Investigating the role of upper ocean fine structure and turbulence on the variability of ocean oxygen levels

Introduction:

The exchange of gases between air and ocean continues to be a topic of intense scientific interest due to the important role it plays in Earth system energy budgets, global climate and ocean health. Oxygen concentrations in surface waters are directly influenced on air-sea exchange and the subsequent transfer of oxygen to deeper layers have an important role to play in ventilating our oceans to maintain healthy and productive seas. Regions where ocean oxygen levels are depleted to potentially unhealthy levels are growing globally, both in the open-ocean and coastal areas (Diaz and Rosenberg, 2009) due to changing temperatures, nutrient supply and atmospheric forcing. This has important and potentially dangerous implications for marine ecosystems and has the potential to change global carbon cycles.

Project Summary:

Many of the physical and biogeochemical mechanisms that regulate air-sea transfer of gases such as oxygen are determined by turbulent (mixing) processes, both at the surface and in the ocean interior. To fully understand the impacts on current and future climate scenarios it is therefore important to first understand how the different mechanisms that drive this mixing influence air-sea gas exchange. Turbulence however is notoriously chaotic and difficult to measure but new developments at Liverpool (Palmer et al, 2015) using autonomous ocean gliders provide improved capability in resolving fine-scale ocean structure and turbulence up to the sea surface that has the potential to enhance our understanding of gas exchange at this critical interface. This studentship combines these data will measurements made over a series of campaigns in open-ocean and shelf sea regions to address the role of changing climate on oxygen levels in the global ocean.

Data for this project comes from a range of both shelf sea and open ocean sites including the Celtic Sea, Porcupine Abyssal Plain and at the mid-Atlantic ridge and will be complemented by additional data collected during this project. Each dataset provides measurements of near surface finescale and microscale temperature and velocity collected by autonomous ocean robots that provide measurements of turbulent mixing in the near surface layer and upper ocean thermocline. Combined with supporting physical, oxygen and pCO2 data collected from ship based and moored instrumentation, this studentship will investigate the links between variable meteorological and ocean forcing on air-sea gas transfer.

The student will develop expert understanding in processing and analysing turbulence and other observational data and will also spend a period of time at PML learning about air-sea gas transfer mechanisms and parameterisations (Carpenter & Nightingale, 2015). Combining this new dataset with 1-D models of the ocean surface mixed layer and global ERA-Interim data the student will then develop an improved understanding of how changing weather, waves and ocean conditions impact on oxygen uptake to address the key question:

How will predicted future climate scenarios impact on the turbulent transfer of oxygen between our ocean and atmosphere?

In addition to the training provided by our DTP the student will also benefit from the expertise of their supervisory team who will provide training in,

Data processing and analysis techniques relating to a wide range of ocean measurements inc. ocean microstructure (turbulence), gliders, ADCP and CTD.
Understanding of air-sea gas transfer mechanisms and parameterisations.