Abstract:Typical sinking rates of marine phytoplankton cover a range extending from a few meters up to several hundred meters.per day. If it were not for a process which maintains plankton near the sea surface, in the euphotic layer, it would sink to depths of thousands of meters in the deep ocean during the winter season. Consequently, plankton would not be available for the next spring bloom. In shelf seas and coastal areas, as well as in fjords, deep sinking is prohibited by the proximity of the sea bed. The mechani… Show more
“…As dense water sinks from the surface, less dense water must also rise from deep in the mixed layer to replace it. These upward vertical motions may play a role in maintaining the phytoplankton in the mixed layer for a longer period, and thus reduce the loss terms (Backhaus et al 1999).…”
Section: Discussionmentioning
confidence: 99%
“…; and (2) Why do these concentrations not fall to zero under extremely light-limited winter conditions? The maintenance of the over-wintering stock is an important problem, because it is this stock that provides the seed population for the spring bloom (Backhaus et al 1999). The spring bloom occurs every year in the North Atlantic, to a greater or lesser extent, and the initial growth rate of the bloom has been shown to be dependent on the pre-bloom phytoplankton composition (Waniek 2003).…”
“…As dense water sinks from the surface, less dense water must also rise from deep in the mixed layer to replace it. These upward vertical motions may play a role in maintaining the phytoplankton in the mixed layer for a longer period, and thus reduce the loss terms (Backhaus et al 1999).…”
Section: Discussionmentioning
confidence: 99%
“…; and (2) Why do these concentrations not fall to zero under extremely light-limited winter conditions? The maintenance of the over-wintering stock is an important problem, because it is this stock that provides the seed population for the spring bloom (Backhaus et al 1999). The spring bloom occurs every year in the North Atlantic, to a greater or lesser extent, and the initial growth rate of the bloom has been shown to be dependent on the pre-bloom phytoplankton composition (Waniek 2003).…”
“…Offshore, frontal zones may also harbor vegetative cells as potential propagules (Smayda 2002). A few vegetative cells may even survive nutrient and grazing stress in an area, and these ''fugitive cells'' (Kilham and Kilham 1980) can grow and accumulate once favorable conditions return (Backhaus et al 1999, 2003). Alternatively, planktonic blooms can be initiated by the germination and growth of benthic resting stages.…”
Although phytoplankton blooms are major events in aquatic systems, the importance of benthic resting stages in seeding planktonic blooms is still unclear. Using microcosms, we tested the influence of benthic versus planktonic inocula on the development and taxonomic composition of diatom communities in a temperate fjord. Experiments in early spring 2002, fall 2002, and late spring 2003 showed that the type and quantity of inoculum influenced bloom development and composition. Species composition was vastly different when seeded by cells from the benthos. Species such as Detonula confervacea and Thalassiosira minima showed strong dependence on benthic propagules. Populations of Chaetoceros debilis and Thalassiosira nordenskioeldii were initiated by both benthic and planktonic cells, and benthic seeding was most successful when experiments were preceded by a planktonic bloom. Skeletonema costatum was abundant in all treatments but showed variations in size, depending on the type of inoculum. Species that do not have a resting stage, such as Pseudo-nitzschia spp., were present only in planktontreated microcosms. Seasonal factors were especially important in determining the successful growth of newly seeded populations. Our results indicate that benthic resting stages provide an important source for some species. Because the introduction of benthic resting stages to surface waters can greatly influence species composition of the plankton, it is important that studies of plankton blooms include life-history stages from both the sediments and the water column.
“…In situ light fields fluctuate on timescales ranging from seconds in near surface waters (Schubert et al 2001) to vertical mixing dynamics that range from hours to days (Denman & Gargett 1983, Backhaus et al 1999, D'Asaro 2008 to seasonal patterns in incident light. Phytoplankton respond to fluctuating light by altering their cellular chl and carbon content on time scales less than 1 h (Lewis et al 1984, Cullen & Lewis 1988, Havelková-Doušová et al 2004) and employ photoprotective mechanisms such as nonphotochemical quenching (Havelková-Doušová et al 2004, Miloslavina et al 2009, van de Poll et al 2010, Alderkamp et al 2013) that are active on timescales of microseconds to minutes.…”
Phytoplankton regulate internal pigment concentrations in response to light and nutrient availability. Chlorophyll a to phytoplankton carbon ratios (chl:C phyto ) are commonly reported as a function of growth irradiance (E g ) for evaluating the photoacclimation response of phytoplankton. In contrast to most culture experiments, natural phytoplankton communities experience fluctuating environmental conditions, making it difficult to compare field and lab observations. Observing and understanding photoacclimation in nature is important for deciphering changes in chl:C phyto resulting from environmental forcings and for accurately estimating net primary production (NPP) in models which rely on a parameterized description of photoacclimation. Here we employ direct analytical measurements of C phyto and parallel high-resolution biomass estimates from particulate backscattering (b bp ) and flow cytometry to investigate chl:C phyto in natural phytoplankton communities. Chl:C phyto observed over a wide range of E g in the field was consistent with photoacclimation responses inferred from satellite observations. Field-based photoacclimation observations for a mixed natural community contrast with laboratory results for single species grown in continuous light and nutrient-replete conditions. Applying a carbon-based NPP model to our field data for a north−south transect in the Atlantic Ocean results in estimates that closely match 14 C depth-integrated NPP for the same cruise and with historical records for the distinct biogeographic regions of the Atlantic Ocean. Our results are consistent with previous satellite and model observations of cells growing in natural or fluctuating light and showcase how direct measurements of C phyto can be applied to explore phytoplankton photophysiology, growth rates, and production at high spatial resolution in situ.
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