Posts Tagged 'biogeochemistry'



Carbon and nitrogen accumulation and interspecific competition in two algae species, Pyropia haitanensis and Ulva lactuca, under ocean acidification conditions

If the atmospheric CO2 continues to increase as predicted, Pyropia haitanensis would experience the coupled effects of ocean acidification (OA) and interference from the epiphyte alga Ulva lactuca. In the current study, we evaluated the carbon (C) and nitrogen (N) accumulation in P. haitanensis and U. lactuca under OA conditions, as well as the interspecific competition between these two algae. We found that, under mono-culture conditions, OA significantly enhanced the growth of both P. haitanensis and U. lactuca and markedly increased the soluble carbohydrate (SC) content and C/N ratios in P. haitanensis, but reduced its soluble proteins (SP) content. In U. lactuca, OA reduced its SP content, but increased C/N ratios, while its SC content was not significantly affected. Under biculture conditions, the rapid growth of U. lactuca and its comparatively more efficient use of nutrients resulted in insufficient available N sources for P. haitanensis. Biculture with U. lactuca increased SC but declined SP content. This also resulted in some membrane injuries that were indicated by increased malondialdehyde (MDA) content and depressed growth in P. haitanensis. Biculture with U. lactuca was disadvantageous for carbon and nitrogen accumulation in P. haitanensis. The results demonstrated that under conditions of OA, the negative effects caused by the epiphyte U. lactuca were more pronounced. If the CO2 levels rise as predicted, Ulva algae would severely interfere with maricultivation of P. haitanensis.

Continue reading ‘Carbon and nitrogen accumulation and interspecific competition in two algae species, Pyropia haitanensis and Ulva lactuca, under ocean acidification conditions’

The oceanic sink for anthropogenic CO2 from 1994 to 2007

We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO2 inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year−1 and represents 31 ± 4% of the global anthropogenic CO2 emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.

Continue reading ‘The oceanic sink for anthropogenic CO2 from 1994 to 2007’

Variability of seawater chemistry in a kelp forest environment is linked to in situ transgenerational effects in the purple sea urchin, Strongylocentrotus purpuratus

While the value of giant kelp (Macrocystis pyrifera) as a habitat-forming foundation species is well-understood, it is unclear how they impact the oxygen concentration and pH of the surrounding seawater, and further, how such a dynamic abiotic environment will affect eco-evolutionary dynamics in a context of global change. Here, we profiled the nearshore kelp forest environment in Southern California to understand changes in dissolved oxygen (DO) and pH with high spatiotemporal resolution. We then examined transgenerational effects using sea urchins (Strongylocentrotus purpuratus) as our study organism. Using enclosures on the benthos, we conditioned adult sea urchins in situ at two locations – one inside the kelp forest and one outside the kelp forest. After a 11-week conditioning period timed to coincide with gametogenesis in the adults, the urchins were collected, spawned, and cultures of their progeny were raised in the laboratory in order to assess their performance to simulated ocean acidification. In terms of the physical observations, we observed significant changes in DO and pH not only when comparing sites inside and outside of the kelp forest, but also between surface and benthic sensors at the same site. DO and pH at the benthos differed in mean, the amplitude of the diel signal, and in the profile of background noise of the signal. Ultimately, these results indicated that both DO and pH were more predictably variable inside of the kelp forest environment. On the biological side, we found that adult sea urchins inside the kelp forest produced more protein-rich eggs that developed into more pH-resilient embryos. Overall, this study in a temperate kelp forest ecosystem is one of the first studies to not only observe biological response to highly characterized environmental variability in situ, but also to observe such changes in a transgenerational context.

Continue reading ‘Variability of seawater chemistry in a kelp forest environment is linked to in situ transgenerational effects in the purple sea urchin, Strongylocentrotus purpuratus’

Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean

Models project that with current CO2 emission rates, the Southern Ocean surface will be undersaturated with respect to aragonite by the end of this century1,2,3,4. This will result in widespread impacts on biogeochemistry and ocean ecosystems5,6,7, particularly the health of aragonitic organisms, such as pteropods7, which can dominate polar surface water communities6. Here, we quantify the depth of the present-day Southern Ocean aragonite saturation horizon using hydrographic and ocean carbon chemistry observations, and use a large ensemble of simulations from the Community Earth System Model (CESM)8,9 to track its evolution. A new, shallow aragonite saturation horizon emerges in many Southern Ocean locations between now and the end of the century. While all ensemble members capture the emergence, internal climate variability may affect the year of emergence; thus, its detection may have been overlooked by ensemble average analysis in the past. The emergence of the new horizon is driven by the slow accumulation of anthropogenic CO2 in the Southern Ocean thermocline, where the carbonate ion concentration exhibits a local minimum and approaches undersaturation. The new horizon is also apparent under an emission-stabilizing scenario indicating an inevitable, sudden decrease in the volume of suitable habitat for aragonitic organisms.

Continue reading ‘Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean’

Greenhouse gases, nutrients and the carbonate system in the Reloncaví Fjord (Northern Chilean Patagonia): implications on aquaculture of the mussel, Mytilus chilensis, during an episodic volcanic eruption

Highlights
• A large bloom of phytoplankton was detected in the surface waters of the Reloncaví fjord following the Calbuco volcano eruption.

• Subsequent to the Calbuco volcano eruption, higher N2O, CH4 and SO42− concentrations were observed in Fjord surface waters close to areas of river discharge.

• Optimal juvenile mussel growth was observed in refugee subsurface depths coinciding with increased aragonite saturation.

