mmaheigan :: Ocean Carbon & Biogeochemistry

Studying marine ecosystems and biogeochemical cycles in the face of environmental change

Author Archive for mmaheigan

Ocean Optics Summer Class 2019

Posted by mmaheigan

· Wednesday, February 13th, 2019

Ocean Optics Summer Class Calibration and Validation of Ocean Color Remote Sensing

Dates: June 3 – June 28, 2019
Instructors: Emmanuel Boss (coordinator), Ivona Cetinic, Curt Mobley, Collin Roesler, Ken Voss, and Jeremy Werdell.

An intensive four-week, cross-disciplinary, graduate-level course in Optical Oceanography at the University of Maine’s Ira C. Darling Marine Center in summer 2019.

This class is a continuation of the Optical Oceanography course first offered at the Friday Harbor Laboratories in 1985 and since 2001 at the Darling Marine Center. Past graduates are many of today’s leaders in oceanography.

The major theme of the course is calibration and validation of ocean color remote sensing. The course will provide students with a fundamental knowledge of ocean optics and optical sensor technology that will enable them to make quality measurements, be able to assess the uncertainties associated with the measurements, and compare these data with remotely sensed ocean color measurements and derived products.

The course is sponsored by NASA and the University of Maine, with the goal of preparing a new generation of oceanographers trained in the use of optics to study the oceans.

Course elements include:

lectures on the basic theory of the light interaction with matter in aquatic environments ocean color remote sensing and its inversion; optical sensor design and function ocean biogeochemistry; computation and propagation of measurement uncertainties
laboratory sessions using optical instrumentation and radiative transfer software
field sampling of optical and biogeochemical variables in the environmentally diverse waters of coastal Maine
analysis of optical and biogeochemical data sets
collaborative student projects

See: https://sites.google.com/site/oceanopticsclass/ and http://misclab.umeoce.maine.edu/OceanOpticsClass2017/ for previous class content and activities.

Costs: University of Maine tuition, room and board will be covered through a grant for qualified participants.

Registration: Apply by 10th of March 2019, with notification by 1st of April 2019. Application

Acceptance criteria: Likely impact of the class on the individual’s career, transcripts, letter from the academic advisor/supervisor, and diversity. Twenty students will be accepted. While the majority of the class will likely be composed of early career graduate students, advanced graduate students and post-doctoral fellows will be considered for admission.

For more information about the Ira C. Darling Marine Center, see: http://dmc.umaine.edu

Tropical Pacific Observing System 2020 is seeking community input

Posted by mmaheigan

· Monday, February 11th, 2019

Dear Tropical Pacific Observing System Experts and Stakeholders:

We write to invite your review of the Draft of the TPOS 2020 Second Report.

This draft is being circulated to experts and stakeholders who we believe can critically assess the draft and provide guidance on how it should be adjusted and improved. This will be the ONLY round of review for the Second Report of TPOS 2020.

The TPOS 2020 project was established in 2014 to review all aspects of the Tropical Pacific Observing System, and to consider a redesign to meet the science needs of coming decades, taking full advantage of both satellite observations and evolving in situ sampling technology. The Project, its objectives and its major sponsors and stakeholders, are described in documents available at http://www.tpos2020.org, as is the TPOS 2020 First Report.

The TPOS 2020 Steering Committee agreed to provide a sequence of three Reports, the first of which was completed in 2016. The Second Report builds on the First; it does not replace it. Except where necessary, material from the First Report is not repeated in the Second. Rather, the Second Report updates the evolving design, draws on new research and evidence including feedback received on the First Report, and responds to gaps identified by sponsors of the Project. As before, drivers and users of the observing system guide the sampling requirements; these are described, and techniques and strategies available to meet them are evaluated.

Because the Second Report does not restate all topics from the First, focussing instead on what is new, it has a different structure. Its Table of Contents is listed below. We appreciate that your time is valuable and that you may wish to review only those parts most relevant to your expertise.

While every effort has been made to present a complete draft, there are several placeholders where TPOS 2020 is seeking guidance or has not yet completed its work.

