Seasonal variation in aragonite saturation states and the controlling factors in the southeastern Yellow Sea


• Aragonite saturation state was determined in the southeastern Yellow Sea (Korea territory) for the first time.

• Aragonite undersaturation occurred in the bottom waters of the southeastern Yellow Sea during the fall.

• Aragonite undersaturation may be associated with ocean dumping of organic materials.


The aragonite saturation state (Ωarag) was determined to assess its seasonal variations and the major controlling factors in the southeastern Yellow Sea (YS) over four seasons. Ωarag showed large seasonal variation in the surface waters, with dissolved inorganic carbon (DIC) as a major factor controlling the seasonal variation. In the bottom waters, Ωarag exhibited only small seasonal variation compared with the surface waters; DIC and total alkalinity were the main factors contributing to the variation. The bottom water of the southeastern YS was undersaturated with aragonite during the fall, even though the southeastern YS was not typically associated with upwelling, freshwater discharge, or eutrophication processes. Aragonite undersaturation was most likely due to ocean dumping of organic materials. Therefore, ocean pumping should be prohibited in shallow marginal seas to prevent aragonite undersaturation.

Continue reading ‘Seasonal variation in aragonite saturation states and the controlling factors in the southeastern Yellow Sea’

PhD opportunity: physiological and evolutionary responses of marine copepods to Arctic climate change

The Norwegian Polar Institute (NPI) in Tromsø, Norway invites applications for a three-year PhD student fellowship investigating the physiological and evolutionary responses of marine organisms to climate change and ocean acidification in the Arctic. The work will be conducted in our Research Department, Section for Ecotoxicology.

The position is linked to NPI’s ongoing research on the effects of ocean acidification on marine zooplankton and will be a key component of the larger project “EvoCal, Arctic Marine Evolution: using local adaptation to infer future evolutionary responses of Calanus copepods to a changing environment”, which has several Norwegian and foreign collaborators. Climate change and ocean acidification are presenting marine organisms with significant physiological challenges. Arctic regions are expected to undergo the fastest changes with regards to warming and acidification. The degree to which evolutionary processes can help marine organisms survive these changes in the environment is an important and timely focus of research.

Continue reading ‘PhD opportunity: physiological and evolutionary responses of marine copepods to Arctic climate change’

Meet the researcher: Samantha Siedlecki, Marine Sciences

When Samantha Siedlecki was a young girl in land-locked Chicago, she would go on family vacations to the beach, excursions that gave her a chance to play in the waves, build sandcastles, watch crabs, and fall in love with the ocean.

In high school, Siedlecki worked as a volunteer at the Shedd Aquarium in Chicago. As her fascination with the ocean grew, she began looking into college programs in marine sciences.

“I was always fascinated by what was going on in the ocean,” says Siedlecki, who received her bachelor’s degree in marine sciences with a concentration in marine geology from Eckerd College and her Ph.D. from the University of Chicago.

“In grad school I mostly focused on theoretical questions, but real-world applications of my questions required less-idealized approaches,” Siedlecki says. “I wanted to learn about more realistic simulations in my post-doc work.”

Now an assistant professor of marine sciences at the University of Connecticut, Siedlecki spearheads research on coastal environments. She recently received a grant from the National Oceanic and Atmospheric Administration (NOAA) to develop a regional model of ocean acidification for the East Coast.

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Opportunities for increasing ocean action in climate strategies

The global ocean is warming, acidifying and losing oxygen, and sea level is rising. As a result, keystone species and ecosystems such as warm-water coral reefs, seagrass meadows and kelp forests will face high to very high risks by the end of this century even under low carbon dioxide (CO2) emissions (IPCC, 2019). Moreover, low-lying coastal settlements will face moderate to high sea-level rise risks by the end of the century, even under full and timely implementation of the Paris Agreement, unless comprehensive and intense adaptation efforts are undertaken. This calls for a dramatic scaling up of efforts towards ambitious mitigation and adaptation.

The ocean offers opportunities to reduce the causes and consequences of climate change, globally and locally, as shown by The Ocean Solutions Initiative (Gattuso et al., 2018) and other recent reports (Hoegh-Guldberg et al., 2019; Because the Ocean 20192). However, countries have poorly used ocean-based measures for tackling climate change and its impacts, in their Nationally Determined Contributions (NDCs; Gallo et al. 2017) under the Paris Agreement. The process towards the 5-year revision of NDCs, culminating at the 26th Conference of the Parties of UNFCCC, offers an opportunity for countries to adopt more ocean-inclusive mitigation and adaptation strategies.

