The Southern Ocean ecosystem under multiple climate change stresses – an integrated circumpolar assessment

A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.

Continue reading ‘The Southern Ocean ecosystem under multiple climate change stresses – an integrated circumpolar assessment’

Effect of climate change on crustose coralline algae at a temperate vent site, White Island, New Zealand

Natural CO2 vents allow study of the effects of climate change on marine organisms on a different scale from laboratory-based studies. This study outlines a preliminary investigation into the suitability of natural CO2 vents near White Island, Bay of Plenty, New Zealand (37°31.19′S, 117°10.85′E) for climate change research by characterising water chemistry from two vent and three control locations on a seasonal basis, as well as examining their effects on skeletons of the local calcifying crustose coralline algae. pH measurements at vent sites, calculated from dissolved inorganic carbon and alkalinity, showed reduced mean pH levels (7.49 and 7.85) relative to background levels of 8.06, whereas mean temperatures were between 0.0 and 0.4°C above control. Increases in sulfur and mercury at sites near White Island were probably a result of volcanic unrest. Crustose coralline algae did not show significant variability in skeletal Mg-calcite geochemistry, but qualitative comparisons of calcite skeletons under scanning electron microscopy saw greater deformation and dissolution in coralline algae calcite crystals from vent sites compared to controls. Although additional monitoring of pH fluctuations and hydrogen sulphides is still needed, the low pH and increased temperatures indicate potential for studying multistressor effects of projected climate changes in a natural environment.

Continue reading ‘Effect of climate change on crustose coralline algae at a temperate vent site, White Island, New Zealand’

Subaqueous soils and coastal acidification: a hydropedology perspective with implications for calcifying organisms

In the coastal zone, biological and biogeochemical processes, influenced by anthropogenic inputs, drive pH variability and contribute to coastal acidification. Spatial patterns of these processes across coastal estuaries are unknown. In this study, we used a hydropedological approach to assess the spatial variability of coastal acidification within two coastal lagoons and embayments in Rhode Island by measuring oyster shell dissolution, pH within the water column, and pore water pH within the upper 5 cm of the underlying subaqueous soils. Sampling and monitoring sites were stratified based on submerged soil-landscape types mapped at the Great Group level as Haplowassents, Sulfiwassents, and Psammowassents. We found that pore water pH varied significantly among soils and with depth. Median pore water pH was significantly greater in sandy, low organic matter content Psammowassents (7.97) than the finer textured, higher soil organic matter content Sulfiwassents (7.35), and the Haplowassents (6.57) that receive groundwater discharge from the surrounding subaerial soils. Juvenile calcifying organisms can experience acidic stress at pH values below 7.6; thus, current pH values within the upper few centimeters of Sulfiwassents and Haplowassents may be low enough to impact recently set juvenile calcifying organisms inhabiting these soils. Consequently, mean shell loss during a 4-wk period was significantly greater in the Sulfiwassents (1.54) than the Psammowassents (0.96%), with the greatest shell loss (18.62%) in one of our Haplowassent sites with groundwater discharge. Our research suggests that measures of pore water pH and shell dissolution may be helpful in developing soil interpretations regarding the effects of coastal acidification on calcifying organisms.

Continue reading ‘Subaqueous soils and coastal acidification: a hydropedology perspective with implications for calcifying organisms’

Environmental physiology of the jumbo squid, Dosidicus gigas (d’Orbigny, 1835) (Cephalopoda: Ommastrephidae): implications for changing climate

Dosidicus gigas (d’Orbigny, 1835) is a large, active squid that undergoes a diel vertical migration in the Eastern Tropical and Temperate Pacific. It is a voracious predator on zooplankton and micronekton and supports a large fishery. It is further preyed upon by large vertebrate predators, including whales. Its horizontal distribution is closely tied to productive upwelling regions that are characterized by strong oxygen minimum zones (OMZs). The apparent association with extreme hypoxia is surprising given its large size and high oxygen demand. As part of its daily vertical migration, D. gigas experiences daily temperature changes of 15–20°C, oxygen partial pressures ranging from near anoxia (< 0.8 kPa) to air-saturation (21 kPa) and pH changes from ∼8.1 to < 7.6 at depth. Oxygen minimum zones are believed to be expanding due to climate change, with minimum oxygen levels in the core of the OMZ declining and the low oxygen horizon shoaling. Simultaneously, surface waters are becoming more acidic and temperatures are rising. Here I review the extensive studies of this species that have been conducted over the past decade. D. gigas has a high affinity respiratory protein in the blood that supports a low critical oxygen partial pressure (3.8 kPa at 20 °C) and aerobic survival at night in the upper 200 meters of the water column. A pronounced pH- and temperature sensitivity of oxygen binding promotes oxygen transport across a depth range and in support of high rates of oxygen utilization but may impose constraints on high-temperature and CO2 tolerance. At its deeper, colder daytime habitat depth, D. gigas undergoes a pronounced metabolic suppression. Reduced activity levels and an apparent suspension of transcription and translation contribute to a ∼80% reduction in oxygen demand under 1% oxygen (0.8 kPa at 10 °C). Anaerobic metabolic pathways contribute some energy under these conditions. This metabolic suppression likely limits feeding at depth. Sub-critical oxygen levels, rather than temperature, predator avoidance or prey availability, appear to set the daytime depth distribution. Thus, expanding oxygen minimum zones will alter the daytime depth of peak abundance for these squids while ocean acidification and warming may impose a shallow ceiling above which squid performance is limited. The role of climate change in setting the vertical and horizontal distribution of the species is discussed.

