Update on the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project

Principal Investigator

At a Glance

Biological and geological processes occurring in the Southern Ocean around Antarctica have important impacts on global carbon and climate cycles. Recent modeling results show that the Southern Ocean acts as a key sink for atmospheric carbon dioxide (CO₂), thus mitigating global temperature increases caused by rising levels of CO₂. To examine the dynamics of these processes across space and time, Jorge Sarmiento is directing the world’s first large-scale deployment of robotic floats equipped with biogeochemical measurement instruments. The project will enable unprecedented observations of pH, biological productivity, carbon cycling, and phytoplankton dynamics in the Southern Ocean.

Research Highlight

Launched in September 2014, the National Science Foundation-funded Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project, directed by CMI member Jorge Sarmiento, is the world’s first large-scale deployment of biogeochemical (BGC) Argo floats. Aiming to dramatically increase biogeochemical observations in the harsh and remote ocean around Antarctica, SOCCOM scientists have augmented conventional robotic Argo floats, which measure ocean temperature and salinity, with newly developed biogeochemical sensors to measure pH, nitrate, and oxygen. The project will allow unprecedented year-round monitoring of ocean pH, biological productivity, carbon cycling, and phytoplankton bloom dynamics in the Southern Ocean (for example, see Figure 1.2).

Currently more than 30 SOCCOM BGC floats are operating and by June, the end of the second float deployment season, 52 floats will be reporting from the Southern Ocean—more than a quarter of the way to the goal of 200 floats within six years. Data from the floats are made available to the public in real time on the SOCCOM website (http://soccom.princeton.edu), and will soon also be incorporated into the global Argo data system to provide easy access to researchers around the world.

Analysis of two years of data shows that the ice-capable floats successfully survive Antarctic winters beneath the ice and re-emerge to transmit data via satellite back to SOCCOM scientists on shore. The new biogeochemical sensors are also performing well—shipboard observations made when each SOCCOM float is deployed are used to calibrate the biogeochemical sensors, and have shown that the sensors’ measurements are consistent with shipboard data. Newly developed methods for evaluating float measurements after deployment (including air calibration for oxygen, and an alkalinity algorithm for assessing nitrate and pH sensor performance over time), suggest that the sensors will likely be stable in the long term and that the floats may eventually be suitable for deployment without calibration by other research vessels and cargo ships, as is the case with conventional Argo floats.

In addition to actively participating in the SOCCOM project, the Sarmiento group continues to carry out model simulations of Southern Ocean biogeochemistry with support from CMI. This research provided the primary motivation for the SOCCOM project by illustrating the importance of the Southern Ocean to the planet’s carbon and climate cycles, and modeling results continue to inform observational efforts.

New research initiated this year has focused on using high-resolution climate models to separate carbon cycle trends due to climate change from those due to natural climate variability, and to determine “times of emergence” of these signals. This work highlights the role of natural variability in enhancing or suppressing carbon cycle trends that observational programs like SOCCOM aim to quantify, and is helping to inform strategies for detecting changes in the ocean carbon sink.

Figure 1.2. Annual net CO₂ flux estimated from data collected by SOCCOM floats deployed in the Southern Ocean in April 2014. Negative fluxes indicate CO₂ uptake by the ocean. Inset map shows trajectories of floats after two years; gray land area at upper left is New Zealand. Fluxes were calculated using float-measured pH, estimated alkalinity, ERA-Interim 6-hourly winds, and Wanninkhof gas exchange coefficient.¹

Reference

Wanninkhof, R., 2014. Relationship between wind speed and gas exchange over the ocean revisited. Limnol. Oceanogr. Methods, 12(6): 351-362. doi:10.4319/lom.2014.12.351.