Archive for October, 2020

Behind the paper: ocean acidification, plankton, and the biological carbon pump

How marine ecosystems will be affected by ocean acidification is still largely unknown. Large-scale field experiments revealed the complex and variable responses of plankton communities to increasing CO2, and how this could alter biogeochemical cycling and the oceanic carbon sink in the future.

The paper in Nature Climate Change is available here: Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification



By Tim Boxhammer and Jan Taucher

In 2010, when we first set out for a field study to examine how ocean acidification would affect marine plankton and their role in the cycling of carbon and nitrogen in the ocean, we did not have any clue about the long road ahead of us. For our research over the coming years, we collected data in marine ecosystems ranging from the high Artic over remote Scandinavian fjords, to the vast subtropical gyres. 
These different environments did not just mean a change in marine ecosystems, but also affected our working conditions in many ways.

Continue reading ‘Behind the paper: ocean acidification, plankton, and the biological carbon pump’

The Olympic Coast as a sentinel – tribal communities at the forefront of ocean change (video)

Indigenous people have depended on Olympic Coast marine species for their livelihoods, food security and cultural practices for thousands of years. Today, these species—and the tribal communities that depend on them—are at risk from ocean acidification. Washington Sea Grant, in partnership with the Olympic Coast Treaty Tribes, federal and academic scientists and coastal managers, is working to understand and plan for the impacts of ocean change to tribal community well-being.

Continue reading ‘The Olympic Coast as a sentinel – tribal communities at the forefront of ocean change (video)’

Princeton project expands to create a worldwide fleet of robotic floats to monitor ocean health

On October 29, the National Science Foundation (NSF) announced a $53 million grant — shared among a consortium of the country’s top ocean research institutions — to build a global network of chemical and biological sensors that will monitor ocean health.

Scientists at Princeton University, Monterey Bay Aquarium Research Institute (MBARI), University of Washington, Scripps Institution of Oceanography at UC San Diego and Woods Hole Oceanographic Institution will use this grant to build and deploy 500 robotic ocean monitoring floats around the globe. The new program builds on the successful Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project based at Princeton that has deployed similar floats in the ocean around Antarctica, proving their usefulness as year-round reporters of ocean chemistry and biological activity.

Continue reading ‘Princeton project expands to create a worldwide fleet of robotic floats to monitor ocean health’

Reaching consensus on assessments of ocean acidification trends

Scientists are working to establish a common methodology for evaluating rates of change in—and the various mechanisms that affect—acidification across ocean environments.

Media coverage concerning carbon dioxide (CO2) emissions into Earth’s atmosphere most often focuses on how these emissions affect climate and weather patterns. However, atmospheric CO2 is also the primary driver for ocean acidification, because the products of atmospheric CO2 dissolving into seawater reduce seawater’s pH and its concentration of carbonate ions. Since the beginning of the Industrial Revolution, the acidity of the ocean has increased by over 30%.

Some organisms in the ocean may struggle to adapt to increasingly acidified conditions, and even resilient life-forms may have a harder time finding food. Higher CO2 levels in ocean water also make it difficult for shellfish to build their shells and corals to form their reefs, both of which are made of carbonate compounds.Ocean acidification affects the overall health of marine ecosystems as well as societal concerns about food security.Ocean acidification, which affects the overall health of marine ecosystems as well as societal concerns about food security, has emerged as a major concern for decision-makers on local, regional, and global scales. Indeed, ocean acidification is now a headline climate indicator for the World Meteorological Organization.

Continue reading ‘Reaching consensus on assessments of ocean acidification trends’

Autonomous measurement of seawater total alkalinity as an enhancement of ocean carbon observations: from performance characterization to long-term field deployment

