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