Posts Tagged 'Arctic'

« Previous Entries
Next Entries »

Atlantic-origin water extension into the Pacific Arctic induced an anomalous biogeochemical event

Published 15 November 2023 Science Closed
Tags: , , , , , , , , , , ,

The Arctic Ocean is facing dramatic environmental and ecosystem changes. In this context, an international multiship survey project was undertaken in 2020 to obtain current baseline data. During the survey, unusually low dissolved oxygen and acidified water were found in a high-seas fishable area of the western (Pacific-side) Arctic Ocean. Herein, we show that the Beaufort Gyre shrinks to the east of an ocean ridge and forms a front between the water within the gyre and the water from the eastern (Atlantic-side) Arctic. That phenomenon triggers a frontal northward flow along the ocean ridge. This flow likely transports the low oxygen and acidified water toward the high-seas fishable area; similar biogeochemical properties had previously been observed only on the shelf-slope north of the East Siberian Sea.

…

Fig. 1: Schematic of the Arctic Ocean circulation and the study area with hydrographic stations.

a, b Maps of the Arctic Ocean and the study area. In a, yellow, blue, and red arrows represent flows from the shelf-slope at the north of the East Siberian Sea (ESS), and from the Pacific and Atlantic oceans in 2017–2020. Ocean circulation and water masses are abbreviated as follows: Beaufort Gyre (BG), Transpolar Drift (TPD), Pacific Water (PW), Lower Halocline Water (LHW), and Atlantic Water (AW). Geographical locations are abbreviated as follows: Canada Basin (CB), Chukchi Plateau (CP), Mendeleyev Ridge (MR), Makarov Basin (MB), and Lomonosov Ridge (LR). In b red, green, and blue dots denote the hydrographic stations conducted by the Research Vessel (R/V) Araon (Korea), R/V Mirai (Japan), and Canadian Coast Guard Ship Louis S. St-Laurent (Canada), under the 2020 Synoptic Arctic Survey project. Black dots indicate other hydrographic stations between 2002 and 2019 listed in Supplementary Table 1.

Continue reading ‘Atlantic-origin water extension into the Pacific Arctic induced an anomalous biogeochemical event’

Global synthesis of the status and trends of ocean acidification impacts on shelled pteropods

Published 13 November 2023 Science Closed
Tags: , , , , , , , ,

The accumulation of anthropogenic CO₂ in the ocean has major ecological, socioeconomic, and biogeochemical impacts, with repercussions for the ocean as a critical carbon sink. Ocean acidification (OA) disproportionately affects marine calcifiers, among which pelagic zooplanktonic pteropods play a significant role in carbonate export. The pteropod, due to the susceptibility of its aragonite shell to rapid dissolution, is one of most vulnerable groups and a key indicator for OA regional monitoring, but its regional sensitivities have not yet been extrapolated over global scales. To delineate spatial and temporal changes in pteropod shell dissolution, global OA status and the OA rate of change were evaluated, based on gridded climatologies of observations and using a Regional Ocean Modeling System (ROMS) biogeochemical/ecosystem model. Pteropods, which dominate in the polar and subpolar regions, are characterized by low aragonite saturation state and low buffering capacity, where extended pteropod subsurface dissolution is projected. We show that pteropods are most susceptible to OA in the polar regions, subpolar North Pacific, and eastern boundary upwelling system regions, particularly the California and Humboldt Current Systems. Rates of acidification and corresponding increases in pteropod shell dissolution are projected to be the fastest in the North and South Equatorial Currents. These are the regions with the greatest impacts on pteropods and biogeochemical implications.

Continue reading ‘Global synthesis of the status and trends of ocean acidification impacts on shelled pteropods’

Impacts of glacial and sea-ice meltwater, primary production, and ocean CO2 uptake on ocean acidification state of waters by the 79 North Glacier and northeast Greenland shelf

