محیط زیست و توسعه فرابخشی (Apr 2024)
Assessing Changes in Sink and Source Intensities of Carbon Dioxide in the West Asian Seas
Abstract
Introduction: The rising CO2 levels in the atmosphere are a major concern for the environment due to their potential impact on future global climate and the anthropogenic oceanic CO2 sink. Greenhouse gas emissions in the Middle East and Eastern Mediterranean regions have significantly increased since the 1950s. Oceans are crucial carbon reservoirs on Earth. Understanding the spatio-temporal variability in CO2 exchange between the atmosphere and sea, as well as its drivers, is essential for assessing ocean vulnerability and quantifying their ability to store carbon under future climate conditions. This study examines the spatial and temporal changes in sea surface CO2 (PCO2) and atmosphere-sea CO2 flux (FCO2) in the Persian Gulf, Red Sea, Caspian Sea, Arabian Sea, and Mediterranean Sea from 1982 to 2019. Additionally, the research will investigate the underlying mechanisms of seasonal PCO2 variability.Materials and Methods: This study utilizes data from the Max Planck Institute to examine the temporal and spatial changes of air-sea CO2 exchange. The data was obtained by fitting a biogeochemistry diagnostic model of the ocean mixed layer to the ocean surface CO2 partial pressure data. Reanalysis data of temperature and wind speed was used to investigate the factors controlling the variability of FCO2 and PCO2. Additionally, the study examined the factors influencing the variability of PCO2 in each pixel, including the effects of temperature change and non-thermal components such as circulations, vertical mixing, biological changes, dissolved inorganic carbon, and upwelling systems.Results: CO2 flux has been estimated at up to 50 g C m-2 year-1 over the western regions of the Arabian Sea. The Red Sea is a source of CO2 in all seasons, except for the northern regions, which is a sink of CO2 in winter and spring. The intensity of the CO2 sink has increased in the Persian Gulf and the western areas of the Mediterranean Sea, and decreased in the eastern areas of the Mediterranean Sea and the Black Sea. The CO2 source intensity has decreased in most of the seas, including the Arabian Sea, the Red Sea and the central areas of the Mediterranean Sea during the studied period. Temperature is the most important driver of the seasonal cycle of PCO2 in the Mediterranean Sea, Caspian Sea, Persian Gulf and Red Sea. In addition to temperature, the non-thermal component also plays an important role in the central regions of the Red Sea and the southern regions of the Persian Gulf. The CO2 flux over the seas of West Asia follow the pattern of sea surface partial pressure of CO2. The CO2 flux has a high correlation of +0.80 with the wind speed in the western regions of the Arabian Sea, which is related to the summer monsoon. The high PCO2 (500 μatm) and FCO2 (140 g C m-2 year-1) over the northwestern Arabian Sea in the summer season are due to the monsoon driven upwelling of CO2-rich waters from the lower levels.Discussion: Significant changes were most noticeable in the western Arabian Sea. This signifies positive steps towards reducing anthropogenic CO2 emissions. This region holds great socio-economic importance for the coastal countries, with its inhabitants relying heavily on fishing for their livelihood. This underscores the immediate need for science-based management strategies to address the effects of climate change and safeguard the socio-economic well-being of coastal communities in this area.
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