• Thus, the observed trends in the carbonate system and nutrient outputs may be valuable for developing effective management strategies for mussel aquaculture in the Reloncaví Fjord.

Abstract
This study investigates the immediate and mid-term effects of the biogeochemical variables input into the Reloncaví fjord (41°40′S; 72°23′O) as a result of the eruption of Calbuco volcano. Reloncaví is an estuarine system supporting one of the largest mussels farming production within Northern Chilean-Patagonia. Field-surveys were conducted immediately after the volcanic eruption (23–30 April 2015), one month (May 2015), and five months posterior to the event (September 2015). Water samples were collected from three stations along the fjord to determine greenhouse gases [GHG: methane (CH4), nitrous oxide (N2O)], nutrients [NO3−, NO2−, PO43−, Si(OH)4, sulphate (SO42−)], and carbonate systems parameters [total pH (pHT), temperature, salinity, dissolved oxygen (O2), and total alkalinity (AT)]. Additionally, the impact of physicochemical changes in the water column on juveniles of the produced Chilean blue mussel, Mytilus chilensis, was also studied. Following the eruption, a large phytoplankton bloom led to an increase in pHT, due to the uptake of dissolved-inorganic carbon in photic waters, potentially associated with the runoff of continental soil covered in volcanic ash. Indeed, high surface SO42− and GHG were observed to be associated with river discharges. No direct evidence of the eruption was observed within the carbonate system. Notwithstanding, a vertical pattern was observed, with an undersaturation of aragonite (ΩAr < 1) both in brackish surface (10 m), and saturated values in subsurface waters (3 to 7 m). Simultaneously, juvenile mussel shells showed maximized length and weight at 4 m depth. Results suggest a localized impact of the volcanic eruption on surface GHG, nutrients and short-term effects on the carbonate system. Optimal conditions for mussel calcification were identified within a subsurface refuge in the fjord. These specific attributes can be integrated into adaptation strategies by the mussel aquaculture industry to confront ocean acidification and changing runoff conditions.

Continue reading ‘Greenhouse gases, nutrients and the carbonate system in the Reloncaví Fjord (Northern Chilean Patagonia): implications on aquaculture of the mussel, Mytilus chilensis, during an episodic volcanic eruption’

Meeting climate targets by direct CO2 injections: what price would the ocean have to pay?

We investigate the climate mitigation potential and collateral effects of direct injections of captured CO2 into the deep ocean as a possible means to close the gap between an intermediate CO2 emissions scenario and a specific temperature target, such as the 1.5 °C target aimed for by the Paris Agreement. For that purpose, a suite of approaches for controlling the amount of direct CO2 injections at 3000 m water depth are implemented in an Earth System Model of intermediate complexity.

Following the representative concentration pathway RCP4.5, which is a medium mitigation CO2 emissions scenario, cumula-tive CO2 injections required to meet the 1.5 °C climate goal are found to be 390 Gt C by the year 2100 and 1562 Gt C at the end of simulations, by the year 3020. The latter includes a cumulative leakage of 602 Gt C that needs to be re-injected in order to sustain the targeted global mean temperature.

CaCO3 sediment and weathering feedbacks reduce the required CO2 injections that comply with the 1.5 °C target by about 13 % in 2100 and by about 11 % at the end of the simulation.

With respect to the injection-related impacts we find that average pH values in the surface ocean are increased by about 0.13 to 0.18 units, when compared to the control run. In the model, this results in significant increases in potential coral reef habi-tats, i.e., the volume of the global upper ocean (0 to 130 m depth) with omega aragonite > 3.4 and ocean temperatures be-tween 21 °C and 28 °C, compared to the control run. The potential benefits in the upper ocean come at the expense of strongly acidified water masses at depth, with maximum pH reductions of about −2.37 units, relative to preindustrial, in the vicinity of the injection sites. Overall, this study demonstrates that massive amounts of CO2 would need to be injected into the deep ocean in order to reach and maintain the 1.5 °C climate target in a medium mitigation scenario on a millennium timescale, and that there is a trade-off between injection-related reductions in atmospheric CO2 levels accompanied by reduced upper-ocean acidification and adverse effects on deep ocean chemistry, particularly near the injection sites.

Continue reading ‘Meeting climate targets by direct CO2 injections: what price would the ocean have to pay?’

Accurate determination of total alkalinity in estuarine waters for acidification studies

Highlights
• This work studies the best way to determine alkalinity in estuarine waters.

• The usefulness of some available stability constants of the CO2 system were tested.

• A mixing of two existing sets of stability constants gave the optimum results.

• Non-linear least square regression was the best approach to determine alkalinity.

Abstract
One of the effects of the atmospheric CO2 increase is the ocean acidification. Over the past 20 years, accurate measurements of the seawater carbonate system have become a high priority because this is the main system controlling seawater acidity. However, this phenomenon has not been widely studied in estuaries, even if they are among the most productive natural habitats in the world, lodging some of the highest biotic diversity and production. Due to that lack of information, this work aims to develop and discuss new strategies for the determination of total alkalinity (TA), one of the most measured parameters in the study of acidification, in estuarine waters in the wide range of salinities that can be found in these systems. For that purpose, a new set of stability constants for the carbonate system was established and compared with those most widely used up to date. For the determination of TA, different approaches were studied for the data treatment of the potentiometric titration data.

Continue reading ‘Accurate determination of total alkalinity in estuarine waters for acidification studies’


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Ocean acidification in the IPCC AR5 WG II

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