mmaheigan :: Ocean Carbon & Biogeochemistry

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

Author Archive for mmaheigan

OceanHackWeek 2020

Posted by mmaheigan

· Wednesday, July 1st, 2020

OceanHackWeek is a small hands-on, interactive virtual workshop focused on data science and oceanography that will be held during August 10-14, 2020. Join us for five days of tutorials, data exploration, software development and community networking!

Please visit our website https://oceanhackweek.github.io/ for details.

To apply, see https://oceanhackweek.github.io/applicant-info.html

Application deadline: July 13, 2020. We expect to accommodate approximately 50 participants. Accepted applicants will be notified no later than July 22, 2020.
We look forward to seeing you online!

OCB Kicks Off Summer Webinar Series

Posted by mmaheigan

· Wednesday, June 24th, 2020

Join us on Tuesday, July 14 at 2-3 pm EDT (GMT-04:00) to hear our next speakers in summer webinar series: Joan Llort (Barcelona Supercomputing Centre) - The four dimensions of the biological carbon pump; and Hilary Palevsky (Boston College, Department of Earth and Environmental Sciences) - The influence of winter ventilation on the ocean’s biological carbon pump.

After a brief introduction, the ~25 minute presentations and a moderated Q&A session will follow. We will record and share via our YouTube channel and below to accommodate those who cannot participate in real time.

Please REGISTER ahead of time, then you will receive connection details via email from Webex.

Use the Twitter hashtag #OCBwebinar to join and follow the discussion.

The biweekly OCB summer webinar series will span diverse science across OCB’s current research priorities. We received numerous high-quality abstracts and look forward to a stimulating OCB webinar series this summer!

Watch online now

DATE

THEME

SPEAKER(S)

TITLE(S)

SESSION CHAIR(S)

30-Jun

Space-based ocean measurements

Jeremy Werdell (NASA)

Socially distant by design: How the evolution of ocean color remote sensing contributes to aquatic biological and biogeochemical studies (NASA PACE)

Benway

Upcoming

DATE	THEME	SPEAKER(S)	TITLE(S)	SESSION CHAIR(S)

14-Jul	Physical and biogeochemical processes that drive the biological pump	Joan Llort (Barcelona Supercomputing Centre)	The four dimensions of the biological carbon pump	Bushinsky, Fassbender
		Hilary Palevsky (Boston College, Department of Earth and Environmental Sciences)	The influence of winter ventilation on the ocean’s biological carbon pump

28-Jul	Physical drivers of marine biogeochemistry and ecology	Mara Freilich (MIT-WHOI Joint Program)	Phytoplankton community structure in response to meso- and submeso-scale physics (Mediterranean)	Palter, Friedrichs
		Natalie Freeman (University of Colorado Boulder)	On the recent increase in surface silicate-to-nitrate availability in the southern Drake Passage

11-Aug	Advancing understanding of biological feedbacks on ocean biogeochemistry	Emily Zakem (University of Southern California)	Redox-informed models of global biogeochemical cycles	Coles, Maas
		Severine Martini (Mediterranean institute of Oceanography)	Shedding light (literally!) on biological carbon pump

25-Aug	Modeling and machine learning approaches to study climate, carbon, and the ocean	Katarzyna (Kasia) Tokarska (ETH Zürich)	Climate-carbon response: carbon budgets in overshoot scenarios, and in high warming models	Long, Stock
		Christopher Holder (Johns Hopkins University)	Machine Learning and Some Potential Uses in Oceanography

8-Sep	Changes in the ocean's organic carbon cycle	Cristina Romera-Castillo (Instituto de Ciencias del Mar-CSIC)	Net production of dissolved organic carbon in the deep ocean	Rafter, Hood
		Emma Cavan (Imperial College London)	Anthropogenic disturbance of ecological feedbacks to the ocean organic carbon cycle

OCB 2021: NEW DATES

Posted by mmaheigan

· Friday, June 19th, 2020

The OCB 2021 Summer Workshop will be held June 14-17, 2021 in Woods Hole, MA. Dive into past workshops here (including recordings of talks) and stay tuned for session, logistics and other details on our workshop website.

SOCATv2020

Posted by mmaheigan

· Thursday, June 18th, 2020

SOCATv2020 is available now via www.socat.info!

SOCAT version 2020 contains 28.2 million in situ surface ocean fCO2 (fugacity of CO2) measurements for the global ocean and coastal seas with an accuracy < 5 μatm, while a further 2.3 million fCO2 values with an accuracy of 5 to 10 μatm are made available separately. The Surface Ocean CO2 Atlas (www.socat.info) documents the increase in surface ocean CO2 (carbon dioxide), a critical measure as the oceans are taking up one quarter of the global CO2 emissions from human activity. The SOCAT community-led synthesis product is a key step in the value chain based on in situ inorganic carbon measurements of the oceans, which provides policy makers with essential information on ocean CO2 uptake in climate negotiations. The global need for accurate knowledge of ocean CO2 uptake and its variation makes sustained funding for in situ surface ocean CO2 observations imperative. The annual SOCAT release is a Voluntary Commitment for SDG 14.3 (#OceanAction20464) and contributes to the UN Decade of Ocean Science for Sustainable Development.

A massive thank you to everyone who has contributed to the timely, annual release of SOCATv2020!

Physics vs. biology in Southern Ocean nutrient gradients

Posted by mmaheigan

· Tuesday, June 16th, 2020

In the Southern Ocean, surface water silicate (SiO₄) concentrations decline very quickly relative to nitrate concentrations along a northward gradient toward mode water formation regions on the northern edge (Figure 1a, b). These mode waters play a critical role in driving global nutrient concentrations, setting the biogeochemistry of low- and mid-latitude regions around the globe after they upwell further north. To explain this latitudinal surface gradient, most hypotheses have implicated diatoms, which take up and export silicon as well as nitrogen: (1) Diatoms, including highly-silicified species such as Fragilariopsis kerguelensis, are more abundant in the Southern Ocean than elsewhere; (2) Iron limitation, which is prevalent in the Southern Ocean, elevates the Si:N ratio of diatoms; (3) Mass export of empty diatom frustules pumps silicate but not nitrate to deeper waters.

Figure 1: (a) and (b) nitrate and silicate concentrations in surface waters of the Southern Ocean (GLODAPv2_2019 data). (c) Model results of a standard run (black diamonds), a run without biology (red diamonds) and a run without mixing (blue diamonds).

In a recent paper published in Biogeosciences, the authors use an idealized model to explore the relative roles of biological vs. physical processes in driving the observed latitudinal surface nutrient gradients. Over timescales of a few years, removing the effects of biology (no SiO₄uptake or export) from the model elevates silicate concentrations slightly over the entire latitudinal range, but does not remove the strong latitudinal gradient (Figure 1c). However, if the effects of vertical mixing processes such as upwelling and entrainment are removed from the model by eliminating the observed deep [SiO₄] gradient, the observed surface nutrient gradient is greatly altered (Figure 1c). These model results suggest that, over short timescales, physics is more important than biology in driving the observed surface water gradient in SiO₄:NO₃ ratios and forcing silicate depletion of mode waters leaving the Southern Ocean. These findings add to our understanding of Southern Ocean dynamics and the downstream effects on other oceans.

Authors:
P. Demuynck (University of Southampton)
T. Tyrrell (University of Southampton)
A.C. Naveira Garabato (University of Southampton)
C.M. Moore (University of Southampton)
A.P. Martin (National Oceanography Centre)

Arctic rivers as carbon highways

Posted by mmaheigan

· Tuesday, June 16th, 2020

Rapid environmental changes in the Arctic will potentially alter the atmospheric emissions of heat-trapping greenhouse gases such as methane (CH₄) and carbon dioxide (CO₂). A recent study on the Canadian Arctic published in Geophysical Research Letters reveals that spring meltwater delivery drives episodic outgassing events along the lake-river-bay continuum. This spring runoff period is not well-represented in prior studies, which, due to ease of sampling access, have focused more on summertime low-ice conditions. Study authors established a community-based monitoring program in Cambridge Bay and an adjacent inflowing river system in Nunavut, Canada from 2017-2018. These time-series data revealed that at the onset of the melt season river water contains methane concentrations up to 2000 times higher than observed in the bay from late summer through early spring (Figure 1 panel a). In addition, the authors deployed a novel robotic chemical sensing kayak (the ChemYak) in the Bay for five days in 2018 to densely sample water CH₄and CO₂levels in space and time during the spring thaw (Figure 1 panel b). The ChemYak observations revealed that river water containing elevated levels of both of these greenhouse gases flowed into the bay and outgassed to the atmosphere over a period of 5 days! The authors estimate that river inflow during the short melt season drives >95% of all annual methane emissions from the bay. These results demonstrate the need for seasonally-resolved sampling to accurately quantify greenhouse gas emissions from polar systems.

Figure 1: Panel a) Measurements of methane concentration in Cambridge Bay and an adjacent river showed strong seasonality; elevated concentrations were associated with river inflow at the start of the freshet. Panel b) Observations with the ChemYak robotic surface vehicle in Cambridge Bay revealed that excess methane was rapidly ventilated to the atmosphere following ice melt in the bay.

Authors
Cara Manning (University of British Columbia)
Victoria Preston (Woods Hole Oceanographic Institution and Massachusetts Institute of Technology)
Samantha Jones (University of Calgary)
Anna Michel (Woods Hole Oceanographic Institution)
David Nicholson (Woods Hole Oceanographic Institution)
Patrick Duke (University of Calgary and University of Victoria)
Mohamed Ahmed (University of Calgary)
Kevin Manganini (Woods Hole Oceanographic Institution)
Brent Else (University of Calgary)
Philippe Tortell (University of British Columbia)

A quest for change

Posted by mmaheigan

· Friday, June 5th, 2020

“The only way we can change the geoscience culture is by a massive shift in individual mindsets, with the aim of moving the field from passively non-racist to actively anti-racist.” – Kuheli Dutt (2019) – Nature Geoscience

“Racism, injustice and police brutality are awful on their own, but are additionally pernicious because of the brain power and creative hours they steal from us.“ - Ayana E. Johnson (2020) – Washington Post

Many people are subjected to racism on a daily basis, enduring everything from minor inconveniences to fatal interactions. This is intolerable. This week many individuals, organizations, and institutions are issuing thoughtful and powerful statements on their intolerance of racism and injustice. They also are committing to proactive measures to promote inclusion, equity, and diversity in their networks.

OCB pledges to implement anti-racism in its decision-making about leadership, community activities, and capacity building. We all need to educate ourselves as individuals, institutions, and networks, to listen to our colleagues, to self-reflect, and to take part in difficult conversations in order to be the change we want to see. OCB leadership is committed to listening, educating, and engaging with our network in anti-racist action, and we welcome your feedback and participation.

Call for a Robust Anti-Racism Plan for The Geosciences

A Methane-Charged Carbon Pump in Shallow Marine Sediments

Posted by mmaheigan

· Wednesday, June 3rd, 2020

Ocean margins are often characterized by the transport of methane, a potent greenhouse gas, entering from the subsurface and moving towards the seafloor. However, a significant portion of subsurface methane is consumed within shallow sediments via microbial driven anaerobic oxidation of methane (AOM). AOM converts the methane carbon to dissolved inorganic carbon (DIC) and reduces the amount of sulfate that diffuses down from the seafloor towards a sediment interval known as the sulfate-methane transition zone (SMTZ). The SMTZ is where the upward flux of methane encounters the downward diffusive sulfate flux (Figure 1). While the mechanisms of methane production and consumption have been extensively studied, the fate of the DIC that is produced in methane-charged sediments is not well constrained.

In a recent study published in Frontiers in Marine Science, authors used existing reports of methane and sulfate flux values to the SMTZ and synthesized a carbon flow model to quantify the DIC cycling in diffusive methane flux sites globally. They report an annual average of 8.7 Tmol (1 Tmol = 10¹² moles) of DIC entering the diffusive methane-charged shallow marine sediments due to sulfate reduction coupled with AOM and organic matter degradation, as well as DIC input from depth (Figure 1). Approximately 75% (average of 6.5 Tmol year^–1) of this DIC pool flows upward toward the water column, making it a potential contributor to oceanic CO₂and ocean acidification. Further, an average of 1.7 Tmol year^–1DIC precipitates as methane-derived authigenic carbonates. This synthesis emphasizes the importance of the SMTZ, not only as a methane sink but also an important biogeochemical front for global DIC cycling.

Figure 1: A simplified representation of DIC cycling at diffusive methane charged settings.

The study highlights that regions characterized by diffusive methane fluxes can contribute significantly to the oceanic inorganic carbon pool and sedimentary carbonate accumulation. DIC outflux from the methane-charged sediments is comparable to ~20% global riverine DIC flux to oceans. Methane-derived authigenic carbonate precipitation is comparable to ~15% of carbonate accumulation on continental shelves and in pelagic sediments, respectively. These pathways must be included in coastal and geologic carbon models.

Authors:
Sajjad Akam (Texas A&M University-Corpus Christi)
Richard Coffin (Texas A&M University-Corpus Christi)
Hussain Abdulla (Texas A&M University-Corpus Christi)
Timothy Lyons (University of California, Riverside)

Global Ocean DOM Data Collection Under Construction

Posted by mmaheigan

· Wednesday, May 27th, 2020

Dennis Hansell and Craig Carlson are compiling DOM data (DOC/TDN) from the global ocean with the intention of making those available to current and future generations of ocean scientists. Please contribute your data.

We are compiling the long line (U.S. GO-SHIP and earlier) DOC/TDN and affiliated hydrographic data into a single collection. Our intention is to make the data more easily accessible to users now and in the future via the ODV and OCADS websites, among others. The GO-SHIP data, while plentiful, do not have the spatial coverage the collection needs, so we are asking others to contribute their important data to cover as much of the ocean system as possible.

Caption: Some of the US GO-SHIP lines on which DOC/TDN were measured, which serve as the foundation for the collection.

While the focus is on DOC/TDN because there are so many more of those data, we have extended the collection to include a few CDOM wavelengths, some composition (DCNS), and 13C/14C isotopes (for both DOC and DIC). But DOC values have to be included in order to submit the other variables. At present, the target is shelf seas and the open ocean since the near shore would be too big a challenge at the start. The focus is on survey work, including repeat occupations. Even isolated profiles will be considered for inclusion. Strictly time-series data such as from BATS and HOT are available elsewhere, so we are not bringing those data into this collection.

Contact Dennis Hansell (dhansell@rsmas.miami.edu) if you wish to discuss adding data to the collection.

New recording: OCB Working Group Mtg: Filling the gaps in observation-based estimates of air–sea carbon fluxes

Posted by mmaheigan

· Friday, May 22nd, 2020

Thank you to everyone who participated! The recordings are now on the OCB YouTube channel.

The first meeting of the OCB Working Group on Filling the gaps in observation-based estimates of air–sea carbon fluxes convened, May 5-6, 2020 via Webex. The first day of the meeting (May 5) was open to everyone and included presentations on the current state of understanding of the global ocean carbon sink. Please visit the working group website to view the meeting agenda.

About this Working Group
This working group was assembled in 2019 to assess critical uncertainties in existing observation-based air-sea carbon fluxes, determine how best to integrate observation-based open-ocean and coastal-ocean CO₂ air–sea fluxes, and quantify uncertainties in the natural (pre-industrial) outgassing of CO₂. These efforts will lead to better constraints on the contemporary ocean carbon sink and its variability. The results of this OCB Working Group will assist the global carbon community in understanding the state of the global carbon cycle so as to contribute to international efforts to address climate change.

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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