Inorganic Nutrients in the Deep Water Region of the Gulf of Mexico: What Have we Learnt from a Baseline Study of the CIGoM Project.

Victor F Camacho-Ibar1, Augusto Valencia2, Cristian Hakspiel3, Jorge Velasquez4, María del Carmen Ávila López5, Mauricio Muñoz-Anderson1 and Erika Lee4, (1)Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas, Ensenada, BJ, Mexico, (2)Autonomous University of Baja California, Instituto de Investigaciones Oceanologicas, Ensenada, BJ, Mexico, (3)Autonomous University of Baja California, Instituto de Investigaciones Oceanologicas, Enesenada, BJ, Mexico, (4)Universidad Autónoma de Baja California, Facultad de Ciencias Marinas, Ensenada, BJ, Mexico, (5)Autonomous University of Baja California, Instituto de Investigaciones Oceanologicas, Ensenada, Mexico
Abstract:
As part of the CIGoM (Consorcio de Investigación del Golfo de México) project, a baseline study of inorganic nutrients (nitrate+nitrite, NN; phosphate, PO4; and silicic acid, H4SiO4) was carried out in the deep water region (>1000 m) of the Gulf of Mexico (GoM) in the Mexican Exclusive Economic Zone. During four oceanographic campaigns (XIXIMI-04 to XIXIMI-07) carried out mostly during the warm seasons from 2015 to 2018, water samples were collected (and measured against certified reference materials for nutrients in seawater) from the surface down to near the bottom, at stations spanning from the Yucatan Channel to the Bay of Campeche at the southeastern GoM. In this work a synthesis of the results of these campaigns is presented, focusing on features characteristic of different water masses. Nutrient concentrations are relatively constant below 1200 m, the domain of the Labrador Seawater, and an enrichment in H4SiO4 compared to source waters suggests that this Upper Labrador Seawater is supplied from the North Atlantic through the Windward passage into the Caribbean. NN and PO4 in the GoM show a maximum at the core of the AAIW, but maxima of these nutrients seem to be slightly uncoupled. The vertical distribution of nutrients in intermediate (300-1000 m) and upper (0-300 m) water masses is clearly influenced by mesoscale dynamics. Recently shed intense LCEs show the lowest nutrient concentrations throughout the upper 1000 m as compared to cyclonic eddies and also compared to the previously shed LCE. Such difference has implications in the availability of nutrients in the euphotic zone throughout the gulf, as indicated by nutrient concentrations integrated from 0 to 150 m (the assumed depth of the euphotic zone). For example, during the XIXIMI-05 campaign NN integrated values range from 21 to 260 mmol m-2 in LCEs and from 412 to 886 mmol m-2 in cyclonic eddies while the range for H4SiO4 is 187-239 and 260-438 mmol m-2, respectively.
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