Posts Tagged 'field'

The influence of upwelling on key bivalves from the Humboldt and Iberian current systems

Eastern Boundary Upwelling Systems (EBUS) deliver cold, nutrient-rich waters, influencing coastal biota from the molecular to the ecosystem level. Although local upwelling (U) and downwelling (DU) conditions are often known, their influence on body attributes of relevant species has not been systematically compared within and between EBUS (i.e., below and above regional scales). Hence, we compared the physical-chemical characteristics of U and DU sites in the Humboldt Current system (Chile) and the Iberian Current system (Portugal). We then assessed the influence of U and DU upon eight body attributes in purple mussels (Perumytilus purpuratus) and Mediterranean mussels (Mytilus galloprovincialis), from the Humboldt and Iberian systems, respectively. We hypothesized that bivalves from U sites display better fitness, as measured by body attributes, regardless of their origin (EBUS). As expected, waters from U sites in both systems showed lower temperatures and pH, and higher nitrite concentrations. We also found that mussels from U sites showed better fitness than those in DU sites in 12 out of 16 direct U vs DU comparisons. Shell length, shell volume, organic content of soft-tissues, and mechanical properties of the shell averaged consistently higher in mussels from U sites in both Current systems. In addition, total weight, soft-tissue weight, shell weight and shell thickness were all higher in the U site at the Humboldt system but had less consistent differences at the Iberian system. Altogether, most results supported our working hypothesis and indicate that U conditions support better fitted mussels. The few attributes that did not exhibit the expected U vs DU differences in the Iberian system suggest that local and species-specific differences also play a role on the attributes of these species. These results may also serve as a reference point for further studies addressing the influence of upwelling in these productive, critically important systems.

Continue reading ‘The influence of upwelling on key bivalves from the Humboldt and Iberian current systems’

Strong variation in sedimental antibiotic resistomes among urban rivers, estuaries and coastal oceans: evidence from a river-connected coastal water ecosystem in northern China

Sediment is thought to be a vital reservoir to spread antibiotic resistance genes (ARGs) among various natural environments. However, the spatial distribution patterns of the sedimental antibiotic resistomes around the Bohai Bay region, a river-connected coastal water ecosystem, are still poorly understood. The present study conducted a comprehensive investigation of ARGs among urban rivers (UR), estuaries (ES) and Bohai Bay (BHB) by metagenomic sequencing. Overall, a total of 169 unique ARGs conferring resistance to 15 antimicrobial classes were detected across all sediment samples. The Kruskal-Wallis test showed that the diversity and abundance of ARGs in the UR were all significantly higher than those in the ES and BHB (p < 0.05 and p < 0.01), revealing the distance dilution of the sedimental resistomes from the river to the ocean. Multidrug resistance genes contained most of the ARG subtypes, whereas rifamycin resistance genes were the most abundant ARGs in this region. Our study demonstrated that most antimicrobial resistomes were highly accumulated in urban river sediments, whereas beta-lactamase resistance genes (mainly PNGM-1) dramatically increased away from the estuary to the open ocean. The relative abundance of mobile genetic elements (MGEs) also gradually decreased from rivers to the coastal ocean, whereas the difference in pathogenic bacteria was not significant in the three classifications. Among MGEs, plasmids were recognized as the most important carriers to support the horizontal gene transfer of ARGs within and between species. According to co-occurrence networks, pathogenic Proteobacteria, Actinobacteria, and Bacteroidetes were recognized as potential and important hosts of ARGs. Heavy metals, pH and moisture content were all recognized as the vital environmental factors influencing the distribution of ARGs in sediment samples. Overall, the present study may help to understand the distribution patterns of ARGs at a watershed scale, and help to make effective policies to control the emergence, spread and evolution of different ARG subtypes in different habitats.

