Reanalyses of existing satellite data, similarly, may help exclude one or other hypothesis. Our model is largely ‘bottom-up’ driven, where the timing of the annual cycle is controlled by the timing of the physical drivers, but ‘top-down’ processes (e.g. which offspring feed on phytoplankton). turbulence) is low enough, phytoplankton can stratify within a deep ML and a near-surface bloom can take place before the ML shoals. 2). Thus the OSH allows for winter blooms in Ctot. This concept is valid and can be used successfully to test primary production in winter, but not in spring. In autumn, heat fluxes become negative (i.e. Similarly, temporal variability in losses does not invalidate the concept of a critical depth, however, it leads to corresponding variability Zcrit (as seen in Fig. }. The spring season tends to result in large blooms as the spring sun warms the top level of the water, creating a warm layer above the colder deeper water drawing the phytoplankton to the surface. Smetacek and Passow, 1990; Dale et al., 1999; Dutkiewicz et al., 2001; Franks, 2014). As spring progresses, the water column continues to stratify. Once these important distinctions are made, the annual cycles and blooms in surface and depth-integrated phytoplankton can be described straightforwardly in terms of the physical drivers and biotic responses. Light levels are at their highest, Zeu is deepest, and any primary production is likely to be sustained by a flux of nutrients across the thermocline along with in situ nutrient regeneration.
The timing of spring blooms is often correlated with a shoaling ML (e.g. Synthesis study demonstrates phytoplankton can bloom below Arctic sea ice. We present a view of the spring bloom and the annual phytoplankton cycle that recognizes these issues. The x-axis shows northern and southern hemisphere months. During the low-turbulence regime, the ML becomes remnant, and vertical mixing becomes less than the critical value, so that as described by the CTH, phytoplankton concentrations increase in the photic zone, but decrease below it (Fig. Physical conditions and nutrient levels can lead to high abundances of … μ=ρ+g. Your email. 2). Backhaus J. O. Hegseth E. N. Wehde H. Irigoien X. Hatten K. Logemann K. (, Bishop J. K. B. Conte M. H. Wiebe P. H. Roman M. R. Langdon C. (, Chiswell S. M. Bradford-Grieve J. Hadfield M. G. Kennan S. C. (, Dutkiewicz S. Follows M. Marshall J. Gregg W. W. (, Ferreira A. S. A. Hátún H. Counillon F. Payne M. R. Visser A. W. (, Fischer A. Moberg E. Alexander H. Brownlee E. Hunter-Cevera K. Pitz K. Rosengard S. Sosik H. (, Henson S. A. Dunne J. P. Sarmiento J. L. (, Huisman J. Our perspective recognizes that phytoplankton are not always mixed throughout the so-called ML, and that it is important to distinguish blooms in surface phytoplankton from blooms in depth-integrated phytoplankton. Indeed, the notion of a shoaling ML leading to a spring bloom has become well established in the literature (e.g. A paper published in Science last month indicated that phytoplankton biomass is increasing in the Arctic. The vertical scale of the mixing is indicated by overturn arrows; (c) surface plankton concentration, C0; and (d) depth-integrated phytoplankton, Ctot, for the two hypothetical Oceans. (, Nodder S. D. Boyd P. W. Chiswell S. M. Pinkerton M. H. Bradford-Grieve J. M. Greig M. J. N. (, Shiozaki T. Ito S.-I. Argo floats equipped with sensors such as fluorometers, and/or transmissometers). Ontogenetic migration of mesozooplankton into the upper water column in early spring may be timed to take advantage of this seasonal growth. . 08051333. Similar schematics elsewhere (e.g., Dutkiewicz et al., 2001; Behrenfeld and Boss, 2014) point to what appears to be a common interpretation of Sverdrup (Sverdrup, 1953) where spring blooms are thought to begin when the seasonal ML shoals to become less than Zcrit, and this concept is often called the ‘Critical depth hypothesis'. These theories appear to be mutually exclusive and none of them describe the annual cycle of phytoplankton biomass. Ocean II is the classic light-limited ocean that is the necessary winter precursor in the SMLH. Your name. Also shown are critical depths (Zcrit, dashed and continuous lines) for hypothetical Oceans I and II, where Ocean II is light-limited in winter, whereas Ocean I is not. The resulting bloom then increases prey–predator interactions and ultimately predation consumes the bloom in the ‘Recovery’ phase. 3). In this view, deep winter mixing entrains phytoplankton-free water from below the ML, and so dilutes phytoplankton concentration as a ‘Disturbance’. Findlay, 2005; Henson et al., 2009; Chiswell et al., 2013). These blooms occur within waters that have sufficient sunlight and nutrients, with the latter being a particular driver for the species. AU - Sakamoto, Carole. The vertical scale of the mixing is indicated by the overturn arrows, and the ML depth (MLD) is shown based on a density difference relative to surface values. The ML continues to deepen through autumn and winter, driven primarily by convective overturn. The typical phytoplankton bloom lasts just a few weeks or less. For photos of Harmful Algal Blooms and red tides, click here. During this deep-mixing regime, the Sverdrup assumptions are met (assuming nutrients are not limiting), and the CDH holds, so that depth-integrated accumulation will be positive if the ML is shallower than Zcrit. 8
Click on image to view animation (2.5 MB) Credit: NASA Previous research has relied largely on sporadic, incomplete data from ships to understand how and when near-surface phytoplankton bloom. when r0 becomes positive), whereas the OSH considers the bloom start when r0 reaches near maximum values. The Arctic isn’t the only area to see a bloom in recent weeks. However, focussed experiments can eliminate one or other hypothesis, using relatively cheap instrumentation such as Bio-Argo (i.e. During the transition from deep mixing to stratified regimes, diapycnal mixing across the pycnocline, causes a MLD defined by a density difference criterion to rise. Nodder et al., 2005). Time limit is exhausted. Definition from Wiktionary, the free dictionary. It is worth commenting on the validity of the existing hypotheses. Ocean I is where depth-integrated accumulation increases throughout winter, whereas in Ocean II, the phytoplankton within the water column become light-limited. When surface heat fluxes become positive into the ocean, near-surface stratification can support a bloom in surface phytoplankton. Time limit is exhausted. Examination of his Fig. 4. In the spring, the sun heats the surface waters of the ocean making them less dense. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. However, since correlation can be coincidental, rather than causal, reanalyses of such data should be aimed at excluding hypotheses. Townsend et al. Published by Oxford University Press. All rights reserved. We then discuss the difference between mixed and mixing layers (and why phytoplankton may not be well mixed in the ML). Understanding phytoplankton bloom patterns and their effects on fish populations could spawn new management practices that help safeguard the future of the Alaska fishing industry. 5) show that none of chlorophyll, particle backscatter, nor particle beam attenuation, are well mixed throughout the ML during the spring, suggesting the SMLH can be immediately discarded for the subpolar North Atlantic. was supported by University of Tasmania. Tiny round cells of the alga Phaeocystis are only a few micrometers in diameter, but they form large colonies of hundreds of individual cells held together with a gel-like substance. Behrenfeld (Behrenfeld, 2010, 2014) suggested that a coupled trophic cycle controls primary production. We suspect that the SMLH stems from misinterpretation of Sverdrup's statement ‘On 4 April the depth of the mixed layer was for the first time smaller than the critical depth, and on the following day an appreciable phytoplankton population was recorded’. After this time (deepest ML), the MLD appears to shoal because of diapycnal mixing across the pycnocline. … MODIS uses an Ocean Colour 3 (OC3M) algorithm to measure phytoplankton pigment concentrations using a blue/green band ratio. AU - Chavez, Francisco P. AU - Ferioli, Laurie. Image courtesy of Copernicus/ESA. As phytoplankton bloom, they release organic molecules into the surrounding seawater. Mahadevan is a 2014-2015 Radcliffe Fellow. Schematic of annual cycles in biotic processes. Stramska and Stramski, 2005). AU - Coale, Kenneth H. AU - Johnson, Kenneth S. AU - Fitzwater, Steve E. AU - Gordon, R. Michael. The onset of the spring bloom (OSB) occurs when phytoplankton growth exceeds losses and is promoted by a transition from deep convection to a shallow mixing layer concurrent with increasing light intensities in nutrient-enriched waters. He also suggested that the CDH is valid in winter, whether this is true globally has yet to be tested. 1, with those directly affecting production at any given time emphasized. He suggested that the spring bloom develops in shallow weak stratification that appears once deep-mixing ceases. Spring phytoplankton blooms in the absence of vertical water column stratification, Seasonal variations of bio-optical properties and their interrelationships observed by Bio-Argo floats in the subpolar North Atlantic. However, once this ML becomes remnant, this level does not represent the level of vertical mixing. The compensation depth, Zco, is where photosynthesis matches all losses, i.e. They are then light-limited below the photic zone but can bloom within it. Last month there was a large coccolithophore bloom in the English Channel, just off the coast from Plymouth, seen in the image on the right from the 23rd June acquired by Sentinel-2. This error led Chiswell (Chiswell, 2011) to propose an onset of stratification hypothesis (OSH), where the spring bloom develops in shallow weakly stratified layers that develop in the spring. National Institute of Water and Atmospheric Research. The DRH does not provide an explanation for the timing of blooms in surface phytoplankton. (Townsend et al., 1992) reported that in the Gulf of Maine, ‘blooms can precede the onset of water column stability’, and Evans and Parslow (Evans and Parslow, 1985) thought trophic-interactions may be more important than shoaling MLs, ‘The occurrence of a bloom does not require a shallowing of the ML; it does require a low rate of primary production in winter.’ Such observations led Huisman et al.
2020 when do phytoplankton bloom