Gignoux-Wolfsohn et al., New framework reveals gaps in US ocean biodiversity protection, OneEarth (2023), https:// doi.org/10.1016/j.oneear.2023.12.014. (accompanying fact sheet)
The ultimate goal of marine carbon dioxide (CO2) removal (mCDR) is to sequester more atmospheric CO2 in the ocean than the ocean already does today. As such, any mCDR deployment must lead to quantifiably more CO2 sequestration in the ocean than would have happened without the deployment. This requirement is referred to as “additionality.”
To understand how additionality of CO2 removal is relevant for Ocean Alkalinity Enhancement (OAE) we need to recall what OAE seeks to do. Essentially, OAE accelerates a natural process (weathering) that absorbs protons (H+) in liquid media through geochemical reactions. This anthropogenically enhanced “buffering” results in fewer freely available protons and thus a shift in the marine carbonate system away from CO2 and towards carbonate ions (CO32+), a shift that enables oceanic uptake of atmospheric CO2. However, the anthropogenically buffered protons are then no longer available to be absorbed by natural weathering processes (e.g., calcium carbonate dissolution). Therefore, anthropogenic buffering of seawater pH partially replaces natural buffering (and associated CO2 sequestration) that would have occurred in the absence of OAE. A recent paper (Bach, 2024) describes this “additionality problem” in the context of OAE, and through a series of incubation experiments that emulate a high-energy wave zone (constant mixing), the author investigates how different forms of anthropogenic alkalinity (e.g., sodium hydroxide, steel slag, and olivine) interact with natural alkalinity sources (beach sand) and the subsequent impacts on atmospheric CO2 drawdown. While many questions will require more targeted study, this study represents a foundational baseline for future OAE experimentation and provides preliminary insights on siting and methods of anthropogenic alkalinity addition.
Figure caption: Simple schematic of the additionality problem. In the baseline state (left), alkalinity sources and sinks are (assumed to be) in equilibrium. The addition of an anthropogenic alkalinity source (right) to the baseline system may reduce alkalinity inputs via natural sources. The reduction of natural sources must be subtracted from the anthropogenic sources to correctly calculate the additional CO2 sequestration potential of OAE.
Author
Lennart Bach (Univ. Tasmania)
With an increasingly wide variety of technology and innovations, from buoys to satellites, we now understand the open ocea n better than ever. Yet, existing technologies cannot cost-effectively provide accurate, up-to-date data on coastal and shelf ocean environments, especially beneath the surface. These dynamic regions impact billions of people in profound and varied ways.
Figure caption: Alongside other major global ocean observing technologies and networks, the Fishing Vessel Ocean Observing Network is built around the concept of “fishing for data” to collect high-quality ocean data such as temperature and salinity profiles. These measurements inform critical policy decisions, are integrated into sustainability efforts for fishers, scientists, and other relevant stakeholders, and can improve climate resiliency while protecting the health, well-being, and livelihoods of coastal communities and participants in the blue economy.
As described in a recent publication, the Fishing Vessel Ocean Observing Network (FVON) is reimagining the global data collection paradigm of coastal and shelf oceans by partnering with fishers and regional observation networks around the world. With more than four million fishing vessels worldwide, fishers cover much of the data-sparse nearshore ocean environments, vitally important regions of the ocean. By outfitting sensors onto vessels and on fishing gear, programs from New Zealand to Japan to New England, including researchers at WHOI, demonstrate that fishers can participate actively in the ongoing data revolution and eliminate critical oceanic data gaps without changing their standard fishing activities. Exponentially increasing the scale of data collection through fishing vessel and gear-based observations in nearshore marine environments has and will continue to democratize ocean observation, improve weather forecasting and ocean monitoring, and promote sustainable fishing while safeguarding lives and livelihoods. Already a proven concept regionally, FVON, alongside fishers and regional observation networks, will expand fishing-based observation to a global initiative.
