Archive for January, 2019

Ecosystem metabolism drives pH variability and modulates long-term ocean acidification in the Northeast Pacific coastal ocean

Ocean acidification poses serious threats to coastal ecosystem services, yet few empirical studies have investigated how local ecological processes may modulate global changes of pH from rising atmospheric CO2. We quantified patterns of pH variability as a function of atmospheric CO2 and local physical and biological processes at 83 sites over 25 years in the Salish Sea and two NE Pacific estuaries. Mean seawater pH decreased significantly at −0.009 ± 0.0005 pH yr−1 (0.22 pH over 25 years), with spatially variable rates ranging up to 10 times greater than atmospheric CO2-driven ocean acidification. Dissolved oxygen saturation (%DO) decreased by −0.24 ± 0.036% yr−1, with site-specific trends similar to pH. Mean pH shifted from 8.0 in summer concomitant to the seasonal shift from heterotrophy (%DO  100) and dramatic shifts in aragonite saturation state critical to shell-forming organisms (probability of undersaturation was >80% in winter, but <20% in summer). %DO overwhelmed the influence of atmospheric CO2, temperature and salinity on pH across scales. Collectively, these observations provide evidence that local ecosystem processes modulate ocean acidification, and support the adoption of an ecosystem perspective to ocean acidification and multiple stressors in productive aquatic habitats.

Continue reading ‘Ecosystem metabolism drives pH variability and modulates long-term ocean acidification in the Northeast Pacific coastal ocean’

Aquaculture and acidification: field testing the alpha SeapHOx V2

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Installing sensors on the South ORCA mooring. The SeapHOx V2 and a current meter were cabled to a battery and data logger, then installed through an opening on the mooring.

On the northern edge of Hood Canal, a major basin in Washington State’s Puget Sound, a patch of Saccharina latissima (also known as Sugar Kelp) is helping to identify if seaweed aquaculture can help combat ocean acidification. Started in 2015, this project is primarily funded by a $1.5 million grant from the Paul G. Allen Family Foundation. It is a collaborative effort led by the Puget Sound Restoration Fund in partnership with various collaborators, including the University of Washington and NOAA’s Pacific Marine Environmental Lab.

In theory, the premise is straightforward—kelp such as Saccharina latissima harness carbon dioxide that would otherwise acidify the surrounding water, helping to mitigate the unwanted decreases in pH that result in ocean acidification. Whether this CO2 uptake is enough to reduce acidification on a wider scale, and if the impact of the kelp can affect natural variations in the environment, are the questions that draw interest in the experiment.

Continue reading ‘Aquaculture and acidification: field testing the alpha SeapHOx V2’

Upwelling modulation of functional traits of a dominant planktonic grazer during “warm-acid” El Niño 2015 in a year-round upwelling area of Humboldt Current

Climate change is expected to exacerbate upwelling intensity and natural acidification in Eastern Boundaries Upwelling Systems (EBUS). Conducted between January-September 2015 in a nearshore site of the northern Humboldt Current System directly exposed to year-round upwelling episodes, this study was aimed at assessing the relationship between upwelling mediated pH-changes and functional traits of the numerically dominant planktonic copepod-grazer Acartia tonsa (Copepoda). Environmental temperature, salinity, oxygen, pH, alkalinity, chlorophyll-a (Chl), copepod adult size, egg production (EP), and egg size and growth were assessed through 28 random oceanographic surveys. Agglomerative clustering and multidimensional scaling identified three main di-similitude nodes within temporal variability of abiotic and biotic variables: A) “upwelling”, B) “non-upwelling”, and C) “warm-acid” conditions. Nodes A and B represented typical features within the upwelling phenology, characterized by the transition from low temperature, oxygen, pH and Chl during upwelling to higher levels during non-upwelling conditions. However, well-oxygenated, saline and “warm-acid” node C seemed to be atypical for local climatology, suggesting the occurrence of a low frequency oceanographic perturbation. Multivariate (LDA and ANCOVA) analyses revealed upwelling through temperature, oxygen and pH were the main factors affecting variations in adult size and EP, and highlighted growth rates were significantly lower under node C. Likely buffering upwelling pH-reductions, phytoplankton biomass maintained copepod reproduction despite prevailing low temperature, oxygen and pH levels in the upwelling setting. Helping to better explain why this species is among the most recurrent ones in these variable yet productive upwelling areas, current findings also provide opportune cues on plankton responses under warm-acid conditions, which are expected to occur in productive EBUS as a consequence of climate perturbations.

Continue reading ‘Upwelling modulation of functional traits of a dominant planktonic grazer during “warm-acid” El Niño 2015 in a year-round upwelling area of Humboldt Current’

The world’s shellfish are under threat as our oceans become more acidic

An acidic seawater environment can produce thinner shells in oysters that can be more easily damaged in transit.

