MIT researchers have delivered a stark new outlook on the ocean’s role in attenuating atmospheric carbon dioxide levels in the face of weakening ocean circulation, a relationship far more complex than scientists previously anticipated. In a study led by MIT's Jonathan Lauderdale and published in Nature Communications, the expected benefits of the ocean's carbon sequestration ability may not only be reduced but reversed, indicating an increase in atmospheric CO2 concentrations with slowed ocean turnover.
The ocean's role in carbon sequestration has traditionally been viewed as a balancing act, where weaker circulation would slow both the uptake of atmospheric CO2 and its release from the deep ocean, maintaining an overall mitigation effect, albeit at a slower pace. However, new findings by Lauderdale cast doubt on this assumption due to a cycle involving iron availability, nutrient upwelling, surface microorganisms like phytoplankton, and a class of molecules known as ligands—a complex web of factors that elevate CO2 expulsion into the atmosphere as ocean circulation wanes. Lauderdale asserts, "What we thought is going on in the ocean is completely overturned," signaling a fundamental shift in understanding the interplay between oceanic processes and climate change, as reported by MIT News.
Lauderdale's team, through their modeling efforts, also debunked the notion that seeding oceans with iron would significantly boost global phytoplankton growth, uncovering the limiting factor of ligand concentrations—organic molecules that maintain iron's solubility and availability to phytoplankton. This pioneering work unraveled how increased iron in one region could shift nutrient distribution globally, leading to reduced ligand production and collateral effects on local iron resources and carbon uptake. While previous models assumed constant ligand concentration, Lauderdale’s research, augmented by data from the international study GEOTRACES, demonstrates that variability in ligand concentrations is a significant reality. This factor fundamentally alters the predicted outcome of ocean circulation changes on atmospheric CO2.
Looking at the broader implications of this research raises concerns over the fate of climate change mitigation efforts. Lauderdale told MIT News, "We can't count on the ocean to store carbon in the deep ocean in response to future changes in circulation," a stance that serves as a call to arms for more proactive and immediate reduction in emissions instead of relying on slower, natural carbon sequestration by the oceans. His findings take on added significance considering that some climate models predict a 30 percent slowdown in ocean circulation, mainly linked to melting ice sheets around Antarctica. This, combined with the new understanding of ligand activity, could mean accelerated warming beyond current forecasts.
