Sea Ice and Nitrogen as Major Controls on Phytoplankton Production in the Pacific Arctic PDF Download
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Author: Zachary West Brown
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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.
Author: Zachary West Brown
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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.
Author: Jacques Nihoul
Publisher: Springer
ISBN: 1402094604
Category : Science
Languages : en
Pages : 236
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Book Description
The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years. The melting is accelerating, and researchers were unable to identify natural processes that might slow the deicing of the Arctic. Such substantial additional melting of Arctic and Antarctic glaciers and ice sheets would raise the sea level worldwide, flooding the coastal areas where many of the world's population lives. Studies, led by scientists at the National Center for Atmospheric Research (NCAR) and the University of Arizona, show that greenhouse gas increases over the next century could warm the Arctic by 3-5°C in summertime. Thus, Arctic summers by 2100 may be as warm as they were nearly 130,000 years ago, when sea levels eventually rose up to 6 m higher than today.
Author: Jacqueline M. Grebmeier
Publisher: Springer
ISBN: 9401788634
Category : Science
Languages : en
Pages : 461
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Book Description
The Pacific Arctic region is experiencing rapid sea ice retreat, seawater warming, ocean acidification and biological response. Physical and biogeochemical modeling indicates the potential for step-function changes to the overall marine ecosystem. This synthesis book was coordinated within the Pacific Arctic Group, a network of international partners working in the Pacific Arctic. Chapter topics range from atmospheric and physical sciences to chemical processing and biological response to changing environmental conditions. Physical and biogeochemical modeling results highlight the need for data collection and interdisciplinary modeling activities to track and forecast the changing ecosystem of the Pacific Arctic with climate change.
Author: Courtney Michelle Payne
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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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.
Author: David J. Suggett
Publisher: Springer Science & Business Media
ISBN: 9048192684
Category : Science
Languages : en
Pages : 332
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Book Description
Measurements of variable chlorophyll fluorescence have revolutionised global research of photosynthetic bacteria, algae and plants and in turn assessment of the status of aquatic ecosystems, a success that has partly been facilitated by the widespread commercialisation of a suite of chlorophyll fluorometers designed for almost every application in lakes, rivers and oceans. Numerous publications have been produced as researchers and assessors have simultaneously sought to optimise protocols and practices for key organisms or water bodies; however, such parallel efforts have led to difficulties in reconciling processes and patterns across the aquatic sciences. This book follows on from the first international conference on “chlorophyll fluorescence in the aquatic sciences” (AQUAFLUO 2007): to bridge the gaps between the concept, measurement and application of chlorophyll fluorescence through the synthesis and integration of current knowledge from leading researchers and assessors as well as instrument manufacturers.
Author: Alain Sournia
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 366
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Book Description
Author: Simon Jungblut
Publisher: Springer
ISBN: 3319932845
Category : Science
Languages : en
Pages : 259
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Book Description
This open access book presents the proceedings volume of the YOUMARES 8 conference, which took place in Kiel, Germany, in September 2017, supported by the German Association for Marine Sciences (DGM). The YOUMARES conference series is entirely bottom-up organized by and for YOUng MARine RESearchers. Qualified early career scientists moderated the scientific sessions during the conference and provided literature reviews on aspects of their research field. These reviews and the presenters’ conference abstracts are compiled here. Thus, this book discusses highly topical fields of marine research and aims to act as a source of knowledge and inspiration for further reading and research.
Author: Katelyn Marie Lewis
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Situated at the northernmost region of the planet, the Arctic Ocean (AO), the smallest of the world's oceans, supports a rich, but vulnerable, ecosystem. Despite seemingly inhospitable conditions, the extreme seasonal pulses of primary production by phytoplankton in the AO fuel an abundant food-web composed of both endemic and migratory higher trophic level organisms. Alas, the Arctic is warming at approximately twice the global rate in response to anthropogenic climate change and the rising temperatures in this region have already triggered profound ecological changes. In the oceans, disappearing sea ice has shifted the phytoplankton growing season earlier in the year and led to a significant increase in net primary production (NPP). In order to understand the multi-layered effects of AO biogeochemistry and ecology as the climate continues to warm, it is imperative to accurately monitor changes in the magnitude and timing of NPP. Because of the harsh conditions that make the region both difficult and expensive to access for most of the year, field measurements in the AO are relatively limited. Luckily, satellite remote sensing can supplement limited in situ measurements by imaging the ocean surface from space. However, because of the unique oceanic optical conditions and phytoplankton photophysiology, global ocean color algorithms fail to accurately estimate Chl a when applied to the AO. Hence, this dissertation work utilizes in situ bio-optical measurements to inform accurate parameterization of ocean color algorithms which are then applied to assess long term changes of AO NPP. To understand the phytoplankton photophysiological responses to environmental changes as the Arctic Ocean shifts seasonally from ice-covered to open water, we evaluated photoacclimation strategies of phytoplankton during the low-light, high-nutrient, ice-covered spring and the high-light, low-nutrient, ice-free summer (Chapter 2). Field results show that phytoplankton effectively acclimated to reduced irradiance beneath the sea ice and that abundant nutrients enable pre-bloom phytoplankton to become "primed" for increases in irradiance. I used these bio-optical measurements to characterize regional and seasonal patterns in phytoplankton photophysiology and optical conditions to examine the impact on ocean color remote sensing in the Chukchi Sea (Chapter 1) and the AO (Chapter 3). Results show that phytoplankton pigment packaging (an acclimation to low light) and high absorption by colored dissolved organic matter (CDOM), especially on the interior shelves, cause default ocean color ocean algorithms to overestimate chlorophyll a (Chl a) at low phytoplankton biomass, but underestimate at high biomass throughout the AO. By assembling the largest database of in situ measurements for these waters, I successfully parameterized multiple ocean color algorithms to optimize retrievals of Chl a, absorption by CDOM and detritus, and backscattering of particles. Using the new ocean color algorithm parameterized for the Arctic Ocean, we show that primary production increased by 57% between 1998 and 2018 (Chapter 4). Surprisingly, while increases were due to widespread sea ice loss during the first decade, the subsequent rise in primary production was driven primarily by increased phytoplankton concentration, which could only be sustained by an influx of new nutrients. This suggests a future Arctic Ocean that, as long as there are enough nutrients, can support higher trophic-level production and additional carbon export. Together, the results of this dissertation demonstrate that the unique bio-optical properties of the AO must be addressed in order to accurately employ satellite remote sensing and, when doing so, we reveal dramatic ecosystem changes in response to anthropogenic climate change.
Author: David N. Thomas
Publisher: John Wiley & Sons
ISBN: 0470756926
Category : Technology & Engineering
Languages : en
Pages : 419
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Book Description
Sea ice, which covers up to 7% of the planet’s surface, is a major component of the world’s oceans, partly driving ocean circulation and global climate patterns. It provides a habitat for a rich diversity of marine organisms, and is an extremely valuable source of information in studies of global climate change and the evolution of present day life forms. Increasingly sea ice is being used as a proxy for extraterrestrial ice covered systems. Sea Ice provides a comprehensive review of our current available knowledge of polar pack ice, the study of which is severely constrained by the logistic difficulties of working in such harsh and remote regions of the earth. The book’s editors, Drs Thomas and Dieckmann have drawn together an impressive group of international contributing authors, providing a well-edited and integrated volume, which will stand for many years as the standard work on the subject. Contents of the book include details of the growth, microstructure and properties of sea ice, large-scale variations in thickness and characteristics, its primary production, micro-and macrobiology, sea ice as a habitat for birds and mammals, sea ice biogeochemistry, particulate flux, and the distribution and significance of palaeo sea ice. Sea Ice is an essential purchase for oceanographers and marine scientists, environmental scientists, biologists, geochemists and geologists. All those involved in the study of global climate change will find this book to contain a wealth of important information. All libraries in universities and research establishments where these subjects are studied and taught will need multiple copies on their shelves. David Thomas is at the School of Ocean Sciences, University of Wales, Bangor, UK. Gerhard Dieckmann is at the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Author: Rüdiger Stein
Publisher: Springer Science & Business Media
ISBN: 3642189121
Category : Science
Languages : en
Pages : 394
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Book Description
The flux, preservation, and accumulation of organic carbon in marine systems are controlled by various mechanisms including primary p- duction of the surface water, supply of terrigenous organic matter from the surrounding continents, biogeochemical processes in the water column and at the seafloor, and sedimentation rate. For the world's oceans, phytoplankton productivity is by far the largest organic carbon 9 source, estimated to be about 30 to 50 Gt (10 tonnes) per year (Berger et al. 1989; Hedges and Keil 1995). By comparison, rivers contribute -1 about 0. 15 to 0. 23 Gt y of particulate organi.