Authors
Cooper Van Vranken (Ocean Data Network)
Julie Jakoboski (MetOcean Solutions, New Zealand)
John W. Carroll (Ocean Data Network)
Christopher Cusack (Environmental Defense Fund)
Patrick Gorringe (Swedish Meteorological and Hydrological Institute)
Naoki Hirose (Kyushu University, Japan)
James Manning (NOAA Northeast Fisheries Science Center (retired))
Michela Martinelli (National Research Council−Institute of Marine Biological Resources and Biotechnologies, Italy)
Pierluigi Penna (National Research Council−Institute of Marine Biological Resources and Biotechnologies, Italy)
Mathew Pickering (Environmental Defense Fund)
A. Miguel Piecho-Santos (Portuguese Institute for Sea and Atmosphere)
Moninya Roughan (University of New South Wales, Australia)
João de Souza (MetOcean Solutions, New Zealand)
Hassan Moustahfid (NOAA Integrated Ocean Observing System (IOOS))
To maintain marine ecosystem health and human well-being, it is important to understand coastal water quality changes. Water clarity is a key component of water quality, which can be measured in situ by tools such as Secchi disks or by satellites with high spatial and temporal coverage. Coastal environments pose unique challenges to remote sensing, sometimes resulting in inaccurate estimates of water clarity.
Figure caption: Maps of model-corrected Landsat-8 derived Secchi depths from monthly clear sky images (2019–2021).
In this study, we couple low-cost in situ methods (Secchi disk depths) with open-access, high-resolution satellite (Landsat-8 and Sentinel-2) data to improve estimates of water clarity in a shallow, turbid lagoon in Virginia, USA. Our model allows the retrieval of water clarity data across an entire water body and when field measurements are unavailable. This approach can be implemented in dynamic coastal water bodies with limited in situ measurements (e.g., as part of routine water quality monitoring). This can improve our understanding of water clarity changes and their drivers to better predict how water quality may change in the future. Improved water clarity predictions can lead to better coastal ecosystem management and human well-being.
Figure caption: Workflow for obtaining Secchi disk depth with l2gen in NASA SeaDAS, bio-optical algorithms, and empirical adjustments.
Authors
Sarah E. Lang (University of Rhode Island’s Graduate School of Oceanography)
Kelly M.A. Luis (Jet Propulsion Laboratory, California Institute of Technology)
Scott C. Doney (University of Virginia)
Olivia Cronin-Golomb (University of Virginia)
Max C.N. Castorani (University of Virginia)
Twitter / Mastodon
@sarah_langsat8 on Twitter
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The ocean is the most important sink of anthropogenic emissions and is being considered as a medium to manipulate to draw down even more. Essential in the ocean’s role as a natural carbon-sponge is the net production of organic matter by phytoplankton, some of which sinks and is stored for 100s-1000s of years. Successfully simulating this biological carbon pump is essential for projecting any climate scenario, but it appears that massive uncertainties in the way zooplankton consume phytoplankton are compromising predictions of future climate and our assessment of some strategies to deliberately engineer it.
Figure caption. Grazing pressure is largest source of uncertainty for marine carbon cycling in CMIP6 models a) The global and zonal median winter grazing pressure is shown for all models. b) the coefficient of variation across models (std/mean) is largest for grazing pressure compared 14 major terms in the marine carbon cycle.
A new publication in Communications Earth and Environment explains how our poor understanding of zooplankton biases our best projections of marine carbon sequestration. We compared 11 IPCC climate models and found zooplankton grazing is largest source uncertainty in marine carbon cycling. This uncertainty is over three times larger than that of net primary production and is driven by large differences in different models assumptions about the rate at which zooplankton can consume phytoplankton. Yet, very small changes in zooplankton grazing dynamics (roughly only 5% of the full range used across IPCC models) can increase carbon sequestrations by 2 PgC/yr, which is double the maximum theoretical potential of Southern Ocean Iron Fertilization! Moving forward, to move beyond merely treating zooplankton as a closure term, modelers must look towards novel observational constraints on grazing pressure.
Authors
Tyler Rohr, Anthony J. Richardson, Andrew Lenton, Matthew A. Chamberlain, and Elizabeth H. Shadwick
See also the Conversation article
Despite the importance of particulate organic carbon (POC) export on carbon sequestration and marine ecology, there have been few multi-decade studies in the world’s oceans. A new analysis published in Nature analyzed two decades of POC export data in the West Antarctic Peninsula and found that export oscillates on a 5-year cycle.
Figure caption: A) Particulate organic carbon (POC) export oscillates on a 5-year timescale in sync with the oscillation in the body size of the krill Euphausia superba on the West Antarctic Peninsula. B) POC export is significantly correlated with krill body size (p = 0.01).
Using a unique combination of krill data from penguin diet samples and net tows over two decades, Trinh et al. found that the cycle of POC export is intimately tied to the Antarctic krill (Euphausia superba) life cycle, as the bulk of the POC in their sediment traps was krill fecal pellets. Surprisingly, more krill did not lead to more POC export. Instead, when the krill population size was smaller but dominated by larger, older adults, POC export increased.
E. superba is the longest-lived (5-6 years) and largest krill species. They exhibit continuous annual growth throughout their life cycle. After about five years a krill population reaches its end stage and the population size is at a minimum. This end-stage population is composed of large, 50-60 mm long individuals that produce large, fast-sinking fecal pellets, leading to increased POC export. Increasing temperatures and deterioration of sea ice cover during the winter season due to climate change will likely impact the recruitment of new cohorts of krill and their success in replenishing aging populations. It is unclear how changes in the krill population and life cycle will impact long-term carbon sequestration on the West Antarctic Peninsula and nutrients exported to the benthic ecosystem
Authors:
Rebecca Trinh (Lamont Doherty Earth Observatory, Columbia University)
Hugh Ducklow (Lamont Doherty Earth Observatory, Columbia University)
Deborah Steinberg (Virginia Institute of Marine Science, College of William and Mary)
William Fraser (Polar Oceans Research Group)
Carbon dioxide removal (CDR) is “unavoidable” in efforts to limit end-of-century warming to below 1.5 °C. This is because some greenhouse gas emissions sources—non-CO2 from agriculture, and CO2 from shipping, aviation, and industrial processes—will be difficult to avoid, requiring CDR to offset their climate impacts. Policymakers are interested in a wide variety of ways to draw down CO2 from the atmosphere, but to date, the modeling scenarios that inform international climate policies have mostly used biomass energy with carbon capture and storage (BECCS) as a proxy for all CDR. It is critical to understand the potential of a full suite of CDR technologies, to understand their interactions with energy-water-land systems and to begin preparing for these impacts.
Figure caption: Each of the six carbon dioxide removal approaches identified in recent U.S. legislation and modeled for this study could bring unique benefits and tradeoffs to the energy-water-land system. This image depicts afforestation, direct ocean capture, direct air capture, biochar, enhanced weathering, and bioenergy with carbon capture and storage in clockwise order. Floating carbon dioxide molecules hover above the landscape (image credit: Nathan Johnson, PNNL).
A recent study published in the journal Nature Climate Change was the first to model six major CDR pathways in an integrated assessment model. The modeled pathways range from bioenergy with carbon storage and afforestation (already represented by most models), also direct air capture, biochar and crushed basalt spreading on global croplands, and electrochemical stripping of CO2 from seawater aka direct ocean capture. The removal potential contributed by each of the six pathways varies widely across different regions of the world. Direct ocean capture showed the smallest removal potential but has important potential synergies with water desalination. This method could help arid regions such as the Middle East meet their water needs in a warming world. Enhanced weathering has much larger (GtCO2-yr-1) removal potential and could potentially help ameliorate ocean acidification. Overall, similar total amounts of CO2 are removed compared to other modeling scenarios, but broader set of technologies lessens the risk that any one of them would become politically or environmentally untenable.
Authors:
Jay Fuhrman (Joint Global Change Research Institute)
Candelaria Bergero (Joint Global Change Research Institute)
Maridee Weber (Joint Global Change Research Institute)
Seth Monteith (ClimateWorks Foundation)
Frances M. Wang (ClimateWorks Foundation)
Andres F. Clarens (University of Virginia)
Scott C. Doney (University of Virginia)
William Shobe (University of Virginia)
Haewon McJeon (Joint Global Change Research Institute )
Twitter: @pnnlab @climateworks @uva
Phytoplankton are small, drifting photosynthetic organisms that form the base of marine food webs and play an important role in carbon and nutrient cycling. Analyses of how they vary in space and time (through variables like the concentration of pigment chlorophyll-a, a proxy for their biomass) are therefore important. Because phytoplankton drift with ocean currents, their variability and rates of change should be analyzed in a Lagrangian frame (observer moves with a water parcel) as opposed to an Eulerian frame (observer is fixed in space). However, Lagrangian observations are less available and it is difficult to separate the effects of physical and biological processes in Eulerian observations.
Figure 1: The decorrelation time and length scales of chlorophyll-a in the Lagrangian (Tl,Chl and Ll,Chl) and Eulerian (Te,Chl and Le,Chl) frames are related by the underlying mesoscale velocity field. (a) Ratio Tl,Chl / Te,Chl as a function of u’ / c*Chl computed from anomalies relative to a climatology, where u’ is a scale for the mesoscale eddy velocities and c*Chl = Le,Chl / Te,Chl is an evolution speed for the chlorophyll field. (b) As in (a) but for ratio of length scales, Ll,Chl / Le,Chl. In (a) and (b), hollow (filled) circles come from all surface drifters (all BGC-Argo floats) in a 5º x 5º bin and crosses weight the float-derived scales by the inverse square of a Quasi-Planktonic Index (so that float segments more similar to a surface trajectory count more; see below). Triangles come from two floats that profiled frequently. Solid line is an empirical curve: as u’ / c*Chl → ∞, Lagrangian decorrelation is entirely determined by Fickian diffusion and the ratio of length scales approaches qChl = π/2. (c) Example demonstrating the Quasi-Planktonic Index (QPI), which quantifies the average distance between a float (squares) and the best-fit synthetic trajectory generated from surface currents (circles). Altimetric geostrophic currents are shown as vectors, initial particle locations are black dots, and final forward (backward) particle locations are blue (orange) dots. A smaller QPI indicates a float segment more similar to a surface geostrophic trajectory.
A recent study used observations of chlorophyll-a concentration in the upper ocean from satellites and BGC-Argo profiling floats to quantify the statistics of phytoplankton (time and length scales obtained from autocorrelation functions) in the Lagrangian and Eulerian frames and to understand how the two frames are related by the underlying velocity field. At the mesoscale (the size of swirling, balanced flows), the Eulerian scales of chlorophyll-a anomalies relative to a seasonal cycle matched those of velocity, suggesting ocean dynamics play a role in setting phytoplankton scales. The ratio of Lagrangian to Eulerian length scales of chlorophyll depends on the magnitude of turbulent velocity fluctuations relative to how fast the chlorophyll field translates, following an empirical curve with an asymptotic limit consistent with stirring by mesoscale eddies (Figure 1a,b). They conclude that when velocity fluctuations are relatively large, turbulent diffusion drives decorrelation, but when they are relatively small, biological sources drive decorrelation.
Figure 2: A composite view of the physical and biological processes at mesoscale ocean fronts. (a) Example of a straining maximum in altimetric geostrophic currents and rotated coordinate system, along with a coincident float trajectory. Lagrangian time series from 18 floats in the North Atlantic are matched to all straining maxima and averaged in rotated coordinates, utilizing only profiles where the Quasi-Planktonic Index (QPI) is less than 5 km; (b) strain rate (color) and relative vorticity (contours); (c) time derivative of mixed layer depth; (d) phytoplankton accumulation rate; (e) chlorophyll-a accumulation rate. Fronts are characterized by a shoaling mixed layer and increasing chlorophyll-a over the front.
Finding that floats can sample a mixed layer tracer somewhat like a surface Lagrangian observer when their trajectory is similar to a surface trajectory (Figure 1c), the authors conducted a follow-up study where they used floats under those conditions to better understand the biological-physical interactions at straining fronts, which are regions between mesoscale eddies where lateral gradients are sharpened, force balances break down, and episodic vertical velocities may be important for mixed layer budgets of carbon and nutrients. By averaging rates of phytoplankton accumulation (from the along-track derivative of mixed-layer averaged chlorophyll-a) in coordinates aligned with ocean fronts, they found that these dynamical structures are characterized by a shoaling mixed layer and increasing phytoplankton carbon and chlorophyll (Figure 2). They conclude that the vertical motions at ocean fronts restratify the mixed layer which increases average light levels experienced by cells, accelerating division rates and causing their accumulation.
The results of these studies provide important insights into the space-time evolution of reactive tracers like chlorophyll-a in a mesoscale flow. The results also provide insight into how to interpret time series obtained from BGC-Argo floats, which are observing platforms that are neither Lagrangian nor Euleran, and highlight floats’ potential to address problems of biological-physical interactions under certain sampling conditions.
Authors:
Darren C. McKee (University of Virginia, USA)
Scott C. Doney (University of Virginia, USA)
Alice Della Penna (University of Auckland, NZ)
Emmanuel S. Boss (University of Maine, USA)
Peter Gaube (University of Washington, USA)
Michael J. Behrenfeld (Oregon State University, USA)
David M. Glover (Woods Hole Oceanographic Institution, USA)
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