mmaheigan :: Ocean Carbon & Biogeochemistry

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

Author Archive for mmaheigan – Page 9

Unveiling the Past and Future of Ocean Acidification: A Novel Data Product covering 10 Global Surface OA Indicators

Posted by mmaheigan

· Wednesday, August 23rd, 2023

Accurately predicting future ocean acidification (OA) conditions is crucial for advancing research at regional and global scales, and guiding society’s mitigation and adaptation efforts.

As an update to Jiang et al. 2019, this new model-data fusion product:
1. Utilizes an ensemble of 14 distinct Earth System Models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) along with three recent observational ocean carbon data products –>instead of relying on just one model (i.e., the GFDL-ESM2M) this approach reduces potential projection biases in OA indicators.
2. Eliminates model biases using observational data, and model drift with pre-Industrial controls.
3. Covers 10 OA indicators, an expansion from the usual pH, acidity, and buffer capacity.
4. Incorporates the new Shared Socioeconomic Pathways (SSPs).

The use of the most recent observational datasets and a large Earth System Model ensemble is a major step forward in the projection of future surface ocean OA indicators and provides critical information to guide OA mitigation and adaptation efforts.

Figure X. Temporal changes of global average surface ocean OA indicators as reconstructed and projected from 14 CMIP6 Earth System Models after applying adjustments with observational data: (a) fugacity of carbon dioxide (fCO₂), (b) total hydrogen ion content ([H⁺]_total), (c) carbonate ion content ([CO₃^2-]), (d) total dissolved inorganic carbon content (DIC), (e) pH on total scale (pH_T), (f) aragonite saturation state (Ω_arag), (g) total alkalinity content (TA), (h) Revelle Factor (RF), and (i) calcite saturation state (Ω_calc). The asterisk signs on the left-side y-axes show the values in 1750. The numbers along right-side y-axes, i.e., 1-1.9, 1-2.6, 2-4.5, 3-7.0, and 5-8.5, indicate the shared socioeconomic pathway SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, respectively. These are missing from panel g because the trajectories were more dependent on the model than the SSP.

Authors
Li-Qing Jiang (University Maryland)
John Dunne (NOAA/Geophysical Fluid Dynamics Laboratory)
Brendan R. Carter (University of Washington)
Jerry F. Tjiputra (NORCE Norwegian Research Centre Bjerknes)
Jens Terhaar (Woods Hole Oceanographic Institution)
Jonathan D. Sharp (University of Washington)
Are Olsen (University of Bergen and Bjerknes Centre for Climate Research)
Simone Alin (NOAA/Pacific Marine Environmental Laboratory)
Dorothee C. E. Bakker (University of East Anglia)
Richard A. Feely (NOAA/Pacific Marine Environmental Laboratory)
Jean-Pierre Gattuso (Sorbonne Université)
Patrick Hogan (NOAA/National Centers for Environmental Information)
Tatiana Ilyina (Max Planck Institute for Meteorology)
Nico Lange (GEOMAR Helmholtz Centre for Ocean Research)
Siv K. Lauvset (NORCE Norwegian Research Centre)
Ernie R. Lewis (Brookhaven National Laboratory)
Tomas Lovato (Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici)
Julien Palmieri (National Oceanography Centre)
Yeray Santana-Falcón (Université de Toulouse)
Jörg Schwinger (NORCE Norwegian Research Centre)
Roland Séférian (Université de Toulouse)
Gary Strand (US National Center for Atmospheric Research)
Neil Swart (Canadian Centre for Climate Modelling and Analysis)
Toste Tanhua (GEOMAR Helmholtz Centre for Ocean Research)
Hiroyuki Tsujino (JMA Meteorological Research Institute)
Rik Wanninkhof (NOAA/Atlantic Oceanographic Meteorological Laboratory)
Michio Watanabe (Japan Agency for Marine-Earth Science and Technology)
Akitomo Yamamoto (Japan Agency for Marine-Earth Science and Technology)
Tilo Ziehn (CSIRO Oceans and Atmosphere)

Twitter:
@JiangLiqing, @JensTerhaar, @jpGattuso, @j_d_sharp, @AreOlsen, @SimoneAlin, @Dorothee_Bakker, @RFeely, @ilitat, @sivlauvset, @yeraysf, @TosteTanhua,

OCB supports ECR participation in 2023 Cornell Satellite Remote Sensing course

Posted by mmaheigan

· Tuesday, August 15th, 2023

OCB supports ECR participation in 2023 Cornell Satellite Remote Sensing course

The Cornell Satellite Remote Sensing course, an intensive 2-week summer training course took place June 5-16 in Ithaca, NY. The goal of the course was to teach participants the basic skills needed to work independently to acquire, analyze and visualize data sets derived from a variety of satellite sensors. The course also covered image analysis methods to work with satellite imagery of 1) sea surface temperature, 2) ocean wind speed, and 3) sea surface height.

OCB supported six students to attend the 2023 course. Read about the students and their experiences below:

Ardian Rizal’s research interest is in the area of physical oceanography process and how it explains the interconnected system of the Earth. After graduation from his bachelor’s study in Bandung Institute of Technology, Indonesia, he became an academic assistant at the same institution. His work was to describe the wind-wave climate characteristics and its potential as a renewable energy in the Indonesian Seas. He utilized numerical simulation along with the observation from buoy and altimetry satellites to assess the model’s fidelity. Currently, he is in the 2nd year of his master’s study in the division of Marine Science at the University of Southern Mississippi. He is examining the tidal influences on the mechanism of circulation in the west Mississippi Sound as his theses project under the supervision of Dr. Jerry Wiggert.

On the course: It was a blast! The program serves as a comprehensive foundation for the acquisition, data analysis, and visualization of the imagery and altimetry satellite geophysical product. The course was delivered with a perfect balance of lectures and practical activities. I feel I can independently navigate myself to do my own project after the program. Outside of the course, there are a lot of fantastic things to do with amazing participants such as exploring the gorgeous gorges, visiting the renowned ornithology lab of Cornell, and many more. I am full of gratitude to Dr. Bruce for the amazing stories and guidance, the helpful and patient teaching assistants: Danielle and Nour, and OCB for the wonderful opportunity to participate in this course. This program is highly recommended to any marine scientists who want to do remote sensing studies or learn useful tools of Python and SeaDAS through UNIX environment for ocean studies.

Meg Yoder is a 4th year PhD student at Boston College. Her research focuses on the biological, chemical, and physical processes that govern the flux of carbon between the surface ocean, deep ocean, and atmosphere in the subpolar North Atlantic. Her current research in the Irminger Sea uses autonomous sensor data from Ocean Observatories Initiative including pH, pCO2, oxygen, and chlorophyll, as well as lab measurements.

On the course: The Cornell Ocean Satellite Remote Sensing course opened the door to satellite data for me, and not just for ocean color but sea surface temperature, wind, and altimetry data as well. I’m excited to integrate these new data sources and compare them to the in situ data I’m currently working with. The course was extremely well structured and well taught, I can’t thank Bruce, the TAs, and OCB for their support in participating enough!

James Lin is a second-year Ph.D. student in the Ocean Processes and Analysis Laboratory at the University of New Hampshire. Advised by Dr. Robert Letscher, his current project focuses on constraining the production, age, and biochemical fate of dissolved organic carbon (DOC) based on its sources (allochthonous vs autochthonous) and sinks (abiotic vs biotic) using isotope 13C and radiocarbon (14C) in the ocean biogeochemistry component (Marine Biogeochemistry Library- MARBL) of the Community Earth System Model V2 (CESM).

On the course: I am very happy to have taken the Cornell Satellite Remote Sensing 2023 workshop. A huge thank you to Dr. Bruce Monger and the supporting staff and TAs for their mentorship and patience in learning satellite imagery with Python. Learning how to access and process satellite data, such as sea surface temperature, altimetry, chlorophyll, and wind speed, is immensely valuable in my current carbon modeling research to provide long-term observations throughout the global ocean. I also appreciate meeting and getting to know other participants from different parts of the world working on Satellite-derived observations. This training workshop is a must to become a part of the Satellite Remote Sensing community. Thank you again to Dr. Bruce Monger, the Cornell workshop staff and participants, and Ocean Carbon & Biogeochemistry (OCB) for making this workshop experience unforgettable.

Mitch Torkelson is a 2nd year master’s student in Marine Science at the University of North Carolina-Wilmington. Under the guidance of Dr. Phil Bresnahan, his research primarily centers around assessing the accuracy of the SeaHawk CubeSat in measuring key oceanic water column constituents such as chlorophyll a and CDOM. His research interests lie in the field of water quality, where he utilizes bio-optical modeling and remote sensing techniques to conduct statistical analyses on the optically-detectable particles and sediments observed in satellite imagery captured near the Masonboro inlet, situated along the North Carolina coast.

On the course: I cannot praise the Ocean Color training program led by Bruce Monger enough. Prior to enrolling in the course, my knowledge of programming and ocean color satellite analysis was basic at best. However, after completing the 2 weeks, I emerged equipped with an entire new arsenal of skills and tools that not only will aid in the completion of my thesis research but also position me for success in my future endeavors!

Jessie Wynne is a 2nd year Master of Marine Science Student at the University of North Carolina Wilmington and is advised by Dr. Phil Bresnahan. Her research is focused on the development of low-cost water quality sensors as well as satellite water quality analysis. Jessie will be working with SeaHawk/HawkEye imagery and chlorophyll coastal analysis.

On the course: The Cornell Satellite Remote Sensing course was a fantastic experience. It provided me with so many tools to process satellite imagery, especially ocean dolor data. This course also equipped me with python programming skills. Dr. Bruce Monger was an excellent instructor, providing thorough explanations of satellite imagery analysis algorithms while being very patient with all questions directed his way. I really enjoyed this course and would recommend it to anyone pursuing satellite remote sensing and ocean color analysis. I would like to say thank you to Dr. Bruce Monger and OCB for this amazing experience!

Nick Baetge is a postdoctoral scholar in the laboratories of Dr. Michael Behrenfeld and Dr. Kimberly Halsey at Oregon State University. He has been examining variability in phytoplankton physiology and bio-optical properties over the day-night cycle using cultivation-based experiments and from publicly archived in situ data. He will soon be investigating the physiological and diversity-based responses of marine phytoplankton and bacterioplankton to wildfire ash deposition off the U.S. West Coast.

On the course: It can be hard for new ocean color data users to know how to approach remote sensing analyses, including coding in a different programming language. Dr. Monger breaks down the process and provides several resources that makes it less daunting for new users to start, giving them the confidence to use Python, retrieve level 1 satellite data, process it to level 3, and generate composite imagery from individual scenes. I left the Cornell Remote Sensing workshop with not only a new set of tools that I can continue to refine and use to view the oceans, but also some wonderful new colleagues and friends. Thank you so much to Dr. Monger, OCB, and all the course participants for the opportunity to connect and learn!

Are you interested in a primer on ocean biogeochemical modeling with hands-on examples?

Posted by mmaheigan

· Thursday, May 11th, 2023

Look no further. This primer article explains what an ocean biogeochemical model is, how such a model is designed and applied, and includes easily accessible code examples. Refresh your memory on commonly used metrics for model evaluation through model-data comparison. Get introduced to the underlying rationale, mechanics, applications, and pitfalls of data assimilation for parameter optimization, state estimation, and observing system design. Peruse overviews of available community code repositories and observational databases. And tour some of the important applications of ocean biogeochemical models for carbon accounting, ocean deoxygenation and acidification studies, and fisheries yield projections. The primer also includes recommendations for best practices in ocean biogeochemical modeling and discusses current limitations and anticipated future developments and challenges. First and foremost, the article is an invitation to get involved.

Figure caption: Schematic representation of the varying level of complexity in biogeochemical models. State variables are indicated by the boxes where different colors correspond to different elemental currencies. The black arrows indicate selected biogeochemical transformations. The simplest, the nutrient–phytoplankton– zooplankton–detritus (NPZD) model, includes four state variables and one nutrient currency, often nitrogen. A typical low-complexity model includes several nutrients and nutrient currencies. Chlorophyll is omitted in the schematic, although many models have a chlorophyll state variable for each phytoplankton group to account for photoacclimation.

Authors
Katja Fennel (Dalhousie University)
Jann Paul Mattern (University of California, Santa Cruz)
Scott C. Doney (University of Virginia)
Laurent Bopp (Institute Pierre Simon Laplace)
Andrew M. Moore (University of California, Santa Cruz)
Bin Wang (Dalhousie University)
Liuqian Yu (Hong Kong University of Science and Technology)

Twitter @katjafennel @ScottDoney1 @laurent_bopp @DalhousieU @uvaevsc

Adaptive emission pathways to stabilize global temperatures

Posted by mmaheigan

· Thursday, May 11th, 2023

Around the world, countries have agreed in the Paris Agreement to limit global warming well below 2°C and to pursue efforts to reduce global warming to 1.5°C. However, large uncertainties remain about which emission pathways will allow us to reach this goal. A recent paper presents a new adaptive approach to create emission pathways and estimate the necessary emission reductions every five years, following the stocktake process of the Paris Agreement. This Adaptive Emissions Reduction Approach (AERA) is solely based on past warming rates, and emissions of CO₂ and non-CO₂ radiative agents, and explicitly does not rely on projections by Earth System Models. Updating the emission pathways every five years, circumvents uncertainties in the climate system and its transient response to cumulative emissions (TCRE). Testing with the Bern3D-LPX Earth System Model of Intermediate Complexity shows that the approach works robustly across a wide range of TCREs, avoids large overshoots, and only small changes to the emission pathways are necessary every five years. This approach will allow policymakers to estimate emission pathways and create a base for international negotiations. Furthermore, it allows simulations with Earth System Models that all converge to the same temperature target to compare the climate at stabilized warming levels.

Figure caption: The three steps of the Adaptive Emission Reduction Approach: 1) Estimating the past anthropogenic warming, 2) estimating the remaining emission budget, and 3) redistributing it over the future years.

Authors
Jens Terhaar (University of Bern, now Woods Hole Oceanographic Institution)
Thomas L Frölicher (University of Bern)
Mathias T Aschwanden (University of Bern)
Pierre Friedlingstein (University of Exeter, Ecole Normale Superieure)
Fortunat Joos (University of Bern)

Twitter @JensTerhaar @froeltho @PFriedling @unibern @snsf_ch @4C_H2020 @ExeterUniMaths @Geosciences_ENS @IPSL_outreach

Hydrostatic pressure substantially reduces deep-sea microbial activity

Posted by mmaheigan

· Thursday, May 11th, 2023

Deep sea microbial communities are experiencing increasing hydrostatic pressure with depth. It is known that some deep sea microbes require high hydrostatic pressure for growth, but most measurements of deep-sea microbial activity have been performed under atmospheric pressure conditions.

In a recent paper published in Nature Geoscience, the authors used a new device coined ‘In Situ Microbial Incubator’ (ISMI) to determine prokaryotic heterotrophic activity under in situ conditions. They compared microbial activity in situ with activity under atmospheric pressure at 27 stations from 175 to 4000 m depths in the Atlantic, Pacific, and the Southern Ocean. The bulk of heterotrophic activity under in situ pressure is always lower than under atmospheric pressure conditions and is increasingly inhibited with increasing hydrostatic pressure. Single-cell analysis revealed that deep sea prokaryotic communities consist of a small fraction of pressure-loving (piezophilic) microbes while the vast majority is pressure-insensitive (piezotolerant). Surprisingly, the piezosensitive fraction (~10% of the total community) responds with a more than 100-fold increase of activity upon depressurization. In the microbe proteomes, the authors uncovered taxonomically characteristic survival strategies in meso- and bathypelagic waters. These findings indicate that the overall heterotrophic microbial activity in the deep sea is substantially lower than previously assumed, which implies major impacts on the carbon budget of the ocean’s interior.

Figure caption: Deep sea microbial activity under varying pressure. (a) In situ bulk leucine incorporation rates normalized to rates obtained at atmospheric pressure conditions. (b) A microscopic view of a 2000 m sample collected in the Atlantic and incubated under atmospheric pressure conditions. The black halos around the cells are silver grains corresponding to their activities. The highly active cells (indicated by arrows) were rarely found in in situ pressure incubations. (c) Depth-related changes in the metaproteome of three abundant deep sea bacterial taxa (Alteromonas, Bacteroidetes, and SAR202). The number indicates shared and unique up- and down-regulated proteins in different depth zones.

Authors
Chie Amano (University of Vienna, Austria)
Zihao Zhao (University of Vienna, Austria)
Eva Sintes (University of Vienna, IEO-CSIC, Spain)
Thomas Reinthaler (University of Vienna, Austria)
Julia Stefanschitz (University of Vienna, Austria)
Murat Kisadur (University of Vienna, Austria)
Motoo Utsumi (University of Tsukuba, Japan)
Gerhard J. Herndl (University of Vienna, Netherlands Institute for Sea Research)

Twitter @microbialoceanW

Does dark carbon fixation supply labile DOC to the deep ocean?

Posted by mmaheigan

· Thursday, March 30th, 2023

Nitrifying microbes are the most abundant chemoautotrophs in the dark ocean. Though better known for their role in the nitrogen cycle, they also fix dissolved inorganic carbon (DIC) into biomass and thus play an important role in the global carbon cycle. The release of organic compounds by these microbes may represent an as-yet unaccounted for source of dissolved organic carbon (DOC) available to heterotrophic marine food webs. Quantifying how much DIC these microbes fix and release again into the ambient seawater is critical to a complete understanding of the carbon cycle in the deep ocean.

To address this knowledge gap, a recent study grew ten diverse nitrifier cultures and measured their cellular carbon (C) content, DIC fixation yields and DOC release rates. The results indicate that nitrifiers release between 5 and 15% of their recently fixed DIC as DOC (Figure 1). This would equate to global ocean fluxes of 0.006–0.02 Pg C yr⁻.

Figure 1. DOC release by ten different chemoautotrophic nitrifying (ammonia- and nitrite-oxidizing) microbes. The diversity of marine nitrifiers used in this study comprises all genera currently available as axenic cultures. Species and strain names are given for completeness.

Our results provide values for biogeochemical models of the global carbon cycle, and help to further constrain the relationship between C and N fluxes in the nitrification process. Elucidating the lability and fate of carbon released by nitrifiers will be the crucial next step to understand its implications for marine food-web functioning and the biological sequestration of carbon in the ocean.

Authors:
Barbara Bayer (University of California, Santa Barbara and University of Vienna)
Kelsey McBeain (University of California, Santa Barbara)
Craig A. Carlson (University of California, Santa Barbara)
Alyson E. Santoro (University of California, Santa Barbara)

Enhanced-warming Kuroshio Current experiences rapid seawater acidification and CO2 increase

Posted by mmaheigan

· Thursday, March 30th, 2023

In order to project the future states of the climate and the marine ecosystem it is vital to understand the long-term changes in ocean carbon chemistry driven by anthropogenic influence. A paucity of data make the rates of seawater acidification and partial pressure of CO₂ (pCO₂) rise on ocean margins highly uncertain.

Figure 1. Graphic summary of 9 years of data from the Kuroshio Current time-series: (a) under the influences of only atmospheric CO2 increase, (b) the combined effect of atmospheric CO2 increase, SST increase, and additional DIC supply, (c) annually averaged air-sea CO2 flux decrease, (d) Projected seawater pCO2 increase under SST rise and sustained DIC increase.

A recent study in Marine Pollution Bulletin documented the rapid increase of seawater pCO₂ (3.70±0.57 matm year^-1) and acidification (pH at -0.0033±0.0009 unit year^-1) along Kuroshio in the East China Sea (Figure 1). These findings were based on nine years of time-series data ( 2010-2018) which are now available on the website of Japan Meteorological Agency (JMA). These trends are significantly greater than the expected rates from CO₂air-sea equilibrium and those reported from other oceanic time-series studies. Interestingly, they showed the contribution of each parameter such as sea surface temperature (SST), sea surface salinity (SSS), and normalized dissolved inorganic carbon (nDIC) and total alkalinity (nTA) to the pCO₂ variability. Seawater warming caused rapid rates of pCO₂increase and acidification under sustained DIC increase. The faster pCO₂growth relative to the atmosphere resulted in the CO₂uptake through the air-sea exchange declining by ~50% (~-0.8 to -0.4 mol C m^-2 y^-1) over the study period.

If this trend continues and the atmospheric CO₂increases at its current rate, the rapid warming Kuroshio regions could change from a sink to a source of CO₂ , and cause a loss of oceanic CO₂ uptake in the near future (ca. 2030-2040). Further, other “warming hotspots” in the global ocean along western boundary currents with a continuous DIC supply may exhibit similarly accelerated acidification and pCO₂ rise. This could lead to a significant reduction in ocean CO₂ uptake.

Authors:
Shou-En Tsao (Institute of Oceanography, National Taiwan University, Taiwan)
Po-Yen Shen (Institute of Oceanography, National Taiwan University, Taiwan)
Chun-Mao Tseng^* (Institute of Oceanography, National Taiwan University, Taiwan)

Severe warming = 15% increase in bacterial respiration: Southern Ocean most impacted

Posted by mmaheigan

· Thursday, March 30th, 2023

The utilization, respiration, and remineralization of organic matter exported from the ocean surface to its depths are key processes in the ocean carbon cycle. Marine heterotrophic Bacteria play a critical role in these activities. However, most three-dimensional (3-D) coupled physical-biogeochemical models do not explicitly include Bacteria as a state variable. Instead, they rely on parameterization to account for the bacteria’s impact on particle flux attenuation.

A recent study examined how bacteria respond to climate change by employing a 3-D coupled ocean biogeochemical model that incorporates explicit bacterial dynamics. The model (CMCC-ESM2) is a part of the Coupled Model Intercomparison Project Phase 6. The authors first evaluated the reliability of century-scale forecasts (2015-2099) for bacterial stocks and rates in the upper 100 m layer against the compiled measurements from the contemporary period (1988-2011). Next the authors analyzed the predicted trends in bacterial stocks and rates under diverse climate scenarios and explored their association with regional differences in temperature and organic carbon stocks. Three crucial findings were revealed. There is a global-scale decrease in bacterial biomass of 5-10%, with a 3-5% increase in the Southern Ocean (Figure 1). In the Southern Ocean, the rise in semi-labile dissolved organic carbon (DOC) leads to an increase in DOC uptake rates of free-living bacteria; in the northern high and low latitudes, the increase in temperature drives the increase in their DOC uptake rates. Importantly, extreme warming could result in a global increase (up to 15%) and even higher in the Southern Ocean (21% increase) in bacterial respiration (Figure 1), potentially leading to a decline in the biological carbon pump.

This analysis is an unprecedented and early effort to understand the climate-induced changes in bacterial dynamics on a global scale in a systematic manner. This study takes us one step closer to comprehending how bacteria influence the functioning of the biological carbon pump and the distribution of organic carbon pools between surface and deep layers, especially their response to climate change.

Figure 1. Global projections of bacterial carbon stocks and rates during the baseline period (1990-2013) and their changes as anomalies under the most-severe climate change scenario (i.e., SSP5-8.5) relative to the baseline period (2076-2099). The stocks and rates during the baseline period (a, b, c, g, h, i) and their changes as anomalies under the most-severe climate change scenario (d, e, f, j, k, l). All variables are depth-integrated in the upper 100 m. Solid-line contours as standard deviation from averaging over 1990-2013. Anomalies are 2076-2099 average values relative to 1990-2013 average values. Global bacterial biomass has decreased by 5-10%, with a 3-5% increase in the Southern Ocean. However, extreme warming may increase bacterial respiration worldwide, thereby reducing the efficiency of the biological carbon pump. This study provides an early attempt to understand the response of bacteria to climate change and their impact on the distribution of organic carbon in the ocean.

Author
Heather Kim, Woods Hole Oceanographic Institution

Small particles contribute significantly to the biological carbon pump in the subpolar North Atlantic

Posted by mmaheigan

· Monday, February 13th, 2023

The ocean’s biological carbon pump (BCP) is a collection of processes that transport organic carbon from the surface to the deep ocean where the carbon is sequestered for decades to millennia. Variations in the strength of the BCP can substantially change atmospheric CO₂ levels and affect the global climate. It is important to accurately estimate this carbon flux, but direct measurement is difficult so this remains a challenge.

Figure 1. (a) A schematic illustrating the downward transport of small and large POC into the deep ocean and the subsequent remineralization and fragmentation which breaks large POC into small POC. (b) Trajectories of BGC-Argo float segments. (c) Relative contributions to the annually averaged vertical carbon flux show the dominant role of gravitational sinking flux of large POC as well as the significant contributions from small POC at 100 m due to different mechanisms and at 600 m due to fragmentation.

A recent paper published in Limnology and Oceanography performed a novel mass budget analysis using observations of dissolved oxygen and particulate organic carbon (POC) from BGC-Argo floats in the subpolar North Atlantic. The authors assessed relative importance of different mechanisms contributing to the BCP and related processes, the sinking velocity and remineralization rate of different particle size classes as well as the rate of fragmentation which breaks large particles into smaller ones. Results suggest that on annual timescales, the gravitational settling of large POC is the dominant mechanism. Small POC supplements the vertical carbon flux at 100 m significantly, through various mechanisms, and contributes to carbon sequestration below 600 m due to fragmentation of large POC. In addition, sensitivity experiments highlight the importance of considering remineralization and fragmentation when estimating the vertical carbon flux of small POC.

This novel method provides additional independent constraints on current estimates and improves our mechanistic understanding of the BCP. In addition, it demonstrates the great potential of BGC-Argo float data for studying the biological carbon pump.

Authors:
Bin Wang (Dalhousie University)
Katja Fennel (Dalhousie University)

An expanding understanding of Southern Ocean productivity and export

Posted by mmaheigan

· Monday, February 13th, 2023

Biology in the Southern Ocean is known to help regulate Earth’s climate by capturing and eventually sequestering carbon from its surface. Unfortunately, accurate estimates of the magnitude of the Southern Ocean (SO) biological carbon sink are limited and subject to ongoing debate. However, a recently published study used the expanding Southern Ocean BGC-Argo fleet to provide new estimates of SO Annual Net Community Production (ANCP) and export production.

Over long enough time and space scales (>1000 km and seasons), ANCP is equal to the amount of carbon fixed during photosynthesis that is not remineralized in the surface layer. What remains is available to be exported to depth. As this organic matter sinks out of the surface ocean, most of it is eventually remineralized by bacteria, leaving behind a signature of depleted oxygen. With enough floats, basin-scale ANCP can be estimated from the seasonal oxygen drawdown measured across their profiles. While similar studies have been carried out on single floats, here, the authors construct a composite of all available profiles and include a greater depth range than previously considered.

Figure 1. All available BGC-ARGO float profiles (25,512) were used to create an A) ensemble seasonal cycle in surface chlorophyll and sub-surface oxygen. B) Annual Net Community Production (ANCP) was then estimated by computing the depth-integrated oxygen depletion during the productive period. C) ANCP was estimated across 12 major regions, separated by the Indian, Pacific and Atlantic basins and Subantarctic (SAZ), Polar (PFZ), Antarctic (AZ), and Southern (S) frontal zones. Each region used 100s-1000s of individual float profiles (color-coded scatter points).

Results from this novel approach estimate SO ANCP (and ~export) at 3.89 GT C year^-1, with basin-scale regional estimates as much as a factor 2.8 larger than previous studies. Moreover, nearly 30% of remineralization was measured at depths not typically considered, with 14% below 500 m and another 15% immediately below the euphotic depth but above 100 m. These values suggest a more critical role for the Southern Ocean in regulating oceanic carbon storage, atmospheric CO₂ exchange, and climate than previously thought.

Authors:
Jiaoyang Su (University of Tasmania, Australia)
Christina Schallenberg (University of Tasmania, and Australian Antarctic Program Partnership)
Tyler Rohr (Australian Antarctic Program Partnership)
Peter G. Strutton (University of Tasmania, Australia)
Helen E. Phillips (University of Tasmania, and Australian Antarctic Program Partnership)

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.

Author Archive for mmaheigan – Page 9

OCB supports ECR participation in 2023 Cornell Satellite Remote Sensing course

Filter by Keyword