Articles | Volume 14, issue 24
Research article
15 Dec 2017
Research article |  | 15 Dec 2017

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

Orens Pasqueron de Fommervault, Paula Perez-Brunius, Pierre Damien, Victor F. Camacho-Ibar, and Julio Sheinbaum

Abstract. Chlorophyll concentration is a key oceanic biogeochemical variable. In the Gulf of Mexico (GOM), its distribution, which is mainly obtained from satellite surface observations and scarce in situ experiments, is still poorly understood. In 2011–2012, eight profiling floats equipped with biogeochemical sensors were deployed for the first time in the GOM and generated an unprecedented dataset that significantly increased the number of chlorophyll vertical distribution measurements in the region. The analysis of these data, once calibrated, permits us to reconsider the spatial and temporal variability of the chlorophyll concentration in the water column. At a seasonal scale, results confirm the surface signal seen by satellites, presenting maximum concentrations in winter and low values in summer. It is shown that the deepening of the mixed layer is the primary factor triggering the chlorophyll surface increase in winter. In the GOM, a possible interpretation is that this surface increase corresponds to a biomass increase. However, the present dataset suggests that the basin-scale climatological surface increase in chlorophyll content results from a vertical redistribution of subsurface chlorophyll and/or photoacclimation processes, rather than a net increase of biomass. One plausible explanation for this is the decoupling between the mixed-layer depth and the deep nutrient reservoir since mixed-layer depth only reaches the nitracline in sporadic events in the observations. Float measurements also provide evidence that the depth and the magnitude of the deep chlorophyll maximum is strongly controlled by the mesoscale variability, with higher chlorophyll biomass generally observed in cyclones rather than anticyclones.

Short summary
The Gulf of Mexico is known to be characterized by a low abundance in phytoplankton. However, observations across the basin are scarce and prevent an accurate description of the mechanism controlling its distribution and dynamics. The recent deployment of autonomous profiling floats equipped with bio-optical sensors was a great opportunity to explore the phytoplankton in the Gulf Of Mexico. This study presents the analysis of this novel dataset.
Final-revised paper