Comments may be provided anonymously or attributed. The TPOS 2020 Distributed Project Office will manage all correspondence and can maintain your anonymity if desired. We will track all comments (please use the template provided), and for transparency will retain a brief account of how each comment has been handled by the authors.

The report is available for download at http://tpos2020.org/2nd-report-draft/; the reviewer template is also available there. Please use this template to provide your feedback to the report.

Comments should be received by 28 February 2019. If you need more time, please contact peter.strutton@utas.edu.au.

Correspondence and questions should be addressed to tpos2020@gmail.com.

Please do not hesitate to contact us if you need further clarification.

Pete Strutton, peter.strutton@utas.edu.au

and

Adrienne Sutton, adrienne.sutton@noaa.gov

Co-Chairs of the TPOS 2020 Biogeochemistry Task Team

Table of Contents of the draft TPOS 2020 Second Report:

1. Introduction and Background
2. The Current State of Coupled Models for Sub-Seasonal to Interannual Predictions
3. Coupled Weather and Sub-seasonal Applications
4. Biogeochemical and Ecosystem Observations
5. Developing an Eastern Pacific Observing System
6. Considerations guiding the new Backbone
7. The TPOS 2020 Backbone Observing System
8. TPOS data flow and access
9. Emerging Technologies: Assessing potential for the Backbone
10. Summary and Conclusions
Annex A: Winds
Annex B: Acronym List

Newly Funded OCB Activities

Posted by mmaheigan

· Friday, February 8th, 2019

OCB is pleased to announce the outcomes of the recent OCB proposal solicitation. With 11 proposals, the decision process was challenging this year. The proposals were scored based on scientific merit, relevance to OCB, potential benefits to the broader OCB community, and timeliness. The following new OCB activities have been selected for funding in 2019-2020. More information on these activities, including timelines, participation, and dedicated web pages on the OCB website will be announced soon.

Ocean-Atmosphere Interactions: Scoping directions for U.S. research – PIs: Ocean-Atmosphere Interaction Committee
Ocean Carbonate System Intercomparison Forum – PIs: Brendan Carter, Marta Álvarez, Andrew Dickson, Yui Takeshita, Nancy Williams, Akihiko Murata, Leticia Barbero, Robert Byrne, Andrea Fassbender, Melissa Chierici, Wei Jun Cai, Ryan Woosley, Regina Easley
Ocean nucleic acids ‘omics intercalibration and standardization workshop – PIs: Bethany Jenkins, Andrew Allen, Paul Berube, Scott Gifford, Adrian Marchetti, Alyson Santoro

OCIM Workshop June 23 at OCB 2019

Posted by mmaheigan

· Tuesday, February 5th, 2019

A 1-day workshop will be held in Woods Hole on Sunday, June 23 just before the OCB workshop for those interested in using an ocean circulation inverse model (OCIM) in their research. The OCIM is a data-constrained, lightweight, MATLAB-based ocean circulation model for global modeling of biogeochemical tracers. It has been used to model nutrients, carbon, oxygen, trace metals, and marine food webs, among others. Workshop participants will be provided with model code and instructions, and will engage in tutorial sessions designed to promote familiarity with the model and ability to design and run biogeochemical simulations. Examples of topics that might be covered include: age and water-mass tracers, preformed tracers, diagnostic calculations, transient tracers, air-sea gas exchange, organic matter production and remineralization, isotopes, non-linear models and Newton’s method, iterative solvers, and optimization. Workshop is limited to 20 participants. Requirements: a laptop computer with MATLAB installed and at least 8 GB RAM. Recommended: Working knowledge of MATLAB. Please direct questions to Tim DeVries at tdevries@geog.ucsb.edu.

Biological and physical controls on estuarine nitrous oxide emissions

Posted by mmaheigan

· Tuesday, February 5th, 2019

Nitrous oxide (N₂O) is a potent greenhouse gas with rising atmospheric concentrations. Atmospheric emissions of N₂O are predicted to increase with continued anthropogenic perturbation of the nitrogen cycle, yet the magnitude of these emissions is uncertain, particularly in coastal systems where N₂O fluxes are poorly constrained. How do N₂O emissions from a eutrophic estuary vary in space and time?

