Patterns in the temporal complexity of global chlorophyll concentration

Abstract

Decades of research have relied on satellite-based estimates of chlorophyll-a concentration to identify oceanographic processes and plan in situ observational campaigns; however, the patterns of intrinsic temporal variation in chlorophyll-a concentration have not been investigated on a global scale. Here we develop a metric to quantify time series complexity (i.e., a measure of the ups and downs of sequential observations) in chlorophyll-a concentration and show that seemingly disparate regions (e.g., Atlantic vs Indian, equatorial vs subtropical) in the global ocean can be inherently similar. These patterns can be linked to the regularity of chlorophyll-a concentration change and the likelihood of anomalous events within the satellite record. Despite distinct spatial changes in decadal chlorophyll-a concentration, changes in time series complexity have been relatively consistent. This work provides different metrics for monitoring the global ocean and suggests that the complexity of chlorophyll-a time series can be independent of its magnitude.

Contrasted Trends in Chlorophyll‐a Satellite Products

“…The discrepancy between Globcolour-GSM and the four other purely radiometric derived products emerges when the VIIRS sensor is embedded in the Globcolour-GSM time series. Our results bring a new perspective to studies using only one merged product to assess and explain global Schl trend (e.g., Agarwal et al, 2024;Tian & Zhang, 2023). Care should also be taken when analyzing the spatio-temporal patterns of such trends, as biases such as the one reported here in Globcolour-GSM may lead to hasty conclusions.…”

“…Nowadays, several Schl "time-series for climate" exist and they have begun to be used in Schl trends assessment. Some recent studies have notably considered only one multi-sensors product to draw conclusions about Schl trends (e.g., Agarwal et al, 2024;Tian & Zhang, 2023). Indeed, in the latter study, the authors reported a robust decrease of Schl at global scale over the last 25 years.…”