Major impacts of climate change on deep-sea benthic ecosystems

Andrew K Sweetman,Roberto Danovaro,Laura Würzberg,Benjamin M Grupe,Jeroen Ingels,Moriaki Yasuhara,Katherine M Dunlop,Lisa A Levin,Christina A Frieder,Daniel O B Jones,Kirstin S Meyer,Craig R Smith,J Murray Roberts,Andrew J Gooday,Camilo Mora,Henry A Ruhl,Andrew R Thurber,Alexis L Pasulka ,Michael A Rex ,Amy R Baco ,Lea‐Anne Henry ,Chih‐Lin Wei

doi:10.1525/elementa.203

Abstract

The deep sea encompasses the largest ecosystems on Earth. Although poorly known, deep seafloor ecosystems provide services that are vitally important to the entire ocean and biosphere. Rising atmospheric greenhouse gases are bringing about significant changes in the environmental properties of the ocean realm in terms of water column oxygenation, temperature, pH and food supply, with concomitant impacts on deep-sea ecosystems. Projections suggest that abyssal (3000–6000 m) ocean temperatures could increase by 1°C over the next 84 years, while abyssal seafloor habitats under areas of deep-water formation may experience reductions in water column oxygen concentrations by as much as 0.03 mL L–1 by 2100. Bathyal depths (200–3000 m) worldwide will undergo the most significant reductions in pH in all oceans by the year 2100 (0.29 to 0.37 pH units). O2 concentrations will also decline in the bathyal NE Pacific and Southern Oceans, with losses up to 3.7% or more, especially at intermediate depths. Another important environmental parameter, the flux of particulate organic matter to the seafloor, is likely to decline significantly in most oceans, most notably in the abyssal and bathyal Indian Ocean where it is predicted to decrease by 40–55% by the end of the century. Unfortunately, how these major changes will affect deep-seafloor ecosystems is, in some cases, very poorly understood. In this paper, we provide a detailed overview of the impacts of these changing environmental parameters on deep-seafloor ecosystems that will most likely be seen by 2100 in continental margin, abyssal and polar settings. We also consider how these changes may combine with other anthropogenic stressors (e.g., fishing, mineral mining, oil and gas extraction) to further impact deep-seafloor ecosystems and discuss the possible societal implications.

Highlights

The oceans are a major sink for CO2 produced by the burning of fossil fuels (Pauchauri et al, 2014) as well as for the heat produced by the greenhouse effect (Glecker et al, 2016)
Nutrients produced during the re-mineralization of organic matter at the deep seafloor are used by phytoplankton to produce organic matter that fuels secondary production
Given that deep-sea ecosystems are vitally important to the Earth system (Danovaro et al, 2014) and are at considerable risk from ongoing climate change (Mora et al, 2013; Jones et al, 2014; Levin and Le Bris, 2015), our goal in this paper is to understand and predict the nature and consequences of climate change at the deep seafloor until 2100

Summary

Introduction

The oceans are a major sink for CO2 produced by the burning of fossil fuels (Pauchauri et al, 2014) as well as for the heat produced by the greenhouse effect (Glecker et al, 2016). Given that deep-sea ecosystems are vitally important to the Earth system (Danovaro et al, 2014) and are at considerable risk from ongoing climate change (Mora et al, 2013; Jones et al, 2014; Levin and Le Bris, 2015), our goal in this paper is to understand and predict the nature and consequences of climate change at the deep seafloor until 2100 To this end, we describe the present status of four major environmental variables at the seabed that are likely to be altered by increased CO2 emissions to the atmosphere: temperature, oxygenation, pH and food supply (or POC flux).

Methods

Atlantic Pacific Indian Southern Arctic

Findings

Depth zonea Dissolved oxygen