Continue reading ‘Strong variation in sedimental antibiotic resistomes among urban rivers, estuaries and coastal oceans: evidence from a river-connected coastal water ecosystem in northern China’

Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)

Volcanic eruptions with increase in the amount of carbon dioxide (CO2) and other gases are responsible for the extinction of many species because of decreased pH and carbonate availability which creates ocean acidification. Here we show how benthic foraminifera have evolved, by studying sediments from U1485A (1145 m water depth) core in the Papua New Guinea (PNG) collected during IODP Expedition 363 in the Western Pacific Warm Pool (WPWP), one of the warmest marine waters of the world. High-stressed environments dominated by low diversity of opportunistic species after volcanic activity was detected by the presence of tephra and volcanic ashes within the last 0.8 Mya. The decrease in the diversity patterns show an inverse correlation to the presence of tephra and ash right after Pleistocene volcanic eruptions in the past. Deep-water fauna is dominated by Cibicidoides pachiderma, from the early Oligocene through the Pleistocene, Uvigerina hispida from early Miocene through Pleistocene, U. prosbocidae from late Oligocene through Pleistocene, and an outer neritic upper bathyal Uvigerina mediterranea from high salinities, warm waters, low dissolved oxygen, and high organic matter. Bolivinita quadrilatera characteristic of 200-500m depth, Bolivina robusta from 3 to 900m, and the Rotalinoides compressiusculus, a shallow warm water species, from 2-37m depth show higher diversity peaks in interglacial cycles. High-stress conditions with mass extinction after volcanic eruptions leads to enhanced weathering, global warming and cooling afterwards, and ocean acidification, resulting in a crisis in the marine environment in terms of carbonate. Diversity gradients suggested that foraminiferal species responded to the cyclic pulses of volcanic eruptions, and its unstable ecological conditions created by the increase in the temperature and CO2. Here we show that tephra layers and ash record a periodicity of explosive volcanism within the last 0.8 Myr maintaining a strong 100 kyr periodicity, and that earth’s orbital cycles might trigger peaks of volcanic eruptions 41,000-year cycle.

Continue reading ‘Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)’

Differential roles of anthropogenic CO2 in mediating seasonal amplitudes of ocean acidification metrics over a coastal coral habitat

Seasonal-scale local forcings sharply reduce the coastal pH and aragonite saturation state (Ωaragonite). However, habitat-specific seasonality and control change signatures under increasing atmospheric CO2 are still poorly characterized. Here, we investigated carbonate system parameter dynamics over a Dongshan coral habitat that is greatly influenced by seasonal current patterns on the western Taiwan Strait coast. Specifically, relatively low pH and Ωaragonite were observed in the trial zone throughout the seasons. Using a first-order Taylor decomposition considering biological carbon metabolism, we suggest that the higher net aerobic respiration related to intense local human activities produced worse ocean acidity in the trial zone. Seasonally, a decreasing Ωaragonite trend was observed from the transition to the northeast monsoon seasons, mainly controlled by dissolved inorganic carbon (DIC) divergence among seasons. The pH/hydrogen ion concentration ([H+]) seasonal cycle was determined by both DIC and temperature components, revealing the lowest/highest value in the southwest monsoon season. Based on ocean acidification scenario modeling forced with a business-as-usual emissions scenario, the Ωaragonite seasonal amplitude attenuation was projected to exceed 30% during the 21st century. However, [H+] seasonal amplitude was amplified over 170%. The attenuation in the Ωaragonite seasonal amplitude mainly resulted from an increase in anthropogenic CO2 seasonal divergence. The increase in [H+] seasonal amplitude mostly followed from an increase in the [H+] sensitivities to DIC and temperature changes.

Continue reading ‘Differential roles of anthropogenic CO2 in mediating seasonal amplitudes of ocean acidification metrics over a coastal coral habitat’

The Paleocene-Eocene transition in the Gulf of Guinea: evidence of the Petm in the Douala Basin, Cameroon

