Effect of demographic noise in a phytoplankton-zooplankton model of bloom dynamics

An extension of the Truscott-Brindley model (Bull. Math. Biol. {\bf 56}, 981 (1994)) is derived to account for the effect of demographic fluctuations. In the presence of seasonal forcing, and sufficiently shallow water conditions, the fluctuations induced by the discreteness of the zooplankton component appear sufficient to cause switching between the bloom and no-bloom cycle predicted at the mean-field level by the model.The destabilization persists in the thermodynamic limit of a water basin infinitely extended in the horizontal direction.Comment: 10 pages, 8 figure

A Global Diatom Database- Abundance, Biovolume and Biomass in the World Ocean

Phytoplankton identification and abundance data are now commonly feeding plankton distribution databases worldwide. This study is a first attempt to compile the largest possible body of data available from different databases as well as from individual published or unpublished datasets regarding diatom distribution in the world ocean. The data obtained originate from time series studies as well as spatial studies. This effort is supported by the Marine Ecosystem Model Inter-Comparison Project (MAREMIP), which aims at building consistent datasets for the main plankton functional types (PFTs) in order to help validate biogeochemical ocean models by using carbon (C) biomass derived from abundance data. In this study we collected over 293 000 individual geo-referenced data points with diatom abundances from bottle and net sampling. Sampling site distribution was not homogeneous, with 58% of data in the Atlantic, 20% in the Arctic, 12% in the Pacific, 8% in the Indian and 1% in the Southern Ocean. A total of 136 different genera and 607 different species were identified after spell checking and name correction. Only a small fraction of these data were also documented for biovolumes and an even smaller fraction was converted to C biomass. As it is virtually impossible to reconstruct everyone\u27s method for biovolume calculation, which is usually not indicated in the datasets, we decided to undertake the effort to document, for every distinct species, the minimum and maximum cell dimensions, and to convert all the available abundance data into biovolumes and C biomass using a single standardized method. Statistical correction of the database was also adopted to exclude potential outliers and suspicious data points. The final database contains 90 648 data points with converted C biomass. Diatom C biomass calculated from cell sizes spans over eight orders of magnitude. The mean diatom biomass for individual locations, dates and depths is 141.19 μg Cl-1, while the median value is 11.16 μg Cl-1. Regarding biomass distribution, 19% of data are in the range 0-1 μg Cl-1, 29% in the range 1-10 μg Cl-1, 31% in the range 10-100 μg Cl-1, 18% in the range 100-1000 μg Cl-1, and only 3% \u3e 1000 μg Cl-1. Interestingly, less than 50 species contributed to \u3e90% of global biomass, among which centric species were dominant. Thus, placing significant efforts on cell size measurements, process studies and C quota calculations of these species should considerably improve biomass estimates in the upcoming years. A first-order estimate of the diatom biomass for the global ocean ranges from 444 to 582 Tg C, which converts to 3 to 4 Tmol Si and to an average Si biomass turnover rate of 0.15 to 0.19 d-1. Link to the dataset: doi:10.1594/PANGAEA.777384

A multi-trophic marker approach reveals high feeding plasticity in Barents Sea under-ice fauna

Microalgae growing within and attached to the bottom of Arctic sea ice (sympagic algae) can serve as a nutritious food resource for animals inhabiting the sea-ice water interface (under-ice fauna), particularly during the bottom ice-algal bloom in spring. As a consequence, under-ice fauna is likely impacted by sea-ice decline and changes in ice-algal primary production. To investigate this, samples of pelagic (=PPOM) and ice-associated particulate organic matter (=IPOM) and the iceassociated amphipods Apherusa glacialis and Eusirus holmii, and polar cod (Boreogadus saida), collected below ridged sea ice at two locations with pronounced differences in productivity in the northern Barents Sea during May 2021, were assessed for their trophic marker content. Specifically, we investigated the composition of diatom- and dinoflagellate-produced fatty acids (FAs), pelagic and sympagic highly branched isoprenoid (HBI) lipids as well as sterols to determine the animals’ dietary preferences and trophic association to the sea-ice habitat during spring. Relative proportions of FAs differed strongly between PPOM and IPOM, indicating differences in species composition and degradation state between pelagic and sympagic habitats, respectively. FA signatures and sterol content of the consumers largely resembled known diet compositions with a strong reliance on diatom-derived carbon in A. glacialis, a higher degree of carnivory in E. holmii and evidence of Calanus-feeding in polar cod. Sympagic HBIs were detected at either low concentrations or not at all, in both producers and consumers, likely as a result of the very low abundance of their source diatoms. Pronounced trophic marker variability in A. glacialis collected at the highly productive shelf slope station versus the less productive central Arctic Basin station suggests a surprisingly high flexibility in carbon-source composition with a stronger reliance on pelagic food when available versus a higher importance of ice algal carbon when pelagic production is low. Nevertheless and despite the general lack (below detection limit) of sympagic HBIs in our dataset, high ice-algal biomass and elevated proportions of polyunsaturated FAs in IPOM compared to other seasons indicate that ice algae constitute a valuable nutritional carbon source as alternative to pelagic carbon during spring

Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

The Barents Sea is a hotspot for environmental change due to its rapid warming, and information on dietary preferences of zooplankton is crucial to better understand the impacts of these changes on food-web dynamics. We combined lipid-based trophic marker approaches, namely analysis of fatty acids (FAs), highly branched isoprenoids (HBIs) and sterols, to compare late summer (August) and early winter (November/December) feeding of key Barents Sea zooplankters; the copepods Calanus glacialis, C. hyperboreus and C. finmarchicus and the amphipods Themisto libellula and T. abyssorum. Based on FAs, copepods showed a stronger reliance on a diatom-based diet. Phytosterols, produced mainly by diatoms, declined from summer to winter in C. glacialis and C. hyperboreus, indicating the strong direct linkage of their feeding to primary production. By contrast, C. finmarchicus showed evidence of year-round feeding, indicated by the higher winter carnivory FA ratios of 18:1(n-9)/18:1(n-7) than its larger congeners. This, plus differences in seasonal lipid dynamics, suggests varied overwintering strategies among the copepods; namely diapause in C. glacialis and C. hyperboreus and continued feeding activity in C. finmarchicus. Based on the absence of sea ice algae-associated HBIs (IP25 and IPSO25) in the three copepod species during both seasons, their carbon sources were likely primarily of pelagic origin. In both amphipods, increased FA carnivory ratios during winter indicated that they relied strongly on heterotrophic prey during the polar night. Both amphipod species contained sea ice algae-derived HBIs, present in broadly similar concentrations between species and seasons. Our results indicate that sea ice-derived carbon forms a supplementary food rather than a crucial dietary component for these two amphipod species in summer and winter, with carnivory potentially providing them with a degree of resilience to the rapid decline in Barents Sea (winter) sea-ice extent and thickness. The weak trophic link of both zooplankton taxa to sea ice-derived carbon in our study likely reflects the low abundance and quality of ice-associated carbon during late summer and the inaccessibility of algae trapped inside the ice during winter.</jats:p

Leads in Arctic pack ice enable early phytoplankton blooms below snow-covered sea ice

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 40850, doi:10.1038/srep40850.The Arctic icescape is rapidly transforming from a thicker multiyear ice cover to a thinner and largely seasonal first-year ice cover with significant consequences for Arctic primary production. One critical challenge is to understand how productivity will change within the next decades. Recent studies have reported extensive phytoplankton blooms beneath ponded sea ice during summer, indicating that satellite-based Arctic annual primary production estimates may be significantly underestimated. Here we present a unique time-series of a phytoplankton spring bloom observed beneath snow-covered Arctic pack ice. The bloom, dominated by the haptophyte algae Phaeocystis pouchetii, caused near depletion of the surface nitrate inventory and a decline in dissolved inorganic carbon by 16 ± 6 g C m−2. Ocean circulation characteristics in the area indicated that the bloom developed in situ despite the snow-covered sea ice. Leads in the dynamic ice cover provided added sunlight necessary to initiate and sustain the bloom. Phytoplankton blooms beneath snow-covered ice might become more common and widespread in the future Arctic Ocean with frequent lead formation due to thinner and more dynamic sea ice despite projected increases in high-Arctic snowfall. This could alter productivity, marine food webs and carbon sequestration in the Arctic Ocean.This study was supported by the Centre for Ice, Climate and Ecosystems (ICE) at the Norwegian Polar Institute, the Ministry of Climate and Environment, Norway, the Research Council of Norway (projects Boom or Bust no. 244646, STASIS no. 221961, CORESAT no. 222681, CIRFA no. 237906 and AMOS CeO no. 223254), and the Ministry of Foreign Affairs, Norway (project ID Arctic), the ICE-ARC program of the European Union 7th Framework Program (grant number 603887), the Polish-Norwegian Research Program operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009–2014 in the frame of Project Contract Pol-Nor/197511/40/2013, CDOM-HEAT, and the Ocean Acidification Flagship program within the FRAM- High North Research Centre for Climate and the Environment, Norway

Ballasting by cryogenic gypsum enhances carbon export in a Phaeocystis under-ice bloom

Mineral ballasting enhances carbon export from the surface to the deep ocean; however, little is known about the role of this process in the ice-covered Arctic Ocean. Here, we propose gypsum ballasting as a new mechanism that likely facilitated enhanced vertical carbon export from an under-ice phytoplankton bloom dominated by the haptophyte Phaeocystis. In the spring 2015 abundant gypsum crystals embedded in Phaeocystis aggregates were collected throughout the water column and on the sea floor at a depth below 2 km. Model predictions supported by isotopic signatures indicate that 2.7 g m-2 gypsum crystals were formed in sea ice at temperatures below -6.5 °C and released into the water column during sea ice melting. Our finding indicates that sea ice derived (cryogenic) gypsum is stable enough to survive export to the deep ocean and serves as an effective ballast mineral. Our findings also suggest a potentially important and previously unknown role of Phaeocystis in deep carbon export due to cryogenic gypsum ballasting. The rapidly changing Arctic sea ice regime might favour this gypsum gravity chute with potential consequences for carbon export and food partitioning between pelagic and benthic ecosystems.Publisher PDFPeer reviewe