the United States. Most recent posts will be at the top.
After a long transit home, we’re just a few days away from port in Virginia. In certain ways, being at sea has prepared me for going into quarantine. I’m certainly familiar with life confined to small spaces. The social isolation, however, will be very new. Since everyone on the ship is healthy, we don’t have to worry about social distancing. I will miss the many conversations about science and life with all on board, which have been the highlight of the cruise.
A few weeks ago, we had a barbecue outside on the ship’s fantail to celebrate crossing the equator. The air was thick with moisture, but everyone was in high spirits. Some people were playing cornhole. Others were splashing around in an inflatable kiddie pool. I remember observing the whole scene from a picnic table and realizing: once I’m back on land, it could be weeks or even months before I’m at a gathering with this many people. It was a sobering thought.
|The view from the fantail of the R/V Ron Brown|
Sometimes I think about the SOCCOM floats, and picture what interesting processes they are observing, wherever they might be. Out here, the immensity of the ocean is perceptible, which makes it even more amazing to me that these tiny floats are changing our understanding of the climate system.
|The blog author just before the final SOCCOM float deployment several weeks ago.|
The ocean regulates the climate system by absorbing nearly one-third of global carbon dioxide (CO2) emissions. Once dissolved, CO2 causes chemical reactions that lower the pH of seawater, a measure of its acidity. This means that the ocean is becoming more acidic as it takes up the excess carbon emitted by burning fossil fuels, shifting the carbonate equation and causing a phenomenon known as ocean acidification. Ocean acidification is bad news for millions of tiny organisms, like the pteropod below, whose shells’ get corroded in these conditions. Therefore, monitoring pH levels in the ocean, for example by using the pH sensors on the SOCCOM floats, is necessary to determine how climate change will impact marine ecosystems.
|Unhealthy pteropod with dissolving shell ridges showing the |
effects of ocean acidification (NOAA Fisheries Collection)
In addition to telling us about ocean acidification, the pH of seawater can also reveal important information about the carbon cycle. Since pH levels are directly related to ocean carbon uptake through known chemical reactions, they can be used to calculate the amount of dissolved CO2 in seawater. This, in turn, allows scientists to estimate air-sea carbon fluxes, as described in a recent paper led by University of Washington professor Alison Gray. The Southern Ocean is typically thought to play an outsized role in the global ocean carbon uptake, but Alison’s study showed that it may not be absorbing as much CO2 as we thought. In fact, certain regions even released carbon into the atmosphere, acting as a source rather than sink for atmospheric CO2.
Much of this previously undetected ocean carbon release occurred in winter in the icy regions close to Antarctica, highlighting (as we’ve seen before) the importance of year-round sampling and expanded data coverage. Accurately quantifying air-sea carbon exchange, through studies like Alison’s, is essential to improve global climate models. Furthermore, combining information from all the different float sensors can help us untangle the complex set of physical, chemical, and biological processes that control the fluxes of carbon between the ocean and atmosphere.
While I’ve focused each post in this series on a particular sensor, the temperature, salinity, bio-optical properties, nitrate, oxygen, and pH of the ocean are all connected. In fact, we’ve seen that some of the most groundbreaking science happens when we consider how these properties interact and influence each other. Another key theme has been the unprecedented spatial and temporal resolution provided by the float array. The Southern Ocean is inaccessible, and numerous scientific discoveries resulted simply from having measurements during winter and in ice-covered regions. Only by continuing to observe these remote places can we hope to understand and predict how the climate will change in the future.
|Map of the SOCCOM float array as of March 29, 2020, |
including the 6 floats we deployed on this cruise! (SOCCOM)
And that is the power of SOCCOM! The new insights gained from this novel dataset are changing our understanding of the Southern Ocean and its impact on global biogeochemical cycles. Furthermore, the SOCCOM project has a team of world-renowned climate modelers using those findings to inform models and improve future climate projections. The breadth of work being done is truly remarkable, and the studies I’ve featured in this series are just the tip of the iceberg (more than 100 publications have already resulted from this program!). And as the size of the float array increases, so too will the number of questions that we’re able to answer about the ocean and its role in the climate system.
In the last two posts, we talked about phytoplankton, microscopic algae that play a key role in marine ecosystems and the global climate. You’ve heard about how phytoplankton absorb carbon dioxide (CO2) through photosynthesis, but they also produce oxygen (O2) through this process. In fact, phytoplankton photosynthesis is responsible for roughly half of the oxygen in our atmosphere, which makes earth habitable. So be sure to thank these tiny organisms the next time you take a breath!
Oxygen is also central to the carbon cycle and can be used by scientists to partition ocean and land carbon sinks from atmospheric data. This is because terrestrial carbon uptake, by trees and other land plants, leaves an imprint on atmospheric oxygen levels in a known ratio based on the chemical reaction that takes place during photosynthesis. Ocean carbon uptake, on the other hand, occurs independently from air-sea oxygen exchange and thus does not affect atmospheric O2. The different influences of these processes can be used to separate the total global carbon uptake into land and ocean components from measurements of atmospheric O2 and CO2. The largest source of uncertainty in this calculation, however, is air-sea oxygen fluxes, which are poorly constrained due to lack of observations. Therefore, oxygen concentrations in seawater, which can be measured using the oxygen sensor on the SOCCOM floats, contain essential information about the climate system.
|Schematic of the global carbon cycle showing both land |
and ocean sinks (NASA Earth Observatory)
Using the float temperature and salinity data, Seth determined that this wintertime oxygen uptake was driven by ventilation, the process by which surface waters are transported into the ocean interior and away from their source region. These results highlight the value of the SOCCOM dataset, both by increasing the number of ocean oxygen measurements and by allowing us to relate that information to specific physical drivers. The improved estimates of ocean oxygen uptake, stemming from the float data, can reduce the uncertainty in the quantification of ocean and land carbon sinks from atmospheric O2 and CO2 measurements. This, in turn, will help reconcile differences between observations and models of the global climate.
|Map showing location of SOCCOM float profiles (left) compared to all previously |
available data collected by ships (right) (Bushinsky et al., 2017)
|Microscope image of diatoms, a major phytoplankton group |
in the Southern Ocean (Wikimedia Commons).
|Floats used to estimate biologically-driven carbon export in Ken’s paper. |
There are many more floats now than when the paper was published! (Johnson et al., 2017).
|October (spring in the southern hemisphere) satellite chlorophyll in the Southern Ocean showing |
the signature of the Scotia Sea phytoplankton bloom. Image created by Channing Prend.
|Schematic showing how vertical mixing at topography can deliver nutrients (in this case iron or Fe)|
to the upper ocean and support phytoplankton growth. Image created by Channing Prend.
|Satellite image of the 2017 polynya at Maud Rise (NASA Earth Observatory)|
|Schematic of the global overturning circulation, which is driven, in part, |
by gradients in density due to temperature and salinity changes
(Robert Simmon via Wikimedia Commons)
|Floaty McFloatface ready to join the fleet of SOCCOM floats collecting data |
in the Southern Ocean. - photo by Channing Prend
|The blog author enjoying sunrise over the Atlantic before deploying Sylvia Whirl |
(photo by Susan Becker)
|The blog author standing proudly with Knight Drifter just before deployment. photo by Molly Martin.|
|See Turtles ready to begin its journey around the Southern Ocean. Photo by Channing Prend>|
March 24, 2020
|Bobcat's Be-bopping Bobber on the deck of the R/V Ron Brown before deployment. Photo by Channing Prend|
|Gloria's Gulper takes the plunge into the cold Southern Ocean waters. Photo by Channing Prend|