Chapter 2: Ocean Processes

Introduction

The UK vision of clean, healthy, safe, productive and biologically diverse oceans and seas depends above all on the state of the physical environment. Variables such as the oceans’ temperature, salinity, circulation, degree of acidification, sea level, strength of waves, turbidity and morphology, in turn set the context for the different components of the vision. For example, storms and currents affect habitats and offshore operations; acidification affects plankton physiology, especially calcification; sedimentary processes affect the distribution of hazardous material. Thus most ocean process variables are affected by climate and mediate how future climate change will affect the marine environment in many ways.

In this chapter, based on the Feeder Report prepared by the Ocean Processes Evidence Group, we assess the physical state of the UK seas to lay out the framework for the chapters to follow. This chapter bears a strong relationship with Chapter 6 which looks at the impacts of climate change and makes projections about how the ocean process variables might change over time.

In 2005, Charting Progress reported evidence that climate change was affecting the marine ecosystem. In the physical environment it identified rising air and sea temperatures, increasing winter wave heights (to the mid­1990s), more frequent winter storms since the mid-20th century, and rising sea level as key evidence.

Since Charting Progress we have made considerable progress in our ability to assess the state of ocean process variables. This chapter builds on the findings of Charting Progress. Although the conclusions in this assessment generally reinforce those from 2005, recent awareness of ocean acidification, and concerns about the ability of our seas to continue to take up carbon dioxide from the atmosphere, means we have added this issue as an explicit topic.

We have based our assessment on a combination of direct measurements from ongoing and new monitoring programmes, understanding of processes, and models.

This combination is very powerful. The variables that define ocean processes – such as currents, storm surges, waves, temperature and salinity– are typically not distributed according to local inputs by humans but follow patterns that depend on physical laws. Therefore, we do not need to measure them at every point in order to assess the overall state. Rather we can obtain enough measurements to keep the forecast models on track, and then use the models to assess the state in places where there are few or no measurements. This ability has improved since Charting Progress.

Since we have no clear reference point, baseline or criterion against which we can sensibly assess the ideal state of the physical environment, we focus here on the present state and trends. Note that Chapter 6 will describe our projections of the future state of the physical environment, based on models of likely changes in climate.

There are two levels at which we affect the physical environment of UK seas. Locally, and directly, design and control of construction and activities can influence temperature, currents, waves and suspended matter. For example, offshore wind farms can affect winds; tidal energy barrages or breakwaters can change currents, the height of the sea surface, waves and suspended matter; coastal developments, defences and dredging can all affect suspended particulate matter and coastal power stations can raise the temperature of the cooling water they release back to the sea. Such activities are subject to environmental impact assessments and/or licensing which require such changes to be considered. Less directly, and more broadly, greenhouse gas emissions will influence future temperatures, salinity, pH, sea level, and possibly winds and waves. At either level, we are restricted as to how much we can control.

Our confidence in the estimated state and variability or trends is generally high. We found representative data on appropriate scales for all variables except where affected locally by shoals, proximity to land or river outflows. Morphology, rainfall, salinity and circulation are most susceptible to variability on small spatial scales.

FRV Scotia in rough seas

© Marie Russell, Marine Scotland Science