The Paleocene-Eocene Thermal Maximum (PETM) was identified for the first time in two sections (Bongue and Dibamba) from the Douala sub-basin located in the Gulf of Guinea, Cameroon. This discovery was based on a multi-disciplinary approach including benthic and planktic foraminifera, ostracods, major and trace elements, mercury, carbon stable isotope (δ13C values), total organic carbon (TOC), whole-rock and clay mineralogy. A combination of lithology, microfossil assemblage, and carbon isotope data indicate zone P5 and the top of the Paleocene enabling the definition of the Paleocene-Eocene boundary (PEB). A negative carbon-isotope excursion (CIE) spanning from the uppermost Paleocene deposits to the earliest Eocene sediments (PETM interval) shows a shift in δ13Corg values of 1.5 ‰ in Bongue and 3.0 ‰ in Dibamba. In both sections, this interval is affected by widespread acidification, as revealed by carbonate dissolution and microfossil preservation (i.e., species are dwarfed, broken, thin shelled, and with holes). The very low carbonate content and the scarcity of microfauna indicate the severity of acidification during the PETM, especially in the early Eocene where only one species was identified (Igorina broedermanni). Mercury anomalies, TOC contents, and trace element concentration ratios, point to volcanic activity linked to the Cameroon Volcanic Line (CVL) intrusive magma, and a decrease in productivity prior to the PETM. In addition to climate change, our geochemical and mineralogical data support the hypothesis that other environmental perturbations such as an increase in productivity and detrital input, as well as a decrease in bottom water oxygenation occurred during the PETM in the Douala sub-basin.

Continue reading ‘The Paleocene-Eocene transition in the Gulf of Guinea: evidence of the Petm in the Douala Basin, Cameroon’

Direct H2S, HS− and pH measurements of high-temperature hydrothermal vent fluids with in situ Raman spectroscopy


Hydrothermal H2S is an important energy source for hydrothermal ecosystems. However, it is difficult to obtain accurate hydrogen sulfide concentrations in high-temperature hydrothermal fluids because they are highly susceptible to oxidation and compositional variability with mixing. In this study, a new in situ approach for measuring H2S, HS and pH in hydrothermal fluids was developed and applied to the detections of Okinawa Trough hydrothermal activities. The in situ total H2S concentrations in the Jade and Biwako fluids were determined to be 31.4 and 76.7 mmol/kg, respectively. The in situ measured pH of the Jade fluids was determined to be 6.3, which has exceeded that of a neutral fluid at a specific temperature and pressure, indicating that the pH of Jade fluids is weakly alkaline. The pH transition of hydrothermal fluids from alkaline to acidic may be attributed to the thermal decomposition of organic matter and sulfide precipitation.

Key Points

  • The first in situ measured pH of high-temperature hydrothermal vent fluids at arc-back arc basins was reported
  • A new approach to obtain in situ H2S/HS concentration and in situ pH of high temperature hydrothermal vent fluids was established
  • The pH transition of hydrothermal fluids from alkaline to acidic should attributes to the precipitation of sulfide minerals
Continue reading ‘Direct H2S, HS− and pH measurements of high-temperature hydrothermal vent fluids with in situ Raman spectroscopy’

Technical note: Enhancement of float-pH data quality control methods: a study case in the Subpolar Northwestern Atlantic region

Since a pH sensor has become available that is suitable for this demanding autonomous measurement platform, the marine CO2 system can be observed independently and continuously by BGC-Argo floats. This opens the possibility to detect variability and long-term changes in interior ocean inorganic carbon storage and quantify the ocean sink for atmospheric CO2. In combination with a second parameter of the marine CO2 system, pH can be a useful tool to derive the surface ocean CO2 partial pressure (pCO2).

The large spatiotemporal variability of the marine CO2 system requires sustained observations to decipher trends and punctual events (e.g., river discharge, phytoplankton bloom) but also puts a high emphasis on the quality control of float-based pH measurements. In consequence, as the interpretation of changes depends on accurate data, and because sensor offsets or drifts might appear, a consistent and rigorous correction procedure to process and quality-control the data has been established. By applying standardized routines of the Ago data management to pH measurements from a pH/O2 float pilot array in the subpolar North Atlantic Ocean, we investigate the uncertainties and lack of objective criteria associated with the standardized routines, notably the choice of the reference method for the pH correction (CANYON-B or LIRPH) as well the reference depth for this correction. For the studied float array, significant differences of ca. 0.02 pH units are observed between the two reference methods which can be used to correct float-pH data from water samples. Through comparison against discrete pH data from water samples, an assessment of the adjusted float-pH data quality is presented. The results point out noticeable discrepancies near the surface of > 0.01 pH units. In the context of converting surface ocean pH measurements into pCO2 data for the purpose to derive air-sea CO2 fluxes, we conclude that the minimum accuracy requirement of 0.01 pH units (equivalent to the minimum pCO2 accuracy of 10 µatm for potential future inclusion into the SOCAT database) is not systematically achieved in the upper ocean.

