Changes In Carbonate Chemistry Research Articles

Carbonate system data tracing freshwater inflow into the Ross Sea through the eastern gate and along the Ross Ice Shelf (Antarctica)

The eastern Ross Sea is a key area to understand the role of the Amundsen Sea inflow of freshwater that can influence the Ross Sea water properties and salt budget. A survey was carried out in the eastern Ross Sea during the austral summer 2019–20 to evaluate the contribution of the Amundsen Sea Water (ASW) to the salinity variability. A total of 248 seawater samples were collected f\or the analysis of total alkalinity (AT) and pH. The data collected were used together with temperature and salinity to obtain a full description of the carbonate system properties including total inorganic carbon (CT), CO2 partial pressure (pCO2), calcium carbonate saturation state of aragonite and calcite (Ω), and Revelle factor. Moreover, we estimated the anthropogenic carbon (Cant) throughout the TrOCA method to better understand the carbon cycle, also considering the effect of atmospheric CO2 uptake on ocean acidification. We used principal component analysis (PCA) to investigate the major controls on the carbonate system parameters with the aim of defining their sensitivity as chemical tracers. The changes in carbonate chemistry in surface waters were mainly due to the physical properties. AT and pH traced the entry of the ASW showing limited mixing between water masses on the shelf area. Shelf waters were enriched in Cant, which resulted lower than the estimated value for shelf waters produced in western Ross Sea.

Acidification impacts and acclimation potential of Caribbean benthic foraminifera assemblages in naturally discharging low-pH water

Abstract. Ocean acidification (OA) is expected to negatively affect many ecologically important organisms. Here we report the response of Caribbean benthic foraminiferal assemblages to naturally discharging low-pH waters with a composition similar to that expected for the end of the 21st century. At low pH ∼ 7.8 and low saturation state with respect to calcite (Ωcalcite < 4), the relative abundance of hyaline, agglutinated, and symbiont-bearing species increased, indicating higher resistance to potential carbonate chemistry changes. Diversity and other taxonomical metrics (i.e., richness, abundance, and evenness) declined steeply with decreasing pH despite exposure of this ecosystem to low-pH conditions for millennia, suggesting that tropical foraminiferal communities will be negatively impacted under acidification scenarios SSP3-7.0 (Shared Socioeconomic Pathways) and SSP5-8.5. The species Archaias angulatus, a major contributor to sediment production in the Caribbean, was able to calcify at more extreme conditions (7.1 pH) than those projected for the late 21st century, but the calcified tests had a lower average density than those exposed to higher-pH conditions (7.96), indicating that reef foraminiferal carbonate production might decrease this century. Smaller foraminifera were particularly sensitive to low pH, and our results demonstrate their potential use to monitor OA conditions.

Influences of Atlantic Ocean thermohaline circulation and Antarctic ice-sheet expansion on Pliocene deep Pacific carbonate chemistry

Quantifying changes in seawater carbonate chemistry is crucial to deciphering of patterns and drivers of the oceanic carbon cycle and climate change. Here, we present a new deep-water carbonate ion saturation state (Δ[CO32−]) record for the Pliocene western tropical Pacific, reconstructed from the size-normalized weight of the planktonic foraminifer Trilobatus sacculifer of IODP Site U1490. A steep decline in deep-water Δ[CO32−] occurred at ∼4.6 Ma synchronous to the enhanced production of North Atlantic Deep Water (NADW) related to the closure of the Panamanian Gateway. Subsequently, at the onset of the Northern Hemisphere glaciation at ∼2.7 Ma the weakening of NADW formation resulted in a deep-water Δ[CO32−] peak. The changes in NADW production rate likely controlled a seesaw-like fluctuation in deep-water Δ[CO32−] between the Pacific and Atlantic oceans. During the late Pliocene (∼3.8–2.8 Ma), Antarctic ice-sheet/sea-ice expansions sequestered CO2 in the deep Pacific through ventilation of the deep watermass, leading to a long-term decrease in deep Pacific Δ[CO32−]. We infer that fluctuating NADW production rates at ∼4.6 Ma and ∼2.7 Ma influenced inter-basinal fractionation of deep-ocean carbon between the Atlantic and Pacific, and that deep Pacific carbon storage linked to expansions of Antarctic ice sheet/sea ice contributed to the lowering of atmospheric pCO2 and global cooling during the late Pliocene.