Published 20 October 2023 Science Closed
Tags: , , ,

The waters adjacent to the Nioghalvfjerdsbræ (79 North Glacier, 79NG) are influenced by Greenland Ice Sheet (GrIS) melt, sea-ice meltwater, and waters on the adjacent northeast Greenland shelf (NEGS). We investigated ocean acidification (OA) variables and the role of freshening, primary production, and air-sea CO2 exchange in Dijmphna Sound (DS) and on the NEGS in the summers of 2012 and 2016. The upper 150 m consisted of Polar Water with Arctic origin that was divided into a fresh surface layer (SL<50 m) and a cold halocline layer (CHL, 50 to 150 m). The layer below 150 m was of Atlantic origin. The SL freshwater was larger in 2012 than in 2016, mainly originated from local 79NG (and GrIS) runoff in DS, whereas on the NEGS in both years, it was mainly from sea-ice melt. The lowest aragonite saturation state (ΩAr) of 1.13 was found in the SL in 2012. Biological CO2 drawdown at primary production caused increased ΩAr in SL, which compensated for most of the ΩAr decrease due to the freshwater dilution of carbonate ions reducing total alkalinity, hence preventing corrosive conditions. This was most pronounced near the 79NG front in 2012, where surface stratification was most pronounced coinciding with large glacial meltwater fractions. Freshening decreased ΩAr by 0.4 at the 79NG front was compensated by biological CO2 drawdown by ~0.5. In 2016, a well-mixed water column in DS and NEGS, with dilution by sea-ice meltwater, caused less compensation on ΩAr by biological CO2 drawdown than in 2012. In future with changing climate and changing ocean chemistry, the increased meltwater effects may overcome the alleviating effects of biological CO2 drawdown on OA with unfavorable conditions for calcifying organisms. However, our study also suggests that primary production may be stimulated by stratification from surface meltwater. In addition, Atlantification and subglacial discharge may result in upwelling of inorganic nutrients that could promote primary production.

Continue reading ‘Impacts of glacial and sea-ice meltwater, primary production, and ocean CO2 uptake on ocean acidification state of waters by the 79 North Glacier and northeast Greenland shelf’

Seasonality of marine calcifiers in the northern Barents Sea: spatiotemporal distribution of planktonic foraminifers and shelled pteropods and their contribution to carbon dynamics

Published 22 September 2023 Science Closed
Tags: , , , , , , , , , ,

Highlights

  • In the northern Barents Sea there is a seasonal pattern of production and size distribution of planktonic foraminifers and pteropods, increasing from winter (March) to summer (July–August) and late autumn (December).
  • In general, pteropods dominate over planktonic foraminifera in the Arctic influenced stations.
  • In the study area, pteropods contribute the most (>80%) to carbon standing stocks and export production.
  • The highest values of carbon standing stocks and export production were found in the seasonal ice zone during all seasons.

Abstract

The Barents Sea is presently undergoing rapid warming and the sea-ice edge and the productive zones are retreating northward at accelerating rates. Planktonic foraminifers and shelled pteropods are ubiquitous marine calcifiers that play an important role in the carbon budget and being particularly sensitive to ocean biogeochemical changes and ocean acidification. Their distribution at high latitudes have rarely been studied, and usually only for the summer season. Here we present results of their distribution patterns in the upper 300 m in the water column (individuals m−3), protein content and size distribution on a seasonal basis to estimate their inorganic and organic carbon standing stocks (µg m−3) and export production (mg m−2 d−1). The study area constitutes a latitudinal transect in the northern Barents Sea from 76˚ N to 82˚ N including seven stations through both Atlantic, Arctic, and Polar surface water regimes and the marginal and seasonal sea-ice zones. The transect was sampled in 2019 (August and December) and 2021 (March, May, and July). The highest carbon standing stocks and export production were found at the Polar seasonally sea-ice covered shelf stations with the contribution from shelled pteropods being significantly higher than planktonic foraminifers during all seasons. We recorded the highest production of foraminifers and pteropods in summer (August 2019 and July 2021) and autumn (December 2019) followed by spring (May 2021), and the lowest in winter (March 2021).

Continue reading ‘Seasonality of marine calcifiers in the northern Barents Sea: spatiotemporal distribution of planktonic foraminifers and shelled pteropods and their contribution to carbon dynamics’

Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth

Published 22 August 2023 Science Closed
Tags: , , , , , , , , , ,

Highlights

  • Ocean acidification has caused the carbonate compensation depth (CCD) to rise by ~98 m.
  • Seafloor area below the CCD has increased by 3.6% in the last 200 years.
  • Risk of impact of rising CCD is greatest in the western equatorial Atlantic Ocean.
  • Different geomorphic features impacted by rising CCD in different ocean areas.

