor), altimeter (height above seafloor, so we don’t crash into it!) and spaces for mounting 24 GoFlo bottles (see post: 1 down, 34 to go!) which are used to collect highly contamination-prone samples. The GEOTRACES program is mainly driven to establish the baseline concentrations and to resolve the processes controlling extremely low concentrations of metallic elements (called trace metals or trace elements) in the oceans.

2. The standard rosette (nickname Rosie): this is a frame also equipped with a CTD, transmissometer, altimeter, and 12 very large Niskin bottles. These bottles are similar to GoFlo bottles, but are used to collect less contamination-prone seawater samples. For example, dissolved oxygen concentrations and nitrate isotope samples. This rosette is also able to carry a coring device down, so when it is close to the seafloor this device can grab seafloor sediments and bring them back up for analysis in the future.

3. The McLane pumps: these pumps are used to filter large volumes (~1500 L) of seawater while they’re still suspended from a wire in the water column. They have fine-grained filters which are used to trap small particles of living, dead, and non-biological “stuff”. After several hours of pumping seawater through them, they have accumulated a sufficient amount of particles and are brought back on board where a scientist retrieves the filter for future analysis.

4. The GeoFISH: this is our surface sampler, which is deployed most of the time and in action when we’re transiting between stations. Like a fish, it is towed / it swims alongside our boat and is capable of collecting seawater through a strong pump and what feels like miles of tubing plumbed into multiple shipboard lab spaces. It’s named the GeoFISH after Geoffrey Smith who built it and is responsible for it here on board.

In addition, there are a few other minor ops that happen at select stations, to be detailed later.

Today we arrived at our 7th station around 3:30 a.m. The GEOTRACES carousel was the first cast deployed with a goal of ~4,000m depth. After 1.5 hours it became apparent that our salinity sensor in the CTD was malfunctioning, and resulting in a bunch of other malfunctions. We’ve had a few minor glitches with it in previous casts, but this time the issue was so great that we had to abort and pull the bottles back to the surface. What’s so important about Carlson’s CTD sensor, especially when Rosie has one, too?

The ocean is a lot like your friend’s 7-layer bean dip at a Super Bowl party: each layer is unique, and occasionally too much of it can make you sick. The first cast of each station has the added responsibility of generating the basic hydrographic parameters (salinity, temperature, water clarity) for the whole water column, which is used to establish the ocean’s layers (and which depths the first 3 players above will collect their samples at). We like to sample at least one depth in each of the interesting layers of our water profile. Without the CTD data it becomes very difficult to differentiate

 the layers, and therefore pick the depths.

 

This is a photo of one of the plots (from when the sensors were all still working). You can tell that the very surface has a layer, there’s another unique one from 100 and 500 m, a transition layer from 500 to 2,000 m, and below that it seems to all be very similar.

While Carlson and the GEOTRACES team is temporarily delayed in deployments, Rosie and her team have jumped into action and generated the hydrographic parameters necessary for this station. Ops will continue until repairs are complete, and then the GEOTRACES group will get going again.