While the limited dataset and regional focus of our study provides only one showcase, it still calls for an additional independent pH reference in the surface ocean. We therefore propose a way forward to enhance the float-pH quality control procedure. In our analysis, the current philosophy of pH data correction against climatological reference data at one single depth in the deep ocean appears insufficient to assure adequate data quality in the surface ocean. Ideally, an additional reference point should be taken at or near the surface where the resulting pCO2 data are of the highest importance to monitor the air-sea exchange of CO2 and would have the potential to very significantly augment the impact of the current observation network.

Continue reading ‘Technical note: Enhancement of float-pH data quality control methods: a study case in the Subpolar Northwestern Atlantic region’

Exposure to extremes in multiple global change drivers: characterizing pH, dissolved oxygen, and temperature variability in a dynamic, upwelling dominated ecosystem

In upwelling systems, fluctuations in seawater pH, dissolved oxygen (DO), and temperature can expose species to extremes that differ greatly from the mean conditions. Understanding the nature of this exposure to extremes, including how exposure to low pH, low DO concentrations, and temperature varies spatiotemporally and in the context of other drivers, is critical for informing global change biology. Here, we use a 4-yr time series of coupled pH, DO, and temperature observations at six nearshore kelp forest sites spanning the coast of California to characterize the variability and covariance among these drivers. We further compare observed properties to those derived from a high-resolution coupled physical-biogeochemical simulation for the central California current system. We find the intensity, duration, and severity of exposure to extreme conditions beyond heuristic, biologically relevant pHT (< 7.7), and DO (< 4.6 mg L−1) values were greatest at sites with strong upwelling. In contrast, sites with relatively weaker upwelling had little exposure to pH or DO conditions below these heuristic values but had higher and more variable temperature. The covariance between pH, DO, and temperature was highest in sites with strong upwelling and weakest in sites with limited upwelling. These relationships among pH, DO, and temperature at the observation locations were mirrored in the model, and model output highlighted geographic differences in exposure regimes across the California marine protected area network. Together, these results provide important insight into the conditions marine ecosystems are exposed to relevant to studies of global change biology.

Continue reading ‘Exposure to extremes in multiple global change drivers: characterizing pH, dissolved oxygen, and temperature variability in a dynamic, upwelling dominated ecosystem’

Taphonomy and dissolution rates of the razor clam Ensis magnus shells: current status and projected acidification scenarios


  • Natural variability of seawater (TaΩaragonite and pCO2) revealed an increase of acidification though such change did not suppose abrupt detrimental effects for taphonomic characteristics of shells (length, thickness, organic content or strength).
  • Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would disturb the individual characterization of environmental parameters.
  • Dissolution rates of shells subjected to projected laboratory scenarios were significantly greater for cold-acidic environment (more corrosive) as compared to warm-acidic. Mean dissolution time (DT50) for cold-acidic scenario was reduced by half (15 years) as compared to current water chemistry conditions (30 years).
  • More recent shells are being secreted in a progressively less saturated carbonate environment (at an annual rate of change of −0.0127 for Ωaragonite) and accordingly, were more prone to suffer dissolution (and weakening) in projected laboratory scenarios.
  • Marine shells support ecosystem services including refuge for multiple species, substrate to attach and settle of fauna that may change in future environments or may bring changes in the ecological interactions of our coastal areas affecting biodiversity and optimal functioning of the ecosystem services.


The analysis of the natural variability of seawater (TaΩaragonite and pCO2) at Rodas Beach (NW Iberian Peninsula, Spain) revealed an increase of acidification. However, such pH change was not linked to any detrimental effect of the shell taphonomic characteristics of live razor clams harvested during distinct temporal series (length, thickness, organic content or strength). Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would limit the individual characterization. Modelled trends in pH (and Ωaragonite) showed a significant decrease in the last 20 years, despite Ω > 1. Therefore, more recent shells are being secreted in a progressively less saturated carbonate environment and, consequently, more prone to suffer dissolution (and weakening) in projected climatic scenarios. When shells of harvested razor clams were exposed to projected climatic scenarios in the laboratory, dissolution rates were significantly greater for cold-acidic scenarios (more corrosive) as compared to warm-acidic. The median dissolution time (DT50) for shells under the cold-acidic scenario was reduced by half (15 years) when compared to the values observed for shells under current water chemistry conditions (30 years).

