A conversation with Nathalí Cordero Quirós: Postdoctoral Researcher, Oceanographer

  • 13 January 2021

Nathalí diving in a kelp forest in coastal waters near Ensenada, Baja California, Mexico. Photo courtesy of Nathalí Cordero Quirós.

Nathalí Cordero Quirós, a Postdoctoral Researcher at the University of California, Santa Cruz, explains what drove her to make her career as an Oceanographer. Dr. Quirós speaks of the impacts El Niño events have on the California Current System and their research using models to understand the California Current’s physical/biological response to ENSO variability. This work was funded in part by the MAPP program, in partnership with NMFS.

Our conversation follows:

What drove you to choose a career path in science?

I decided when I was a kid. I was about six years old, and I never changed my mind. I guess it was because of curiosity. I was always very curious about the ocean, specifically.

What made you curious about the ocean?

The animals. I was fascinated with whales - I actually wanted to be a marine biologist, and then I discovered I could study other stuff that I liked about the ocean, but in the beginning, I wanted to be a marine biologist.

Dr. Quirós on a SCRIPPS research cruise near the islands of Palau . Photo courtesy of Nathalí Cordero Quirós.

So is this curiosity because you like to dive or that you live really close to the sea?

I grew up in Tijuana which is very close to the ocean. I like to dive, I’ve done it a couple of times, but when I was a kid I was fascinated by all of that. I would go out to the sea all the time and wonder all the time, and now that’s not the case. Now I get to study the ocean and it’s biogeochemistry and physics.

What’s the deepest dive that you’ve ever done?

30m is the deepest I’ve ever gone. I was kind of nervous at the beginning but everything is so beautiful that you forget you’re 30m deep.

Before you started your PhD research in Scripps, you were trained as a physical oceanographer and worked as a research assistant in the Stable Isotopes Paleoceanography Laboratory in Ensenada, Mexico. Why and how did you make the transition from field and lab research to working with models? What drives your interest in modeling?

When I was a research assistant at the Stable Isotopes Laboratory, we were studying the changes in the overturn and circulation of the ocean. Stable isotopes of carbon and oxygen can be used as proxies to understand the past environment in the ocean, and they give us clues to reconstruct variables such as temperature and salinity and see how they were in the past. In the big picture, this helps us to track changes in the overturning circulation which can affect ocean productivity, food webs and climate. I wanted to understand better the currents and the physical systems of the ocean and in the long term I wanted to combine both the biochemistry and physics, but my way of thinking was, “okay if I want to combine both I better understand the physics of both and what they do” so that’s when I decided to pursue my Masters in Physical Oceanography.

Photo courtesy of Nathalí Cordero Quirós.

Your PhD research was NOAA-funded, focusing on using models to understand the California Current’s physical/biological response to ENSO variability. Why did you choose this NOAA project to work on in the first place?

I was really interested in the biogeochemistry and physics of the California Current System because this is where I grew up and it's a highly productive ecosystem. Also, because I’m a local, I’ve always been very close to the vulnerability of this coast. This research would allow me to do exactly what I wanted to do, which was combining physical oceanography and ecosystem variables -- chlorophyll, oxygen.

What happens to the California Current System during El Niño events? How do the changes in physical conditions affect the California Current System ecosystem?
 

There are two main mechanisms through which El Niño affects the physics and ecosystem in the California Current System. The first one is related to atmospheric variability which
significantly alters the main wind pattern along the U.S. West Coast during El Niño conditions; the second mechanism is related to oceanic Kelvin Waves (KW).

During normal (non-El Niño) conditions, upwelling brings cool waters to the photic zone. Those waters are nutrient-rich and favor the photosynthetic primary producers. When there is an El Niño, the main winds (blowing from North to South) along the U.S West Coast weaken, resulting in less upwelling of cool waters, so El Niño’s influence over the California Current System is associated with anomalous warming of sea surface temperatures (SST). In addition, Kelvin waves, originating at the equatorial Pacific, travel along the coast, suppress the thermocline, acting as a “cap” for upwelling.

In a nutshell, during El Niño conditions, weaker upwelling fails to supply enough nutrients to the photic zone and primary production decreases. These changes at the bottom of the food web cascade to the top levels, affecting not only planktonic communities but top predators like sardine and anchovies as well.

Maps of sea surface temperature anomaly in the Pacific Ocean during a strong La Niña (top, December 1988) and El Niño (bottom, December 1997). Maps by NOAA Climate.gov, based on data provided by NOAA.

