In this image, the milky blue color strongly suggests that the bloom contains coccolithophores, microscopic plankton that are plated with white calcium carbonate.
When viewed through ocean water, a coccolithophore bloom tends to be bright blue. The species is most likely Emiliana huxleyi Emily for short , whose blooms tend to be triggered by high light levels during the hour sunlight of Arctic summer.
The variations in bloom brightness and color in satellite images is partly related to its depth: E. Other colors in the scene may come from sediment or other species of phytoplankton, particularly diatoms. The Barents Sea usually witnesses two major bloom seasons each year, with diatoms peaking in May and June, then giving way to coccolithophores as certain nutrients run out and waters grow warmer and more layered stratified. Environmental factors that limit the size, longevity and timing of phytoplankton blooms will also limit the efficiency of the oceanic biological pump.
Sunlight and nutrients are the most important ingredients for a phytoplankton bloom to occur. When nutrients and sunlight are plentiful, microscopic phytoplankton reproduce quickly. Some blooms are so massive that they tint the water and can be seen from space. The phytoplankton bloom at the top of the page is a excellent example. There are many biotic and abiotic environmental variables factors that influence the formation of phytoplankton blooms.
The most important ones include:. What do phytoplankton need to produce large blooms? Choose all that apply. Sunlight Nutrients nitrogen, phosphorus, iron, sulfur, magnesium CO 2 Stratified water column with warm water sitting on top preventing mixing Why are phytoplankton important? Because phytoplankton blooms and the oceanic biological pump are important to climate, scientists are interested in studying:.
Scientists use both in situ sea water samples and Ocean Color measurements from satellites such as Terra to monitor changes in size, location and timing of phytoplankton blooms and the impact of these changes on the Earth's system. You can easily observe ocean colors in this image above of a phytoplankton bloom off the coast of France. Ocean color is created when sunlight reflects off chlorophyll pigment molecules in the cells of phytoplankton floating in the upper surface of the ocean.
Light reflected from sediments and dissolved organic material also contribute to ocean color. Different shades of the phytoplankton bloom depend on the types of species and the density of the phytoplankton population inside the bloom. Ocean color chlorophyll data is used to determine the net primary productivity NPP net primary productivity NPP : a measure of the amount of carbon dioxide taken in by phytoplankton via photosynthesis and converted into carbon compounds.
Net primary productivity tells scientists how much CO 2 carbon is being drawn down from the atmosphere by phytoplankton and moved into the oceanic biological pump. Image credit: NASA Visualizations of ocean color can come in two formats: true-color natural images and false-color images. Click to enlarge. Modeled arctic-wide properties of under-ice light from CESM2. Ensemble mean value is bold line, individual ensemble members thin lines. G—I Area of regions supporting light-limited UIBs to 20 m depth black, left axis , and blue, right axis fraction of compact ice zone permitting such UIBs.
The remaining compact ice, however, is more transparent. These model results are consistent with recent observations by Castellani et al. Up to 2. That is, historical light conditions could occasionally be sufficient for UIBs to develop, though their frequency has likely greatly increased over the past several decades. The geographical pattern of modeled light field changes for the months of June to August also provides some interesting insights Figure 4.
The difference between these two areas is largely broad-based and non-regional, with the signature of larger changes in sea-ice thickness and melt state rather than the imprint of regional variability. Figure 4. Geography of modeled light transmission through Arctic sea ice. The white point of the colormap is the threshold value for initiating an UIB i. D—F Same, but for the historical period — Dashed contour is the modern ensemble mean compact ice zone contour in each month.
The present-day CIZ contour is given as a black dashed line. While the overall under-ice light availability increased with decreasing ice thickness over recent decades, small-scale sea-ice features such as the geometry of melt ponds at the ice surface, ridges, hummocks, leads, and the horizontal distribution of light absorbing ice impurities cause spatial heterogeneity in PAR transmission Ehn et al.
The resulting complexity of the under-ice light field creates difficulties in measuring and estimating light availability for UIB phytoplankton since algal cells drifting in under-ice surface waters are exposed to large variations in PAR throughout the day. Overlooking the complexity of the under-ice light field and its characteristic optical parameters can oversimplify model development and our general understanding of UIB phenology.
