Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold.

The Great Calcite Belt (GCB) is a region of elevated surface reflectance in the Southern Ocean (SO) covering~16% of the global ocean and is thought to result from elevated, seasonal concentrations of coccolithophores. Here we describe field observations and experiments from two cruises that crossed the GCB in the Atlantic and Indian sectors of the SO. We confirm the presence of coccolithophores, their coccoliths, and associated optical scattering, located primarily in the region of the subtropical, Agulhas, and Subantarctic frontal regions. Coccolithophore-rich regions were typically associated with high-velocity frontal regions with higher seawater partial pressures of CO 2 (pCO 2 ) than the atmosphere, sufficient to reverse the direction of gas exchange to a CO 2 source. There was no calcium carbonate (CaCO 3 ) enhancement of particulate organic carbon (POC) export, but there were increased POC transfer efficiencies in high-flux particulate inorganic carbon regions. Contemporaneous observations are synthesized with results of trace-metal incubation experiments, 234 Th-based flux estimates, and remotely sensed observations to generate a mandala that summarizes our understanding about the factors that regulate the location of the GCB.

We report surface observations of a mesoscale coccolithophore bloom at the shelf break of the Patagonian Shelf during December 2008, representing the densest coccolithophore population in the Southern Ocean. The bloom was most intense within the Falklands Current, northeast of the Falkland Islands. Emiliania huxleyi dominated bloom waters, with a mixed E. huxleyi and Prorocentrum sp. dinoflagellate bloom to the west and mixed assemblage of diatoms, dinoflagellates, and flagellates to the east. Optical measurements of coccolith light scattering, analytical measurements of their calcite, and microscopic counts all showed this to be an intense coccolithophore bloom. Average particulate inorganic carbon per coccolith in the bloom was low, typical of the B coccolith morphotype and in agreement with independent measurements made by scanning electron microscopy. Highest particulate inorganic carbon (measured optically and chemically) was observed when residual nitrate (defined as the difference, [NO { 3 ] 2 [Si(OH) 4 ]) was 10-17 mmol L 21 and nitrate to phosphate ratios were close to Redfield values. Elevated particle backscattering was observed in the E. huxleyi bloom, whereas the highest particle scattering occurred in the adjoining Prorocentrum sp. bloom. Backscattering from coccolithophores represented up to 50% of the total backscattering (from organic and inorganic particles) along the main axis of the E. huxleyi bloom. Chlorophyll-specific absorption in the coccolithophore bloom was typical of marine phytoplankton. Residual nitrate plotted vs. temperature showed that the E. huxleyi bloom was associated with waters between 5uC and 15uC, with depleted silicate. Results suggest that previous drawdown of silicate by diatoms occurred prior to the densest E. huxleyi blooms over the Patagonian Shelf. We speculate that such conditions might also be important for annual development of the broader Great Calcite Belt and other coccolithophore blooms.

Abstract. 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.

A time series of organic carbon export from Gulf of Maine (GoM) watersheds was compared to a time series of biological, chemical, bio-optical, and hydrographic properties, measured across the GoM between Yarmouth, NS, Canada, and Portland, ME, U.S. Optical proxies were used to quantify the dissolved organic carbon (DOC) and particulate organic carbon in the GoM. The Load Estimator regression model applied to river discharge data demonstrated that riverine DOC export (and its decadal variance) has increased over the last 80 years. Several extraordinarily wet years (2006)(2007)(2008)(2009)(2010) resulted in a massive pulse of chromophoric dissolved organic matter (CDOM; proxy for DOC) into the western GoM along with unidentified optically scattering material (<0.2 μm diameter). A survey of DOC in the GoM and Scotian Shelf showed the strong influence of the Gulf of Saint Lawrence on the DOC that enters the GoM. A deep plume of CDOM-rich water was observed near the coast of Maine which decreased in concentration eastward. The Forel-Ule color scale was derived and compared to the same measurements made in 1912-1913 by Henry Bigelow. Results show that the GoM has yellowed in the last century, particularly in the region of the extension of the Eastern Maine Coastal Current. Time lags between DOC discharge and its appearance in the GoM increased with distance from the river mouths. Algae were also a significant source of DOC but not CDOM. Gulf-wide algal primary production has decreased. Increases in precipitation and DOC discharge to the GoM are predicted over the next century.