Calmer Seas Ahead
Yesterday morning I awoke to the sight of Unalaska Island off the stern of the R/V Oscar Dyson. We had sought refuge overnight within the protected harbor, waiting for the 40 knot winds offshore to die down. Around 2 pm, we set back out, and science resumed in seas that were still populated with 10-12 foot waves, not uncommon for the Bering Sea. You can imagine how challenging it is to measure out precise volumes of seawater and even just stay on your feet when the ship is rolling back and forth! Conditions today are somewhat improved with even a few breaks in the clouds, allowing little hints of sunshine.
I continue to learn interesting facts about fish larvae from our NOAA colleagues. One of the things that Morgan Busby finds so interesting about these creatures is that the larvae can look so completely unlike the adults.
For example, some of the cool larvae that he and Chrissy Jump frequently find in their Bongo nets are of Pacific Black Smelt (Bathylagus pacificus). These larvae have stalked eyes and are nearly translucent, looking almost nothing like the adults they will grow into. The amount of time a larval fish spends in the plankton also varies with species. Some will spend several months over winter in the plankton, while others will only drift to and fro about for a month or less. Once they settle out of the plankton, larvae undergo further development and become juveniles and, ultimately, adult fish.
We are back near the Unimak Pass area, and the amount of phytoplankton in our samples has plummeted, likely because of mixing caused by the winds that we were hiding from yesterday. This means that we need to concentrate up to half a gallon of seawater onto a single filter for some of the samples, leading to longer hours of filtering water samples from the Niskin bottles. In addition to carrying the Niskin bottles from which we collect water, the CTD rig is outfitted with many sensors which measure Conductivity, Temperature, and Depth (hence the name), as well as chlorophyll and light. We also brought with us a special sensor, a Fast Repetition Rate Fluorometer (FRRF) manufactured by Kimoto, which we affix to the CTD rig. The FRRF uses a rapidly flashing blue light to measure photosynthetic efficiency, or how well the phytoplankton in the water are able to use light from the sun and convert it to carbon. This efficiency can be impacted by many factors, and many phytoplankton show lowered efficiency when they do not have enough nutrients (e.g. nitrogen, phosphorus, iron) or when light is too high at the very surface of the ocean. The FRRF will provide us with information on how efficiency changes with depth and location, allowing us to determine if there are physiological differences in Spring blooms during warm v. cold years and with different dominant types of phytoplankton.
We had a little bit of fun a few days ago when we sent the CTD rig to 1000 meters (3300 feet). For every ten meters you go down into the ocean, you add about one atmosphere of pressure. So at 1000 meters deep, the pressure is about 100 times that on a boat at the surface. With so much pressure, things tend to get compressed, and to illustrate that we affixed some Styrofoam cups to the CTD rig for that station. You can see the difference a little pressure makes in the photos!
We are continuing to head northwest, sampling water every 4-6 hours and keeping our fingers crossed that the weather continues to improve. We are past the half-way point of the cruise, so it will be a hard push for the next 5 days as we try to maximize our time here in the Bering Sea!