ChapterPDF Available

Abstract

This chapter gives an overview over proposals to increase the ocean's carbon drawdown capacity using so-called 'marine carbon dioxide removal' (mCDR) techniques. The recent surge of interest in mCDR techniques poses many technical, environmental, political, legal and regulatory challenges. These techniques are all still at early stages of development with much still to be learned about them and their effects on the ocean carbon cycle before any decisions could be made about large-scale deployment.
State of the Ocean Report 2024
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STATE OF THE
OCEAN REPORT
2024
2 / STATE OF THE OCEAN REPORT 2024
/ 3
Report team
Editors
Henrik Enevoldsen, Intergovernmental Oceanographic
Commission of UNESCO
Kirsten Isensee, Intergovernmental Oceanographic
Commission of UNESCO
Yun Jie Lee, Intergovernmental Oceanographic Commission
of UNESCO
State of the Ocean Report Advisory Board
Faiza Y. Al-Yamani, Kuwait Institute for Scientific Research,
Kuwait
Roberto de Pinho, Ministry of Science, Technology and
Innovation, Brazil
Mariama Dioh, Ministère des Pêches et de l’Economie
Maritime/Direction des Pêches Maritimes, Senegal
Juan José Fierro, Servicio Hidrográfico de la Armada,
Colombia
Rafael González-Quirós, Instituto Español de Oceanografía,
Spain
Yutaka Michida, University of Tokyo, Japan
Joseph Naughton, National Oceanic and Atmospheric
Administration, USA
Louise Wicks, Bureau of Meteorology, Australia
Matthias Wunsch, Bundesamt für Hydrographie, Germany
Julian Barbière, Intergovernmental Oceanographic
Commission of UNESCO
Mathieu Belbéoch World Meteorological Organization,
OceanOPS
Emma Heslop, Intergovernmental Oceanographic
Commission of UNESCO
Peter Pissierssens, Intergovernmental Oceanographic
Commission of UNESCO
Bernardo Aliaga, Intergovernmental Oceanographic
Commission of UNESCO
Authors
Molly Ahern, Food and Agriculture Organization of the
United Nations
Bernardo Aliaga, Intergovernmental Oceanographic
Commission of UNESCO
Victoria Alis, Sustainability and Environmental Consultant,
Seychelles
Enrique Alvarez Fanjul, Mercator Ocean International,
France
Faiza Y. Al-Yamani, Kuwait Institute for Scientific Research,
Kuwait
Michael Angove, Independent scientist, USA
Joseph O. Ansong, University of Liverpool, UK
Ward Appeltans, Intergovernmental Oceanographic
commission of UNESCO
Pierre Bahurel, Mercator Ocean International, France
Rick Bailey, Intergovernmental Oceanographic Commission
of UNESCO
Manuel Barange, Food and Agriculture Organization of the
United Nations
Mathieu Belbéoch, World Meteorological Organization,
OceanOPS
Elisabetta Bonotto, Intergovernmental Oceanographic
Commission of UNESCO
Miranda Böttcher, German Institute for International
and Security Affairs, Germany; Utrecht University, the
Netherlands
Courtney Bouchard, National Oceanic and Atmospheric
Administration, USA
Alexander F. Bouwman, Utrecht University, the Netherlands
Daniel Bowie-MacDonald, Chartered Financial Analyst, UK
Philip W. Boyd, University of Tasmania, Australia
Tim Boyer, National Oceanic and Atmospheric
Administration, USA
Eileen Bresnan, Marine Directorate of the Scottish
Government, UK
Bethanie Carney Almroth, University of Gothenburg, Sweden
Anny Cazenave, Laboratoire d'Etudes en Géophysique
et Océanographie Spatiales - Centre National d'Études
Spatiales, France
Silvia Chacon-Barrantes, National University Costa Rica,
Costa Rica
Lijing Cheng, Chinese Academy of Sciences, China
Ronaldo Christofoletti, Federal University of São Paulo,
Brazil
Giovanni Coppini, Fondazione CMCC - Centro Euro-
Mediterraneo sui Cambiamenti Climatici, Italy
Mark J. Costello, Nord University, Norway
Nigel T. Crawhall, United Nations Educational, Scientific and
Cultural Organization
Anne de Carbuccia, One Planet One Future Foundation,
Italy/France
Louis Demargne, Intergovernmental Oceanographic
Commission of UNESCO
Alex Driedger, Anthropocene Institute, USA
4 / STATE OF THE OCEAN REPORT 2024
Yan Drillet, Mercator Ocean International, France
Henrik Enevoldsen, Intergovernmental Oceanographic
Commission of UNESCO
Afiq D. B. M. Fahmi, University Malaysia Terengganu,
Malaysia
Ivan Federico, Fondazione CMCC - Centro Euro-
Mediterraneo sui Cambiamenti Climatici, Italy
Diana Fernandez Reguera, Food and Agriculture
Organization of the United Nations
Hernan Garcia, National Oceanic and Atmospheric
Administration, USA
Gustaaf Hallegraeff, University of Tasmania, Australia
John A. Harrison, Washington State University Vancouver,
USA
Emma Heslop, Intergovernmental Oceanographic
Commission of UNESCO
Daniela Hill Piedra, Fundación Amiguitos del Océano,
Ecuador
Bruce M. Howe, University of Hawai’i at Mânoa, USA
Khalissa Ikhlef, United Nations Educational, Scientific and
Cultural Organization
Ingela Isaksson, Swedish Agency for Marine and Water
Management, Sweden
Kirsten Isensee, Intergovernmental Oceanographic
Commission of UNESCO
Takamitsu Ito, Georgia Institute of Technology, USA
Daniel Kasnick, Newton College, Peru
Peter Kershaw, Independent scientist, UK
Villy Kourafalou, University of Miami, USA
Xiaochen Liu, Deltares, the Netherlands
Raquel Costa, Estrutura de Missão para a Extensão da
Plataforma Continental, Portugal
Emma McKinley, Cardiff University, UK
Jamie McMichael-Phillips, The Nippon Foundation - GEBCO
Seabed 2030, UK
Audrey Minière, Mercator Ocean International, France
Gary Mitchum, University of South Florida, USA
Daniele Moretti, Sky TG24, Italy
Pilar Muñoz Muga, Universidad de Valparaíso, Chile
Shweta K. Naik, Jane Goodall Institute, India
Janet A. Newton, University of Washington, USA
Kevin O’Brien, University of Washington, National Oceanic
and Atmospheric Administration, USA
Andreas Oschlies, GEOMAR Helmholtz Centre for Ocean