Galician coastline, often characterised by pCO2-rich and cold waters due to upwelling system, would represent the most corrosive scenario for the shells according to the responses monitored in our survey which highlight future compromise for the ecosystem services supplied by these hard skeletons. Future climate scenarios might condition performance of bivalves but also more complex processes related to carbonate structures. Local biodiversity may be lowered which may reduce the possibility that many species find shelter and feeding grounds, diminishing the optimal substrate for other organisms as needed elements for optimal services in the ecosystems.

Continue reading ‘Taphonomy and dissolution rates of the razor clam Ensis magnus shells: current status and projected acidification scenarios’

Short-term variation of pH in seawaters around coastal areas of Japan: characteristics and forcings

The pH of coastal seawater varies based on several local forcings, such as water circulation, terrestrial inputs, and biological processes, and these forcings can change along with global climate change. Understanding the mechanism of pH variation in each coastal area is thus important for a realistic future projection that considers changes in these forcings. From 2020 to 2021, we performed parallel year-round observations of pH and related ocean parameters at five stations around the Japanese coast (Miyako Bay, Shizugawa Bay, Kashiwazaki Coast, Hinase Archipelago, and Ohno Strait) to understand the characteristics of short-term pH variations and their forcings. Annual variability (~1 standard deviation) of pH and aragonite saturation state (Ωara) were 0.05–0.09 and 0.25–0.29, respectively, for three areas with low anthropogenic loadings (Miyako Bay, Kashiwazaki Coast, and Shizugawa Bay), while it increased to 0.16–0.21 and 0.52–0.58, respectively, in two areas with medium anthropogenic loadings (Hinase Archipelago and Ohno Strait in Seto Inland Sea). Statistical assessment of temporal variability at various timescales revealed that most of the annual variabilities in both pH and Ωara were derived by short-term variation at a timescale of < 10 days, rather than seasonal-scale variation. Our analyses further illustrated that most of the short-term pH variation was caused by biological processes, while both thermodynamic and biological processes equally contributed to the temporal variation in Ωara. The observed results showed that short-term acidification with Ωara < 1.5 occurred occasionally in Miyako and Shizugawa Bays, while it occurred frequently in the Hinase Archipelago and Ohno Strait. Most of such short-term acidified events were related to short-term low-salinity events. Our analyses showed that the amplitude of short-term pH variation was linearly correlated with that of short-term salinity variation, and its regression coefficient at the time of high freshwater input was positively correlated with the nutrient concentration of the main river that flows into the coastal area.

Continue reading ‘Short-term variation of pH in seawaters around coastal areas of Japan: characteristics and forcings’

Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools

Human CO2 emissions are modifying ocean carbonate chemistry, causing ocean acidification, and likely already impacting marine ecosystems. In particular, there is concern that coastal, benthic calcifying organisms will be negatively affected by ocean acidification, a hypothesis largely supported by laboratory studies. The inter-relationships between carbonate chemistry and marine calcifying communities in situ are complex and natural mesocosms such as tidal pools can provide useful community-level insights. In this study, we manipulated the carbonate chemistry of intertidal pools to investigate the influence of future ocean acidification on net community production (NCP) and calcification (NCC) at emersion. Adding CO2 at the start of the tidal emersion to simulate future acidification (+1500 μatm pCO2, target pH: 7.5) modified net production and calcification rates in the pools. By day, pools were fertilized by the increased CO2 (+20 % increase in NCP, from 10 to 12 mmol O2 m−2 hr−1), while there was no measurable impact on NCC. During the night, pools experienced net community dissolution (NCC < 0), even in present-day conditions, when waters were supersaturated with regards to aragonite. Adding CO2 in the pools increased nocturnal dissolution rates by 40 % (from −0.7 to −1.0 mmol CaCO3 m−2 hr−1) with no consistent impact on night community respiration. Our results suggest that ocean acidification is likely to alter temperate intertidal community metabolism on sub-daily timescales, enhancing both diurnal community production and nocturnal calcium carbonate dissolution.