Acclimatory gene expression of primed clams enhances robustness to elevated pCO2.

Sublethal exposure to environmental challenges may enhance ability to cope with chronic or repeated change, a process known as priming. In a previous study, pre-exposure to seawater enriched with pCO2 improved growth and reduced antioxidant capacity of juvenile Pacific geoduck Panopea generosa clams, suggesting that transcriptional shifts may drive phenotypic modifications post-priming. To this end, juvenile clams were sampled and TagSeq gene expression data were analysed after (i) a 110-day acclimation under ambient (921 μatm, naïve) and moderately elevated pCO2 (2870 μatm, pre-exposed); then following (ii) a second 7-day exposure to three pCO2 treatments (ambient: 754 μatm; moderately elevated: 2750μatm; severely elevated: 4940 μatm), a 7-day return to ambient pCO2 and a third 7-day exposure to two pCO2 treatments (ambient: 967 μatm; moderately elevated: 3030 μatm). Pre-exposed geoducks frontloaded genes for stress and apoptosis/innate immune response, homeostatic processes, protein degradation and transcriptional modifiers. Pre-exposed geoducks were also responsive to subsequent encounters, with gene sets enriched for mitochondrial recycling and immune defence under elevated pCO2 and energy metabolism and biosynthesis under ambient recovery. In contrast, gene sets with higher expression in naïve clams were enriched for fatty-acid degradation and glutathione components, suggesting naïve clams could be depleting endogenous fuels, with unsustainable energetic requirements if changes in carbonate chemistry persist. Collectively, our transcriptomic data indicate that pCO2 priming during post-larval periods could, via gene expression regulation, enhance robustness in bivalves to environmental change. Such priming approaches may be beneficial for aquaculture, as seafood demand intensifies concurrent with increasing climate change in marine systems.

Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification-like conditions

Spiny lobsters rely on multiple biomineralized exoskeletal predator defenses that may be sensitive to ocean acidification (OA). Compromised mechanical integrity of these defensive structures may tilt predator-prey outcomes, leading to increased mortality in the lobsters’ environment. Here, we tested the effects of OA-like conditions on the mechanical integrity of selected exoskeletal defenses of juvenile California spiny lobster, Panulirus interruptus. Young spiny lobsters reside in kelp forests with dynamic carbonate chemistry due to local metabolism and photosynthesis as well as seasonal upwelling, yielding daily and seasonal fluctuations in pH. Lobsters were exposed to a series of stable and diurnally fluctuating reduced pH conditions for three months (ambient pH/stable, 7.97; reduced pH/stable 7.67; reduced pH with low fluctuations, 7.67 ± 0.05; reduced pH with high fluctuations, 7.67 ± 0.10), after which we examined the intermolt composition (Ca and Mg content), ultrastructure (cuticle and layer thickness), and mechanical properties (hardness and stiffness) of selected exoskeletal predator defenses. Cuticle ultrastructure was consistently robust to pH conditions, while mineralization and mechanical properties were variable. Notably, the carapace was less mineralized under both reduced pH treatments with fluctuations, but with no effect on material properties, and the rostral horn had lower hardness in reduced/high fluctuating conditions without a corresponding difference in mineralization. Antennal flexural stiffness was lower in reduced, stable pH conditions compared to the reduced pH treatment with high fluctuations and not correlated with changes in cuticle structure or mineralization. These results demonstrate a complex relationship between mineralization and mechanical properties of the exoskeleton under changing ocean chemistry, and that fluctuating reduced pH conditions can induce responses not observed under the stable reduced pH conditions often used in OA research. Furthermore, this study shows that some juvenile California spiny lobster exoskeletal defenses are responsive to changes in ocean carbonate chemistry, even during the intermolt period, in ways that can potentially increase susceptibility to predation among this critical life stage.