Continue reading ‘Environmental physiology of the jumbo squid, Dosidicus gigas (d’Orbigny, 1835) (Cephalopoda: Ommastrephidae): implications for changing climate’

Changes in pteropod distributions and shell dissolution across a frontal system in the California Current System

We tested the sensitivity of the vertical distributions and shell dissolution patterns of thecosome pteropods to spatial gradients associated with an eddy-associated front in the southern California Current System. The aragonite saturation horizon (Ωarag = 1.0) shoaled from >200 to <75 m depth across the front. The vertical distribution of thecosome pteropods tracked these changes, with all 5 species showing reduced occurrence at depths below 100 m where waters were less saturated with respect to aragonite. Shell dissolution patterns of the numerically dominant thecosome Limacina helicina corresponded to the cross-frontal changes in Ωarag saturation state. Severe shell dissolution (categorized here as Type II and Type III) was low in near-surface waters where Ωarag > 1.4, while peak dissolution occurred in depths where Ωarag = 1.0 to 1.4. Vertical habitat compression and increased shell dissolution may be expected to accompany future shoaling of waters that are undersaturated with respect to aragonite.

Continue reading ‘Changes in pteropod distributions and shell dissolution across a frontal system in the California Current System’

Morphology and classification of hemocytes in Pinctada fucata and their responses to ocean acidification and warming

Hemocytes play important roles in the innate immune response and biomineralization of bivalve mollusks. However, the hemocytes in pearl oysters are poorly understood. In the present study, we investigated the morphology and classification of hemocytes in the pearl oyster, P. fucata. Three types of hemocytes were successfully obtained by light microscopy, electron microscopy and flow cytometry methods: small hyalinocytes, large hyalinocytes and granulocytes. The small hyalinocytes are the major hemocyte population. Morphological analyses indicated that these hemocytes have species-specific characterizations. In addition, we assessed the potential effects of ocean acidification (OA) and ocean warming (OW) on the immune parameters and calcium homeostasis of the hemocytes. OA and OW (31°C) altered pH value of hemolymph, increased the total hemocyte count, total protein content, and percentage of large hyalinocytes and granulocytes, while it decreased the neutral red uptake ability, suggesting active stress responses of P. fucata to these stressors. Exposure to OW (25 °C) resulted in no significant differences, indicating an excellent immune defense to heat stress at this level. The outflow of calcium from hemocytes to hemolymph was also determined, implying the potential impact of OA and OW on hemocyte-mediated biomineralization. This study, therefore, provides insight into the classification and characterization of hemocyte in the pearl oyster, P. fucata, and also reveals the immune responses of hemocytes to OA and OW, which are helpful for a comprehensive understanding of the effects of global climate change on pearl oysters.

Continue reading ‘Morphology and classification of hemocytes in Pinctada fucata and their responses to ocean acidification and warming’

Climate driven variability in the Southern Ocean carbonate system

We investigate seasonal and interannual variability in the Southern Ocean carbonate system using output from a historically forced (1948-2007) ocean general circulation model with embedded biogeochemistry. Atmospheric CO2 is fixed at pre-industrial levels to investigate carbonate system variability in the absence of an anthropogenic CO2 perturbation. We find that nearly one quarter of interannual variability in Southern Ocean Pacific sector surface carbonate ion concentration (CO23-) can be explained by variability in ENSO, with Pacific sector surface CO23- decreasing by 0.43 mmol m−3 per standard deviation decrease in the ENSO 3.4 index. ENSO related variability in vertical advection of dissolved inorganic carbon (DIC) drives this relationship between ENSO and surface CO23-. We also find that positive phases of the Southern Annular Mode (SAM) are associated with decreased Southern Ocean surface CO23-, an association driven by SAM-related variability in vertical advection of DIC. Despite the influence of SAM on interannual variability in surface CO23-, we find that only 4.5% of the trend in natural Southern Ocean surface CO23- exhibits linear congruence with the trend in wind stress. Given this, we predict that the positive trend in SAM will not have a substantial impact on ocean acidification. Lastly, we find that ENSO alters the wintertime minimum in surface CO23-. Assuming a business-as-usual acidification rate of 0.5 mmol m−3 yr−1, exacerbation of the wintertime minimum during La Niña conditions may advance the date of aragonite undersaturation within the central Pacific sector of the Southern Ocean by as many as 8 years.

Continue reading ‘Climate driven variability in the Southern Ocean carbonate system’

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Ocean acidification in the IPCC AR5 WG II

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