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  • 1
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    Oceanic ambient noise in the Arctic on the Chukchi Shelf: broadband characteristics and environmental drivers (2022)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2023-01-18
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
    Description: This thesis encompasses an analysis of underwater ambient noise collected by the yearlong Canada Basin Acoustic Propagation Experiment (CANAPE) on the Chukchi Shelf of the Arctic. This location contained the Beaufort Duct, a significant effect of climate change on the Arctic’s underwater soundscape. A study of the statistical and probability metrics was conducted on a frequency band of 50-1900 Hz to examine the relation between environmental drivers and noise patterns. The presence of ice typically decreases broadband ambient noise, when compared to ice-free seas. However, the Beaufort Duct under ice increases the ambient noise levels below 1 kHz. The relationship between ambient noise and the environment is further explored by studying the link between distant ice movements and ambient levels Correlation between the two is found to exist from 300-1500 Hz, as distant ( 500 km) ice drift motion appears to drive noise levels at the receiver.
    Description: Funding sources include the US Navy and Office of Naval Research.
    Keywords: Arctic ; Ambient ; Noise
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 2
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    Warming effects on arctic tundra biogeochemistry are limited but habitat-dependent: a meta-analysis (2022)
    Ecological Society of America
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Pold, G., Baillargeon, N., Lepe, A., Rastetter, E. B., & Sistla, S. A. Warming effects on arctic tundra biogeochemistry are limited but habitat-dependent: a meta-analysis. Ecosphere, 12(10), (2021): e03777, https://doi.org/10.1002/ecs2.3777.
    Description: Arctic tundra consists of diverse habitats that differ in dominant vegetation, soil moisture regimes, and relative importance of organic vs. inorganic nutrient cycling. The Arctic is also the most rapidly warming global area, with winter warming dominating. This warming is expected to have dramatic effects on tundra carbon and nutrient dynamics. We completed a meta-analysis of 166 experimental warming study papers to evaluate the hypotheses that warming changes tundra biogeochemical cycles in a habitat- and seasonally specific manner and that the carbon (C), nitrogen (N), and phosphorus (P) cycles will be differentially accelerated, leading to decoupling of elemental cycles. We found that nutrient availability and plant leaf stoichiometry responses to experimental warming were variable and overall weak, but that both gross primary productivity and the plant C pool tended to increase with growing season warming. The effects of winter warming on C fluxes did not extend into the growing season. Overall, although warming led to more consistent increases in C fluxes compared to N or P fluxes, evidence for decoupling of biogeochemical cycles is weak and any effect appears limited to heath habitats. However, data on many habitats are too sparse to be able to generalize how warming might decouple biogeochemical cycles, and too few year-round warming studies exist to ascertain whether the season under which warming occurs alters how ecosystems respond to warming. Coordinated field campaigns are necessary to more robustly document tundra habitat-specific responses to realistic climate warming scenarios in order to better understand the mechanisms driving this heterogeneity and identify the tundra habitats, communities, and soil pools most susceptible to warming.
    Description: Funding for this project was provided by NSF Signals in the Soil grant number 1841610 to SAS and ER. SAS and ER conceived of and acquired funding for the project. NB completed the literature search.
    Keywords: Arctic ; Biogeochemistry ; Climate change ; Experimental warming ; Meta-analysis ; Stoichiometry ; Tundra
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  • 3
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    Environmental effects of the Beaufort Lens on underwater acoustic communications during Arctic operations (2021)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2021.
    Description: Operations in the Arctic Ocean are increasingly important due to the changing environment and the resulting global implications. These changes range from the availability of new global trade routes, accessibility of newly available resources in the area, and national security interests of the United States in the region. It’s necessary to build a greater understanding of the undersea environment and how it’s changing since these environmental changes have a direct impact on adjusting future operations in the region and looming global changes as less Arctic ice is present. The recent presence of the Beaufort Lens is changing the acoustic propagation paths throughout the Arctic region. Here a network of buoys were employed to communicate with an Autonomous Undersea Vehicle (AUV) while it operated under the ice throughout the Beaufort Lens with the goal of achieving near GPS quality navigation. The acoustic communications paths were compared using a vertical array throughout the Beaufort Lens. This beam forming was compared to the prediction from BELLHOP. As well, since acoustic communications are affected by multi-path, attenuation and interference from other sources it was interesting to note that bottom bounce was sometimes a reliable acoustic path.
