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

Archive for New OCB Research – Page 2

Fast-sinking salp and fish detritus impacts OMZ size and ocean biogeochemical cycles

Posted by mmaheigan

· Thursday, September 12th, 2024

Marine fishes and filter-feeding gelatinous zooplankton such as salps and pyrosomes generate detritus in the form of poop and dead carcasses, which sink ~10 times faster than other oceanic detritus. This detritus is hypothesized to have a disproportionally large impact on the marine biological pump as it sequesters carbon and nutrients deeper in the water column. Until now, global models had not considered these fluxes, thus, their impacts on ocean biogeochemical cycles were not well understood.

A recent study in Geophysical Research Letters investigated the sensitivity of deep ocean carbon, oxygen, and nutrient cycles to fast-sinking detritus from filter-feeding gelatinous zooplankton (pelagic tunicates) and fishes, using a modified version of the NOAA-GFDL ocean biogeochemical model COBALT (“GZ-COBALT”). We found the fast-sinking detritus decreased surface productivity and export, while increasing transfer efficiency and sequestration at depth. Ocean oxygen minimum zones (OMZs) also decreased in size: fast-sinking detritus triggered less remineralization, particularly in the mid-depths, resulting in less oxygen consumption and a reduced expansion of OMZs.

Figure caption: Flux of detrital carbon at various depths (A, B, C), shows that incorporating fast-sinking detritus counter-intuitively decreases carbon export from the surface while increasing sequestration at depth. Particulate organic carbon (POC) export flux at (A) 100 m, (B) 1,000 m and (C) seafloor (mgC/m2/d), shows (left) the control simulation with no fast-sinking detritus, (center) the experiment with fast-sinking fish and gelatinous zooplankton detritus, and (right) the differences between the control and fast-sinking detritus simulation. (D) Total ocean volume over the 300-year simulation at the suboxic (O2 ≤ 5 mmol/m3) level, shows the simulation with fast-sinking particulate organic carbon (red) had lower suboxia than the control (black). Large hypoxic and suboxic zones are a common model bias; these results suggest that fast-sinking detritus may be one biogeochemical mechanism to reduce the expansion of these low oxygen zones.

Past observations have shown that fast-sinking, highly reactive detritus reaching the seafloor can fuel significant benthic consumption and respiration. On a global scale, we suggest that the increased fluxes to the seafloor in the model can be supported by observational constraints of seafloor oxygen consumption, suggesting that these processes could be realistically incorporated into future generations of Earth System Models.

Authors
Jessica Y. Luo (NOAA GFDL)
Charles A. Stock (NOAA GFDL)
John P. Dunne (NOAA GFDL)
Grace K. Saba (Rutgers University)
Lauren Cook (Rutgers University)

The fate of the 21st century marine carbon cycle could hinge on zooplankton’s appetite

Posted by mmaheigan

· Wednesday, September 11th, 2024

Both climate change and the efforts to abate have the potential to reshape phytoplankton community composition, globally. Shallower mixed layers in a warming ocean and many marine CO₂ removal (CDR) technologies will shift the balance of light, nutrients, and carbonate chemistry, benefiting certain species over others. We must understand how such shifts could ripple through the marine carbon cycle and modify the ocean carbon reservoir. Two new publications in Geophysical Research Letters and Global Biogeochemical Cycles highlight an often over looked pathway in this response: The appetite of zooplankton.

We have long known that the appetite of zooplankton—i.e. the half-saturation concertation for grazing—varies dramatically. This variability is largely based on laboratory incubations of specific species. An open-ocean perspective has been much more elusive. Using two independent inverse modelling approaches, both studies reached the same conclusion: Even at the community level, the appetite of zooplankton in the open-ocean is incredibly diverse.

Moreover, variability in zooplankton appetites maps well onto the biogeography of phytoplankton species. As these phytoplankton niches evolve, the composition of the zooplankton will likely follow. To help understand the impact of this response on the biological pump, we compared two models, one with only two types of zooplankton, and another with an unlimited amount, each with different appetites, all individually tuned to their unique environment. Including more realistic diversity reduced the strength of the biological pump by 1 PgC yr^-1.