Continue reading ‘Ocean acidification enhances primary productivity and nocturnal carbonate dissolution in intertidal rock pools’

Impacts of ocean acidification and warming on post-larval growth and metabolism in two populations of the great scallop (Pecten maximus L.) 

Ocean acidification and warming are key stressors for many marine organisms. Some organisms display physiological acclimatisation or plasticity, but this may vary across species ranges, especially if populations are adapted to local climatic conditions. Understanding how acclimatisation potential varies among populations is therefore important in predicting species responses to climate change. We carried out a common garden experiment to investigate how different populations of the economically important great scallop (Pecten maximus) from France and Norway responded to variation in temperature and pCO2 concentration. After acclimation, post-larval scallops (spat) were reared for 31 days at one of two temperatures (13°C and 19°C) under either ambient or elevated pCO2 (pH 8.0 and pH 7.7). We combined measures of proteomic, metabolic, and phenotypic traits to produce an integrative picture of how physiological plasticity varies between the populations. The proteome of French spat showed significant sensitivity to environmental variation, with 12 metabolic, structural and stress-response proteins responding to temperature and/or pCO2. Principal component analysis revealed seven energy metabolism proteins in French spat that were consistent with countering ROS stress under elevated temperature. Oxygen uptake in French spat did not change under elevated temperature, but increased under elevated pCO2. In contrast, Norwegian spat reduced oxygen uptake under both elevated temperature and pCO2. Metabolic plasticity seemingly allowed French scallops to maintain greater energy availability for growth than Norwegian spat. However, increased physiological plasticity and growth in French spat may come at a cost, as French (but not Norwegian) spat showed reduced survival under elevated temperature.

Continue reading ‘Impacts of ocean acidification and warming on post-larval growth and metabolism in two populations of the great scallop (Pecten maximus L.) ‘

Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate change

Pteropods are a key part of biogeochemical cycling and epipelagic food webs in the Southern Ocean. However, shelled pteropods are vulnerable to climate change, due to their aragonite shells being particularly sensitive to ocean acidification. Currently our understanding of pteropod responses to environmental change is hindered by uncertainties surrounding their life cycles and population dynamics. In this study, we describe polar shelled pteropod diversity in the north-eastern Scotia Sea, inferring life history and population structures of the dominant pteropod species, Limacina rangii (formerly Limacina helicina antarctica) and Limacina retroversa. An annual timeseries of Limacina shell morphometrics was derived from individuals collected in a moored sediment trap at 400 m depth. We found that L. rangii and L. retroversa have contrasting life history strategies. L. rangii has a continuous spawning and recruitment period from November to March and can overwinter as juveniles and adults. L. retroversa has discrete spawning events from November to May, producing non–overlapping cohorts of juveniles and adults. Their development to the adult stage takes between two and five months, upon which they overwinter as adults. Our findings suggest different vulnerabilities of L. rangii and L. retroversa to a changing ocean. For example, since all life stages of L. rangii co-exist, vulnerability of one cohort is not detrimental to the stability of the overall population whereas, if one L. retroversa cohort fails to recruit, the entire population is threatened. Changes in pteropod populations could have cascading ramifications to Antarctic ecosystems and carbon cycling.

Continue reading ‘Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate change’

Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry

Understanding the variations in past ocean carbonate chemistry is critical to elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complex physiological and ecological response to the carbonate system during an organisms’ life cycle and the potential for preservation at the seafloor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi > 2 µm, and small Gephyrocapsa spp.). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks) of coccoliths in a laboratory dissolution experiment and surface sediment samples from the South China Sea. The coccolith morphological data in surface sediments were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicates that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs. length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain the main variations observed in our work. We propose that the normalized ks variation (), which is the ratio between the standard deviation of ks (σ) and the mean ks, could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. Applied together with the  ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.

