mmaheigan :: Ocean Carbon & Biogeochemistry

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

Author Archive for mmaheigan

Does dark carbon fixation supply labile DOC to the deep ocean?

Posted by mmaheigan

· Thursday, March 30th, 2023

Nitrifying microbes are the most abundant chemoautotrophs in the dark ocean. Though better known for their role in the nitrogen cycle, they also fix dissolved inorganic carbon (DIC) into biomass and thus play an important role in the global carbon cycle. The release of organic compounds by these microbes may represent an as-yet unaccounted for source of dissolved organic carbon (DOC) available to heterotrophic marine food webs. Quantifying how much DIC these microbes fix and release again into the ambient seawater is critical to a complete understanding of the carbon cycle in the deep ocean.

To address this knowledge gap, a recent study grew ten diverse nitrifier cultures and measured their cellular carbon (C) content, DIC fixation yields and DOC release rates. The results indicate that nitrifiers release between 5 and 15% of their recently fixed DIC as DOC (Figure 1). This would equate to global ocean fluxes of 0.006–0.02 Pg C yr⁻.

Figure 1. DOC release by ten different chemoautotrophic nitrifying (ammonia- and nitrite-oxidizing) microbes. The diversity of marine nitrifiers used in this study comprises all genera currently available as axenic cultures. Species and strain names are given for completeness.

Our results provide values for biogeochemical models of the global carbon cycle, and help to further constrain the relationship between C and N fluxes in the nitrification process. Elucidating the lability and fate of carbon released by nitrifiers will be the crucial next step to understand its implications for marine food-web functioning and the biological sequestration of carbon in the ocean.

Authors:
Barbara Bayer (University of California, Santa Barbara and University of Vienna)
Kelsey McBeain (University of California, Santa Barbara)
Craig A. Carlson (University of California, Santa Barbara)
Alyson E. Santoro (University of California, Santa Barbara)

Enhanced-warming Kuroshio Current experiences rapid seawater acidification and CO2 increase

Posted by mmaheigan

· Thursday, March 30th, 2023

In order to project the future states of the climate and the marine ecosystem it is vital to understand the long-term changes in ocean carbon chemistry driven by anthropogenic influence. A paucity of data make the rates of seawater acidification and partial pressure of CO₂ (pCO₂) rise on ocean margins highly uncertain.

Figure 1. Graphic summary of 9 years of data from the Kuroshio Current time-series: (a) under the influences of only atmospheric CO2 increase, (b) the combined effect of atmospheric CO2 increase, SST increase, and additional DIC supply, (c) annually averaged air-sea CO2 flux decrease, (d) Projected seawater pCO2 increase under SST rise and sustained DIC increase.

A recent study in Marine Pollution Bulletin documented the rapid increase of seawater pCO₂ (3.70±0.57 matm year^-1) and acidification (pH at -0.0033±0.0009 unit year^-1) along Kuroshio in the East China Sea (Figure 1). These findings were based on nine years of time-series data ( 2010-2018) which are now available on the website of Japan Meteorological Agency (JMA). These trends are significantly greater than the expected rates from CO₂air-sea equilibrium and those reported from other oceanic time-series studies. Interestingly, they showed the contribution of each parameter such as sea surface temperature (SST), sea surface salinity (SSS), and normalized dissolved inorganic carbon (nDIC) and total alkalinity (nTA) to the pCO₂ variability. Seawater warming caused rapid rates of pCO₂increase and acidification under sustained DIC increase. The faster pCO₂growth relative to the atmosphere resulted in the CO₂uptake through the air-sea exchange declining by ~50% (~-0.8 to -0.4 mol C m^-2 y^-1) over the study period.

If this trend continues and the atmospheric CO₂increases at its current rate, the rapid warming Kuroshio regions could change from a sink to a source of CO₂ , and cause a loss of oceanic CO₂ uptake in the near future (ca. 2030-2040). Further, other “warming hotspots” in the global ocean along western boundary currents with a continuous DIC supply may exhibit similarly accelerated acidification and pCO₂ rise. This could lead to a significant reduction in ocean CO₂ uptake.

