Author: Matthew GalePublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
On The Biophysical Factors That Control Under-Ice Phytoplankton Bloom Onset in the Central Canadian Archipelago
Author: Matthew GaleEvaluating the Frequency, Magnitude, and Biogeochemical Consequences of Under-ice Phytoplankton Blooms
Author: Courtney Michelle PaynePublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
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.
Factors Initiating Phytoplankton Blooms and Resulting Effects on Dissolved Oxygen in Duwamish River Estuary, Seattle, Washington
Author: Eugene B. WelchPublisher:
ISBN:
Category : Algal blooms
Languages : en
Pages : 72
Book Description
Primary Productivity and Biogeochemical Carbon Cycling in the Beaufort and Chukchi Seas, Arctic Ocean
Author: Molly Alyse PalmerPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The Arctic Ocean has undergone unprecedented changes in sea ice extent and thickness in recent years, including record-setting sea ice minimums in 2007 and 2012. These changes are predicted to affect Arctic marine primary productivity (the photosynthetic fixation of carbon dioxide by tiny algae called phytoplankton) because the timing and intensity of the summer phytoplankton bloom are strongly controlled by the dynamics of sea ice and water column stabilization. Satellite-based estimates indicate that primary production in ice-free waters has increased dramatically over the last few decades as a result of the increases in open water and length of the growing season associated with the thinning ice cover. In addition, climate models predict that the Arctic will experience greater and more rapid warming than other areas of the planet over the next century, suggesting that these changes may become even more prevalent in the future. The thinning sea ice has already had a dramatic impact on regional biogeochemistry: in 2011, we observed one of the most massive phytoplankton blooms ever recorded under the sea ice in the Chukchi Sea, an area traditionally thought of as too dark and too cold for massive blooms to occur. In the Chukchi, melt-ponds on the ice surface have proliferated to an extent that, in combination with the thinning ice cover, light penetration through the ice to surface waters is now sufficient for net photosynthesis to occur. The bloom we witnessed in 2011 extended for over 100 km into the> 1 m thick ice pack, and was characterized by extraordinarily high diatom biomass and rates of production. These changes represent a marked shift in our conception of Arctic marine ecosystems and have potential global-scale implications due to feedbacks relating to sea ice albedo, global atmospheric and ocean circulation patterns, and natural greenhouse gas exchanges between the atmosphere and ocean. Chapter 1 presents an overall introduction to the Arctic and discusses the causes and consequences of this changing seasonal cycle of productivity. Chapter 2 presents results from field work performed in the Beaufort Sea in the summer of 2008 exploring the spatial and temporal variability of phytoplankton photosynthesis in the ice-associated region of the flaw-lead polynya (area of perennially open water that rings the Arctic Ocean between land-fast ice and the central Arctic ice pack; it can be used somewhat as an analog for future open-water and ice-edged based productivity). Continuing with this theme of exploring primary productivity and biogeochemical cycles in the changing Arctic, Chapter 3 details the results from photophysiological experiments performed during the summer of 2010-2011 that highlight the unique features allowing Arctic phytoplankton to reach high levels of biomass in the extreme environment under the ice. In Chapter 4, I present data from recent 1-D modeling efforts that utilize the light and nutrient-controlled responses of phytoplankton growing under the ice to explore the consequences and implications of this shifting bloom cycle on regional biogeochemical processes.
Sea Ice and Nitrogen as Major Controls on Phytoplankton Production in the Pacific Arctic
Author: Zachary West BrownPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The Pacific Arctic, encompassing the Bering and Chukchi Seas between Alaska and Russia, is a highly productive region characterized by extreme seasonality in light and temperature. These seas host prolific stocks of seabirds and marine mammals, and are the sites of expanding human industrial exploration, including our nation's largest fishery. Seasonally ice-covered, the Bering and Chukchi Seas experience intense phytoplankton blooms as sea ice retreats each spring, fueled by high surface nutrient concentrations replenished over the winter. Of these nutrients, nitrogen (N) by far is in highest demand, owing to high rates of microbial N loss in the shallow, organic matter-rich sediments. The Pacific Arctic is also in the midst of unprecedented change due to anthropogenic warming. Field, modeling, and satellite-based studies have shown that the Chukchi Sea ice pack is thinning and diminishing in area. Compared to a decade ago, sea ice in this region retreats earlier, advances later, and covers far less total area during the summer. In turn, these changes profoundly alter the environment for phytoplankton, the single-celled photosynthetic organisms at the base of the Arctic food web. This thesis explores the roles of sea ice and nitrogen as the key factors that promote and ultimately set limits on phytoplankton production in the dynamic Pacific Arctic ecosystem.
The Physical and Biological Mechanisms Controlling the Winter-spring Phytoplankton Bloom in Long Island Sound
Author: Jennifer Ayako GeorgePublisher:
ISBN:
Category : Marine phytoplankton
Languages : en
Pages : 96
Book Description
Physical Controls on Light and Nutrients in Coastal Regions Receiving Large Fluxes of Glacial Meltwater
Author: Hilde OliverPublisher:
ISBN:
Category :
Languages : en
Pages : 526
Book Description
Rates of polar glacial melting are accelerating with rising global temperatures; these increasingly large freshwater fluxes impact coastal marine ecosystems. The meltwater delivered to the coastal ocean can affect light and/or nutrient availability for phytoplankton, which can potentially influence rates of primary productivity. With three idealized modeling studies, I examined the controls on light and nutrient availability in these high-latitude regions receiving large fluxes of glacial meltwater. The first of these studies investigates the potential for extreme melt events of the Greenland Ice Sheet (GrIS) to impact light availability for phytoplankton offshore. I used a 1-D phytoplankton model informed by the mixed layer depths from a Regional Ocean Modeling System (ROMS) forced with subglacial runoff fluxes derived from a hydrological runoff model of the GrIS. The model shows that Greenland meltwater has the potential to extend the phytoplankton growing season into fall, and has the largest potential impact for light-limited primary production under lower-light conditions. The second study focuses on the intense phytoplankton bloom in the Amundsen Sea Polynya (ASP), which is the most productive of all Antarctic coastal polynyas. Observations from the polynya show that the ASP phytoplankton experience both light and iron stress. I used a 1-D light-, nitrate, and iron-limited phytoplankton model to investigate light and iron controls on primary productivity in the Amundsen Sea Polynya. The model suggests that light limitation from phytoplankton self-shading is most controlling for most of the bloom, and that combined light and iron limitation drive the bloom into decline. The third modeling study concerns the marine-terminating glacial fjords of Greenland, where meltwater discharged at depth can result in delivery of buoyantly-upwelled nutrient-rich water near the surface, where it may supply phytoplankton blooms. I used an idealized 3-D coupled physical-biogeochemical model of a fjord to investigate the fjord conditions best suited for export of these upwelled nutrients out of the fjord and onto the shelf. The model shows that shelf forcing, the discharge rate, and the discharge depth are the most important controls on the export of nutrients out of the fjord.
Factors controlling phytoplankton ice-edge blooms in the marginal ice-zone of the northwestern Weddell Sea, during sea ice retreat 1988
Author: C. LANCELOTPhytoplankton bloom produced by a receding ice edge in the Ross Sea
Author: W.O. SMITHLeads in Arctic Pack Ice Enable Early Phytoplankton Blooms Below Snow-covered Sea Ice
Author: Christopher M. PolashenskiPublisher:
ISBN:
Category : Carbon cycle (Biogeochemistry)
Languages : en
Pages :
Book Description
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.