Research Kiel, Germany
Diana L. Payne, University of Connecticut, USA
Nadia Pinardi, University of Bologna, Italy
Peter Pissierssens, Intergovernmental Oceanographic
Commission of UNESCO
Molly Powers-Tora, The Pacific Community, Fiji
Silas C. Principe, Intergovernmental Oceanographic
Commission of UNESCO
Pieter Provoost, Intergovernmental Oceanographic
Commission of UNESCO
Michele Quesada da Silva, Intergovernmental
Oceanographic Commission of UNESCO
Harkunti P. Rahayu, Institute of Technology Bandung,
Indonesia
James Reagan National Oceanic and Atmospheric
Administration, USA
Arturo Rey da Silva, University of Edinburgh, UK
Marzia Rovere, Consiglio Nazionale delle Ricerche, Italy
Emanuela Rusciano, World Meteorological
Organization,OceanOPS
Francesca Santoro, Intergovernmental Oceanographic
Commission of UNESCO
Carolyn Scheurle, Institute de la Mer, Sorbonne Université –
CNRS, France
Katherina L. Schoo, Intergovernmental Oceanographic
Commission of UNESCO
Lucy Scott, Intergovernmental Oceanographic Commission
of UNESCO
Jan Seys, Flanders Marine Institute, Belgium
Joanna Smith, The Nature Conservancy, Canada
Helen Snaith, National Oceanography Centre, UK
Pegah Souri, Shearwater Global, UK
Aslak Sverdrup, Innovation Norway, Norway
Joaquin Tintoré, Sistema de Observación y Predicción
Costero de las Islas Baleares, Spain
Jogeir Toppe, Food and Agriculture Organization of the
United Nations
Srinivasa K. Tummala, Indian National Centre for Ocean
Information Services, India
Jacqueline Uku, Kenya Marine and Fisheries Research
Institute, Kenya
Andrea Valentini, Agency for Prevention, Environment and
Energy of Emilia-Romagna, Italy
Stefania Vannuccini, Food and Agriculture Organization of
the of the United Nations
Chris Vivian, The Joint Group of Expert on the Scientific
Aspects of Marine Environmental Protection, UK
Christa von Hillebrandt-Andrade, International Tsunami
Information Center, Caribbean Office, USA
Karina von Schuckmann, Mercator Ocean International,
France
/ 5
Zhankun Wang, National Oceanic and Atmospheric
Administration, USA
Pauline Weatherall, National Oceanography Centre, UK
Tom Webb, University of Sheffield, UK
Yong Wei, University of Washington, National Oceanic and
Atmospheric Administration, USA
Steve Widdicombe, Plymouth Marine Laboratory, UK
Joseph Zelasney, Food and Agriculture Organization of the
United Nations
Zhiwei Zhang, Intergovernmental Oceanographic
Commission of UNESCO
Adriana Zingone, Stazione Zoologica Anton Dohrn, Italy
Reviewers
Kouadio Affian, Intergovernmental Oceanographic
Commission of UNESCO
Kentaro Ando, Japan Agency for Marine-Earth Science and
Technology, Japan
Swadhin K. Behera, Japan Agency for Marine-Earth Science
and Technology, Japan
Ken Buesseler, Woods Hole Oceanographic Institution, USA
Eric Chassignet, Florida State University, USA
María P. Chidichimo, Argentine Scientific Research Council
and Universidad Nacional de San Martín, Argentina
Dave Clarke, Marine Institute, Ireland
John Cortinas, National Oceanic and Atmospheric
Administration, USA
Carla Edworthy, Nelson Mandela University, South Africa
Ghada El Serafy, Deltares, the Netherlands
Peer Fietzek, Kongsberg Discovery, Germany
Helen Findlay, Plymouth Marine Laboratory, UK
Lotta Fyrberg, Swedish Meteorological and Hydrological
Institute, Sweden
Véronique Garçon, Centre National de la Recherche
Scientifique, Institut de Physique du Globe de Paris, France
Claudine Hauri, University of Alaska Fairbanks, USA
Shigeki Hosoda, Japan Agency for Marine-Earth Science
and Technology, Japan
Izwandy Idris, Universiti Malaysia Terengganu, Malaysia
Gil S. Jacinto, University of the Philippines, Philippines
Hrissi K. Karapanagioti, University of Patras, Greece
Nimit Kumar, Indian National Center for Ocean Information
Services, India
Marine Lecerf, Ocean & Climate Platform, France
John Lyman, National Oceanic and Atmospheric
Administration and University of Hawaiʻi, USA
Sarah Mahadeo, World Maritime University - Sasakawa
Global Ocean Institute, Sweden
Kimberly Mathisen, HUB Ocean, Norway
Jen McRuer, Canadian Ocean Literacy Coalition, Canada
Mathieu Morlighem, Dartmouth College, USA
Flower E. Msuya, Zanzibar Seaweed Cluster Initiative,
Tanzania
Chenae Neilson, Department of Climate Change, Energy,
the Environment and Water, Australia
Marck Oduber, Science Liaison UNESCO Commission,
Aruba
Erik Olsen, Institute of Marine Research, Norway
Dwight Owens, Ocean Networks Canada, Canada
Eric Rignot, University of California and Jet Propulsion
Laboratory, USA
Chelsea M. Rochman, University of Toronto, Canada
Marinez Scherer, Federal University of Santa Catarina
Ministry of the Environment and Climate Change, Brazil
Lisa Schindler Murray, Rare, Germany
Sybil P. Seitzinger, University of Victoria, Canada
Cândida I. Sete, Mozambique Oceanographic Institute,
Mozambique
Rebecca Shellock, University of Tasmania, Australia
Soraya J. Silva, Instituto Venezolano de Investigaciones
Cientificas, Venezuela
Inés Sunesen, Consejo Nacional de Investigaciones
Científicas y Técnicas, Universidad Nacional de La Plata,
Argentina
Aileen Tan Shau Hwai, Universiti Sains Malaysia, Malaysia
Ariel H. Troisi, Servicio de Hidrografía Naval, Argentina
Leonardo A. Venerus, Centro para el Estudio de Sistemas
Marinos, Consejo Nacional de Investigaciones Científicas y
Técnicas, Argentina
Phil Williamson, University of East Anglia, UK
Sylke Wohlrab, Alfred Wegener Institute, Helmholtz Centre
for Polar and Marine Research, Germany
Acknowledgements
The Intergovernmental Oceanographic Commission of
UNESCO wishes to express its gratitude to those who have
made the production of this report possible: the members of
the Advisory Board, the many authors and the experts who
have agreed to provide an independent review of its findings.
