The Gulf of Maine holds significant ecological and economic value for fisheries and communities in north-eastern North America. However, there is apprehension regarding its vulnerability to the effects of increasing atmospheric CO2. Substantial recent warming and the inflow of low alkalinity waters into the Gulf of Maine have raised concerns about the impact of ocean acidification on resident marine calcifiers (e.g. oysters, clams, mussels). With limited seawater pH records, the natural variability and drivers of pH in this region remain unclear. To address this, we present coastal water pH proxy records using boron isotope (δ11B) measurements in long-lived, annually banded, crustose coralline algae (1920–2018 CE). These records indicate seawater pH was low (~ 7.9) for much of the last century. Contrary to expectation, we also find that pH has increased (+ 0.2 pH units) over the past 40 years, despite concurrent rising atmospheric CO2. This increase is attributed to an increased input of high alkalinity waters derived from the Gulf Stream. This delayed onset of ocean acidification is cause for concern. Once ocean circulation-driven buffering effects reach their limit, seawater pH decline may occur swiftly. This would profoundly harm shellfisheries and the broader Gulf of Maine ecosystem.
Continue reading ‘Delayed onset of ocean acidification in the Gulf of Maine’Posts Tagged 'biogeochemistry'
Delayed onset of ocean acidification in the Gulf of Maine
Published 23 January 2025 Science ClosedTags: biogeochemistry, chemistry, North Atlantic, paleo
Oceanic enrichment of ammonium and its impacts on phytoplankton community composition under a high-emissions scenario
Published 21 January 2025 Science ClosedTags: biogeochemistry, biological response, globalmodeling, modeling, phytoplankton
Ammonium (NH4+) is an important component of the ocean’s dissolved inorganic nitrogen (DIN) pool, especially in stratified marine environments where intense recycling of organic matter elevates its supply over other forms. Using a global ocean biogeochemical model with good fidelity to the sparse NH4+ data that is available, we project increases in the NH4+:DIN ratio in over 98% of the ocean by the end of the 21st century under a high-emission scenario. This relative enrichment of NH4+ is driven largely by circulation changes, and secondarily by warming-induced increases in microbial metabolism, as well as reduced nitrification rates due to pH decreases. Supplementing our model projections with geochemical measurements and phytoplankton abundance data from Tara Oceans, we demonstrate that shifts in the form of DIN to NH4+ may impact phytoplankton communities by disadvantaging nitrate-dependent taxa like diatoms while promoting taxa better adapted to NH4+. This could have cascading effects on marine food webs, carbon cycling, and fisheries productivity. Overall, the form of bioavailable nitrogen emerges as an potentially underappreciated driver of ecosystem structure and function in the changing ocean.
Continue reading ‘Oceanic enrichment of ammonium and its impacts on phytoplankton community composition under a high-emissions scenario’Carbon cycling and ocean acidification studies in Baffin Bay and Nares Strait
Published 20 January 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, modeling, regionalmodeling
The marine carbon cycle in Canadian Arctic waters, particularly in Nares Strait and Baffin Bay, is undergoing rapid change due to a shifting climate. Despite this, there’s been a paucity of research into the carbonate chemistry and biogeochemical processes in these regions. This thesis addresses this gap by investigating the complex carbon dynamics in these waters, critical for understanding their role in the global carbon cycle. The first research chapter evaluates the strength of the biological carbon pump during the spring ice-edge bloom in Baffin Bay. We found stark differences in springtime net community production (NCP) between Arctic and Atlantic water domains, in western and eastern Baffin Bay, respectively. Arctic outflow waters exhibited low spring NCP (< 1 mol C m-2) due to persistent sea-ice cover and strong stratification of the upper water column, whereas the Atlantic water domain displayed high NCP rates (up to 5.7 mol C m-2). The first comprehensive examination of the marine carbon dynamics in Nares Strait is also presented. Using a multi-tracer linear mixing model, we distinguished the role of physical and biological processes on the distribution of dissolved inorganic carbon in Nares Strait. We identified water mass mixing as the dominant control on marine carbon dynamics, with primary production also playing an important role in decreasing surface pCO2. Importantly, this investigation also provided the first documented evidence of Siberian river waters arriving in Nares Strait. The final research chapter of this thesis investigates the biogeochemical processes affecting aragonite saturation states (ΩAr), and the state of ocean acidification in Baffin Bay, with a focus on the west Greenland continental shelf region, which has remained under-studied in terms of its marine biogeochemistry. We identify two main depth-dependent processes shaping the ΩAr distribution throughout Baffin Bay; within the upper 200 metres, lower ΩAr coincides with increasing fractions of Arctic-outflow waters, while below 200 metres organic matter respiration is responsible for decreasing ΩAr. Surprisingly, substantial Arctic-outflow waters were identified on the west Greenland shelf, challenging what is currently known of circulation patterns in the bay, and underscoring the need for further research.