Abstract

Due to burning of fossil fuels, carbon dioxide is being absorbed by the ocean where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modeling suggests that the carbonate compensation depth (CCD) has already risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters more this century. Potentially millions of square kilometres of ocean floor will undergo a rapid transition in terms of the overlying water chemistry whereby calcareous sediment will become unstable causing the carbonate “snow line” to rise.We carried out a spatial analysis of seafloor geomorphology to assess the area newly submerged below the rising CCD. We found that shoaling of the CCD since the industrial revolution has submerged 12,432,096 km2 of ocean floor (3.60% of total ocean area) below the CCD. Further hypothetical shoaling of the CCD by 100 m increments illustrated that the surface area of seafloor submerged below the CCD has risen by 14% with 300 m of shoaling, such that 51% of the ocean area will be below the CCD. All categories of geomorphic feature mapped in one global database intersect the lysocline and will be (or already are) submerged below the CCD with much regional variation since the rise in CCD depth during the last 150 years varies significantly between different ocean regions. For seamounts, the highest percentages of increase in area submerged below the CCD occurred in the Southern Indian Ocean and the South West Atlantic regions (6.3% and 5.9%, respectively). For submarine canyons we found the South West Atlantic increased from 3.9% in pre-industrial times to 8.0% at the present time, the highest percentage of canyons found below the CCD in any ocean region.We also carried out a relative risk assessment for future submergence of ocean floor below the CCD in 17 ocean regions. In our assessment we assumed that the change in CCD from pre-industrial times to the present is an indicator of the likelihood and the change in percentage of seafloor submerged below the CCD due to a hypothetical 300 m rise in the CCD is an indicator of the consequences. We found that the western equatorial Atlantic is at high risk and 9 other Ocean Regions are at moderate risk. Overall, geomorphic features in the Atlantic Ocean and southern Indian Ocean are at greater risk of impact from a rising CCD than Pacific and other Indian Ocean regions.A separate analysis of the Arctic Ocean points to the possible submergence of glacial troughs incised on the continental shelf within a mid-depth (400–800 m) acidified water mass. We also found that the area of national Exclusive Economic Zones submerged below the rising CCD exhibits extreme variability; with 300 m of CCD shoaling we found a > 12% increase in area submerged below the CCD for 23 national EEZs, whereas there was virtually no change for other countries.

Continue reading ‘Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth’

Large-scale culturing of Neogloboquadrina pachyderma, its growth in, and tolerance of, variable environmental conditions

Published 18 August 2023 Science Closed
Tags: , , , , , , ,

The planktic foraminifera Neogloboquadrina pachyderma is a calcifying marine protist and the dominant planktic foraminifera species in the polar oceans, making it a key species in marine polar ecosystems. The calcium carbonate shells of foraminifera are widely used in palaeoclimate studies because their chemical composition reflects the seawater conditions in which they grow. This species provides unique proxy data for past surface ocean hydrography, which can provide valuable insight to future climate scenarios. However, little is known about the response of N. pachyderma to variable and changing environmental conditions.Here, we present observations from large-scale culturing experiments where temperature, salinity and carbonate chemistry were altered independently. We observed overall low mortality, calcification of new chambers and addition of secondary calcite crust in all our treatments. In-culture asexual reproduction events also allowed us to monitor the variable growth of N. pachyderma’s offspring. Several specimens had extended periods of dormancy or inactivity after which they recovered. These observations suggest that N. pachyderma can tolerate, adapt to and calcify within a wide range of environmental conditions. This has implications for the species-level response to ocean warming and acidification, for future studies aiming to culture N. pachyderma and use in palaeoenvironmental reconstruction.

Continue reading ‘Large-scale culturing of Neogloboquadrina pachyderma, its growth in, and tolerance of, variable environmental conditions’

Dynamics of the seawater carbonate system in the East Siberian Sea: the diversity of driving forces

Published 15 August 2023 Science Closed
Tags: , ,

The East Siberian Sea (ESS) is a large and the shallowest part of the Arctic Ocean. It is characterized by high biogeochemical activity, but the seawater carbonate system remains understudied, especially during the late autumn season. Data from the research vessel (RV) “Professor Multanovsky” cruise were used to assess the dynamics of the seawater carbonate system, air–sea CO2 fluxes, and the calcium carbonate corrosive waters in the two biogeochemical provinces of the ESS shortly before freeze-up. The ESS waters were mainly a sink for atmospheric CO2 due to the limited dispersion of river waters, autumn water cooling, and phytoplankton blooms in its eastern autotrophic province. The mean value of the CO2 air–sea flux was 11.2 mmol m−2 day−1. The rate of CO2 uptake in the eastern ESS was an order of magnitude larger than that in the western ESS. The specific waters and ice cover dynamics determined intensive photosynthesis processes identified on the eastern shelf and in the northern deep oligotrophic waters. A part of the surface and most of the bottom ESS waters were corrosive with respect to calcium carbonate, with the lowest saturation state of aragonite (0.22) in the bottom layer of the eastern ESS. The eastern ESS was the main source of these waters into the deep basin. The observed export of corrosive shelf waters to the deep sea can have a potential impact on the ocean water ecosystem in the case of mixing with layers inhabited by calcifying organisms.