We further thank the Republic of Korea, Iceland and the Back
to Blue Initiative for the financial and in-kind support which
has enabled the IOC Secretariat to develop the StOR 2024.
6 / STATE OF THE OCEAN REPORT 2024
© Unsplash/Shifaaz Shamoon
7
Table of contents
Report team 3
Table of contents 7
Foreword 9
State of the Ocean Report Key messages 10
A clean ocean, free of plastic pollution 13
Trends of eutrophication and alteration of nutrient ratios 13
Status and trends of plastic pollution, including strategies on how to reduce them 18
A healthy and resilient ocean where marine ecosystems are understood,
protected, restored and managed 21
Status and trends of ocean acidification 21
Ocean warming 24
Global ocean deoxygenation: Status and challenges 28
Biodiversity knowledge and threats on marine life: Assessing no-take zones
as a refuge for marine species 31
Marine spatial planning A global update 34
Protecting coastal blue carbon ecosystems 37
A productive ocean supporting sustainable food supply and a sustainable ocean economy 41
The contribution of aquatic foods to food security and nutrition 41
A predicted ocean where society understands and can respond to changing ocean conditions 45
Assessing ocean prediction capabilities for sustainable development 45
Sea level rise 52
Potential of marine carbon dioxide removal (mCDR) to increase the ocean carbon sink 55
A safe ocean where life and livelihoods are protected from ocean-related hazards 59
Trends and impacts of warning systems for ocean-related hazards: Outcome vs status 59
Harmful algal bloom impacts increase amid rising sea food demand and coastal development 63
An accessible ocean with open and equitable access to data, information
and technology and innovation 67
Global Ocean Observing System status and expansion 67
Open access to ocean data from global to local scales 71
Ocean data sharing – A global and essential requirement in the value chain 73
The pivotal role of bathymetry in safeguarding the future of the planet 75
An inspiring and engaging ocean where society understands and values
the ocean in relation to human well-being and sustainable development 79
Status and trends in building global ocean literacy 79
Involving civil society and the private sector in the Global Ocean Observing System 83
Progress to include Indigenous and traditional knowledge in ocean science 86
8 / STATE OF THE OCEAN REPORT 2024
9
Foreword
Considering just how much the ocean means to people
and planet, the world ought to be kept up to date about its
state. The fact is: we don’t know (enough).
When the first State of the Ocean Report (StOR) was
launched in 2022, we learnt that the quantitative
description of the ocean is drastically incomplete and, as
a result, current knowledge is insufficient to effectively
inform solutions to the multiple ocean crises that
humanity is now facing.
In this State of the Ocean Report 2024, the message
remains that observations and research is falling short
and hence there is a lack of adequate and aggregated
data. But as more states, industries and organizations
realize that we need to measure in order to manage and
protect marine ecosystems, we gradually get more data,
get deeper into the issues, and can include new topics of
research.
Every indication is, however, that the ocean crisis is
developing faster than our knowledge of it. We therefore
need to accelerate the mobilization which is under way
in the UN Decade for Ocean Science for Sustainable
Development 2021-2030. We need to transform ocean
science and our relationship to it. We need better
knowledge as a basis for sustainable ocean planning
and management, within and beyond areas of national
jurisdiction. And we need a much stronger, much faster
and more dynamic interplay between ocean knowledge,
policy and action.
The StOR is intended to be complementary to multi-year
assessments informing major international environmental
conventions, such as the UN World Ocean Assessment,
IPCC and IPBES. It is essential to keep the general public,
industries and governments fully informed of the rapidly
evolving situation in the ocean, and what is being done.
The StOR will also help to monitor the progress of the UN
Decade of Ocean Science for Sustainable Development,
2021–2030, thus contributing to mobilizing global action
towards ‘the ocean we need for the future we want’.
The 2024 StOR is the result of dedicated efforts on the part
of leading experts in the broad family of ocean research.
Without their time and engagement, the StOR would not
be possible.
I offer my grateful thanks to all those who contributed
their expertise, time and goodwill to the this edition. And
I offer you, the reader, an important encounter with the
State of the Ocean.
Vidar Helgesen
Executive Secretary of the Intergovernmental Ocenographic Commission of UNESCO
10 / STATE OF THE OCEAN REPORT 2024
The State of the Ocean Report (StOR) has the ambition to
inform policy-makers about the state of the ocean and to
stimulate research and policy actions towards ‘the ocean
we need for the future we want’, contributing to the 2030
Agenda and in particular SDG 14, which reads ‘Conserve
and sustainably use the oceans, seas and marine
resources, as well as other global processes such as the
UNFCCC, the Convention on Biological Diversity and the
Sendai Framework for Disaster Risk Reduction.