Continue reading ‘Carbon cycling and ocean acidification studies in Baffin Bay and Nares Strait’The contrasting role of marine- and land-terminating glaciers on biogeochemical cycles in Kongsfjorden, Svalbard
Published 15 January 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field
This case study of Kongsfjorden, western coastal Svalbard, provides insights on how freshwater runoff from marine- and land-terminating glaciers influences the biogeochemical cycles and distribution patterns of carbon, nutrients, and trace elements in an Arctic fjord system. We collected samples from the water column at stations along the fjord axis and proglacial river catchments, and analyzed concentrations of dissolved trace elements, together with dissolved nutrients, as well as alkalinity and dissolved inorganic carbon. Statistical tools were applied to identify and quantify biogeochemical processes within the fjord that govern the constituent distributions. Our results suggest that the glacier type affects nutrient availability and, therefore, primary production. Glacial discharge from both marine-terminating glaciers and riverine discharge from land-terminating glaciers are important sources of dissolved trace elements (dAl, dMn, dCo, dNi, dCu, and dPb) that are involved in biological and scavenging processes within marine systems. We identified benthic fluxes across the sediment-water interface to supply fjord waters with silicate, dFe, dCu, and dZn. Our data show that intensive carbonate weathering in proglacial catchments supplies fjord waters with additional dissolved carbonates and, therefore, attenuates reduced buffering capacities caused by glacial runoff. Our study provides valuable insight into biogeochemical processes and carbon cycling within a climate-sensitive, high-latitude fjord region, which may help predict Arctic ecosystem changes in the future.
Key Points
- Nutrient, trace element, and carbon species distributions are influenced by glacial discharge of land- and marine-terminating glaciers
- Discharge of marine- and land-terminating glaciers is an important source of bio-essential trace elements
- Progressive glacier retreat will likely impact biotic and abiotic carbon uptake in the future
Plain Language Summary
Arctic regions are particularly vulnerable to climate change and are considerably influenced by anthropogenic impacts. However, the scientific community currently lacks sufficient information on the mechanisms and drivers of these environmental changes, and the consequences that may arise for Arctic ecosystems. Our study provides insights into the distribution patterns of carbon, nutrients, and trace elements in fjord systems influenced by freshwater supply from melting glaciers. We collected water samples from the water column of Kongsfjorden (Svalbard, Norway) and from glacier-fed rivers draining into the fjord. Our results show that freshwater from glaciers is an important source of nutrients, and trace elements that are involved in biological processes within coastal areas. In the future, we predict Arctic fjords will become less productive ecosystems, as a result of the progressive melting and glacier retreat. Ultimately, this has the potential to alter the circulation of water masses and consequently change the redistribution of nutrients and essential trace elements in the water column.
Continue reading ‘The contrasting role of marine- and land-terminating glaciers on biogeochemical cycles in Kongsfjorden, Svalbard’Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes
Published 9 January 2025 Science ClosedTags: biogeochemistry, biological response, laboratory, mesocosms, morphology, multiple factors, North Atlantic, phanerogams, physiology, primary production, respiration, temperature
Highlights
- 45-days mesocosm experiment with whole-benthic community to mimic nature conditions
- Global warming (GW) and ocean acidification (OA) modify C dynamics on seagrasses.
- OA enhances GPP and NCP and synergistic effects when combined with GW.
- DOC production decreased with OA and GW separately, but increased when combined.
- Climate change potentially increases the blue carbon service of C. nodosa populations.
Abstract
Ocean acidification (OA) and global warming (GW) drive a variety of responses in seagrasses that may modify their carbon metabolism, including the dissolved organic carbon (DOC) fluxes and the organic carbon stocks in upper sediments. In a 45-day full-factorial mesocosm experiment simulating forecasted CO2 and temperature increase in a Cymodocea nodosa community, we found that net community production (NCP) was higher under OA conditions, particularly when combined with warming (i.e., synergistic effect). Moreover, under OA conditions, an increase in aboveground biomass and photosynthetic shoot area was recorded. Interestingly, DOC fluxes were reduced when exposed to OA; however, an increase occurred when both factors acted together (i.e., antagonistic effect), which was attributable to increased DOC release by plants. Our results suggest that C. nodosa populations in temperate latitude may favor blue carbon service in future scenarios of OA and GW by increasing the NCP, the DOC export with lower labile:recalcitrant ratio, and accumulating more organic carbon in upper sediments. These findings offer additional arguments for the urgent need to protect and conserve this valuable ecosystem.
Continue reading ‘Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes’Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent
Published 3 January 2025 Science ClosedTags: biogeochemistry, biological response, BRcommunity, community composition, field, Mediterranean, otherprocess, phanerogams, prokaryotes, sediment, vents
Highlights
- Shallow CO2 vents generate pH gradients that influence sediment biogeochemistry
- Sedimentary organic matter (SOM) and prokaryotic community were analysed along a pH gradient
- Environmental gradients drive distribution and abundance of benthic prokaryotic communities and origin of SOM
- Vent-derived sources contributed largely to SOM up to 350 m from the vent
- CO2-driven benthic community shifts affect spatial dynamics of SOM origin and composition with expected rebounds on biota
Abstract
Volcanic emissions in shallow vents influence the biogeochemistry of the sedimentary compartment, creating marked abiotic gradients. We assessed the spatial dynamics of the sediment compartment, as for the composition and origin of organic matter and associated prokaryotic community, in a volcanic shallow CO2 vent (Vulcano Island, Italy). Based on elemental (carbon, nitrogen content and their ratio) and isotopic composition (δ13C, δ15N and δ34S), the contribution of vent-derived organic matter (microbial mats) to sedimentary organic matter was high close to the vent, while the marine-derived end-members (seagrasses) contributed highly at increasing distance. Chemoautotrophic Campylobacterota and hyperthermophilic Achaea prevailed close to the vent, whilst phototrophic and chemoheterotrophic members dominated at increasing distance. Abiotic gradients generated by the volcanic CO2 vent drive relevant changes in the composition, origin and nutritional quality of sedimentary organic matter, and influence the structure and complexity of associated prokaryotic communities, with expected relevant impact on the entire food-web.
Continue reading ‘Extreme abiotics drive sediment biocomplexity along pH gradients in a shallow submarine volcanic vent’Acceleration of warming, deoxygenation, and acidification in the Arabian Gulf driven by weakening of summer winds
Published 1 January 2025 Science ClosedTags: biogeochemistry, modeling, regionalmodeling
The Arabian Gulf (AG) exports hypersaline, dense waters into the Sea of Oman (SOO), replaced by fresher inflowing surface waters from the Indian Ocean. We investigate the impact of recent AG warming on its exchange with the SOO and the implications this has on the AG biogeochemistry. Using an eddy-resolving hindcast model simulation, we analyze the hydrography and biogeochemistry of the AG and the SOO from 1980 to 2018. Our study reveals that changes in summer surface winds have accelerated AG warming and weakened it in the SOO, reducing the density gradient and water exchange between the two seas during late summer. This has led to nutrient buildup, increased productivity, and heightened deoxygenation and acidification in the AG. These findings underscore how subtle wind changes can exacerbate the vulnerability of marginal seas to climate change and stress the need to properly represent regional winds in global climate models.
Continue reading ‘Acceleration of warming, deoxygenation, and acidification in the Arabian Gulf driven by weakening of summer winds’Arctic Ocean acidification and carbonate undersaturation enhanced by coastal permafrost erosion
Published 31 December 2024 Science ClosedTags: Arctic, biogeochemistry, modeling, regionalmodeling
Increasing atmospheric CO2 drives ocean acidification, with some of the fastest rates observed on Arctic shelves. Lowest pH levels occur near the coasts due to the additional effects of land-derived carbon sources. However, the impact of anthropogenic climate change on seawater acidity mediated by increasing permafrost thaw and coastal erosion remains unknown. Here, we find that the increase in organic matter release by coastal permafrost erosion over the 20th century enhances the interannual variability of seawater pH in Arctic near-shore areas. As a consequence, carbonate undersaturation events, stressing marine ecosystems, become more frequent, intense, and longer-lasting. We account for synergistic effects of anthropogenic climate change by combining increasing atmospheric CO2 levels and coastal erosion rates, utilizing a novel global model with high-resolution grid refinement towards coastal regions and improved process representation of shelf-specific carbon dynamics. By considering the role of coastal permafrost erosion, we conclude that critical Arctic Ocean acidification states will emerge earlier than simulated by the current generation of Earth system models. Our results emphasize the importance of understanding permafrost-ocean interactions and their increasing impact on marine ecosystems, especially in the rapidly changing Arctic region.
