Coccolithophore Growth and Calcification in an Acidified Ocean: Insights From Community Earth System Model Simulations

Krumhardt, Kristen M.; Lovenduski, Nicole S.; Long, Matthew C.; Lévy, Marina; Lindsay, Keith; Moore, J. Keith; Nissen, Cara

doi:10.1029/2018ms001483

“…The ocean ecosystem is simulated using the Marine Biogeochemical Library (MARBL; marbl‐ecosys.github.io). Our simulations with MARBL include an explicit coccolithophore phytoplankton functional type (PFT; Krumhardt et al, 2019). The coccolithophore PFT parameterization is based on physiological studies, where the ratio of CaCO 3 production to photosynthesis in the PFT responds to environmental conditions (temperature, nutrients, and CO 2 concentration).…”

Section: Methodsmentioning

confidence: 99%

Southern Ocean Calcification Controls the Global Distribution of Alkalinity

Krumhardt

¹

,

Long

²

,

Lindsay

³

et al. 2020

Global Biogeochemical Cycles

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Biological processes in Southern Ocean surface waters have widespread impacts on global productivity and oceanic CO 2 storage. Here, we demonstrate that biological calcification in the Southern Ocean exerts a strong control on the global distribution of alkalinity. The signature of Southern Ocean calcification is evident in observations as a depletion of potential alkalinity within portions of Subantarctic Mode and Intermediate Water. Experiments with an ocean general circulation model indicate that calcification and subsequent sinking of biogenic carbonate in this region effectively transfers alkalinity between the upper and lower cells of the meridional overturning circulation. Southern Ocean calcification traps alkalinity in the deep ocean; decreasing calcification permits more alkalinity to leak out from the Southern Ocean, yielding increased alkalinity in the upper cell and low-latitude surface waters. These processes have implications for atmosphere-ocean partitioning of carbon. Reductions in Southern Ocean calcification increase the buffer capacity of surface waters globally, thereby enhancing the ocean's ability to absorb carbon from the atmosphere. This study highlights the critical role of Southern Ocean calcification in determining global alkalinity distributions, demonstrating that changes in this process have the potential for widespread consequences impacting air-sea partitioning of CO 2. Plain Language Summary Plankton living in the Southern Ocean affect the composition of seawater through biological processes. Due to the particular oceanic circulation in the Southern Ocean, these biologically driven changes in ocean chemistry can have widespread effects on the global ocean. Species of plankton that form shells of calcium carbonate remove alkalinity from surface waters through the process of calcification. The amount of alkalinity in surface waters is important because it affects how much CO 2 the ocean can absorb from the atmosphere. We show that Southern Ocean calcifying plankton affect the global distribution of alkalinity through the presence of a Southern Ocean "alkalinity trap." More Southern Ocean calcification yields a stronger alkalinity trap, with more alkalinity being retained in the Southern Ocean and in deep waters, away from the atmosphere. Reduced calcification in the Southern Ocean permits more alkalinity to escape the Southern Ocean and remain in the upper ocean globally. These changes affect oceanic CO 2 uptake from the atmosphere.

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“…In particular because metaanalysis (Ridgwell et al, 2009;Krumhardt et al, 2017) and modelling (Ridgwell et al, 2007;Krumhardt et al, 2019) suggest a shift towards lower global calcification rates in response to ocean acidification and warming. It should, however, be noted that the response of heterococcolithophores to ocean acidification is both strain and species dependent (Langer et al, 2006(Langer et al, , 2009Meyer and Riebesell, 2015), and global calcification rates might be more impacted by shifts in species composition rather than individual responses (Ridgwell et al, 2009). Furthermore, contradicting evidence suggesting increased coccolithophore abundance in response to higher CO 2 has been noted in situ (Rivero-Calle et al, 2015) Finally, additional experiments on the numerical response of heterococcolithophores and holococcolithophores to various environmental drivers such as those performed on E. huxleyi would allow a better understanding of individual environmental pressures and will furthermore be highly valuable for future modelling approaches.…”

Section: Discussionmentioning

confidence: 99%

Haplo-diplontic life cycle expands coccolithophore niche

Vries

¹

,

Monteiro

²

,

Wheeler

³

et al. 2021

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Abstract. Coccolithophores are globally important marine calcifying phytoplankton that utilize a haplo-diplontic life cycle. The haplo-diplontic life cycle allows coccolithophores to divide in both life cycle phases and potentially expands coccolithophore niche volume. Research has, however, to date largely overlooked the life cycle of coccolithophores and has instead focused on the diploid life cycle phase of coccolithophores. Through the synthesis and analysis of global scanning electron microscopy (SEM) coccolithophore abundance data (n=2534), we find that calcified haploid coccolithophores generally constitute a minor component of the total coccolithophore abundance (≈ 2 %–15 % depending on season). However, using case studies in the Atlantic Ocean and Mediterranean Sea, we show that, depending on environmental conditions, calcifying haploid coccolithophores can be significant contributors to the coccolithophore standing stock (up to ≈30 %). Furthermore, using hypervolumes to quantify the niche of coccolithophores, we illustrate that the haploid and diploid life cycle phases inhabit contrasting niches and that on average this allows coccolithophores to expand their niche by ≈18.8 %, with a range of 3 %–76 % for individual species. Our results highlight that future coccolithophore research should consider both life cycle stages, as omission of the haploid life cycle phase in current research limits our understanding of coccolithophore ecology. Our results furthermore suggest a different response to nutrient limitation and stratification, which may be of relevance for further climate scenarios. Our compilation highlights the spatial and temporal sparsity of SEM measurements and the need for new molecular techniques to identify uncalcified haploid coccolithophores. Our work also emphasizes the need for further work on the carbonate chemistry niche of the coccolithophore life cycle.

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“…If this holds true on a global level, and holococcolithophores inhabit lower pH waters in terms of their niche space, this would have important implication in the context of ocean acidification. In particular because meta-analysis (Ridgwell et al, 2009;Krumhardt et al, 2017) and modelling (Ridgwell et al, 2007;Krumhardt et al, 2019) suggest a shift towards lower global calcification rates in response to ocean acidification and warming.…”

Section: Discussionmentioning

confidence: 99%

The haplo-diplontic life cycle expands niche space of coccolithophores

Vries¹,

Monteiro²,

Wheeler³

et al. 2020

Preprint

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Abstract. Coccolithophores are globally important marine calcifying phytoplankton that utilize a haplo-diplontic life cycle. The haplo-diplontic life cycle allows coccolithophores to divide in both life cycle phases, and has been proposed to allow coccolithophores to expand their niche space. To-date research has however largely overlooked the life cycle of coccolithophores, and has instead focused on the diploid life cycle phase. Through a synthesis of global scanning electron microscopy (SEM) coccolithophore abundance data (n = 2534), we show that the haploid life cycle phase contributes significantly to coccolithophore abundance, constituting ≈18 % of species abundance for which haploid-diploid pairs are defined. Using hypervolumes to quantify the niche space of coccolithophores, we furthermore show that the haploid and diploid life cycle phases inhabit contrasting niches, and that this allows coccolithophores to expand their niche space by ≈17 %. Our results highlight that future coccolithophore research should consider both life cycle stages, as omission of the haploid life cycle phase in current research limits our understanding of coccolithophore ecology.

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Coccolithophore Growth and Calcification in an Acidified Ocean: Insights From Community Earth System Model Simulations

Cited by 54 publications

References 94 publications

Southern Ocean Calcification Controls the Global Distribution of Alkalinity

Southern Ocean Calcification Controls the Global Distribution of Alkalinity

Haplo-diplontic life cycle expands coccolithophore niche

The haplo-diplontic life cycle expands niche space of coccolithophores

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