Structured around the seven Outcomes of the UN Decade
of Ocean Science for Sustainable Development, the Report
provides important information about the achievements
of the UN Ocean Decade and, in the longer term, about
ocean well-being. The StOR will be used to inform policy
and administrative priorities and identify research focus
areas that need to be strengthened or developed.
More than 98 authors from 25 countries contributed to the
Report. The different sections provide insights on ocean-
related scientific activities and analyses describing the
current and future state of the ocean, addressing physical,
chemical, ecological, socio-economic and governance
aspects.
A clean ocean where sources of pollution are
identified and reduced or removed
Continuous measurements show that eutrophication –
excess nutrients in the ocean – persist and continue to
increase. There is a need to better quantify the dominant
sources of nitrogen (N) and phosphorus (P) across all
large marine ecosystems to develop strategies and
policies for their reduction.
Since the 1990s, the amount of plastics in the ocean has
significantly increased and is trending to continue to
increase at a worsening rate, which will result in impacts
that are beyond the safe operating space for humanity.
Global mechanisms to track the extent and distribution of
nutrient and plastic pollution in our oceans are urgently
required to support mitigation and adaptation strategies.
A healthy and resilient ocean where marine
ecosystems are understood, protected,
restored and managed
The ocean is continuing to act as a carbon sink, absorbing
large amounts of carbon, which are predicted to increase
ocean acidification by more than 100% by the end of
the century. Adaptation and mitigation, however, will
require national and subnational action, which can only
be delivered once local and regional variations in ocean
acidification and its impacts are understood.
State of the Ocean Report
Key messages
At the same time, ocean warming from the surface down
to the abyss is happening at an unprecedented pace
and the rate is accelerating. The main and well-known
consequences include rising sea levels, alterations
in ocean currents and dramatic changes in marine
ecosystems.
And as if that would not be sufficient to disturb the
provision of ocean services, the ocean oxygen content is
decreasing, resulting in worsening hypoxia and larger low
oxygen areas. New research will be required to estimate
the rate change and to predict the consequences.
Marine Protected Areas provide shelter for marine life
against these stressors. More than 70% of endangered
species are reported to seek shelter in Marine Protected
Areas. These hotspots of marine biodiversity are crucial
for supporting both food security and the overall health of
our oceans now and in the future.
Another refuge against a warmer, more acidic ocean,
which holds less oxygen are coastal blue carbon
ecosystems (mangroves, seagrasses and tidal marshes).
They continue to be an important store of carbon; however
protection is not guaranteed and 20–35% have been lost
since 1970.
Marine spatial planning is an important policy mechanism
to help reduce the pressures on marine ecosystems. As of
2023, 126 countries and territories (a 20% increase since
2022) have applied area-based policies to sustainably
manage activities in the ocean. The continuance of this
positive trend will be an important contribution to action
under SDG 14.
A productive ocean supporting sustainable
food supply and a sustainable ocean economy
The world will see an additional 2 billion people in the
next 25 years, adding pressure to already impacted food
supplies on land and in the ocean. Aquatic foods are a
major source of food with 182 million tonnes of aquatic
animals and an additional 36 million tonnes of algae used
for food and food production. Fisheries and aquaculture
production continues to grow, reaching a record of
218 million tonnes in 2021. A deeper appreciation and
understanding of the role that aquatic foods can play is
essential to harness their unique capacity for addressing
nutritional, social and environmental food system
challenges in the future.
STATE OF THE OCEAN REPORT KEY MESSAGES / 11
A predicted ocean where society understands
and can respond to changing ocean conditions
After four decades of investment, global, regional and
coastal operational, ocean prediction systems have
matured, providing accurate forecasts to diverse users.
However, a significant inequality between the prediction
capacity in the Northern and Southern Hemisphere
persists.
There is no doubt that the sea level is rising and that this
will accelerate in the future. Melting ice masses from the
Greenland and West Antarctica ice sheets and stronger
ocean warming are contributing to the expansion of
marine waters.
Even today, the ocean contains 40 times as much
carbon as the atmosphere. Future climate scenarios are
considering the potential of marine carbon dioxide removal
techniques to increase this stock. A variety of techniques
have been proposed, but large-scale deployment cannot
be implemented without an increased understanding
about how these new approaches will interact with ocean
carbon cycle and marine ecosystems, and their risks and
benefits.
A safe ocean where life and livelihoods are
protected from ocean-related hazards
Tsunamis are a major threat to human life, expected to
intensify with climate change and rising sea level. They
can cause extensive damage to critical infrastructure
and homes, disrupt economies and livelihoods, and
lead to loss of life, especially with the current growth in
coastal population and tourism worldwide. Nearly 90%
of tsunamis have been generated by large earthquakes
or landslides triggered by earthquakes. Considerable
efforts have now led to 150 countries and territories
actively contributing to global efforts in tsunami hazard
resilience by countries and territories. Despite these
advances, tsunamis from non-seismic sources remain a
key challenge to be addressed.
Similarly, harmful algae blooms continue to impact
ocean ecosystems at an increasing rate amid rising
seafood demand and coastal development. Among the
approximately 10,000 species of marine phytoplankton in
the world’s oceans today, some 200 taxa produce toxins.
Despite this risk to food security, identifying the drivers
and causes remains challenging, as a global synthesis is
lacking.
An accessible ocean with open and equitable
access to data, information and technology
and innovation
Observations of the ocean’s physical, chemical and
biological characteristics are the basis of sustainable
development. To date, the Global Ocean Observing System
comprises 8,000 observing platforms, operated by 84
countries through 300 programmes, delivering more
than 120,000 observations daily. However, spatial and
temporal observation gaps need to be closed to provide
the information required for action.
