The northern Gulf of Mexico is one of the largest hypoxic zones in global coastal oceans. Although the hypoxia area has been expanding in recent years, it remains unclear how severe the hypoxia develops during past decades and what are human and climate contribution to the variation of it. Therefore, a comprehensive index is helpful to quantify the severity of the hypoxia in terms of multiple observable properties, such as volume , thickness, longitude span etc.. On the other hand, the contribution of direct and indirect factors is also helpful to be quantified for better understanding the influencing pathways and relative importance of human activities and climate change. In this study we performed a principal component analysis (PCA) of the observable characteristics of hypoxic events in the Gulf of Mexico during summer 1985-2014 and defined the first principal component as the Hypoxia Index (HI). The thickness and longitude span are decreasing, while bottom average DO, area and volume are increasing. Then the severity in terms of HI showed a slowly alleviating trend of 0.01 yr-1. Then, we attribute three direct hypoxia drivers--- residence time, stratification and solubility@(T, S), ---as climate change-originated, and one other direct hypoxia driver---respiration---as human activities-originated. Multi-regression analysis showed that these four direct drivers explained 50% of the total variation of HI. Moreover, using a coupling model in this half variation, we revealed that climate change contributes 65% and human 35 % to the nGOM hypoxia variation during 1985-2014. The quota for the four direct drivers are 8% for DO solubility, 35% for respiration, 18% for residence time, 39% for stratification, respectively. Our model suggests reducing respiration and stratification are the two major pathways for alleviating hypoxia in nGOM under the fast-changing climate background.
Primary Presenter: Kui Wang, Zhejiang University (kwi@zju.edu.cn)
Authors:
Climate and human-driven Inter-annual variability of hypoxia in the northern Gulf of Mexico
Category
Scientific Sessions > SS050 Disentangling Complex Long-Term pH and O2 Trends in Coastal and Estuarine Systems From Global and Regional Drivers
Description
Time: 06:30 PM
Date: 7/6/2023
Room: Mezzanine