Figure 1: Depth profiles of nitrous oxide (N₂O) (circles), salinity (dashed line), and dissolved oxygen (solid line) in the Chesapeake Bay at three stations. Solid circles indicate oversaturation of N₂O with respect to equilibrium with the atmosphere, and open circles indicate undersaturation.

In a recent publication in Estuaries and Coasts, Laperriere et al. (2018) examined how physical and biological processes influence the distribution of N₂O in Chesapeake Bay using dissolved gas measurements (N₂O and N₂/Ar) and stable isotope tracer incubations. During stratified summer conditions, the mesohaline region of the Chesapeake Bay was always a source of N₂O to the atmosphere. The highest N₂O concentrations occurred in the pycnocline at the interface between reducing bottom waters and oxygenated surface waters (Figure 1). Vertical mixing of surface waters across the pycnocline caused elevated rates of ammonia oxidation, a biological source of N₂O, and resulted in the accumulation of nitrite (NO₂^–) below the pycnocline. During periods of weak mixing, ammonia oxidation rates and N₂O concentrations were lower, and low dissolved oxygen concentrations below the pycnocline set the stage for N₂O consumption via denitrification (Figure 1). The interplay between biological and physical processes controlling fluctuations in N₂O concentration was examined using a mass balance approach. Mass balance estimates indicated that both biological processes and physical transport contribute to local changes in N₂O concentration. The authors suggest that the fate of N₂O during stratified summer conditions is governed by vertical mixing across the pycnocline, controlling whether N₂O is released to the atmosphere or consumed at depth.

Authors:
Sarah M. Laperriere (University of California, Santa Barbara)
Nicholas J. Nidzieko (University of California, Santa Barbara)
Rebecca J. Fox (Washington College)
Alexander W. Fisher (University of California, Santa Barbara)
Alyson E. Santoro (University of California, Santa Barbara)

Evidence against an Arctic Ocean methane bomb

Posted by mmaheigan

· Tuesday, February 5th, 2019

Gas hydrates are an ice-like storehouse of the greenhouse gas methane found in continental margins of the world ocean. Warming waters can cause hydrates to decompose and release ancient methane to overlying sediment and waters. The continental shelves of the Arctic Ocean have been thought of as “ground zero” for the potential release of methane from hydrates, since the Arctic is warming rapidly and hydrates are found at relatively shallow water depths there. Another potential ancient methane input to Arctic shelf waters is the methane produced by microorganisms from the gradual thawing of permafrost carbon within seafloor sediment and/or transported to the shelf from terrestrial permafrost via rivers. But, can large stores of ancient-sourced methane reach surface waters and enter the atmosphere, contributing to greenhouse warming?

Figure caption: Map showing the fraction of methane in each surface water sample that was derived from ancient hydrate or permafrost, on a scale from 0 (modern, 0% ancient; indigo) to 1 (100% ancient; yellow). While some of the near-shore surface methane samples have a significant (~50%) ancient component, in waters deeper than 20 m, the surface water methane was mostly (90-95%) derived from modern sources.

To answer this question and understand the role of these ancient sources of methane (hydrates and permafrost), the authors of a 2018 study in Science Advances measured the natural abundance of radiocarbon (¹⁴C) in dissolved methane in the shallow shelf waters of the Alaskan Arctic Ocean (U.S. Beaufort Sea); methane derived from ancient sources has little to no measurable ¹⁴C because of radioactive decay over time. The ¹⁴C-methane results show that ancient sources are contributing methane to the study area’s waters, as the authors predicted. However, ancient methane emitted to seawater can be consumed by microorganisms or transported away by currents before reaching the atmosphere, though these mechanisms have not been known to be effective at removing methane in waters <100 m. This study revealed that these removal processes are surprisingly efficient in shallow shelf waters, especially at the study area’s deepest stations of 30 and 40 m depth, where only ~10% of the methane in surface waters was derived from ancient sources. These results add to a growing body of evidence against the likelihood of a large methane emission to the atmosphere occurring from ancient sources like hydrates, since the authors expect that methane removal processes in the water column are much more efficient in waters 100s of meters deep, where the bulk of the hydrate reservoir resides.