Continue reading ‘Dynamics of the seawater carbonate system in the East Siberian Sea: the diversity of driving forces’

Canada’s marine carbon sink: an early career perspective on the state of research and existing knowledge gaps

Published 26 July 2023 Science Closed
Tags: , , , ,

Improving our understanding of how the ocean absorbs carbon dioxide is critical to climate change mitigation efforts. We, a group of early career ocean professionals working in Canada, summarize current research and identify steps forward to improve our understanding of the marine carbon sink in Canadian national and offshore waters. We have compiled an extensive collection of reported surface ocean air–sea carbon dioxide exchange values within each of Canada’s three adjacent ocean basins. We review the current understanding of air–sea carbon fluxes and identify major challenges limiting our understanding in the Pacific, the Arctic, and the Atlantic Ocean. We focus on ways of reducing uncertainty to inform Canada’s carbon stocktake, establish baselines for marine carbon dioxide removal projects, and support efforts to mitigate and adapt to ocean acidification. Future directions recommended by this group include investing in maturing and building capacity in the use of marine carbon sensors, improving ocean biogeochemical models fit-for-purpose in regional and ocean carbon dioxide removal applications, creating transparent and robust monitoring, verification, and reporting protocols for marine carbon dioxide removal, tailoring community-specific approaches to co-generate knowledge with First Nations, and advancing training opportunities for early career ocean professionals in marine carbon science and technology.

Continue reading ‘Canada’s marine carbon sink: an early career perspective on the state of research and existing knowledge gaps’

Sea ice loss translates into major shifts in the carbonate environmental conditions in Arctic Shelf Sea

Published 19 July 2023 Science Closed
Tags: , ,

Healthy Arctic marine ecosystems are essential to the food security and sovereignty, culture and wellbeing of Indigenous Peoples in the Arctic. At the same time, Arctic marine ecosystems are highly susceptible to impacts of climate change and ocean acidification. While increasing ocean and air temperatures and melting sea ice act as direct stressors on the ecosystem, they also indirectly enhance ocean acidification, accelerating the associated changes in the inorganic carbon system. Yet, much is to be learned about the current state and variability of the inorganic carbon system in remote places. Here, we present pH and pCO2 time-series (2016–2020) from the Chukchi Ecosystem Observatory. The subsurface observatory is located in the midst of a biological hotspot with high primary productivity and a rich benthic food web that support coastal Iñupiat, whales, ice seals, walrus (Odobenus rosmarus), and Arctic cod (Boreogadus saida). Our observations suggest that near-bottom waters (33 m depth, 13 m above the seafloor) are a high carbon dioxide and low pH and aragonite saturation state environment in summer and fall, when organic material from the highly productive summer remineralizes. During this time, the aragonite saturation state can be as low as 0.4, triggering free CaCO3 dissolution. During the sea ice covered winter period, pH was < 8 and aragonite remained undersaturated under the sea ice. There are only two short seasonal periods with relatively higher pH and Ωarag, which we term ocean acidification relaxation events. In spring, high primary production from sea ice algae and phytoplankton blooms and ikaite dissolution lead to spikes in pH (pH > 8) and aragonite oversaturation. In late fall, strong wind driven mixing events that bring CO2 depleted surface water to the shelf also lead to events with elevated pH and Ωarag. Given the recent observations of high rates of ocean acidification, and sudden and dramatic shift of the physical, biogeochemical, and ecosystem conditions in the Chukchi Sea, it is possible that the observed extreme conditions at the Chukchi Ecosystem Observatory are significantly deviating from the carbonate conditions to which many species are adapted and may have negative impacts on the ecosystem.

Continue reading ‘Sea ice loss translates into major shifts in the carbonate environmental conditions in Arctic Shelf Sea’

Ocean acidification altered microbial functional potential in the Arctic Ocean

Published 30 June 2023 Science Closed
Tags: , , , , , , , , , ,

Ocean acidification (OA) has considerably changed the metabolism and structure of plankton communities in the ocean. Evaluation of the response of the marine bacterioplankton community to OA is critical for understanding the future direction of bacterioplankton-mediated biogeochemical processes in the ocean. Understanding the diversity of functional genes is important for linking the microbial community to ecological and biogeochemical processes. However, the influence of OA on the functional diversity of bacterioplankton remains unclear. Using high-throughput functional gene microarray technology (GeoChip 4), we investigated the functional gene structure and diversity of bacterioplankton under three different pCO2 levels (control: 175 μatm, medium: 675 μatm, and high: 1085 μatm) in a large Arctic Ocean mesocosm experiment. We observed a higher evenness of microbial functional genes under elevated pCO2 compared with under low pCO2. OA induced a more stable community as evaluated by decreased dissimilarity of functional gene structure with increased pCO2. Molecular ecological networks under elevated pCO2 became more complex and stable, supporting the central ecological tenet that complexity begets stability. In particular, increased average abundances were found under elevated pCO2 for many genes involved in key metabolic processes, including carbon degradation, methane oxidization, nitrogen fixation, dissimilatory nitrite/nitrate reduction, and sulfide reduction processes. Altogether, these results indicate a significant influence of OA on the metabolism potential of bacterioplankton in the Arctic Ocean. Consequently, our study suggests that biogeochemical cycling mediated by these microbes may be altered by the OA in the future.

Continue reading ‘Ocean acidification altered microbial functional potential in the Arctic Ocean’

Planktic foraminiferal resilience to environmental change associated with the PETM

Published 28 June 2023 Science Closed
Tags: , , , , , , , , , , ,

Carbonate-forming organisms play an integral role in the marine inorganic carbon cycle, yet the links 21 between carbonate production and the environment are insufficiently understood. Carbonate production is driven by the abundance of calcifiers, and the amount of calcite produced by each individual (their size and weight). Here we investigate how foraminiferal carbonate production changes in the Atlantic, Pacific and Southern Ocean in response to a 4-5°C warming and a 0.3 surface ocean pH reduction during the Palaeocene-Eocene Thermal Maximum (PETM). To put these local data into a global context, we apply a trait-based plankton model (ForamEcoGEnIE) to the geologic record for the first time. Our data illustrates negligible change in the assemblage test size and abundance of foraminifers. ForamEcoGEnIE resolves small reductions in size and biomass, but these are short-lived. The response of foraminifersshowsspatial variability linked to a warming-induced poleward migration and suggested differences in nutrient availability between open-ocean and shelf locations. Despite low calcite saturation at high latitudes, we reconstruct stable foraminiferal size-normalised weight. Based on these findings, we postulate that sea surface warming had a greater impact on foraminiferal carbonate production during the PETM than ocean acidification. Changes in the composition of bulk carbonate suggest a higher sensitivity of coccolithophores to environmental change during the PETM than foraminifers.

Continue reading ‘Planktic foraminiferal resilience to environmental change associated with the PETM’

Light, ammonium, pH, and phytoplankton competition as environmental factors controlling nitrification

Published 12 May 2023 Science Closed
Tags: , , ,

The biogeochemical cycling of nitrogen (N) plays a critical role in supporting marine ecosystems and controlling primary production. Nitrification, the oxidation of ammonia (NH3) by microorganisms, is an important process in the marine N cycle, supplying nitrate (NO3−), the primary source of N that fuels new phytoplankton growth, and the primary substrate for the microbial process of denitrification. Understanding nitrification in the Chukchi Sea, the shallow sea overlying the continental shelf north of Alaska and the Bering Strait, is particularly important as phytoplankton growth there has been shown to be limited by N. However, the controls on nitrification in the water column and potential effects of climate change remain unknown. This study seeks to characterize the controls on nitrification in the Chukchi Sea. We found light to be a strong control on nitrification rates. Nitrification was undetectable at light levels above 23 μmol photons m−2 s−1. Subsequently, sea ice concentration was related to nitrification, with rates being higher at stations with high ice cover where light transmission to the water column was reduced. High ammonium (NH4+) concentrations also enhanced nitrification, suggesting that nitrifying organisms were substrate-limited, likely due to competition for NH4+ from phytoplankton. Unlike previous experimental studies, we found that nitrification rates were higher under low pH conditions. As the effects of ocean acidification and warming disproportionately impact the Arctic, nitrification rates will undoubtedly be affected. Our results will help guide future studies on potential implications of climate change on the biogeochemistry of N in the Chukchi Sea.