    Keywords: Arctic ; Beaufort Lens ; Acoustic communications
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  • 4
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    Arctic amplification of global warming strengthened by sunlight oxidation of permafrost carbon to CO2 (2020)
    Wiley
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bowen, J. C., Ward, C. P., Kling, G. W., & Cory, R. M. Arctic amplification of global warming strengthened by sunlight oxidation of permafrost carbon to CO2. Geophysical Research Letters, 47(12), (2020): e2020GL087085, doi:10.1029/2020GL087085.
    Description: Once thawed, up to 15% of the ∼1,000 Pg of organic carbon (C) in arctic permafrost soils may be oxidized to carbon dioxide (CO2) by 2,100, amplifying climate change. However, predictions of this amplification strength ignore the oxidation of permafrost C to CO2 in surface waters (photomineralization). We characterized the wavelength dependence of permafrost dissolved organic carbon (DOC) photomineralization and demonstrate that iron catalyzes photomineralization of old DOC (4,000–6,300 a BP) derived from soil lignin and tannin. Rates of CO2 production from photomineralization of permafrost DOC are twofold higher than for modern DOC. Given that model predictions of future net loss of ecosystem C from thawing permafrost do not include the loss of CO2 to the atmosphere from DOC photomineralization, current predictions of an average of 208 Pg C loss by 2,299 may be too low by ~14%.
    Description: This research was supported by National Science Foundation (NSF) CAREER 1351745 (R.M.C.), DEB 1637459 and 1754835 (G.W.K.), the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry (R.M.C. and C.P.W.), the Frank and Lisina Hock Endowed Fund (C.P.W.), and the NOSAMS Graduate Student Internship Program (J.C.B.).
    Keywords: Photochemistry ; Permafrost ; Arctic ; Carbon cycling ; Dissolved organic carbon
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  • 5
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    Radium isotopes and radon-222 as tracers of sediment-water interaction in Arctic coastal and lacustrine environments (2020)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-10-20
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2020.
    Description: Arctic marine and lacustrine systems are experiencing rapid warming due to climate change. These changes are especially important at the interface between sediments and surface waters because they are hotspots for biogeochemical transformations such as redox reactions, nutrient consumption and regeneration, organic matter leaching and degradation, and mineral weathering. Radium isotopes (223Ra, 224Ra, 226Ra, 228Ra) and radon-222, naturally occurring radioactive isotopes produced in sediments, are well-suited as tracers of nutrients, trace metals, and organic matter cycling processes at the sediment-water interface. In this thesis, I have applied radon-222 and the quartet of radium isotopes to study fundamental processes in subarctic lakes and on the Arctic continental shelf. First, radon-222 is used to quantify groundwater discharge into a shallow, tundra lake on the Yukon-Kuskokwim Delta in Alaska in summer of 2017. Radon-derived groundwater fluxes were then paired with methane (CH4) measurements to determine delivery rates of methane into the lake via groundwater. Groundwater CH4 fluxes significantly exceeded diffusive air-water fluxes from the lake to the atmosphere, suggesting that groundwater is an important source of CH4 to Arctic lakes and may drive observed CH4 emissions. Higher CH4 emissions were observed compared to those reported previously in high latitude lakes, like due to higher CH4 concentrations in groundwater. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for methane release across Arctic landscapes. Then, the quartet of radium isotopes is used to study the impacts of storms and sea ice formation as drivers of sediment-water interaction on the Alaskan Beaufort shelf. The timeseries presented in this study is among the first to document the combined physical and chemical signals of winter water formation in the Beaufort Sea, made possible by repeat occupations of the central Beaufort shelf. Radium measurements are combined with inorganic nitrogen and hydrographic measurements to elucidate the episodic behavior of winter water formation and its ability to drive exchange with bottom sediments during freeze-up.
