Narrator: Okay, so clearly something was really different during these years and it affected the whole system. The clues led Yosty to talk to Seth Danielson, a Gulf Watch oceanographer with the University of Alaska Fairbanks.

Yosty: Hey Seth, so what do you mean when you use the term “oceanic conditions”?

Seth: As oceanographers, we can measure the temperature and the salinity of the water column, and from temperature and salinity we can compute the water density. Just like warm air rises, the ocean is layered with colder, more dense water sitting below warmer and fresher waters near the surface.

Yosty: Was there anything unusual about the oceanic conditions in 2015?

Seth: 2015 was one of a number of years in a row where the ocean conditions in the northern Gulf of Alaska were particularly warm. We’ve been measuring temperature and salinity at the mouth of Resurrection Bay since 1970, and over the past 45 years we’re finding the warmest temperatures that we’ve ever seen.

In the winter of 2013-2014, some scientists from Canada noticed that we had extremely strong temperature anomalies in the North Pacific. These were anomalies that were three to four standard deviations away from average, which is an anomaly that would happen once every couple thousand years if it was just a random event. So we assume that this is not just a random event, it’s been forced by something in the atmosphere. And through analysis of the sea surface data and our understanding of the weather patterns, we see that the North Pacific Ocean was able to retain a lot of heat in the last few winters, and that led to the creation of this “blob”. The blob is a feature that was created, in large part, by a lack of cooling during the winter months.

Yosty: Anomalies? Deviations? Blob? Wait, did he say “blob”?

Seth: An anomaly is a deviation from what we consider to be normal conditions. Cool anomalies are when the water is not as warm as we expect it to be. We had a prolonged period of cool anomalies in the early 1970s and another period of cool anomalies in the first decade of the 2000s. Interspersed between this long-term trend of warming over the Gulf of Alaska, we have periods of warm anomalies and cool anomalies. Often the warm anomalies are associated with events such as El Niño. That happened in 2015 for example: there was a large El Niño event.

Yosty: How could this anomaly of warmer water – this “blob” – cause problems for animals living in the Gulf of Alaska?

Seth: The temperature and the salinity both help regulate the “communication” of subsurface waters to the near-surface waters, and it’s the availability of nutrients and light up near the surface that make those waters productive for phytoplankton growth. By increasing our stratification – for example during years where it’s warmer than normal near the surface layers – you can cut down the communication between the subsurface waters and the near-surface waters, and that reduces the nutrient supply to the surface layers. So an increase of stratification would tend to reduce the amount of nutrients available for phytoplankton growth, and over the course of the last three years – 2014, 2015 and 2016 – we’ve seen stronger than average stratification across the Gulf of Alaska shelf.

As Yosty learned from Seth, the processes going on in the Gulf of Alaska can be quite complex. In the Gulf of Alaska during a normal cooling season from October to March, the water column is separated into an upper and lower section with a thermocline diving the two layers. Let’s pop over to the laboratories in the Alaska SeaLife Center to discover what a thermocline is.

Hi everyone, and welcome to the laboratories here at the Alaska SeaLife Center. I’ve set up a quick demonstration to show you visually what a thermocline is.

Bodies of water – like oceans or lakes – are broken up into layers, and these layers are determined by two different things: temperature and salinity. Variations in the temperature and salinity create variations in the density of water, and density is what determines whether some water will sink below or rise above other layers of water.

Now warm water is generally less dense than cold water, which means that warm water will actually sit above cold water. And the area where the warm water and cold water meet – that’s called the thermocline. So the thermocline is just that layer between the two different densities of water.

Have any of you ever jumped into a lake? If you have, when you were diving down deep – just a little bit below the surface – did you feel a large change in the temperature of the water? If so, then you’ve felt a thermocline!

Over here, I have created a little demo to show us what that looks like. On one half of this container I have cool, blue water; and on the other half I have warm, red water. Now let’s watch what happens when I remove the divider and the two waters combine.

As you can see here, the two layers of water are going to start to separate. And once they are separated this will be called “stratified” water. At the top we will have the warmer, less dense water; and at the bottom we will have the colder, denser water. And that purple layer that will form right in between? That will be the thermocline. So our thermocline is just the area of rapid transition between the two different layers.

