Published in Science Advances is the study conducted by CNR-Ismar and Stazione Zoologica Anton Dohrn that takes a novel approach to understanding how the oceans, over the past 25 years, have responded to global climate change and the impact of those changes on microscopic marine organisms.
A research team involving the Institute of Marine Sciences of the National Research Council in Naples (CNR-Ismar) and theStazione Zoologica “Anton Dohrn” in Naples (SZN) has for the first time applied a climate model to 3D reconstructions based on observations to understand the health of the oceans over the past 25 years: the goal was to quantify and describe the dynamics of changes over that time frame and their impact on phytoplankton and other marine organisms. The results are published in Science Advances.
The study adopted a novel empirical methodology to identify emerging long-term behaviors of ocean dynamics and their effects on marine organisms: in particular, it examined six fundamental physical components to describe the dynamics of surface ocean layers-temperature, salinity, depth of the surface mixed layer, energy associated with horizontal and vertical currents, and energy input to the oceans by wind-and a quantitative indicator of the abundance of phytoplanktonic organisms, the microalgae that form the basis of the food chain and contribute to the sequestration of atmospheric CO2.
“Our approach combines oceanographic data, empirical climate modeling, and machine learning, differs from previous work based on single variables, and allows us to obtain a more complete picture of changes in the state and dynamics of the oceans,” explains Bruno Buongiorno Nardelli (CNR-Ismar), who led the study together with Daniele Iudicone (SZN). “Although much focus is placed on the analysis of global warming, the response of marine ecosystems, and microalgae in particular, is regulated by several other factors, such as the supply of nutrients from the deep layers and the availability of light for photosynthesis, both of which are modulated by the physical processes that drive the dynamic evolution of the system. Indeed, climate change acts on the oceans through complex processes that cannot be fully described or understood by analyzing individual variables separately. For example, an alteration in precipitation or wind may locally have a greater impact than surface warming. In addition, it is important to quantify changes over the long term by separating them of natural oscillations in the system that occur on multiyear scales.”
The study led to several pieces of evidence. A first consideration is that the response of the oceans to global warming affects not only surface water temperature, but also the hydrological cycle, currents, surface mixing, and cascading exchanges between the surface and deep layers. With regard to water temperature, it was found that the warming of the sea surface appears to be faster overall (about 0.022 °C/year instead of 0.014 °C/year) once natural oscillations, particularly those in the tropical Pacific belt, are properly isolated. In addition, some of the major marine current systems are shifting latitudinally and vertical exchanges are intensifying, changing the renewal of deep ocean waters and heat storage by the oceans. The long-term change in heat and salinity content along the water column also reveals a more complex response than the simple increase in stratification associated with surface warming.
As for the consequences of the observed changes on phytoplankton abundance, these were analyzed through a geographic classification that allowed local physical factors to be taken into account. “In this way, thanks to machine learning techniques, we have offered a solid basis to study the impact of climate change on marine ecosystems, which will allow in the future to better understand the relationship between ocean dynamics and plankton response, also through the use of innovative approaches such as the study of DNA and RNA of organisms, a new field of research for the scientific community,” adds Daniele Iudicone. “This knowledge will also be able to guide the development of more effective strategies for monitoring the oceans, such as optimizing autonomous observational systems based on the characteristics of a given region, designing targeted observational campaigns, developing innovative forecasting tools, and defining more effective measures for the preservation of marine ecosystems.”
Further info:
Bruno Buongiorno Nardelli
Cnr-Ismar
bruno.buongiornonardelli@cnr.it
081/5423852
Daniele Iudicone, Stazione Zoologica Anton Dohrn, email: daniele.iudicone@szn.it
Left side image: Representation of the geographic classification of oceanic regions showing homogeneous change dynamics, obtained by the K-means algorithm.