Continue reading ‘Arctic Ocean acidification and carbonate undersaturation enhanced by coastal permafrost erosion’Development of a high-resolution ocean ensemble future projection dataset for the North Pacific incorporating simple biogeochemical processes
Published 27 December 2024 Science ClosedTags: biogeochemistry, modeling, North Pacific, regionalmodeling
In this study, we developed a new version of the future ocean regional projection dataset in the North Pacific (FORP-NP10) by performing an ensemble of historical and multi-scenario future projection simulations from 1960 to 2100 using a high-resolution ocean downscaling model system driven by surface forcings based on the atmospheric data of the Coupled Model Intercomparison Project (Phase 5). This version is characterized by the inclusion of simple biogeochemical processes within the simulations of the multi-case (four forcing cases) and multi-future projection scenarios (representative concentration pathway 2.6 and 8.5) using a mesoscale eddy-resolving (approximately 10 km) horizontal resolution. The dataset reasonably represented the main biogeochemical properties in the North Pacific and around Japan, such as surface CO2 flux, pH, subsurface oxygen, surface nitrate, and chlorophyll, as well as the ocean physics of the regions, including the mesoscale/frontal structures of the Kuroshio, Kuroshio Extension, and mixed layer depth. We assessed the bias tendencies and structures of these properties by comparing them with observational reference data and the low-resolution model results. Our ensemble dataset consistently projected future upper-ocean warming, acidification, deoxygenation, and changes in nutrient and primary production in the twenty-first century (reported as global analyses in recent reports of the Intergovernmental Panel on Climate Change) in the regions surrounding Japan, revealing that the future changes exhibited spatial contrasts or varying tendencies in the regions.
Continue reading ‘Development of a high-resolution ocean ensemble future projection dataset for the North Pacific incorporating simple biogeochemical processes’A regional physical-biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)
Published 25 December 2024 Science ClosedTags: Arctic, biogeochemistry, biological response, field, modeling, North Pacific, regionalmodeling, zooplankton
Regional ocean models enable generation of computationally-affordable and regionally-tailored \ ensembles of near-term forecasts and long-term projections of sufficient resolution to serve marine resource management. Climate change, however, has created marine resource challenges, such as shifting stock distributions, that cut across domestic and international management boundaries and have pushed regional modeling efforts toward “coastwide” approaches. Here we present and evaluate a multidecadal hindcast with a Northeast Pacific (NEP) regional implementation of the Modular Ocean Model version 6 with sea ice and biogeochemistry that extends from the Chukchi Sea to the Baja California Peninsula at 10-km horizontal resolution (MOM6-COBALT-NEP10k, or “NEP10k”). This domain includes an Arctic-adjacent system with a broad shallow shelf seasonally covered by sea ice (the Eastern Bering Sea, EBS), a sub-Arctic system with upwelling in the Alaska Gyre and predominant downwelling winds and large freshwater forcing along the coast (the Gulf of Alaska, GoA), and a temperate, eastern boundary upwelling ecosystem (the California Current Ecosystem, CCE). The coastwide model was able to recreate seasonal and cross-ecosystem contrasts in numerous ecosystem-critical properties including temperature, salinity, inorganic nutrients, oxygen, carbonate saturation states, and chlorophyll. Spatial consistency between modeled quantities and observations generally extended to plankton ecosystems, though small to moderate biases were also apparent. Fidelity with observed zooplankton biomass, for example, was limited to first-order seasonal and cross-system contrasts. Temporally, simulated monthly surface and bottom temperature anomalies in coastal regions (< 500m deep) closely matched estimates from data-assimilative ocean reanalyses. Performance, however, was reduced in some nearshore regions coarsely resolved by the model’s 10-km resolution grid, and the time series of satellite-based chlorophyll anomaly estimates proved more difficult to match than temperature. System-specific ecosystem indicators were also assessed. In the EBS, NEP10k robustly matched observed variations, including recent large declines, in the area of the summer bottom water “cold pool” (< 2 °C) which exerts a profound influence on EBS fisheries. In the GoA, the simulation captured patterns of sea surface height variability and variations in thermal, oxygen and acidification risk associated with local modes of inter-annual to decadal climate variability. In the CCE, the simulation robustly captured variations in upwelling indices and coastal water masses, though discrepancies in the latter were evident in the Southern California Bight. Enhanced model resolution may reduce such discrepancies, but any benefits must be carefully weighed against computational costs given the intended use of this system for ensemble predictions and projections. Meanwhile, the demonstrated NEP10k skill level herein, particularly in recreating cross-ecosystem contrasts and the time variation of ecosystem indicators over multiple decades, suggests considerable immediate utility for coastwide retrospective and predictive applications.
