Seawater carbonate chemistry and primary and bacterial production in Antarctic coastal waters during austral summer

• Main Authors: Westwood, Karen, Thomson, Paul G, van den Enden, Rick, Maher, L E, Wright, S, Davidson, Andrew T
• Format: Dataset
• Language: English
• Published: PANGAEA 2018
• Subjects: Alkalinity; total; Ammonium; Antarctic; Aragonite saturation state; Bacteria; Bacterial production of carbon; Bacterial production of carbon per cell; Bicarbonate ion; Biomass/Abundance/Elemental composition; Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; organic; particulate; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chlorophyll a; Coast and continental shelf; Community composition and diversity; Containers and aquaria (20-1000 L or < 1 m**2); Davis_Station_OA; Entire community; EXP; Experiment; Experiment duration; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Gross primary production of carbon; Gross primary production of oxygen; Laboratory experiment; Maximum photosynthetic efficiency per chlorophyll a biomass; Nanoflagellates; heterotrophic; Net community production of oxygen; Nitrate and Nitrite; OA-ICC; Ocean Acidification International Coordination Centre; Other metabolic rates; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Phosphate; Photosynthetic efficiency; Antarc*; Antarctica; East Antarctica; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.902309; https://doi.org/10.1594/PANGAEA.902309

Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650 L) were filled with 200 μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12 days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mg C mg/chl a/h) decreased with elevated CO2, clearly reducing rates of total gross primary production (mg C/L/h). Rates of cell-specific bacterial productivity (μg C/cell/h) also decreased under elevated CO2, yet total bacterial production (μg C/L/h) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations > 2 × present day (> 780 ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate + nitrite (NOx) availability. At NOx concentrations < 1.5 μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may ...