Authors:
K.J. Sparrow (University of Rochester; current address: Florida State University)
J.D. Kessler (University of Rochester)
J.R. Southon (University of California Irvine)
Garcia-Tigreros (University of Rochester)
K.M. Schreiner (University of Minnesota Duluth)
C.D. Ruppel (USGS)
J.B. Miller (University of Colorado Boulder; NOAA)
S.J. Lehman (University of Colorado Boulder)
Xu (University of California Irvine)

NCAR Early Career Faculty Innovator Program

Posted by mmaheigan

· Wednesday, January 23rd, 2019

NCAR Early Career Faculty Innovator Program

The Early Career Faculty Innovator Program is a new funding opportunity for early career faculty in the social sciences and STEM outside of NCAR’s core expertise to co-develop interdisciplinary research projects in partnership with scientists and engineers at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. The Innovators Program aims to fund six faculty and one graduate student of each faculty participant for two years, starting in summer 2019. Research themes that align with NSF and NCAR strategic priorities are selected for each two-year cohort.

2019-2020 Research Theme: Coastal Regions and Human Settlements
Prospective applicants to the Innovators Program are invited to propose an interdisciplinary research project that can leverage expertise at NCAR and occur over a 2-year period. NCAR is committed to broadening participation in the geosciences and specifically invites scholars from Minority Serving Institutions to apply.

Applications to the Innovators Program will be accepted from January 15th, 2019 until March 1st, 2019. Before the start of the program, faculty are expected to nominate a graduate student who will be part of this project.

Some NCAR ocean contacts: Matt Long, Joanie Kleypas, Frank Bryan

Dust-borne iron in the Southern Ocean was more bioavailable during glacial periods

Posted by mmaheigan

· Wednesday, January 23rd, 2019

The Southern Ocean is iron (Fe)-limited, and increased fluxes of dust-borne Fe to the Southern Ocean during the Last Glacial Maximum (LGM) have been associated with phytoplankton growth and CO₂ drawdown. Dust contains different mixes of Fe-bearing minerals, depending on the source region. Fe(II) silicate minerals from physical weathering are more bioavailable than Fe(III) oxyhydroxide minerals from chemical weathering. The Fe(II) silicates are dominant in dust sources that have been weathered from bedrock by glaciers in Patagonia, but the impact of glacial activity on dust-borne Fe speciation (Fe oxidation state and mineral composition) and bioavailability over the last glacial cycle has not previously been quantified.

Figure 1. The fraction of Fe(II) in dust (Fe(II)/Fetotal, dominated by Fe(II) silicates, shown as blue dots connected with dotted lines on blue axes) in marine sediment cores from (A) the South Atlantic and (B) the South Pacific plotted with the total dust flux (grey lines on grey axes).

A recent study in PNAS reconstructs the speciation of dust-borne Fe over the last glacial cycle in South Atlantic and South Pacific marine sediment cores using Fe K-edge X-ray absorption spectroscopy. The authors observed that the highly bioavailable Fe(II) silicate content of dust-borne Fe is higher in both regions during cold glacial periods, suggesting that a given flux of Fe is more bioavailable in glacial versus interglacial periods (Figure 1). Therefore, all Fe cannot be considered equal in biogeochemical models working on glacial-interglacial timescales. The bioavailability of a given flux of Fe at the LGM was likely a dominant driver of phytoplankton growth, with more bioavailable Fe driving increased phytoplankton activity and associated atmospheric CO₂ drawdown and subsequent cooling. The observed association between glacial periods and increased Fe bioavailability in the Southern Ocean may indicate an important positive feedback mechanism between glacial activity and cold glacial temperatures through Fe speciation and the efficiency of the biological pump.

