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1. Exploring the impact of climate change on the global distribution of non‐spinose planktonic foraminifera using a trait‐based ecosystem model

   https://doi.org/10.1111/gcb.15964  

   Grigoratou, Maria ; Monteiro, Fanny M. ; Wilson, Jamie D. ; Ridgwell, Andy ; Schmidt, Daniela N. ( November 2021 , Global Change Biology)

   Planktonic foraminifera are one of the primary calcifiers in the modern ocean, contributing 23%–56% of total global pelagic carbonate production. However, a mechanistic understanding of how physiology and environmental conditions control their abundance and distribution is lacking, hindering the projection of the impact of future climate change. This understanding is important, not only for ecosystem dynamics, but also for marine carbon cycling because of foraminifera's key role in carbonate production. Here we present and apply a global trait‐based ecosystem model of non‐spinose planktonic foraminifera (‘ForamEcoGEnIE’) to assess their ecology and global distribution under future climate change. ForamEcoGEnIE considers the traits of calcium carbonate production, shell size, and foraging. It captures the main characteristic of biogeographical patterns of non‐spinose species – with maximum biomass concentrations found in mid‐ to high‐latitude waters and upwelling areas. The model also reproduces the magnitude of global carbonate production relatively well, although the foraminifera standing stock is systematically overestimated. In response to future scenarios of rising atmospheric CO₂(RCP6 and RCP8.5), on a regional scale, the modelled foraminifera biomass and export flux increases in the subpolar regions of the North Atlantic and the Southern Ocean while it decreases everywhere else. In the absence of adaptation, the biomass decline in the low‐latitude South Pacific suggests extirpation. The model projects a global average loss in non‐spinose foraminifera biomass between 8% (RCP6) and 11% (RCP8.5) by 2050 and between 14% and 18% by 2100 as a response to ocean warming and associated changes in primary production and ecological dynamics. Global calcium carbonate flux associated with non‐spinose foraminifera declines by 13%–18% by 2100. That decline can slow down the ocean carbonate pump and create short‐term positive feedback on rising atmosphericpCO₂.

    

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2. Shallow Calcium Carbonate Cycling in the North Pacific Ocean

   https://doi.org/10.1029/2022GB007388  

   Subhas, Adam V. ; Dong, Sijia ; Naviaux, John D. ; Rollins, Nick E. ; Ziveri, Patrizia ; Gray, William ; Rae, James W. B. ; Liu, Xuewu ; Byrne, Robert H. ; Chen, Sang ; et al ( May 2022 , Global Biogeochemical Cycles)

   The cycling of biologically produced calcium carbonate (CaCO₃) in the ocean is a fundamental component of the global carbon cycle. Here, we present experimental determinations of in situ coccolith and foraminiferal calcite dissolution rates. We combine these rates with solid phase fluxes, dissolved tracers, and historical data to constrain the alkalinity cycle in the shallow North Pacific Ocean. The in situ dissolution rates of coccolithophores demonstrate a nonlinear dependence on saturation state. Dissolution rates of all three major calcifying groups (coccoliths, foraminifera, and aragonitic pteropods) are too slow to explain the patterns of both CaCO₃sinking flux and alkalinity regeneration in the North Pacific. Using a combination of dissolved and solid‐phase tracers, we document a significant dissolution signal in seawater supersaturated for calcite. Driving CaCO₃dissolution with a combination of ambient saturation state and oxygen consumption simultaneously explains solid‐phase CaCO₃flux profiles and patterns of alkalinity regeneration across the entire N. Pacific basin. We do not need to invoke the presence of carbonate phases with higher solubilities. Instead, biomineralization and metabolic processes intimately associate the acid (CO₂) and the base (CaCO₃) in the same particles, driving the coupled shallow remineralization of organic carbon and CaCO₃. The linkage of these processes likely occurs through a combination of dissolution due to zooplankton grazing and microbial aerobic respiration within degrading particle aggregates. The coupling of these cycles acts as a major filter on the export of both organic and inorganic carbon to the deep ocean.

    

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3. Constraining CaCO 3 Export and Dissolution With an Ocean Alkalinity Inverse Model

   https://doi.org/10.1029/2022GB007535  

   Liang, Hengdi ; Lunstrum, Abby M. ; Dong, Sijia ; Berelson, William M. ; John, Seth G. ( February 2023 , Global Biogeochemical Cycles)

   Ocean alkalinity plays a fundamental role in the apportionment of CO₂between the atmosphere and the ocean. The primary driver of the ocean's vertical alkalinity distribution is the formation of calcium carbonate (CaCO₃) by organisms at the ocean surface and its dissolution at depth. This so‐called “CaCO₃counterpump” is poorly constrained, however, both in terms of how much CaCO₃is exported from the surface ocean, and at what depth it dissolves. Here, we created a steady‐state model of global ocean alkalinity using Ocean Circulation Inverse Model transport, biogeochemical cycling, and field‐tested calcite and aragonite dissolution kinetics. We find that limiting CaCO₃dissolution to below the aragonite and calcite saturation horizons cannot explain excess alkalinity in the upper ocean, and that models allowing dissolution above the saturation horizons best match observations. Linking dissolution to organic matter respiration, or imposing a constant dissolution rate both produce good model fits. Our best performing models require export between 1.1 and 1.8 Gt PIC y⁻¹(from 73 m), but all converge to 1.0 Gt PIC y⁻¹export at 279 m, indicating that both high‐ and low‐export scenarios can match observations, as long as high export is coupled to high dissolution in the upper ocean. These results demonstrate that dissolution is not a simple function of seawater CaCO₃saturation (Ω) and calcite or aragonite solubility, and that other mechanisms, likely related to the biology and ecology of calcifiers, must drive significant dissolution throughout the water column.

    

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4. Middle to Late Eocene Changes of the Ocean Carbonate Cycle

   https://doi.org/10.1029/2020PA004168  

   Borrelli, C. ; Katz, M. E. ; Toggweiler, J. R. ( November 2021 , Paleoceanography and Paleoclimatology)

   Sedimentary records show that calcium carbonate (CaCO₃) preservation fluctuated during the Eocene. These fluctuations are well documented for the equatorial Pacific. However, data from other basins are sparse. In this study, we report new middle and late Eocene bulk calcium carbonate percentages and accumulation rates from the northwestern Pacific (Ocean Drilling Program—ODP—Site 884) and the Atlantic (ODP Sites 1053, 1090, and 1263) Oceans; in addition, we calculate CaCO₃accumulation rates for sites with published percentage bulk CaCO₃to expand geographic and paleobathymetric coverage. Using these data, we investigate the response of the carbonate cycle to environmental changes (e.g., temperatures, primary productivity, weathering, and ocean circulation) at the beginning of the greenhouse‐icehouse transition (∼43–34 Ma). Our results show that in the middle to late Eocene CaCO₃accumulation rates were highly variable at different paleodepths and ocean basins suggesting that the evolution of carbonate accumulation rates over the Eocene was influenced by different processes in different locations. In particular, our data emphasize the role of surface CaCO₃production and ocean ventilation in driving changes in CaCO₃preservation and burial at the seafloor. Our study also highlights the need for a better understanding of the processes regulating CaCO₃surface production today in order to correctly interpret geological records.

    

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5. Parental exposure of Eastern oysters ( Crassostrea virginica ) to elevated pCO2 mitigates its negative effects on early larval shell growth and morphology

   https://doi.org/10.1002/lno.12162  

   McNally, Elise M. ; Downey‐Wall, Alan M. ; Titmuss, F. Dylan ; Cortina, Camila ; Lotterhos, Kathleen ; Ries, Justin B. ( June 2022 , Limnology and Oceanography)

   Larvae of marine calcifying organisms are particularly vulnerable to the adverse effects of elevatedpCO₂on shell formation because of their rapid calcification rates, reduced capacity to isolate calcifying fluid from seawater, and use of more soluble polymorphs of calcium carbonate. However, parental exposure to elevatedpCO₂could benefit larval shell formation through transgenerational plastic responses. We examined the capacity of intergenerational exposure to mitigate the adverse effects of elevatedpCO₂on Eastern oyster (Crassostrea virginica) early larval shell growth, shell morphology, and survival. Adult oysters were exposed to control (572 ppmpCO₂) or elevatedpCO₂(2827 ppmpCO₂) conditions for 30 d during reproductive conditioning. Offspring from each parental treatment were produced using a partial North Carolina II cross design and grown under control and elevatedpCO₂conditions for 3 d. We found evidence of transgenerational plasticity in early larval shell growth and morphology, but not in survival, in response to the parentalpCO₂exposure. Larvae from parents exposed to elevatedpCO₂exhibited faster shell growth rates than larvae from control parents, with this effect being significantly larger when larvae were grown under elevatedpCO₂compared to control conditions. Parental exposure to elevatedpCO₂, however, was insufficient to completely counteract the adverse effects of the prescribed elevatedpCO₂on early larval shell formation and survival. Nevertheless, these results suggest that oysters have some capacity to acclimate intergenerationally to ocean acidification.

    

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