Holocene book review: Introducing Sea Level Change

Abstract

This book is a timely publication due to current debates on climate change and is part of a series that focuses on introducing a particular subject area. It is a good format, not too long (only 84 pages, excluding glossary and further reading) and written in a way that is accessible to those at undergraduate level. The aim of the book is to introduce the subject of sea level change in a concise, readable way and to provide the reader with the key scientific information that is needed to understand the complex nature of sea level change. Sea level rise is an important issue within the broader topic of climate change. As about half the world’s population lives near the coast, sea level rise is a real cause for concern for many people. However, sea level rise is not simply due to the melting of ice sheets and glaciers due to climate change, nor is the change uniform across the globe. Alistair Dawson attempts and succeeds to produce a ‘rough guide’ to sea level change by producing simple and straightforward explanations of a highly complicated topic. The book presents the evidence of the most recent investigations, details the history of scientific discoveries that explain the patterns of sea level change and brings together evidence from many different fields of investigation. The author begins by explaining what sea level change means and how it is measured. He also illustrates how the concept can mean different things to different scientists: for example, the existence of land bridges, identification of past shorelines or the alteration of the Earth’s radius and the subsequent changes in the Earth’s rotation. The book considers the key processes that drive sea level change, what has happened in the past, the timescales of past sea level change and compares the present rates with those in the past. Complex processes are introduced in an accessible way, but while the author does not explain in great depth, the theories and evidence are put forward as a starting point for further in-depth study should the reader wish. Chapter 2 identifies the different landforms that provide evidence for former relative sea level changes, such as erosional and depositional shoreline features, along with other evidence, for example, submerged forests. Sedimentary evidence provided by foraminifera, diatoms, testate amoebae and marine macrofossils is used to support the evidence provided by the landforms in order to assess changes in former sea levels. It is well illustrated, with examples used from across the globe. Chapters 3 and 4 look at the longterm changes of relative sea level change and how past changes in relative sea level can be reconstructed. Marine isotopic curves are introduced, along with the role that ocean temperature plays in sea level change. These chapters illustrate key ideas/concepts using good, simple sketch diagrams to aid the understanding. The effect that the viscosity of the asthenosphere has on sea level change is discussed in Chapter 5. This process is an influence that is not well known and not often discussed when thinking about sea level change. While it is important and needs to be considered, it seems to be slightly out-of-place compared with the rest of the book. In Chapters 6 and 7, the author explains the main processes of sea level change, focussing on the key issues of eustasy and isostasy, along with changes in global ocean volume. Again, these chapters are well illustrated with many examples of past shorelines. Focus is given to the remarkable sea levels during marine sub-stage 5e and the role that the partial melting of the East and West Antarctic ice sheets and the Greenland ice sheet had at this time. Chapter 8 specifically investigates the relative sea level change during the Last Glacial Maximum. The geographical extent and the timing of the maximum extent of the former ice sheets are investigated. The melting histories of the various ice sheets following the Last Glacial Maximum are explored in Chapter 9 and it illustrates how the ice melt from that time still plays an important part in contributing to the present patterns of sea level change. Changes in ocean mass, in flow within the Earth’s mantle and gravitational changes along with the hydroisostatic changes and glacio-isostatic changes are also considered. This chapter illustrates the complex nature of the changes, processes and patterns of relative sea level change that are associated with the melting of the last great ice sheets and clearly highlights the need to consider a combination of factors. The use of global sea level curves is discussed in Chapter 10. It highlights a paradigm shift in our understanding and interpretation of past changes in relative sea level. The argument put forward is that during the Holocene, sea level changes were primarily due to fluctuations in valley glaciers and small ice caps, rather than the Greenland or Antarctic ice sheets. Numerical modelling in recent decades and the fact that these glaciers responded differently to Holocene climate change in different parts of the world suggest that there could be no such thing as a single global eustatic sea level curve. This led to the abandonment of the once established concept. Alistair Dawson charts the history and the studies behind this paradigm shift in a succinct, understandable way and uses several examples from around the world to highlight this change in thinking. The concluding chapters consider the present and future relative sea level change and attempt to answer six key questions surrounding the sea level rise debate. The stability and/or the potential collapse of the Antarctic and Greenland ice sheets is discussed in terms of what this would mean for sea level rise. Thermal expansion of the ocean water due to rising ocean temperatures is considered and the modelling of future changes is discussed. Reference to the IPCC reports are made throughout these concluding chapters, along with the highlighted discrepancy between the observed rate of sea level rise and the amount estimated by adding together the contributions from Holocene book review 865060 HOL0010.1177/0959683619865060The HoloceneHolocene book review book-review2019