Archive for carbon sequestration

New evidence suggests that tiny zooplankton might be the biggest problem with carbon cycling in IPCC climate models

Posted by mmaheigan 
· Friday, December 1st, 2023 

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

Size does matter: larger krill leads to more POC export in the West Antarctic Peninsula

Posted by mmaheigan 
· Friday, December 1st, 2023 

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)

 

A suite of CO2 removal approaches modeled for the 1.5 ˚C future

Posted by mmaheigan 
· Thursday, August 31st, 2023 

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

How atmospheric and oceanographic forcing impact the carbon sequestration in an ultra-oligotrophic marine system

Posted by mmaheigan 
· Wednesday, August 11th, 2021 

Sinking particles are a critical conduit for the export of material from the surface to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the composition and seasonal variability of sinking particles which reach abyssal depths. Oligotrophic waters cover ~75% of the ocean surface and contribute over 30% of the global marine carbon fixation. Understanding the processes that control carbon export to the deep oligotrophic areas is crucial to better characterize the strength and efficiency of the biological pump as well as to project the response of these systems to climate fluctuations and anthropogenic perturbations.

In a recent study published in Frontiers in Earth Science, authors synthesized data from atmospheric and oceanographic parameters, together with main mass components, and stable isotope and source-specific lipid biomarker composition of sinking particles collected in the deep Eastern Mediterranean Sea (4285m, Ierapetra Basin) for a three-year period (June 2010-June 2013). In addition, this study compared the sinking particulate flux data with previously reported deep-sea surface sediments from the study area to shed light on the benthic–pelagic coupling.

Figure Caption: a) Biplot of net primary productivity vs export efficiency (top and bottom horizontal dashed lines indicate threshold for high and low export efficiency regimes). b) Biplot of POC-normalized concentrations of terrestrial vs. phytoplankton-derived lipid biomarkers of the sinking particles collected in the deep Eastern Mediterranean Sea (Ierapetra Basin, NW Levantine Basin) from June 2010–June 2013, and surface sediments collected from January 2007 to June 2012 in the study area.

Both seasonal and episodic pulses are crucial for POC export to the deep Eastern Mediterranean Sea. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Overall, summer particle export fuels more efficient carbon sequestration than the other seasons. The results of this study highlight that the combination of extreme weather events and aerosol deposition can trigger an influx of both marine labile carbon and anthropogenic compounds to the deep. Finally, the comparison of the sinking particles flux data with surface sediments revealed an isotopic discrimination, as well as a preferential degradation of labile organic matter during deposition and burial, along with higher preservation of land-derived POC in the underlying sediments. This study provides key knowledge to better understand the export, fate and preservation vs. degradation of organic carbon, and for modeling the organic carbon burial rates in the Mediterranean Sea.

 

Authors:
Rut Pedrosa-Pamies (The Ecosystems Center, Marine Biological Laboratory, US; Research Group in Marine Geosciences, University of Barcelona, Spain)
Constantine Parinos (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Anna Sanchez-Vidal (Group in Marine Geosciences, University of Barcelona, Spain)
Antoni Calafat (Group in Marine Geosciences, University of Barcelona, Spain)
Miquel Canals (Group in Marine Geosciences, University of Barcelona, Spain)
Dimitris Velaoras (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Nikolaos Mihalopoulos (Environmental Chemical Processes Laboratory, University of Crete; National Observatory of Athens, Greece)
Maria Kanakidou (Environmental Chemical Processes Laboratory, University of Crete Greece)
Nikolaos Lampadariou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Alexandra Gogou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)

Blue hole in the South China Sea reveals ancient carbon

Posted by mmaheigan 
· Wednesday, July 8th, 2020 

Blue holes are unique depositional environments that are formed within carbonate platforms. Due to an enclosed geomorphology that restricts water exchange, blue hole ecosystems are typically characterized by steep biogeochemical gradients and distinctive microbial communities. For the past three decades, studies have described vertical gradients in physical, chemical, and biological parameters that typify blue hole water columns, but their elemental cycles, particularly carbon, remain poorly understood.

Figure 1. Aerial photo of the Yongle Blue Hole in the South China Sea (Credit: P. Yao et al./JGR Biogeosciences)

In July 2016, the Yongle Blue Hole (YBH) was discovered to be the deepest known blue hole on Earth (~300 m). YBH is located in the Xisha Islands of the South China Sea. The unique features and ease of accessibility make YBH an ideal natural laboratory for studying carbon cycling in marine anoxic systems. In a recent study published in JGR Biogeosciences, the authors reported extremely low concentrations of dissolved organic carbon (DOC) (e.g., 22 µM) and very high concentrations of dissolved inorganic carbon (DIC) (e.g., 3,090 µM) in YBH deep waters. Radiocarbon dating revealed that the YBH DOC and DIC were unusually old, yielding ages (6,810 and 8270 years BP, respectively) that are much more typical of open ocean deep water. Based on H2S and microbial community composition profiles, the authors concluded that sharp redox gradients and a high abundance of sulfur cycling bacteria were likely responsible for much of the DOC consumption in YBH. The unusually low concentrations and old DOC ages in the relatively shallow YBH suggest short-term cycling of recalcitrant DOC in oceanic waters, which has been recognized as a long-term microbial carbon sink in the global ocean. The stoichiometry of DIC and total alkalinity changes suggested that the accumulation of DIC in the deep layer of the YBH was largely derived from both the dissolution of carbonate and OC decomposition through sulfate reduction. However, the role of carbonate dissolution from the walls of the blue hole in affecting the old ages of carbon in this system remain uncertain, yet there appears to no evidence of subterranean freshwater into the bottom waters of the blue hole. In the face of expanding oxygen minimum zones and anthropogenically-induced coastal hypoxia, blue holes such as YBH can provide an accessible natural laboratory in which to study the microbial and biogeochemical features that typify these low-oxygen systems.

 

Authors:
Peng Yao (Ocean University of China)
Thomas S. Bianchi (University of Florida)
Xuchen Wang (Ocean University of China)
Zuosheng Yang (Ocean University of China)
Zhigang Yu (Ocean University of China)

A role for tropical nitrogen fixers in glacial CO2 drawdown

Posted by mmaheigan 
· Wednesday, December 4th, 2019 

Iron fertilization of marine phytoplankton by Aeolian dust is a well-established mechanism for atmospheric carbon dioxide (CO2) drawdown by the ocean. When atmospheric CO2 decreased by 90-100 ppm during previous ice ages, fertilization of iron-limited phytoplankton in the high latitudes was thought to have contributed up to 1/3 (30 ppm) of the total CO2 drawdown. Unfortunately, recent modeling studies suggest that substantially less CO2 (only 2-10 ppm) is sequestered by the ocean in response to high latitude fertilization.

The limited capacity for high latitude CO­2 sequestration in response to iron enrichment motivated the authors of a new study published in Nature Communications to address how lower latitude phytoplankton could contribute to CO2 drawdown. The authors used an ocean model to show that in response to Aeolian iron fertilization, dinitrogen (N2) fixers, specialized phytoplankton that introduce bioavailable nitrogen to tropical surface waters, drive the sequestration of an additional 7-16 ppm of CO2 by the ocean.

Figure 1: Scenarios of Fe supply to the tropical Pacific. In the low iron scenario, analogous to the modern climate, N2 fixation (yellow zone and dots) is concentrated in the Northwest and Southwest subtropical Pacific where aeolian dust deposition is greatest. Non-limiting PO4 concentrations (green zone and dots) exist within the tropics and spread laterally from the area of upwelling near the Americas and at the equator (blue zone). In the high Fe scenario, analogous to the glacial climate, N2 fixation couples to the upwelling zones in the east Pacific, enabling strong utilisation of PO4, the vertical expansion of suboxic zones (grey bubbles) and a deeper injection of carbon-enriched organic matter (downward squiggly arrows).

These results provide evidence of a tropical ocean CO2 sequestration pathway, the mere existence of which is hotly debated. Importantly, the study describes an additional mechanism of CO2 drawdown that is complementary to the high latitude mechanism. When combined, their contributions elevate iron-driven CO2 drawdown towards the expected 30 ppm, making iron fertilization a driver of a stronger biological pump on a global scale.

 

Authors:
Pearse Buchanan (University of Liverpool, University of Tasmania, CSIRO Oceans and Atmosphere, ARC Centre of Excellence in Climate System Science)
Zanna Chase (University of Tasmania)
Richard Matear (CSIRO Oceans and Atmosphere, ARC Centre of Excellence in Climate Extremes)
Steven Phipps (University of Tasmania)
Nathaniel Bindoff (University of Tasmania, CSIRO Oceans and Atmosphere, ARC Centre of Excellence in Climate Extremes, Antarctic Climate and Ecosystems Cooperative Research Centre)

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