The first plenary talk at the OCEANS 2021 conference San Diego-Porto was delivered by Pedro Madureira, a geologist working at the Task Group for the Extension of the Portuguese Continental Shelf (EMEPC). The talk covered a snapshot of Pedro's deep-sea cruises and expeditions and a myriad of thoughts and lessons he had learnt from these many cruises about the importance of better exploring the Earth's depths.

Pedro has been coordinating the scientific and technical work related with acquisition of data to explore the outer limits of the continental shelf as submitted by Portugal to the UN. He is Auxiliary Professor at the University of Évora. Since 2012 he is a member of the Legal and Technical Commission of the International Seabed Authority. 

Pedro started the talk with the concept of a Global Ocean and its importance to Earth's environment, that has been even highlighted in medieval art sculptures (Figure 1) which show Oceans holding hands and guiding the seasons. The depths of the global Ocean is undiscovered and holds the clue to many riddles, including mineral resources and biodiversity. It is also impacted by the effects of man-made marine litter and climate change.

Medieval sculpture showing the dependence of seasons on the Oceans.

Polymetallic nodules found on the deep sea-bed are a potential source of critical metals for renewable energy applications.

Next, Pedro spoke about the mineral resources in the form of polymetallic crusts. These crusts are important not only as a potential source of metals, but they also contain information on earth's history. To understand how this can reveal geological insights, scientists used this crust and profiled its different layers, which represent different points in history. They made distribution maps of the mineral profiles over time in slices (Figure 2). This reveals a lot about how these minerals got there in the first place. For example at some times, we can see the same pattern as observed at other locations in the world. So we can see the mineral distribution at these times was controlled by a process at a regional scale. At some other times, the mineral distribution pattern is unique, indicating they were formed by geological processes only at local scale. So EMEPC has been promoting work on this scientific analysis into deep-sea crusts, and has funded some Master's thesis on this topic to study these interesting results.

Also, this is not only about geology, but also reveals a picture of the deep-sea biodiversity. The ROV used in their exploration was able to collect 10s of 100s of hours of footage of subsea animals, which tells them a lot about the state of deep-sea fauna. EMEPC are keen to map and understand the abiotic factors that control the growth of these creatures. They are also focusing on using machine learning to automate identification of organisms in the camera to understand the biodiversity.

A snapshot of the rich biodiversity that can be found in deep-sea environments.

EMEPC are also aiming to study thermal vents along the Mid-Atlantic ridge. They are also developing systematic techniques to understand the vents, similar to those used by German researcher during their cruises in the Indian Ocean. They were able to develop terrain descriptor metrics like 'aspect of chimney', 'slope' etc. Using these predictors, and they were able to construct predictive models on what kind of creatures can be found on what kind of terrain. This represents an understanding of how the terrain can affect biodiversity.

EMEPC also complement their scientific cruises with educational and outreach programmes after the cruises. They are also exploring the seriousness of the marine litter problem, which is obvious during their cruises which show the extent to which human waste can be found on the planet.

The scientists also brainstorm how their science can be used to help the developing world. Some of the key needs of the developing world are clean water and food, but they also need electricity, access to information and technology like computers and phones. And for the latter three, it is important to keep the energy supply going on by developing renewable sources, better battery technology, and increase production of enabling technologies. For these, raw materials in the form of key metals are still needed. The deep ocean provides a potential source for these in the form of polymetallic nodules and crusts, which contain high amounts of these rare earth metals in addition to Iron, Manganese, Copper, Nickel and Cobalt.

A schematic of the circular economy, which requires some amount of raw input. Developing a circular economy will be vital to lift countries of of poverty by enabling renewable energy technologies.

In order to create a sustainable future, we need to work towards a circular economy, where all metals are recycled as much as possible. However, as shown in the figure, the circular economy can only recover some percentage of the resources used, and it still needs some raw input to sustain the flow of necessary resources needed to build technology. The reason for this becomes clear when we look at the recycling efficiency of metals. The figure below shows that for many metals, the recycling percentage is quite good, but usually it is below 50% . Especially for rare earth metals, the percentage of metal that can be recovered at the end of its cycle is still very low. However, these rare-earths are key components required for transition of energy from using fossil fuels to renewables.

Recycling efficiency of different metals.

A scale visualization showing the volume of copper produced from Chile in 2019 (5.6 Mton.

To understand the volume of raw metal needed for development, Pedro showed the example of the volume of copper produced from Chile in 2019, which was 5.6 Mton (Chile is the primary producer of copper). In order to produce this much copper, a much larger percentage of rock needs to be removed from the land areas. To get an idea of the scale of this in terms of known landmarks - this rock content removed from the mine in one year, is equivalent to a large fraction of the famous Central park landmark in New York ! This highlights why we need to explore new resources while we perfect the circular economy.

In concluding, Pedro emphasized that we need to understand the interaction between different spheres of Earth - the geosphere, hydrosphere and atmosphere. The solution lies in this interdisciplinary science. For example, climate change is not only affecting the surface of Earth, but even the depths. Marine calcifier organisms are facing problems in their growth due to ocean acidification, so this highlights how the deep-ocean is still affected by human activity. We need better tools to address these problems and get solutions, and we need to better study and monitor these ecosystems and organisms. We also need to study the water column where there are organisms of which we know so little.