PUPCYCLE Day 5 – Insights into the PUPCYCLE

Tuesday, May 28, 2019 – Transiting

PUPCYCLE 2019 – Insights into PUPCYCLE 2019

A science meeting was held after dinner to discuss the logistics for the remainder of the research cruise with everyone in attendance, unlike the first attempt when heavy seas kept most of the science crew in their bunks struggling with seasickness. Calmer seas the past two days have allowed more time for us to gain our sea legs and we enjoyed getting to know the crew of the R/V Oceanus and each other.

I had a few minutes to chat with Adrian Marchetti, the Chief Scientist for PUPCYCLE, to review some of his goals and objectives for the cruise. Adrian’s primary goal is to determine how specific groups of phytoplankton respond to the Upwelling Conveyor Belt Cycle (UCBC) and how phytoplankton will be affected by changing ocean conditions.

Figure 11 – Chief scientist Adrian Marchetti (UNC-CH) (right) and Ben Freiberger (HSU) (left) locate possible upwelling sites using satellite imagery. [Image credit: Miriam Sutton]
Adrian hypothesizes that, “Diatoms are uniquely adapted to thrive under UCBC conditions compared to other phytoplankton groups.” He also notes that, “diatoms adaptability may be altered by ocean acidification and low iron availability.” During PUPCYCLE 2019, the researchers are using RNA-sequencing to analyze the expressed genes of phytoplankton during various stages of the UCBC. This allows the scientists to observe which genes are being expressed in response to the different stimuli associated with upwelling: light, temperature, and nutrient availability (including iron). The incubation systems, or bioassay experiments, facilitate these observations by allowing the scientists to control the various stimuli, (i.e., variables) throughout the various stages of the UCBC. The researchers are also observing the physiological response of the phytoplankton throughout the UCBC by measuring their uptake rates of Nitrate (NO3) and carbon (C). Nitrates are a key nutritional component for phytoplankton that promotes growth rate, which will also be measured. Iron is also a key nutritional requirement for phytoplankton and the scientists are observing the variations in molecular and physiological responses during the UCBC based on the availability or limitation of iron in the natural marine environment.

The California Upwelling Zone contains broad and narrow continental shelf regions that have very different physical, chemical, and geologic features. These differences generate large variations in the productivity between these two regions.

Figure 12 – Large chain-forming diatoms flourish in aquatic environments where iron is readily available. [Image credit: Emily Pierce (UNC-CH), using the onboard FloCam]
Narrow shelf regions (the location for Incubation Site #2) are more likely to run out of iron (Fe) before NO3. Fe-limited environments reduce the ability of diatoms to take up nitrate and other important nutrients. Higher iron concentrations are found along broad continental shelf regions (the location for Incubation Site #1) and this abundance increases the consumption of nitrate and other nutrients, allowing large chain-forming diatoms to flourish.

The incubation/bioassay experiments provide the scientists with a “snapshot” of the community and their responses to the UCBC conditions based on the location of each incubation site. Continuous data is also being recorded from the microbial community using a FIRe Fluorometer System as the R/V Oceanus transits along the California Upwelling Zone. This continuous data set allows researchers to measure the amount of fluorescence being emitted by the microbial communities throughout the various study regions. When iron is available (broad shelf regions), diatoms absorb light and produce energy mostly in the form of photochemical energy. When iron is limited (narrow shelf regions), diatoms cannot absorb the light and repel the light as fluorescence of a different wavelength. The FIRe System measures this fluorescence. In addition, underway sensors are also measuring dissolved oxygen and NO3 concentrations. Analyzing these nutrients will provide the researchers with a continual assessment of the health status of the phytoplankton community in relation to their chemical environment.

Today’s Certificate Challenge: The California Upwelling Zone (CUZ) is found off the coast of California where variations in the width of the continental shelf contain different levels of key nutrients for phytoplankton and the aquatic food web. Which type of shelf results in an increased abundance of iron to support this food web?