Marine coastal chemistry related to inland inputs in San Jorge gulf and the adjacent north coast.

Coastal regions are sectors where human activities impact the marine ecosystem, and if necessary control measures are not taken, they can generate negative consequences for health and ecosystem services. Within the framework of the Pampa Azul initiative and under the One Health paradigm, the interconnection between the terrestrial and marine environments of the San Jorge Gulf and the adjacent north coast has been studied. In November, 2022, a campaign was carried out aboard the R/V "Mar Argentino" at thirty-four stations near the coast. There, for the first time, simultaneously with in-situ measurements of physical variables, macronutrients (NO3-, PO4-3, Si(OH)4 and NH4+), particulate silica (BSi and LSi), trace metals in the particulate material (Cd, Cu, Cr, Fe and Pb) and the phytoplankton community were analyzed. The results showed a high nutrient dynamic, with a significant influence of natural stratification and anthropogenic condition due to the discharge of effluents off the cities of Comodoro Rivadavia and Caleta Olivia. Under natural conditions, NO3- and Si(OH)4 limited the surface primary production by 47 % and 41 %, respectively. Additionally, due to the anthropogenic contribution, NH4+ concentration reached 3 µM, increasing the proliferation of nanophytoplankton, among other consequences. As a result of nutrient dynamics, the uptake of Si(OH)4, the growth rate of diatoms and their production of BSi were decoupled. Furthermore, a significant correlation between LSi and Fe in particulate matter was evidenced, opening new lines of research that relate dust storms to primary productivity in this marine environment. The measured concentrations of trace metals do not appear to be a biological risk; however, contamination by Cd (37.6 µg g- 1 d.w.) and Cu (214.97 µg g- 1 d.w.) off Camarones poses a significant concern that must be addressed in the immediate future.

Global variability in seawater Mg:Ca and Sr:Ca ratios in the modern ocean.

Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth-ocean-atmosphere dynamic exchange of elements. The ratios' dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios' variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect.