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Archive for New OCB Research – Page 7

The most important 234Th disequilibrium compilation you ever saw

Posted by mmaheigan

· Thursday, August 25th, 2022

Thorium-234 (²³⁴Th), a naturally radioactive element present in nature, is one of the most actively used tracers in oceanography. ²³⁴Th is widely used to study the removal rate of material on sinking particles from the upper ocean, known as “scavenging,” and for determining the downward flux of carbon. Starting in 1969, ocean measurements of the ²³⁴Th temporal distribution in the hydrologic cycle comprise an indispensable component of oceanographic expeditions. However, even after five decades and extensive use of ²³⁴Th to understand natural aquatic processes, there are major gaps in this tool, no unified compilation of ²³⁴Th measurements and no centralized source for ²³⁴Th data.

A new study aims to fill these gaps with a comprehensive global oceanic compilation of ²³⁴Th measurements in a single open-access, long-term, and dynamic repository. They collated over 50 years of results from researchers and laboratories, 379 oceanographic expeditions, and more than 56 600 ²³⁴Th data points from over 5000 locations spanning every ocean. These data are archived on PANGAEA® (Ceballos-Romero et al., 2021, see references below).

This paper introduces the dataset in context via informative and descriptive graphics and a broad overview of the data sets, with potential uses for future studies. A historical review of 50 years of the ²³⁴Th technique is included also, covering four well-distinguished eras that are marked by four seminal publications that changed the course of the ²³⁴Th technique and impact on oceanography.

Map showing the distribution of sampling stations cataloged as i) unpublished (yellow diamonds), ii) published exclusively in repositories (blue square), and iii) published in referred journals (magenta circles).

This compilation is especially relevant to present and future investigations of the biological carbon pump (BP), which transports carbon to the deep ocean and regulates atmospheric CO₂ levels. In the last few decades, scientists have made considerable progress on unraveling the behavior of the BP. However, many questions on how the mechanisms function and shape carbon dynamics and the ocean carbon cycle remain unknown. The authors emphasize that many analyses of BP processes could benefit from utilizing ²³⁴Th data. The authors list a number of applications that could derive from this impressive data set, such as establishing the distribution of the probability of ²³⁴Th reaching equilibrium (or not) with its parent at 100 m. This distribution allows extracting i) the number of data points in the compilation that could be used to evaluate processes in the upper ocean (e.g., export flux and export efficiency) or ii) scavenging rates of trace metals or particle sinking velocities using “deficit” ratios, as well as those that could be used to study processes such as particle remineralizations by using the “excess” ratios. This compilation provides a valuable resource to better understand and quantify how the contemporary oceanic carbon uptake functions and how it may change in the future. This tool can be served as a focal point for the ²³⁴Th community under the principles of openness and reproducibility.

Authors

Elena Ceballos-Romero (University of Sevilla and WHOI)
Ken O. Buesseler (WHOI)
María Villa-Alfageme (University of Sevilla)

References
Ceballos-Romero, E., Buesseler, K. O. and Villa-Alfageme, M. (2022) ‘Revisiting five decades of 234Th data: a comprehensive global oceanic compilation’, Earth System Science Data, 14(6), pp. 2639–2679. doi: 10.5194/essd-14-2639-2022.

Ceballos-Romero, E., Buesseler, K. O., Muñoz-Nevado, C., and Villa-Alfageme, M. (2021) ‘More than 50 years of Th-234 data: a comprehensive global oceanic compilation‘, PANGAEA. doi: 10.1594/PANGAEA.918125.

Chemical thermodynamic models of artificial seawater and the Tris buffers used to define the ‘total’ pH scale

Posted by mmaheigan

· Thursday, August 25th, 2022

The total pH scale used by oceanographers (for salinities 20 – 40, and temperatures 0 to 45°C) is calibrated from a combination of electromotive force measurements of artificial seawaters containing either added HCl of various molalities, or equimolal Tris and its protonated form TrisH⁺. In both cases, the added H⁺ or TrisH⁺ is substituted for Na⁺ on a mole-for-mole-basis, so as to change the properties of the artificial seawater medium as little as possible. The artificial seawater itself consists of the major ions of seawater (those present in constant ratios to one another in natural seawater), with substitutions for the inorganic acid-base species present in natural seawater (principally carbonate and borate). Figure 1 shows the composition of a typical Tris buffer.

Figure 1. The composition of a buffer solution containing 0.04 mol kg-1 of Tris and TrisH+ in artificial seawater of salinity 35. The TrisH+ is substituted for an equal amount of Na+, so that the buffer has the same ionic strength as a pure artificial seawater of the same nominal salinity.

The operational definition of the total pH scale in use today involves a number of assumptions associated with the small differences between pure artificial seawater, and artificial seawater containing the buffer substance. These cannot be determined experimentally. However, a chemical thermodynamic model of the ion activities and concentrations in the buffer solutions can be used to calculate these quantities and to link measured total pH to the conventional thermodynamic total of H⁺ and HSO₄^–. Such a model can also address a series of important future applications and uses of the total pH scale:

The measurement of the total pH of natural waters whose compositions differ from seawater stoichiometry, and the extension of the scale to low salinity waters
Conversion between total pH, a measure of [H⁺] + [HSO₄^–], and ‘free’ pH (a measure of [H⁺])
Calibration of electrode pairs such as H⁺/Cl^– or H⁺/Na⁺ for the potentiometric measurement of pH

Figure 2 shows a model simulation of the operationally defined total pH and the conventional thermodynamic sum [H⁺] + [HSO₄^–] in a buffer solution of salinity 35. The linear extrapolation to zero buffer molality yields a hypothetical total pH that is used by oceanographers and is shown to be the same for both cases, demonstrating that they are the same.

Figure 2. Modelled values of the operational total pH (dashed blue line) and the conventional thermodynamic total pH (solid red line) plotted against buffer molality (mBuffer) for a salinity 35 artificial seawater at 25°C. The fine dotted lines are extrapolations of linear fits to the two groups of points. The vertical distance between marked points A and B (about 0.0045 pH units) represents the effect of differences between the two solutions – hitherto assumed out of necessity to be zero, and here calculated for the first time. The two extrapolations (fine dotted lines) intercept at point C, for which mBuffer is equal to zero and the two definitions are numerically the same.

In these two papers, we describe the development of the model of solutions containing the ions of artificial seawater plus Tris buffer. The models include uncertainty propagation (a first, for models of this type). We assess the needs for further measurements to both improve the accuracy of the model and extend it over the full range of temperatures of interest to oceanographers. We have an ongoing programme of measurements to support this work involving colleagues at the National Institute of Standards and Technology and its equivalents in Germany and Japan. In late 2022, we will be releasing for public use the software that implements two models, and also one of seawater electrolyte. If interested, please contact Heather Benway to be added to our email list, and check the website of SCOR Working Group 145 (marchemspec.org).

Read the papers about the pH buffer and artificial seawater in Marine Chemistry.

Authors:
Simon L. Clegg (School of Environmental Sciences, University of East Anglia, United Kingdom)
Matthew P. Humphreys (NIOZ Royal Netherlands Institute for Sea Research, Netherlands)
Jason F. Waters (National Institute of Standards and Technology, Gaithersburg, USA
David R. Turner (University of Gothenburg, Sweden)
Andrew G. Dickson (Scripps Institution of Oceanography, La Jolla, USA)

A new ocean state after a nuclear war

Posted by mmaheigan

· Thursday, August 25th, 2022

Russia’s invasion of Ukraine brings the threat of nuclear warfare to the forefront. But how would modern nuclear detonations impact the world today? If used accidentally or intentionally, nuclear arsenals would endanger all life on Earth. A new study published in AGU Advances provides stark information on the global impact of nuclear war in a global earth system model, with a focus on marine environments. In the simulation, nuclear firestorms release soot and smoke into the upper atmosphere that would block out the sun. This results in terrestrial crop failure and a major expansion of sea ice, but also dramatic and long-lived changes to marine biogeochemistry.

The sudden drop in light and ocean temperatures, especially in the Arctic to the North Atlantic and North Pacific, would decimate marine algae, the foundation of the marine food web, essentially creating a famine in the ocean. Eventually, marine productivity recovers, but the underlying biogeochemical cycles remain substantially altered. This occurs because even though the ocean cools rapidly after the initial conflict, when the smoke clears it does not return to the pre-war state. Instead, deep mixing and overturning during the cooling event drive a new ocean state, characterized by cooler subsurface temperatures and a shoaling of the nitracline that results in higher surface nitrate delivery. This new state favors a transition from smaller phytoplankton to diatoms with lower light requirements but higher nutrient demands. This leads to a decrease in surface iron as diatoms strip more of it from the water column once they sink. Ironically, an initial increase in surface nutrients (including iron) eventually leads to more iron stress in traditionally High Nutrient-Low Chlorophyll regions. In contrast, nitrate-limited regions such as subtropical gyres experience higher productivity. These changes last for decades, possibly centuries, following the war. We expect similar ocean biogeochemical perturbations after large cooling events driven by volcanic eruptions and asteroid impacts.

Figure Caption: A global earth system model of impacts following a large nuclear event. Net Primary Production (NPP) is dramatically reduced in the immediate aftermath of the conflict (2020-2022). Productivity begins to recover, relative to the control run, in the tropics and subtropics (2023-2026) but globally integrated NPP does not until 2029, and remains depressed at high latitudes for decades longer, despite globally integrated gains (2040). This change is largely driven by the competing effects of elevated nutrient (Surface Nitrate) and light (Surface PAR) availability.

As we come to terms with the reality that negative emissions technologies may be required to meet acceptable emissions pathways, there is an obvious and troubling analog. The inertia of physical and biogeochemical processes in the ocean means that once they have been sufficiently disturbed, they may not recover rapidly, if ever.

Authors:

Cheryl S. Harrison, Tyler Rohr, Alice DuVivier, Elizabeth A. Maroon, Scott Bachman, Charles G. Bardeen, Joshua Coupe, Victoria Garza, Ryan Heneghan, Nicole S. Lovenduski, Philipp Neubauer, Victor Rangel, Alan Robock, Kim Scherrer, Samantha Stevenson, Owen B. Toon

Powerful new tools for working with Argo data

Posted by mmaheigan

· Thursday, June 9th, 2022

No single program has been as transformative for ocean science over the past two decades as Argo: the fleet of robotic instruments that collect measurements of temperature and salinity in the upper 2 km of the ocean around the globe. The Argo program has been instrumental in revealing changes to ocean heat content, global sea level, and patterns of ice melt and precipitation. In addition, Biogeochemical Argo—the branch of the Argo program focused on floats with additional biological and chemical sensors—has recently shed light on topics such as regional patterns of carbon production and export, the magnitude of carbon dioxide air-sea flux in the Southern Ocean (thanks to the SOCCOM project), and the dynamics modulating ocean oxygen concentrations and oxygen minimum zones. While Argo data are publicly available in near-real-time via two Global Data Assembly Centers, there tends to be a steep learning curve for new users seeking to access and utilize the data.

To address this issue, a team led by scientists at NOAA’s Pacific Marine Environmental Laboratory developed a software toolbox available in two programming languages for accessing and visualizing Argo data— OneArgo-Mat for MATLAB and OneArgo-R for R. The toolbox includes functions to identify and download float data that adhere to user-defined time and space constraints, and other optional requirements like sensor type and data mode; plot float trajectories and their current positions; filter and manipulate float data based on quality flags and additional metadata; and create figures (profiles, time series, and sections) displaying physical, biological, and chemical properties measured by floats. Examples of figures created using the OneArgo-Mat toolbox are given below (Figure 1).

Figure 1. Example figures created using the OneArgo-Mat toolbox: (A) the trajectory of a float deployed in the North Atlantic from the R/V Johan Hjort in May of 2019, (B) a time series of dissolved oxygen at 80 dbars from that float, and (C) a vertical section plot of nitrate concentrations along the float track from the surface to 300 dbars. The black contour line in panel C denotes the mixed layer depth (MLD) based on a temperature criterion and the red line denotes the depth of the time series shown in panel B. The effects of seasonal phytoplankton blooms are evident in panel C, with mixed layer shoaling in the spring followed by drawdown of nitrate in the surface ocean. Panel B shows that, as the mixed layer deepens through the winter, the oxygen concentration at 80 dbars increases as a result of the oxygenated surface waters reaching that depth. The MATLAB code to download the required data and create all of these plots is shown (D).

The OneArgo-Mat and OneArgo-R toolboxes are intended for newcomers to Argo data, seasoned users, data managers, and everyone in between. For this reason, toolbox functions are equipped with options to streamline float selection, data processing, and figure creation with minimal user coding, if desired. Alternatively, the toolbox also provides rapid and straightforward access to the entire Argo database for experienced users who simply want to download up-to-date profile data for further processing and analysis. The authors hope these new tools will empower current Argo data users and entrain new users, especially as the US GO-BGC Project and US and international Argo partners move toward a global biogeochemical Argo fleet, which will create myriad new opportunities for novel studies of ocean biogeochemistry.

Authors
Jonathan Sharp – Cooperative Institute for Climate, Ocean, and Ecosystem Studies (CICOES) & NOAA Pacific Marine Environmental Laboratory (PMEL)
Hartmut Frenzel – CICOES & NOAA PMEL
Marin Cornec – University of Washington & NOAA PMEL
Yibin Huang – University of California Santa Cruz & NOAA PMEL
Andrea Fassbender – NOAA PMEL

What can algae tell us about translating laboratory science to nature?

Posted by mmaheigan

· Thursday, June 9th, 2022

Ocean acidification research has grown over the past few decades. Much of recent research documents negative impacts of changing carbonate chemistry on calcifying marine organisms in laboratory experiments. At the 2018 Ocean Acidification PI Meeting, a group of us asked “Can these laboratory responses to ocean acidification be scaled up to accurately predict the responses of marine ecosystems?” To answer this research question, we developed a semi-quantitative synthesis of benthic calcifying algae responses to ocean acidification, recently published in the ICES Journal of Marine Science.

Figure 1. Comparing directional responses of individuals and communities to acidification in laboratory and field settings highlights mismatches. Specifically, field studies document higher proportion of negative responses compared to laboratory experiments. We provide a series of recommendations for future research to better bridge this gap of understanding in responses to ocean acidification. Figure modified from Page et al. 2022.

We detail in the paper how the proportion of positive, neutral, and negative responses in laboratory experiments often didn’t match field observations. Additionally, laboratory experiments mainly report short-term responses (days to weeks) across tropical and temperate locations. In contrast, field studies emphasize long-term responses (months to years) from fewer global locations. Using our synthesis, we developed nine recommendations that will enhance our ability to translate laboratory experiment results into actual responses of marine taxa to ongoing and future acidification in the natural environment. These future research directions are applicable not only to ocean acidification studies but can be directly applied to the broader field of climate change. We hope these recommendations will lead to greater confidence in our projections of climate change impacts at different ecological scales, and better inform the conservation and management of our valuable marine ecosystems.

Backstory

Initially, we set out to answer this research question through a meta-analysis comparing the effect size of the impacts of ocean acidification on benthic calcifying macroalgae in laboratory and field settings. We quickly realized this approach was not going to work because of the much smaller number of responses recorded in field settings, the different methods used, and response parameters measured between the laboratory and field; these differences made calculating and comparing effect sizes impossible. Therefore, we landed on the approach of conducting a semi-quantitative synthesis to compare directional responses in laboratory and field settings. The results of this synthesis and the process of developing a robust research approach to answer our question inspired us to discuss and develop the recommendations for future research presented in the paper.

Authors (affils and Twitter handles)
Heather N. Page (Sea Education Association) @heathernicopage
Keisha D. Bahr (Texas A&M University – Corpus Christi) @thebahrlab
Tyler Cyronak (Nova Southeastern University) @tcyronak
Elizabeth B. Jewett (National Oceanic and Atmospheric Administration) @LibbyJewett
Maggie D. Johnson (King Abdullah University of Science and Technology) @MaggieDJohnson
Sophie J. McCoy (University of North Carolina at Chapel Hill) @MarEcology

What drives decadal changes in the Chesapeake Bay carbonate system?

Posted by mmaheigan

· Tuesday, May 3rd, 2022

Understanding decadal changes in the coastal carbonate system (CO₂-system) is essential for predicting how the health of these waters is affected by anthropogenic drivers, such as changing atmospheric conditions and terrestrial inputs. However, studies that quantify the relative impacts of these drivers are lacking.

A recent study in Journal of Geophysical Research: Oceans identified the primary drivers of acidification in the Chesapeake Bay over the past three decades. The authors used a three-dimensional hydrodynamic-biogeochemistry model to quantify the relative impacts on the Bay CO₂-system from increases in atmospheric CO₂, temperature, oceanic dissolved inorganic carbon (DIC) concentrations, terrestrial loadings of total alkalinity (TA) and DIC, as well as decreases in terrestrial nutrient inputs. Decadal changes in the surface CO₂-system in the Chesapeake Bay exhibit large spatial and seasonal variability due to the combination of influences from the land, ocean and atmosphere. In the upper Bay, increased riverine TA and DIC from the Susquehanna River have increased surface pH, with other drivers only contributing to decadal changes that are one to two orders of magnitude smaller. In the mid- and lower Bay, higher atmospheric CO₂ concentrations and reduced nutrient loading are the two most critical drivers and have nearly equally reduced surface pH in the summer. These decadal changes in surface pH show significant seasonal variability with the greatest magnitude generally aligning with the spring and summer shellfish production season (Figure 1).

Figure 1: Overall changes in modeled surface pH (ΔpH_all) due to all global and terrestrial drivers combined over the past 30 years (i.e., 2015–2019 relative to 1985–1989). ΔpH_all includes changes in surface pH due to increased atmospheric CO2, increased atmospheric thermal forcing, increased oceanic dissolved inorganic carbon concentrations, decreased riverine nitrate concentrations, decreased riverine organic nitrogen concentrations, and increased riverine total alkalinity and dissolved inorganic carbon concentrations.

These results indicate that a number of global and terrestrial drivers play crucial roles in coastal acidification. The combined effects of the examined drivers suggest that calcifying organisms in coastal surface waters are likely facing faster decreasing rates of pH than those in open ocean ecosystems. Decreases in surface pH associated with nutrient reductions highlight that the Chesapeake Bay ecosystem is returning to a more natural condition, e.g., a condition when anthropogenic nutrient input from the watershed was lower. However, increased atmospheric CO₂ is simultaneously accelerating the rate of change in pH, exerting increased stress on estuarine calcifying organisms. For ecosystems such as the Chesapeake Bay where nutrient loading is already being managed, controlling the emissions of anthropogenic CO₂ globally becomes increasingly important to decelerate the rate of acidification and to relieve the stress on estuarine calcifying organisms. Future observational and modeling studies are needed to further investigate how the decadal trends in the Chesapeake Bay CO₂-system may vary with depth. These efforts will improve our current understanding of long-term change in coastal carbonate systems and their impacts on the shellfish industry.

Authors:
Fei Da (Virginia Institute of Marine Science, William & Mary, USA)
Marjorie A. M. Friedrichs (Virginia Institute of Marine Science, William & Mary, USA)
Pierre St-Laurent (Virginia Institute of Marine Science, William & Mary, USA)
Elizabeth H. Shadwick (CSIRO Oceans and Atmosphere, Australia)
Raymond G. Najjar (The Pennsylvania State University, USA)
Kyle E. Hinson (Virginia Institute of Marine Science, William & Mary, USA)

Unmixing deep sea sedimentary records identifies sensitivity of marine calcifying zooplankton to abrupt warming and ocean acidification in the past

Posted by mmaheigan

· Tuesday, May 3rd, 2022

Ocean acidification and rising temperatures have led to concerns about how calcifying organisms foundational to marine ecosystems, will be affected in the near future. We often look to analogous abrupt climate change events in Earth’s geologic past to inform our predictions of these future communities. The Paleocene-Eocene thermal maximum (PETM) is an apt analog for modern climate change. The PETM was a global warming and ocean acidification event driven by geologically abrupt changes to the global carbon cycle approximately 56 million years ago. Much of what we know about the PETM is from the study of deep sea sedimentary records and the microfossils within them. However, these records can experience intense sediment mixing—from bottom water currents and burrowing by organisms living along the seafloor—which can blur or distort the primary climate and ecological signals in these paleorecords.

PETM corrected foram graphic - see caption for detail

Figure 1. A) Frequency distribution of single-shell stable carbon isotope (δ13C) values for planktic foraminiferal shells from a deep sea sedimentary PETM record from the equatorial Pacific (n = 548). Note that 50% of shells measured record distinctly PETM values, while 49.5% record distinctly pre-PETM values. B) Comparison of diversity metric (Shannon-H) between the isotopically filtered (i.e., unmixed) and unfiltered (i.e., mixed) planktic foraminiferal assemblages.

A recent study in the Proceedings of the National Academy of Sciences used geochemical signatures measured from individual microfossil shells of planktic foraminifera (surface-dwelling marine calcareous zooplankton) to deconvolve the effects of sediment mixing on a deep sea PETM record from the equatorial Pacific. Use of this “isotopic filtering” (unmixing) method revealed that nearly 50% of shells in the PETM interval were reworked contaminants that lived before the global warming event (Figure 1A). The identification and removal of these older shells from fossil census counts drastically changed interpretations of how these organisms responded to the PETM. Prior interpretations assumed that planktic foraminiferal communities living near the equator diversified during the PETM. However, by deconvolving the effects of sediment mixing on the same equatorial deep sea record, researchers found that these communities actually suffered an abrupt decrease in diversity at the onset of the PETM (Figure 1B). This decrease is likely due to several taxa migrating towards the poles to escape the extreme heat of the tropics and lower oxygen conditions found at deeper water depths (i.e., thermocline) during the PETM. Additionally, some taxa may have undergone morphological changes, signaling reduced calcification, in response to extreme acidifying conditions. Today, anthropogenic carbon emission rates are ~10 times faster than the carbon cycling perturbation that triggered the PETM. Although planktic foraminifera and other key zooplankton survived the PETM, these communities suffered at the hands of extreme sea surface temperatures and acidifying waters, and may not be able to cope the rate of environmental changes in our ocean over the coming centuries.

Authors:
Brittany N. Hupp (University of Wisconsin-Madison)
D. Clay Kelly (University of Wisconsin-Madison)
John W. Williams (University of Wisconsin-Madison)

How do coccolithophores survive the darkness?

Posted by mmaheigan

· Friday, April 1st, 2022

Coccolithophores have survived several major extinction events over geologic time. The most significant was the asteroid impact at the K/T boundary, followed by months of darkness. Additionally, coccolithophores regularly reside in the twilight zone, just beyond the reach of sunlight. A paper recently published in the New Phytologist addresses how these photosynthetic algae can persist and grow, albeit slowly, in darkness using osmotrophy.

The authors discovered that the osmotrophic uptake of certain types of dissolved organic carbon (DOC) can support survival in low light. They completed a 30-day darkness experiment to determine how the concentration of several DOC compounds affects growth. The coccolithophore species Cruciplacolithus neohelis growth rate increased with the increasing concentration of dissolved organic compounds. They also examined the kinetics of short-term uptake of radiolabeled DOC compounds and found that the uptake rate generally showed Michaelis-Menten-like saturation kinetics. All radiolabeled DOC compounds were incorporated into the POC fraction, but surprisingly also into the particulate inorganic carbon (PIC) fraction (i.e., calcite coccoliths).

These results suggest that osmotrophic uptake in coccolithophores may be significant enough to be included in carbon cycle models, especially if they can simultaneously take up a wide range of organic compounds. Surprisingly, we detected ¹⁴C-DOC in the PIC fraction after only 24 hours. This remarkably rapid incorporation is most likely due to the respiration of radiolabeled DOC into dissolved inorganic carbon (DIC), subsequently used by coccolithophores for calcification. These results have implications for the biological carbon pump and alkalinity pump paradigms, as we confirmed that both POC and PIC originate from DOC on short time scales.

Predators Set Range for the Ocean’s Most Abundant Phytoplankton

Posted by mmaheigan

· Friday, April 1st, 2022

Prochlorococcus is the world’s smallest phytoplankton (microscopic plant-like organisms) and the most numerous, with more than ten septillion individuals. This tiny plankton lives ubiquitously in warm, blue, tropical waters but is conspicuously absent in more polar regions. The prevailing theory was the cold: Prochlorococcus doesn’t grow at low temperatures. In a recent paper, the authors argue ecological control, in particular, predation by zooplankton. Cold polar waters are greener because they contain more nutrients, leading to more life and more organic matter production. This production feeds more and larger heterotrophic bacteria, who then feed larger predators—specifically the same zooplankton that consume Prochlorococcus. If the shared zooplankton increases enough, it will consume Prochlorococus faster than it can grow, causing the species to collapse at higher latitudes. These results show that an understanding of both ecology and temperature is required to predict how these ecosystems will shift in a warming ocean.

Figure 1: Surface populations of Prochlorococcus collapse (dashed lines) moving northward from Hawaii as seen in transects (transect line shown in red on map, lower left) from cruises in April 2016 (black dots) and September 2017 (green triangles). This collapse of the Prochlorococcus emerges in dynamical computer models (lower right, color indicates Prochlorococcus biomass in mgC/m3) when heterotrophic bacteria and Prochlorococcus share a grazer (top schematic). Increased organic production heading poleward first increases the heterotrophic bacterial population, increasing the shared zooplankton population which eventually consumes Prochlorococcus faster than it can grow (dashed contour).

Authors
Christopher L. Follett (MIT)
Stephanie Dutkiewicz (MIT)
François Ribalet (UW)
Emily Zakem (USC)
David Caron (USC)
E. Virginia Armbrust (UW)
Michael J. Follows (MIT)

Decline in spring chlorophyll-a concentrations in response to COVID-19 lockdown in the Yellow Sea

Posted by mmaheigan

· Friday, February 18th, 2022

Recently, it was reported that the coronavirus (COVID-19) pandemic-related lockdowns have led to a reduction in anthropogenic emissions of pollutant nitrogen on a global scale. This reduction may have induced a change in marine environmental conditions, providing a natural experiment for determining its impact on marine ecosystems. However, a direct cause-effect relationship between COVID-19 and the phytoplankton biomass has not yet been fully explored.

A recent study published in Marine Pollution Bulletin, investigated a change in satellite-derived chlorophyll-a concentrations (Chl-a) as a result of the COVID-19 lockdown. The high productivity of the Yellow Sea ecosystem is considered to be significantly attributable to high nutrient supply via atmospheric deposition from nearby anthropogenic sources of air pollution, making it an ideal location to observe this natural experiment. Further, they evaluated a significant contributing factor to change in irradiance, vertical mixing, coastal influence, and air pollutant deposition through a comparative analysis of in situ, reanalysis, and satellite-derived datasets during February‒May 2020 (representing the period of COVID-19 lockdown effect) as compared to the same period in the previous five-years (2015–2019; representing the period of no COVID-19 lockdown).

Figure 1. (a) The spatial distribution of the difference in the monthly mean Chl-a concentrations over the Yellow Sea between 2020 and 2015–2019 (ΔChl-a_{2020 ‒ mean} (2015–2019)) in February, March, April, and May. (b) The monthly mean Chl-a averaged for the Yellow Sea (32.625–41.625 °N, 117.375–127.375 °E) during February to May 2015–2019 (pink marker) and 2020 (cyan marker). The vertical solid lines represent their standard deviation for the 2015–2019.

The authors captured a significant decline in Chl-a (~30%) over the Yellow Sea during February‒May 2020 compared to February‒May 2015‒2019 (Figure 1). Variations of irradiance, vertical mixing, and river discharges, were not major factors affecting this decline. Based on the analysis of transportation and constituent of atmospheric pollutants from Northern China (i.e., representing main source region of atmospheric pollutants) to Yellow Sea, the decline in Chl-a over the Yellow Sea during spring 2020 was mainly attributed to decreased atmospheric nutrient deposition due to the COVID-19 lockdown effect, a consequence of decreased anthropogenic emissions in the Northern China. Thus, further investigation is required to assess the Yellow Sea ecosystem response to re-increasing anthropogenic activities once the COVID-19 lockdown restrictions are lifted.

Authors:
Joo-Eun Yoon (Centre for Climate Repair at Cambridge, Cambridge University)
Seunghyun Son (CIRA, Colorado State University)
Il-Nam Kim (Department of Marine Science, Incheon National University)

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

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