Continue reading ‘A regional physical-biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)’Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin
Published 12 December 2024 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, field, otherprocess, phytoplankton, South Pacific
A predicted consequence of ocean acidification is its negative effect on the pools of Particulate Inorganic Carbon (PIC) that are essential for ‘ballasting’ the sinking of organic carbon, potentially leading to decreased subsurface oxygen. To explore such possible feedbacks, we investigated the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved oxygen in the Southeast Pacific open ocean oxygen minimum zone, which naturally exhibits extremely low dissolved oxygen, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore counts during late-spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, significantly contributed to PIC through the shedding of coccoliths in the upper waters. On average, about a half of the PIC was attributed to countable coccoliths, with significantly diminished quotas observed below the euphotic depth. Temperature, oxygen, and pH were identified as key variables influencing PIC variation. PIC quotas were similar to those reported in other upwelling zones. However, PIC:POC ratios were substantially lower than what has been reported both in other open ocean and coastal margin areas, an effect that was more pronounced within the vertically defined oxygen minimum zone core. This study contributes to understanding the role of coccolithophores in PIC pools and suggests that the presence of low O2/low pH subsurface waters does not inhibit coccolithophore PIC quotas but may decrease the role of PIC in ballasting the export of organic carbon.
Continue reading ‘Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin’The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow
Published 18 November 2024 Science ClosedTags: biogeochemistry, biological response, North Atlantic, phanerogams, primary production
The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ34S, δ18O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates.
Continue reading ‘The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow’Competitive dissolution of mixed carbonate solids under simulated ocean acidification
Published 12 November 2024 Science ClosedTags: algae, biogeochemistry, biological response, BRcommunity, laboratory, sediment
It is estimated that at least 25 % of the anthropogenic carbon dioxide (CO2) emitted to the atmosphere since the start of the industrial revolution has been absorbed and dissolved by the oceans. The uptake of CO2 by the oceans leads to an increase in the seawater proton concentration ([H+]), and decreases in seawater pH, carbonate ion concentration ([CO32–]), and saturation state (Ω) with respect to calcium carbonate (CaCO3) minerals; a process commonly referred to as “ocean acidification”. Shallow-water (<200 m), high-magnesium, biogenic calcites are expected to be amongst the first to respond to ocean acidification, and it has been proposed that they will dissolve selectively and sequentially according to their solubility in seawater. In this study, we test this competitive dissolution hypothesis by reacting a mixture of biogenic and synthetic carbonates of varying Mg content with acidified, natural seawater to simulate the progressive acidification of surface-ocean waters by anthropogenic CO2. The results of this study confirm the hypothesis that carbonates will dissolve sequentially according to their respective solubility. They also reveal that the dissolution of high Mg-calcites will proceed incongruently. The originality of this contribution rests with the demonstration that the presence of a single high Mg-calcite will generate, like in a sediment of mixed mineralogy, a continuum of transient states as lower Mg-calcites of greater stability are precipitated and dissolved. Consequently, in a semi-closed or closed system, the pH buffering of the acidified seawater solution will be progressive rather than occur in steps according to changes in the solubility of the individual carbonate phases that compose a sediment. Hence, we expect that, as the oceans take up more anthropogenic CO2 and further acidify, the average mineralogy and composition (Mg content) of shallow-water carbonate sediments and reef structures will change over the next few centuries as the most soluble carbonate phases (high-Mg calcites) are dissolved and no longer precipitated.
Continue reading ‘Competitive dissolution of mixed carbonate solids under simulated ocean acidification’Inter-annual and spatial variations of air-sea CO2 fluxes and acidification mechanism in the coastal waters of Qingdao, China during 2011–2019
Published 11 November 2024 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Highlights
- pH and Ωarag showed a decrease and then upward trend in 2011–2019.
- Biological processes controlled spatio-temporal differences in pCO2 and Ωarag.