For example, of the 120,000 daily observations, many are
missing auxiliary information necessary to define quality
and suitability, resulting in 10–15% of this data not being
utilized. Cooperative efforts to align data reporting and
access are required to increase use.
A prerequisite to ensure equitable global sharing of data
and information is free and open access. Worldwide
efforts, coordinated by IODE, have successfully led to the
establishment of a global network of 101 data centres in
68 countries that cooperate to improve data access and
interoperability. Further expansion of this network will
continue to support greater information accessibility and
usability as part of action under SDG14.
Additionally, greater global effort on increasing our
knowledge of the seafloor is required, with more than
75% of the ocean floor remaining unmapped. New
technologies and partnerships are, however, aiming to
close this gap. Since 2022, 5.4 million km2 of new data,
equating to an area twice the size of Argentina, have been
obtained.
An inspiring and engaging ocean where
society understands and values the ocean in
relation to human wellbeing and sustainable
development
Ocean literacy, an effort to increase the knowledge and
understanding of the pivotal role of the ocean for human
well-being and sustainable development, is an exciting
global movement involving the efforts of hundreds of
stakeholders in 2023. Future activities will aim to increase
participation from the Southern Hemisphere, as more
than 70% of ocean literacy efforts are taking place in the
Northern Hemisphere.
The importance of the ocean in safeguarding lives now
and in the future is no longer a topic addressed by ocean
scientists alone. Non-academic partners are becoming
increasingly involved in ocean science and observation.
The ambition is to equip the global fleet, including
container ships, fishing and leisure vessels with ocean
sensors to exponentially increase ocean observations.
It is important to remember that Indigenous peoples have
been observing, using and conserving the ocean and its
resources for hundreds of years. These include peoples
living at different latitudes, from the Arctic to the tropics.
Their knowledge on maintaining the intricate balance
between nature and humanity remains an important
resource for researchers and policy-makers to draw upon.
Increased effort is required to better engage Indigenous
peoples in marine policy and planning to transition to 'the
ocean we need for the future we want'.
12 / STATE OF THE OCEAN REPORT 2024
A CLEAN OCEAN, FREE OF PLASTIC POLLUTION / 13
Introduction
The world’s coastal ocean has experienced rapidly
increasing inputs of plant nutrients nitrogen (N) and
phosphorus (P) from land-based sources. The mobilization
of these nutrients during the production of food, feed and
other products in agriculture, aquaculture and through
discharge of household and industrial wastewater has
increased rapidly in recent decades (Beusen et al., 2022;
Seitzinger et al., 2010), leading to increased plant and
phytoplankton growth in many coastal waters. Increased
plant and phytoplankton growth leads to oxygen depletion
when oxygen consumption during decomposition of plant
material exceeds oxygen exchange with the atmosphere,
leading to temporary or permanent hypoxic conditions,
as observed in an increasing number of sites (Breitburg
et al., 2018). At the same time, human activities have
changed the proportion of different nutrients exported to
the coastal zone (Beusen and Bouwman, 2022) (Figure 1),
which can alter the types of plants and plankton that grow
in fresh and coastal waters, sometimes causing toxic or
otherwise harmful algal blooms (Glibert, 2020).
Findings: Status and trends
Alterations in the structure of food webs due to
eutrophication are occurring in many coastal marine
ecosystems with changes in the structure of benthic
communities (Lim et al., 2006) and act as stressors on
biodiversity, plankton community structure and food webs
(Borja et al., 2016; Clark et al., 2017; Holland et al., 2023;
Korpinen et al., 2021). Coastal habitat loss is a global
problem – for example, a rapid decline of warm-water
coral reefs, seagrass meadows and coastal wetlands
(mangrove forests and salt marshes; see Breitburg et
al. (2018) and references therein). It is now recognized
that these phenomena are not only caused by nutrient
enrichment of the marine system, but also by the changes
in the proportions in which nutrients are delivered to
coastal waters, i.e. nutrient stoichiometry. The Redfield
carbon:nitrogen:phosphorus:silicon ratio (molar ratio of
C:N:P:Si = 106:16:1:20) is a generalized representation of
the approximate nutrient requirement of marine diatoms
(Brzezinski, 1985; Redfield et al., 1963). Non-diatom
phytoplankton, often harmful, species like dinoflagellates
may develop in waters where N and P are available in
excess relative to the diatom Si demand, a condition
expressed by the Indicator for Coastal Eutrophication
Potential (ICEP) (Billen and Garnier, 2007) (Figure 2).
ICEP has been proposed as the indicator for Sustainable
Development Goal 14.1.1a on eutrophication, which is to:
By 2025, prevent and significantly reduce marine pollution
of all kinds, in particular from land-based activities,
including marine debris and nutrient pollution.
A clean ocean,
free of plastic
pollution
Trends of eutrophication and alteration
of nutrient ratios
Alexander F. Bouwman,1 John A. Harrison2 and Xiaochen Liu3
1 Utrecht University, the Netherlands
2 Washington State University Vancouver, USA
3 Deltares, the Netherlands
14 / STATE OF THE OCEAN REPORT 2024
Non-diatom phytoplankton species are generally of
lower food quality and less grazed upon than diatoms;
consequently a larger fraction becomes detritus and as
a result there is substantial oxygen demand upon settling
and degradation (Cloern, 2001; Officer and Ryther, 1980).
Many non-diatom phytoplankton species causing high
biomass and sometimes harmful blooms proliferate
under conditions of elevated N:P conditions (Glibert et
al., 2014). Currently, many global rivers are experiencing
a trend of increasing nutrient loads, with rising N:P ratios
and either stable or declining silicon (Si) loads. However,
an exception to this trend is the North Sea, where both N
and P loads are decreasing but N:P ratios are increasing
(Beusen and Bouwman, 2022; Devlin et al., 2023). At the
global scale, 36% of the total N export to coastal waters
is from rivers dominated by anthropogenic sources and
with N:P ratios exceeding the Redfield ratio (Figure
1). Additional N comes from submarine groundwater
discharge in many coastal waters (Beusen et al., 2013;
Slomp and Van Capellen, 2004), at times even exceeding
river inputs (Santos et al., 2021). While in industrialized
countries the anthropogenic N load with high N:P has
been declining in recent years, in other parts of the world
N:P ratios are still steadily increasing, particularly in the
Brazil, India, China (BIC) region (Figure 1). Coastal waters
receiving discharge from rivers draining the most densely
populated countries of the world (India and China) show
the highest eutrophication risk of harmful algal blooms
and hypoxia (Figure 2).