Continue reading ‘Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry’

Drivers of marine CO2-carbonate chemistry in the northern Antarctic Peninsula


The Bransfield Strait is a climate change hotspot at the tip of the northern Antarctic Peninsula (NAP). The region is marked by a mixture of relatively warm waters from the Bellingshausen Sea with cold shelf waters from the Weddell Sea. Additionally, its deep central basin (>800 m) preserves seawater properties from the north-western Weddell Sea continental shelf. This study assessed long-term changes in carbonate chemistry in the Bransfield Strait and found that the hydrographic setting (i.e., a mixture between modified-Circumpolar Deep Water with Dense Shelf Water [DSW]) drives temporal variability of carbonate parameters. The western basin has experienced decreases in pH (seawater scale) over the last three decades (1996–2019), varying from −0.003 to −0.017 pH units yr−1, while Ωar decreased from −0.01 to −0.07 yr−1 throughout the water column. The central basin was characterized by a high contribution of DSW with high carbon dioxide (CO2) content and the decomposition of organic matter produced and transported into its deep layer. With lower variability for all carbonate system variables, the eastern basin was likely regulated by internal mixing. Overall, the entire strait is almost reaching a CO2-saturated condition, highlighting how sensitive subpolar regions are to the effects of human-induced climate change.

Key Points

  • The western basin experiences steeper pH decreases than the surrounding areas at a rate of −0.017 pHsws units yr−1 due to Circumpolar Deep Water intrusions
  • Dense Shelf Water inflow into the deep layer of the central basin promoted a CT increase of about 50 μmol kg−1 in the 2010s relative to the 2000s
  • Internal mixing has likely reduced spatiotemporal variability of carbonate chemistry in the eastern basin since the 1990s
Continue reading ‘Drivers of marine CO2-carbonate chemistry in the northern Antarctic Peninsula’

Chapter 4: ocean chemistry – Irish Ocean Climate And Ecosystem Status Report 2023

Carbon dioxide (CO2) emissions to the atmosphere have increased inexorably since the industrial revolution, due to fossil fuel combustion, cement production and land-use change. This has resulted in an average global atmospheric partial pressure of CO2 of ~ 415.7 +/- 0.2 ppm in 2021, which is 149% of preindustrial levels (WMO 2022). Today’s atmospheric CO2 levels would likely be much higher, had the oceans not absorbed about one quarter to one third of the total anthropogenic CO2 emissions (IPCC, 2019; Bindoff et al., 2019). Increasing carbon dioxide in the Earth’s atmosphere results in changes to ocean chemistry, which impact marine life. The uptake of CO2 in the oceans has caused the ocean to become more acidic due to the increase of protons (H+ ions) as a result of reactions of CO2 with the surrounding seawater. This change is measured using the (logarithmic) pH scale and the process is known as ocean acidification (OA).

Not only is the pH of seawater decreasing with ocean acidification, the carbonate ion concentration (CO3 2-) is decreasing at the same time, which particularly affects calcifying organisms. The two most common forms of calcium carbonate used by calcifying organisms to produce their shells and skeletons are aragonite and calcite. Calcifying organisms such as bivalves and corals will find it particularly difficult to build their protective hard parts when CO3 2- is diminishing. In addition, the ocean depths below which aragonite and calcite tend to dissolve is getting shallower. The aragonite saturation horizon (ASH) has already shoaled by 80–400 m in the North Atlantic since pre-industrial times (Feely et al., 2004; Tanhua et al., 2007) and is projected to rise further from 2600 m to as shallow as 200 m depth by the end of the century (Orr et al., 2005). Benthic deep-sea ecosystems such as cold-water coral reefs that currently live in supersaturated waters with respect to aragonite are projected to be exposed to aragonite undersaturation by the end of the century due to OA (about 70% of known habitats, Guinotte et al., 2006; Zheng and Cao, 2015).