In this Policy Brief we assess 18 ocean-based measures to support climate policies and the revision of NDCs in the areas of mitigation and adaptation. Ocean-related measures should not be considered as a substitute for climate mitigation on land, which must also be strongly pursued for the benefit of the atmosphere as well as the ocean.

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Early life stages of Calanus pacificus are neither exposed nor sensitive to low pH waters

We characterized the vertical distribution of Calanus pacificus eggs and larvae and the carbonate chemistry that they are exposed to in Puget Sound, WA. We found that, under stratified conditions, more than 90% of eggs and nauplii stages 1–4 were distributed above the pycnocline, in seawater with pH higher than 7.7. In addition, eggs and larvae from 101 females were reared for 5 days under a range of pH conditions (7.2–8.0) to investigate how pH sensitivity varies among individuals. We observed a slight increase in naupliar survival at pH 7.3 in Individual Brood experiments, while in Mixed Brood experiments, exposure to pH 7.3 led to a small decline in hatching success. In a Split Brood experiment, inter-individual variability among different females’ broods masked pH effects. These results indicate that C. pacificus early life stages are generally tolerant to short-term direct effects of ocean acidification.

Continue reading ‘Early life stages of Calanus pacificus are neither exposed nor sensitive to low pH waters’

Season affects strength and direction of the interactive impacts of ocean warming and biotic stress in a coastal seaweed ecosystem

The plea for using more “realistic,” community‐level, investigations to assess the ecological impacts of global change has recently intensified. Such experiments are typically more complex, longer, more expensive, and harder to interpret than simple organism‐level benchtop experiments. Are they worth the extra effort? Using outdoor mesocosms, we investigated the effects of ocean warming (OW) and acidification (OA), their combination (OAW), and their natural fluctuations on coastal communities of the western Baltic Sea during all four seasons. These communities are dominated by the perennial and canopy‐forming macrophyte Fucus vesiculosus—an important ecosystem engineer Baltic‐wide. We, additionally, assessed the direct response of organisms to temperature and pH in benchtop experiments, and examined how well organism‐level responses can predict community‐level responses to the dominant driver, OW. OW affected the mesocosm communities substantially stronger than acidification. OW provoked structural and functional shifts in the community that differed in strength and direction among seasons. The organism‐level response to OW matched well the community‐level response of a given species only under warm and cold thermal stress, that is, in summer and winter. In other seasons, shifts in biotic interactions masked the direct OW effects. The combination of direct OW effects and OW‐driven shifts of biotic interactions is likely to jeopardize the future of the habitat‐forming macroalga F. vesiculosus in the Baltic Sea. Furthermore, we conclude that seasonal mesocosm experiments are essential for our understanding of global change impact because they take into account the important fluctuations of abiotic and biotic pressures.

Continue reading ‘Season affects strength and direction of the interactive impacts of ocean warming and biotic stress in a coastal seaweed ecosystem’

The changing ocean and freshwater CO2 system

On a global scale, ocean carbon dioxide levels and therefore the rate of surface ocean acidification (lowering of pH) is generally set by how much anthropogenic CO2 humans emit to the atmosphere. Under human influence, the oceans will experience not just acidification but also warming, enhanced stratification, and deoxygenation. Under IPCC RCP8.5, a future greenhouse gas concentration trajectory that reflects very limited emission abatement, ocean CO2 levels are expected to reach as high as 900 μatm by the end of century, lowering surface average pH by about 0.4 units and amplifying the seasonality of surface PCO2 by up to 10-fold. However, on a local scale, the rate, magnitude, and variability of future acidification is not just a function of atmospheric CO2 levels, but how chemical, biological and physical processes in the ocean mediate the uptake of anthropogenic CO2. Such local processes can strongly modulate the overall long-term anthropogenic acidification from CO2 uptake. Key regions where local processes modulate ocean acidification include biologically productive waters, intense mixing/upwelling zones, regions of recent sea-ice melt and coastal oceans. Coastal regions in particular, with large biological productivity or eutrophication have been shown to accelerate the magnitude and onset of anthropogenic ocean acidification on the regional scale. For inland freshwater systems (lakes and rivers), although data are sparse, CO2 is generally supersaturated and subject to large variability via unique local conditions (e.g., runoff, eutrophication, local pollution etc.), implying that local processes will dominate the CO2 conditions in the future. The large variability makes detection of acidification in inland waters a challenge. Understanding how local conditions and processes modulate the long-term rate of anthropogenic acidification will be important in order to predict the likely levels of CO2 exposure that aquatic organisms will encounter in the future.

Continue reading ‘The changing ocean and freshwater CO2 system’

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Ocean acidification in the IPCC AR5 WG II

OUP book