Gina Henderson: Samples Aplenty, August 23, 2012

NOAA Teacher at Sea
Prof. Gina Henderson
Aboard NOAA Ship Ronald H. Brown
August 19 – 27, 2012

Mission: Western Atlantic Climate Study (WACS)
Geographical area of cruise: Northwest Atlantic Ocean
Date: Thursday, August 23, 2012
Weather conditions: calm conditions overnight leading to widespread radiation fog immediately following sunset. Ship had to make use of foghorn for a couple of hours overnight. Today, cloudy with possible rain showers. Winds SW from 10-15 kts, with gust up to 20 in rain showers. Seas from the SW at 3-5 ft.

Science and Technology Log

WACS Field Campaign Update:

This morning we reached the 3-day mark for sampling at station 1, which was in the high chlorophyll concentration off of Georges Bank. During these 3 days, we have been continuously sampling aerosols using both the Sea Sweep and the Bubble Generator (see last post for descriptions of each of these methods).

Some issues that have cropped up throughout this time are linked to our extremely calm and settled weather. Although the calm winds have made for minimal seas, ideal conditions for the Sea Sweep, those scientists sampling ambient air have been picking up ship exhaust in their measurements, despite the bridge keeping our bow head-to-wind. However, during our transit this complication should not be an issue and ambient sampling can take place continuously.

Conductivity, Temperature and Depth:

CTD rosette
Conductivity, temperature, and depth (CTD) rosette after deployment. Niskin bottles can be tripped at different depths for seawater sampling at various levels.

We also took a Conductivity, Temperature and Depth (CTD) profile using the CTD rosette on the 21st, collecting water near the bottom at 55m and other levels on the way to the surface.  These water samples were utilized by numerous scientists on board for experiments such as, testing for surface tension, biological testing and chlorophyll measurement.

The science plan for today involved one final CTD cast while at station 1, with all Niskin bottles being tripped at 5m. This large volume is necessary for a Bubble Generator experiment that will be run with this CTD water during the transit to station 2.

After the CTD cast was completed, the Sea Sweep was recovered and other necessary preparations for the transition to our new station. While underway for approximately 24 hours, intake hoses were switched to enable sampling of ambient aerosols along the way.

How to sample aerosols?

One of the tasks that I have been helping out with is the changing of aerosol impactors that are used to collect aerosol samples. These impactors consist of metal cylinders with various “stages” or levels (upper left photo below). Each level has different sizes of small holes, over which a filter is laid. During sampling, these impactors are hooked up to intake hoses where airflow is pumped through them and as the air is forced through the different “stages” or levels, the aerosols are “impacted” on the filters.

Filters being changed inside aerosol impactors (upper left). Picture of me unhooking impactors from inlet hoses for filter switching (upper right). Kristen just finished changing filters in a clean box (bottom).

This all seems simple enough…. However can be a little more cumbersome as the impactors are heavy, climbing up ship ladders with heavy things can be tricky depending on current sea state, and 2 of our impactor changes happen routinely in the dark, making things a little interesting at times!

Seawater sampling for chlorophyll:

Megan filtering raw seawater for chlorophyll extraction and measurement.

Another type of sampling I have helped out with involves the filtration of raw seawater to extract chlorophyll. This is done in the seawater van where we have a continuous flow of in situ water that is taken in at the bow at a depth of approximately 5m. This is done with two different types of filters, a couple of times a day. The photo below shows Megan running a sample through one type of filter, which will later be prepared with an acetone solution and after a resting period, be measured for chlorophyll concentration using a fluorometer.

Lots of sightings during transit:

As we headed south during our transit to station 2, we had an afternoon full of sightings! An announcement from the bridge informing us that we were now in “shark infested waters” sent an air of excitement around the ship as we all raced to the bridge for better viewing. Some loggerhead turtles were also spotted. Our final sighting of the day was a huge pod of porpoises riding the wake from our bow.

Pod of porpoises riding the bow wave during our transit south to station 2.
Everyone races to the bridge after an announcement about “shark infested waters!”

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