Introduction
As I previously conveyed, the Fall mooring survey is an annual survey that focuses on deploying and recovering oceanographic moorings and collecting ship-board biophysical samples at and between those mooring locations. Measurements from the survey provide baseline fisheries and oceanographic data to support modeling efforts and ongoing management of our nation's fisheries and marine life in the Gulf of Alaska, and the rapidly changing Bering Sea. In this final post about the survey, I invited my colleague Heather Tabisola to share more about the other aspects of the survey that I didn't cover in my first two posts. This post will focus on the oceanographic research of our long-time partner in EcoFOCI, NOAA’s Pacific Marine Environmental Laboratory, and work by the Alaska Fisheries Science Center Marine Mammal Laboratory.
Biophysical Oceanographic Moorings
The EcoFOCI moorings provide the pulse of Alaska’s ecosystems for the last 20-30 years. The primary goal of this survey was to recover 18 and deploy 17 biophysical moorings (aka. large floats, with scientific instruments distributed below, and anchors at the sea floor), sample dozens of predetermined locations, and recover an uncrewed glider. One mooring (M2) has a surface buoy, an above water platform that allows surface and atmospheric measurements (e.g., air temperature, humidity, CO2) to coincide with the water column measurements. This was the 30th consecutive year M2 was deployed in the southeast Bering Sea. Scientists observed a deeper surface mixed layer in 2024, most likely from the persistent storms in the region, which resulted in lower sea surface temperature. In addition, a strong fall phytoplankton bloom began in late August. Understanding where heat is in the ocean and the food availability will help fisheries managers better understand how to apply stock assessment recommendations.
Real Time Forecasts & Science Operations
Conducting research in Alaska, even during the ice-free summer months, can be harsh and unwelcoming. A few intense storms passed through the survey region, but the team largely managed to avoid those storms and continue working. Only once did the team need to wait out weather, in the gorgeous setting of the Shumagin Islands.
Uncrewed Systems
An ocean glider was deployed on August 7 from the R/V Sikuliaq. Over the month it was collecting measurements and the glider completed just more than 1,700 dives. Unfortunately, hours before recovery, the land team lost communications with the glider and it was lost at sea. Data from the glider is displayed in near real-time, so the team did not lose all of the collected measurements. Similar to the M2 mooring, scientists observed a deeper surface mixed layer and two chlorophyll blooms—one at the mixed layer and another at the surface. This information is essential to understanding how the ecosystem is primed for species that need food over the dark, not-as-productive winter months. Uncrewed systems can enhance our observational capabilities to provide scientific basis for the North Pacific Fisheries Management Council and in the Ecosystem Status Reports.
Water Samples using a CTD Rosette
During a water column profile cast of the CTD (conductivity, temperature, and depth instrument), Niskin bottles are closed at select depths. When the CTD returns to the ship, the sea water collected is sampled for chlorophyll-a and other oceanographic parameters. Samples can be frozen, preserved and filtered depending on the measurement. Some samples are are processed and analyzed on board the ship instead of returning to the land-based laboratory for post-field work analysis. This time around, the teams on board conducted a total of 96 deployments (or casts) of the CTD. The team got some extra unexpected CTD transects in the Shumagin Islands, Shelikof Strait (where it all started!) and Kennedy Stevenson entrances. These measurements will help us better understand how much and how fast water is moving through the region, the nutrients it brings and the water properties in those areas that eventually make their way from the Gulf of Alaska and flow through passes into the Bering Sea.
