Bio-optical evidence for increasing Phaeocystis dominance in the Barents Sea

Abstract

Increasing contributions of prymnesiophytes such as Phaeocystis pouchetii and Emiliania huxleyi to Barents Sea (BS) phytoplankton production have been suggested based on in situ observations of phytoplankton community composition, but the scattered and discontinuous nature of these records confounds simple inference of community change or its relationship to salient environmental variables. However, provided that meaningful assessments of phytoplankton community composition can be inferred based on their optical characteristics, ocean-colour records offer a potential means to develop a synthesis between sporadic in situ observations. Existing remote-sensing algorithms to retrieve phytoplankton functional types based on chlorophyll-a ( chl-a ) concentration or indices of pigment packaging may, however, fail to distinguish Phaeocystis from other blooms of phytoplankton with high pigment packaging, such as diatoms. We develop a novel algorithm to distinguish major phytoplankton functional types in the BS and apply it to the MODIS-Aqua ocean-colour record, to study changes in the composition of BS phytoplankton blooms in July, between 2002 and 2018, creating time series of the spatial distribution and intensity of coccolithophore, diatom and Phaeocystis blooms. We confirm a north-eastward expansion in coccolithophore bloom distribution, identified in previous studies, and suggest an inferred increase in chl-a concentrations, reported by previous researchers, may be partly explained by increasing frequencies of Phaeocystis blooms. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.

Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer

“…Whether diatoms or P. pouchetii dominated the bloom had an impact on the carbon export, as the highest export fluxes were found in stations dominated by diatoms (Figure 9). If Phaeocystis blooms become more common in the Arctic (Orkney et al, 2020), it is likely to reduce absolute mass flux and thus limit pelagic-benthic coupling in the future Arctic SIZ, especially if no special circumstances are present to facilitate their export (e.g., Wollenburg et al, 2018). The presence of advected Atlantic water masses likely affected the magnitude of export fluxes by changing the growth conditions of phytoplankton blooms and their synchrony with the large zooplankton grazers.…”

“…This shift toward smaller cells has further been modeled to increase the length of the food web and, consequently, retain phytoplankton carbon and to be respired in the upper water column (Vernet et al, 2017). In addition, the decline in silicic acid concentrations, an essential nutrient for diatom growth, in the Nordic seas and Barents Sea (Hátún et al, 2017) seems to have led to the increased dominance of Phaeocystis in the Barents Sea (Orkney et al, 2020). Shifts in bloomforming protists' composition, as well as their seasonal timing in relation to heterotrophic consumers, will greatly influence vertical export.…”

“…As the Arctic is warming and stratification is strengthening as a result of freshening, generally reducing nutrient supply, the flagellated species, such as Phaeocystis spp., have been predicted to become more dominant, because their high surface-area-tovolume ratio makes them more efficient at acquiring nutrients, and their size and colonies embedded in polysaccharide gel matrixes make them hydrodynamically resistant to sinking (Li et al, 2009;Peter and Sommer, 2012;Metfies et al, 2016). A recent study has found bio-optical evidence for increasing dominance of Phaeocystis pouchetii in the Barents Sea (Orkney et al, 2020). This shift toward smaller cells has further been modeled to increase the length of the food web and, consequently, retain phytoplankton carbon and to be respired in the upper water column (Vernet et al, 2017).…”

DMS emissions from the Arctic marginal ice zone

“…This plasticity, the ability to use regenerated nitrogen forms (Sanderson et al, 2008), no silicate requirement (Ardyna et al, 2020), the protection from zooplankton predators provided by mucilaginous colonies (Long et al, 2007;Verity et al, 2007), and even allelopathy (Hansen and Eilertsen, 2007) may explain the ability of Phaeocystis to outcompete diatoms and form massive blooms under certain conditions. The northward expansion of Phaeocystis along with Atlantic waters in the Barents Sea detected by remote sensing (Orkney et al, 2020), analogous to that of its temperate relative Emiliania huxleyi in subpolar waters, indicates ongoing floristic shifts are impacting Arctic E DMS . Still, what factors control Phaeocystis abundance and eventual dominance elsewhere in the Arctic remains unknown.…”

The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning

“…Using these data, they develop and test a bio-optical model that links commonly measured parameters from glider-mounted sensors with satellite-derived measurements of bulk optical properties. Combining satellite data with discrete shipboard measurements, Orkney et al [25] adopt a similar philosophy to highlight the northward migration of certain phytoplanktonic groups (especially Phaeocystis algae) in the Barents Sea. They confirm previous suggestions of a north-eastward expansion in coccolithophore blooms and suggest that observations of increased levels of chlorophyll a in the region may, at least in part, be explained by increasing frequencies of Phaeocystis blooms.…”