Seawater carbonate chemistry and dissolved organic matter dynamics during an oligotrophic ocean acidification experiment using large-scale mesocosms (KOSMOS 2014)

• Main Authors: Zark, Maren, Broda, Nadine, Hornick, Thomas, Grossart, Hans-Peter, Riebesell, Ulf, Dittmar, Thorsten
• Format: Dataset
• Language: English
• Published: PANGAEA 2023
• Subjects: Alkalinity; total; Aragonite saturation state; Bicarbonate ion; Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; organic; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; DATE/TIME; Day of experiment; Entire community; Event label; Field experiment; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); KOSMOS_2014; KOSMOS_2014_Atlantic-Reference; KOSMOS_2014_Mesocosm-M1; KOSMOS_2014_Mesocosm-M2; KOSMOS_2014_Mesocosm-M3; KOSMOS_2014_Mesocosm-M4; KOSMOS_2014_Mesocosm-M5; KOSMOS_2014_Mesocosm-M6; KOSMOS_2014_Mesocosm-M7; KOSMOS_2014_Mesocosm-M8; KOSMOS_2014_Mesocosm-M9; MESO; Mesocosm experiment; Mesocosm or benthocosm; Nitrogen; total dissolved; North Atlantic; OA-ICC; Ocean Acidification International Coordination Centre; Other studied parameter or process; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Salinity; Sample code/label; Subtropical North Atlantic; Temperate; Temperature; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.958964; https://doi.org/10.1594/PANGAEA.958964

Dissolved organic matter (DOM) represents a major reservoir of carbon in the oceans. Environmental stressors such as ocean acidification (OA) potentially affect DOM production and degradation processes, e.g., phytoplankton exudation or microbial uptake and biotransformation of molecules. Resulting changes in carbon storage capacity of the ocean, thus, may cause feedbacks on the global carbon cycle. Previous experiments studying OA effects on the DOM pool under natural conditions, however, were mostly conducted in temperate and coastal eutrophic areas. Here, we report on OA effects on the existing and newly produced DOM pool during an experiment in the subtropical North Atlantic Ocean at the Canary Islands during an (1) oligotrophic phase and (2) after simulated deep water upwelling. The last is a frequently occurring event in this region controlling nutrient and phytoplankton dynamics. We manipulated nine large-scale mesocosms with a gradient of pCO2 ranging from 350 up to 1,030 μatm and monitored the DOM molecular composition using ultrahigh-resolution mass spectrometry via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). An increase of 37 μmol L−1 DOC was observed in all mesocosms during a phytoplankton bloom induced by simulated upwelling. Indications for enhanced DOC accumulation under elevated CO2 became apparent during a phase of nutrient recycling toward the end of the experiment. The production of DOM was reflected in changes of the molecular DOM composition. Out of the 7,212 molecular formulae, which were detected throughout the experiment, 50% correlated significantly in mass spectrometric signal intensity with cumulative bacterial protein production (BPP) and are likely a product of microbial transformation. However, no differences in the produced compounds were found with respect to CO2 levels. Comparing the results of this experiment with a comparable OA experiment in the Swedish Gullmar Fjord, reveals similar succession patterns for individual compound pools during a ...