Since around the mid of the 18th century, the global atmospheric carbon dioxide (CO2) concentration has significantly increased due to anthropogenic activities. For 2018, around 11.5 GtC yr−1 were emitted by fossil fuel combustion and cement production, and land use changes. A sink for the atmospheric CO2 is the ocean, which has taken up around 2.6 GtC yr−1 in 2018. The relative good understanding of the current global mean oceanic uptake of anthropogenic CO2 is contrasted by a lack of knowledge how the natural carbon cycle will respond regionally to changes introduced by anthropogenic CO2 emissions, like global warming, ocean acidification or ocean deoxygenation. In view of the central role of the oceanic CO2 sink and its vulnerability to these changes, extensive ocean carbon observations are necessary. Over several years, the Ships of Opportunity (SOOP) network provides high-quality CO2 partial pressure (p(CO2)) data of the surface ocean, and, therefore, forms the backbone of the global observation system for the oceanic CO2 sink. However, to get full insight into the marine CO2 system, at least two of the four measurable carbonate variables are required, which are p(CO2), total alkalinity (AT), dissolved inorganic carbon (CT) and pH. The so far common workaround is the prediction of AT by using established temperature-salinity based parameterizations. However, compared with direct measurements, this procedure leads to higher uncertainties and spatiotemporal biases. Therefore, autonomous SOOP-based AT measurements are of great interest and, in the end, should enhance ocean carbon observations. In order to achieve this enhancement, this thesis goals to provide an example of a successful implementation of a novel autonomous analyzer for seawater AT, the CONTROS HydroFIA TA (-4H-JENA engineering GmbH, Germany), on a Carbon-SOOP station operating in the subpolar North Atlantic (together with fundamental guidelines and recommendations leading to high-quality AT data).

Continue reading ‘Autonomous measurement of seawater total alkalinity as an enhancement of ocean carbon observations: from performance characterization to long-term field deployment’

Autonomous observation of seasonal carbonate chemistry dynamics in the Mid‐Atlantic Bight

Ocean acidification alters the oceanic carbonate system, increasing potential for ecological, economic, and cultural losses. Historically, productive coastal oceans lack vertically‐resolved high‐resolution carbonate system measurements on timescales relevant to organism ecology and life history. The recent development of a deep ISFET‐based pH sensor system integrated into a Slocum glider has provided a platform for achieving high‐resolution carbonate system profiles. From May 2018 to November 2019, seasonal deployments of the pH glider were conducted in the central Mid‐Atlantic Bight. Simultaneous measurements from the glider’s pH and salinity sensors enabled the derivation of total alkalinity and calculation of other carbonate system parameters including aragonite saturation state. Carbonate system parameters were then mapped against other variables, such as temperature, dissolved oxygen, and chlorophyll, over space and time. The seasonal dynamics of carbonate chemistry presented here provide a baseline to begin identifying drivers of acidification in this vital economic zone.

Continue reading ‘Autonomous observation of seasonal carbonate chemistry dynamics in the Mid‐Atlantic Bight’

High light alongside elevated PCO2 alleviates thermal depression of photosynthesis in a hard coral (Pocillopora acuta)

The absorbtion of human-emitted CO2 by the oceans (elevated PCO2) is projected to alter the physiological performance of coral reef organisms by perturbing seawater chemistry (i.e. ocean acidification). Simultaneously, greenhouse gas emissions are driving ocean warming and changes in irradiance (through turbidity and cloud cover), which have the potential to influence the effects of ocean acidification on coral reefs. Here, we explored whether physiological impacts of elevated PCO2 on a coral–algal symbiosis (Pocillopora acuta–Symbiodiniaceae) are mediated by light and/or temperature levels. In a 39 day experiment, elevated PCO2 (962 versus 431 µatm PCO2) had an interactive effect with midday light availability (400 versus 800 µmol photons m−2 s−1) and temperature (25 versus 29°C) on areal gross and net photosynthesis, for which a decline at 29°C was ameliorated under simultaneous high-PCO2 and high-light conditions. Light-enhanced dark respiration increased under elevated PCO2 and/or elevated temperature. Symbiont to host cell ratio and chlorophyll a per symbiont increased at elevated temperature, whilst symbiont areal density decreased. The ability of moderately strong light in the presence of elevated PCO2 to alleviate the temperature-induced decrease in photosynthesis suggests that higher substrate availability facilitates a greater ability for photochemical quenching, partially offsetting the impacts of high temperature on the photosynthetic apparatus. Future environmental changes that result in moderate increases in light levels could therefore assist the P. acuta holobiont to cope with the ‘one–two punch’ of rising temperatures in the presence of an acidifying ocean.