Passive Acoustic Moorings
Thirteen passive acoustic recorders were serviced during this cruise. Eight are on individual moorings and others are co-located on EcoFOCI moorings, to record ocean sounds, specifically whales, during the year the mooring is deployed. Passive acoustic devices do not emit sound but instead quietly listen using an underwater microphone, or hydrophone. A passive acoustics hydrophone records noises made by marine mammals, fish, invertebrates like shrimp, ships, ice, wind storms, rain, earthquakes, seismic activity, and any other noise source. Low frequency noises (such as fin and blue whale calls) can travel great distances, while high frequency noises (such as killer whale clicks and whistles) decay rapidly away from their source. At each mooring site, the recordings occur for about 6 hours per day through the whole year. All sounds in these recordings will be formally analyzed back in Seattle. At sea, the team checks to ensure the instrument recorded data successfully, downloads the data to make a secure copy, and prepares the instrument for its next deployment. Marine mammal biologists at the Alaska Fisheries Science Center use this information to monitor whale behavior, distribution, and movements in Alaska marine ecosystems.
eDNA
Since 2020, Pacific Marine Environmental Laboratory scientists have maintained seawater environmental DNA (eDNA) time series in the U.S. Arctic region. eDNA refers to the genetic material that organisms leave behind in the environment when they shed their skin, release mucus, etc. We use eDNA to examine the regional biodiversity of microbes, phytoplankton, zooplankton, fishes, mammals, and much more. With academic partners, the eDNA will also be used to further study harmful algal blooms (HABs) diversity and presence in the region.
During this survey, the team filtered 110 eDNA water samples collected from CTD Niskin bottles. In addition to these efforts, since the summer of 2023, an autonomous eDNA sampler at site M2, collected samples every 2 weeks for an entire year. The sampler was recovered in August; it had quite the journey before returning underwater. First the unit traveled from Nome, Alaska to Dutch Harbor, Alaska, but flight delays meant it missed the boat. The NOAA Ship Oscar Dyson returned to Dutch Harbor a few days after sailing, and the amazing crew were able to snag the sampler with a small boat. Upon receiving the unit, we quickly learned the unit was malfunctioning and kept turning itself off. With the help of the ship’s Chief Engineer (a true MacGyver), foam ear plugs, and some new springs, a solution was found just 3 hours before the unit was successfully deployed!
Harmful Algal Blooms
EcoFOCI has partnered with the NOAA Northwest Fisheries Science Center and Woods Hole Oceanographic Institute, collecting at-sea water samples of particulate domoic acid, as well as specific zooplankton samples at a subset of stations throughout the Bering Sea. Harmful algal blooms in the U.S. Arctic can pose a threat to food security and public health. Samples will be used to quantify cell densities of two harmful algae species (Pseudo-nitzschia and Alexandrium species) and concentrations of the corresponding algal toxins (domoic acid and saxitoxin) in multiple trophic levels in the food web in Arctic and subarctic waters of Alaska. Sampling of trophic levels includes phytoplankton, zooplankton, sediment, shellfish and planktivorous fish, as available. This naturally occurring marine biotoxin, domoic acid, can cause illness and death in humans, marine mammals, and birds.
Ocean Acidification and CO2
The long-term monitoring site M2 in the Bering Sea is not only measuring the pulse of the Bering Sea using biophysical sensors, but is also part of the National Ocean Acidification Observing Network. The University of Alaska Fairbanks Ocean Acidification Research Center (UAF-OARC) maintains a system observing surface seawater carbon dioxide at M2. In 2024, the surface sensors were deployed after the onset of the spring bloom and seawater carbon dioxide was lower than atmospheric carbon dioxide for the duration of the deployment. This fits in well with previous year's data showing on average, the surface ocean in the Bering Sea is a sink to atmospheric carbon dioxide. This critical monitoring informs our understanding of regional ocean carbon variability and marine ecosystem sensitivity to ocean acidification.
Alaska’s Large Marine Ecosystems are a tremendous area to monitor. EcoFOCI is a 40-year old program with an extensive history studying emerging and immediate changes in the region. The program provides foundational measurements that support a myriad of products and programs across NOAA and beyond. It is a north star of NOAA efforts to ensure sustainability of our coastal and marine resources and provides key data to those that provide weather and climate forecasts.
Thanks for checking out this blog! If you got this far, you’re likely hungry for more. If so, check out our website, https://www.ecofoci.noaa.gov.
Guest blog writing by Heather Tabisola.
