Gray shares findings from SOCCOM program in lecture

Alison Gray, a postdoctoral fellow at the program in Atmospheric and Oceanic Sciences, presented her work on the ongoing Southern Ocean Carbon and Climate Observations and Modeling program in a lecture Monday afternoon.

SOCCOM seeks to fill in the gaps left by prior in situ studies of the Southern Ocean, which have had limited available windows for sampling, especially in the winter, due to the harsh conditions of the Antarctic.

Gray noted that current estimates allot to the Southern Ocean approximately 50 percent of the total global ocean uptake of anthropogenic CO2, despite only accounting for 30 percent of the total global ocean surface area. Thus, climatologists are particularly interested in better understanding this system's forcings.

This comes as the National Oceanic and Atmospheric Administration recently reported the hottest August on record. Global climate change is attributed to rising levels of greenhouse gasses including carbon dioxide. Average global temperatures for the past 16 months have set records, according to NOAA.

Gray said more than 50 biogeochemical profiling floats have been deployed into the Southern Ocean across four different regions. The floats store the collected data and later transmit the information to satellites upon resurfacing. Gray said that the floats’ primary strength is their autonomy.

“They don’t mind being out in the Southern Ocean when it’s windy, […] cold,” Gray said in the lecture.

The floats can also collect data when the surface has iced over, giving them another advantage over the existing method of collecting data from cruises.

Of the nearly 50 floats deployed thus far, 13 have collected more than a year’s worth of data, which comprises the team’s initial analyses. Gray added that, while her team's calculations were dependent upon alkalinity levels in the water near the floats, the floats have not been designed to measure this property. However, using existing, shipboard measurements made in the region, she and her team were able to approximate this value. She justified this approach by noting that her team’s calculations were not particularly sensitive to alkalinity, meaning, a reasonable approximation for this value suffices. She stated that current estimates place the approximate uncertainty associated with the pCO2 in their calculations at two percent.

With this information, Gray and the team were able to determine the annual air-sea CO2 flux in the region. The results already distinguish themselves from those of prior studies, with significantly higher measurements for these fluxes than have been provided by estimates based on existing datasets. The implications, however, suggest that researchers must review the current understanding of forcings at the level of the sea-atmosphere interface.

Gray chalked the stark difference present in the graphs she provided to three potential causes.

The first is that one cannot discount the possibility of a sampling bias in the study.

“It’s pretty concerning that we’re extrapolating from a relatively little number of data points," she said.

Her team further investigated this lead in their analyses, studying the locations where the operational floats had been placed, and comparing their measurements to those of existing climatologies in those regions. Although sampling bias obviously factored into their calculations, it alone was not enough to account for the significantly higher levels of outgassing that their study indicated.

Gray said that if a sampling bias could not wholly account for this deviation, then perhaps the conditions of the time period during which these floats were operating was just particularly exceptional. She noted that, since 2014, wind speed and sea-surface temperature have been particularly anomalous, possibly affecting the fluxes the team found. Once again, however, their analyses showed that even this possibility insufficiently accounts for the deviation.

Gray then rested her case on a third option – that existing climatologies are severely underestimating the flux during wintertime. This proposal does not come as a surprise, given the scarcity of data collected in the winter.

Of course, there is still more work to be done to lend more credibility to this idea, she said. 16 floats will have collected a year’s worth of data by the end of this year, at which time their data will be incorporated into the aforementioned study. Furthermore , over 100 additional floats will be deployed over the span of three years.

The lecture, titled “A Southern Ocean source of carbon dioxide detected with autonomous biogeochemical floats," took place at Guyot Hall Lecture Hall 10 at 12:30 p.m., and was sponsored by the Department of Geosciences.