After the return of the sun in spring, transmission of PAR through refrozen leads in the dynamic ice cover can trigger early season phytoplankton blooms beneath the still snow-covered sea ice Assmy et al.
Earlier bottom ablation and termination of the ice algal bloom also improves the under-ice light climate for phytoplankton and can contribute to the initiation of UIBs Mundy et al. Another key prerequisite for the initiation of an UIB is stratification of the surface layer induced by melt water addition Oziel et al.
Figure 5. Schematic of under-ice light field during the sea ice spring melt. Changes in the depth of the euphotic zone black dashed line , mixed layer black solid line , and nitracline gray solid line are presented in relation to the ice surface melt progression and the development of an under-ice bloom UIB and subsurface chlorophyll maximum SCM from late spring to late summer. State of photoacclimation is given for under-ice and open water phytoplankton communities.
As the euphotic zone starts to deepen until enhanced light attenuation by blooming phytoplankton reverses this process Figure 5 , Oziel et al. Higher light transmission through more transparent nearby structures i.
During the melt season, the under-ice light field can change over a relatively short time and, in turn, can cause a large error in regional estimates of under-ice PAR availability for marine primary production. Single-location transmittance measurements beneath one ice surface type may not be representative of the average PAR experienced by phytoplankton cells that drift at a different rate and direction relative to the overlying sea ice.
Using this approach, regional light transmission can be calculated as the sum of average transmission values for each surface type melt ponds, bare ice, open water multiplied by its areal fraction e. Subsurface maxima in PAR from higher light transmission through adjacent melt pond-covered ice alter the vertical light distribution, resulting in a non-exponential decrease in PAR with depth and difficulties in estimating K d Ehn et al.
Several studies investigated separation of the effects of water column attenuation from local spatial heterogeneity in transmittance through sea ice using semi-empirical models Frey et al. Considering this lateral photon transport, scalar radiometers with a spherical collector that capture PAR from all directions provide a more realistic measurement of light availability for primary production Morel and Gentili, ; Pavlov et al. During pre-bloom conditions, light availability limits photosynthesis and under-ice phytoplankton communities are acclimated to low-light conditions.
In this time period, the impact of errors in the under-ice light field parametrization on calculated primary production rates is largest due to the linear relationship between the rate of photosynthesis and increasing light levels before reaching saturation levels Matthes et al.
Phytoplankton are well acclimated to the low-light under-ice environment by maximizing light absorption and photosynthetic capacity Palmer et al. As light transmission increases through melt pond formation and sea-ice melt, phytoplankton cells modify their pigment composition Hill et al. Changes in the photoprotective to photosynthetic pigment ratio of under-ice phytoplankton communities to acclimate to the changing light availability have been observed as blooms progress.
During pre-bloom and early bloom conditions, intracellular concentrations of Chl a and accessory pigments increase, supported by the abundant nutrients in the surface layer required for biosynthesis Geider et al. Although the high nutrient availability further supports large cell sizes, phytoplankton cells are heavily packed with pigments resulting in reduced cross sectional absorption when absorption is normalized to pigment due to self-shading package effect; Morel and Bricaud, ; Hill et al.
Interestingly, the light saturation parameter, E k , was found to be higher than the available average light intensity Johnsen et al. Lewis et al. Hence, shade-acclimation allows algae to maximize their growth rate and to utilize the limited nutrient reservoir immediately once light levels increase through melt pond formation and ice melt.
This acclimation strategy also enables phytoplankton to adjust quickly to the higher light conditions at ice edges e. In particular, pelagic diatoms were found to be able to rapidly acclimate successfully to drastically increased light conditions, in strong contrast to that of sea-ice diatoms Kvernvik et al. During bloom conditions at higher light intensities, under-ice communities increasingly synthesize photoprotective carotenoids Hill et al. This process of non-photochemical quenching enables a high degree of plasticity of the photosynthetic performance of bloom-forming species such as Phaeocystis , promoting its dominance under highly variable light regimes Arrigo et al.
However, nitrate that is needed to synthesize proteins and pigments is often depleted during the late stage of an UIB, and thus impedes the photo-acclimation responses to increasing light levels by reducing the number of functional reaction centers and the photochemical efficiency of the photosynthetic machinery Lewis et al. As shade-acclimated phytoplankton transition from a low-light regime beneath the ice into a high-light regime in open water, carbon fixation rates can decrease due to super-saturating light intensities Figure 5 , Palmer et al.