    Description: Financial support for Chapter 2 was funded by National Science Foundation awards OCE-1458305 to M.A.C., 1561437 to S.M.N, J.D.S., and R.M.H and 1624927 to S.M.N., P.J.M. and R.M.H. The work completed for Chapter 3 was funded by the Montrym Fund at the Massachusetts Institute of Technology, the Academic Programs Office at Woods Hole Oceanographic Institution, and the NSF Arctic GEOTRACES (OCE-1458305), Pacific GEOTRACES (OCE-1736277), and Arctic Observing Network programs (OPP-1733564).
    Keywords: Arctic ; Sediment ; Radionuclides
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  • 6
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    Underwater & out of sight: towards ubiquity in underwater robotics (2019)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2019.
    Description: The Earth's oceans holds a wealth of information currently hidden from us. Effective measurement of its properties could provide a better understanding of our changing climate and insights into the creatures that inhabit its waters. Autonomous underwater vehicles (AUVs) hold the promise of penetrating the ocean environment and uncovering its mysteries; and progress in underwater robotics research over the past three decades has resulted in vehicles that can navigate reliably and operate consistently, providing oceanographers with an additional tool for studying the ocean. Unfortunately, the high cost of these vehicles has stifled the democratization of this technology. We believe that this is a consequence of two factors. Firstly, reliable navigation on conventional AUVs has been achieved through the use of a sophisticated sensor system, namely the Doppler velocity log (DVL)-aided inertial navigation system (INS), which drives up vehicle cost, power use and size. Secondly, deployment of these vehicles is expensive and unwieldy due to their complexity, size and cost, resulting in the need for specialized personnel for vehicle operation and maintenance. The recent development of simpler, low-cost, miniature underwater robots provides a solution that mitigates both these factors; however, removing the expensive DVL-aided INS means that they perform poorly in terms of navigation accuracy. We address this by introducing a novel acoustic system that enables AUV self-localization without requiring a DVL-aided INS or on-board active acoustic transmitters. We term this approach Passive Inverted Ultra-Short Baseline (piUSBL) positioning. The system uses a single acoustic beacon and a time-synchronized, vehicle-mounted, passive receiver array to localize the vehicle relative to this beacon. Our approach has two unique advantages: first, a single beacon lowers cost and enables easy deployment; second, a passive receiver allows the vehicle to be low-power, low-cost and small, and enables multi-vehicle scalability. Providing this new generation of small and inexpensive vehicles with accurate navigation can potentially lower the cost of entry into underwater robotics research and further its widespread use for ocean science. We hope that these contributions in low-cost underwater navigation will enable the ubiquitous and coordinated use of robots to explore and understand the underwater domain.
    Description: This research was funded and supported by a number of sponsors; we gratefully acknowledge them below. Defense Advanced Research Projects Agency (DARPA) and SSC Pacific via Applied Physical Sciences Corp. (APS) under contract number N66001-11-C-4115. SSC Pacific via Applied Physical Sciences Corp. (APS) under award number N66001-14-C-4031. Air Force via Lincoln Laboratory under award number FA8721-05-C-0002. Office of Naval Research (ONR) via University of California-San Diego under award number N00014-13-1-0632. Defense Advanced Research Projects Agency (DARPA) via Applied Physical Sciences Corp. (APS) under award number HR0011-18-C-0008. Office of Naval Research (ONR) under award number N00014-17-1-2474.
    Keywords: Ocean ; Submersibles ; Robotics ; Sound ; Navigation
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  • 7
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    The response of ocean salinity patterns to climate change: implications for circulation (2019)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2019.