Continue reading ‘Chapter 4: ocean chemistry – Irish Ocean Climate And Ecosystem Status Report 2023’

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

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’

Southern Ocean acidification revealed by Biogeochemical-Argo floats


Ocean acidification has potentially large impacts on calcifying organisms and ecosystems. Argo floats equipped with biogeochemical (BGC) sensors have been continuously measuring Southern Ocean pH since 2014. These BGC-Argo floats were deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. Here we present a SOCCOM-era Objectively Mapped pH (SOM-pH) 2014-2019 climatology and explain the method for constructing this product. We show example SOM-pH fields demonstrating the spatial and temporal structure of Southern Ocean pH. Comparison with previous ship-based measurements reveals decreases in pH of up to 0.02 per decade, with a structure decaying with depth. An assessment of the trend structure reveals a pattern indicative of the meridional overturning circulation. Upwelling waters that have not been in recent contact with the atmosphere show negligible or small trends, while surface and downwelling waters that have had more exposure to the atmosphere show the strongest trends. Thus comparison of this new BGC-Argo mapped pH estimate to historic observations allows quantifying the structure of Southern Ocean acidification.

Key Points

  • We present a novel 12-month Southern Ocean pH mapped product, made possible by the Biogeochemical-Argo array initiated in 2014.
  • Comparing to ship-based measurements above 1500 m reveals a decrease in pH of up to 0.02 per decade.
  • pH changes are widespread with varying magnitudes reflecting the pattern of the meridional overturning circulation.
Continue reading ‘Southern Ocean acidification revealed by Biogeochemical-Argo floats’

Ocean acidification: future effects to ocean environments and biologic response

Ocean acidification has become one of many consequences of our modern civilization that potentially could cause major changes to Earth’s undersea environments. There are several physical and chemical effects from acidification, one of which affects the undersea acoustic environment. There are various empirical models for acoustic absorption, but an empirical model by Francois and Garrison has a pH dependent contribution. As the ocean becomes more acidic, the pH decreases from its current value and the model predicts a reduction in the amount of acoustic absorption. The result of this absorption reduction changes the overall transmission loss of sound propagation and makes the underwater environment a “louder” place. The consequences of which would be minor complications to ocean exploration but will have a greater impact upon the undersea fauna. As the environment becomes louder, those animals that use acoustics to echolocate food, will find it more difficult to do so and others may find the environment to not be amenable to their survival. These changes are occurring on a time scale on the order of decades, so environmental acoustic monitoring of ambient conditions and large-scale migration can be utilized as an indicator of the changes to the water space.

Continue reading ‘Ocean acidification: future effects to ocean environments and biologic response’

Quantitative assessment of the response of seawater environmental quality to marine protection policies under regional economic development – a case study of Xiamen Bay, China

Xiamen is the epitome of having steady economic growth and non-negligible environmental stress over decades. Several restoration programs have been applied to address the conflicts between heavy environmental pressures and human activities, but the response of current coastal protection policies to the marine environment remains to be assessed. Therefore, to assess the effectiveness and efficiency of marine conservation policies under regional economic growth in Xiamen, quantitative techniques including elasticity analysis and dummy variable regression models were applied. Here we show the potential relationship between seawater quality (pH, COD, DIN and DRP) and economic growth including Gross Domestic Product (GDP) and Gross Ocean Product (GOP), to evaluate the ongoing related policies by using over 10 years of data (2007–2018). According to our estimates, a GDP growth rate of 8.5% represents a stable economic climate that is favorable for the overall rehabilitation of the local coastal environment. The results of the quantitative research indicate a strong relationship between economic development and seawater quality, with marine protection regulations serving as the direct cause. As GDP growth and pH are significantly positively correlated (coef. = 0.8139, p = 0.012), ocean acidification has decreased over the last decade. With an inversely proportional correlation with GDP (coef. = 0.8456, p = 0.002) and GOP (coef. = 0.8046, p = 0.005), the trend in COD concentrations effectively meets the targets of current pollution control legislation. By using a dummy variable regression model, we found that legislation is the most effective way in seawater recovery in the GOP section, and positive externalities of marine protection frameworks are also estimated. Meanwhile, it is predicted that the negative effects from the non-GOP section will gradually affect the coastal environmental quality gradually. An overall framework for controlling marine pollutant discharges, giving equal attention to maritime and non-maritime anthropogenic activities should be promoted and updated.

Continue reading ‘Quantitative assessment of the response of seawater environmental quality to marine protection policies under regional economic development – a case study of Xiamen Bay, China’

  • Reset


OA-ICC Highlights

%d bloggers like this: