Archive for March, 2020

COVID-19 update: 5th Intl. Symposium on the Ocean in a High-CO2 World

In view of the current situation with COVID-19, the Organizing Committee of the 5th International Symposium on the Ocean in a High CO2 World has extended the deadline for submissions of abstracts and travel support applications until Friday, 24 April 2020. Applicants for travel support will be notified on the outcome of their application by 7 May. A decision will be made by mid-May on whether to continue with the proposed date (7-10 September 2020) or delay the Symposium. The Symposium organizers are monitoring the situation closely and updates will be posted on the Symposium website.

Continue reading ‘COVID-19 update: 5th Intl. Symposium on the Ocean in a High-CO2 World’

Total alkalinity minus dissolved inorganic carbon as a proxy for deciphering ocean acidification mechanisms

Highlights

• [TA–DIC] can be used for measuring OA and deciphering OA processes in global ocean.

• [TA–DIC] is conservative to ocean mixing and insensitive to temperature and pressure.

• Biological influences on OA rates can be directly linked via Redfield ratio and AOU.

Abstract

Ocean acidification (OA) defined as the decline of ocean pH and calcium carbonate saturation state (Ω) as a result of ocean uptake of CO2 from the atmosphere may have considerable negative impacts on global marine organisms and may substantially modify ocean biogeochemistry. However, as changes of pH and Ω are not conservative or linear with respect to ocean physical processes (e.g., mixing, temperature and pressure changes), the influences of anthropogenic CO2 uptake and ocean biogeochemical processes on OA rates cannot be easily identified. Here, we examine whether a composite property [TA–DIC] or the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC), which is conservative to ocean mixing and is not sensitive to temperature and pressure changes, can be used for measuring OA rates and deciphering the underlying OA mechanisms in the global ocean as it in surface waters of several regional oceans. Based on Global Ocean Data Analysis Project Version 2 (GLODAPv2), we demonstrate using this property for measuring OA rates can be applied on a global ocean scale, except at low salinity e.g., <20 and when [TA–DIC] is <~50 μmol kg−1, where the relationships of [TA–DIC] with pH and/or Ω are nonlinear. However, there are almost no limitations when using this property for deciphering the underlying OA mechanisms since the change of [TA–DIC] with time is relatively small on OA timescales of decades or more. Using [TA–DIC], we can readily quantify the influences from freshwater inputs and upwelling on OA rates based on a two end-member mixing model. More importantly, through the Redfield ratio and apparent oxygen utilization, we can directly link biological influences to OA rates and conveniently quantify the biological modulation on OA rates. Therefore, we argue that using [TA–DIC] as a proxy for OA would provide a simple but powerful way of deciphering acidification mechanisms and predicting future development of acidification.

Continue reading ‘Total alkalinity minus dissolved inorganic carbon as a proxy for deciphering ocean acidification mechanisms’

Upcoming webinar: Are we already seeing impacts of OA? biological studies and research from around the world

Date: Wednesday, April 15 at 11:00am PST

Description: Join us for our first webinar of the year and a discussion about the potential impacts of OA on seafood. Presentations will include a focus on Dungeness Crab in the Pacific, oysters in the Atlantic and finfish in the Pacific. Speakers will answer questions like:

How are culturally and economically significant species being impacted by OA and other stressors?
How might some seafood economies be affected?
How is science being prioritized to better examine these impacts?

Continue reading ‘Upcoming webinar: Are we already seeing impacts of OA? biological studies and research from around the world’

Variation of pCO2 concentrations induced by tropical cyclones “Wind-Pump” in the middle-latitude surface oceans: a comparative study

The Bermuda Testbed Mooring (BTM) and Bay of Bengal Ocean Acidification (BOBOA) mooring measurements were used to identify changes in the partial pressure of CO2 at the sea surface (pCO2sea) and air-sea CO2 fluxes (FCO2) associated with passage of two tropical cyclones (TCs), Florence and Hudhud. TC Florence passed about 165 km off the BTM mooring site with strong wind speeds of 24.8 m s–1 and translation speed of 7.23 m s–1. TC Hudhud passed about 178 km off the BOBOA mooring site with wind speeds of 14.0 m s–1 and translation speed of 2.58 m s–1. The present study examined the effect of temperature, salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), air-sea CO2 flux, and phytoplankton chlorophyll a change on pCO2sea as a response to TCs. Enhanced mixed layer depths were observed due to TCs-induced vertical mixing at both mooring sites. Decreased pCO2sea (–15.16±5.60 μatm) at the BTM mooring site and enhanced pCO2sea (14.81±7.03 μatm) at the BOBOA mooring site were observed after the passage of Florence and Hudhud, respectively. Both DIC and TA are strongly correlated with salinity in the upper layer of the isothermal layer depth (ILD). Strong (weak) vertical gradient in salinity is accompanied by strong (weak) vertical gradients in DIC and TA. Strong vertical salinity gradient in the upper layer of the ILD (0.031 psu m–1), that supply much salinity, dissolved inorganic carbon and total alkalinity from the thermocline was the cause of the increased pCO2sea in the BOBOA mooring water. Weak vertical salinity gradient in the upper layer of the ILD (0.003 psu m–1) was responsible for decreasing pCO2sea in the BTM mooring water. The results of this study showed that the vertical salinity gradient in the upper layer of the ILD is a good indicator of the pCO2sea variation after the passages of TCs.

Continue reading ‘Variation of pCO2 concentrations induced by tropical cyclones “Wind-Pump” in the middle-latitude surface oceans: a comparative study’

Multiple global change stressor effects on phytoplankton nutrient acquisition in a future ocean

Predicting the effects of multiple global change stressors on microbial communities remains a challenge because of the complex interactions among those factors. Here, we explore the combined effects of major global change stressors on nutrient acquisition traits in marine phytoplankton. Nutrient limitation constrains phytoplankton production in large parts of the present-day oceans, and is expected to increase owing to climate change, potentially favouring small phytoplankton that are better adapted to oligotrophic conditions. However, other stressors, such as elevated pCO2, rising temperatures and higher light levels, may reduce general metabolic and photosynthetic costs, allowing the reallocation of energy to the acquisition of increasingly limiting nutrients. We propose that this energy reallocation in response to major global change stressors may be more effective in large-celled phytoplankton species and, thus, could indirectly benefit large-more than small-celled phytoplankton, offsetting, at least partially, competitive disadvantages of large cells in a future ocean. Thus, considering the size-dependent responses to multiple stressors may provide a more nuanced understanding of how different microbial groups would fare in the future climate and what effects that would have on ecosystem functioning.

Continue reading ‘Multiple global change stressor effects on phytoplankton nutrient acquisition in a future ocean’

Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)

Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. Here we examine interaction strengths between juvenile giant kelp (Macrocystis pyrifera) and four common grazers under hypoxia and ocean acidification using short-term laboratory experiments and field data of grazer abundances to estimate population-level grazing impacts. We found that grazing is a significant source of mortality for juvenile kelp and, using field abundances, estimate grazers can remove on average 15.4% and a maximum of 73.9% of juveniles per m2 per day. Short-term exposure to low oxygen, not acidification, weakened interaction strengths across the four species and decreased estimated population-level impacts of grazing threefold, from 15.4% to 4.0% of juvenile kelp removed, on average, per m2 per day. This study highlights potentially high juvenile kelp mortality from grazing. We also show that the effects of hypoxia are stronger than the effects of acidification in weakening these grazing interactions over short timescales, with possible future consequences for the persistence of giant kelp and energy flow through these highly productive food webs.

Continue reading ‘Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp (Macrocystis pyrifera)’

A sediment trap evaluation of B/Ca as a carbonate system proxy in asymbiotic and nondinoflagellate hosting planktonic foraminifera

The ratio of boron to calcium (B/Ca) in a subset of foraminifera has been shown to covary with seawater carbonate chemistry, making this geochemical signature a promising proxy for carbon cycle science. Some studies suggest complications with the B/Ca proxy in photosymbiont‐bearing planktonic foraminifera, while relatively few studies have investigated B/Ca in species that lack large dinoflagellate symbionts. For the first time, we use a sediment trap time series to evaluate B/Ca of subtropical and subpolar planktonic foraminifera species that are asymbiotic (Globigerina bulloides and Neogloboquadrina incompta) and a species that hosts small intrashell photosymbionts (Neogloboquadrina dutertrei). We find that B/Ca measurements across size fractions indicate overall little to no size‐dependent uptake of boron that has previously been reported in some symbiont‐bearing foraminifera. Neogloboquadrina incompta and N. dutertrei B/Ca are strongly correlated with calcite saturation, pH, and carbonate ion concentration, which is in good agreement with the limited number of published core top results. While G. bulloides B/Ca trends with seasonal fluctuations in carbonate chemistry, during discrete periods considerable B/Ca offsets occur when a cryptic G. bulloides species is known to be seasonally present within the region. We confirm presence and significant B/Ca offset between cryptic species by individual LA‐ICP‐MS analyses. This finding calls into question the use of traditional morphological classification to lump what might be genetically distinct species for geochemical analyses. Our overall results highlight the utility of G. bulloides, N. incompta, and N. dutertrei B/Ca while bringing to light new considerations regarding divergent geochemistry of cryptic species.