    Description: Global patterns of ocean salinity arise from the exchange of freshwater between the sea surface and the atmosphere. For a quasi-steady state system, these surface fluxes are balanced by compensating transports of salt in the ocean interior. In a warming climate, the atmosphere holds additional water vapor which acts to intensify the global water cycle. Amplified freshwater fluxes are then absorbed at the surface and propagate along ocean circulation pathways. Here, we use coupled model results from the CMIP5 experiment to identify coherent responses in the atmospheric water cycle and in ocean salinity patterns. Some aspects of the response are consistent across models, while other regions show large inter-model spread. In particular, the salinity response in the North Atlantic subpolar gyre, where the mean salinity plays a role in maintaining high surface density for deep-water formation, has low confidence in CMIP5 models. To understand how differences in ocean circulation may affect this response, we use two techniques to diagnose the role of salt transports in the present-day climate. The first is a salt budget within the surface mixed layer, which identifies major transport processes. The second is a Lagrangian particle tracking tool, used to understand the regional connectivity of water masses. From this analysis, we find that anomalous freshwater signals become well mixed within the ocean gyres, but can be isolated on larger scales. The subpolar Atlantic salinity response generally shows freshening at the surface, but is sensitive to the transport of anomalously salty water from the subtropics, a largely eddy-driven process. As CMIP5 models use a range of eddy parameterizations, this is likely a source of uncertainty in the salinity response. Finally, we investigate the effect of salinity changes on the deep overturning cells and other circulations, and find a complex influence that also depends on the details of advective pathways. In a warming scenario, water cycle amplification actually works to strengthen the Atlantic meridional overturning circulation due to the influence of enhanced subtropical evaporation.
    Description: Funding for this thesis was provided by NASA grant NNX12AF59GS03, a NASA Earth and Space Science Fellowship award 80NSSC17K0372, and the WHOI Academic Programs Office.
    Keywords: Salinity ; Climatic changes ; Ocean ; Dissertations, Academic ; North Atlantic Ocean
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  • 8
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    An investigation of basin-scale controls on upper ocean export and remineralization (2018)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2018.
    Description: The biological carbon pump (BCP) helps to moderate atmospheric carbon dioxide levels by bringing carbon to the deep ocean, where it can be sequestered on timescales of centuries to millennia. Climate change is predicted to decrease the efficiency of the global BCP, however, the magnitude and timescale of this shift is largely uncertain and will likely impact some areas of the global ocean more significantly than others. Therefore, it is imperative that we (1) accurately quantify surface export and remineralization of particulate organic carbon (POC) via the BCP over large regions of the global ocean, (2) examine the factors controlling these POC fluxes and their variability, which includes the cycling of biologically-relevant trace metals, and (3) establish if and how the BCP is changing over time. This thesis focuses on addressing various aspects of these objectives using the 234Th-238U method across basin-scale GEOTRACES transects. First, the export and remineralization of POC were examined across large gradients in productivity, upwelling, community structure, and dissolved oxygen in the southeastern tropical Pacific Ocean. Although low oxygen zones are traditionally thought to have decreased POC flux attenuation relative to other regions of the global ocean and the low oxygen Pacific locations followed this pattern, regions that were functionally anoxic had enhanced attenuation in the upper 400 m. Second, trace metal export and remineralization were quantified across the Pacific transect. Because many trace metals are necessary for the metabolic functions of marine organisms and can co-limit marine productivity, the controls on the cycling of trace metals in the upper ocean were examined. Lastly, POC export was determined across two transects in the Western Arctic Ocean, where light and nutrient availability drive the biological pump. Upper ocean export estimates in the central basin did not reflect a substantial change in the biological pump compared to studies from the last three decades, however, an extensive maximum in 234Th relative to 238U deeper in the water column indicated that rapid vertical transport had occurred, which could suggest a more efficient biological pump in the Arctic Ocean.
    Description: I was funded under the NASA Earth and Space Science Fellowship Program grant (NNX13AP31H) for three years. I was also funded for work on the U.S. Pacific and Arctic GEOTRACES campaigns under two National Science Foundation grants (OCE-1232669 and OCE- 1458305). The MIT Henry G. Houghton Fund provided support for the purchase of computers and textbooks and the MIT Scurlock Fund allowed for my travel to Bermuda for cruise training. WHOI Academic Programs supplemented the aforementioned funding and also provided additional support for travel to conferences.
    Keywords: Carbon ; Climatic changes ; Ocean ; Thomas G. Thompson (Ship) Cruise TN303
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  • 9
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    The marine biogeochemistry of chromium isotopes (2018)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2018
    Description: In the ocean, chromium (Cr) is a redox-sensitive trace metal. The reduction of Cr(VI) to Cr(III) occurs in oxygen deficient zones (ODZs), and Cr reduction in general has been identified as a significant Cr isotope fractionation mechanism. This thesis presents the first Cr isotope variations (d53Cr) in ODZs of the ocean and adds to the sparse Cr isotope data published for modern seawater. I developed a precise and accurate Cr isotope method for seawater samples. Seawater acidification converts total Cr to Cr(III) which is preconcentrated by Mg(OH)2 coprecipitation. A three-column anion exchange chromatography scheme separates Cr from isobaric and polyatomic interferences present in the seawater and reagent matrixes. Isotope analysis is performed on a MC-ICP-MS IsoProbe. The addition of a 50Cr-54Cr double spike allows for accurate correction of procedural and instrumental Cr mass fractionations. The first Cr isotope ratio data for a full water column profile in the Pacific Ocean is presented. This station serves as a fully oxic counterpart to stations located within the ODZ of the Eastern Tropical North Pacific. At one station, Cr concentrations are lower and d53Cr values are heavier within the ODZ. This is consistent with Cr reduction resulting in isotopically lighter, particlereactive Cr(III), which is scavenged and exported from the water column. A strong correlation of d53Cr and d15NNO3- at this station suggests that Cr reduction may be microbially mediated instead of simply being a product of thermodynamic equilibrium. Alternatively, Cr may be reduced by Fe(II). In the anoxic bottom waters of the Santa Barbara Basin a strong Cr reduction signal (lower [Cr], heavier d53Cr) is observed, which may result from the same aforementioned Cr reduction mechanisms. A shift to the heaviest seawater Cr isotope signatures yet observed was detected in the oxic bottom waters of the shallow Arctic Chukchi shelf, while Cr concentrations decreased. This extreme isotope signal may result from Cr reduction by a reduced species (e.g. Fe(II)), which was released from the underlying anoxic shelf sediments. Cr in the Atlantic layer and in the bottom water of a central Arctic station appears to be shaped by a novel, unidentified process.
    Description: This research was supported by the US National Science Foundation (NSF Award No. OCE- 0926197, OCE-1233749, OCE-1357224), the Singapore National Research Foundation through the Singapore-MIT Alliance for Research and Technology (Award No. WBS 6916070), and the Center for Microbial Research and Education (NSF-OIA Award No. EF-0424599). In the last year of my studies, I was supported by a MIT-WHOI Joint Program Science Fellowship.
    Keywords: Ocean ; Chromium ; Seawater ; Isotopes
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  • 10
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    Geophysical and petrological constraints on ocean plate dynamics (2017)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2017
    Description: This thesis investigates the formation and subsequent motion of oceanic lithospheric plates through geophysical and petrological methods. Ocean crust and lithosphere forms at mid-ocean ridges as the underlying asthenosphere rises, melts, and flows away from the ridge axis. In Chapters 2 and 3, I present the results from partial melting experiments of mantle peridotite that were conducted in order to examine the mantle melting point, or solidus, beneath a mid-ocean ridge. Chapter 2 determines the peridotite solidus at a single pressure of 1.5 GPa and concludes that the oceanic mantle potential temperature must be ~60ºC hotter than current estimates. Chapter 3 goes further to provide a more accurate parameterization of the anhydrous mantle solidus from experiments over a range of pressures. This chapter concludes that the range of potential temperatures of the mantle beneath mid-ocean ridges and plumes is smaller than currently estimated. Once formed, the oceanic plate moves atop the underlying asthenosphere away from the ridge axis. Chapter 4 uses seafloor magnetotelluric data to investigate the mechanism responsible for plate motion at the lithosphere-asthenosphere boundary. The resulting two dimensional conductivity model shows a simple layered structure. By applying petrological constraints, I conclude that the upper asthenosphere does not contain substantial melt, which suggests that either a thermal or hydration mechanism supports plate motion. Oceanic plate motion has dramatically changed the surface of the Earth over time, and evidence for ancient plate motion is obvious from detailed studies of the longer lived continental lithosphere. In Chapter 5, I investigate past plate motion by inverting magnetotelluric data collected over eastern Zambia. The conductivity model probes the Zambian lithosphere and reveals an ancient subduction zone previously suspected from surface studies. This chapter elucidates the complex lithospheric structure of eastern Zambia and the geometry of the tectonic elements in the region, which collided as a result of past oceanic plate motion. Combined, the chapters of this thesis provide critical constraints on ocean plate dynamics.
    Description: Funding for this research was provided by the National Science Foundation Division of Earth Sciences (EAR) grant number 1010432, Division of Ocean Sciences (OCE) grant numbers 1459649 and 0928663, WHOI Deep Ocean Exploration Institute, and the WHOI Academic Programs Office.
    Keywords: Lithosphere ; Ocean ; Temperature ; Mid-Atlantic Ridge
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  • 11
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    Long-term experimental warming and nutrient additions increase productivity in tall deciduous shrub tundra (2014)
    Ecological Society of America
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecosphere 5 (2014): art72, doi:10.1890/ES13-00281.1.
    Description: Warming Arctic temperatures can drive changes in vegetation structure and function directly by stimulating plant growth or indirectly by stimulating microbial decomposition of organic matter and releasing more nutrients for plant uptake and growth. The arctic biome is currently increasing in deciduous shrub cover and this increase is expected to continue with climate warming. However, little is known how current deciduous shrub communities will respond to future climate induced warming and nutrient increase. We examined the plant and ecosystem response to a long-term (18 years) nutrient addition and warming experiment in an Alaskan arctic tall deciduous shrub tundra ecosystem to understand controls over plant productivity and carbon (C) and nitrogen (N) storage in shrub tundra ecosystems. In addition, we used a meta-analysis approach to compare the treatment effect size for aboveground biomass among seven long-term studies conducted across multiple plant community types within the Arctic. We found that biomass, productivity, and aboveground N pools increased with nutrient additions and warming, while species diversity decreased. Both nutrient additions and warming caused the dominant functional group, deciduous shrubs, to increase biomass and proportional C and N allocation to aboveground stems but decreased allocation to belowground stems. For all response variables except soil C and N pools, effects of nutrients plus warming were largest. Soil C and N pools were highly variable and we could not detect any response to the treatments. The biomass response to warming and fertilization in tall deciduous shrub tundra was greater than moist acidic and moist non-acidic tundra and more similar to the biomass response of wet sedge tundra. Our data suggest that in a warmer and more nutrient-rich Arctic, tall deciduous shrub tundra will have greater total deciduous shrub biomass and a higher proportion of woody tissue that has a longer residence time, with a lower proportion of C and N allocated to belowground stems.
    Description: This research was supported by NSF grants DEB-0516041, DEB-0516509 and the Arctic LTER (DEB-0423385).
    Keywords: Arctic ; Carbon pools ; Climate change ; Deciduous shrubs ; Manipulated warming ; Meta-analysis ; Nitrogen pools ; Nutrient additions ; Tundra
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  • 12
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    Biogeography of bacterioplankton in lakes and streams of an arctic tundra catchment (2007)
    Ecological Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Ecological Society of America, 2007. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 88 (2007): 1365–1378, doi:10.1890/06-0387
    Description: Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA. Bacterioplankton communities in streams draining tundra were very different than those in streams draining lakes. Communities in streams draining lakes were similar to communities in lakes. In a connected series of lakes and streams, the stream communities changed with distance from the upstream lake and with changes in water chemistry, suggesting inoculation and dilution with bacteria from soil waters or hyporheic zones. In the same system, lakes shared similar bacterioplankton communities (78% similar) that shifted gradually down the catchment. In contrast, unconnected lakes contained somewhat different communities (67% similar). We found evidence that dispersal influences bacterioplankton communities via advection and dilution (mass effects) in streams, and via inoculation and subsequent growth in lakes. The spatial pattern of bacterioplankton community composition was strongly influenced by interactions among soil water, stream, and lake environments. Our results reveal large differences in lake-specific and stream-specific bacterial community composition over restricted spatial scales (〈10 km) and suggest that geographic distance and connectivity influence the distribution of bacterioplankton communities across a landscape.
    Description: This research was supported in part by the University of Michigan and University of Maryland, and by National Science Foundation grants OPP-0408371, OPP-9911681, OPP- 9911278, DEB-0423385, DEB-9810222, and ATM-0423385.
    Keywords: Arctic ; Bacteria ; Bacterial production ; Bacterioplankton ; Biogeography ; Diversity ; Denaturing gradient gel electrophoresis ; DGGE ; Metacommunity
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