Paper link: https://doi.org/10.1073/pnas.1809755115

Authors:
Elizabeth M. Shoenfelt (Lamont-Doherty Earth Observatory, Columbia University)
Gisela Winckler (Lamont-Doherty Earth Observatory, Columbia University)
Frank Lamy (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research)
Robert F. Anderson (Lamont-Doherty Earth Observatory, Columbia University)
Benjamin C. Bostick (Lamont-Doherty Earth Observatory, Columbia University)

The past, present, and future of artificial ocean iron fertilization experiments

Posted by mmaheigan

· Wednesday, January 23rd, 2019

Since the beginning of the industrial revolution, human activities have greatly increased atmospheric CO₂ concentrations, leading to global warming and indicating an urgent need to reduce global greenhouse gas emissions. The Martin (or iron) hypothesis suggests that ocean iron fertilization (OIF) could be a low-cost effective method for reducing atmospheric CO₂ levels by stimulating carbon sequestration via the biological pump in iron-limited, high-nutrient, low-chlorophyll (HNLC) ocean regions. Given increasing global political, social, and economic concerns associated with climate change, it is necessary to examine the validity and usefulness of artificial OIF (aOIF) experimentation as a geoengineering solution.

Figure 1. (a) Global annual distribution of surface chlorophyll concentrations (mg m^-3) with locations of 13 aOIF experiments. Maximum and initial values in (b) maximum quantum yield of photosynthesis (Fv/Fm ratios) and (c) chlorophyll-a concentrations (mg m^-3) during aOIF experiments. (d) Changes in primary productivity (ΔPP = [PP]_{post-fertilization (postf)} ‒ [PP]_{pre-fertilization (pref)}; mg C m^-2 d^-1). (e) Distributions of chlorophyll-a concentrations (mg m^-3) on day 24 after iron addition in the Southern Ocean iron experiment-north (SOFeX-N) from MODIS Terra Level-2 daily image and on day 20 in the SOFeX-south (SOFeX-S) from SeaWiFS Level-2 daily image (white dotted box indicates phytoplankton bloom during aOIF experiments). (f) Changes in nitrate concentrations (ΔNO₃^– = [NO₃^–]_postf ‒ [NO₃^–]_pref; μM). (g) Changes in partial pressure of CO₂ (ΔpCO₂ = [pCO₂]_postf ‒ [pCO₂]_pref; μatm). The color bar indicates changes in dissolved inorganic carbon (ΔDIC = [DIC]_postf ‒ [DIC]_pref; μM). The numbers on the X axis indicate the order of aOIF experiments as given in Figure 1a and are grouped according to ocean basins; Equatorial Pacific (EP) (yellow bar), Southern Ocean (SO) (blue bar), subarctic North Pacific (NP) (red bar), and subtropical North Atlantic (NA) (green bar).

A review paper published in Biogeosciences on aOIF experiments provides a thorough overview of 13 scientific artificial OIF experiments conducted in HNLC regions over the last 25 years. These aOIF experiments have demonstrated that iron addition stimulates substantial increases in phytoplankton biomass and primary production, resulting in drawdown of macro-nutrients and dissolved inorganic carbon (Figure 1). Many of the aOIF experiments have also precipitated community shifts from smaller (pico- and nano-) to larger (micro) phytoplankton. However, the impact on the net transfer of CO₂ from the atmosphere to below the winter mixed layer via the biological pump is not yet fully understood or quantified and appears to vary with environmental conditions, export flux measurement techniques, and other unknown factors. These results, including possible side effects, have been debated among those who support and oppose aOIF experimentation, and many questions remain about the effectiveness of scientific aOIF, possible side effects, and international aOIF law frameworks. Therefore, it is important to continue undertaking small-scale, scientifically controlled studies to better understand natural processes in the HNLC regions, assess the associated risks, and lay the groundwork for evaluating the potential effectiveness and impacts of large-scale aOIF as a geoengineering solution to anthropogenic climate change. Additionally, this paper suggests considerations for the design of future aOIF experiments to maximize the effectiveness of the technique and begin to answer open questions under international aOIF regulations.

Authors:
Joo-Eun Yoon (Incheon National University)
Il-Nam Kim (Incheon National University)
Alison M. Macdonald (Woods Hole Oceanographic Institution)

Autonomous measurement of N-loss in the Eastern Tropical North Pacific ODZ: An Invitation for Collaboration

Posted by mmaheigan

· Thursday, January 10th, 2019

By Mark A. Altabet (SMAST/U. Mass. Dartmouth), Craig McNeil, and Eric D’Asaro (both at APL / U. Washington)

Oxygen deficient zones (ODZs) constitute a small fraction of total oceanic volume yet play an important role in regulating global ocean carbon and nitrogen cycles. They are critical for regulating the ocean’s nitrogen budget, as loss of biologically available nitrogen to N₂ gas (N-loss) within ODZs is estimated to be 30 to 50% of the global total. However, temporal and spatial variability in N-loss rates have been undersampled by ship-based process studies leaving substantial uncertainty in overall rates. While local and short-term regulation of N-loss by O₂ and organic matter availability is well documented, little is known about the larger scale temporal/spatial variability in N-loss that may result from physical forcings such as remote ventilation, seasonal variability in vertical exchange with the near-surface layer, and mesoscale eddies. Understanding the impact of larger scale physical forcings on N-loss as mediated through O₂ and organic flux is needed to fully understand the causes and consequences of any future ODZ expansion. To achieve this, we need sustained observations by a distributed array capable of detecting synoptic variability.

To address these issues, a new NSF-funded project will carry out a multiyear, autonomous float-based observational program to answer the following questions:

How does biogenic N₂ production in ODZs vary over weekly to annual time scales and space scales of 10s to 1000s km?
What are the major scales of variability and their associated oceanographic phenomena and how do they relate to control by organic matter flux and O₂ concentration?
How does this variability influence regionally integrated N-loss?

Figure 1. The ETNP ODZ roughly defined by O₂ <1.5 μmol/kg (orange, World Ocean Atlas 2013). Our new NSF-funded project will sample across these patterns of spatial and temporal variability for 2 years with 10 subsurface ODZ floats (red/blue) each measuring profiles of T, S, O₂ (50 nmol/kg LOD) and N₂ (0.1 μmol/kg precision), and the in situ rate of N₂ change. Four Argo floats with O₂ sensors and BioOptical floats provided by collaborators will supplement this array. Bright bar symbols are the planned deployment positions; dimmed bar symbols suggest possible displacements after 2 years. Ship-based measurements (yellow stars) along the deployment cruise track (magenta) will be used for float sensor calibration and identification of ETNP source water properties. The 2-year track of our prototype GasFloat is also shown (black line).

This project will exploit our ability to make in situ, ultra-high precision measurement of N₂ concentration (~0.1 umol/kg) and use commercially available O₂ sensors to measure O₂ in the 10s of nM range. Our study area is the Eastern Tropical North Pacific (ETNP), the largest ODZ and the region of our successful pilot deployments (Figure 1). Over a multi-year period, our study will determine in situ nM-level O₂ and biogenic N₂ on float profiles distributed throughout the ETNP and encompassing geographic gradients in O₂ and surface productivity. For the first time, our study will also determine in situ N-loss rates from changes in N₂ concentration during one- to two-week Lagrangian float deployments drifting along a constant density surface (Figure 2). A pilot two-year float (‘GasFloat, Figure 1) deployment in the ETNP has documented our ability to do so. Critically, our float-based approach more closely matches the frequency and distribution of observations to the expected variability in biogenic N₂ production, as compared to prior work. This study will also dramatically increase the data density in this region by acquiring >500 profiles/drifts for N₂ and >1000 profiles for nM O₂.

Figure 2. (a) Schematic of float system to be deployed (b) Example of float mission including 2-week isopycnal drift.

We anticipate float deployment in summer 2020 via a UNOLS vessel. Investigators interested in collaborative participation through contribution of autonomous instrumentation and/or making shipboard measurements are encouraged to contact the lead PI Mark Altabet at maltabet@umassd.edu. Similarly, students interested in graduate research opportunities through this project should contact the lead PI.

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

Author Archive for mmaheigan

Filter by Keyword