On Wednesday, 2 October 2024, Dr Tessa Hill presented insights and lessons from her book, At Every Depth: Our Growing Knowledge of the Changing Oceans (Columbia, 2024) to a webinar audience at the IIEA. Dr Hill is an oceanographer and professor of earth and planetary sciences at the University of California, Davis, whose research interests include climate change, both past and present, and understanding the response of marine species to environmental perturbation.  

Introduction 

At Every Depth, co-authored by Dr Tessa Hill and Eric Simons, is the accumulation of eight years of research, with an emphasis on primary sources. Three themes that emerged from the book were that of knowledge, connection and action, and these would form the basis of Dr Hill’s lecture to the IIEA. The authors gathered knowledge of the earth’s oceans from indigenous people, fishermen, policymakers, politicians and local communities. Dr Hill emphasised that this range of knowledge was an important element of her research and adds a valuable dimension to the work.  She explained the journey the book takes, beginning at the tidepool, where sea meets land, and from there travelling deeper into the ocean, with the last chapter of the book situated in the deep sea. The idea of “connection” is at the heart of the book, and Dr Hill began her IIEA lecture by asking participants to recall a time when they felt a connection to the ocean. Dr Hill asserted that by “regaining and maintaining that connection" this could motivate people to build a better future and act to protect the oceans.  

Stories of Connection and Knowledge 

The book is presented as a series of stories or vignettes exploring human connection to the ocean throughout history. Dr Hill recounted two intertwining stories from the book to the IIEA audience. The first story began in 1931, when Willis G. Hewatt, a graduate student, sought to study the arrangement of animals living in the tidepools of Monterey, California. He counted and categorised the creatures living along a transect of the pools and submitted his research for his PhD thesis in 1935. Dr Hill next transported the audience to the 1990s, when researchers Jim Barry and Chuck Baxter of the Monterey Bay Aquarium Research Institute began to think about whether the still-new science of global warming may be impacting on marine creatures in the tidepools. Along with two undergraduate students, the scientists found the iron bolts drilled in by Hewatt 60 years earlier and documented the marine inhabitants along the same transect. Their results, published in Science in 1995, showed that eight out of nine warm-water species had increased in abundance, while five of the eight cold-water species had decreased in abundance since 1935, thus proving the effects of climate change on marine life. Because the tide pool survey connects humanity’s past with its present, its publication had a profound impact on the scientific community, and Dr Hill cited it as particularly influential in defining her own career.  

At the same time, another discovery connecting the past to the present at the very same site of the Monterey tide pools was occurring. Linda Yamane, a member of the Rumsen Ohlone Tribal Community of Monterey, was seeking to reconnect with her Rumsen culture in the 1990s when she came across a trove of archives at San José State University library from the 1930s that recorded details on Ohlone languages, songs, basket-weaving and canoe building techniques, as told by Isabel Meadows, the last speaker of the Rumsen language. Linda Yamane taught herself how to build canoes using the techniques of her ancestors, often paddling close to where the four scientists had conducted their research, and began designing Ohlone shell jewellery, using abalone shells that once were plentiful on Monterey shorelines.  Dr Hill noted the parallels in terms of the two stories’ synchronicity and proximity. But even beyond this, according to her, there were lessons to be drawn of the value – only discovered decades later – of documenting and recording information about the world, observing harmful changes and taking preservative action. The stories shared by Dr Hill were two of many such stories depicted in the book. She highlighted the necessity of continued observation in a changing world, even if at the time we might not fully know why we are taking notes, beyond the hope that someone in the future will find them useful.  

Taking Action 

Dr Hill next moved on to present to the IIEA audience the theme of action explored in her book. Although the book did not focus on Ireland, she mentioned that she had been struck by how similarly the south-west coast of Ireland resembled her own California coast, which for her emphasised the ‘universality’ of the challenges the world faces. Beyond these universal challenges, she selected four key areas which had direct regional relevance to Ireland to discuss in the lecture. These were: 

1. Marine Protected Areas; 
2. Marine Energy Sources; 
3. Impacts of Global Climate Change; and 
4. Deep Sea Management and Protection. 

Marine Protected Areas 

Dr Hill explained that currently 7% of Ireland’s maritime areas are protected. However, there is a global goal of achieving 30% protection by 2030, as integrated within the United Nations Sustainable Development Goals. There are challenges associated with achieving this, and Dr Hill mentioned explicitly the challenges of monitoring and enforcement and the fact that the level of protection can vary significantly country by country.  

Marine Energy Sources 

Noting that one of the stated goals of Ireland’s Climate Action Plan is to increase renewable energy sources by 2030, Dr Hill pointed out that wave and wind energy must be key targets for renewable energy sources in Ireland. Therefore, understanding the environmental impacts on marine life, commercial fishing and local communities is crucial.  

Impacts of Global Climate Change  

Ireland’s position in the North Atlantic Ocean means it is particularly vulnerable to the effects of climate change. Dr Hill cited studies which have shown that the North Atlantic Ocean is warming faster than the global average, while the Arctic region is warming at four times the global average. The North Atlantic is crucial for distributing heat and salt levels: as waters cool off Greenland and Iceland, they sink to the deep ocean, forming what is akin to a deep ocean conveyor belt, called the Atlantic Meridional Overturning Circulation. Disturbance of this is likely to cause significant weather fluctuations for Ireland. Furthermore, rising sea levels constitute a real threat to Ireland. 

Deep Sea Management and Protection 

Finally, Dr Hill turned to the deep sea: the final chapter of her book, and the least known. Ireland is reliant on the deep sea in many ways. The global network of 600 deep sea cables that provide the world with telecommunication channels and internet require knowledge of processes occurring on the sea floor. Fossil fuel extraction has expanded into deeper and deeper waters, and companies have begun to express intense interest in the extraction of mineral deposit from the sea floor. On this, Dr Hill cautioned the participants of the danger of moving too fast and refusing to learn lessons from past experiences.  

Key Takeaways 

Connection 

For Dr Tessa Hill, connecting and reconnecting with earth’s oceans is crucial to motivate change in human behaviour. At Every Depth sought to strengthen that connection by illustrating stories from people whose livelihoods, cultures, and academic expertise, have brought them closer to the ocean.  

Knowledge 

At Every Depth was written with the intent of valuing and showcasing different knowledges across peoples and professions. The western-focused approach to scientific research was present in the book, but so were the experiences and knowledge gained from people who have spent their lives near the ocean, and observing the ocean over multiple generations, including indigenous communities and local fishing communities. The work is presented therefore as a ‘tapestry’ of knowledge.  

Action 

At Every Depth illustrates not only stories of experience, but stories of people taking action for the sake of their shared future. Its intention is for its readers not only to gain knowledge, but for the book to be a call to action and to inspire change in their relationship and behaviours towards the oceans.