- The Ulva prolifera bloom event had a strong influence on the carbonate system.
- The study area all exhibited a sink for atmospheric CO2 in the spring of 2011–2019.
Abstract
The interplay of global climate change and anthropogenic activities has significantly affected the carbon cycle in coastal ocean environments. Consequently, further investigation into the carbonate system, carbon source and sink processes, and acidification mechanisms is essential. This study examined the surface carbonate system offshore of Qingdao, utilizing data from nine spring cruises in 2011–2019. The inter-annual variations in sea surface temperature revealed a gradual upward trend, whereas chlorophyll a (Chl-a) and apparent oxygen utilization (AOU) exhibited alternating trends of increase and decrease. Over the period from 2011 to 2019, pH levels ranged from 8.00 to 8.19, partial pressure of CO2 (pCO2) values varied between 187.8 and 364.1 μatm, and calcium carbonate saturation (Ωarag) ranged from 3.22 to 4.79. From 2011 to 2017, both pH and Ωarag showed a decreasing trend, attributed to the increasing influence of respiration. In contrast, an upward trend was observed for both parameters during 2018 and 2019, indicating a decline in respiration’s contribution. Biological processes, especially the increase in respiration caused by the nutrients and organic matter released through human activities, were pivotal in determining spatial variations in pCO2 and Ωarag offshore, while the impact of mixing processes and temperature was comparatively negligible. Furthermore, the Ulva prolifera bloom event in July 2015 significantly affected the coastal waters of Qingdao’s carbonate system when compared to the no-bloom period in March 2015. Overall, the study area functioned as a sink for atmospheric CO2 in the spring. The fluctuations in air-sea CO2 fluxes corresponded with changes in ΔpCO2 and wind speeds, with surface seawater air-sea CO2 fluxes ranging from −17.7 to 12.2 mmol m−2 d−1 between 2011 and 2019, yielding an average flux of −9.4 ± 5.3 mmol m−2 d−1.
Continue reading ‘Inter-annual and spatial variations of air-sea CO2 fluxes and acidification mechanism in the coastal waters of Qingdao, China during 2011–2019’Climate change driven effects on transport, fate and biogeochemistry of trace element contaminants in coastal marine ecosystems
Published 24 October 2024 Science ClosedTags: Arctic, biogeochemistry, policy
Human activities and climate change substantially threaten coastal areas, impacting ecosystem functions, services, and human-wellbeing. Trace elements, from both natural and anthropogenic sources, can contaminate coastal regions, and at high concentrations may become toxic to marine biota. Climate change is likely to affect the sources, sinks and cycling of trace elements in coastal systems: for example, riverine runoff is set to increase as precipitation in the Arctic intensifies, and more frequent extreme floods are expected to activate previously deeply buried trace elements. Furthermore, changes in human activity under a warming climate, such as increased Arctic shipping and potential geoengineering projects such as ocean alkalinity enhancement, will likely introduce more trace elements to coastal ecosystems. Advancing our understanding of trace element cycling is at present limited by factors including lack of data coverage in the Global South, challenges in studying multi-stressor effects and ecosystem responses, lack of long-term data, and the difficulty in parametrizing robust models in coastal environments.
Continue reading ‘Climate change driven effects on transport, fate and biogeochemistry of trace element contaminants in coastal marine ecosystems’Experimental studies on CO2 sequestration via enhanced rock weathering in seawater: insights for climate change mitigation strategies in coastal and open ocean environments
Published 30 September 2024 Science ClosedTags: biogeochemistry, mitigation
Enhanced weathering (EW) of ultramafic rocks from the Muslim Bagh Ophiolite, Pakistan, has been studied in laboratory experiments to explore carbon sequestration as a climate change mitigation strategy for coastal and open sea environments. The research focused on a cost-effective ex situ experiment to examine the effects of EW reaction pathways arising from the interactions among rock powder, seawater and CO2. The experimental filtrates from different milled peridotite samples exhibit a decrease in the Mg/Ca ratio as the specific surface area increases, which accelerates reaction rates. This suggests that the leached Mg from the original rock may have been consumed in the formation of brucite, serpentine and carbonates during EW. Similar reaction pathways are also responsible for the chemical alterations observed in amphibolite, albeit to varying degrees. On the other hand, the experimental residues showed an increase in loss on ignition compared to the original rock, indicating that EW has facilitated the incorporation of H2O and CO2 into secondary mineral structures through various reaction pathways, leading to the formation of brucite, serpentine and carbonates. Thermal gravimetric analysis of the experimental residues confirms the presence of these minerals based on their decomposition temperatures. Additionally, XRD analysis identified a range of carbonates in the residues of both peridotite and amphibolite samples, validating the occurrence of carbonation reactions. SEM images reveal textural changes in both samples, supporting the formation of secondary minerals through EW, consistent with observations from the petrographic study of untreated samples. Control experiments on CO2 absorption in seawater showed a decrease in pH, highlighting ocean acidification from increased CO2 emissions. However, when rock powder was added to the seawater-CO2 mixture, the pH increased. This suggests that the EW of ultramafic rock powders can sequester CO2 while raising seawater pH through the formation of secondary minerals. This research could serve as an analog for EW applications, considering the worldwide abundance of ultramafic rocks and the availability of coastal and open ocean environments. However, further research is required to understand the behavior of other elements and their impacts on ocean chemistry in EW processes before applying CO2 sequestration strategies.