Figure Caption. A) Variability in the abundance and characteristic composition of phytoplankton drives B) large differences in the associated appetite and characteristic composition of zooplankton in two independent inverse modelling studies. C) When more realistic diversity in the appetite of zooplankton is simulated in models, the strength of biological pump is dramatically reduced.

That is the same order as the most optimistic scenarios for ocean iron fertilization. This means that when simulating the efficacy of many CDR scenarios, the bias introduced by insufficiently resolved zooplankton diversity could be just as large as the signal. Moving forward, it is imperative to improve the representation of zooplankton in Earth System Models to understand how the marine carbon sink will respond to inadvertent and deliberate perturbations.

Authors (GRL):
Tyler Rohr (The University of Tasmania; Australian Antarctic Program Partnership)
Anthony Richardson (The University of Queensland; CSIRO)
Andrew Lenton (CSIRO)
Matthew Chamberlain (CSIRO)
Elizabeth Shadwick (Australian Antarctic Program Partnership; CSIRO)

Authors (GBC):
Sophie Meyjes (Cambridge)
Colleen Petrick (Scripps Institute of Oceanography)
Tyler Rohr (The University of Tasmania; Australian Antarctic Program Partnership)
B.B. Cael (NOC)
Ali Mashayek (Cambridge)

Plankton plummet in one of the world’s longest time series

Posted by mmaheigan

· Friday, August 2nd, 2024

Phytoplankton are the main primary producers in the ocean and fuel marine food webs. Long-term shifts in phytoplankton biomass are useful for understanding the context of short-term changes and for examining the relationships between climate indices and phytoplankton dynamics. However, current monitoring programs often offer too short a time frame to disentangle these relationships.

In a recent publication in the Proceedings of the National Academy of Sciences, data from the Narragansett Bay, RI Long-Term Plankton Time Series, were used to examine long-term trends in Chlorophyll a, a proxy for phytoplankton biomass. The magnitude of the winter-spring bloom and of annual phytoplankton biomass declined by about half from 1968 to 2019 (Figure 1). The winter–spring bloom, which fuels coastal ecosystems, occurred about five days earlier each decade. The authors found these changes were associated with multiple environmental factors impacted by climate change, including warming surface seawater temperatures and reduced nutrient concentrations.

Figure 1: In addition to long-term trends, the authors observed that phytoplankton biomass in Narragansett Bay was highly variable similar to other coastal and open ocean time series they analyzed. A high degree of variation in phytoplankton biomass means that it can take decades to identify a trend from the noise in a dataset. This highlights the need to sustain ecosystem monitoring of phytoplankton and other environmental factors for the long term globally. These results provide the first step to understanding the effect of climate change and anthropogenic inputs at the base of the food web, which will inform future research to determine how this change implicates the rest of the ecosystem.

A major secondary component of this study was the digitization of much of the historical dataset from 1959-1999, which required the lead author to obtain, organize, and digitally record 30 years of physical data from a storage closet and harmonize it with digitized data from 2000-2019. All biological and environmental data from this time series are now publicly available at BCO-DMO for scientists, managers, and educators to explore and utilize.

Authors:
Patricia S. Thibodeau (University of New England) @PattyPlankton
Gavino Puggioni (University of Rhode Island)
Jacob Strock (University of Rhode Island)
David G. Borkman (Rhode Island Department of Environmental Management, Office of Water Resources–Shellfish)
Tatiana A. Rynearson (University of Rhode Island) @RynearsonLab

A New Insight into Ocean Carbon Sequestration

Posted by mmaheigan

· Thursday, August 1st, 2024

How does the microbial carbon pump (MCP) redefine our understanding of oceanic carbon sequestration and climate change mitigation?

A recent study published in Nature Reviews Microbiology reviews the pivotal role of the microbial carbon pump (MCP) a novel concept differing from the known mechanisms for carbon sequestration in the ocean, the Biological Carbon Pump (BCP), the Carbonate Counter Pump (CCP), and the Solubility Carbon Pump (SCP) (Figure 1).

Figure 1 Illustration of the microbial carbon pump (MCP) and other carbon pumps, outlining their relationships and modes of carbon transformation and sequestration in the ocean.