Continue reading ‘Light, ammonium, pH, and phytoplankton competition as environmental factors controlling nitrification’

Climate change and the sea: a major disruption in steady state and the master variables

Published 26 April 2023 Science Closed
Tags: , , , , ,

Since the beginning of the industrial revolution, humans have burned enormous quantities of coal, oil, and natural gas, rivaling nature’s elemental cycles of C, N, and S. The result has been a disruption in a steady state of CO2 and other greenhouse gases in the atmosphere, a warming of the planet, and changes in master variables (temperature, pH, and pε) of the sea affecting critical physical, chemical, and biological reactions. Humans have also produced copious quantities of N and P fertilizers producing widespread coastal hypoxia and low dissolved oxygen conditions, which now threaten even the open ocean. Consequently, our massive alteration of state variables diminishes coral reefs, fisheries, and marine ecosystems, which are the foundation of life on Earth. We point to a myriad of actions and alternatives which will help to stem the tide of climate change and its effects on the sea while, at the same time, creating a more sustainable future for humans and ecosystems alike.

Continue reading ‘Climate change and the sea: a major disruption in steady state and the master variables’

High-frequency, year-round time series of the carbonate chemistry in a high-Arctic fjord (Svalbard)

Published 20 April 2023 Science Closed
Tags: , ,

The Arctic Ocean is subject to high rates of ocean warming and acidification, with critical implications for marine organisms as well as ecosystems and the services they provide. Carbonate system data in the Arctic realm are spotty in space and time and, until recently, there was no time-series station measuring the carbonate chemistry at high frequency in this region, particularly in coastal waters. We report here on the first high-frequency (1 h), multi-year (5 years) dataset of salinity, temperature, dissolved inorganic carbon, total alkalinity, CO2 partial pressure (pCO2) and pH at a coastal site (11 m) in a high-Arctic fjord (Kongsfjorden, Svalbard). We show that (1) the choice of formulations for calculating the dissociation constants of the carbonic acid remains unsettled for Arctic waters, (2) the water column is generally somewhat stratified despite the shallow depth, (3) the saturation state of calcium carbonate is subject to large seasonal changes but never reaches undersaturation (Ωa ranges between 1.4 and 3.0) and (4) pCO2 is lower than atmospheric CO2 at all seasons, making this site a sink for atmospheric CO2 (16.8 mol CO2 m−2 yr−1).

Continue reading ‘High-frequency, year-round time series of the carbonate chemistry in a high-Arctic fjord (Svalbard)’

How ocean warming and acidification affect the life cycle of six worldwide commercialised sea urchin species: a review

Published 19 April 2023 Science Closed
Tags: , , , , , , , , , , , , , , , ,

Ongoing global changes are expected to affect the worldwide production of many fisheries and aquaculture systems. Because invertebrates represent a relevant industry, it is crucial to anticipate challenges that are resulting from the current environmental alterations. In this review, we rely on the estimated physiological limits of six commercialised species of sea urchins (Loxechinus albus, Mesocentrotus franciscanus, Paracentrotus lividus, Strongylocentrotus droebachiensis, Strongylocentrotus intermedius and Strongylocentrotus purpuratus) to define the vulnerability (or resilience) of their populations facing ocean warming and acidification (OW&A). Considering that coastal systems do not change uniformly and that the populations’ response to stressors varies depending on their origin, we investigate the effects of OW&A by including studies that estimate future environmental mutations within their distribution areas. Cross-referencing 79 studies, we find that several sea urchin populations are potentially vulnerable to the predicted OW&A as environmental conditions in certain regions are expected to shift beyond their estimated physiological limit of tolerance. Specifically, while upper thermal thresholds seem to be respected for L. albus along the SW American coast, M. franciscanus and S. purpuratus southern populations appear to be vulnerable in NW America. Moreover, as a result of the strong warming expected in the Arctic and sub-Arctic regions, the local productivity of S. droebachiensis is also potentially largely affected. Finally, populations of S. intermedius and P. lividus found in northern Japan and eastern Mediterranean respectively, are supposed to decline due to large environmental changes brought about by OW&A. This review highlights the status and the potential of local adaptation of a number of sea urchin populations in response to changing environmental conditions, revealing possible future challenges for various local fishing industries.

