Statistical identification of coastal hypoxia events controlled by wind-induced upwelling - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Continental Shelf Research Year : 2022

Statistical identification of coastal hypoxia events controlled by wind-induced upwelling

Abstract

Coastal areas are inhabited by a large fraction of the human population and provide many important ecosystem services, notably those related to fisheries. Hypoxia occurs when dissolved oxygen (DO) levels are so low that affect metabolic processes of many organisms, causing stress or even death. During the last decades, coastal hypoxia events have increased and nowadays these are one of the largest impacts of global change on coastal ecosystems. The entrance area of the Gulf of California is a region characterized by a shallow oxygen minimum zone and seasonal coastal upwelling events that may cause hypoxia by shoaling the oxycline. Under the hypothesis that some of the observed hypoxia episodes are controlled by coastal upwelling events, the objective of this work was to propose a novel statistical methodology to identify these events. From two oceanographic cruises, we observed the top of the oxycline depth at ∼30 m near the coast, while hypoxia was reached at ∼55 m. Also, DO time-series were recorded with autonomous sensors from early 2014 to late 2016 every 30 min in surface waters (5 m depth) off the Mazatlán City coastal zone (Mexico). This time series showed hypoxia events (and even anoxia, DO < detection limit = 0.06 mg L-1) at surface waters lasting from days to weeks. We propose a novel methodology to identify coastal hypoxia events controlled by coastal upwelling, which involves statistical and frequency analyses performed in conjunction with other physical variables such as sea surface temperature (SST), sea level, and the coastal upwelling index (CUI). Results confirmed that coastal wind-induced upwelling controls at least half of the hypoxia events identified. Further research is needed to understand the processes responsible for the other events, likely including mesoscale processes (such as eddies and internal waves) and the degradation of organic matter during eutrophic conditions. The methodology could be used in other eastern boundary upwelling systems of the world. These results should be of interest to coastal zone managers, local fishing communities, and the large fishing industry of this region to discriminate between natural and anthropogenic hypoxia events.
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Dates and versions

insu-03746454 , version 1 (05-08-2022)

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Carlos Alberto Herrera-Becerril, Joan-Albert Sanchez-Cabeza, León Felipe Álvarez Sánchez, Andrea Rebeca Lara-Cera, Ana Carolina Ruiz-Fernández, et al.. Statistical identification of coastal hypoxia events controlled by wind-induced upwelling. Continental Shelf Research, 2022, 233, ⟨10.1016/j.csr.2021.104634⟩. ⟨insu-03746454⟩
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