Monsoon- and ENSO-driven surface-water pCO2 variation in the tropical West Pacific since the Last Glacial Maximum

The East Asian monsoon (EAM) and El Niño-Southern Oscillation (ENSO) are large-scale oceanic-atmospheric fluctuations that dominate climate variability in the tropical Pacific Ocean. Although the effects of EAM and ENSO on physical and biological processes are increasingly understood, little is known about their influence on seawater carbonate chemistry in the tropical Pacific, especially in the geological past. Here, we present reconstructed variations in surface-water pCO2 (pCO2(sw)) and their deviation from atmospheric pCO2 (ΔpCO2(sw-atm)) in the western Philippine Sea (WPS) since 27 ka. Our record displays covariation between ΔpCO2(sw-atm) and the intensity of the East Asian summer monsoon (EASM) since the Last Glacial Maximum (LGM), suggesting that EASM-driven upwelling controls long-term changes in surface-water carbonate chemistry and air-sea CO2 fluxes. Rapid changes in ΔpCO2(sw-atm) were linked to the ENSO-like state and, to a lesser extent, the East Asian winter monsoon (EAWM) during the Last Deglaciation, with low values corresponding to La Niña-like phases and strong EAWM during Heinrich Event 1, the Allerød and the Younger Dryas, and high values corresponding to El Niño-like phases and weak EAWM during the Bølling and Pre-Boreal. This interpretation is supported by the relationship of EAM and ENSO to modern surface-water carbonate chemistry in the WPS. Our new record, combined with previously published data, suggests that the tropical Pacific played a minimal role in sequestering CO2(atm) during the LGM. Tropical Pacific surface waters overall became a pronounced CO2 source to the atmosphere during the Last Deglaciation, possibly making a substantial contribution to the deglacial pCO2(atm) rise. We infer that this flux was mainly due to ENSO-related patterns of vertical stratification or lateral advection, perhaps in addition to equatorial upwelling of southern-sourced waters already enriched in dissolved inorganic carbon. Our findings indicate that tropical conditions (i.e., EAM and ENSO-like state) played a crucial role in glacial-interglacial pCO2(atm) changes, suggesting that this is an important area for future research into the causes of glacial pCO2(atm) cycles.

Molecular response of Sargassum vulgare to acidification at volcanic CO2 vents: Insights from proteomic and metabolite analyses.

Ocean acidification is impacting marine life all over the world. Understanding how species can cope with the changes in seawater carbonate chemistry represents a challenging issue. We addressed this topic using underwater CO2 vents that naturally acidify some marine areas off the island of Ischia. In the most acidified area of the vents, having a mean pH value of 6.7, comparable to far-future predicted acidification scenarios (by 2300), the biomass is dominated by the brown alga Sargassum vulgare. The novelty of the present study is the characterization of the S. vulgare proteome together with metabolite analyses to identify the key proteins, metabolites, and pathways affected by ocean acidification. A total of 367 and 387 proteins were identified in populations grown at pH that approximates the current global average (8.1) and acidified sites, respectively. Analysis of their relative abundance revealed that 304 proteins are present in samples from both sites: 111 proteins are either higher or exclusively present under acidified conditions, whereas 120 proteins are either lower or present only under control conditions. Functionally, under acidification, a decrease in proteins related to translation and post-translational processes and an increase of proteins involved in photosynthesis, glycolysis, oxidation-reduction processes, and protein folding were observed. In addition, small-molecule metabolism was affected, leading to a decrease of some fatty acids and antioxidant compounds under acidification. Overall, the results obtained by proteins and metabolites analyses, integrated with previous transcriptomic, physiological, and biochemical studies, allowed us to delineate the molecular strategies adopted by S. vulgare to grow in future acidified environments, including an increase of proteins involved in energetic metabolism, oxidation-reduction processes, and protein folding at the expense of proteins involved in translation and post-translational processes.

Ocean acidification induced changes in Ulva fasciata biochemistry may improve Dicentrarchus labrax aquaculture via enhanced antimicrobial activity

Changes in seawater carbonate chemistry including increased seawater carbon dioxide concentrations (pCO2), commonly known as ocean acidification (OA), can impact metabolic activities and phytochemical production in marine algae. While OA impacts typically reduce animal health, this study investigated the potential of OA-induced changes in methanol bioactivity from the macroalgae Ulva fasciata, to enhance larval European sea bass (Dicentrarchus labrax) aquaculture via increasing antimicrobial activity. After exposing U. fasciata to four pCO2 levels ~280, 550, 750 and 1050 μatm, macroalgae methanol extracts at pCO2–750 exhibited the highest total phenolic content (TPC), flavonoid content (TFC) and yielded the highest antioxidant and antimicrobial activities. After using extracts as a daily water additive for sea bass larvae, U. fasciata methanolic extract at pCO2–750 yielded the greatest reduction in pathogenic bacterial community and the highest survival rate for sea bass larvae. Sea bass larvae growth was also highest after exposure to methanolic extract of U. fasciata grown at pCO2–750, potentially due to higher TPC, TFC and polyunsaturated fatty acid levels. Such nutritional benefits may have been acquired by sea bass larvae via direct uptake or via indirect transfer, by which live feed (Brachionus or Artemia) consumed by larvae accumulated more nutrients. Our results suggest that pCO2–750 has a significant physiological impact on U. fasciata, potentially allowing macroalgae under OA conditions to function as nutritional supplements to increase the performance of sea bass aquaculture

Reduced H+ channel activity disrupts pH homeostasis and calcification in coccolithophores at low ocean pH

Coccolithophores are major producers of ocean biogenic calcite, but this process is predicted to be negatively affected by future ocean acidification scenarios. Since coccolithophores calcify intracellularly, the mechanisms through which changes in seawater carbonate chemistry affect calcification remain unclear. Here we show that voltage-gated H+ channels in the plasma membrane of Coccolithus braarudii serve to regulate pH and maintain calcification under normal conditions but have greatly reduced activity in cells acclimated to low pH. This disrupts intracellular pH homeostasis and impairs the ability of C. braarudii to remove H+ generated by the calcification process, leading to specific coccolith malformations. These coccolith malformations can be reproduced by pharmacological inhibition of H+ channels. Heavily calcified coccolithophore species such as C. braarudii, which make the major contribution to carbonate export to the deep ocean, have a large intracellular H+ load and are likely to be most vulnerable to future decreases in ocean pH.

Porewater chemistry of Louisiana marshes with contrasting salinities and its implications for coastal acidification

Dissolved inorganic carbon (DIC) and total alkalinity (TA) are fundamental components of carbonate systems that control pH and buffering capacity of a water body. Three coastal marshes with contrasting salinities in Barataria Basin, Louisiana, USA, were sampled five times between December 2018 and October 2019 to understand seasonal changes in porewater carbonate chemistry and its impact on surrounding water bodies. Porewater DIC and TA increased with depth irrespective of marsh type and ranged from 4.47 to 31.61 mmol/kg and from 1.78 to 28.56 mmol/kg, respectively. The salt marsh had higher porewater DIC and TA compared to the lower salinity intermediate and brackish marshes, probably due to sulfate reduction in the salt marsh. However, it is likely that denitrification is also an important anaerobic respiration pathway in these marshes because of high nitrate concentrations in this region and low porewater TA/DIC ratios in all three marshes. Porewater TA and DIC concentrations were generally higher during warmer months than colder months. However, the marsh flooding regime had a profound influence on TA and DIC concentrations by changing the redox potential of the marsh soil. Porewater TA/DIC ratios in all three marshes were generally less than 1, while surface water TA/DIC ratios were around 1, suggesting that export of DIC and TA from coastal marshes has the potential to contribute to coastal acidification.

Summer Surface CO2 Dynamics on the Bering Sea and Eastern Chukchi Sea Shelves From 1989 to 2019

AbstractBy compiling boreal summer (June to October) CO2 measurements from 1989 to 2019 on the Bering and eastern Chukchi Sea shelves, we find that the study areas act as a CO2 sink except when impacted by river runoff and wind‐driven upwelling. The CO2 system in this area is seasonally dominated by the biological pump especially in the northern Bering Sea and near Hanna Shoal, while wind‐driven upwelling of CO2‐rich bottom water can cause episodic outgassing. Seasonal surface ΔfCO2 (oceanic fCO2 – air fCO2) is dominantly driven by temperature only during periods of weak CO2 outgassing in shallow nearshore areas. However, after comparing the mean summer ΔfCO2 during the periods of 1989–2013 and 2014–2019, we suggest that temperature does drive long‐term, multi‐decadal patterns in ΔfCO2. In the northern Chukchi Sea, rapid warming concurrent with reduced seasonal sea‐ice persistence caused the regional summer CO2 sink to decrease. By contrast, increasing primary productivity caused the regional summer CO2 sink on the Bering Sea shelf to increase over time. While additional time series are needed to confirm the seasonal and annual trajectory of CO2 changes and ocean acidification in these dynamic and spatially complex ecosystems, this study provides a meaningful mechanistic analysis of recent changes in inorganic carbonate chemistry. As high‐resolution time series of inorganic carbonate parameters lengthen and short‐term variations are better constrained in the coming decades, we will have stronger confidence in assessing the mechanisms contributing to long‐term changes in the source/sink status of regional sub‐Arctic seas.

Under pressure: Nanoplastics as a further stressor for sub-Antarctic pteropods already tackling ocean acidification

In the Southern Ocean (SO), plastic debris has already been found in waters and sediments. Nanoplastics (<1 μm) are expected to be as pervasive as their larger counterparts, but more harmful to biological systems, being able to enter cells and provoke toxicity. In the SO, (nano)plastic pollution occurs concomitantly with other environmental threats such as ocean acidification (OA), but the potential cumulative impact of these two challenges on SO marine ecosystems is still overlooked. Here the single and combined effects of nanoplastics and OA on the sub-Antarctic pteropod Limacina retroversa are investigated under laboratory conditions, using two surface charged polystyrene nanoparticles (PS NPs) as a proxy for nanoplastics. Sub-Antarctic pteropods are threatened by OA due to the sensitivity of their shells to changes in seawater carbonate chemistry. Short-term exposure (48 h) to PS NPs compromised the ability of pteropods to counteract OA stress, resulting in a negative effect on their survival. Our results highlights the importance of addressing plastic pollution in the context of climate change to identify realistic critical thresholds of SO pteropods.

Multi‐Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean

AbstractThe oceanic absorption of anthropogenic carbon dioxide (CO2) is expected to continue in the following centuries, but the processes driving these changes remain uncertain. We studied these processes in a simulation of future changes in global climate and the carbon cycle following the RCP8.5 high emission scenario. The simulation shows increasing oceanic uptake of anthropogenic CO2 peaking towards the year 2080 and then slowing down but remaining significant in the period up to the year 2300. These multi‐century changes in uptake are dominated by changes in sea‐air CO2 fluxes in the tropical and southern oceans. In the tropics, reductions in upwelling and vertical gradients of dissolved carbon will reduce the vertical advection of carbon‐rich thermocline waters, suppressing natural outgassing of CO2. In the Southern Ocean, the upwelling of waters with relatively low dissolved carbon keeps the surface carbon relatively low, enhancing the uptake of CO2 in the next centuries. The slowdown in CO2 uptake in the subsequent centuries is caused by the decrease in CO2 solubility and storage capacity in the ocean due to ocean warming and changes in carbon chemistry. A collapse of the Atlantic Meridional Overturning Circulation (AMOC) predicted for the next century causes a substantial reduction in the uptake of anthropogenic CO2. In sum, predicting multi‐century changes in the global carbon cycle depends on future changes in carbon chemistry along with changes in oceanic and atmospheric circulations in the Southern and tropical oceans, together with a potential collapse of the AMOC.

Distribution and Abundances of Planktic Foraminifera and Shelled Pteropods During the Polar Night in the Sea-Ice Covered Northern Barents Sea

Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ecosystems. Here we provide, for the first time, information on the under-ice planktic foraminifera and shelled pteropod abundance, species composition and vertical distribution along a transect (82°–76°N) covering the Nansen Basin and the northern Barents Sea during the polar night in December 2019. The two groups of calcifiers were examined in different environments in the context of water masses, sea ice cover, and ocean chemistry (nutrients and carbonate system). The average abundance of planktic foraminifera under the sea-ice was low with the highest average abundance (2 ind. m–3) close to the sea-ice margin. The maximum abundances of planktic foraminifera were concentrated at 20–50 m depth (4 and 7 ind. m–3) in the Nansen Basin and at 80–100 m depth (13 ind. m–3) close to the sea-ice margin. The highest average abundance (13 ind. m–3) and the maximum abundance of pteropods (40 ind. m–3) were found in the surface Polar Water at 0–20 m depth with very low temperatures (–1.9 to –1°C), low salinity (&amp;lt;34.4) and relatively low aragonite saturation of 1.43–1.68. The lowest aragonite saturation (&amp;lt;1.3) was observed in the bottom water in the northern Barents Sea. The species distribution of these calcifiers reflected the water mass distribution with subpolar species at locations and depths influenced by warm and saline Atlantic Water, and polar species in very cold and less saline Polar Water. The population of planktic foraminifera was represented by adults and juveniles of the polar speciesNeogloboquadrina pachydermaand the subpolar speciesTurborotalita quinqueloba. The dominating polar pteropod speciesLimacina helicinawas represented by the juvenile and veliger stages. This winter study offers a unique contribution to our understanding of the inter-seasonal variability of planktic foraminfera and shelled pteropods abundance, distribution and population size structure in the Arctic Ocean.

Disentangling the Effects of Ocean Carbonation and Acidification on Elemental Contents and Macromolecules of the Coccolithophore Emiliania huxleyi.

Elemental contents change with shifts in macromolecular composition of marine phytoplankton. Recent studies focus on the responses of elemental contents of coccolithophores, a major calcifying phytoplankton group, to changing carbonate chemistry, caused by the dissolution of anthropogenically derived CO2 into the surface ocean. However, the effects of changing carbonate chemistry on biomacromolecules, such as protein and carbohydrate of coccolithophores, are less documented. Here, we disentangled the effects of elevated dissolved inorganic carbon (DIC) concentration (900 to 4,930μmolkg−1) and reduced pH value (8.04 to 7.70) on physiological rates, elemental contents, and macromolecules of the coccolithophore Emiliania huxleyi. Compared to present DIC concentration and pH value, combinations of high DIC concentration and low pH value (ocean acidification) significantly increased pigments content, particulate organic carbon (POC), and carbohydrate content and had less impact on growth rate, maximal relative electron transport rate (rETRmax), particulate organic nitrogen (PON), and protein content. In high pH treatments, elevated DIC concentration significantly increased growth rate, pigments content, rETRmax, POC, particulate inorganic carbon (PIC), protein, and carbohydrate contents. In low pH treatments, the extents of the increase in growth rate, pigments and carbohydrate content were reduced. Compared to high pH value, under low DIC concentration, low pH value significantly increased POC and PON contents and showed less impact on protein and carbohydrate contents; however, under high DIC concentration, low pH value significantly reduced POC, PON, protein, and carbohydrate contents. These results showed that reduced pH counteracted the positive effects of elevated DIC concentration on growth rate, rETRmax, POC, PON, carbohydrate, and protein contents. Elevated DIC concentration and reduced pH acted synergistically to increase the contribution of carbohydrate–carbon to POC, and antagonistically to affect the contribution of protein–nitrogen to PON, which further shifted the carbon/nitrogen ratio of E. huxleyi.

The primary controls on U/Ca and minor element proxies in a cold-water coral cultured under decoupled carbonate chemistry conditions

