High Frequency Monitoring of Marine Carbonates System in a Northern Upwelling Ecosystem of the Humboldt Current System

Chair: Yuri Artioli

Victor M. Aguilera (1,2)*, Carolina Araya (1), Cristian A. Vargas (2,3)

1 Laboratorio de Oceanografía Desértico-Costera (LODEC), Instituto de Cs. Naturales Alexander von Humboldt, Universidad de Antofagasta, Antofagasta, Postcode 124000, Chile
2 Millennium Institute of Oceanography (IMO), Universidad de Concepción, Concepción, Postcode 4030000, Chile
3 Laboratorio de Funcionamiento de Ecosistemas Acuáticos (LAFE), Department of Aquatic Systems, Faculty of Environmental Sciences & Environmental Sciences Center, Concepción, Postcode 4030000, Chile

Background
Natural changes in the marine carbonate system (MCS) as well as their temporal and spatial fluctuations remain unstudied in upwelling ecosystems (UE). Among these, the northern upwelling area off Antofagasta in the Humboldt Current System (HCS) provides multiple and increasing ecosystem services whose connection with the CMS is unknown.

Methods
A bimonthly sub-surface sampling was performed between January and October 2015 in the northern upwelling region off Antofagasta, Chile (23°27′ S). Sampling, considering seawater pH, CO2 pressure (PCO2), carbonate concentration [CO3] and aragonite saturation state (ΩAr), was conducted at the base of the thermocline (10 m depth). Variables of the MCS were measured and estimated accordingly to good practices in ocean acidification (OA).

Findings
Sub-surface levels of pH were frequently lower than 8 (average 7.909 pH-units). Low values were concentrated in the upwelling favourable season (Jan. to Apr.) although an extremely low pH-episode also took place in winter months (< 7.6 pH-units). The PCO2 varied between 400 to >700, averaging 517 µatm during the study. Higher levels of PCO2, exceeding 400 µatm, were concentrated in the upwelling months. On the contrary to these temporal patterns, [CO3] which fluctuated between 100 and 1650 µM kg-1, were lower during upwelling season similarly to ΩAr whose most common values were <2. A strong correlation (R=0.6; p<0.001) was observed between salinity variability and variations in parameters of the MCS.

Conclusions
Beyond seasonal variations observed in this UE, sub-surface waters were permanently corrosive (low pH), CO2 over-saturated and overall different than typical ocean conditions. Interacting with oceanographic variables and propitiating mostly sub-optimal conditions for biocalcification, this UE may thus has the potential to influence, directly and indirectly, the response of local coastal marine functioning to current and future OA, in a place where mining, desalination and thermoelectric plants stands among anthropogenic stressors