According to the observations by Palmer et al. The AO is surrounded by land and has a complex topography of shelves, slopes, basins, channels, and sills. These features strongly constrain ocean circulation, primarily driven by both wind and buoyancy processes Timmermans and Marshall, and are influenced by the Atlantic and Pacific inflows.
These warmer and saltier inflows are the main source of inorganic nutrients for the colder and fresher Arctic domain. Stratification is generally driven by salinity rather than temperature in the AO beta rather than alpha oceans; sensu Carmack, Indeed, the AO generally acts as a freshwater reservoir especially in the anticyclonic Beaufort Gyre Proshutinsky et al. Light availability above the sea-ice surface is dictated by the annual light cycle, which itself depends on latitude.
The occurrence of UIBs, like open water phytoplankton blooms, is governed by bottom-up e. Here we synthesize the currently available knowledge on the atmosphere-snow-ice-ocean processes that have been shown to control UIB dynamics. This approach enables both an assessment of the relevance of regional specificities bathymetry, tides , as well as the influence of changing environmental conditions i.
Figure 6. Schematic drawing of the regional environmental settings favoring UIBs. The present and future different environmental settings for upwelling system inflowing A Pacific and B Atlantic sectors, C the outflow shelves, and D the Central Arctic.
The atmospheric, sea-ice, and the water column compartments are shown. Figure 7. Maps of the changes that occurred from to in sea ice and surface circulation versus unchanging geographic features i.
The green shading illustrates the shelf break depth between and m. The thinner the green band, the steeper the shelf break is. Dark gray: multiyear ice, medium gray: summer sea ice extent, light gray: winter sea ice extent, white: open ocean. The modern Seasonal Ice Zone SIZ is delimited by the winter sea ice extent and the summer sea ice extent which corresponds to the light gray area.
Warm and salty currents carrying Pacific and Atlantic waters poleward are in red. Currents associated with fresher and colder Arctic waters are in blue. They are localized in the bottom panel. Wind-driven upwelling along the continental shelves, shelf breaks, and ice edges are a source of substantial change in water masses and cross-shelf transport Williams and Carmack, They allow nutrient-rich subsurface water masses to shoal up to the surface over shelves.
Such processes have been documented in several regions such as the Beaufort Pickart et al. There, these upwelling systems are characterized by an eastward flowing Pacific shelf break jet overlying the offshore Atlantic boundary current see Figures 6A , 7. The continental slope of the Beaufort Sea appears to present the most favorable upwelling conditions Carmack and Chapman, for inducing UIBs because: 1 the shelf break is the shallowest and steepest of the AO see Figure 6A ; Randelhoff et al.
Thus, when the wind regime allows it, nutrients are upwelled from the Beaufort basin at depth typically winter Pacific or Atlantic waters; Schulze and Pickart, ; Pickart et al. On the Atlantic side, the presence of warm and nutrient-rich Atlantic waters at the surface in the region north and west of Svalbard during winter has been attributed to upwelling Falk-Petersen et al. The occurrence of wind-driven upwelling in the European sector is rather unlikely because the area is not subject to upwelling-favorable winds i.
By contrast, the Atlantic sector is much more sensitive to vertical mixing, wintertime convection and advection Lind et al. The European sector is the most dynamic region of the AO, particularly along the Atlantic waterway which closely follows the slope of the Barents Sea continental shelf.
At the very end of one of the branches of the Atlantic Current i. The authors suggested that Atlantic waters could play a second order role in seeding polar surface waters with phytoplankton cells from below and that light penetration through leads is likely to be the main environmental driver behind initiation of the UIB. Other studies have highlighted advective origins of UIBs in the region north of Svalbard Johnsen et al. The Arctic outflow shelves are highly heterogeneous Michel et al.
Arctic sea ice advected over the East Greenland shelf extends offshore from the shelf break. Mayot et al. These UIBs that occur in the Canadian Archipelago are typically driven by mixing nutrient availability processes and increased light availability during the spring ice melt Figure 6C. The most recent studies collecting time series under landfast sea ice in the Canadian Archipelago Resolute Bay: Mundy et al. These sea ice camp studies helped resolve early temporal evolution of UIBs and revealed different key processes.
