Evaluation of Particulate Organic Carbon from Modis-Aqua in a Marine-Coastal Water Body

Abstract

Abstract La Paz Bay (LPB) in Mexico is one of the largest marine-coastal bodies of water in the Gulf of California (GC) and is ecologically important for the feeding, reproduction, and refuge of marine species. Although Particulate Organic Carbon (POC) is an important reservoir of oceanic carbon and an indicator of productivity in the euphotic zone, studies in this region are scarce. This study evaluates the performance of satellite-derived POC in LPB from January 2003 to December 2020. Data from POC and Chlorophyll-a (Chla-a) from MODIS-Aqua and sea surface temperature (SST) from MUR were used. Initially, a match-up analysis was applied to compare the satellite products with in situmeasurements obtained from a sediment trap installed in Alfonso Basin, Mexico. Subsequently, spatial and seasonal variability patterns of POC were analyzed using Empirical Orthogonal Functions (EOFs), power spectral density (PSD), geospatial correlations of each pair of variables, the POC:Chla-a ratio, and multivariate techniques. The results of the matchmaking analysis between in situ and satellite series show that the satellite estimates consistently represent the variability and mean values measured in situ. The distribution of POC characterizes two seasons with their respective transition periods and five subregions where POC exhibits its maximum variability. Two of these subregions coincide with the reported locations of winter and summer eddies in BP, while the remaining three correspond to the coastal zone and the two regions where LPB interacts with the GC. Associations, variability nodes, and multiple linear regression analysis suggest that POC fluctuations in LPB are mainly driven by biological processes and, to some extent, by seasonal SST and wind intensity. Finally, based on the concentrations obtained in this study, this area can be considered as a reservoir of POC for the marine and atmospheric regions of northwest Mexico.