Salinity matters

A press release from the European Space Agency: Measurements of salt held in surface seawater are becoming ever-more important for us to understand ocean circulation and Earth’s water cycle. ESA’s SMOS mission is proving essential to the quest.

The Soil Moisture and Ocean Salinity satellite, SMOS, is monitoring changes in the amount of water held in the surface layers of soil and concentrations of salt in the top layer of seawater – both of which are a consequence of the continuous exchange of water between the oceans, the atmosphere and the land. Launched in 2009, SMOS has provided the longest continuous record of sea-surface salinity measurements from space.

The salinity of surface seawater is controlled largely by the balance between evaporation and precipitation, but fresh water from rivers and the freezing and melting of ice also changes the concentrations. With a wealth of salinity data from SMOS now in hand complemented by measurements from the US–Argentinian Aquarius satellite, which uses a different technique, scientists gathered recently at the UK Met Office to review the benefits this has brought to science.

Speaking at the Ocean Salinity Science and Salinity Remote-Sensing Workshop, Prof. Dame Julia Slingo, Met Office Chief Scientist, said, “We need to understand the role of salinity in the closure of the hydrology cycle – arguably the weakest point in global climate modelling.

“Salinity, and particularly sea-surface salinity, is a challenging but important topic for ocean circulation and climate variability about which we need to know more, especially given the recent climate-warming hiatus. The SMOS mission, now celebrating five years in orbit, is providing detailed global measurements of ocean-surface salinity that are now used to address some of these challenges.”....

From the European Space Agency: Average sea-surface salinity values. Areas of red indicate regions of high salinity, and areas of green indicate regions of low salinity. The map is overlaid with the simplified global circulation pattern called the ‘thermohaline circulation’. The blue arrows indicate cool deeper currents and the red indicate warmer surface currents. Temperature (thermal) and salinity (haline) variations are key variables affecting ocean circulation.

Salinity matters when it comes to sea level changes

A press release from Lawrence Livermore National Laboratory: Using ocean observations and a large suite of climate models, Lawrence Livermore National Laboratory scientists have found that long-term salinity changes have a stronger influence on regional sea level changes than previously thought.

“By using long-term observed estimates of ocean salinity and temperature changes across the globe, and contrasting these with model simulations, we have uncovered the unexpectedly large influence of salinity changes on ocean basin-scale sea level patterns,” said LLNL oceanographer Paul Durack, lead author of a paper appearing in the November issue of the journal Environmental Research Letters (link is external).

Sea level changes are one of the most pronounced effects of climate change impacts on the Earth and are primarily driven by warming of the global ocean along with added water from melting land-based glaciers and ice sheets. In addition to these effects, changes in ocean salinity also can affect the height of the sea, by changing its density structure from the surface to the bottom of the ocean.

The team found that there was a long-term (1950-2008) pattern in halosteric (salinity-driven) sea level changes in the global ocean, with sea level increases occurring in the Pacific Ocean and sea level decreases in the Atlantic. These salinity-driven sea level changes have not been thoroughly investigated in previous long-term estimates of sea level change. When the scientists contrasted these results with models, the team found that models also simulated these basin-scale patterns, and that the magnitude of these changes was surpri
singly large, making up about 25 percent of the total sea level change.

“By contrasting two long-term estimates of sea level change to simulations provided from a large suite of climate model simulations, our results suggest that salinity has a profound effect on regional sea level change,” Durack said. “This conclusion suggests that future sea level change assessments must consider the regional impacts of salinity-driven changes; this effect is too large to continue to ignore.”...

Lined with bottles triggered at different levels of the ocean, this conductivity, temperature and depth profiler bearing a suite of sampling bottles is a mainstay of oceanography. It can be deployed to depths of 6,000 meters to study changes in ocean temperature and salinity. Photo courtesy of Ann Thresher/CSIRO

Effects of growing rice in low water, high salt conditions

Research Asia News: Rice is a staple food across Asia, with both people and economies reliant on its successful harvest. One paper finds that low water input does not affect rice growth as much as the levels of nutrients in soil can, and the second suggests that, although rice is seriously stressed by high salt levels in soil, this can be countered by the application of locally produced compost.

Approximately 576 million tonnes of rice are produced globally each year, with about 90% produced and consumed in Asia. 75% of the world's rice is grown in irrigated lowlands, and with water for agriculture becoming increasingly scarce, the question of the effect of low water levels on rice growth is becoming more critical. Jahan, M. S. and colleagues at the Faculty of Agriculture at Universiti Putra Malaysia, set out to determine the effect, on both rice production and the chemical properties of the soil in which rice grows. They found that iron content in soil slowly increases as rice is growing, but even more so after water is drained off. Manganese, on the other hand, increased sharply after flooding, but decreased after that. They found that water levels did not affect the growth of rice as much as expected. Their results provide recommendations for water management as saturation throughout the cultivation process does not seem to be as important as is believed. Low water input rice production could be implemented and fresh water saved for other sectors.

In a second paper in the same issue, Muhammad Ibrahim and colleagues from Pakistan’s University College of Agriculture and Government College University as well as the South Korea’s National Academy of Agricultural Science, looked at salt levels in soil and the effect on rice growth. They took twenty day old rice plants and transplanted them into clay pots filled with either normal or saline soil. They found that the saline soil had a significant effect on the growth of the rice, but when they applied compost the results improved. Further work is needed to optimise the compost mixture and resulting growth but their work provides hope for many poor rice farmers as compost can be locally made and produced from a variety of waste materials.

A rice terrace in Yangshuo, China, shot by McKay Savage, Wikimedia Commons via Flickr,  under the Creative Commons Attribution 2.0 Generic license

Exploring the saltiness of the ocean to study climate change

National University of Ireland, Galway: Details are emerging from a recent research expedition to the Sub-Tropical North Atlantic. The objective of the expedition was to study the salt concentration (salinity) of the upper ocean. Scientists aboard the Spanish research vessel Sarmiento de Gamboa, including National University of Ireland Galway’s Dr Brian Ward with two of his PhD students, Graig Sutherland and Anneke ten Doeschate, explored the essential role of the ocean in the global water cycle.

This oceanographic research campaign is aimed at understanding the salinity of the upper ocean, which is a much more reliable indicator of the water cycle than any land-based measurement. How the water cycle evolves in response to global warming is one of the most important climate change issues.

The experiment was located in the North Atlantic Salinity Maximum, which has the highest salt concentration of any of the world’s oceans. Dr Ward explains: “It is not the depths of the ocean which is its most important aspect, but its surface. Everything that gets exchanged between the ocean and atmosphere, such as water, must cross the air-sea interface. We are trying to better understand how small scale turbulence is responsible for the air-sea exchange of freshwater. What is surprising is that these small-scale processes can affect large-scale patterns over the North Atlantic, and we are trying to connect the dots.”

The initial part of this ocean field campaign was to conduct a survey of the area to map out horizontal and vertical distribution of salinity using an instrument that was towed behind the ship. “We found quite a lot of fresher water intermingled with the background salty water, but it is moving around quite a bit due to ocean currents, and when we returned to the fresh patch, it had moved. We were currently hunting for this freshwater, as one of the objectives is to understand the spatial inhomogeneity of the upper ocean salinity”, explains Dr Ward.

Studying the processes at the ocean surface requires specialised instrumentation, as most measurements ‘miss’ the upper few meters. The National University of Ireland Galway’s AirSea Group are measuring the salinity, temperature, and turbulence of the upper 10 metres of the ocean with very fine detail using their Air-Sea Interaction Profiler (ASIP). The torpedo-shaped device, which is deployed into the water to gather data autonomously, is unique and the only one of its kind...

Researchers from the NUI Galway AirSea Laboratory deploy the ASIP device, from left: Dr Brian Ward, and PhD students Graig Sutherland and Anneke ten Doeschate. From the NUI Galway's website

Salinisation of rivers: a global environmental problem

Universitat de Barcelona: The salinisation of rivers is a global problem that affects to countries all over the world and it causes a high environmental and economic cost, and poses a high risk to global health. Climate change and the increasing water consumption can worsen even more the future scene, according to an article published on the journal Environmental Pollution based on the research developed by an international team led by the experts of the Department of Ecology of the UB Narcís Prat and Miguel Cañedo-Argüelles. The article is also signed by Ben J. Kefford from the University of Technology of Sydney (Australia); Christophe Piscart from the University of Lyon (France); Ralf B. Schäfer from the University Koblenz-Landau (Germany); and Claus-Jürgen Schulz from the Thuringian State Institute for Environment and Geology (TLUG, Germany).

River salinity can be natural, caused by the geology of the area or the climatology, or anthropogenic, in other words, caused by domestic and industrial waste discharges, mining activity, agricultural and farming residues, etc. In worldwide river ecosystems, excessive salt concentrations caused by human activity are a threat to the survival of organisms and communities, biodiversity, the ecosystem’s biological balance, and it produces severe economical and public health problems.

According to Miguel Cañello-Argüelles, the main author of the article, “this article aims at giving a integrating view and emphasize the seriousness of the ecological, economic and global health effects that secondary salinisation has”. The expert remarks that it is a global process: “It happens in many regions from all over the world, although there is a great ignorance about the problem”. The most extreme case of salinisation occurs in some Australian rivers. “However —Cañedo-Argüelles adds—, in this case local studies have been done in order to clearly diagnose the problem; therefore, all the agents who make use of the natural resources of some rivers (farmers, industrialists, etc.) have collaborated in the process of finding solutions”.

In Europe, the process of river salinisation by human action is getting worse as years goes by. “It is also a problem in Spain”, declares the professor Narcís Prat, director of the Research Group Freshwater Ecology and Management (FEM) of the UB. “ In the Ebro plain, due to soil’s characteristic and the kind of agricultural activity performed, rivers are saltier than in Australia —he explains—, but here river conservation is not among the priorities of water resources management”, so these problems are not solved. According to Prat, the question is even worse in the region of Murcia: “It is a semi-arid area where irrigation is a common activity and rivers are saline as a result of the excessive exploitation of water resources”...

The Ebro River delta from the air, shot by Gons, Wikimedia Commons,  under the Creative Commons Attribution-Share Alike 3.0 Unported license