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  • 1
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    Multicentury changes in ocean and land contributions to the climate-carbon feedback (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 29 (2015): 744–759, doi:10.1002/2014GB005079.
    Description: Improved constraints on carbon cycle responses to climate change are needed to inform mitigation policy, yet our understanding of how these responses may evolve after 2100 remains highly uncertain. Using the Community Earth System Model (v1.0), we quantified climate-carbon feedbacks from 1850 to 2300 for the Representative Concentration Pathway 8.5 and its extension. In three simulations, land and ocean biogeochemical processes experienced the same trajectory of increasing atmospheric CO2. Each simulation had a different degree of radiative coupling for CO2 and other greenhouse gases and aerosols, enabling diagnosis of feedbacks. In a fully coupled simulation, global mean surface air temperature increased by 9.3 K from 1850 to 2300, with 4.4 K of this warming occurring after 2100. Excluding CO2, warming from other greenhouse gases and aerosols was 1.6 K by 2300, near a 2 K target needed to avoid dangerous anthropogenic interference with the climate system. Ocean contributions to the climate-carbon feedback increased considerably over time and exceeded contributions from land after 2100. The sensitivity of ocean carbon to climate change was found to be proportional to changes in ocean heat content, as a consequence of this heat modifying transport pathways for anthropogenic CO2 inflow and solubility of dissolved inorganic carbon. By 2300, climate change reduced cumulative ocean uptake by 330 Pg C, from 1410 Pg C to 1080 Pg C. Land fluxes similarly diverged over time, with climate change reducing stocks by 232 Pg C. Regional influence of climate change on carbon stocks was largest in the North Atlantic Ocean and tropical forests of South America. Our analysis suggests that after 2100, oceans may become as important as terrestrial ecosystems in regulating the magnitude of the climate-carbon feedback.
    Description: We are grateful for support from the U.S. Department of Energy Office of Science and the National Science Foundation (NSF). J.T.R. and F.H. received support from the Regional and Global Climate Modeling Program in the Climate and Environmental Sciences Division of the Biological and Environmental Research (BER) Program in the U.S. Department of Energy Office of Science. J.T.R., K.L., E.M., W.F., J.K.M., S.C.D., and N.N.M. received funding from the NSF project “Collaborative Research: Improved Regional and Decadal Predictions of the Carbon Cycle“ (AGS-1048827, AGS-1021776, and AGS-1048890). The Community Earth System Modeling project receives support from both NSF and BER.
    Description: 2015-12-02
    Keywords: Atlantic meridional overturning circulation ; Net primary production ; Stratification ; Ecosystems ; Carbon-concentration feedback
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    The multiple fates of sinking particles in the North Atlantic Ocean (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 29 (2015): 1471–1494, doi:10.1002/2014GB005037.
    Description: The direct respiration of sinking organic matter by attached bacteria is often invoked as the dominant sink for settling particles in the mesopelagic ocean. However, other processes, such as enzymatic solubilization and mechanical disaggregation, also contribute to particle flux attenuation by transferring organic matter to the water column. Here we use observations from the North Atlantic Ocean, coupled to sensitivity analyses of a simple model, to assess the relative importance of particle-attached microbial respiration compared to the other processes that can degrade sinking particles. The observed carbon fluxes, bacterial production rates, and respiration by water column and particle-attached microbial communities each spanned more than an order of magnitude. Rates of substrate-specific respiration on sinking particle material ranged from 0.007 ± 0.003 to 0.173 ± 0.105 day−1. A comparison of these substrate-specific respiration rates with model results suggested sinking particle material was transferred to the water column by various biological and mechanical processes nearly 3.5 times as fast as it was directly respired. This finding, coupled with strong metabolic demand imposed by measurements of water column respiration (729.3 ± 266.0 mg C m−2 d−1, on average, over the 50 to 150 m depth interval), suggested a large fraction of the organic matter evolved from sinking particles ultimately met its fate through subsequent remineralization in the water column. At three sites, we also measured very low bacterial growth efficiencies and large discrepancies between depth-integrated mesopelagic respiration and carbon inputs.
    Description: U.S. Environmental Protection Agency (EPA) STAR Grant Number: FP-91744301-0; National Science Foundation Grant Numbers OCE-1061883, EF-0424599, OCE-1155438, OCE-1059884, OCE-1031143; Gordon and Betty Moore Foundation Grant Numbers: 3301, 3789; Gordon and Betty Moore Foundation; Woods Hole Oceanographic Institution
    Description: 2016-03-25
    Keywords: Carbon cycle ; Particle flux ; Bacterial growth efficiency ; Bacterial respiration ; Microbial respiration
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    A phytoplankton model for the allocation of gross photosynthetic energy including the trade‐offs of diazotrophy (2018)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 123 (2018): 1796-1816, doi:10.1029/2017JG004263.
    Description: Gross photosynthetic activity by phytoplankton is directed to linear and alternative electron pathways that generate ATP, reductant, and fix carbon. Ultimately less than half is directed to net growth. Here we present a phytoplankton cell allocation model that explicitly represents a number of cell metabolic processes and functional pools with the goal of evaluating ATP and reductant demands as a function of light, nitrate, iron, oxygen, and temperature for diazotrophic versus nondiazotrophic growth. We employ model analogues of Synechoccocus and Crocosphaera watsonii, to explore the trade‐offs of diazotrophy over a range of environmental conditions. Model analogues are identical in construction, except for an iron quota associated with nitrogenase, an additional respiratory demand to remove oxygen in order to protect nitrogenase and an additional ATP demand to split dinitrogen. We find that these changes explain observed differences in growth rate and iron limitation between diazotrophs and nondiazotrophs. Oxygen removal imparted a significantly larger metabolic cost to diazotrophs than ATP demand for fixing nitrogen. Results suggest that diazotrophs devote a much smaller fraction of gross photosynthetic energy to growth than nondiazotrophs. The phytoplankton cell allocation model model provides a predictive framework for how photosynthate allocation varies with environmental conditions in order to balance cellular demands for ATP and reductant across phytoplankton functional groups.
    Description: DOC | NOAA | Climate Program Office (CPO) Grant Number: NA100AR4310093; National Science Foundation (NSF) Grant Number: EF‐0424599; Center for Microbial Oceanography Research and Education (CMORE) Grant Number: NSF EF‐0424599; NOAA Global Carbon Program Grant Number: NA100AR4310093
    Description: 2018-11-01
    Keywords: Phytoplankton ; Diazotroph ; Photosynthesis ; Resource allocation ; Biogeochemistry
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Humic substances may control dissolved iron distributions in the global ocean : implications from numerical simulations (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 27 (2013): 450-462, doi:10.1002/gbc.20039.
    Description: This study used an ocean general circulation model to simulate the marine iron cycle in an investigation of how simulated distributions of weak iron-binding ligands would be expected to control dissolved iron concentrations in the ocean, with a particular focus on deep ocean waters. The distribution of apparent oxygen utilization was used as a proxy for humic substances that have recently been hypothesized to account for the bulk of weak iron-binding ligands in seawater. Compared to simulations using a conventional approach with homogeneous ligand distributions, the simulations that incorporated spatially variable ligand concentrations exhibited substantial improvement in the simulation of global dissolved iron distributions as revealed by comparisons with available field data. The improved skill of the simulations resulted largely because the spatially variable ligand distributions led to a more reasonable basin-scale variation of the residence time of iron when present at high concentrations. The model results, in conjunction with evidence from recent field studies, suggest that humic substances play an important role in the iron cycle in the ocean.
    Description: S. C. Doney acknowledges support from the U.S. National Science Foundation (EF- 0424599). This work was also supported by NSF grant OCE-0928204 to J. K. Moore.
    Description: 2013-11-20
    Keywords: Iron ; Organic ligands ; General circulation model
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Annual cycles of ecological disturbance and recovery underlying the subarctic Atlantic spring plankton bloom (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 27 (2013): 526–540, doi:10.1002/gbc.20050.
    Description: Satellite measurements allow global assessments of phytoplankton concentrations and, from observed temporal changes in biomass, direct access to net biomass accumulation rates (r). For the subarctic Atlantic basin, analysis of annual cycles in r reveals that initiation of the annual blooming phase does not occur in spring after stratification surpasses a critical threshold but rather occurs in early winter when growth conditions for phytoplankton are deteriorating. This finding has been confirmed with in situ profiling float data. The objective of the current study was to test whether satellite-based annual cycles in r are reproduced by the Biogeochemical Element Cycling–Community Climate System Model and, if so, to use the additional ecosystem properties resolved by the model to better understand factors controlling phytoplankton blooms. We find that the model gives a similar early onset time for the blooming phase, that this initiation is largely due to the physical disruption of phytoplankton-grazer interactions during mixed layer deepening, and that parallel increases in phytoplankton-specific division and loss rates during spring maintain the subtle disruption in food web equilibrium that ultimately yields the spring bloom climax. The link between winter mixing and bloom dynamics is illustrated by contrasting annual plankton cycles between regions with deeper and shallower mixing. We show that maximum water column inventories of phytoplankton vary in proportion to maximum winter mixing depth, implying that future reductions in winter mixing may dampen plankton cycles in the subarctic Atlantic. We propose that ecosystem disturbance-recovery sequences are a unifying property of global ocean plankton blooms.
    Description: This work was supported by the National Aeronautics and Space Administration, Ocean Biology and Biogeochemistry Program (grants NNX10AT70G, NNX09AK30G, NNX08AK70G, NNX07AL80G, and NNX08AP36A) and the Center for Microbial Oceanography Research and Education (C-MORE; grant EF-0424599), a National Science Foundation-supported Science and Technology Center.
    Keywords: Phytoplankton ; Bloom ; Atlantic ; Satellite ; Model ; Ecosystems
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Reply to a comment by Stephen M. Chiswell on: “Annual cycles of ecological disturbance and recovery underlying the subarctic Atlantic spring plankton bloom” by M. J. Behrenfeld et al. (2013) (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, [year]. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 27 (2013): 1294–1296, doi:10.1002/2013GB004720.
    Description: 2014-06-12
    Repository Name: Woods Hole Open Access Server
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  • 7
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    North-South asymmetry in the modeled phytoplankton community response to climate change over the 21st century (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 27 (2013): 1274–1290, doi:10.1002/2013GB004599.
    Description: Here we analyze the impact of projected climate change on plankton ecology in all major ocean biomes over the 21st century, using a multidecade (1880–2090) experiment conducted with the Community Climate System Model (CCSM-3.1) coupled ocean-atmosphere-land-sea ice model. The climate response differs fundamentally in the Northern and Southern Hemispheres for diatom and small phytoplankton biomass and consequently for total biomass, primary, and export production. Increasing vertical stratification in the Northern Hemisphere oceans decreases the nutrient supply to the ocean surface. Resulting decreases in diatom and small phytoplankton biomass together with a relative shift from diatoms to small phytoplankton in the Northern Hemisphere result in decreases in the total primary and export production and export ratio, and a shift to a more oligotrophic, more efficiently recycled, lower biomass euphotic layer. By contrast, temperature and stratification increases are smaller in the Southern compared to the Northern Hemisphere. Additionally, a southward shift and increase in strength of the Southern Ocean westerlies act against increasing temperature and freshwater fluxes to destratify the water-column. The wind-driven, poleward shift in the Southern Ocean subpolar-subtropical boundary results in a poleward shift and increase in the frontal diatom bloom. This boundary shift, localized increases in iron supply, and the direct impact of warming temperatures on phytoplankton growth result in diatom increases in the Southern Hemisphere. An increase in diatoms and decrease in small phytoplankton partly compensate such that while total production and the efficiency of organic matter export to the deep ocean increase, total Southern Hemisphere biomass does not change substantially. The impact of ecological shifts on the global carbon cycle is complex and varies across ecological biomes, with Northern and Southern Hemisphere effects on the biological production and export partially compensating. The net result of climate change is a small Northern Hemisphere-driven decrease in total primary production and efficiency of organic matter export to the deep ocean.
    Description: I. Marinov was supported by National Science Foundation (NSF) Grant ATM06-28582 while at WHOI and by NASA Grant NNX13AC92G while at Penn. I. Lima and S. Doney were supported by the Center for Microbial Oceanography, Research, and Education (CMORE), an NSF Science and Technology Center (EF-0424599).
    Description: 2014-06-20
    Keywords: Phytoplankton ; Climate change ; Ocean models
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    Quantifying subtropical North Pacific gyre mixed layer primary productivity from Seaglider observations of diel oxygen cycles (2015)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 4032–4039, doi:10.1002/2015GL063065.
    Description: Using autonomous underwater gliders, we quantified diurnal periodicity in dissolved oxygen, chlorophyll, and temperature in the subtropical North Pacific near the Hawaii Ocean Time-series (HOT) Station ALOHA during summer 2012. Oxygen optodes provided sufficient stability and precision to quantify diel cycles of average amplitude of 0.6 µmol kg−1. A theoretical diel curve was fit to daily observations to infer an average mixed layer gross primary productivity (GPP) of 1.8 mmol O2 m−3 d−1. Cumulative net community production (NCP) over 110 days was 500 mmol O2 m−2 for the mixed layer, which averaged 57 m in depth. Both GPP and NCP estimates indicated a significant period of below-average productivity at Station ALOHA in 2012, an observation confirmed by 14C productivity incubations and O2/Ar ratios. Given our success in an oligotrophic gyre where biological signals are small, our diel GPP approach holds promise for remote characterization of productivity across the spectrum of marine environments.
    Description: The authors acknowledge support from the National Science Foundation (NSF) through an NSF Science and Technology Center, the Center for Microbial Oceanography Research and Education (C-MORE; NSF EF-0424599). D.N. also was supported by NSF (OCE-1129644) and an Independent Study Award from the Woods Hole Oceanographic Institution (WHOI). D.M.K. was also supported by the Gordon and Betty Moore Foundation. WHOI Summer Student Fellow Cole Stites-Clayton, Stanford University, contributed to early stages of Seaglider data analysis and was supported by an NSF REU grant to WHOI (OCE-1156952).
    Keywords: Primary productivity ; Glider ; Diel ; Oxygen ; Net community production ; Hawaii
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Ocean circulation and biogeochemistry moderate interannual and decadal surface water pH changes in the Sargasso Sea (2015)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 4931–4939, doi:10.1002/2015GL064431.
    Description: The oceans absorb anthropogenic CO2 from the atmosphere, lowering surface ocean pH, a concern for calcifying marine organisms. The impact of ocean acidification is challenging to predict as each species appears to respond differently and because our knowledge of natural changes to ocean pH is limited in both time and space. Here we reconstruct 222 years of biennial seawater pH variability in the Sargasso Sea from a brain coral, Diploria labyrinthiformis. Using hydrographic data from the Bermuda Atlantic Time-series Study and the coral-derived pH record, we are able to differentiate pH changes due to surface temperature versus those from ocean circulation and biogeochemical changes. We find that ocean pH does not simply reflect atmospheric CO2 trends but rather that circulation/biogeochemical changes account for 〉90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO2 alone.
    Description: Funding to N.F.G. was provided by the University of Hong Kong and the National Research Foundation Singapore under its Singapore NRF Fellowship scheme (National Research Fellow Award NRF-RF2012-03), as administered by the Earth Observatory of Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative. S.C.D. and K.A.H. acknowledge support from the National Science Foundation and Woods Hole Oceanographic Institution.
    Keywords: AMO ; NAO ; Coral del11B proxy ; pH
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Variability in the mechanisms controlling Southern Ocean phytoplankton bloom phenology in an ocean model and satellite observations (2017)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 31 (2017): 922–940, doi:10.1002/2016GB005615.
    Description: A coupled global numerical simulation (conducted with the Community Earth System Model) is used in conjunction with satellite remote sensing observations to examine the role of top-down (grazing pressure) and bottom-up (light, nutrients) controls on marine phytoplankton bloom dynamics in the Southern Ocean. Phytoplankton seasonal phenology is evaluated in the context of the recently proposed “disturbance-recovery” hypothesis relative to more traditional, exclusively “bottom-up” frameworks. All blooms occur when phytoplankton division rates exceed loss rates to permit sustained net population growth; however, the nature of this decoupling period varies regionally in Community Earth System Model. Regional case studies illustrate how unique pathways allow blooms to emerge despite very poor division rates or very strong grazing rates. In the Subantarctic, southeast Pacific small spring blooms initiate early cooccurring with deep mixing and low division rates, consistent with the disturbance-recovery hypothesis. Similar systematics are present in the Subantarctic, southwest Atlantic during the spring but are eclipsed by a subsequent, larger summer bloom that is coincident with shallow mixing and the annual maximum in division rates, consistent with a bottom-up, light limited framework. In the model simulation, increased iron stress prevents a similar summer bloom in the southeast Pacific. In the simulated Antarctic zone (70°S–65°S) seasonal sea ice acts as a dominant phytoplankton-zooplankton decoupling agent, triggering a delayed but substantial bloom as ice recedes. Satellite ocean color remote sensing and ocean physical reanalysis products do not precisely match model-predicted phenology, but observed patterns do indicate regional variability in mechanism across the Atlantic and Pacific.
    Description: NDSEG Graduate Fellowship; National Aeronautics and Space Administration Ocean Biology and Biogeochemistry Program Grant Number: NNX14L86G; NSF Poloar Programs Award Grant Number: 1440435; National Aeronautics and Space Administration Grant Number: NNX14AL86G; NDSEG; National Science Foundation Grant Number: 1440435
    Description: 2017-11-30
    Keywords: Southern Ocean ; Phytoplankton ; Bloom phenology ; Top-down controls ; Bottom-up controls ; Modeling
    Repository Name: Woods Hole Open Access Server
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