In addition to the distortion of nutrient ratios, a shift in
the nutrient composition, particularly towards more
organic (as opposed to inorganic) N and P forms, may
lead to the proliferation of specific harmful algal species
(Glibert, 2017). It is known that urea fertilizers, the world’s
most common N fertilizer, contribute substantially to
river-dissolved organic N (Glibert et al., 2006). Reservoirs
can also play a role in nutrient transformations and coastal
nutrient delivery by preferentially retaining inorganic N
and P forms (Ou et al., 2018; Wang et al., 2011).
Finally, there is mounting evidence that climate change
will exacerbate eutrophication and its associated
negative impacts through multiple processes (Meerhoff
et al., 2022; Paerl and Paul, 2012; Rabalais et al., 2009).
One of the primary mechanisms through which climate
change influences eutrophication is by enhancing
vertical water column stability due to increased density
stratification caused by climate-driven changes in surface
temperatures and salinities. This condition fosters the
Figure 1. River N export for rivers with >50% anthropogenic sources and N:P ratio >25. By including only rivers with strong
human influence, rivers such as the Amazon with a dominant natural signature and with high Si load relative to N and P are
excluded. INDUS = industrialized countries (North America, Europe, Japan, Oceania), BIC = Brazil, India, China, ROW = rest
of the world. Source: Adapted after Beusen and Bouwman (2022).
b) BIC
a) WORLD
c) INDUS d) ROW
A CLEAN OCEAN, FREE OF PLASTIC POLLUTION / 15
Figure 2. Indicator of Coastal Eutrophication Potential (ICEP) values for coastal river inputs aggregated to the scale of LMEs
for years 1900 (top), 1970 (middle) and 2010 (bottom). ICEP is calculated as the excess of N or P over the requirement of
diatoms based on the Redfield ratio and is expressed as the potential growth of non-diatom species in kg C-equivalents per
km2 per day (Beusen and Bouwman, 2022; Liu et al., 2020). High values suggest a high potential for the formation of HABs.
Pronounced increases in ICEP have occurred over time, particularly in South and Southeast Asia and off the coast of eastern
South America. Source: Authors’ compilation.
1900
1970
2010
kg C km-2 day-1
-150 -100 -50 0 50 150
75
50
25
0
-25
-50
-75
75
50
25
0
-25
-50
-75
75
50
25
0
-25
-50
-75
16 / STATE OF THE OCEAN REPORT 2024
formation and proliferation of some HABs (Michalak,
2016). Furthermore, potential interactions between
ocean acidification and coastal eutrophication are
being investigated, although these relationships remain
largely uncertain (Kessouri et al., 2021). Major causes
of this uncertainty are the interactions between coastal
eutrophication and other ongoing human-driven changes
in coastal waters.
Some non-diatom phytoplankton species may be
harmful or even toxic. HABs can produce toxins that can
cause massive fish kills or cause ecological damage
through the development of hypoxia or anoxia and other
habitat alterations, with a series of important negative
consequences for human health, economy, society and
recreation. Many international research efforts since
the start of the Global Ecology and Oceanography of
HABs (GEOHAB) programme (Cullen, 1998; GEOHAB,
2006) have contributed to a growing consensus that
coastal eutrophication, combined with climate change,
is contributing to the apparent worldwide increase in
the frequency and areal extent of coastal HABs (Glibert,
2020). Due to their harmful or toxic effects, even a modest
increase in the abundance of HAB species can promote
noticeable differences in ecosystems, while also affecting
shellfisheries and human health. It should be noted,
however, that not all geographic regions and not all HAB
species respond in a uniform manner to eutrophication
and climate change (see ‘Harmful algal bloom impacts
increase amid rising sea food demand and coastal
development’).
Conclusions and next steps
We need to better quantify the dominant sources of N and
P across all large marine ecosystems to develop strategies
and policies for their reduction. From the above, it is clear
that strategies and policies to reduce nutrients need to
be balanced. Controlling loads of P without concomitant
strategies to control N may lead to unexpected and
unwanted impacts such as HABs (Glibert, 2017). The
escalating global nutrient cycles and distortion of nutrient
ratios under continuing global warming underscores the
urgency to develop approaches to examine interactions
among these disturbances and to incorporate ecological
principles into management and restoration of coastal
environments.
References
Beusen, A.H. and Bouwman, A.F. 2022. Future projections
of river nutrient export to the global coastal ocean show
persisting nitrogen and phosphorus distortion. Frontiers
in Water, Vol. 4, p. 893585. https://doi.org/10.3389/
frwa.2022.893585
Beusen, A.H.W., Slomp, C.P. and Bouwman, A.F. 2013.
Global land–ocean linkage: Direct inputs of nitrogen
to coastal waters via submarine groundwater
discharge.Environmental Research Letters,Vol. 8, No. 3,
p.034035. https://doi.org/10.1088/1748-9326/8/3/034035
Beusen, A.H.W., Doelman, J.C., Van Beek, L.P.H., Van
Puijenbroek, P.J.T.M., Mogollón, J.M., Van Grinsven,
H.J.M., Stehfest, E., Van Vuuren, D.P. and Bouwman,
A.F. 2022. Exploring river nitrogen and phosphorus
loading and export to global coastal waters in the
Shared Socio-economic pathways.Global Environmental
Change,Vol. 72, p. 102426. https://doi.org/10.1016/j.
gloenvcha.2021.102426
Billen, G. and Garnier, J., 2007. River basin nutrient delivery
to the coastal sea: Assessing its potential to sustain new
production of non-siliceous algae. Marine Chemistry,
Vol. 106 (1–2), pp. 148–60. https://doi.org/10.1016/j.
marchem.2006.12.017
Borja, A., Elliott, M., Andersen, J.H., Berg, T., Carstensen, J.,
Halpern, B.S., Heiskanen, A.S., Korpinen, S., Lowndes,
J.S.S., Martin, G. et al. 2016. Overview of integrative
assessment of marine systems: The ecosystem
approach in practice. Frontiers in Marine Science, Vol. 3,
p. 20. https://doi.org/10.3389/fmars.2016.00020
Breitburg, D., Levin, L. A., Oschlies, A., Grégoire, M., Chavez,
F. P., Conley, D. J., Garçon, V., Gilbert, D., Gutiérrez, D.,
Isensee, K. et al. 2018. Declining oxygen in the global
ocean and coastal waters. Science, Vol. 359, No. 6371.
https://doi.org/10.1126/science.aam7240
Brzezinski, M. A. 1985. The Si:C:N ratio of marine
diatoms: Interspecific variability and the effect of some
environmental variables. Journal of Phycology, Vol.
21, No. 3, pp. 347–57. https://doi.org/10.1111/j.0022-
3646.1985.00347.x
Clark, C.M., Bell, M.D., Boyd, J.W., Compton, J.E., Davidson,
E.A., Davis, C., Fenn, M.E., Geiser, L., Jones, L. and Blett,
T.F. 2017. Nitrogen-induced terrestrial eutrophication:
Cascading effects and impacts on ecosystem services.
Ecosphere, Vol. 8, No. 7. https://doi.org/10.1002/
ecs2.1877
Cloern, J.E. 2001. Our evolving conceptual model of the
coastal eutrophication problem. Marine Ecology Progress
Series, Vol. 210, pp. 223–53. http://dx.doi.org/10.3354/
meps210223
Cullen, J. 1998. GEOHAB: Global ecology and oceanography
of harmful algal blooms. A plan for co-ordinated
scientific research and co-operation to develop
international capabilities for assessment, prediction
and mitigation. Report from a Joint IOC/ SCOR Workshop.
Havreholm, Denmark, 13–17 October 1998.
A CLEAN OCEAN, FREE OF PLASTIC POLLUTION / 17
Devlin, M.J., Prins, T.C., Enserink, L., Leujak, W., Heyden, B.,
Axe, P.G., Ruiter, H., Blauw, A., Bresnan, E., Collingridge,
K. et al. 2023. A first ecological coherent assessment of
eutrophication across the North-East Atlantic waters
(2015–2020). Frontiers in Ocean Sustainability, Vol. 1.
https://doi.org/10.3389/focsu.2023.1253923
GEOHAB 2006. Global Ecology and Oceanography of Harmful
Algal Blooms. Harmful Algal Blooms in Eutrophic Systems
(ed. P. Glibert). Paris and Baltimore, Intergovernmental
Oceanographic Commission (IOC) and Scientific
Committee on Oceanic Research (SCOR).
Glibert, P.M. 2017. Eutrophication, harmful algae and
biodiversity — Challenging paradigms in a world of
complex nutrient changes. Marine Pollution Bulletin,
Vol. 124, No. 2, pp. 591–606. https://doi.org/10.1016/j.
marpolbul.2017.04.027
______. 2020. Harmful algae at the complex nexus of
eutrophication and climate change. Harmful Algae, Vol.
91, p. 101583. https://doi.org/10.1016/j.hal.2019.03.001
Glibert, P., Harrison, J., Heil, C. and Seitzinger, S. 2006.
Escalating worldwide use of urea – A global change
contributing to coastal eutrophication. Biogeochemistry,
Vol. 77, No. 3, pp. 441–63. http://dx.doi.org/10.1007/
s10533-005-3070-5
Glibert, P.M., Maranger, R., Sobota, D.J. and Bouwman, L.
2014. The Haber Bosch-harmful algal bloom (HB-HAB)
link. Environmental Research Letters, Vol. 9, p. 105001.
https://doi.org/10.1088/1748-9326/9/10/105001
Holland, M.M., Louchart, A., Artigas, L.F., Ostle, C.,
Atkinson, A., Rombouts, I., Graves, C.A., Devlin, M.,
Heyden, B., Machairopoulou et al. 2023. Major declines
in NE Atlantic plankton contrast with more stable
populations in the rapidly warming North Sea. Science of
the Total Environment, Vol. 898. https://doi.org/10.1016/j.
scitotenv.2023.165505
Kessouri, F., McWilliams, J.C., Bianchi, D., Sutula, M.,
Renault, L., Deutsch, C., Feely, R.A., McLaughlin, K.,
Ho, M., Howard, E.M. et al. 2021. Coastal eutrophication
drives acidification, oxygen loss, and ecosystem change
in a major oceanic upwelling system. Proceedings of
the National Academy of Sciences of the United States
of America, Vol. 118, No. 21. https://doi.org/10.1073/
pnas.2018856118
Korpinen, S., Laamanen, L., Bergström, L., Nurmi, M.,
Andersen, J.H., Haapaniemi, J., Harvey, E.T., Murray,
C.J., Peterlin, M., Kallenbach, E. et al. 2021. Combined
effects of human pressures on Europe’s marine
ecosystems. Ambio, Vol. 50, No. 7, pp. 1325–36. https://
doi.org/10.1007/s13280-020-01482-x
Lim, H.-S., Diaz, R.J., Hong, J.-S. and Schaffner, L.C. 2006.
Hypoxia and benthic community recovery in Korean
coastal waters,. Marine Pollution Bulletin, Vol. 52, pp.
