mmaheigan :: Ocean Carbon & Biogeochemistry

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

Author Archive for mmaheigan

Sea ice loss and the changing Arctic carbon cycle

Posted by mmaheigan

· Friday, September 18th, 2020

Loss of Arctic Ocean ice cover is altering the carbon cycle in ways that are not well understood. Effectively “popping the top off” the Arctic Ocean, ice loss exposes the sea surface to warming and exchange of CO₂ with the atmosphere. These processes are expected to increase CO₂ levels in the Arctic Ocean, changing its contribution to the global carbon cycle, but limited data collection in the region has thus far precluded the establishment of a clear relationship between CO₂ and ice cover. In a recent study published in Geophysical Research Letters, authors report on observed partial pressure of CO₂ (pCO₂) trends from several years of data collection in the surface waters of the Canada Basin of the Arctic Ocean. These data show that the pCO₂ is higher during years when ice cover is low. Uptake of atmospheric CO₂ and heating are the primary sources of the CO₂ increase, with only a small counteracting offset from biological production. These processes vary significantly from year to year, masking the likely increase in pCO₂ over time. Based on these results, we can expect that, while the Arctic Ocean has thus far been a significant sink for atmospheric CO₂, if ice loss continues the uptake of CO₂ will diminish in coming years.

Figure caption: Sea surface pCO₂ increases with decreasing ice concentration (left), determined using the mean of spatially gridded data. The sea surface pCO₂ data were collected on five research cruises on the Canadian icebreaker, CCGS Louis S. St-Laurent, from 2012 to 2017 (shown at right for 2017). The pCO₂ levels are indicated by the color along the ship cruise track (right color bar). The dark shading (left color bar) represents sea ice concentration averaged from the daily satellite data collected during the cruise.

Authors:
Michael DeGrandpre (University of Montana-Missoula)
Wiley Evans (Hakai Institute)
Mary-Louise Timmermans (Yale University)
Richard Krishfield (Woods Hole Oceanographic Institution)
Bill Williams (Institute of Ocean Sciences)
Michael Steele (University of Washington)

Estuarine sediment resuspension drives non-local impacts on Biogeochemistry

Posted by mmaheigan

· Friday, September 18th, 2020

Sediment processes, including resuspension and transport, affect water quality in estuaries by altering light attenuation, primary productivity, and organic matter remineralization, which then influence oxygen and nitrogen dynamics. In a recent paper published in Estuaries and Coasts, the authors quantified the degree to which sediment resuspension and transport affected estuarine biogeochemistry by implementing a coupled hydrodynamic-sediment transport-biogeochemical model of the Chesapeake Bay. By comparing summertime model runs that either included or neglected seabed resuspension, the study revealed that resuspension increased light attenuation, especially in the northernmost portion of the Bay, which subsequently shifted primary production downstream (Figure 1). Resuspension also increased remineralization in the central Bay, which experienced higher organic matter concentrations due to the downstream shift in primary productivity. When combined with estuarine circulation, these resuspension-induced shifts caused oxygen to increase and ammonium to increase throughout the Bay in the bottom portion of the water column. Averaged over the channel, resuspension decreased oxygen by ~25% and increased ammonium by ~50% for the bottom water column. Changes due to resuspension were of the same order of magnitude as, and generally exceeded, short-term variations within individual summers, as well as interannual variability between wet and dry years. This work highlights the importance of a localized process like sediment resuspension and its capacity to drive biogeochemical variations on larger spatial scales. Documenting the spatiotemporal footprint of these processes is critical for understanding and predicting the response of estuarine and coastal systems to environmental changes, and for informing management efforts.

Figure 1: Schematic of how resuspension affects biogeochemical processes based on HydroBioSed model estimates for Chesapeake Bay.

Authors:
Julia M. Moriarty (University of Colorado Boulder)
Marjorie A. M. Friedrichs (Virginia Institute of Marine Science)
Courtney K. Harris (Virginia Institute of Marine Science)

OCB Webinar Series

Posted by mmaheigan

· Friday, September 4th, 2020

OCB is extending the series - now accepting new titles and abstracts. Click to submit

For each webinar, REGISTER to receive connection details via email from Webex.

Format: A brief introduction, then two 20 minute presentations followed by a moderated Q&A. We will record and share via our YouTube channel and below to accommodate those who cannot participate in real time.

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

The biweekly OCB summer webinar series spans diverse science across OCB’s current research priorities. Thank you to all of our speakers this summer!

Upcoming

Recent Webinars

DATE	THEME	SPEAKER(S)	TITLE(S)	SESSION CHAIR(S)
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)	Ecological feedbacks to the ocean organic carbon cycle: Fishing and climate change

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

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

August 11 recording coming soon!

Watch online now

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	Palter, Friedrichs
		Natalie Freeman (University of Colorado Boulder)	On the recent increase in surface silicate-to-nitrate availability in the southern Drake Passage

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

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

The role of nutrient trapping in promoting shelf hypoxia in the southern Benguela upwelling system

Posted by mmaheigan

· Thursday, September 3rd, 2020

The southern Benguela upwelling system (SBUS) off southwest Africa is an exceptionally fertile ocean region that supports valuable commercial fisheries. The productivity of this system derives from the upwelling of nutrient-rich Subantarctic Mode Water, and from the concurrent entrainment of nutrients regenerated proximately on the expansive continental shelf. The SBUS is prone to severe seasonal hypoxic events that decimate regional fisheries, occurrences of which are inextricably linked to the inherent nutrient dynamics. In a study recently published in JGR Oceans, the authors sought to understand the mechanisms sustaining elevated concentrations and seasonally-variable distributions of nutrients in the SBUS, in relation to the subsurface oxygen content. Inter-seasonal measurements of nutrients and nitrate isotope ratios across the SBUS in 2017 revealed that upwards of 48% (summer) and 63% (winter) of the on‐shelf nutrients derived from regeneration in situ. The severity of hypoxia at the shelf bottom, in turn, correlated with the incidence of regenerated nutrients. The accrual of nutrients at the shelf bottom appears to be aided by hydrographic fronts that restrict offshore transport, trapping regenerated nutrients on the SBUS shelf and increasing the pool of nutrients available for upwelling – ultimately contributing to hypoxic events. This study underscores the need – if we are to develop a mechanistic and predictive understanding of hypoxia in the SBUS and elsewhere – to elucidate the role of shelf circulation in promoting the accrual of regenerated nutrients on the continental shelf. The next step is to combine new and existing observations with quantitative simulations to further interrogate the coupled physical-biogeochemical mechanisms that modulate the intensity of hypoxia.

Figure caption: Schematic of proposed nutrient-trapping mechanism: Deep nutrient-rich Subantarctic Mode Water (SAMW) acquires more nutrients as it passes over the shelf sediments from the regeneration of exported particulate organic material (POM). The production of this POM is fueled by nutrients stripped from the surface waters advecting back off-shore. The thickness of the arrows represents nutrient concentrations. Triangles indicate the positions of the Shelf Break Front (SBF) and Columbine Front (CF), coincident with an observed subduction of the Ekman layer and downwelling at the inner front boundary.

Authors
Raquel Flynn (University of Cape Town)
Julie Granger (University of Connecticut)
Jennifer Veitch (South African Environmental Observation Network)
Samantha Siedlecki (University of Connecticut)
Jessica Burger (University of Cape Town)
Keshnee Pillay (South Africa Department of Environment, Forestry and Fisheries)
Sarah Fawcett (University of Cape Town)

Profiling floats reveal fate of Southern Ocean phytoplankton stocks

Posted by mmaheigan

· Tuesday, September 1st, 2020

More observations are needed to constrain the relative roles of physical (advection), biogeochemical (downward export), and ecological (grazing and biological losses) processes in driving the fate of phytoplankton blooms in Southern Ocean waters. In a recent paper published in Nature Communications, authors used seven Biogeochemical Argo (BGC-Argo) floats that vertically profiled the upper ocean every ten days as they drifted for three years across the remote Sea Ice Zone of the Southern Ocean. Using the floats’ biogeochemical sensors (chlorophyll, nitrate, and backscattering) and regional ratios of nitrate consumption:chlorophyll synthesis, the authors developed a new approach to remotely estimate the fate of the phytoplankton stocks, enabling calculations of herbivory and of downward carbon export. The study revealed that the major fate of phytoplankton biomass in this region is grazing, which consumes ~90% of stocks. The remaining 10% is exported to depth. This pattern was consistent throughout the entire sea ice zone where the floats drifted, from 60°-69° South.

Figure Caption: Southern Ocean Chlorophyll a climatology and floats’ trajectories (top panel). Total losses of Chlorophyll a (including grazing and phytodetritus export, left panel). Phytodetritus export (right panel).

This study region comprises two of the three major krill growth and development areas—the eastern Weddell and King Haakon VII Seas and Prydz Bay and the Kerguelen Plateau—so the observed grazing was probably due to Antarctic krill, underscoring their pivotal importance in this ecosystem. Building upon the greater understanding of ocean ecosystems via satellite ocean colour development in the 1990s, BGC-Argo floats and this new approach will allow remote monitoring of the different fates of phytoplankton stocks and insights into the status of the ecosystem.

Authors:
Sebastien Moreau (Norwegian Polar Institute, Tromsø, Norway)
Philip Boyd (Institute for Marine and Antarctic Studies, Hobart, Australia)
Peter Strutton (Institute for Marine and Antarctic Studies, Hobart, Australia)

ROSES-20 Amendment 49: Carbon Cycle Science Final Text and Due Dates Released

Posted by mmaheigan

· Wednesday, August 26th, 2020

ROSES-2020 Program Element A.5 Carbon Cycle Science solicits proposals for research focused on carbon stocks and fluxes between and within freshwater, marine systems, and land ecosystems, and their exchange with the atmosphere. It also targets improving understanding of carbon cycle processes and feedbacks in critical ecosystems that are particularly vulnerable to environmental change. Substantive use of remote sensing and/or airborne data is required in all studies.

The research topics of interest for this program element are divided into two sub-elements, which are further divided into five research topics:

3.1: Carbon Fluxes between and within Land, Freshwater, and Marine Systems

3.1.1. The Land-Ocean Continuum

3.1.2. Carbon Cycle of Critical Ecosystems: Vulnerability of Tropical Forests

3.1.3. Fluxes and Biogeochemistry of Carbon within Oceans

3.2: Carbon Fluxes between Ecosystems and the Atmosphere

3.2.1. Carbon Fluxes between Terrestrial Ecosystems and the Atmosphere

3.2.2. Carbon Fluxes between Oceans and the Atmosphere

ROSES-2020 Amendment 49 releases final text for A.5 Carbon Cycle Science. Notices of intent are requested by September 28, 2020 and the due date for proposals is December 3, 2020.

On or about August 26, 2020, this Amendment to the NASA Research Announcement “Research Opportunities in Space and Earth Sciences (ROSES) 2020” (NNH20ZDA001N) will be posted on the NASA research opportunity homepage at http://solicitation.nasaprs.com/ROSES2020 and will appear on SARA’s ROSES blog at:https://science.nasa.gov/researchers/sara/grant-solicitations/roses-2020/.

Questions concerning A.5 Carbon Cycle Science may be directed Laura Lorenzoni, who may be reached at Laura.Lorenzoni@nasa.gov.

A close-up view of biomass controls in Southern Ocean eddies

Posted by mmaheigan

· Thursday, August 20th, 2020

Southern Ocean biological productivity is instrumental in regulating the global carbon cycle. Previous correlative studies associated widespread mesoscale activity with anomalous chlorophyll levels. However, eddies simultaneously modify both the physical and biogeochemical environments via several competing pathways, making it difficult to discern which mechanisms are responsible for the observed biological anomalies within them. Two recently published papers track Southern Ocean eddies in a global, eddy-resolving, 3-D ocean simulation. By closely examining eddy-induced perturbations to phytoplankton populations, the authors are able to explicitly link eddies to co-located biological anomalies through an underlying mechanistic framework.

Figure caption: Simulated Southern Ocean eddies modify phytoplankton division rates in different directions of depending on the polarity of the eddy and background seasonal conditions. During summer anticyclones (top right panel) deliver extra iron from depth via eddy-induced Ekman pumping and fuel faster phytoplankton division rates. During winter (bottom right panel) the extra iron supply is eclipsed by deeper mixed layer depths and elevated light limitation resulting in slower division rates. The opposite occurs in cyclones.

In the first paper, the authors observe that eddies primarily affect phytoplankton division rates by modifying the supply of iron via eddy-induced Ekman pumping. This results in elevated iron and faster phytoplankton division rates in anticyclones throughout most of the year. However, during deep mixing winter periods, exacerbated light stress driven by anomalously deep mixing in anticyclones can dominate elevated iron and drive division rates down. The opposite response occurs in cyclones.

The second paper tracks how eddy-modified division rates combine with eddy-modified loss rates and physical transport to produce anomalous biomass accumulation. The biomass anomaly is highly variable, but can exhibit an intense seasonal cycle, in which cyclones and anticyclones consistently modify biomass in different directions. This cycle is most apparent in the South Pacific sector of the Antarctic Circumpolar Current, a deep mixing region where the largest biomass anomalies are driven by biological mechanisms rather than lateral transport mechanisms such as eddy stirring or propagation.

It is important to remember that the correlation between chlorophyll and eddy activity observable from space can result from a variety of physical and biological mechanisms. Understanding the nuances of how these mechanisms change regionally and seasonally is integral in both scaling up local observations and parameterizing coarser, non-eddy resolving general circulation models with embedded biogeochemistry.

Authors:
Tyler Rohr (Australian Antarctic Partnership Program, previously at MIT/WHOI)
Cheryl Harrison (University of Texas Rio Grande Valley)
Matthew Long (National Center for Atmospheric Research)
Peter Gaube (University of Washington)
Scott Doney (University of Virginia)

Multiyear predictions of ocean acidification in the California Current System

Posted by mmaheigan

· Thursday, August 20th, 2020

The California Current System is a highly productive coastal upwelling region that supports commercial fisheries valued at $6 billion/year. These fisheries are supported by upwelled waters, which are rich in nutrients and serve as a natural fertilizer for phytoplankton. Due to remineralization of organic matter at depth, these upwelled waters also contain large amounts of dissolved inorganic carbon, causing local conditions to be more acidic than the open ocean. This natural acidity, compounded by the dissolution of anthropogenic CO₂ into coastal waters, creates corrosive conditions for shell-forming organisms, including commercial fishery species.

A recent study in Nature Communications showcases the potential for climate models to skillfully predict variations in surface pH—thus ocean acidification—in the California Current System. The authors evaluate retrospective predictions of ocean acidity made by a global Earth System Model set up similarly to a weather forecasting system. The forecasting system can already predict variations in observed surface pH fourteen months in advance, but has the potential to predict surface pH up to five years in advance with better initializations of dissolved inorganic carbon (Figure 1). Skillful predictions are mostly driven by the model’s initialization and subsequent transport of dissolved inorganic carbon throughout the North Pacific basin.

Figure 1. Forecast of annual surface pH anomalies in the California Current Large Marine Ecosystem for 2020. Red colors denote anomalously basic conditions for the given location and blue colors indicate anomalously acidic conditions.

These results demonstrate, for the first time, the feasibility of using climate models to make multiyear predictions of surface pH in the California Current. Output from this global prediction system could serve as boundary conditions for high-resolution models of the California Current to improve prediction time scale and ultimately help inform management decisions for vulnerable and valuable shellfisheries.

Authors:
Riley X. Brady (University of Colorado Boulder)
Nicole S. Lovenduski (University of Colorado Boulder)
Stephen G. Yeager (National Center for Atmospheric Research)
Matthew C. Long (National Center for Atmospheric Research)
Keith Lindsay (National Center for Atmospheric Research)

2021 OCB Activity Solicitation

Posted by mmaheigan

· Friday, August 14th, 2020

The Ocean Carbon and Biogeochemistry (OCB) Program is soliciting proposals for OCB activities that will take place or begin during the 2021 calendar year. Due to the COVID-19 pandemic, activities that can be conducted remotely (at least for the first half of 2021) are encouraged. Any proposed in-person activities should include contingency plans in case delays or cancellations are necessary. We seek proposals for OCB-relevant workshops and activities as follows:

Scoping workshops (~50-70 people) that bring together an appropriate body of expertise to foster discussions and build momentum within a specific OCB research area (previous OCB scoping workshops)

Working groups (~8-12 members) to address targeted science goals/questions and develop products that benefit and engage the broader OCB community

Synthesis activities to bring together existing data sets, model outputs, etc. to support and inform future research efforts

Intercomparison activities to assess and build consensus on best practices (methodological, modeling, data analysis, etc.) for advancing OCB-relevant research

Training activities (~30-50 participants plus instructors as needed) to build capacity in different areas of OCB research

To get familiar with OCB’s current slate of activities, PIs are strongly encouraged to view the OCB website before preparing and submitting a proposal. If you have questions about the relevance, timeliness, appropriate format, etc. of a proposed activity, please contact the OCB Project Office for guidance, especially PIs who are less familiar with and/or haven’t been involved with OCB and its activities in the past.

We strongly encourage PIs to read OCB’s OCB’s Code of Conduct and Pledge to Implement Antiracism in OCB activities and decision-making. Be mindful and explicit about how you will foster inclusivity in your proposed activity.

READ OCB PROPOSAL GUIDELINES

Register for the first PACE Applications workshop

Posted by mmaheigan

· Tuesday, August 11th, 2020

Dear Science and Applications Team,

Registration for the first PACE Applications workshop is now open! The 2-day virtual workshop scheduled for September 23 & 24, will showcase future uses of PACE satellite data and products to support decision-making for water resource management, air quality and health monitoring, climate modeling, disasters response and mitigation, and ecological forecasting. The workshop will encourage open collaboration engaging stakeholders, PACE Early Adopters, and scientists/researchers across disciplines and organizations, including universities, government agencies, and commercial, non-profit, and private sectors.

This workshop is open to all participants. Registration (free) is required. Sign up here.

As a member of the PACE SAT we encourage you and your co-PIs to participate in the workshop. Your insight and participation are valuable to the success of the PACE Applications Program. Further, to grow the PACE community of practice and potential, we would appreciate it if you could help spread the word and promote the event to your data users, community, and colleagues.

Workshop Highlights:

Keynote presentations by Dr. Blake Schaeffer (US EPA), Dr. Stephanie Schollaert Uz (NASA), and Dr. Karl Bates (Duke University)
Live plenary panel sessions and informal Q&As with industry professionals, PACE Early Adopter Members, and PACE Scientists & Researchers
A library of PACE resources and presentations from the PACE Research Community
Breakout discussion groups targeting Stakeholder Engagement, Applied Research Needs, and PACE Science Focus Areas
Networking opportunities and community-building sessions

We look forward to seeing you in September!

Regards,
Erin & Joel

—

Erin Urquhart, PhD
PACE Project Applications Coordinator
Ocean Ecology Lab at NASA Goddard Space Flight Center/SSAI
Contact: erin.urquhart.jephson@nasa.gov
Web: https://science.gsfc.nasa.gov/sed/bio/erin.u.jephson

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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