Continue reading ‘Experimental studies on CO2 sequestration via enhanced rock weathering in seawater: insights for climate change mitigation strategies in coastal and open ocean environments’Reconstructing CO2 uptake capacity and pH dynamics in the Middle Ordovician Taebaeksan Basin, Korea
Published 27 September 2024 Science ClosedTags: biogeochemistry, chemistry, North Pacific
Highlights
- First δ11B record from Mid-Ordovician Taebaeksan carbonates.
- Middle Darriwilian Taebaeksan Basin acted as atmospheric CO2 sink.
- Sea-level rise & anoxia reduced CO2 uptake via less calcification & photosynthesis.
- Boron isotopes reveal ancient shallow marine pH levels.
Abstract
This study presents the first continuous carbonate boron isotope (δ11Bcarb) record from Middle Ordovician carbonate rocks, focusing on the Taebaek section in Korea. The δ11Bcarb values analyzed from the Makgol, Jigunsan, and Duwibong formations range between 7.5 ‰ and 17.8 ‰, falling within the published Paleozoic range. Samples exhibit minimal diagenetic alteration, as evidenced by weak correlations between isotopic factors and elemental ratios ((δ11Bcarb, δ13Ccarb, δ15Nbulk, B/Ca, Mn/Sr, and Na/Ca) as well as mineralogical observations used to select unaltered micrite portions. Using the δ11Bcarb data, we reconstruct pH levels (8.4 to 9.1) which suggest that this shallow shelf environment acted as a CO2 sink during the Middle Darriwilian, despite periods of acidification coinciding with sea level rise and expansion of anoxic zones. Weakening of the basin’s CO2 uptake capacity via reduced CaCO3 precipitation and photosynthesis accompanied these oceanographic changes. Our findings provide new insights into the dynamics of CO2 accumulation and pH in Middle Ordovician shallow marine settings in relation to sea level fluctuations. This work lays the foundation for further research into ocean chemistry and carbon cycle perturbations during this important period in Earth’s history.
Continue reading ‘Reconstructing CO2 uptake capacity and pH dynamics in the Middle Ordovician Taebaeksan Basin, Korea’Influence of rivers, tides, and tidal wetlands on estuarine carbonate system dynamics
Published 26 September 2024 Science ClosedTags: biogeochemistry, chemistry, field, modeling, North Atlantic, regionalmodeling
Variations in estuarine carbonate chemistry can have critical impacts on marine calcifying organisms, yet the drivers of this variability are difficult to quantify from observations alone, due to the strong spatiotemporal variability of these systems. Terrestrial runoff and wetland processes vary year to year based on local precipitation, and estuarine processes are often strongly modulated by tides. In this study, a 3D-coupled hydrodynamic-biogeochemical model is used to quantify the controls on the carbonate system of a coastal plain estuary, specifically the York River estuary. Experiments were conducted both with and without tidal wetlands. Results show that on average, wetlands account for 20–30% of total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes into the estuary, and double-estuarine CO2 outgassing. Strong quasi-monthly variability is driven by the tides and causes fluctuations between net heterotrophy and net autotrophy. On longer time scales, model results show that in wetter years, lower light availability decreases primary production relative to biological respiration (i.e., greater net heterotrophy) resulting in substantial increases in CO2 outgassing. Additionally, in wetter years, advective exports of DIC and TA to the Chesapeake Bay increase by a factor of three to four, resulting in lower concentrations of DIC and TA within the estuary. Quantifying the impacts of these complex drivers is not only essential for a better understanding of coastal carbon and alkalinity cycling, but also leads to an improved assessment of the health and functioning of coastal ecosystems both in the present day and under future climate change.
Continue reading ‘Influence of rivers, tides, and tidal wetlands on estuarine carbonate system dynamics’Off-shelf transport and biogeochemical cycling of terrestrial organic carbon along the East Siberian continental margin
Published 23 September 2024 Science ClosedTags: Arctic, biogeochemistry, chemistry, sediment
Continental margins receive, process and sequester most of the terrestrial organic carbon (terrOC) released into the ocean. In the Arctic, increasing fluvial discharge and collapsing permafrost are expected to enhance terrOC release and degradation, leading to ocean acidification and translocated CO2 release to the atmosphere. However, the processes controlling terrOC transport beyond the continental shelf, and the amount of terrOC that reaches the slope and the rise are poorly described. Here we study terrOC transport to the Laptev Sea continental slope and rise by probing surface sediments with dual-isotope (δ13C/Δ14C) source apportionment, degradation-diagnostic terrestrial biomarkers (n-alkanes, n-alkanoic acids, lignin phenols) and 210Pbxs-based mass accumulation rates (MAR). The MAR-terrOC (g m−2 yr−1) decrease from 14.7 ± 12.2 on the shelf, to 7.0 ± 5.8 over the slope, to 2.3 ± 0.3 for the rise. Scaling this to the respective regimes yields that 80% of the terrOC accumulates on the shelf, while 11% and 9% of the accumulation occurs in slope and rise sediments, respectively. TerrOC remineralization is evidenced by biomarker degradation proxies (CPI of n-alkanes and 3,5Bd/V) indicating 40% and 60% more terrOC degradation from slope to rise, consistent with a decline in terrOC concentrations by 57%. TerrOC degradation only partially explains this decline. An updated Laptev Sea terrOC budget suggests that sediment transport dynamics such as turbidity currents may drive terrOC shelf-basin export, contributing to the observed accumulation pattern. This study quantitatively demonstrates that Arctic shelf seas are key receptor systems for remobilized terrOC, emphasizing their importance in the carbon cycle of the rapidly changing Arctic.
Key Points
- Terrestrial carbon export from the Laptev Sea shelf to the slope and rise is studied using δ13C/Δ14C, biomarkers and 210Pb mass accumulation
- The accumulation of terrestrial carbon declines by 52% at the shelf edge and by 68% from slope to rise due to transport and degradation dynamics
- A terrestrial carbon budget for the Laptev Sea suggests 80%–90% of the input is retained on the shelf via accumulation and re-mineralization
Interactions between ocean acidification and multiple environmental drivers on the biochemical traits of marine primary producers: a meta-analysis
Published 19 September 2024 Science ClosedTags: biogeochemistry
Highlights
- OA acted interactively with other environmental drivers on marine primary producers.
- Additive effects dominated, with smaller proportions of antagonism and synergism.
- Interaction type depends on the specific type of the environmental driver.
Abstract
Ocean acidification (OA) interacts with multiple environmental drivers, such as temperature, nutrients, and ultraviolet radiation (UVR), posing a threat to marine primary producers. In this study, we conducted a quantitative meta-analysis of 1001 experimental assessments from 68 studies to examine the combined effects of OA and multiple environmental drivers (e.g., light, nutrient) on the biochemical compositions of marine primary producers. The results revealed significant positive effects of each environmental driver and their interactions with OA according to Hedge’s d analysis. The results revealed significant positive effects of multiple environmental drivers and their interactions with OA. Additive effects dominated (71%), with smaller proportions of antagonistic (20%) and synergistic interactions (9%). The antagonistic interactions, although fewer, had a substantial impact, causing OA and other environmental drivers to interact antagonistically. Significant differences were observed among taxonomic groups: haptophytes and rhodophytes were negatively affected, while bacillariophytes were positively affected by OA. Our findings also indicated that the interactions between OA and multiple environmental drivers varied depending on specific type of the environmental driver, suggesting a modulating role of OA on the biochemical compositions of marine primary producers in response to global change. In summary, our study elucidates the complex interactions between OA and multiple environmental drivers on marine primary producers, highlighting the varied impacts on biochemical compositions and elemental stoichiometry.
Continue reading ‘Interactions between ocean acidification and multiple environmental drivers on the biochemical traits of marine primary producers: a meta-analysis’