Snow accumulation on landfast sea ice plays a critical role for UIB development by controlling most of the light transmitted to the under-ice water column Mundy et al. In fact, light attenuation is strongly dominated by snow compared to sea ice.
Extensive melt pond formation at the end of the snow melt period concomitant with the early stabilization of the upper water column due to freshwater input led to UIB initiation. As phytoplankton progressively consume nutrients in the surface layers, mixing is again of major importance to tap into deeper nutrient pools to maintain phytoplankton growth.
In the Canadian Archipelago or Baffin Bay, tidal energy was the main source of vertical mixing Mundy et al. The tidal-induced mixing controlled the magnitude and depth of the SCM Mundy et al. Although significant relative to background Chl a levels, these UIBs were characterized by low biomass i. In these regions, surface layers are clearly both light and nutrient limited Figure 6D. It is suggested that modal eddy-induced mixing could help sustain phytoplankton growth by providing nutrients from deeper Atlantic waters Laney et al.
The initiation of an UIB requires a viable seed population of algal cells present in the euphotic zone of the water column under the ice. There are three potential seeding sources for UIBs: a algal cells in the water column, b vegetative cells or resting stages at the sediment surface, and c algal cells or resting stages entrapped in sea ice that are released during melt onset at the underside of the ice Johnsen et al.
Very little is known about the relative importance of these three different seeding strategies, but it likely varies strongly depending on mixing depth, bottom topography, and sea-ice conditions.
In relatively shallow coastal areas, re-suspension of resting stages from sediment surfaces is considered to be an important source seeding the diatom component of the spring bloom Hegseth et al.
In deeper oceanic regions, however, pelagic and sea-ice melt seeding by vegetative cells surviving the winter in the upper part of the water column are probably the most important seeding sources. Other important taxonomic groups of UIBs such as Phaeocystis are not known to form resting stages, but they have been found in single cell state throughout the winter in surface waters Vader et al. While taxonomic composition and maximum biomass of an UIB seems to be strongly correlated with the type and amount of nutrients available e.
Winters in high latitudinal areas are characterized by the Polar night when the sun does not rise above the horizon. This leads to extended periods where ambient irradiances are not sufficient for in situ primary production in ice-free surface waters Kvernvik et al. Phytoplankton communities during wintertime are characterized by very low cell concentrations and a predominance of small, flagellated cells, as well as heterotrophic dinoflagellates Lovejoy et al.
Among the small flagellated cells, two species that periodically dominate phytoplankton assemblages in Arctic waters were found throughout the Polar night: Micromonas polaris and Phaeocystis pouchetii Vader et al. Natural microalgal assemblages, and in particular diatoms, are able to survive extended periods of darkness from months to years Zhang et al. Diatoms also seem to retain their photophysiological characteristics during extended periods of darkness relatively unchanged as compared to flagellates, which possibly enables them to utilize the returning light in early spring very efficiently van de Poll et al.
Furthermore, mixotrophy i. However, important photosynthetic flagellates e. This highlights the need for further study in the field. This overall pattern can be primarily attributed to the larger nutrient inventory and more upwelling-favorable conditions in the Pacific sector and the low silicate relative to nitrate concentrations in the Atlantic sector, respectively Ardyna et al.
A study from Darnley Bay in the Canadian Beaufort Sea showed that upwelling favorable conditions at the ice edge of landfast FYI in combination with the snow melt onset and low ice algal biomass throughout the study period provided both ample nutrients and light, including surface stratification, to fuel a large UIB Mundy et al. Furthermore, advection of high phytoplankton biomass produced in adjacent open water likely increased primary production capacity under the sea-ice cover Mundy et al.
Moderate UIBs max. Chl a concentration of 4. The other two expeditions were representative of the outflow shelves i. All studies were conducted during the last decade, are thus representative of the new FYI regime, and cover the spring and summer season. One caveat common to these studies is that they were not following a Lagrangian design, i. The N-ICE and North Pole expeditions in are representative of ice camps on drifting sea ice during the early spring to summer season while the Resolute Passage studies in and are representative of ice camps on landfast ice covering the late spring to summer season.
Figure 8. Schematic drawing of different A—E under-ice phytoplankton blooms. The development of UIBs is divided in three distinct phases, i. The three potential seeding sources for UIBs are shown by the white arrows: algal cells in the water column, vegetative cells or resting stages at the sediment surface, and algal cells or resting stages from sea ice.
The main environmental drivers controlling UIB dynamics are indicated in red. The size of the arrows is related to the importance of the processes. The main protist assemblages are depicted in the different white circles. The phytoplankton biomass is related to the transparency of the shape of the vertical dynamics of phytoplankton assemblages.
The sea ice, water, and bottom compartments are also displayed. There is a gradual decrease in maximum phytoplankton bloom abundance from the shallower and more nutrient-rich Chukchi Sea and Resolute Passage toward the Atlantic sector and the central AO Figure 9.
Particularly, the central AO shows nearly two orders of magnitude lower peak abundances Figure 9 as was also the case for AO production estimates and Chl a concentrations Table 1. One common feature of all studies is that pennate diatoms and dinoflagellates dominated in the early phase of the UIB development.
In particular Fragilariopsis and Pseudo-nitzschia species, but also other pennate diatoms commonly found in sea ice were prominent during the pre-bloom phase. The switch in dominance toward pelagic diatoms, in particular species of the centric diatom genera Chaetoceros and Thalassiosira , and in the case of N-ICE, P. Chaetoceros , Thalassiosira , and Phaeocystis usually dominate the spring bloom along the Arctic continental margin Degerlund and Eilertsen, In particular, spore-forming species of the former two diatom genera [e.
The comparably low Chaetoceros and Thalassiosira abundances in the deep central AO during the North Pole expedition suggest that, in addition to the low nutrient levels, these taxa might also be limited by dispersal of resting spores from the shallow shelves.
However, maximum centric diatom abundances in were two orders of magnitude lower and about one month later late August than during the North Pole expedition The general trend toward stronger dominance of cryopelagic and pelagic diatom species in the more recent years is also supported by a study covering the MYI to FYI transition in the central AO over the last 40 years Hop et al.
Figure 9. Under-ice phytoplankton assemblages. The map displays the spatially distributed taxonomic inventories for each station and each expedition. The bar plots show the taxonomic inventories. The main assemblages are shown, i. Note that N-ICE flagellates were dominated by Phaeocystis which was not separately counted in the other studies. The general patterns described above are consistent with observations of UIBs in Baffin Bay in and during the Green Edge project Oziel et al.
Notable exceptions are cryopelagic species belonging to the pennate diatom genera Fragilariopsis and Pseudo-nitzschia , which thrive both in sea ice and the water column Hop et al.
Intense grazing pressure is able to decimate phytoplankton biomass during the bloom peak or post-bloom phases Sakshaug, However, the UIB development is generally preceded by an ice algal bloom on which some zooplankton species are able to feed Tourangeau and Runge, ; Wassmann and Slagstad, ; Hirche and Kosobokova, ; Wassmann et al. Fortier et al. Still, the time period of the developing UIB is often associated with a high flux of particulate organic carbon, mostly mediated by vertical sinking of ungrazed phytoplankton and ice algal cells Fortier et al.
Similarly, Tamelander et al. Overall, this suggests that in the early phase of an UIB, zooplankton are swamped by the abrupt increase in concentration and vertical flux of phytoplankton biomass. Hence, UIBs may represent an important and valuable food source for zooplankton grazers, including early recruitment stages, but they are likely not being controlled by grazing.
In addition, sinking of UIB biomass could be an important food source for benthic ecosystems, especially on the shallow continental shelves.
Export of a Phaeocystis -dominated UIB to the seafloor of the continental shelf north of Svalbard was significantly enhanced by ballasting of Phaeocystis aggregates by gypsum minerals released from melting sea ice Wollenburg et al. Recent observations of mass sedimentation of the mat-forming sea-ice diatom Melosira arctica to the deep-sea floor of the central AO during the record summer sea ice minimum year suggest that cryopelagic-benthic coupling might be enhanced under the new Arctic sea ice regime Boetius et al.
Sea-ice loss is the most prominent manifestation of climate-driven changes in the AO. The combined effect of advanced summer sea-ice melt, MYI disappearance in terms of extent, thickness and volume; Kwok, , and increase in storm frequency and intensity Graham et al. It will promote wind-induced shelf-break upwelling and mixing events Figure 6A ; Pickart et al.
Such an increase in bloom magnitude could, however, be mitigated by the still uncertain increase in snow precipitation over the Arctic Bintanja, ; Webster et al. Common among all scenarios is the likely increased pelagic-benthic coupling as a result of an earlier bloom with minimal top-down influence. Sea-ice loss has also direct influences on the hydrodynamical conditions of the AO Figure 7.
Recent studies have shown an overall intensification of AO circulation. According to altimetric-derived satellite observations, surface geostrophic currents have doubled in both the Arctic basin —; Armitage et al.
The increased Atlantic inflow is suspected to be mainly driven by reduced sea-ice export through the Greenland Sea, resulting in lower sea surface height and intensified cyclonic gyre activity in the Nordic Seas Wang et al. The overall intensification of the surface circulation will increase the potential for advection of new nutrients and organisms Vernet et al.
In general, the AO will be more dynamic, and because it is also baroclinically unstable, more meso-scale features will be produced e. Consistent with this, the expansion and shift of the Beaufort Gyre Regan et al.
Over —, annual Bering Strait volume transport from the Pacific to the AO almost doubled as well 0. Therefore, the rapid transformation of local water masses due to the increased addition of freshwater and Atlantic- and Pacific-derived waters will alter the large-scale AO stratification.
Arctic stratification will determine to a large extent nutrient availability in the surface euphotic layer Tremblay and Gagnon, , Ardyna et al.
Stratification is expected to increase in the Beaufort Gyre Toole et al. The fate of freshwater will ultimately depend on the atmospheric and ocean circulation, which has been mainly in an anticyclonic regime during the last two decades, allowing freshwater accumulation Haine et al. However, if the atmospheric circulation over the AO were to shift to a cyclonic regime, freshwater export may increase and ultimately alter the UIB dynamics. Our understanding of UIBs in a changing Arctic environment is based on few year-round and multiannual observations at specific locations.
In view of these requirements, it is generally recognized that autonomous observing systems are well suited to provide observations at spatio-temporal resolutions previously hard to assess in the AO Lee et al. Modified from artwork in Sansoulet et al.
The Argo Program, which maintains a global array of autonomous and freely drifting profiling floats, is extending its array into Arctic regions Jayne et al. All Argo floats carry conductivity-temperature-depth CTD sensors to measure accurate vertical temperature and salinity profiles mostly between and m to the surface, every 5—10 days and for several years Argo Steering Team, These BGC-Argo core variables are quantified with operational and robust sensors, as well as with new and under development technologies e.
While operating beneath the sea-ice cover, profiling floats collect vertical profiles of key biogeochemical variables, and transmit data after surfacing in open water. The presence of sea ice makes it difficult to geolocate ARGO float platforms, so under-ice trajectories are estimated using interpolation methods Wallace et al. In order to prevent risk of colliding with sea ice, floats stop their ascent at 10 m and cannot provide near-surface information.
At deployment time in early spring, the float is placed on the surface of the ice and the cable lowered through a hole that is re-filled with ice and snow. After the sea ice melts in summer, the observing system is floating in open water until the next ice formation cycle begins in late fall.
Similarly, UIBs can be studied with moorings deployed, for example, in fjords and equipped with analogous physical and bio-optical sensors Leu et al. However, recorded data are mostly available only after the mooring is recovered. Ice-borne observing systems are preferentially deployed in such environments. These platforms can provide multiannual datasets with a high-temporal resolution, as demonstrated by data collected in the Arctic Transpolar Drift and the Beaufort Sea Laney et al.
Such long-term monitoring is possible thanks to engineering efforts to improve buoy survivability in thin ice, during ridging events and seasonal freeze-up. AUV platforms equipped with physical and bio-optical sensors were deployed in marginal ice zones in Baffin Bay Green Edge project with glider platforms and north of Svalbard Johnsen et al.
Surveys of the under-ice environment have been increasingly undertaken with remotely operated vehicles ROVs. ROVs enable remote sensing of difficult to access locations across a range of temporal and spatial resolutions and minimize the disturbance of the ice environment in contrast to traditional ice coring techniques.
Observational capabilities of ROVs are manifold due to a wide variety of attached sensors performing physical, chemical, and biological measurements Katlein et al. For the investigation of parameters driving UIBs in Arctic waters, ROVs equipped with spectral radiometers have been frequently used to map under-ice irradiance and transmittance beneath landfast sea ice and moving pack ice in the AO Nicolaus et al.
As an example of the efficiency of autonomous platforms in providing broad spatial coverage, recently deployed autonomous instruments all around the Arctic show the anticipated latitudinal gradient in annual Chl a accumulation Figure Because annual maximum values of measured Chl a concentrations ranged from 0.
According to these time series, accumulation of phytoplankton biomass beneath mobile sea ice first occurred at the southernmost locations e. All annual cycles have been normalized divided by their annual maximum values and smoothed with a days moving average. Data from floats and ITP platforms correspond to the average values collected between 25—35 m. Data from WARM buoys were collected at 5 m. For floats and WARM buoy time series, dashed lines represent periods when platforms were not sampling under ice.
These early increases in phytoplankton biomass frequently show short-term fluctuations. Upcoming concurrent measurements of Chl a concentration, water column mixing, PAR, and nitrate concentrations over a full annual cycle from more frequently deployed autonomous sampling platforms are needed to link and quantify the contribution of each individual bottom-up process to the observed short-term fluctuation in phytoplankton biomass.
As pointed out by Laney et al. Upward-looking cameras mounted on autonomous platforms can provide qualitative pictures of the ice—water interface and detect, for example, sinking aggregates of ice algae e.
Finally, the drift of autonomous sampling platforms over large distances creates difficulties in the observation of UIBs in mobile pack ice over longer time periods. Some observed short-term fluctuations may be the result of the spatial variability in measurements from the drifting observing system used.
An improved ocean observational effort in the pan-AO with an increased number of autonomous observing systems might overcome this issue Smith et al. However, in both cases, reduced vertical mixing and initiation of surface stratification, respectively, was a prerequisite for the UIB to form while extensive lead fraction under cold spring atmospheric forcing inhibited UIB formation due to convective mixing in refreezing leads Lowry et al. In addition, the low but variable light conditions under the heavily snow-covered sea ice, crisscrossed with leads north of Svalbard, favored P.
A study from Resolute Passage in the Canadian Arctic Archipelago conducted in showed that rainfall triggered a rapid sloughing event of ice algae, dominated by pennate diatoms, followed by a pennate diatom-dominated bloom of the same species in the under-ice water column Galindo et al. These observations were in contrast to the slower 3-week melt progression that led to an UIB dominated by centric diatoms of the genera Thalassiosira and Chaetoceros in the same region during the previous year Mundy et al.
In during another rapid melt event in Cambridge Bay, the planktonic diatom composition at the beginning of an UIB was very close to that of the ice algal community C. Mundy, unpublished data , which was dominated by the pennate diatom N.
Campbell et al. Thus, it is possible that the onset of the bloom was seeded in part by ice algae sloughing from the ice bottom. For example, the image above, taken of the Barents Sea on July 15, is odd in that the bloom is two-toned.
Typically, various types of phytoplankton bloom at different times. This is because different species thrive under different conditions, causing the blooms that mark their high points to occur in sequence. In the Barents Sea, the blooms that occur in spring and early summer are typically composed of diatoms , a microscopic form of algae with silica shells and ample chlorophyll, which makes them appear green in satellite images.
Starting in late July, the water becomes warmer and well-defined layers form. This change promotes the rise of coccolithophores , a type of phytoplankton that turns the water milky whitish green in satellite imagery due to their calcium carbonate shells. Such concurrent blooms have been observed before, according Andrew Orkney, of the University of Oxford.
And while this may be the case here as well, Orkney, the author of a paper on phytoplankton in the Barents , reckons that the colour likely results from a coccolithophore bloom occurring in waters rich in what is known as coloured dissolved organic matter , which can make seawater appear anywhere from green to yellow-green to brown. Identifying just what is occurring in the image would require samples of the water to be taken.
But, regardless of what is currently happening, recent research has found that coccolithophore blooms are occupying increasingly more space in the Barents Sea.
Between and , coccolithophore summer blooms have expanded poleward and their surface area in the Barents Sea has doubled.
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