Extreme event waves in marine ecosystems: an application to Mediterranean Sea surface chlorophyll

Abstract

Abstract. We propose a new method to identify and characterise the occurrence of prolonged extreme events in marine ecosystems at the basin scale. There is growing interest in events that can affect ecosystem functions and services in a changing climate. Our method identifies extreme events as the peak occurrences over a predefined threshold (i.e. the 99th percentile) computed from a local time series, and it defines a series of extreme events that are connected over space and time as an extreme event wave (EEW). The main features of EEWs are then characterised by a set of novel indexes, related to initiation, extent, duration and strength. The indexes associated with the areas covered by each EEW were then statistically analysed to highlight the main features of the EEWs in the considered domain. We applied the method to a multidecadal series of winter–spring daily chlorophyll fields that was produced by a validated coupled hydrodynamic–biogeochemical model of the Mediterranean open-sea ecosystem. This application allowed us to identify and characterise surface chlorophyll EEWs in the period from 1994 to 2012. Finally, a fuzzy classification of EEW indexes provided bio-regionalisation of the Mediterranean Sea based on the occurrence of chlorophyll EEWs with different regimes.

High-Resolution Reanalysis of the Mediterranean Sea Biogeochemistry (1999–2019)

“…Among the subbasins, the northern Tyrrhenian Sea (tyr1), which exhibits a high variability and is a transitional area (as reported in several regionalization analyses, e.g., Ayata et al, 2018;Di Biagio et al, 2020), reveals a normalized RMSD value higher than 1 for at least four variables in several layers.…”

“…Most Level 1 and 2 metrics are spatially evaluated for 16 Mediterranean sea subbasins (Figure 1), in the open sea region (defined as the area with a depth greater than 200 m), and for the full water column in selected layers, i.e., 0-10, 10-30 m (for certain metrics these layers are merged into a single layer, namely, 0-30 m), 30-60, 60-100, 100-150, 150-300, 300-600, and 600-1,000 m. In the coastal areas, the reanalysis accuracy can be assessed only for surface chlorophyll using the CMEMS satellite product and for other variables and a few subbasins according to in situ data availability. The 16 subbasins synthesize the heterogeneity in the Mediterranean Sea into homogeneous areas, considering previous bioregionalization analyses (D'Ortenzio and Ribera d'Alcalà, 2009;Ayata et al, 2018;Di Biagio et al, 2020;El Hourany et al, 2021;Novi et al, 2021).…”

The invasive blue crab Callinectes sapidus thermal response: Predicting metabolic suitability maps under future warming Mediterranean scenarios

“…The model parameters were used to predict the current and future potential occurrence of C. sapidus based on the adaptation of respiration rate to the future increase of temperature (Sakallı, 2017;Di Biagio et al, 2020). Parameters related to the maximum respiration rate (rmax), the optimal temperature (Topt) and the full curve width (a) were extracted from the TPC model and used in the thermal habitat suitability maps.…”

Copernicus Ocean State Report, issue 6

“…We introduced an indicator to monitor locally the euphotic layer potential fertilization during the winter season in the Mediterranean Sea and we associated, for each point of the basin, its temporal variability with the large-scale circulation patterns driving the atmospheric circulation over the region. As shown in Di Biagio et al (2020), the choice of a specific threshold in each point of the basin allowed us to analyze the potential fertilization in relation to the local ecosystem properties. We found a relevant influence of the EA on the fertilization indicators in the Gulf of Lion.…”

“…Secondly, we considered in each grid point of the domain the 90th percentile of the daily winter concentration of PO 4 and NO 3 (hereafter: 90th PO4 and 90th NO3 ) in the period 1999-2019, where winter corresponds to December, January and February (hereafter: DJF). The 90th percentile threshold is calculated in each point of the basin in order to evaluate the potential fertilization in relation to the local mean trophic level, as recently proposed for local extreme events in Di Biagio et al (2020).…”