23 October, 1996

Subject: Re: Journal 23 October 1996

Live from the Polar Duke in the Gerlache Strait

Location: 64.08S X 61.54W Wind Speed: 2.7 m/sec

Boat Speed: 0.0 knots Wind Direction: 123.1 degrees

Boat Heading: 337 degrees Barometer: 990.6 mb

Humidity: 62.6 % Air Temp.: -1.6 C

Salinity: 33.8 0/00 Water Temp.: -1.2 C

General Weather Conditions: Another beautiful day, I guess this is the reward for all the lousy weather that we endured at the beginning of the cruise. As you can see the barometer is holding steady in the 990 mb region, this is a good thing, high pressure usually indicates good weather conditions. The sun is so bright today that it hurts your eyes!

This is a post-diel day, which is generally a pretty quiet time on board. Most of us try to catch up on our sleep. Today I worked with Melissa on her experiment. I will discuss that with you tomorrow.

A few days back I discussed how measurements of photolyase, RECa and bacterial damage in the form of dimers or photoproducts is used to assess UV radiation damage to bacterioplankton. We are able to experiment with certain variables in order to determine the extent of bacterial damage at different times of day and at different depths.

These are some examples of the experiments:

1. Everyday a surface water sample is collected at 0600 and 1800, this sample is filtered and analyzed for photoproducts/dimers. This will give a good indication of damage over the course of the cruise and will be correlated with the ozone levels from each day. We should see a pattern emerge of low ozone days having the most bacterial damage.

2. During the diel surface water is collected every two hours over a 24 hour period. This water is filtered and analyzed for photoproducts/dimers, photolyase, and recA. When that data is analyzed we should see photolyase peak around mid-day, that is when the light activated repair would be most active. The RECa numbers should peak later in the day, when the sun sets and the 'SOS' network is implemented.

In addition, during a diel sampling day, water that is collected before sunrise is incubated in the large incubation boxes on the helo deck. This box is UV transparent and water is drawn out at six hour intervals and filtered. These filters will be analyzed for photoproducts/dimers, photolyase and recA. The purpose of this experiment is to compare populations that are being mixed in the water column with populations that are not mixed, such as on a flat calm day at sea. The water

at the surface is in constant motion, mixing with the layers below. The amount of mixing depends on the weather, a great deal of mixing occurs on windy days. The water in the incubation boxes is unable to mix, so we are able to assess the maximum amount of damage.

3. The in situ incubation boxes which are deployed at different depths (victory at sea boxes) are used to determine what patterns of photodamage are observed with depth. The amount of RECa and photolyase should vary according to depth. The boxes in the deepest water should have the least damage because the amount of UV radiation decreases with depth (refer to the discussion on the PUV).

The boxes are held at specific depths with no physical mixing occuring. In reality, physical mixing of the water column is dependant on weather conditions, but usually occuring to some degree. In order to compare the two and determine how mixing effects the distribution of DNA photodamage in the top ten meters of the water column, a depth profile is done immediately after the deployment and retrieval of the boxes. This is accomplished by simply dropping the pump to the same depths as the boxes and grabbing a 60 liter sample from each depth. These samples are also filtered and analyzed for recA, photolyase and photoproducts/dimers.

These are some of the most important experiments that we are doing. They are repeated several times over the course of the cruise to have sufficient data in a variety of conditions.

Thanks for all your mail, I hope to answer all of your questions before the end of the criuse.

Margaret Brumsted

NSF Teacher in Antarctica