NOAA Teacher at Sea
Aboard NOAA Ship Fairweather
June 5 – 26, 2017
Mission: Hydrographic Survey
Geographic Area of Cruise: Southeast Alaska – West Prince of Wales Island
Date: June 17, 2017
Weather Data (on day of bottom sampling –June 14th)
Wind: 27 knots from the west (110° true)
Visibility: 10 nautical miles
Barometer: 1005.3 hPa
Air temperature: 9.4°C
Cloud: 100% cover, 1000’
Science and Technology Log
If you have ever taken a look at a nautical map, other than just depths listed on it, there will be symbols and definitions that provide information to help with safety and knowledge of the area. For example, asterix-like symbols represent rocks, and a branch-like symbol represents kelp. Also written on the maps is information about the seafloor and what it is composed of, such as gravel, sand, or bedrock. Here in southeast Alaska, off the coast of Prince of Wales Island, much of the data that is currently on the charts was collected over 100 years ago. Fairweather’s mission is to collect new information to allow these charts to be updated, and this includes information on the seafloor too.
The other day I was tasked with joining a survey crew to conduct bottom sampling. The assigned bottom sample locations are provided by the Operations branch at headquarters. The sheet managers adapt the locations if they think there are better locations that will provide information for anchoring or to help characterize different regions in the area. With less than glassy water conditions on a windy and rainy day, the boats were launched and we moved to our first sample area.
The technology behind sampling is a little more antiquated than other parts of the research I’ve seen. It involves hooking up a self-closing scoop like device to a rope, and lowering it in to the water until it hits the seafloor. Ideally, the trigger is released when it hits the seafloor and it closes. With closed scoops, the bottom sampler is winched up, ideally full of whatever material is located on the seafloor in that immediate location. There were three different styles of these bottom samplers and we quickly had a firm favorite that seemed to work the best. Easing the boat in the swell to the location, the coxswains, Dennis and Denek, would keep the boat in position so we did not tangle the rope in the motor. We could tell from the rope going slack when the bottom sampler had hit the sea floor, and a mechanical winch made the return journey easy.
Dumping the contents in to a bucket we were able to see the diversity of the seafloor in just a few samples. Occasionally rocks or shells would get stuck in the mechanism and we’d have to repeat the procedure, but overall we had tremendous success.
There are international protocols to follow in collecting bottom samples. These allow for communication and consistency of data on navigational charts. In general, the main medium of the sample is described, such as sand, mud or pebbles, and an adjective used to describe it, such as broken, sticky or soft. Color is also assigned to the sample as well as appropriate size of the grains (fine, medium or coarse). Symbols are used for all this data: For example, ‘the sample is mostly fine brown sand with mud and a little bit of broken shell’ would be written fne br S M brk Sh. Protocols indicate that if sampling is attempted three times in one location and it doesn’t work then ‘unknown’ is documented in that location.
At each of the sampling locations, we marked the spot on the chart and took latitude and longitude coordinates. We also documented additional observations we had about the sample, including findings that were not included as data choices. For example, in our second sampling site we found what we thought initially were mammal hairs. Several sites later we struck ‘gold’ again, finding what appeared to be more hairs in a mud matrix. Upon reflection and discussion, it’s possible they are more likely decomposing kelp fibers. It would be interesting to have the samples analyzed to identify what these fibers/hairs come from. We also found whole clamshells as well as having a sample that only contained water. Our thoughts with the water only samples were that perhaps we were hitting bedrock rather than failing on obtaining any kind of sediments. We also observed that in the more sheltered bays, the samples were very odiferous dark mud. In both of these occasions, the landscape surrounding the bay was heavily logged, and it would be interesting to see if there were correlations between the logging and the dark sediments, perhaps containing higher levels of carbon material washed in from terrestrial sources. In one of these areas, documentation from 100 years ago suggested that at that time, the seafloor was gravel.
The bottom-sampling day was challenging day weather wise, both for the coxswains and the science crew, but very rewarding. Due to the rough seas it wasn’t a good day to collect sonar data, and on days like this, other parts of the total data collection are put in to place. Part of our work that day was to also do crosslines (sonar data verification) but the water conditions were too hazardous in certain directions of travel, and so it was decided that we should focus on bottom samples. To be frank, this was my favorite day as a Teacher At Sea so far. Truth be told, I was reminded that I quite enjoy sticking my hand in a bucket of mystery ‘goop’ and trying to figure out what it is composed of. The diversity of samples was completely surprising and finding hair samples, twice, completely intriguing. It was great also to observe upcoming OPS officer, LT Damian Manda at work logging the data, and realize again, the role technological knowledge plays a role in the success of this research. And, thank you to Coxswain Dennis Brooks for taking most of the photos for this blog entry.
Word of the day:
Hollings Scholarship Program: this NOAA program provides undergraduate students with a ten week internship at a NOAA facility and academic assistance, as well as an orientation and symposium. For more information: http://www.noaa.gov/office-education/hollings-scholarship
Fact of the day:
Backscatter is the intensity of acoustic energy received by the sonar after interacting with the seafloor. Backscatter data can be used to help determine the surface of the seafloor. In softer areas, perhaps a surface of mud, returns a weaker signal, but a harder surface, such as bedrock returns a stronger signal. Hollings scholar Carly LaRoche from American University is on the boat for several legs this summer and is collecting and analyzing backscatter data in the area. Bottom sampling of the area is allowing Carly to compare the backscatter data with the sediments collected to see if there are correlations.
What is this?
(Answer from previous blog: part of the vertical struts of an old pier at a former salmon canning factory.)
Acronym of the day: Used in bottom sampling
NATSUR: Nature of surface -example: mud, gravel, coral
NATQUA: Qualifying terms for NATSUR -example: sticky, soft, calcareous