In your research, you used both a coarse-resolution global model and fine-resolution regional model. Why did you use two types of models and what stories did the model results tell us, respectively?

Coarse resolution models are highly used among the oceanographic community and they are computationally cheaper in comparison to high resolution ones. With this in mind, I wanted to shed some light on the skill and limitations of this popular model and quantify its performance in reproducing ENSO-related variability of the California Current System. With this analysis, we found that cooling of the California Current System associated with La Niña is more consistent than the warming associated with El Niño, and we were able to relate this effect with the origins of ENSO teleconnections over the tropical Pacific (point for the global model!). On the downside, the global model is limited by its resolution which cannot resolve processes that play a key role in the variability of Eastern Boundary Upwelling Systems (EBUs) like the California Current System. For example, the suppressing of the thermocline by the Kelvin waves mentioned before is not well resolved in this type of model, nor is the mesoscale activity in the California Current System. Moreover, the errors in the physical response (e.g. poor representation of upwelling variability) will cascade into the biological realm, leading to more errors and biases in the model ecosystem response.

This is why comparing the first part of my analysis with a high-resolution simulation made sense to me. The biogeochemical representation of the California Current System in the high-resolution model is simpler compared to the one in the global model but the structure of the phytoplankton and zooplankton communities are more sophisticated. In fact, this model captures the diversity of the bottom-up response of the ecosystem during El Niño events, showing a decrease in biomass in the larger zoo- and phyto- plankton groups, while the smaller groups actually thrive during El Niño low-nutrient conditions.

The other interesting feature of the analysis with the high-resolution model is that it allows us to establish relationships between the spatial distribution of biogeochemical properties (such as nutrients) and the mean eddy field over the California Current System. High-frequency mesoscale activity can be seen as “noise” when analyzing seasonal or ENSO time scales, but mesoscale eddies can play an important role in transporting biogeochemical properties. The role of eddies in biogeochemical variability of the California Current System is one of the topics of my on-going and future research.

 

Dr. Quirós presenting her work at the 2019 ASLO (Association for the Sciences of Limnology and Oceanography) meeting in Puerto Rico. Photo courtesy of Nathalíi Cordero Quirós.

What do you consider as the top challenge for the model forecasts of ENSO variability in the California Current System?

Scientists have made great progress in understanding the teleconnections between the tropical Pacific and the extratropics, as well as the regional expressions of ENSO in the California Current System. One of the biggest challenges is that ENSO variability peaks during the winter, and therefore the most coherent response of the California Current System tends to be during this season. ENSO winter variability is also the source for most of the skill in forecasts of physical variables (e.g. SST) in the California Current System. 

The ENSO-related signal of the SST over the California Current System becomes less coherent during the spring season, but this is not true for ecosystem variables, which tend to exhibit their most coherent response around the upwelling season (March-April).

Understanding other potential sources of predictability (besides ENSO) at a regional scale will definitely help to improve the skill of forecasts for physics and biogeochemistry over the California Current System.

What was the most exciting part of your graduate work?

It was actually my first exposure to modeling so at the beginning, there was a steep learning curve. At the beginning I was like “how am I going to do this?” But after a few months of work you start getting your first results and they’re actually good. At the beginning you’re afraid you could have a bunch of results and it not tell a story. And then when you start putting the pieces together and realize that it’s actually a good story. I think that’s very exciting. It’s very encouraging.

What is your current research topic as a Postdoc researcher at UC-Santa Cruz? Can you talk about what your research has found thus far?

I keep working on analyzing model output to understand the physical and biogeochemical variability of the California Current System in response to climate events. One of the things I’m looking into right now is the variability of the eddy field over the California Current System and if it changes significantly during ENSO events.

The research group I just joined at UCSC is very interdisciplinary, which is exciting. As a physical oceanographer, I’m working closely with scientists from the National Oceanic and Atmospheric Administration (NOAA) like Mike Jacox, Steven Bograd, and Mercedes Pozo, to understand the mechanisms for forecast skill and improving future predictions of physics and biogeochemistry in the California Current System.

Do you have any advice for the students who are interested in oceanography and climate science?

Stay curious and focused. A lot of times as scientists, we come across a myriad of topics that we would love to explore and picking one can be challenging.Think of a question (curiosity) that you would really like to work towards answering, there will be small tasks along the way, try not to lose sight of the big picture (focus). At the end, each of us is working on a piece of the big puzzle and you could really benefit from talking to other scientists and engaging in collaboration with them.

 

 

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