Culture experiments are uniquely suited for uncovering the fundamental factors controlling skeletal geochemistry because it is possible to explore conditions beyond what is found in the modern ocean and to decouple parameters that co-vary in nature. We cultured juvenile individuals of a cold-water coral (Balanophyllia elegans) in a set of experiments that decoupled carbonate chemistry parameters over a wide range of pH, DIC, and [CO32−] values. Using a multi-element mixed spike isotope dilution method we then analyzed cultured skeletons for U/Ca, which has been proposed as a potential proxy for seawater pH and [CO32−], as well as Sr/Ca, and Mg/Ca.We find that U/Ca and Sr/Ca ratios in cultured B. elegans are most strongly correlated with solution DIC and not pH or [CO32−]. We also confirm previous observations that Metal/Calcium (Me/Ca) ratios follow the same correlated relationships between and among individuals across different experimental conditions. Interpretation of these robust Me/Ca patterns within the framework of a geochemical model of biomineralization allows us to identify two “rules” of skeletal growth for B. elegans. First, changes in seawater exchange rates can explain variability in B. elegans Me/Ca ratios, correlations between these ratios, and sensitivity of Me/Ca to changes in seawater carbonate chemistry. Second, our model best fits our data if we assume that calcifying fluid pH for B. elegans remains constant across widely varying experimental seawater compositions. Our study has implications for the recently developed Sr-U paleothermometer because it refines our understanding of the environmental parameters affecting this proxy. Our model further demonstrates that U/Ca is not a robust indicator of seawater pH or [CO32−]. Instead, U/Ca may record how calcifying fluid [CO32−] responds to changes in the environment or calcification dynamics, which may be useful in evaluating how corals respond to changes like ocean acidification. Measurements of U/Ca and additional Me/Ca ratios in other coral species, evaluated within a similar framework, may elucidate how those species respond to environmental change.

Centennial to millennial-scale changes in thermocline ventilation in the Arabian Sea: insights from the pteropod preservation record

The Arabian Sea hosts one of the three thickest oxygen minimum zones (OMZs) of the world ocean. Mid–depth oxygen depletion profoundly influences the chemistry of thermocline waters (HCO3ˉ, CO32ˉ and pH), which in turn significantly influences the preservation state of carbonates. The carbonate preservation is primarily controlled by the degree of saturation level of seawater with respect to the calcite and aragonite. The seawater in OMZ is undersaturated with respect to the aragonite (a metastable polymorph of CaCO3). Pteropod test being aragonitic in composition is therefore highly susceptible to the dissolution and dissolves completely below the aragonite compensation depth (ACD). Because of the current condition of intense OMZ due to high primary productivity, enhanced respiration of sinking organic carbon and reduced thermocline circulation; the ACD is shallow, lying in the middle of the OMZ. Hence, preservation record of pteropods in sea–floor sediment archives past changes in thermocline oxygen condition, carbonate chemistry, the ACD and OMZ intensity. High resolution records of various pteropod preservation indices (total pteropod abundance, transparent Limacina inflata abundance, fragmentation index) in a sediment core from the lower OMZ of the Indian margin (off Goa) enabled to investigate aragonite preservation/dissolution events and their links with the changes in ACD and OMZ intensity in the eastern Arabian Sea during the last 70 kyr BP. The proxy records reveal centennial to millennial scale changes in aragonite preservation condition in concert with Northern Hemisphere climatic events (Dansgaard–Oeschger (D–O) cycles and Heinrich events). The pteropod preservation spikes apparently correspond to the Northern Hemisphere cold events (D–O stadials and Heinrich events). Whereas, the pteropod tests were either poorly preserved or completely dissolved during the warm phases of D–O cycles (interstadials). The aragonite preservation events are attributed to the low monsoon induced productivity combined with the increased thermocline ventilation by Subantarctic Mode and Antarctic Intermediate Waters (SAMW–AAIW) resulting a weak OMZ and deeper ACD. The novel proxies (abundances of Globorotalia menardii, a planktic foraminifera and Styliola subula, a pteropod species) are used to gain better insights in to the variability of thermocline ventilation and OMZ intensity through time.

Approaches and involved principles to control pH/pCO2 stability in algal cultures

Experimental cultures of both microalgae and macroalgae are commonly carried out by phycologists or environmental biologists to look into morphological, physiological, and molecular responses to aquatic environmental changes. However, the species of inorganic carbon in algae cultures is often altered by algal photosynthetic CO2 removal and/or bicarbonate utilization. The pH changes associated with altered carbonate chemistry in cultures impact physiological processes in microalgae and macroalgae even at their exponential growth phases, since extra energy is required to sustain intracellular acid–base homeostasis. Usually, pH increases during light period due to inorganic carbon uptake and utilization for photosynthesis and decreases during dark period because of respiratory CO2 release. Therefore, to obtain relevant data aimed for physiological and/or molecular responses of algae to changed levels of environmental factors, stability of pH/pCO2 in the cultures should be considered and controlled to rule out impacts of carbonate chemistry and pH changes. In this work, principles involved in changing pH processes in algal cultures are mechanistically analyzed and several approaches to control pH and pCO2 are introduced. In order to sustain stability of pH/pCO2, the principles underline the following key points: (1) maintaining the rate of photosynthetic C removal less than or equal to the rate of CO2 dissolution into the cultures which are aerated; or (2) sustaining dilute cultures with very low cell density without aeration, so that photosynthetic C removal is small enough not to cause significant pH/pCO2 changes; or (3) stabilizing the changes in micro-environments surrounding the cells or thallus. To maintain pH drift < 1% in growing typical unicellular microalgae, the recommended cell concentration ranges from 50 × 103 to 200 × 103 mL−1 with aeration (air replacement rate of ca 500–1000 mL L−1 min−1) in semi-continuous cultures of < 1 L, and it ranges from 100 to 5000 cells mL−1 for diatoms and from 100 to 100 × 103 cells mL−1 for coccolithophores in dilute cultures without aeration, respectively. For macroalgae, maintaining the thalli in flowing through- system or in semi-continuous cultures (continuously control algal biomass density) is recommended.

Can We Better Constrain the Timing of GNAIW/UNADW Variability in the Western Equatorial Atlantic and Its Relationship to Climate Change During the Last Deglaciation?

AbstractWe have revisited the well‐trod VM28‐122 core retrieved from the deep Colombian Basin, which includes sediments that reflect modern Upper North Atlantic Deep Water and extends through the last deglaciation into the last glacial period when the site was bathed in Glacial North Atlantic Intermediate Water. Here, we leverage the nearby Cariaco Basin's surface water radiocarbon reconstruction (reservoir age, and ΔR) on the IntCal20 timescale to recast the period of the last deglaciation with a newly constrained age model. Based on the revised age model, we observe that the multimillennial decrease in benthic δ13C and B/Ca (which record δ13C of dissolved inorganic carbon and Δ[CO3−2], respectively) began at 18,100 ± 240 (95% CI) calibrated years BP, synchronous with Termination 1, as identified by changes in the Antarctic Ice Sheet composite and by the onset of rapid glacier recession in the Southern Hemisphere (Denton et al., 2010, https://doi.org/10.1126/science.1184119; Denton et al., 2021, https://10.1016/j.quascirev.2020.106771). The beginning of the decrease in benthic δ18O is concurrent with the changes in carbon chemistry or at most, a few hundred years later. It is no later than 17,700 ± 300 (95% CI) yrs BP in our record, at the putative start of Heinrich Stadial 1. With sufficient data density (more than 2–3 control points per kyr) and an independent record of past surface water radiocarbon variations, it is possible to achieve late glacial and deglacial chronologies with fidelities similar to those of ice cores. Doing so in more oceanographic locations should shed light more broadly on the mechanisms instrumental to abrupt climate change.

Community Science for Coastal Acidification Monitoring and Research

Ocean and coastal acidification (OCA) present a unique set of sustainability challenges at the human-ecological interface. Extensive biogeochemical monitoring that can assess local acidification conditions, distinguish multiple drivers of changing carbonate chemistry, and ultimately inform local and regional response strategies is necessary for successful adaptation to OCA. However, the sampling frequency and cost-prohibitive scientific equipment needed to monitor OCA are barriers to implementing the widespread monitoring of dynamic coastal conditions. Here, we demonstrate through a case study that existing community-based water monitoring initiatives can help address these challenges and contribute to OCA science. We document how iterative, sequential outreach, workshop-based training, and coordinated monitoring activities through the Northeast Coastal Acidification Network (a) assessed the capacity of northeastern United States community science programs and (b) engaged community science programs productively with OCA monitoring efforts. Our results (along with the companion manuscript) indicate that community science programs are capable of collecting robust scientific information pertinent to OCA and are positioned to monitor in locations that would critically expand the coverage of current OCA research. Furthermore, engaging community stakeholders in OCA science and outreach enabled a platform for dialogue about OCA among other interrelated environmental concerns and fostered a series of co-benefits relating to public participation in resource and risk management. Activities in support of community science monitoring have an impact not only by increasing local understanding of OCA but also by promoting public education and community participation in potential adaptation measures.