Partitioning of the Open Waters of the Gulf of Mexico Based on the Seasonal and Interannual Variability of Chlorophyll Concentration

Abstract

The seasonal and interannual variability of chlorophyll in the Gulf of Mexico open waters is studied using a three‐dimensional coupled physical‐biogeochemical model. A 5 years hindcast driven by realistic open‐boundary conditions, atmospheric forcings, and freshwater discharges from rivers is performed. The use of recent in situ observations allowed an in‐depth evaluation of the model nutrient and chlorophyll seasonal distributions, including the chlorophyll vertical structure. We find that different chlorophyll patterns of temporal variability coexist in the deep basin which thereby cannot be considered as a homogeneous region with respect to chlorophyll dynamics. A partitioning of the Gulf of Mexico open waters based on the winter chlorophyll concentration increase is then proposed. This partition is basically explained by the amount of nutrients injected into the euphotic layer which is highly constrained by the dynamic of the winter mixed layer. The seasonal and interannual variability appears to be affected by the variability of atmospheric fluxes and mesoscale dynamics (Loop Current eddies in particular). Finally, estimates of primary production in the deep basin are provided.

Picoplankton Carbon Biomass Assessments and Distribution of Prochlorococcus Ecotypes Linked to Loop Current Eddies During Summer in the Southern Gulf of Mexico

“…Due to an increased upper layer heat content in summer, the MLD over the ~23‐ to 23.5‐kg/m 3 isopycnal surface was relatively shallow, especially in XIXIMI‐5 (early summer), when it was on average 34 ± 7 m, while during XIXIMI‐4 and XIXIMI‐6 (late summer), the MLD was deeper at ~51 ± 23 m and 49 ± 12 m, respectively (Figures a–c). This upper layer structure is consistent with the monthly climatology of the MLD shown in Damien et al (), obtained from in situ and modeling data in the GoM, which describes a well‐stratified water column in summer periods and a gradual deepening from fall to winter when it reaches a maximum depth (~100 m).…”

Temporal variability of chlorophyll distribution in the Gulf of Mexico: bio-optical data from profiling floats

“…The major barrier to this is the lack of in situ observations over the water column (specifically in deep waters), which remain essential for model validation (Walsh et al, 1989). This valuable dataset has recently been used to calibrate a coupled biochemical/physical model (NEMO-PISCES) and to evaluate its performances in the GOM (Damien et al, 2017). The model results are consistent with the hypothesis stated in this work, but also highlight that the BOEM floats' sampling scheme is unable to resolve all the scales of temporal and spatial variability.…”

Ocean currents and coastal exposure to offshore releases of passively transported material in the Gulf of Mexico

“…The model includes 75 vertical levels (25 in the first 100 m). The atmospherical forcings are given by the interannual 3h-resolution Drakkar Forcing Sets 5 (DFS5) dataset The GoM circulation and the distribution of chlorophyll, further used in this study, displays consistent patterns with observations (Damien et al 2018).…”

“…The circulation fields (temperature, salinity, currents, diffusivity) have been obtained using a GoM regional configuration based on the Nucleus for European Modelling of the Ocean (NEMO), a state-of-the-art modeling environment of ocean related engines (Madec 2016). The configuration that we employed, called GOLFO12, is described in detail in Damien et al (2018) and similar to the one used in Garcia-Jove Navarro et al (2016). The resolution is 1/12°degree in longitude and latitude.…”

“…The impact of oil on organisms, foodwebs and ecosystems is complex and includes multiple feedbacks (Joye et al 2016, Short et al 2017). The chlorophyll concentration in the upper ocean is directly related with the primary productivity and is simulated by GOLFO12 in a consistent way compared to observations as shown by Damien et al (2018). In a very crude way, we computed a 'Chlorophyll-Tracer Index' (CTI) ( figure 3(d)) to quantify the co-presence of both chlorophyll and tracer.…”