carbon cycle :: Ocean Carbon & Biogeochemistry

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

Archive for carbon cycle

Ocean’s heat cycle shows that atmospheric carbon may be headed elsewhere

Posted by hbenway

· Thursday, August 16th, 2018

Studies over the past 25 years have supported the existence of a large net land biosphere CO₂ sink of 0.5–2 PgC yr^-1. Significant uncertainties remain, however, regarding the long-term partitioning between northern, tropical, and southern land sinks, in part connected to the uncertain ocean carbon sink. These uncertainties limit our capacity to predict earth system response to anthropogenic changes and design effective mitigation strategies.

Land sinks from atmospheric inversion (1990-2010 average) with two different ocean/river fluxes: (top) previous ocean inversion-based carbon fluxes; and (bottom) updated pCO2-based air-sea flux with a scaled-up river flux of 0.78 PgC /yr.

In a recent study published in Nature Geoscience, Resplandy et al. (2018) used models and field observations to demonstrate that the world’s oceans transport heat between the northern and southern hemispheres in the same way that carbon is transported. The transport of heat, however, is easier to observe. By tracking this heat, they showed that the Southern Ocean — while still a substantial carbon sink —may not take up as much carbon as previously thought, and that ocean currents might transport 20 to 100% more carbon from the northern to the southern hemisphere. To maintain this additional transport of carbon, they showed that the amount of carbon entering the ocean from rivers may be as much as 70% higher than estimated in previous global carbon budget studies. These changes in the ocean and river carbon transport imply that up to 40% of the world’s atmospheric carbon absorbed by land ecosystems needs to be reallocated from existing estimates.

Authors
L. Resplandy, Princeton University
Ralph Keeling, Scripps Institution of Oceanography/ UCSD
Christian Rödenbeck, Max Planck Institute
Briton Stephens, NCAR
Matthew Long, NCAR
Samar Khatiwala, University of Oxford
Keith Rodgers, Princeton University
Laurent Bopp, ENS Paris
Pieter Tans, NOAA’s ESRL

Marine Snowfall at the Equator

Posted by mmaheigan

· Thursday, July 19th, 2018

The continual flow of organic particles such as dead organisms and fecal material towards the deep sea is called “marine snow,” and it plays an important role in the ocean carbon cycle and climate-related processes. This snowfall is most intense where high primary production can be observed near the surface. This is the case along the equator in the Pacific and Atlantic Oceans. However, it is not well known how particles are distributed at depth and which processes influence this distribution. A recent study published in Nature Geoscience involved the use of high-resolution particle density data using the Underwater Vision Profiler (UVP) from the equatorial Atlantic and Pacific Oceans down to a depth of 5,000 meters, revealing that several previously accepted ideas on the downward flux of particles into the deep sea should be revisited.

Figure 1. The Underwater Vision Profiler (UVP) during a trial in the Kiel Fjord. The UVP provided crucial data for the new study. Photo: Rainer Kiko, GEOMAR

It is typically assumed that the largest particle density can be found close to the surface and that density attenuates continuously with depth. However, high-resolution particle data show that density increases again in the 300-600-meter depth range. The authors attribute this observation to the daily migratory behavior of organisms such as zooplankton that retreat to these depths during the day, contributing to the particle load via defecation and mortality.

Another surprising result is the observation of many small particles below 1,000 meters depth that contribute a large fraction of the bathypelagic particle flux. This observation counters the general assumption, especially in many biogeochemical models, that particle flux at depth comprises fast sinking particles such as fecal pellets. Diminished remineralization rates of small particles or increased disaggregation of larger particles may contribute to the elevated small particle fluxes at this depth.

Figure 2. Zonal current velocity and Particulate Organic Carbon (POC) content across the equatorial Atlantic at 23˚W as observed in November 2012. From left to right: Zonal current velocity, POC content in small particle fraction and POC content in large particle fraction (adapted from Kiko et al. 2017).

This study highlights the importance of coupled biological and physical processes in understanding and quantifying the biological carbon pump. Further work on this important topic can now also be submitted to the new Frontiers in Marine Science research topic “Zooplankton and Nekton: Gatekeepers of the Biological Pump” (https://www.frontiersin.org/research-topics/8114/zooplankton-and-nekton-gatekeepers-of-the-biological-pump; Co-editors R. Kiko, M. Iversen, A. Maas, H. Hauss and D. Bianchi). The research topic welcomes a broad range of contributions, from individual-based process studies, to local and global field observations, to modeling approaches to better characterize the role of zooplankton and nekton for the biological pump.

Authors:
R. Kiko (GEOMAR)
A. Biastoch (GEOMAR)
P. Brandt (GEOMAR, University of Kiel)
S. Cravatte (LEGOS, University of Toulouse)
H. Hauss (GEOMAR)
R. Hummels (GEOMAR)
I. Kriest (GEOMAR)
F. Marin (LEGOS, University of Toulouse)
A. M. P. McDonnell (University of Alaska Fairbanks)
A. Oschlies (GEOMAR)
M. Picheral (Laboratoire d’Océanographie de Villefranche-sur-Mer, Observatoire Océanologique)
F. U. Schwarzkopf (GEOMAR)
A. M. Thurnherr (Lamont-Doherty Earth Observatory,)
L. Stemmann (Sorbonne Universités, Observatoire Océanologique)

Building ocean biogeochemistry observing capacity, one float at a time: An update on the Biogeochemical-Argo Program

Posted by mmaheigan

· Thursday, July 5th, 2018

By Ken Johnson (MBARI)

The Biogeochemical-Argo (BGC-Argo) Program is an international effort to develop a global network of biogeochemical sensors on Argo profiling floats that has emerged from over a decade of community discussion and planning. While there is no formal funding for this global program, it is being implemented via a series of international research projects that harness the unique capabilities provided by BGC profiling floats. The U.S. Ocean Carbon and Biogeochemistry (OCB) Program maintains and supports a U.S. BGC-Argo subcommittee as a focal point for U.S. community input on the implementation of the global biogeochemical float array and associated science program development.

Figure 1. Steve Riser deploying a SOCCOM float from the R/V Palmer

About BGC-Argo Floats
BGC-Argo floats can carry a suite of chemical and bio-optical sensors (Figure 1 – Float Schematic). They have enough energy to make about 250 to 300 vertical profiles from 2000 m to the surface. At a cycle time of 10 days, that corresponds to a lifetime near 7 years. The long endurance allows the floats to resolve seasonal to interannual variations in carbon and nutrient cycling throughout the water column. These time scales are difficult to study from ships and ocean interior processes are hard to resolve from satellites. BGC profiling floats extend the capabilities of these traditional observing systems in significant ways.

Figure 2. Images of Navis and APEX floats used in the SOCCOM program. These floats carry oxygen, nitrate, pH, and bio-optical (chlorophyll fluorescence and backscatter) sensors.

All of the data from profiling floats operating as part of the Argo program must be available in real-time with no restrictions on access. The Argo Global Data Assembly centers in France and the USA both provide complete listings of all BGC profiles (argo_bio-profile_index.txt) and access to the data. Extensive documentation of the data processing protocols is available from the Argo Data Management Team. Individual research programs, such as SOCCOM (see below), may also provide direct data access to the observed data along with value added products such as best estimates of pCO₂ derived from pH sensor data.

Regional Deployments
In 2018, it is projected that 127 profiling floats with biogeochemical sensors are will be deployed, including ~40 floats by U.S. projects. Most of the U.S. deployments (30+) will be carried out by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project (Figure 2 – Float Deployment). These floats will carry oxygen, nitrate, pH, chlorophyll fluorescence, and backscatter sensors. As part of the NOAA Tropical Pacific Observing System (TPOS) program, Steve Riser’s group (Univ. Washington) will deploy 3 BGC-Argo floats per year in the equatorial Pacific over the next 4 years. These floats will be equipped with oxygen, pH, bio-optical sensors and Passive Acoustic Listener (PAL) sensors, which provide wind speed estimates at 15-minute intervals while the floats are parked at 1000 m. Wind speed is derived from the noise spectrum of breaking waves. Steve Emerson (Univ. Washington), with NSF support, is also deploying floats equipped with oxygen, nitrate and pH sensors in the equatorial Pacific. With funding from NSF, Andrea Fassbender (MBARI) will deploy two floats at Ocean Station Papa in the northeast Pacific in collaboration with the EXPORTS program. These floats will also carry oxygen, nitrate, pH, and bio-optical sensors.

Nearly 90 BGC floats will be deployed in 2018 by other nations in multiple ocean basins. Much of this effort will focus on the North Pacific and North Atlantic. The sensor load on these floats is somewhat variable. Some will be deployed with only oxygen sensors or bio-optical sensors for chlorophyll fluorescence and particle abundance. Others will carry the full suite of six sensors (oxygen, nitrate, pH, chlorophyll fluorescence, backscatter, and irradiance) that are outlined in the BGC-Argo Implementation Plan (BGC-Argo, 2016). These floats will contribute to the existing array of 305 biogeochemical floats (Figure 3 BGC Argo Map).

Community Activities
In response to the tremendous interest in the scientific community in the capabilities of profiling floats, OCB is sponsoring a Biogeochemical Float Workshop at the University of Washington in Seattle from July 9-13, 2018 to begin the process of transferring this expertise to the broader oceanographic community, bringing together potential users of this technology to discuss biogeochemical profiling float technology, sensors, and data management and begin the process of the intelligent design of future scientific experiments. The workshop will provide participating scientists direct access to the facilities of the Float Laboratory operated by Riser. This workshop builds on a previous OCB workshop Observing Biogeochemical Cycles at Global Scales with Profiling Floats and Gliders (Johnson et al., 2009). BGC-Argo will also have a prominent presence at the 6th Argo Science Workshop (October 22-24, 2018, Tokyo, Japan) and OceanObs19 (September 16-20, 2019, Honolulu, HI).

Figure 3. May 2018 map of the location of BGC-Argo floats that have reported in the previous month and sensor types on these floats. From jcommops.org.

BGC-Argo Publications
Several resources now highlight the capabilities of profiling floats to accomplish scientific observing goals. A web-based bibliography of biogeochemical float papers hosted on the Biogeochemical-Argo website currently includes >100 publications and continues to grow. A special issue of Journal of Geophysical Research: Oceans focused on the SOCCOM program is in progress with 11 papers now available and a dozen more forthcoming. These papers include summaries of the technical capabilities of floats and the biogeochemical sensors, comparisons of float bio-optical data with satellite remote sensing observations, seasonal and interannual assessments of air-sea oxygen flux, under-ice biogeochemistry, carbon export, comparisons of pCO₂ estimated from floats with pH vs. time-series data, and net community production. The connection of float observations with numerical models is a special focus of the program and this is highlighted in several papers, including a description of the Biogeochemical Southern Ocean State Estimate (SOSE), which is a data assimilating BGC model. Results from Observing System Simulation Experiments (OSSEs) used to assess the number of floats needed for large-scale observations are also reported. The BGC-Argo steering committee is developing a community white paper for the OceanObs19 conference in September 2019. BGC-Argo also develops and distributes a community newsletter.

For more information, visit the BGC-Argo website or reach out to the U.S. BGC-Argo Subcommittee.

Increased temperatures suggest reduced capacity for carbon

Posted by mmaheigan

· Thursday, January 18th, 2018

The ocean’s biological pump works to draw down atmospheric carbon dioxide (CO₂) by exporting carbon from the surface ocean. This process is less efficient at higher temperatures, implying a possible climate feedback. Recent work by Cael et al. provides an explanation of why this feedback occurs and an estimate of its severity.

In a highly simplified view, carbon export depends on the balance between two temperature-dependent processes: 1) The autotrophic production and 2) the heterotrophic respiration of organic carbon. Cael and Follows (Geophysical Research Letters 2016) recently developed a mechanistic model based on established temperature dependencies for photosynthesis and respiration to explore feedbacks between export efficiency and climate. Heterotrophic growth rates increase more so than phototrophic rates with increasing temperature, which suggests that at higher temperatures, community respiration will increase relative to production, thereby decreasing export efficiency. Although simplistic, the model captures the temperature dependence of export efficiency observations.

Figure: Schematic of the mechanism on which the Cael and Follows (2016) model is based. (a) Photosynthesis (dark grey) and respiration (light grey) respond to temperature differently, yielding (b) a decline in export efficiency at higher temperatures.

More recently, Cael, Bisson, and Follows (Limnology and Oceanography 2017) applied this model to sea surface temperature records and estimated a ~1.5% decline in globally-averaged export efficiency over the past three decades of increasing ocean temperatures as a result of this metabolic mechanism. This ~1.5% decline is equivalent to a reduced ocean sequestration of approximately 100 million fewer tons of carbon annually, comparable to the annual carbon emissions of the United Kingdom. The model provides a framework in which to consider the relationship between climate and ocean carbon export that might also elucidate large-scale (e.g., glacial-interglacial) atmospheric CO₂ changes of the past.

Authors:
B. B. Cael (MIT/WHOI)
Kelsey Bisson (UCSB)
Mick Follows (MIT)

Zooplankton play a key and diverse role in the ocean carbon cycle

Posted by mmaheigan

· Thursday, December 7th, 2017

How does the enormous diversity of zooplankton species, life cycles, size, feeding ecology, and physiology affect their role in ocean food webs and cycling of carbon?

In the 2017 issue of Annual Review of Marine Science, Steinberg and Landry review the fundamental and multifaceted roles that zooplankton play in the cycling and export of carbon in the ocean. Carbon flows through marine pelagic ecosystems are complex due to the diversity of zooplankton consumers and the many trophic levels they occupy in the food web–from single-celled herbivores to large carnivorous jellyfish. Zooplankton also contribute to carbon export processes through a variety of mechanisms (mucous feeding webs, fecal pellets, molts, carcasses, and vertical migrations).

Figure 1. Pathways of cycling and export of carbon by zooplankton in the ocean.

Climate change and other stressors are already affecting zooplankton abundance, distribution, and life cycles, and are predicted to result in widespread changes in zooplankton carbon cycling in the future. These changes will affect both the larger marine food web that depends upon zooplankton for food (fish) or recycled products for growth (primary producers) and the amount of carbon exported into the deep sea–where far from contact with the atmosphere it no longer contributes to global warming.

Authors:

Deborah K. Steinberg, Virginia Institute of Marine Science, The College of William and Mary
Michael R. Landry, Scripps Institution of Oceanography

The changing ocean carbon cycle

Posted by mmaheigan

· Thursday, July 6th, 2017

Since preindustrial times, the ocean has removed from the atmosphere 41% of the carbon emitted by human industrial activities (Figure 1). The globally integrated rate of ocean carbon uptake is increasing in response to rising atmospheric CO₂ levels and is expected to continue this trend for the foreseeable future. However, the inherent uncertainties in ocean surface and interior data associated with ocean carbon uptake processes make it difficult to predict future changes in the ocean carbon sink. In a recent paper, McKinley et al. (2017), review the mechanisms of ocean carbon uptake and its spatiotemporal variability in recent decades. Looking forward, the potential for direct detection of change in the ocean carbon sink, as distinct from interannual variability, is assessed using a climate model large ensemble, a novel approach to studying climate processes with an earth systems model, the “large ensemble.” In a large ensemble, many runs of the same model are done so as to directly distinguish natural variability from long-term trends.

This analysis illustrates that variability in CO₂ flux is large enough to prevent detection of anthropogenic trends in ocean carbon uptake on at least decadal to multi-decadal timescales, depending on location. Earliest detection of trends is most attainable in regions where trends are expected to be largest, such as the Southern Ocean and parts of the North Atlantic and North Pacific. Detection will require sustained observations over many decades, underscoring the importance of traditional ship-based approaches and integration of new autonomous observing platforms as part of a global ocean carbon observing system.

Please see a relevant OCB outreach tool on ocean carbon uptake developed by McKinley and colleagues:
OCB teaching/outreach slide deck Temporal and Spatial Perspectives on the Fate of Anthropogenic Carbon: A Carbon Cycle Slide Deck for Broad Audiences – also download explanatory notes

Quantifying coastal and marine ecosystem carbon storage potential for climate mitigation policy and management

Posted by mmaheigan

· Wednesday, June 21st, 2017

Under the increasing threat of climate change, conservation practitioners and policy makers are seeking innovative and data–driven recommendations for mitigating emissions and increasing natural carbon sinks through nature-based solutions. While the ocean and terrestrial forests, and more recently, coastal wetlands, are well known carbon sinks, there is interest in exploring the carbon storage potential of other coastal and marine ecosystems such as coral reefs, kelp forests, phytoplankton, planktonic calcifiers, krill, and teleost fish. A recent study in Frontiers in Ecology and the Environment reviewed the potential and feasibility of managing these other coastal and marine ecosystems for climate mitigation. The authors concluded, that while important parts of the carbon cycle, coral reefs, kelp forests, planktonic calcifiers, krill, and teleost fish do not represent long-term carbon stores, and in the case of fish, do not represent a sequestration pathway. Phytoplankton do sequester globally significant amounts of carbon and contribute to long-term carbon storage in the deep ocean, but there is currently no good way to manage them to increase their carbon storage capacity; additionally, the vast majority of phytoplankton is located in international waters that are outside national jurisdictions, making it very difficult to include them in current climate mitigation policy frameworks.

Comparatively, coastal wetlands (mangroves, tidal marshes, and seagrasses) effectively sequester carbon long-term (up to 10x more carbon stored per unit area than terrestrial forests with 50-90% of the stored carbon residing in the soil), and fall within clear national jurisdictions, which facilitates effective and quantifiable management actions. In addition, wetland degradation has the potential to release vast amounts of stored carbon back into the atmosphere and water column, meaning that conservation and restoration of these systems can also reduce potential emissions. The authors conclude that coastal wetland protection and restoration should be a primary focus in comprehensive climate change mitigation plans along with reducing emissions.

Authors:
Jennifer Howard (Conservation International)
Ariana Sutton-Grier (University of Maryland, NOAA)
Dorothée Herr (IUCN)
Joan Kleypas (NCAR)
Emily Landis (The Nature Conservancy)
Elizabeth Mcleod (The Nature Conservancy)
Emily Pidgeon (Conservation International)
Stefanie Simpson (Restore America’s Estuaries)

Original paper: http://onlinelibrary.wiley.com/doi/10.1002/fee.1451/full

Biophysical drivers of vigorous carbon cycling near the Kuroshio Extension

Posted by mmaheigan

· Thursday, April 27th, 2017

The Kuroshio Current and its Extension jet in the western North Pacific Ocean form a dynamic western boundary current (WBC) region characterized by large air-sea exchanges of heat and carbon dioxide gas (CO₂). The jet is known to oscillate between stable and meandering states on multi-year timescales that alter the eddy field and depth of winter mixing in the southern recirculation gyre. These dynamic state changes have been shown to imprint biogeochemical signatures onto regional mode waters that can be distributed widely throughout the North Pacific and remain out of contact with the atmosphere for decades.

Figure. ~7 years of (a) AVISO daily sea surface height (SSH) anomalies and (b) upper-ocean temperature from the NOAA Kuroshio Extension Observatory (KEO) surface mooring. Black and gray lines in b show the mixed layer depth (MLD) and 17C contour, respectively. Spring bloom periods are indicated in blue in a. The semi-regular upwelling of cold water and corresponding depression of SSH is caused by cold-core eddies that pass the KEO mooring. Winter ventilation depths increase by ~100 m after 2010 when the extension jet entered a stable phase.

To better characterize carbon cycling in this region, ~7 years of daily-averaged autonomous CO₂ observations from NOAA’s Kuroshio Extension Observatory (KEO) surface mooring were used to close the mixed layer carbon budget. High rates of net community production (NCP; >100 mmol C m^-2 d^-1) were observed during the spring bloom period, and a mean annual NCP of 7±3 mol C m^-2 yr^-1 was determined. Biological processes near KEO largely balance the input of carbon that occurs annually through winter mixing; however, physical processes that deviate from climatology were not resolved in this study. Therefore, it remains unclear how transient features such as eddies influence biological carbon production and export through altered nutrient supply and active vertical transport of organic material. Further work is required to determine how biophysical interactions during mesoscale and submesoscale disturbances contribute to local carbon cycle processes and variability in regional mode water carbon inventories.

Ocean Carbon Hot Spots, an upcoming workshop focused on understanding biophysical drivers of carbon uptake in WBC regions, will be held September 25-26, 2017 at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California. The primary objective of the workshop is to develop a community of observationalists and modelers working on the topic, and to identify critical observational needs that would improve model parameterizations. Ocean Carbon Hot Spots will be co-sponsored by US CLIVAR, US OCB, MBARI, and OMIX.

Written by Andrea J. Fassbender, Monterey Bay Aquarium Research Institute

Mixed-layer carbon cycling at the Kuroshio Extension Observatory (Global Biogeochemical Cycles)

Authors:
Andrea J. Fassbender (Monterey Bay Aquarium Research Institute)
Christopher L. Sabine (NOAA Paciﬁc Marine Environmental Laboratory)
Meghan F. Cronin (NOAA Paciﬁc Marine Environmental Laboratory)
Adrienne J. Sutton (Joint Institute for the Study of the Atmosphere and Ocean, University of Washington)

Oceanic fronts enhance carbon transport to the ocean’s interior through both subduction and amplified sinking

Posted by mmaheigan

· Wednesday, March 1st, 2017

Mesoscale fronts are regions with potentially enhanced nutrient fluxes, phytoplankton production and biomass, and aggregation of mesozooplankton and higher trophic levels. However, the role of these features in transporting organic carbon to depth and hence sequestering CO₂ from the atmosphere has not previously been determined. Working with the California Current Ecosystem Long Term Ecological Research (CCE LTER) program, we determined that the flux of sinking particles at a stable front off the coast of California was twice as high as similar fluxes on either side of the front, or in typical non-frontal waters of the CCE in a recent study by Stukel et al. (2017) published in Proceedings of the National Academy of Sciences.

This increased export flux was tied to enhanced silica-ballasting by Fe-stressed diatoms and to an abundance of mesozooplankton grazers. Furthermore, downward transport of particulate organic carbon by subduction at the front led to additional carbon export that was similar in magnitude to sinking flux, suggesting that these fronts (which are a common feature in productive eastern boundary upwelling systems) are an important conduit for carbon sequestration. These enhanced carbon export mechanisms at episodic and mesoscale features need to be included in future biogeochemical forecast models to understand how a changing climate will affect marine CO₂ uptake.

Authors

Michael R. Stukel (Florida State University)
Lihini I. Aluwihare, Katherine A. Barbeau, Ralf Goericke, Arthur J. Miller, Mark D. Ohman, Angel Ruacho, Brandon M. Stephens, Michael R. Landry (University of California, San Diego)
Hajoon Song (Massachusetts Institute of Technology)
Alexander M. Chekalyuk (Lamont-Doherty Earth Observatory)

Subtropical Gyre Productivity Sustained by Lateral Nutrient Transport

Posted by mmaheigan

· Tuesday, December 20th, 2016

Vertical processes are thought to dominate nutrient resupply across the ocean, however estimated vertical fluxes are insufficient to sustain observed net productivity in the thermally stratified subtropical gyres. A recent study by Letscher et al. (2016) published in Nature Geoscience used a global biogeochemical ocean model to quantify the importance of lateral transport and biological uptake of inorganic and organic forms of nitrogen and phosphorus to the euphotic zone over the low-latitude ocean. Lateral nutrient transport is a major contributor to subtropical nutrient budgets, supplying a third of the nitrogen and up to two-thirds of the phosphorus needed to sustain gyre productivity. Half of the annual lateral nutrient flux occurs during the stratified summer and fall months, helping to explain seasonal patterns of net community production at the time-series sites near Bermuda and Hawaii. Figure from Letscher et al. (2016).

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.

Archive for carbon cycle

Authors

Filter by Keyword