Q: You’re looking at the rate of change in the Bering Sea. What do we know so far and how does it compare to other places?
I combined the 30 years surface carbon dioxide concentration (CO2 ) collected from the Bering Sea and found that the CO2 in the Bering Sea is almost stable over these 30 years, which is very different from the rest of the ocean, where CO2 generally increases around 2 ppm per year (about 0.5% of current air CO2 concentration). I proposed this unique stable surface CO2 in the Bering sea resulted from more intensive oceanic algae growth under global warming through a process known as photosynthesis, which converts CO2 into organic carbon. However, as algae die, their bodies sink to the seafloor, where they are decomposed by bacteria, a process that releases CO2 back into the bottom water. This excess CO2 will release more acid and cause more severe ocean acidification simply because CO2 is a weak acid. Thus, we will expect more severe ocean acidification in the bottom water. We care about ocean acidification because it may reduce the survival rates of young red king crab and Dungeness crab in the Bering Sea. In fact, ocean acidification is also destroying other calcifying organisms, such as coral reefs, oysters, clams, and some algae. All these animals and plants are having difficulty maintaining their external calcium carbonate skeletons or seashells.
Q: Could you explain in simple terms how you go about calculating the rate of change of ocean acidification in the Bering Sea and what factors contribute to different rates in different places?
Due to financial, logistical, and technological challenges, CO2 data is still lacking in the Bering Sea, especially in the cold season. To best take advantage of the current dataset (I mean, very summer-concentrated) accumulated in the Bering sea, we first got the average summer CO2 concentration every five years. Then we compared their average conditions to derive the rate of ocean acidification. Using 30 years of field data, we found that, over time, ocean plants in the Bering Sea have been taking up more and more CO2 each summer, which may lead to much extensive ocean acidification in the bottom water. However, in the Chukchi Sea, warming ocean temperatures have increased the CO2 degassing and resulted in a much higher surface ocean acidification because of its rapid warming in recent years.
Q: Some of your data comes from saildrones. Remind us what a saildrone is and how it’s being used to study ocean acidification.
The saildrone USV is a wind-and solar-powered autonomous ocean-going data collection platform designed for long-range, long-duration missions up to 12 months. Each vehicle consists of a 7m long narrow hull, a 5m tall hard wing, and a keel with a 2.5m draft. In 2016, a CO2 sensor was integrated into saildrone. In 2017, saildrones completed the first autonomous crossing of the Bering Strait to collect high-resolution spatiotemporal surface oceanic CO2 data in the Bering and Chukchi Seas. The application of saildrones can fill in the data gaps to better understand the CO2 dynamics and ocean acidification. For example, they can be deployed quickly and in response to sea ice melt or storms. This immediate accessibility is one of the key challenges of working on ice-breaker ships.
Q: What are some challenges of not having year-round data, and how do you work through those challenges?
Yes, this is an excellent question. I do not have a very good answer yet. Not having year-round data is one of the biggest challenges to get an accurate estimation of CO2 flux. For example, because of strong algae growth in spring and summer, a large amount of CO2 gets pumped into the deep ocean. However, the CO2 may be pump out in the fall season when the strong wind gust sustains for a longer time. Still, the CO2 flux is unknown in the sea ice-covered winter time. Therefore, we do not have enough data to understand CO2 ‘s seasonal cycle. I would say the saildrones will help fill in the data gaps, but they also have some limitations that they may get hurt by hitting the sea ice and even trapped without enough power.
Q: Tell us a bit about your background – how did you get interested in ocean acidification and what keeps you in this field or research?
I attended “Introduction To Oceanography” as an elective course at Ocean University of China in 2008. During the course, the lecturer said something like this “We are fortunate to enough to have the ocean to absorb part of our CO2 emissions”. I agreed with him, but a few seconds later, I raised my hand and asked “But CO2 is an acid, so will the ocean become acidified in future?”. I can guarantee you that my lecturer almost rose and said, “EXACTLY, that is something we called ocean acidification, and we will discuss it in the next class”. This experience planted a seed for me to explore more in ocean acidification. In 2013, I joined Hu’s Carbon Group in Texas A &M University-Corpus Christi to examine the ocean acidification rate in different environments.
I want to say that it is curiosity and responsibility that motivate me every day. I want to know the ocean acidification state in different systems; I want to see whether it is preventable; I want to share my knowledge to awaken the public’s awareness to reduce greenhouse gas emissions.
Q: Can you tell us about a memorable time in the field or in the lab?
After three years of extensively studying the carbon cycle in the Baffin Bay (Texas), I can’t close Baffin Bay’s carbon budget, which means I missed at least one carbon removal mechanism. If you have experience living in Texas, you may remember that plastic containers turn very fragile in only a few weeks under the Texas sunshine. With that, it suddenly occurred that photochemical reaction (the chemical reaction triggered by solar) may play a role in Baffin Bay’s carbon cycle. I then wrote a proposal to Sea Grant to examine the photochemical degradation’s impacts on carbon cycle in Baffin Bay. After a few months’ experiment, I found that the photochemical reaction can quickly convert organic carbon to inorganic carbon with 1/3 of microbial respiration rate. This unique process help close the carbon budget in Baffin Bay. We published this finding in Limnology and Oceanography Letters in early 2020. There was an unexpected event in the middle of the experiment—hurricane Harvey. Because of the evacuation order, I had to move all the experiment bottles to a safe-but-dark room. I was anxious about this interruption at the beginning. However, the final results confirmed no chemical reactions in the absence of solar, which actually confirmed my experiment–only solar did make that difference! So, I added this unexpected benefit to my manuscript.