Continue reading ‘How ocean warming and acidification affect the life cycle of six worldwide commercialised sea urchin species: a review’

The marine carbonate system variability in high meltwater season (Spitsbergen Fjords, Svalbard)

Published 10 March 2023 Science Closed
Tags: , ,

Highlights

  • Spatial variability in hydrography and carbonate chemistry were investigated.
  • Lack of clear relationship between alkalinity and salinity in the surface water.
  • Effect of alkalinity fluxes from sediments on the bottom water was insignificant.
  • Freshening of the surface water reduces significantly saturation state of aragonite.

Abstract

The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity – AT, total inorganic carbon concentration – CT, pH, CO2 partial pressure – pCO2, and the saturation state of aragonite – ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords – Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, hence it is clear that freshwater input generally has a diluting effect and lowers AT in the surface waters of the Spitsbergen fjords. Significant surface water AT variability (1889–2261 µmol kg−1) reveals the complexity of the fjords’ systems with multiple freshwater sources having different alkalinity end-member characteristics and identifies the mean AT freshwater end-member of 595 ± 84 µmol kg−1 for the entire region. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288–2666 μmol kg−1) observed in the pore waters. Low pCO2 results in surface water (200–295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly. This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming.

Continue reading ‘The marine carbonate system variability in high meltwater season (Spitsbergen Fjords, Svalbard)’

The history of chemical concepts and field studies of CO2 in seawater: a tribute to Kurt Buch (1881–1967)

Published 25 January 2023 Science Closed
Tags: , , ,

This review of the research on the marine CO2 system spans the time between the mid-19th century and the first years after World War II. It covers the period from the first attempts to determine the amount of CO2 dissolved in seawater to the first complete physico-chemical characterization of the marine CO2 system. The development of the latter was significantly influenced by the theoretical and experimental work of the Finnish chemical oceanographer Kurt Buch (1881–1967) during the first half of the 20th century. To acknowledge his outstanding achievements in Chemical Oceanography, this review is dedicated to him.

The first part of our discussion is organized along the characteristic variables of the marine CO2 system. The analytical procedures that led successively to the definition of total CO2, alkalinity (“neutral carbonate”), the CO2 partial pressure (“CO2 tension”) and pH are briefly described. We trace the attempts to connect these variables quantitatively through the mass action law. After several failed attempts, CO2 dissociation constants were finally determined with the support of the International Council for the Exploration of the Sea (1931). Their results constituted the basis of the marine CO2 studies conducted after World War II.

The second focus of our review refers to the various field studies, including early measurements of total CO2 and alkalinity during Norwegian (1878) and Danish expeditions (1895/96) in the North Atlantic and Arctic Ocean and the first measurements of surface water pCO2 in the North Atlantic, in 1902. Furthermore, we acknowledge the achievements of the German Atlantic expedition (1925–1927) for the characterization of the vertical and horizontal distribution of pH, pCO2 and CaCO3 saturation in the Atlantic Ocean. Among Buch’s field studies of the CO2 system, we consider the Finnish monitoring program, in which pH and alkalinity were measured at over 70 stations in the northern Baltic Sea.

Whenever it is appropriate, we show the connection between past scientific ideas, concepts and knowledge with current efforts and developments concerning the understanding of the marine carbon cycle and its response to increasing atmospheric CO2.

Continue reading ‘The history of chemical concepts and field studies of CO2 in seawater: a tribute to Kurt Buch (1881–1967)’