Authors:
Shou-En Tsao (Institute of Oceanography, National Taiwan University, Taiwan)
Po-Yen Shen (Institute of Oceanography, National Taiwan University, Taiwan)
Chun-Mao Tseng^* (Institute of Oceanography, National Taiwan University, Taiwan)

Severe warming = 15% increase in bacterial respiration: Southern Ocean most impacted

Posted by mmaheigan

· Thursday, March 30th, 2023

The utilization, respiration, and remineralization of organic matter exported from the ocean surface to its depths are key processes in the ocean carbon cycle. Marine heterotrophic Bacteria play a critical role in these activities. However, most three-dimensional (3-D) coupled physical-biogeochemical models do not explicitly include Bacteria as a state variable. Instead, they rely on parameterization to account for the bacteria’s impact on particle flux attenuation.

A recent study examined how bacteria respond to climate change by employing a 3-D coupled ocean biogeochemical model that incorporates explicit bacterial dynamics. The model (CMCC-ESM2) is a part of the Coupled Model Intercomparison Project Phase 6. The authors first evaluated the reliability of century-scale forecasts (2015-2099) for bacterial stocks and rates in the upper 100 m layer against the compiled measurements from the contemporary period (1988-2011). Next the authors analyzed the predicted trends in bacterial stocks and rates under diverse climate scenarios and explored their association with regional differences in temperature and organic carbon stocks. Three crucial findings were revealed. There is a global-scale decrease in bacterial biomass of 5-10%, with a 3-5% increase in the Southern Ocean (Figure 1). In the Southern Ocean, the rise in semi-labile dissolved organic carbon (DOC) leads to an increase in DOC uptake rates of free-living bacteria; in the northern high and low latitudes, the increase in temperature drives the increase in their DOC uptake rates. Importantly, extreme warming could result in a global increase (up to 15%) and even higher in the Southern Ocean (21% increase) in bacterial respiration (Figure 1), potentially leading to a decline in the biological carbon pump.

This analysis is an unprecedented and early effort to understand the climate-induced changes in bacterial dynamics on a global scale in a systematic manner. This study takes us one step closer to comprehending how bacteria influence the functioning of the biological carbon pump and the distribution of organic carbon pools between surface and deep layers, especially their response to climate change.

Figure 1. Global projections of bacterial carbon stocks and rates during the baseline period (1990-2013) and their changes as anomalies under the most-severe climate change scenario (i.e., SSP5-8.5) relative to the baseline period (2076-2099). The stocks and rates during the baseline period (a, b, c, g, h, i) and their changes as anomalies under the most-severe climate change scenario (d, e, f, j, k, l). All variables are depth-integrated in the upper 100 m. Solid-line contours as standard deviation from averaging over 1990-2013. Anomalies are 2076-2099 average values relative to 1990-2013 average values. Global bacterial biomass has decreased by 5-10%, with a 3-5% increase in the Southern Ocean. However, extreme warming may increase bacterial respiration worldwide, thereby reducing the efficiency of the biological carbon pump. This study provides an early attempt to understand the response of bacteria to climate change and their impact on the distribution of organic carbon in the ocean.

Author
Heather Kim, Woods Hole Oceanographic Institution

Applications open for OCB Working Group on Marine Carbon Dioxide Removal (mCDR)

Posted by mmaheigan

· Friday, March 10th, 2023

As discussed in the January 2023 mCDR webinar (view recording at https://youtu.be/MxtshBFFV_8), a key outcome of the OCB mCDR workshop in Sept. 2022 will be a topical working group. Working Group members will facilitate the connection of scientists with industry representatives, entrepreneurs, foundations, nonprofits and other scientists across disciplines and career stages through the establishment ofregional node mCDR activities around the US. WG members will serve as regional team leaders who will plan and convene regional stakeholder meetings to initiate information exchange, community building, and collaboration (learn more here). We emphasize that the planning and implementation of the nodes will be open-ended, collaborative, and iterative, allowing regional nodes to learn from each other but also tailor their needs to their specific groups. We are seeking a range of expertise, career stage, and sector representation in the WG membership. We anticipate a duration of ~2 years for this WG. If you are interested in applying to serve on this Working Group, please APPLY HERE by April 14. The lead organizers will review the applications and inform applicants by the end of April.

