Beachgrass in the foreground with an ocean beach and headlands in the distance.

A marine heat wave is projected to hit the Oregon coast in the coming months.

Courtesy of Oregon State University


Many remember the record-breaking heat wave that Oregon had over the summer. Now the state will be seeing more high temperatures, but this time in the water. A marine heat wave is projected to hit the state within the next month, causing water on the West Coast to have higher temperatures than normal. Andrew Leising is a research oceanographer at the National Oceanic and Atmospheric Administration and joins us to tell us what these heat waves are and how they might affect us.

The following transcript was created by a computer and edited by a volunteer.

Dave Miller: Rains this past weekend, cleared the air up and down western Oregon and it gave us a taste of the cooler wetter seasons to come. But another heat wave is heading towards the West Coast. It’s a marine heatwave like the so-called “blob” that lingered off the coast about six and seven and eight years ago. Andrew Leising is studying these huge masses of warm ocean water. He’s a Research Oceanographer at NOAA, the National Oceanic and Atmospheric Administration. So let’s start with the basics. What is a marine heatwave?

Andrew Leising: Right now, a marine heatwave is usually defined as being a mass of water that is much warmer than the water at that location would be on that particular day of the year. So we look to see what’s called an anomaly. So we mostly use satellites and we look at the ocean and see if it’s much warmer than it should be. Even much warmer.

Miller: When you say much warmer, what does that mean for the Pacific Ocean or a chunk of the Pacific Ocean?

Leising: It typically means temperatures anywhere from 2-4°F warmer than it usually should be. Even more than that because we’re talking globally about climate change. You know how 1/10°C is really significant and 1°C warming is immense.

Miller: So more than 4°F is a big local change.

Leising: Yes, it is.

Miller: What’s causing these heat waves?

Leising: Our best estimate of what’s causing them is changes in large-scale atmospheric patterns. So if you’re familiar, when you see the weather news on tv, they usually show highs and lows and those are atmospheric pressure cells. And what happens is we get a region of high atmospheric pressure over the ocean, kind of out in the middle of the ocean. And those high pressure cells tend to drive the winds around the cell and rather than going through the cell. And without those winds and storms that come with the winds, you don’t mix up the water. And if you don’t mix up the water it never gets a chance to pool during the wintertime. And so that leads to, basically, a buildup of heat,

Miller: [Does that] mean that the colder, deeper water isn’t cycling up closer to the ocean?

Leising: It’s more that the surface water isn’t getting mixed DOWN.

Miller: So that circulation is not happening to the same extent. It seems like we’ve gotten away from using the term “the blob” which came into popular West Coast parlance in 2014, 2015, 2016. I don’t know if it’s because it didn’t seem particularly scientific?

Leising: There was a paper that came out that dubbed the 2019 heatwave ‘Blob2.0′.


Miller: But it seems like one of the benefits of that term was that it implied that these things can stick around for a while as opposed to a wave that comes and goes relatively quickly. How long do these anomalies last?

Leising: The 2013 one lasted from 2013, 2014 and 2015 [is] the one we called ‘the blob’. That one lasted for all that time. Several years. The [marine heatwaves] that we’ve had now last three years. So 2019, and again this year, these last three heatwaves, have all lasted on the order of maybe 8-9 months each.

Miller: How do the ones in the last couple of years compare in size and scope to the initial ‘blob’?

Leising: The one this year is not quite as large, in terms of the surface area of the ocean. But the ones in 2019 and 2020 actually ended up covering a very similar total area, which is in the order of 8 to 9 million kilometers squared. It’s huge. It’s almost the size of Alaska or more. It’s very big.

And the one this year right now is around 4,000,000 km square in an area. Still gigantic So we’ve been able to measure these things since about 1982 and this current event is probably easily within the top 20 events that have happened, in terms of area. What’s different though, even though the area is huge, the last couple of years they haven’t penetrated as deep into the water as the 2014, 2015 event. That one went down to 100- 120M versus these last couple that are only penetrating anywhere from 20-60M. So they’re not heating as much of the water column as that past event.

Miller: Marine systems have always seemed really complicated to me in terms of the interactions of microorganisms all the way up to enormous marine mammals, all of which are affected by the movement and the temperature of water. So what are the various ways that these heatwaves affect marine life?

Leising: Right off the bat when the temperature changes by that much [the impact is] for the animals that can’t really move around. So some of the fish that actually kind of sit in little nests or just have a rock outcrop on the bottom like to stay there their whole life. Those fish aren’t going to move. And so if the water gets too hot for them, it could kill them or could really cause them a lot of physiological stress. So you have those kinds of direct impacts. But another impact is that when these [marine heatwaves] come in and reach the shore, they tend to change the production of the plankton. And so often, there’s either less food available for the rest of the foodweb, or it’s a different food that is available for the rest of the foodweb.

And then for the animals that can move North to South East to West - mostly they kind of shift North to South - but this might change the range of where these animals normally go. So you’ll get animals that usually are off of California ending up going all the way up off of Alaska or British Columbia. The temperature based changes [affect] both their diet and the temperature that they prefer just for their life. They often have an optimal temperature that they want to stay in to maximize their growth versus their metabolic rate. So they’ll move around because most of them are cold blooded.

Miller: So what’s the connection between these lingering high temperature events and algal blooms?

Leising: A few papers that have come out over the last year that seemed to draw the conclusion that when these warm temperatures come into the coast, it can cause a certain kind of stress to the type of phytoplankton that produce these harmful algal blooms. And once those phytoplankton get stressed by both the water warmth and the right cocktail of nutrients that they like, they start producing those toxins. So there seems to be some linkage there. And indeed we’ve had some of the largest algal blooms on record during ‘the blob’. And then we’ve had a few smaller ones over the last couple years during these heat waves. So there still seems to be a link there.

Miller: So whether it’s algal blooms or migrating fish or marine mammals, is it fair to say that these marine heatwaves could have major effects on commercial fisheries?

Leising: Absolutely, because they’re going to change where the fisheries have to go. They might change the timing of when the fishery may be open or closed to different parts of the fishing community. So yes, these things are definitely having impacts. And that’s the major reason why ‘the blob’ was really a wake up call for us because we hadn’t seen too many things that were quite like this. We’re used to looking at the impacts of El Ninos, which are, in a way, a kind of different heatwave. But now that these events are on our radar, we’re actively watching for them to try to get some ideas of when they might come into the coast and affect our fisheries. So yes, we’re really watching these things.

Miller: How much do we know about the connection between climate change and these heat waves?

Leising: Well, (snicker) there’s most likely a pretty good connection because if you can think about it, the climate change is causing a longterm shift in the underlying temperature. But we also think that as the temperature itself goes up, that leads to higher variability. And these heatwaves you can think of as [having] this higher variability. So it’s like you’ve got a line that’s slowly increasing but the wiggle of the line is also increasing even more dramatically in those. And the shorter term wiggles are the are these heatwave events? So we think there is likely a link. Although we’re still early in the process to estimate [whether there] has there been an increase in the number of heatwaves or their strength. But it does appear to be that we’re headed on that trajectory.

Miller: It seems like there’s so much [the scientific community] still doesn’t know about these heatwaves. What do you see as the most important questions that you want answers to next?

Leising: At this point, we’re really trying to understand more about how we can predict when they’re going to come in, some of the more short-term aspects. So for instance, right now there’s a fairly large heatwave, as I said, this four million kilometers squared sitting offshore. If we had a better way to forecast within the next couple of months when that might be reaching the shore and where and [for] how long it might stick around, that’s really one of our objectives we’re aiming towards. So there’s quite a few people who are [currently] researching that aspect.

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