A new study devoted to historical trends of marine heatwaves around the globe broadens our understanding of climate change. Marine heatwaves have a profound effect on all species and ecosystems that live in the top layer of the oceans. Their “climate” is different in several respects from the one we are familiar with above the surface, but it is changing along a similar pathway. Its overall rate of change is much like the one above the surface, both having started from scratch early in the twentieth century. Here is how the overall trajectory of the marine surface trend looks in the new study, using extreme marine heatwaves as guidance:
The study itself, which has open access at https://journals.plos.org/climate/article, contains figures that break this down regionally in several different ways, covered by a lengthy analysis. For high points of the analysis you can do better by reading several good reviews that quickly emerged, starting with a basic review by Phys.org— https://phys.org/news/2022-02-extreme-ocean.html that ends with this comment: “When marine ecosystems near the tropics experience intolerably high temperatures, key organisms such as corals, seagrass meadows, or kelp forests can collapse,” Van Houtan said. “Altering ecosystem structure and function threatens their capacity to provide life-sustaining services to human communities like supporting healthy and sustainable fisheries, buffering low-lying coastal regions from extreme weather events, and serving as a carbon sink to store the excess carbon put in the atmosphere from human-generated greenhouse emissions.”
A review by WIRED has extra depth about the unique and variable pattern of changes, how and when they unfold, and the resulting complications for life above as well as below—https://www.wired.com/story/extreme-heat-in-the-oceans-is-out-of-control/. In one example effects pertaining to the survival of phytoplankton are described, ending with this quote: “And crucially, phytoplankton produce most of the oxygen in our atmosphere. The reality is that we have two lungs on the planet: One of them’s green—the forests—and the other one’s blue—the ocean. The ocean supplies more than half of the oxygen that we breathe…It’s no understatement to say that the ocean is the beating heart of our climate system, and the ocean is absolutely critical for sustaining human life on this planet.”
A review by Tim Radford at Energy+Mix—https://www.theenergymix.com/2022/02/04/oceans-warming-losing-oxygen-as-coral-reefs-face-new-stress-studies-show%ef%bf%bc/ delivers a special warning tied to the declining productivity of fisheries: “The researchers worked from computer simulations of temperature changes and gas levels in the mesopelagic zones: the water layers between 200 and 1,000 metres deep, home to many of the world’s commercially-fished species. These could be the first to lose significant levels of oxygen as global temperatures rise. By 2080, deoxygenation could begin to affect all zones of the ocean. Tropical seas are naturally marked by lower oxygen levels, and these oxygen minimum zones could be spreading. More unexpectedly, oceans closer to the poles could be particularly vulnerable. Oxygen minimum zones actually are spreading into high latitude areas, both to the north and south.”
Separately, a high-level study published in 2020 in Nature Climate Change—https://news.ucar.edu/132759/climate-change-creating-significantly-more-stratified-ocean-new-study-finds revealed a trend of growing stratification of ocean temperatures during the past half-century. The study ” found that stratification in the upper 200 meters (656 feet) of the ocean increased by about 7% between 1960 and 2018.” According to co-author Kevin Trenberth, “The ocean has absorbed the majority of excess heat due to climate change…If that heat remains trapped at the surface and cannot easily be locked away deeper into the ocean, global warming and its impacts will be intensified, including the possibility of more vicious hurricanes feeding off of an increasingly warm sea surface…..These numbers reveal the distinct and significant impact humans are having on the oceans as we continue to emit greenhouse gases…The impact of these changes will not be limited to the oceans but will affect the entire Earth system and our day-to-day lives.” Marine ecosystems were not directly addressed by this study, but there is a clear relationship adding to one’s interpretation of the story featured above.
Carl