Impact of climate change on Arctic macroalgal communities

Published 4 November 2022 Science Closed
Tags: , , , , , , , ,

The Arctic region faces a warming rate that is more than twice the global average. Seaice loss, increase in precipitation and freshwater discharge, changes in underwater light, and amplification of ocean acidification modify benthic habitats and the communities they host. Here we synthesize existing information on the impacts of climate change on the macroalgal communities of Arctic coasts. We review the shortand long-term changes in environmental characteristics of shallow hard-bottomed Arctic coasts, the floristics of Arctic macroalgae (description, distribution, life-cycle, adaptations), the responses of their biological and ecological processes to climate change, the resulting winning and losing species, and the effects on ecosystem functioning. The focus of this review is on fucoid species, kelps, and coralline algae which are key ecosystem engineers in hard-bottom shallow areas of the Arctic, providing food, substrate, shelter, and nursery ground for many species. Changes in seasonality, benthic functional diversity, food-web structure, and carbon cycle are already occurring and are reshaping Arctic benthic ecosystems. Shallow communities are projected to shift from invertebrate-to algal-dominated communities. Fucoid and several kelp species are expected to largely spread and dominate the area with possible extinctions of native species. A considerable amount of functional diversity could be lost impacting the processing of land-derived nutrients and organic matter and significantly altering trophic structure and energy flow up to the apex consumers. However, many factors are not well understood yet, making it difficult to appreciate the current situation and predict the future coastal Arctic ecosystem. Efforts must be made to improve knowledge in key regions with proper seasonal coverage, taking into account interactions between stressors and across species.

Continue reading ‘Impact of climate change on Arctic macroalgal communities’

Seasonal peak in Arctic Ocean acidity could shift to the summer

Published 12 October 2022 Science Closed
Tags: , , ,
Figure 1 | Simulations of seasonal variation in acidity in the Arctic Ocean. Orr et al. assessed the seasonal cycle of the partial pressure of CO2 (pCO2, which correlates with seawater acidity) in the Arctic Ocean, using simulations from a set of Earth-system models. The simulated data are plotted as the monthly anomaly — the difference between average monthly pCO2 and the annual average, measured in microatmospheres. Currently, pCO2 peaks around April, but declines when sea ice melts, reaching a minimum in the summer months when marine phytoplankton consume dissolved CO2 to grow; darker lines indicate periods of peak growth. Future global warming (simulated data are for 2091 to 2100) causes early melting of sea ice and blooming of phytoplankton, resulting in an earlier seasonal minimum of pCO2. However, pCO2 then reaches a maximum in the summer months, as a consequence of the high summer ocean temperatures. The combination of high temperatures and high acidity in the summer could be devastating for marine ecosystems.

The global ocean is gradually acidifying on multidecadal timescales. This acidification occurs when carbon dioxide generated by human activities is absorbed by the ocean, and produces conditions in which many marine organisms cannot thrive. Writing in Nature, Orr et al.1 present global simulations suggesting that future warming in the Arctic Ocean will cause CO2 levels to peak seasonally in surface waters in the summer, implying that climate change will further accelerate ocean acidification. The resulting increase in acidification would double down on the already heat-stressed ecosystem, with effects that could creep up the food web — further challenging the food security, culture and well-being of Indigenous peoples in the Arctic.

Ocean acidification varies depending on local environmental conditions and processes. For example, acidification of Arctic waters is enhanced by the freshwater input from melting sea ice, precipitation and rivers2. The partial pressure of CO2 (pCO2, which quantifies the pressure generated by CO2 dissolved in seawater, but which can be used as a broad measure of how much CO2 is dissolved) also varies naturally across days, seasons, years and even decades because it depends on a mixture of biological and physical processes.

…

Continue reading ‘Seasonal peak in Arctic Ocean acidity could shift to the summer’

Arctic Ocean annual high in pCO2 could shift from winter to summer

Published 6 October 2022 Science Closed
Tags: , , ,

Long-term stress on marine organisms from ocean acidification will differ between seasons. As atmospheric carbon dioxide (CO2) increases, so do seasonal variations of ocean CO2 partial pressure (pCO2), causing summer and winter long-term trends to diverge1,2,3,4,5. Trends may be further influenced by an unexplored factor—changes in the seasonal timing of pCO2. In Arctic Ocean surface waters, the observed timing is typified by a winter high and summer low6 because biological effects dominate thermal effects. Here we show that 27 Earth system models simulate similar timing under historical forcing but generally project that the summer low, relative to the annual mean, eventually becomes a high across much of the Arctic Ocean under mid-to-high-level CO2 emissions scenarios. Often the greater increase in summer pCO2, although gradual, abruptly inverses the chronological order of the annual high and low, a phenomenon not previously seen in climate-related variables. The main cause is the large summer sea surface warming7 from earlier retreat of seasonal sea ice8. Warming and changes in other drivers enhance this century’s increase in extreme summer pCO2 by 29 ± 9 per cent compared with no change in driver seasonalities. Thus the timing change worsens summer ocean acidification, which in turn may lower the tolerance of endemic marine organisms to increasing summer temperatures.

Continue reading ‘Arctic Ocean annual high in pCO2 could shift from winter to summer’

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources