A Scientist's Life: Sarah N. Giddings

Coastal oceanographer studies the changing nature of estuaries

Sarah Giddings came to Scripps Institution of Oceanography at UC San Diego from the University of Washington in 2014. She studies coastal physical oceanography, in particular the dynamics of estuaries. Her background is in environmental engineering with a specialty in fluid mechanics. This year she is one of several Scripps researchers studying the current El Niño season as a possible preview of future climate conditions that may become more frequent.

explorations now: What do you do for a living?

Sarah Giddings: I am a coastal physical oceanographer and I conduct research that focuses on the regions of the coastline where we have estuaries and bays, where rivers meet the ocean. I look at the physical transport mechanisms within estuaries and bays and also what comes out of them: river plumes that might have sediments or contaminants coming out of them.

I’m particularly interested in estuaries because they’re at the interface where humans use the coastal oceans, they’re very valuable to us in terms of resources and we’ve exploited them so we’re trying to figure out how to manage them most appropriately. I’m also interested in them because they’re at the intersection of what happens on land and what happens in the ocean.

en: What defines an estuary?

SG: An estuary is actually a little hard to define. The traditional definition is that it’s where a river meets the ocean. But in fact there are plenty of places where you don’t have to have a river input to consider it an estuarine environment. For example, here in Southern California and Baja California, we have bays that don’t have much, if any, freshwater input, yet I would consider them an estuary. What really makes them still an estuary is that they have very strong gradients in density, so they range from really salty to really fresh or really hot to really cold. Those density gradients drive circulation and they’re typically much stronger in estuaries than in the coastal ocean.

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en: What are some of the main questions in your field?

SG: We’re still focused on similar questions to those that we were asking a long time ago, which centers on the fact that all estuaries are a little bit different. There’s been a history of really understanding one particular estuary well but not being able to connect that to another estuary. Being able to connect dynamics between systems and classify estuaries and river plumes in terms of their functionality, in terms of physics and of the ecosystem, that’s still one of the biggest goals in estuarine science.

A big question connected to this goal is just being able to understand how an estuary circulates, how does water get from point A to point B and how much mixing occurs? That means the mixing of saltwater with freshwater. It also means mixing of potentially contaminated runoff with less contaminated ocean water and mixing of nutrients and oxygen. We are very interested in trying to come up with a framework that allows us to compare different estuaries of different sizes and shapes and dynamics.

One of the reasons why we’re interested in comparing different estuarine systems and coming up with a classification system for them is really because we want to understand how they are going to function in the future: how are they going to behave under different climate change scenarios and what does that mean for human interactions’ with them? The present El Niño conditions provide us with a really wonderful window into that future. We have extra sea-level rise because of El Niño. We have warmer ocean temperatures. We also have more extreme events, meaning more high-water events due to things such as large waves.

en: What tools do you use for your research?

SG: The tools that I use are a combination of field work – using instruments that measure velocity, salinity, temperature, and numerical modeling – and using a computer to simulate what ocean currents are doing, sort of like what you’d do with a weather model.

We go into the field because these estuarine systems are very complicated and we need to have a way to validate our models. We need to have measurements of, for example, the estuarine salinity as it responds to wave events coming in and mixing the system.

Our field measurements are made with a whole suite of tools. We use boat-based observations where we’re putting instruments over the side of the boat and bringing them back up again. We use tools that we actually walk around with so we spend all day walking around the estuary measuring topography and bathymetry. On the coast we use tools such as dye where we track where stuff goes as a proxy for things like pollution or sediment coming out of these systems. So it’s a whole variety of tools that involve getting wet and muddy and it’s lots of fun!

I do some work internationally, but most of my work has been on the West Coast of the U.S. in the Pacific Northwest and down here in Southern California. Currently I have measurements going on in several different estuaries up and down the coast and in collaboration with other folks, we’re conducting measurements stretching all along California and doing modeling along the entire West Coast.

en: Why did you come to Scripps?

SG: I came to Scripps for a whole variety of reasons but one of the most exciting pieces for me is coming to an institution where people are working in ocean sciences across a whole bunch of different disciplines. I’m a physicist but I really like working with biologists and chemists and so I’m at a place where I can do that very easily. Even amongst physics-minded folks, I get to collaborate with people across disciplines. There are great scientists here working on the hydrology upstream. There are folks working on the waves and the beaches and the nearshore, and certainly in the deep ocean – that’s what Scripps is known for – but at the time that I started here, the connection between what was happening upstream and in the ocean was missing, so it was an exciting niche for me to fill.

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