Webinar & Benthic Ecosystem and Carbon Synthesis Working Group

Posted by mmaheigan

· Monday, March 6th, 2023

First webinar March 14, 11am EST:

Presentation by Cristina Schultz and Jessica Luo introducing the BECS working group in the context of past OCB efforts
Talk by Jack Middelburg, Professor of Geosciences at Utrecht University, The Netherlands.

Dr. Middelburg is a Professor of General Geochemistry in the Department of Earth Sciences at Utrecht University. He is also the current Director of Research for Earth Sciences. He is internationally recognised and awarded as a leading researcher in the aquatic sciences. Among other distinctions, he received the ASLO Hutchinson Award and the Vladimir Ivanovich Vernadsky Medal by the EGU in honor of his outstanding scientific contributions. He is a member of the Royal Netherlands Academy of Arts and Sciences KNAW and was recently elected a fellow of the American Geophysical Union.

Dr. Middelburg is an international leader on ocean biogeochemical cycles, particularly sedimentary inorganic cycles and benthic ecosystems. He has agreed to give the inaugural webinar of the BECS working group to provide a synthesis overview of benthic biogeochemical cycles and ecosystems.

Learn more about the Benthic Ecosystem and Carbon Synthesis Working Group

Apply to new OCB Operational Phytoplankton Observations Working Group

Posted by mmaheigan

· Monday, March 6th, 2023

Participate in a working group to develop standards and best practices for the collection and assessment of Operational Phytoplankton Observations (OPO) using particle imaging instruments (PII). As PII technology has matured in recent years, it is becoming a more routine sampling component of ocean observing programs and networks (e.g., Bio-GO-SHIP). We are looking to gather a broad range of subject matter experts that include phytoplankton image data producers, image and data analysts, and data users to form the core membership of the OPO Working Group.

The goal of this activity is to develop a set of standards and best practices for both the collection and downstream processing of phytoplankton images produced by PIIs. These best practices will result in consistent, quantitative observations of phytoplankton taxonomy and biomass.

The OPO Working Group will identify challenges associated with quantitative sampling of phytoplankton due to:

1) Different oceanic provinces and biomass levels (e.g., coastal, open ocean)

2) Aquatic sampling techniques (e.g., bottle, underway), profiling or towed technologies, ocean observatories (moorings)

3) Operational differences between current phytoplankton imaging instruments (PIIs) and analysis tools.

The OPO Working Group will develop recommendations for specific instruments and sampling techniques to ensure that phytoplankton measurements are consistent, robust, and quantitative. These guidelines will be published as a peer-reviewed paper for distribution to the broader community, and our goal will be to seek endorsement from the Global Ocean Observing System (GOOS) for the best practices recommendations that emerge from this activity. Additionally, the best practices recommendations will be archived as a document in the Ocean Best Practices System repository.

We will convene two in-person working group meetings August 2-4, 2023, and early 2024, along with asynchronous online activities in preparation for the in-person meetings. OPO Working Group members will also participate in regular synchronous virtual meetings occurring between the in-person meetings. Our intention is to create a working group that is inclusive of participants from all backgrounds and a range of career stages.

More detailed information about planned working group activities and the application form to participate in the working group are now available here. Apply by March 27th, 2023.

Application form can be accessed here.

For those who are interested in this activity and its outcomes but who are not able to commit the time to participate in this working group, we will continue to provide updates to the full community about working group progress and products, including at the in-person meeting associated with the 2024 Ocean Science meeting, and the 2024 OCB summer workshop.

Learn more

Small particles contribute significantly to the biological carbon pump in the subpolar North Atlantic

Posted by mmaheigan

· Monday, February 13th, 2023

The ocean’s biological carbon pump (BCP) is a collection of processes that transport organic carbon from the surface to the deep ocean where the carbon is sequestered for decades to millennia. Variations in the strength of the BCP can substantially change atmospheric CO₂ levels and affect the global climate. It is important to accurately estimate this carbon flux, but direct measurement is difficult so this remains a challenge.

Figure 1. (a) A schematic illustrating the downward transport of small and large POC into the deep ocean and the subsequent remineralization and fragmentation which breaks large POC into small POC. (b) Trajectories of BGC-Argo float segments. (c) Relative contributions to the annually averaged vertical carbon flux show the dominant role of gravitational sinking flux of large POC as well as the significant contributions from small POC at 100 m due to different mechanisms and at 600 m due to fragmentation.

A recent paper published in Limnology and Oceanography performed a novel mass budget analysis using observations of dissolved oxygen and particulate organic carbon (POC) from BGC-Argo floats in the subpolar North Atlantic. The authors assessed relative importance of different mechanisms contributing to the BCP and related processes, the sinking velocity and remineralization rate of different particle size classes as well as the rate of fragmentation which breaks large particles into smaller ones. Results suggest that on annual timescales, the gravitational settling of large POC is the dominant mechanism. Small POC supplements the vertical carbon flux at 100 m significantly, through various mechanisms, and contributes to carbon sequestration below 600 m due to fragmentation of large POC. In addition, sensitivity experiments highlight the importance of considering remineralization and fragmentation when estimating the vertical carbon flux of small POC.

This novel method provides additional independent constraints on current estimates and improves our mechanistic understanding of the BCP. In addition, it demonstrates the great potential of BGC-Argo float data for studying the biological carbon pump.

Authors:
Bin Wang (Dalhousie University)
Katja Fennel (Dalhousie University)

An expanding understanding of Southern Ocean productivity and export

Posted by mmaheigan

· Monday, February 13th, 2023

Biology in the Southern Ocean is known to help regulate Earth’s climate by capturing and eventually sequestering carbon from its surface. Unfortunately, accurate estimates of the magnitude of the Southern Ocean (SO) biological carbon sink are limited and subject to ongoing debate. However, a recently published study used the expanding Southern Ocean BGC-Argo fleet to provide new estimates of SO Annual Net Community Production (ANCP) and export production.

Over long enough time and space scales (>1000 km and seasons), ANCP is equal to the amount of carbon fixed during photosynthesis that is not remineralized in the surface layer. What remains is available to be exported to depth. As this organic matter sinks out of the surface ocean, most of it is eventually remineralized by bacteria, leaving behind a signature of depleted oxygen. With enough floats, basin-scale ANCP can be estimated from the seasonal oxygen drawdown measured across their profiles. While similar studies have been carried out on single floats, here, the authors construct a composite of all available profiles and include a greater depth range than previously considered.

Figure 1. All available BGC-ARGO float profiles (25,512) were used to create an A) ensemble seasonal cycle in surface chlorophyll and sub-surface oxygen. B) Annual Net Community Production (ANCP) was then estimated by computing the depth-integrated oxygen depletion during the productive period. C) ANCP was estimated across 12 major regions, separated by the Indian, Pacific and Atlantic basins and Subantarctic (SAZ), Polar (PFZ), Antarctic (AZ), and Southern (S) frontal zones. Each region used 100s-1000s of individual float profiles (color-coded scatter points).

Results from this novel approach estimate SO ANCP (and ~export) at 3.89 GT C year^-1, with basin-scale regional estimates as much as a factor 2.8 larger than previous studies. Moreover, nearly 30% of remineralization was measured at depths not typically considered, with 14% below 500 m and another 15% immediately below the euphotic depth but above 100 m. These values suggest a more critical role for the Southern Ocean in regulating oceanic carbon storage, atmospheric CO₂ exchange, and climate than previously thought.

Authors:
Jiaoyang Su (University of Tasmania, Australia)
Christina Schallenberg (University of Tasmania, and Australian Antarctic Program Partnership)
Tyler Rohr (Australian Antarctic Program Partnership)
Peter G. Strutton (University of Tasmania, Australia)
Helen E. Phillips (University of Tasmania, and Australian Antarctic Program Partnership)

NASA Sponsored Workshop on Calibration and Validation of Ocean Color Remote Sensing – Apply by March 15

Posted by mmaheigan

· Thursday, February 9th, 2023

NASA Sponsored Workshop on Calibration and Validation of Ocean Color Remote Sensing

June 12 – July 7, 2023
Bowdoin College, Schiller Coastal Studies Center (SCSC), Orr’s Island, Maine

An intensive four-week, cross-disciplinary, graduate-level workshop in optical oceanography will be offered at Bowdoin College’s SCSC. This workshop is the latest version of the optical oceanography course first offered at the Friday Harbor Laboratories in 1985, then starting in 2001 at the Darling Marine Center, and since 2021 at the SCSC. Past graduates include many of today’s leaders in oceanography.

The major theme of the workshop 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, 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, the University of Maine and Bowdoin College, 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; optical approaches to ocean biogeochemistry; computation and propagation of measurement uncertainties.

• laboratory sessions for hands-on work with optical instrumentation and training in 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, and

• collaborative student projects.

See:
http://misclab.umeoce.maine.edu/OceanOpticsClass2021/
http://misclab.umeoce.maine.edu/OceanOpticsClass2019/
http://misclab.umeoce.maine.edu/OceanOpticsClass2017/
for previous class content and activities.

Instructors: Emmanuel Boss and Collin Roesler (coordinators), Ivona Cetinić, Meg Estapa, Andrew Barnard, Kelsey Bisson and Jeremy Werdell with Charlotte Begouen Demeaux and Patrick Gray as the teaching assistants and guest lectures by Optics Class alumni.

Dates: June 12-July 7, 2023 (arrive June 11, depart July 8th)

Costs: Room and board, as well as graduate course credits for interested students through the University of Maine will be covered through a grant for qualified participants. OCB will provide travel support for US-based participants.

Application Deadline: March 15th, 2023

Notification by: April 15, 2023

To apply: Submit the following in pdf format to opticaloceanography@maine.edu: (1) a recent transcript, (2) a current CV (two-page maximum), (3) a letter from your advisor (or supervisor), and (4) a one-page statement of how you anticipate that this course will contribute to your professional development

We are committed to bringing a cohort of students together whose background, experiences, and training result in diversity of interest, ideas, and skills from which everyone benefits.

2023 Open Call for Shipboard Fellowships

Posted by mmaheigan

· Thursday, February 9th, 2023

We are pleased to announce the 2023 Open Call for Shipboard training. On its 5th edition, this annual programme offers a number of shipboard fellowship opportunities onboard research vessels throughout the year.
Normally, specific calls are made a minimum of six months before the cruise begins, in order to allow time for large numbers of applications to be reviewed, shortlisted candidates to be interviewed, and for the the successful applicant to put the necessary paperwork in order, eg visas, travel documents, and essential medical/training certifications.

However, sometimes the POGO shipboard training programme is offered an available berth at shorter notice.

In order to make best use of these opportunities, the POGO Secretariat is issuing an Open Call for applications from early career scientists, technicians, postgraduate students (PhD or MSc) and Post-doctoral Fellows involved in oceanographic work at centres in developing countries and countries with economies in transition.

The application form asks about the candidate’s background and specific training interests, including geographical areas and research/training topics. It also asks about availability to travel during 2023. The secretariat will maintain a database of all qualified, interested candidates and, as training opportunities become available, will create shortlists by evalulating suitability for the particular project on offer.

For further information on the Open Call, and to apply, visit http://www.oceantrainingpartnership.org/opencall2023

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.

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