For the past few million years the world’s oceans have existed in a slightly alkaline state, with an average pH of 8.2. Now, with carbon emissions escalating, there is more CO₂ in the world’s atmosphere. This dissolves in the oceans, altering the chemistry of the seawater by lowering the pH and making it more acidic – up to 30% more in the past 200 years. This growing acidification of the oceans is becoming a serious problem for the production of shellfish around the world.

Shellfish are creatures which produce calcium carbonate shells and skeletons, such as mussels, oysters and corals. They create their protective shell structures through a process known as biomineralisation – producing hard minerals such as calcium carbonate by filtering calcium and carbonate from the water. If the amount of carbonate available in the oceans is reduced by acidification, it limits the ability of these creatures to create shells.

Continue reading ‘The world’s shellfish are under threat as our oceans become more acidic’

Remotely forced decadal physical and biogeochemical variability of North Pacific Subtropical Mode Water over the last 40 years

Half‐century‐long observations at the 137°E repeat hydrographic section across the western North Pacific have been analyzed to demonstrate remotely forced decadal physical and biogeochemical variability of Subtropical Mode Water (STMW) over the last 40 years. During unstable periods of the Kuroshio Extension (KE) that lagged the warm phase of the Pacific Decadal Oscillation by 3−4 years, high regional eddy activity reduced the formation rate and salinity of STMW in its main formation region south of the KE. At the 137°E section south of Japan, decreasing southwestward advection of oxygen‐rich STMW from the formation region resulted in decreases of its cross‐sectional area, dissolved oxygen, pH, and aragonite saturation state and increases of nutrients and dissolved inorganic carbon, among which changes of the carbonate system parameters accelerated their long‐term trends. Such changes reversed and acidification slowed down during stable‐KE periods, especially in the current period since 2010 exhibiting a hiatus of acidification.

Continue reading ‘Remotely forced decadal physical and biogeochemical variability of North Pacific Subtropical Mode Water over the last 40 years’

Call for abstracts: IAPSO 2019 coastal ocean acidification session

Abstract deadline: 18 February 2019

Conference: The International Association for the Physical Sciences of the Oceans (IAPSO) 2019

Location: Montreal, Canada

Dates: 10-14 July 2019

Session description: P08 – Coastal Ocean Acidification: Ocean acidification (OA) is causing complex biogeochemical changes over a range of temporal and spatial scales. It can be extremely difficult to understand OA in the highly complex coastal zone. However, this rapidly emerging scientific issue has raised serious concerns across the scientific and resource management communities as to its possible impacts on highly productive coastal fisheries and food webs. This symposium will highlight new research in coastal acidification, including changes in biogeochemistry; complexities associated with other ocean processes (e.g., freshwater mixing; hypoxia; multiple stressors); impacts on ecosystems and economies; and modeling and projection of future OA.

Continue reading ‘Call for abstracts: IAPSO 2019 coastal ocean acidification session’

Analysis of physical and biogeochemical control mechanisms on summertime surface carbonate system variability in the western Ross Sea (Antarctica) using in situ and satellite data

In this study, carbonate system properties were measured in the western Ross Sea (Antarctica) over the 2005–2006 and 2011–2012 austral summers with the aim of analysing their sensitivity to physical and biogeochemical drivers. Daily Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration maps, obtained prior to and during the samplings, were used to analyse the sea ice evolution throughout the experiment periods. Monthly means and 8-day composite chlorophyll concentration maps from the Moderate-resolution Imaging Spectroradiometer (MODIS) Aqua satellite at 4-km resolution were used to investigate inter-annual and basin scale biological variability. Chlorophyll-a concentrations in surface waters estimated by MODIS satellite data contribute to descriptions of the variability of carbonate system properties in surface waters. Mean values of carbonate system properties were comparable across both investigated years; however, the 2012 data displayed larger variability. Sea ice melting also had a pivotal role in controlling the carbonate system chemistry of the mixed layer both directly through dilution processes and indirectly by favouring the development of phytoplankton blooms. This resulted in high pH and ΩAr, and in low CT, particularly in those areas where high chlorophyll concentration was shown by satellite maps.

Continue reading ‘Analysis of physical and biogeochemical control mechanisms on summertime surface carbonate system variability in the western Ross Sea (Antarctica) using in situ and satellite data’

Rising concerns over ocean acidification

The oceans cover over 70 percent of the Earth’s surface. Only 5 percent of this area has been adequately mapped and explored since the dawn of marine science. Such immense entities might seem untouchable, but anything is possible in the Anthropocene, our current geological state marked by heavy human influence on the environment. Since the Industrial Revolution in 1760, the acidity of the ocean has increased by 25 percent.

Ocean acidification occurs when carbon dioxide from the atmosphere dissolves into the ocean. Over a third of emitted CO2 ends up in the ocean, where it then reacts with seawater to form carbonic acid. Carbonic acid lowers the pH of the water, creating detrimental effects on the organisms living there. For some time, acidic environments have been known to disrupt and dissolve the calcium carbonate shelters built by organisms such as coral and shelled creatures. Now, it is clear that more than just shelled animals are in danger.

A recent study published in the Journal of Science states that ocean temperatures are rising at rates 40 percent faster than estimated five years ago, which will likely cause a multitude of other problems, including an increased rate of acidification.

Continue reading ‘Rising concerns over ocean acidification’

Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea

Enhanced release of alkalinity from the seafloor, principally driven by anaerobic degradation of organic matter under low-oxygen conditions and associated secondary redox reactions, can increase the carbon dioxide (CO2) buffering capacity of seawater and therefore oceanic CO2 uptake. The Baltic Sea has undergone severe changes in oxygenation state and total alkalinity (TA) over the past decades. The link between these concurrent changes has not yet been investigated in detail. A recent system-wide TA budget constructed for the past 50 years using BALTSEM, a coupled physical–biogeochemical model for the whole Baltic Sea area revealed an unknown TA source. Here we use BALTSEM in combination with observational data and one-dimensional reactive-transport modeling of sedimentary processes in the Fårö Deep, a deep Baltic Sea basin, to test whether sulfate (SO2−4) reduction coupled to iron (Fe) sulfide burial can explain the missing TA source in the Baltic Proper. We calculated that this burial can account for up to 26 % of the missing source in this basin, with the remaining TA possibly originating from unknown river inputs or submarine groundwater discharge. We also show that temporal variability in the input of Fe to the sediments since the 1970s drives changes in sulfur (S) burial in the Fårö Deep, suggesting that Fe availability is the ultimate limiting factor for TA generation under anoxic conditions. The implementation of projected climate change and two nutrient load scenarios for the 21st century in BALTSEM shows that reducing nutrient loads will improve deep water oxygen conditions, but at the expense of lower surface water TA concentrations, CO2 buffering capacities and faster acidification. When these changes additionally lead to a decrease in Fe inputs to the sediment of the deep basins, anaerobic TA generation will be reduced even further, thus exacerbating acidification. This work highlights that Fe dynamics plays a key role in the release of TA from sediments where Fe sulfide formation is limited by Fe availability, as exemplified by the Baltic Sea. Moreover, it demonstrates that burial of Fe sulfides should be included in TA budgets of low-oxygen basins.

Continue reading ‘Sedimentary alkalinity generation and long-term alkalinity development in the Baltic Sea’

Dominant scales of subtidal variability in coastal hydrography of the Northern Chilean Patagonia

• Upwelling-favorable winds have shifted poleward at a rate of 11 km per years

• Coastal variability follows closely the large-scale atmospheric and oceanic forcing

• Dominant variability of 30-days is associated to the Baroclinic Annular Mode

• Two permanent mixing areas coincide with two recognized hot spot for whales feeding

Northern Patagonia, on the southeastern Pacific Ocean, is one of the largest fjord systems in the world. Its complex topography harbors an aquaculture industry that is among the top exporters of salmon and mussels worldwide. However, little is known about the scales of environmental variability of this region and how climate-related changes can alter the current conditions. This study provides a baseline understanding of the dominant scales of subtidal variability in meteorological forcing and water properties along and across the region that encompasses northern Patagonia and specifically the Inner Sea of Chiloé (ISC). We examined multiple datasets spanning multiple spatial and temporal scales. Reanalysis wind time series were combined with satellite-derived data (MODIS-Aqua) and in situ hydrographic records from the mussel farming industry as well as from instruments moored at various locations in the ISC. We assessed the influence of large-scale forcing on the variability of local conditions and used the assembled datasets to find modes of variability at interannual, seasonal and intraseasonal scales. The patterns of atmospheric and oceanographic variability along northern Patagonia are heterogeneous both in time and space. Long-term sea surface temperature (SST) averages revealed two areas with colder temperatures and attenuated seasonal variability that can be associated with stronger vertical mixing. These areas have been previously related to hotspots for whale sightings and might be important as bottom-up controls of Patagonian food webs. Northern Patagonia is strongly affected by large-scale processes at the South Pacific basin scale. Long-term wind data show a poleward displacement of the transition between upwelling and downwelling favorable conditions during spring-summer months for the last decade. The intraseasonal time scale was dominated by a band centered at 30 days that can be attributed to atmospheric variability driven by the Baroclinic Annular Mode (BAM), which induces the periodic mixing of the water column, but with substantial interannual variability. Variability in local conditions was found to closely track the large-scale variability, even in the small channels and bays. These findings highlight the strong connection between large-scale processes and the conditions faced by aquaculture in the ISC, and the need to consider such scales of variability – as well as climate trends – in planning and management decisions.

Continue reading ‘Dominant scales of subtidal variability in coastal hydrography of the Northern Chilean Patagonia’

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Ocean acidification in the IPCC AR5 WG II

OUP book