Continue reading ‘A sediment trap evaluation of B/Ca as a carbonate system proxy in asymbiotic and nondinoflagellate hosting planktonic foraminifera’

Recent density decline in wild-collected subarctic crustose coralline algae reveals climate change signature

Warming surface ocean temperatures combined with the continued diffusion of atmospheric CO2 into seawater have been shown to have detrimental impacts on calcareous marine organisms in tropical and temperate localities. However, greater oceanic CO2 uptake in higher latitudes may present a higher oceanic acidification risk to carbonate organisms residing in Arctic and subarctic habitats. This is especially true for crustose coralline algae that build their skeletons using high-Mg calcite, which is among the least stable and most soluble of the carbonate minerals. Here we present a century-long annually resolved growth, density, and calcification rate record from the crustose coralline alga Clathromorphum nereostratum, a dominant calcifier in Pacific Arctic and subarctic benthic communities. Specimens were collected from the Aleutian Islands, Alaska (USA), a region that has undergone a long-term decline of 0.08 ± 0.01 pH units since the late 19th century. Growth and calcification rates remain relatively stable throughout the record, but skeletal densities have declined substantially since A.D. 1983. Strong correlations to warming sea-surface temperatures indicate that temperature stress may play a significant role in influencing the ability of corallines to calcify. Decreasing algal skeletal density may offset the benefits of continued growth and calcification due to a weakening in structural integrity, which could have detrimental consequences for the diverse reef-like communities associated with algal structures in mid-to-high latitudes.

Continue reading ‘Recent density decline in wild-collected subarctic crustose coralline algae reveals climate change signature’

Relationship between shell integrity of pelagic gastropods and carbonate chemistry parameters at a Scottish Coastal Observatory monitoring site

Ocean acidification (OA), the anthropogenic carbon dioxide-induced changes in seawater carbonate chemistry, is likely to have a significant impact on calcifying plankton. Most planktonic studies on OA are based on “one-off” cruises focused on offshore areas while observations from inshore waters are scarce. This study presents the first analysis on the shell integrity of pelagic gastropods (holoplanktonic pteropods and planktonic larvae of otherwise benthic species) at the Scottish Coastal Observatory monitoring site at Stonehaven on the east coast of Scotland. The shell integrity of archived pelagic gastropods specimens from 2011 to 2013 was examined using Scanning Electron Microscopy and the relationship with OA (pH and aragonite saturation, Ωarg) and other environmental parameters was investigated. Evidence of shell dissolution was detected in all analysed taxa even though the seawater was supersaturated with respect to aragonite. The shell condition matched the temporal pattern observed in Ωarg, with higher proportion of dissolution associated with decreasing Ωarg, suggesting that the seasonality component of carbonate chemistry might affect the shell integrity of pelagic gastropods. The proportion of shell dissolution differed significantly between larvae and adult stages of pteropods, supporting the hypothesis that early-life stages would be more vulnerable to OA-induced changes. Our data also suggest that sensitivity to OA may differ even between closely related taxonomic groups. The strong interannual variability revealed by the year-to-year shell dissolution and Ωarg illustrates the difficulty in assessing the plankton response to OA in the field and the value of time series studies.

Continue reading ‘Relationship between shell integrity of pelagic gastropods and carbonate chemistry parameters at a Scottish Coastal Observatory monitoring site’

Future HAB science: directions and challenges in a changing climate

Highlights

• HABs develop through the integration of physical, chemical, and temporal drivers.

• We need a mechanistic understanding that reveals how climate affects these drivers.

• Accelerating climate change in coastal regions signals the urgency for action.

• New strategies, tools, and observatories for HABs will improve our forecast skill.

• Focused research on subsets of HAB species would greatly accelerate advances.

Abstract

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends.

Continue reading ‘Future HAB science: directions and challenges in a changing climate’


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Ocean acidification in the IPCC AR5 WG II

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