Investigating Drivers of Phytoplankton Blooms in the North Atlantic Ocean Using High-resolution in Situ Glider Data PDF Download
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Author: Anna Sergeevna Rumyantseva
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Category :
Languages : en
Pages : 0
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Author: Anna Sergeevna Rumyantseva
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ISBN:
Category :
Languages : en
Pages : 0
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Author: Daniel Edward Kaufman
Publisher:
ISBN:
Category : Biogeochemistry
Languages : en
Pages : 183
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As Earth’s climate changes, polar environments experience a disproportionate share of extreme shifts. Because the Ross Sea shelf has the highest annual productivity of any Antarctic continental shelf, this region is of particular interest when striving to characterize current and future changes in Antarctic systems. However, understanding of mesoscale variability of biogeochemical patterns in the Ross Sea and how this variability affects assemblage dynamics is incomplete. Furthermore, it is unknown how the Ross Sea may respond to projected warming, reduced summer sea ice concentrations, and shallower mixed layers during the next century. To investigate these dynamics and explore their consequences over the next century, high-resolution glider observations were analyzed and used in conjunction with a one-dimensional, data-assimilative biogeochemical-modeling framework. An analysis of glider observations from two latitudinal sections in the Ross Sea characterized mesoscale variability associated with the phytoplankton bloom and highlighted potential mechanisms driving change in the assemblage. In particular, an observed increase in the ratio of carbon to chlorophyll (C:Chl) suggested a marked transition from a phytoplankton assemblage dominated by Phaeocystis antarctica- to one dominated by diatoms. The expected control of phytoplankton variability by Modified Circumpolar Deep Water and mixed layer depth were shown to be insignificant relative to the effects of wind and sea surface temperature on the temporal/spatial scales measured by the glider. Additional glider measurements were used to force the Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification, which was adapted for use in the Ross Sea (MEDUSA-RS) to include both solitary and colonial forms of Phaeocystis antarctica. The impacts of climate-induced changes on Ross Sea phytoplankton were investigated with MEDUSA-RS using projections of physical drivers for mid- and late-21st century, and these experiments indicated increases of primary productivity and carbon export flux. Additional scenario experiments demonstrated that earlier availability of low light due to reduction of sea ice early in the growing season was the primary driver of simulated productivity increases over the next century; shallower mixed layer depths additionally contributed to changes of phytoplankton composition and export. Glider data were assimilated into MEDUSA-RS using the Marine Model Optimization Testbed (MarMOT) to optimize eight phytoplankton model parameters. Assimilation experiments that used different data subsets suggest that assimilating observations at the surface alone, as are typically available from remote-sensing platforms, may underestimate carbon export to depth and overestimate primary production. Experiments assimilating observations characteristic of a cruise-based sampling frequency produced a wide range of solutions, depending on which days were sampled, suggesting the potential for large errors in productivity and export. Finally, assimilating data from different spatial areas resulted in less variation of optimal solutions than assimilating data from different time periods in the bloom progression; these temporal differences are primarily driven by decreasing colonial P. antarctica growth rates, increasing colonial P. antarctica C:Chl, and faster sinking of colonies as the bloom progresses from the accumulation stage through dissipation. Overall, this dissertation research demonstrates the value of using bio-optical glider observations in conjunction with modeling to characterize phytoplankton dynamics in a remote marine ecosystem. High-resolution glider data are better able to resolve mesoscale physical-biological relationships, which are typically not discernible from lower frequency data, but it can be difficult to identify mechanistic relationships from in situ measurements alone. In addition, biogeochemical models can be used to extend insights gained by empirical observation, but application is often limited by the quantity and type of in situ data appropriate for evaluation and forcing. The use of gliders for facilitating development and operation of a lower trophic level model demonstrated the effectiveness of a synthetic approach that partly overcomes the individual limitations of these otherwise distinct approaches. Finally, the combination of these approaches is especially useful for gaining a better understanding of ecosystem dynamics in regions similar to the Ross Sea that are undergoing substantive climate-induced changes and where harsh conditions make other means of access difficult.
Author: Jeffrey Chi-Fung Ho
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Category :
Languages : en
Pages :
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The global expansion of harmful algal blooms (HABs) over the past half-century poses a serious threat to human health and ecosystem services in lake systems. HABs dominated by toxic cyanobacteria reduce shoreline recreational opportunities, damage vital fisheries and other aquaculture, and elevate the risk of dangerous toxins in drinking water supplies. While it is well known that phosphorus loading is the main driver of algal blooms in lakes, the apparent proliferation of HABs has prompted deeper examination of the factors contributing to HAB formation and occurrence. Past studies have been limited by the paucity of long-term in situ data in individual lakes, and few have leveraged new opportunities made possible by continental-scale lake surveys to understand drivers of algal blooms in large numbers of lake systems. The studies in this dissertation leverage advances in satellite remote sensing and cloud-based parallel computing over the past decade to study the long-term drivers of lake phytoplankton blooms at regional and global scales. I examine whether different monitoring approaches lead to ambiguity over basic questions of HAB occurrence, spatial extent, and timing, motivating the need for consistent long-term data for understanding HABs. I then describe a novel methodological approach for evaluating satellite remote sensing algorithms that is used to identify an algorithm to detect phytoplankton blooms in Lake Erie, one of the Laurentian Great Lakes. This algorithm is used to hindcast historical algal blooms in Lake Erie since 1984, and the historical record is then used to explore long-term drivers of phytoplankton blooms. The algorithm is also applied to dozens of lakes across six continents in order to characterize long-term trends in historical phytoplankton bloom intensity globally and to examine both climatic and terrestrial drivers at the global scale. In the final component of the dissertation, I explore the hypothesized mechanisms by which climate change is expected to impact harmful algal blooms, doing so by leveraging over twelve hundred summertime lake observations from across the continental U.S. Overall, the findings suggest that management efforts should consider the impacts of global climate change as well as the long-term effects of cumulative nutrient loading in designing mitigation strategies. The research as a whole highlights how knowledge of HABs is being expanded beyond local understanding in a few well-studied systems to a more global understanding based on many systems, and informs strategies to protect water quality within a changing climate.
Author: Ana Filipa Miguel Carvalho
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Category : Phytoplankton
Languages : en
Pages : 130
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The biophysical processes regulating primary productivity and biomass of phytoplankton in Antarctic coastal seas are both highly variable in time and space. This dissertation integrates multi-platform observations to understand the physical drivers of phytoplankton in coastal waters of Antarctica, with a greater focus in the West Antarctic Peninsula (WAP). The heads of cross-shelf canyons in the WAP are considered biological "hotspots", yet the physiology and composition of the phytoplankton blooms and the physical mechanisms driving them are not well understood. Incubation experiments were conducted at three of the WAP canyons to test the role of light availability and upwelling of mUCDW in the increased productivity observed at those locations. Results showed that light, and in particular photoadaptation mechanisms are responsible for increased phytoplankton. This work determined an ecologically relevant MLD for coastal Antarctica to further investigate the role of light in these canyon systems. The mixed layer depth (MLD) determined by the maximum of the buoyancy frequency criteria was found to correlate the best with the vertical distribution of phytoplankton estimated by chlorophyll fluorescence. This metric was then applied to a high-resolution glider dataset with the aim to characterize the dynamics of the spring phytoplankton bloom in submarine canyons in the WAP. Both stability, due to increased freshwater input, and mixed layer depth (MLD), and therefore light availability, have been linked to increased chlorophyll fluorescence. To evaluate how the photophysiology of phytoplankton respond to physical forcing, the glider was equipped with a PAR sensor and integrated with a Fluorescence Induction and Relaxation (FIRe) sensor, the first sensor of its kind to be integrated in a glider. The concurrent high-resolution, vertically-resolved and autonomous measurements of physiological variables together with physical oceanographic data allows investigations on how photosynthetic processes are affected by environmental factors, as it is highly sensitive to environmental stresses. Analyses comparing different MLD regimes have shown different photoadaptations resulting from differences in solar radiation exposure conditions (both time and intensity), reflected in the depth of the ML. Potentially different photoacclimation regimes can be evaluated by comparing light saturation parameters (Ek) determined based on the relationship between Photosynthetic Available Radiation (PAR) and photosystem II photosynthetic efficiency (Fv/Fm). With decreasing sea ice trends and increased winds reported for some Antarctic coastal regions undergoing rapid climatic changes, the increased phytoplankton exposure to highly dynamic irradiance levels, especially with deeper MLD, have significant ecological and biogeochemical implications, particularly in the carbon cycling.
Author: Kristina Dee Anne Mojica
Publisher: Frontiers Media SA
ISBN: 288971652X
Category : Science
Languages : en
Pages : 314
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ISBN: 9789462597723
Category :
Languages : en
Pages : 232
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Author: Seth T. Cowall
Publisher:
ISBN: 9781687974143
Category :
Languages : en
Pages : 91
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Phytoplankton are the base of the marine food web. They are also responsible for much of the oxygen we breathe and they remove carbon dioxide from the atmosphere. The cause of seasonal phytoplankton blooms in the ocean is a debated topic. One hypothesis is that blooms are initiated when seasonally changing environmental conditions disrupt the balance in the predator-prey relationship between zooplankton and phytoplankton. This dissertation follows up on this notion with a Nutrient-Phytoplankton-Zooplankton (NPZ) model incorporating diffusion and depth-dependent coefficients. Full spatiotemporal solutions of this coupled reaction-diffusion system are computed. An explanation of the bloom process in this model is presented that involves a saddle point transient equilibrium state. The saddle point bloom process is demonstrated with an ordinary differential equations NPZ model with time dependent forcing to imitate seasonally oscillating solar radiation. This process is illustrated by an animation (movie1_ODE.avi). The details from this analysis inform the bloom process in the reaction-diffusion NPZ model for which the equilibria must be determined computationally. The bloom process in the reaction-diffusion NPZ model is illustrated by another animation (movie2_PDE.avi). The reaction-diffusion NPZ model, incorporated with seasonal solar radiation and mixed layer depth data, simulates blooms with better timing than the ordinary differential equations model but still leaves much to be desired. However, results from models that simulate blooms more accurately show signs of the saddle point bloom process described in this dissertation. The saddle point bloom mechanism described here could be the mechanism by which the seasonal disruption in ecological balance initiates a high-latitude marine phytoplankton bloom, like that in the North Atlantic Ocean.
Author: E.M. Cosper
Publisher: Springer Science & Business Media
ISBN: 3642752802
Category : Science
Languages : en
Pages : 791
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A massive phytoplankton bloom, locally termed "brown tide", suddenly appeared in Long Island marine bays in 1985, colored the water a dark brown, decimated eelgrass beds and caused catastrophic starvation and recruitment failure of commercially important bay scallop populations. These "brown tide" blooms, caused by a very small, previously undescribed chrysophyte alga, have directly affected the estuarine environments of three northeastern American states: Rhode Island, New York and New Jersey. other phytoplankton blooms such as "red tides" caused by dinoflagellates and "green tides" from chlorophytes as well as blue-green algae blooms have long been recognized and studied world wide, however, the unusual nature of these "brown tide" blooms caught the interest of many people. Scientists were particularly intrigued by the discovery of a previously unknown microalga which provided the opportunity to learn more about small microalgae, picoplankters, which are usually ignored due to the difficulty in identifying species. A symposium entitled, "Novel Phytoplankton Blooms: Causes and Impacts of Recurrent Brown Tides and Other Unusual Blooms", was convened on October 27 and 28 at the State University of New York at Stony Brook on Long Island, with 220 registrants and nearly 50 scientific papers presented by researchers from the united States as well as Europe. The conference documented unusual bloom occurrences of recent and past years on a worldwide basis as well as northeast regional recurrences of the previously unknown "brown tide" blooms.
Author: Courtney Michelle Payne
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Category :
Languages : en
Pages : 0
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The Arctic Ocean has changed substantially because of climate change. The loss of sea ice extent and thickness has increased light availability in the surface ocean during the ice-covered portion of the year. Sea ice loss has also been a factor in the observed increases in sea surface temperatures and likely impacts surface ocean nutrient inventories. These changing environmental conditions have substantially altered patterns of phytoplankton net primary production (NPP) across the Arctic Ocean. While NPP in the Arctic Ocean was previously considered insubstantial until the time of sea ice breakup and retreat, the observation of massive under-ice (UI) phytoplankton blooms in many of the Arctic seas reveals that the largest pulse of NPP may be produced prior to sea ice retreat. However, estimating how much NPP is generated during the UI part of the year is challenging, as satellite observations are hampered by sea ice cover and very few field campaigns have targeted UI blooms for study. This thesis uses a combination of laboratory experiments, biogeochemical modeling, and an analysis of satellite remote sensing data to better understand how the magnitude and spatial frequency of UI phytoplankton blooms has changed over time in the Arctic Ocean, as well as to assess the likely biogeochemical consequences of these blooms. In Chapter 2, I present a one-dimensional ecosystem model (CAOS-GO), which I used to evaluate the magnitude of UI phytoplankton blooms in the northern Chukchi Sea (72°N) between 1988 and 2018. UI blooms were produced in all but four years over that period, accounted for half of total annual NPP, and were the primary drivers of interannual variability in NPP. Further, I found that years with large UI blooms had reduced rates of zooplankton grazing, leading to an intensification of the mismatch between phytoplankton and zooplankton populations. In Chapter 3, I used the same model configuration to investigate the role of UI bloom variability in controlling sedimentary processes in the northern Chukchi Sea. I found that, as total annual NPP increased from 1988 to 2018, there were increases in particle export to the benthos, nitrification in the water column and the sediments, and sedimentary denitrification. These increases in particle export to the benthos and denitrification were driven by higher rates of NPP early in the year (January-June) and were highest in years where under-ice blooms dominate, indicating the importance of UI NPP as drivers of these biogeochemical consequences. Additionally, I tested the system's sensitivity to added N, finding that, if N supply in the region increased, 30\% of the added N would subsequently be lost to denitrification. I subsequently deployed this model in the southern Chukchi Sea (68°N) to understand latitudinal differences in UI bloom importance across the region (Chapter 4). I found that UI blooms were far less important contributors to total NPP in the southern Chukchi Sea. Further, I found that their importance was waning over time; NPP generated in the UI period from 2013-2018 was only 34\% of the 1988-1993 mean. This lower rate of UI NPP was driven by a far shorter UI period as sea ice retreated nearly six weeks earlier than in the northern Chukchi Sea. However, low UI NPP was associated with higher rates of both total NPP and sedimentary denitrification in the southern Chukchi Sea than in the north. In Chapter 5, I used satellite remote sensing to determine how UI bloom frequency changed across the Arctic between 2003 and 2021. I found that UI blooms are a widespread feature and can be generated across 40\% of the observable seasonal sea ice zone in the Arctic Ocean. While there was an increase in observable area as sea ice retreated, there was no change in UI area, driving a nearly 10\% decline in the proportion of UI bloom prevalence. The Chukchi Sea was identified as both the region with the highest prevalence of UI blooms and the region most responsible for the decline in UI blooms. Finally, to understand the functional relationship between co-limiting light and nutrient conditions on phytoplankton growth, I conducted a laboratory experiment (Chapter 6). Phytoplankton growth under co-limiting conditions, which is frequently observed in the field, is often modeled using one of two functional relationships, but these relationships produce vastly different predictions of phytoplankton bloom magnitude. Although this laboratory experiment aimed to quantify the functional relationship of light and nutrient limitation on phytoplankton growth, I faced challenges in quantifying the nitrogen (N) concentration and was unable to meaningfully distinguish between these two functional relationships. However, this work also demonstrated that there is little difference between these functional relationships in areas like the Arctic Ocean, where nutrient concentrations can be rapidly depleted, diminishing from non-limiting to scarce over just a few days. Together, the results of this dissertation suggest that UI phytoplankton blooms can substantially contribute to total NPP, drive reductions in food availability, and change the rate of nitrogen loss. However, this work also demonstrates that UI blooms, which have likely been an important source of NPP across the Arctic since at least the 1980s, are likely an ephemeral feature, with their prevalence likely to decline in coming years as sea ice retreat shifts earlier.
Author: Emerson Allen Sirk
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Category :
Languages : en
Pages : 0
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This study examines decade-scale shifts in annual phytoplankton bloom timing across the North Atlantic Ocean. Phytoplankton blooms in this region play a critical role in regulating the global carbon cycle and marine ecosystem dynamics. Decadal shifts in the mean timing of bloom onset, bloom termination and bloom duration were examined using 22 years of satellite-derived ocean color data. At higher latitudes in the North Atlantic, median bloom onset date was shifted 4.4 days later, median bloom termination was shifted 1.5 days earlier and median bloom duration shifted 3.6 days shorter. At lower latitudes in the North Atlantic, median bloom onset date was shifted 2.9 days earlier, there was no observed shift in median bloom termination and median bloom duration was shifted 3.6 days longer. Interdecadal trends in wind speeds in the North Atlantic have been documented in a recent study, offering an explanation for the observed shifts in bloom timing. This study produces a first look into recent decadal shifts in bloom timing that should continue to be monitored and studied as more satellite ocean color data are collected.