Unlike the others, the MCP operates independently of physical processes like vertical transportation and sedimentation; it is driven by microbial processes at every depth in the water column, and functions as a two-way pump of carbon cycle, thus playing a unique role in regulation of climate change. The MCP’s role in transforming dissolved organic carbon (DOC) from labile states into refractory states, reveals the “enigma” of how the oceanic refractory DOC (RDOC) reservoir is formed. This paper also illustrates the dual functions of the MCP-regulated oceanic carbon reservoir over geological timescales, which may help explain the “eccentricity puzzle” in the Milankovitch climate theory.

The spatial and temporal distribution of RDOC is influenced by various microbial processes and the paper details how the MCP responds to environmental changes across environmental gradients and the entire water column. We also revealed the impacts of climate change on microbial activities and carbon sequestration efficiency, which in turn affect carbon cycles across different oceanic regions and depths. We explored the synergistic effects of the MCP with BCP, CCP, and SCP (BCMS), which could have great potentials in geoengineering. Applications of BCMS approach make it possible for international program on Ocean Negative Carbon Emissions (ONCE) practice for both of carbon sink enhancement and ecosystem sustainable development, such as scenarios of sea-farming areas and wastewater treatment plants, avoiding the potential risks of traditional geoengineering approaches.

Understanding the MCP processes and effects is essential for accurate assessment of the ocean’s capacity to mitigate climate change, and how the MCP can support potential modes of geoengineering. The findings and implications are of profound reference for policymakers, environmental stakeholders, and funding agencies for strategies to fight climate changes, leverage more effective preservation and restoration of ecosystems.

Authors:
Nianzhi Jiao (Xiamen University)
Tingwei Luo (Xiamen University)
Quanrui Chen (Xiamen University)
Zhao Zhao (Xiamen University)
Xilin Xiao (Xiamen University)
Jihua Liu (Shandong University)
Zhimin Jian (Tongji University)
Shucheng Xie (China University of Geosciences)
Helmuth Thomas (Helmholtz-Zentrum Hereon)
Gerhard J. Herndl (University of Vienna)
Ronald Benner (University of South Carolina)
Micheal Gonsior (University of Maryland)
Feng Chen (University of Maryland)
Wei-Jun Cai (University of Delaware)
Carol Robinson (University of East Anglia)

Out of sight, out of mind: extreme signals of ocean acidification hidden in the mesopelagic

Posted by mmaheigan

· Wednesday, July 31st, 2024

Ocean Acidification (OA), caused by the air-to-sea transfer of anthropogenic carbon (C_ant), is intuitively thought to be a surface-intensified process, which makes sense because the concentration of C_ant is greatest near the ocean surface and decreases with depth. But this intuition is not correct for multiple metrics of OA that are less commonly studied below the sea surface, including the partial pressure of carbon dioxide gas (pCO₂) and the hydrogen ion concentration ([H⁺]).

We braved the quiescent seas of a three-dimensionally mapped data product (Lauvest et al., 2016) hunting for signals of OA in the deep. Just like anyone who seeks moss in Seattle, we were successful. We identified massive interior ocean changes in pCO₂ and [H⁺] caused by the accumulation of C_ant (up to the year 2002). Such signals were not clearly identifiable for the more commonly studied pH and aragonite saturation state OA metrics. Extreme pCO₂ and [H⁺] changes induced by smaller amounts of C_ant at depth are caused by greater sensitivities of these parameters to carbon addition in subsurface waters that are weakly buffered because they have experienced significant organic matter respiration. This results in mesopelagic pCO₂ (and [H⁺]) changes that are more than twice as large as overlying surface water changes throughout large expanses of the ocean, outpacing the atmospheric pCO₂ change that drives OA itself (ΔpCO_{2 Air} of ~92 μatm in year 2002).

Yikes! What should we investigate next? Well, it may be that the re-emergence of high-pCO₂, mesopelagic waters at the sea surface could cause elevated CO₂ evasion rates and reduced carbon storage efficiency in regions where waters do not have time to fully equilibrate with the atmosphere before subduction. It is also possible that the elevated signal-to-noise ratio associated with subsurface pCO₂ and [H⁺] changes could prove useful in the assessment of environmental impacts associated with some marine carbon dioxide removal strategies. More work is needed to characterize the evolution of mesopelagic OA metric changes beyond the year 2002, and what they could mean for ocean ecosystems that are already under pressure from a variety of anthropogenic stressors.

Authors:
Andrea J. Fassbender (NOAA Pacific Marine Environmental Laboratory)
Brendan R. Carter (Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington)
Jonathan D. Sharp (Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington)
Yibin Huang (Xiamen University)
Mar C. Arroyo (University of California Santa Cruz)
Hartmut Frenzel (Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington)

Publication: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GB007843

An unexpected shift to a later phytoplankton bloom in the West Antarctic Peninsula

Posted by mmaheigan

· Wednesday, May 29th, 2024

Polar regions are changing: warming, losing sea ice, and experiencing shifts in the phenology of seasonal events. Global models predict that phytoplankton blooms will start earlier in these warming polar environments. What we don’t know is will this be true for all high-latitude regions? Is the timing of phytoplankton growing season moving earlier in the West Antarctic Peninsula as this region experiences climate change?

The authors of a recent paper published in Marine Ecology Progress Series used 25 years of satellite ocean color data to track shifts in bloom phenology—the timing of recurring seasonal events. Contrary to predictions, the results show that the spring bloom start date is shifting later over time. Figure 1 shows that in the waters experiencing seasonal sea ice, from 1997 to 2022, the start and peak date of the phytoplankton growing season are shifting later. However, there is no overall decline in total annual chlorophyll-a, because in the fall (February-April) chlorophyll-a concentrations are increasing over time.

The most likely driver of earlier spring bloom start dates is increased wind mixing. Spring (October-December) wind speed has been increasing over time concurrent with delayed bloom start dates. In an ecosystem with less sea ice than previous decades, more open water exposed to increased wind speed may mix phytoplankton more deeply in spring, delaying the bloom until the onset of summer stratification.

Even though global climate models predict bloom timing will shift earlier with climate change, this may not be the case in specific polar regions like the West Antarctic Peninsula. Later bloom timing could impact surface ocean carbon uptake, phytoplankton community composition, and ecosystem health. If the timing and composition of blooms is changing, that shifts will affect the food quantity and quality available to krill and higher trophic level organisms.

Author
Jessie Turner (University of Connecticut) @jessiesturner

Figure 1: In recent years the timing of the annual phytoplankton bloom in the Mid Shelf region of the West Antarctic Peninsula has shifted: satellite-derived chlorophyll-a concentration in recent years (pink line) shows a significant delayed bloom start date compared to past years (blue line).

Inorganic carbon outwelling as important blue carbon sink

Posted by mmaheigan

· Wednesday, May 29th, 2024

Blue carbon ecosystems—mangroves, saltmarshes, and seagrass meadows—carbon sequestration powerhouses that can help us mitigate climate change. For many years, our community has focused on studying and quantifying organic carbon storage in the soils of these ecosystems and crediting it as Blue Carbon in carbon markets.

A new paper in Nature Communications reveals that much of that carbon sequestered by mangroves and saltmarshes is actually exported as inorganic carbon to the ocean. Inorganic carbon export dominates blue carbon budgets and rivals or even surpasses carbon stored in soils. Inorganic carbon exports had an alkalinity: dissolved inorganic carbon ratio of 0.8 ± 0.2, impacting the carbonate system and carbon cycling along the coast. Most of the inorganic carbon is exported as bicarbonate which stays permanently dissolved in the ocean and is therefore a permanent atmospheric carbon sink. When we ignore inorganic carbon export, we highly underestimate the potential of mangroves and saltmarshes to mitigate climate change. Consequently, inorganic carbon export should be integrated into blue carbon frameworks to adequately inform carbon markets, which encourage landowners to restore and preserve mangrove and saltmarsh ecosystems.

Authors
Gloria M. S. Reithmaier (University of Gothenburg) Twitter: @GReithmaier@Barefoot_Lab
Alex Cabral (University of Gothenburg)
Anirban Akhand (Hong Kong University of Science and Technology)
Matthew J. Bogard (University of Lethbridge)
Alberto V. Borges (University of Liège)
Steven Bouillon (KU Leuven)
David J. Burdige (Old Dominion University)
Mitchel Call (Southern Cross University)
Nengwang Chen (Xiamen University)
Xiaogang Chen (Westlake University)
Luiz C. Cotovicz Jr (Leibniz Institute for Baltic Sea Research)
Meagan J. Eagle (U.S. Geological Survey)
Erik Kristensen (University of Southern Denmark)
Kevin D. Kroeger (U.S. Geological Survey)
Zeyang Lu (Xiamen University)
Damien T. Maher (Southern Cross University)
Lucas J. Pérez-Lloréns (University of Cádiz)
Raghab Ray (University of Tokyo)
Pierre Taillardat (National University of Singapore)
Joseph J. Tamborski (Old Dominion University)
Rob C. Upstill-Goddard (Newcastle University)
Faming Wang (Chinese Academy of Sciences)
Zhaohui Aleck Wang (Woods Hole Oceanographic Institution)
Kai Xiao (Southern University of Science and Technology)
Yvonne Y. Y. Yau (University of Gothenburg)
Isaac R. Santos (University of Gothenburg)

New algorithm unclogs major bottleneck in ocean geochemical and biogeochemical modelling

Posted by mmaheigan

· Thursday, May 16th, 2024

Numerical models are some of the principal tools for understanding the cycling of geochemical and biogeochemical tracers in the ocean, with the latter also being important components of the Earth System Models used to project future climate change. However, in order to use these models they must first be integrated to a seasonally-repeating equilibrium with minimal drift, a computationally expensive calculation that can take months on supercomputers given the long turnover timescale – many thousands of years – of the ocean. This “spin-up” problem has long been a major bottleneck in marine geochemical and biogeochemical modelling.

In a study published last year in J. Adv. Model. Earth Sys (2023, see reference below), a new algorithm was shown to speed-up by a factor of between 10-25 the spin-up of a wide range of geochemical tracers, such as radiocarbon, protactinium/thorium and zinc. It can be applied to any model in a “black box” manner.

Now, a follow up study published recently in Sci. Adv. (2024, see reference below) extends the previous results to complex marine biogeochemical models such as those used in the Coupled Model Intercomparison Project (CMIP) that underpin IPCC reports on climate change. The algorithm can accelerate the spin-up of seasonally-forced models by over an order of magnitude, and by a factor of 5 when driven with interannually forcing as is typical in CMIP simulations.

The ability to efficiently spin-up geochemical and biogeochemical models should enable their more effective use, for example making it feasible to calibrate models against observations and performing simulations at resolutions higher than has been previously possible.

Caption: Spin-up to equilibrium of the PISCES marine biogeochemical model. PISCES is coupled to the NEMO ocean circulation model and has 24 prognostic tracers. Left: Drift in dissolved inorganic nitrate concentration (mean squared difference at all grid points between consecutive years) as a function of time. Right: Globally-integrated air-sea flux of CO2 as a function of time. The solid horizontal line is the criterion for convergence established by the Ocean Model Intercomparison Project (OMIP). The blue lines are the conventional direct integration solution and the red lines the accelerated solution using the new algorithm.

This is a joint highlight with the GEOTRACES program.

Reference:

Khatiwala, S. (2024). Efficient spin-up of Earth System Models using sequence acceleration. Science Advances, 10. Access the paper: 10.1126/sciadv.adn2839

Khatiwala, S. (2023). Fast Spin‐Up of Geochemical Tracers in Ocean Circulation and Climate Models. Journal of Advances in Modeling Earth Systems, 15. Access the paper: 10.1029/2022ms003447

Looking for easy data access to high quality time-series data? SPOTS is out!

Posted by mmaheigan

· Thursday, April 18th, 2024

Whether we aim to disentangle anthropogenic driven trends from naturally variability or we want to assess and improve our ocean model’s capabilities to correctly display changes in time, all require high-quality observational data from multiple fixed time-series data. Until now access to these data was difficult, time-consuming, and often required solving multiple data challenges before these data were fit for the purpose. Following the successful examples set by well-known ocean synthesis products, the idea for SPOTS – the Synthesis Product for Ocean Time-Series – was born from this need to address these challenging.

The recently published SPOTS pilot provides biogeochemical essential ocean variables from 12 ship-based fixed time-series scattered around the globe covering the period from 1983 until 2021. An extensive quality assessment enables the straightforward detection of method changes, and in combination with further introduced data quality indicators, the pilot enhances the inter- and intra-station comparability of the included time-series stations. The stations in SPOTS represent unique open ocean and coastal marine environments in the Atlantic, Pacific, Mediterranean, Caribbean, and the Nordic Seas. More than 100,000 water samples are harmonized into one consistent, FAIR, and readily available data synthesis product.

The SPOTS pilot drastically reduces the amount of time needed to obtain high quality and comparable time-series data from multiple programs around the globe. SPOTS facilitates a variety of applications that benefit from the collective value of biogeochemical time-series observations, complementing relevant products for the global ocean that don’t offer the temporal variability and quality of data that fixed time-series programs have. This pilot gives a first glance of what SPOTS has to offer and hopefully many updates of a sustained time-series living data product, SPOTS, will follow.

Read more in the SPOTS paper and access data via BCODMO at https://www.bco-dmo.org/dataset/896862.

Mixotrophs in the northern North Atlantic

Posted by mmaheigan

· Tuesday, April 16th, 2024

Mixotrophs (or mixoplankton) are now accepted as a third group of plankton alongside phytoplankton and zooplankton. Our knowledge of mixotrophs lags far behind that of the other two groups. We currently have only a limited understanding of mixotrophs’ biogeographical distribution across ocean basins, and what environmental factors are associated with their distribution.

The authors of a study recently published in Frontiers in Marine Science reviewed nearly 230,000 individual microplankton samples collected by the North Atlantic Continuous Plankton Recorder program between 1958 and 2015 and calculated the proportion of organisms that are considered mixotrophs in each sample. They classified protist species in the dataset as phytoplankton, mixotrophs, or microzooplankton (heterotrophs), based on existing literature. Taken together across seasonsin shelf waters (depth ≤ 300m), mixotrophs comprise a greater proportion of the microplankton community when nitrate is high and photosynthetically available radiation (PAR) is low (e.g. during the late fall and winter), or when nitrate is low and PAR is moderate to high (e.g. during the summer and early fall). When both nitrate and PAR are high, mixotrophs comprise less of the community compared to phytoplankton. The same pattern was found in offshore waters (depth > 300m), but the key macronutrient was phosphate rather than nitrate. The annual average proportion of mixotrophs in microplankton samples compared to phytoplankton has increased since 1958 in the offshore portion of the study region, with a notable changepoint in 1993; this increasing trend is strongest in the winter season.

This paper is useful for aquatic ecologists who want to integrate mixotrophic plankton into their understanding of marine food webs and biogeochemical cycles. Understanding mixotroph temporal and spatial distributions, as well as the environmental conditions under which they flourish, is imperative to understanding their impact on trophic transfer and biogeochemical cycling.

Authors
Karen Stamieszkin (Bigelow Laboratory for Ocean Sciences)
Nicole Millette (Virginia Institute of Marine Science)
Jessica Luo (NOAA Geophysical Fluid Dynamics Laboratory)
Elizabeth Follett (University of Liverpool)
Nick Record (Bigelow Laboratory of Ocean Science)
David Johns (Marine Biological Association)

Backstory
This work and the collaboration that made it possible was catalyzed by the Eco-DAS XII symposium, attended by Karen Stamieszkin, Nicole Millette, Jessica Luo, and Elizabeth Follett in 2016. Nicole had an idea for an analysis but lacked collaborators, just as she was ready to give up on it, Karen, Jessica, and Elizabeth expressed interest in the project. Karen, Jessica, and Elizabeth each brought a unique perspective that helped make Nicole’s original idea more practical and ensured that the analysis would come to life.

The collaboration that began with this paper lead to the OCB Mixotrophs & Mixotrophy Working Group led by Karen, Jessica, and Nicole, and a successful grant proposal to study mixotrophy awarded to Nicole and Karen by NSF’s Biological Oceanography program. This story shows the importance and power of programs that connect researchers across disciplines, especially in the early stages of their careers.

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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