Continue reading ‘High light alongside elevated PCO2 alleviates thermal depression of photosynthesis in a hard coral (Pocillopora acuta)’

Current and future trophic interactions in tropical shallow-reef lagoon habitats

Calcium carbonate (CaCO3) sediments are the dominant form of CaCO3 on coral reefs accumulating in lagoon and inter-reefal areas. Owing to their mineralogy and a range of physical parameters, tropical CaCO3 sediments are predicted to be more sensitive to dissolution driven by ocean acidification than the skeleton of living reef organisms. How this scales up to impact infaunal organisms, which are an important food source for higher trophic levels, and thereby ecosystem functioning, is not well explored. We combined seasonal field surveys in a shallow-reef lagoon ecosystem on the Great Barrier Reef, Australia, with stable isotope analyses and a tank-based experiment to examine the potential top-down influence of the deposit-feeding sea cucumber, Stichopus herrmanni, on this infaunal community under current and future ocean pH. Densities of surface-sediment meiofauna were lowest in winter and spring, with harpacticoid copepods (38%) and nematodes (27%) the dominant taxa. Stable isotope analyses showed that S. herrmanni had a top-down influence on meiofauna and microphytes with a distinct δ13C and δ15N trophic position that was homogenous across seasons and locations. Tanks that mimicked sandy shallow-reef lagoon habitats were used to examine the effects of ocean acidification (elevated pCO2) on this trophic interaction. We used outdoor control (sediment only) and experimental (sediment plus S. herrmanni) tanks maintained at present-day and near-future pCO2 (+ 570 µatm) for 24 days, which fluctuated with the diel pCO2 cycle. In sediment-only tanks, copepods were > twofold more abundant at elevated pCO2, with no negative effects documented for any meiofauna group. When included in the community, top-down control by S. herrmanni counteracted the positive effects of low pH on meiofaunal abundance. We highlight a novel perspective in coral reef trophodynamics between surface-sediment meiofauna and deposit-feeding sea cucumbers, and posit that community shifts may occur in shallow-reef lagoon habitats in a future ocean with implications for the functioning of coral reefs from the bottom up.

Continue reading ‘Current and future trophic interactions in tropical shallow-reef lagoon habitats’

The future is now: long-term research shows ocean acidification ramping up on the Reef

A new study has shown ocean acidification is no longer a sombre forecast for the Great Barrier Reef but a present-day reality

Newswise — Ocean acidification is no longer a sombre forecast for the Great Barrier Reef but a present-day reality, a new study reveals.

The study, published in the international Journal Scientific Reports, shows carbon dioxide (CO2) and ocean acidification are rapidly increasing on the Reef. Seawater CO2 has risen 6 per cent over the past 10 years and matches the rate of CO2 increases in the atmosphere, confirming the influence of atmospheric CO2 on seawater CO2 levels.

“People talk about ocean acidification in terms of 50 years’ time, but for the first time our study shows how fast ocean acidification is already happening on the Reef,” said Dr Katharina Fabricius, lead author and Senior Principal Research Scientist at the Australian Institute of Marine Science (AIMS).

Continue reading ‘The future is now: long-term research shows ocean acidification ramping up on the Reef’

Progressive seawater acidification on the Great Barrier Reef continental shelf

Coral reefs are highly sensitive to ocean acidification due to rising atmospheric CO2 concentrations. We present 10 years of data (2009–2019) on the long-term trends and sources of variation in the carbon chemistry from two fixed stations in the Australian Great Barrier Reef. Data from the subtropical mid-shelf GBRWIS comprised 3-h instrument records, and those from the tropical coastal NRSYON were monthly seawater samples. Both stations recorded significant variation in seawater CO2 fugacity (fCO2), attributable to seasonal, daytime, temperature and salinity fluctuations. Superimposed over this variation, fCO2 progressively increased by > 2.0 ± 0.3 µatm year−1 at both stations. Seawater temperature and salinity also increased throughout the decade, whereas seawater pH and the saturation state of aragonite declined. The decadal upward fCO2 trend remained significant in temperature- and salinity-normalised data. Indeed, annual fCO2 minima are now higher than estimated fCO2 maxima in the early 1960s, with mean fCO2 now ~ 28% higher than 60 years ago. Our data indicate that carbonate dissolution from the seafloor is currently unable to buffer the Great Barrier Reef against ocean acidification. This is of great concern for the thousands of coral reefs and other diverse marine ecosystems located in this vast continental shelf system.

Continue reading ‘Progressive seawater acidification on the Great Barrier Reef continental shelf’

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