ALBERT

Description: Ocean acidification has the capacity to impact future coccolithophore growth, photosynthesis, and calcification, but experimental culture work with coccolithophores has produced seemingly contradictory results and has focused on open-ocean species. We investigated the influence of pCO2 (between 250 and 750 µatm) on the growth, photosynthetic, and calcification rates of the estuarine coccolithophore Pleurochrysis carterae using a CO2 manipulation system that allowed for natural carbonate chemistry variability, representing the highly variable carbonate chemistry of coastal and estuarine waters. We further considered the influence of pCO2 on dark calcification. Increased pCO2 conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO2 concentrations of 750 µatm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO2 conditions in both light and dark incubations. This trend of increased calcification at higher pCO2 conditions fits into a recently developed substrate-inhibitor concept, which demonstrates a calcification optima concept that broadly fits the experimental results of many studies on the impact of increased pCO2 on coccolithophore calcification.

Description: Traditional methods for measuring whitecap coverage using digital video systems mounted to measure a large footprint can miss features that do not produce a high enough contrast to the background. Here, a method for accurately measuring the fractional coverage, intensity, and decay time of whitecaps using above-water radiometry is presented. The methodology was developed using data collected in the Southern Ocean under a wide range of wind and wave conditions. Whitecap quantities were obtained by employing a magnitude threshold based on the interquartile range of the radiance or reflectance signal from a single channel. Breaking intensity and decay time were produced from the integration of and the exponential fit to radiance or reflectance over the lifetime of the whitecap. When using the lowest magnitude threshold possible, radiometric fractional whitecap coverage retrievals were consistently higher than fractional coverage from high-resolution digital images, perhaps because the radiometer captures more of the decaying bubble plume area that is difficult to detect with photography. Radiometrically obtained whitecap measurements are presented in the context of concurrently measured meteorological (e.g., wind speed) and oceanographic (e.g., wave) data. The optimal fit of the radiometrically estimated whitecap coverage to the instantaneous wind speed, determined using robust linear least squares, showed a near-cubic dependence. Increasing the magnitude threshold for whitecap detection from 2 to 4 times the interquartile range produced a wind speed–whitecap relationship most comparable to the concurrently collected fractional coverage from digital imagery and previously published wind speed–whitecap parameterizations.

Description: The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region, provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Water samples for phytoplankton enumeration were collected from the upper 30 m during two cruises, the first to the South Atlantic sector (Jan–Feb 2011; 60 °W–15 °E and 36–60 °S) and the second in the South Indian sector (Feb–Mar 2012; 40–120 °E and 36–60 °S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Sub-Tropical, Polar, and Sub-Antarctic Fronts. The influence of environmental parameters, such as sea-surface temperature (SST), salinity, carbonate chemistry (i.e., pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macro-nutrients (i.e., nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB, was assessed statistically. Nanophytoplankton (cells 2–20 μm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, the coccolithophore Emiliania huxleyi and the diatoms Fragilariopsis nana, F. pseudonana and Pseudonitzschia sp. were the most dominant and widely distributed species. A combination of SST, macro-nutrient concentrations and pCO2 were the best statistical descriptors of biogeographic variability of biomineralizing species composition between stations. Emiliania huxleyi occurred in the silicic acid-depleted waters between the Sub-Antarctic Front and the Polar Front, indicating a favorable environment for this coccolithophore in the GCB after spring diatom blooms remove silicic acid to limiting levels. After full consideration of variability in carbonate chemistry and temperature on the distribution of nanoplankton in the GCB, we find that temperature remains the dominant driver of biogeography in a large proportion of the modern Southern Ocean.

Description: The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m) during two cruises, the first to the South Atlantic sector (January–February 2011; 60° W–15° E and 36–60° S) and the second in the South Indian sector (February–March 2012; 40–120° E and 36–60° S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST), salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macronutrients (nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB was assessed statistically. Nanophytoplankton (cells 2–20 µm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species after spring diatom blooms remove silicic acid. Multivariate statistics identified a combination of carbonate chemistry and macronutrients, covarying with temperature, as the dominant drivers of biomineralizing nanoplankton in the GCB sector of the Southern Ocean.