Now in bodies of water, the thermocline isn’t the only cline that exists. And that’s because there are many more factors that go into determining the density of water. For instance, in the ocean, salinity – or the salt content – actually plays a much larger role in determining density than does the temperature. Now these variations in density within the ocean actually drive a global pattern of ocean water mixing. And this global pattern of ocean mixing played a vital role in the cause and effect of the “blob”. So now back to our animation to learn just exactly what is happening in the Gulf of Alaska.

As we begin the fall season, storms build, bringing with them a strong easterly wind, which causes a mixing effect in the water. As we take a closer look into the upper layer, we can see that important nutrients like nitrogen and phosphorus are delivered from the lower layer due to this strong mixing effect.

Now we see a normal warming season. After the winter, the upper water layer is now rich with nitrogen and phosphorus. Combined with the increased amount of daylight, these increased nutrient levels create a phytoplankton bloom that depletes the surface nutrients by late spring. This abundance pf phytoplankton is met by an abundance pf zooplankton. Zooplankton feed upon the phytoplankton and recycle some of the nutrients back into the ocean. The abundance of phytoplankton and zooplankton allow for other animals in the Gulf to thrive.

As zooplankton abundance increases, so does the abundance of fish in the Gulf that eat the zooplankton. Predators like common murres, marine mammals, and humans are then drawn into the Gulf to catch the abundant fish. As you can see, the nutrients that allow the phytoplankton to bloom are important for the health of the entire ecosystem.

In the Gulf of Alaska, during a winter season with less-than-normal cooling, the upper water layer stays warmer than average leading to stronger separation between the upper and lower layers. During this period, there is a ridge of high pressure in the atmosphere that reduces the amount of winds in the winter leading to a weaker mixing effect between the lower and upper layers. Additionally, with less cooling there is glacial melt and river input into the Gulf year-round. This means that the upper water layer receives a lot of fresh water that is less dense than the salt water. Mixing between the upper and lower water layers weakens and the thermocline stratification of the water column strengthens, reducing the transport of nutrients from the lower to upper water layer.

The lack of nutrient mixing over the winter leads to a nutrient-starved upper water layer in the spring. The lack of nutrients in the upper layer greatly reduces the bloom of phytoplankton. In 2014, 2015 and 2016 much of the phytoplankton left was a smaller, thinner variety that may have been less nutritious for the animal zooplankton that fed on them. This lack of nutrition would have worked its way up the food chain, with less nutritious plankton leading to malnourished and less nutritious forage fish – typically a large food source for marine birds like the common murre.

A lack of these forage fish may explain the empty stomachs found by researchers examining the dead murres and why some murres were found inland. They may have been hopelessly looking for the food they weren’t finding in the ocean.

The lingering oil studies occur in western Prince William Sound, which is where the oil from the Exxon Valdez oil spill landed, and actually there’s still some oil out there today – small pockets of oil that’s buried in sediments on beaches, throughout western Prince William Sound. So that’s where the lingering oil issues are still important to track.

From the USGS perspective, we’re looking at effects of that lingering oil on wildlife. So considering effects of exposure to that lingering oil, and also to understand what that might mean to individuals and populations of the wildlife that live out there. The main species that we’re thinking about in terms of lingering oil are harlequin ducks and sea otters, and that’s because there’s a long history of understanding that lingering oil’s been an important constraint on population recovery of those two species, and so we’ve spent a lot of time trying to understand the timeline and the mechanisms by which those species are recovering from the oil spill.

We’ve measured exposure in a number of different ways. For example, with harlequin ducks we’ve used an enzyme called cytochrome P450 1A. It’s a long word basically for an enzyme that gets induced when any vertebrate’s exposed to hydrocarbons. So if you and I were exposed to oil, we would have an induction of that enzyme that would be measurable and then could tell us whether one has been exposed to that.

The enzyme itself is part of a cascade of physiological processes that any vertebrate goes through once they’ve been exposed to oil. And it could be indicative of physiological harm, or it could be indicative of just exposure without physiological harm. So we’re not inferring harm from induction of the enzyme, what we’re inferring is that they’re still exposed to oil with the potential for harm.