1517–26. doi:10.1016/j.marpolbul.2006.05.013
Liu, X., Joost Van Hoek, W., Vilmin, L., Beusen, A., Mogollón,
J.M., Middelburg, J.J. and Bouwman, A.F. 2020.
Exploring long-term changes in silicon biogeochemistry
along the river continuum of the Rhine and Yangtze
(Changjiang). Environmental Science and Technology, Vol.
54, No. 19, pp. 11940–50. https://doi.org/10.1021/acs.
est.0c01465
Meerhoff, M., Audet, J., Davidson, T.A., De Meester, L., Hilt,
S., Kosten, S., Liu, Z., Mazzeo, N., Paerl, H., Scheffer,
M. and Jeppesen, E. 2022. Feedback between climate
change and eutrophication: Revisiting the allied attack
concept and how to strike back. Inland Waters, Vol. 12,
No. 2, pp. 187–204. https://doi.org/10.1080/20442041.20
22.2029317
Michalak, A.M. 2016. Study role of climate change in
extreme threats to water quality. Nature, Vol. 535, pp.
349–50. https://doi.org/10.1038/535349a
Officer, C.B. and Ryther, J.H. 1980. The possible
importance of silicon in marine eutrophication. Marine
Ecology Progress Series, Vol. 3, pp. 83–91. https://doi.
org/10.3354/meps003083
Ou, L., Cai, Y., Jin, W., Wang, Z. and Lu, S. 2018.
Understanding the nitrogen uptake and assimilation
of the Chinese strain of Aureococcus anophagefferens
(Pelagophyceae). Algal Research, Vol. 34, 182–90. https://
doi.org/10.1016/J.ALGAL.2018.07.019
Paerl, H.W., and Paul, V.J. 2012.Climate change: Links
to global expansion of harmful cyanobacteria. Water
Research, Vol. 46, No. 5, pp. 1349–63. https://doi.
org/10.1016/j.watres.2011.08.002
Rabalais, N.N., Turner, R.E., Díaz, R.J. and Justić, D. 2009.
Global change and eutrophication of coastal waters.
ICES Journal of Marine Science, Vol. 66, pp. 1528–37.
https://doi.org/10.1093/icesjms/fsp047
Redfield, A.C., Ketchum, B.H. and Richards, F.A. 1963. The
influence of organisms on the composition of sea-water.
M.N. Hills (ed.), The Sea. New York, Wiley and Sons, pp.
12–37.
Seitzinger, S.P., Mayorga, E., Bouwman, A.F., Kroeze, C.,
Beusen, A.H.W., Billen, G., Van Drecht, G., Dumont, E.,
Fekete, B.M., Garnier, J.et al. 2010. Global river nutrient
export: A scenario analysis of past and future trends.
Global Biogeochemical Cycles, Vol. 24, No. 4, GB0A08.
https://doi.org/10.1029/2009gb003587
Slomp, C. and Van Capellen, P. 2004. Nutrient inputs to
the coastal ocean through submarine groundwater
discharge: Controls and potential impact. Journal of
Hydrology, Vol. 295, pp. 64–86. https://doi.org/10.1016/j.
jhydrol.2004.02.018
Wang, Z. Hui, Liang, Y. and Kang, W. 2011. Utilization of
dissolved organic phosphorus by different groups of
phytoplankton taxa. Harmful Algae, Vol. 12, pp. 113–18.
https://doi.org/10.1016/J.HAL.2011.09.005
18 / STATE OF THE OCEAN REPORT 2024
Status and trends of plastic pollution,
including strategies on how to reduce
them
Bethanie Carney Almroth1 and Peter Kershaw2
1 University of Gothenburg, Sweden
2 Independent scientist, UK
Introduction
Plastics have become integral to many industrial and
societal functions since widespread industrial production,
starting in the 1950s. The rapid increase in plastic
production resulted in uncontrolled leakage into the
environment. Reports of plastic pollution in the ocean
started to emerge in the late 1960s but remained rather
a niche interest. However, in the past two decades, the
pervasive and ubiquitous presence of plastics in marine
ecosystems has become better documented, revealing
complex environmental, social and economic impacts
(MacLeod et al., 2021). The global extent of plastic pollution
has led some researchers to conclude that the impact of
plastics is beyond the safe operating space for humanity
(Persson et al., 2022). A major challenge in the coming
decade will be to identify and implement measures to
ensure sustainable and transparent plastic production,
restrict the generation of plastic waste, prevent further
leakage into the ocean and carefully remediate affected
ecosystems.
Findings: Status and trends
The distribution, behaviour and impacts of marine plastic
litter and microplastics have become a major research
area, attracting researchers from a wide variety of natural
and social sciences, as well as engaging environmental
NGOs, citizens’ groups, industry, governments, and IGOs.
Research ranges from laboratory-based experiments and
small-scale descriptive studies to attempts to provide a
global perspective. For example, it has been estimated
that there are over 170 trillion plastic particles floating in
the ocean, based on data from 11,777 stations, weighing
between 1.1 and 4.9 million tonnes (Figure 3; Eriksen et
al., 2023). The authors observed no detectable trend in
abundance until 1990 and then, after a period of fluctuating
concentrations, a rapid increase from 2005 until present.
In another development, the output from a GESAMP
international workshop highlighted the importance of the
atmospheric transport of micro- and nano-plastics, and
exchanges across the ocean atmosphere interface (Allen
et al., 2022). The authors estimated that 0.013–25 million
metric tons per year of micro-(nano-) plastics may be
deposited in the ocean via atmospheric transport alone.
Observations of macro-litter are still rather limited, apart
from shoreline surveys. However, some of the gaps in
ocean observations are being filled; for example, one
study revealed the distribution of seafloor litter around
the Atlantic and Indian Ocean coasts of Africa and in
the Bay of Bengal, based on litter recorded as by-catch
in demersal trawl surveys for fisheries resources (Buhl-
Mortensen et al., 2022). This represents one component
of the EAF-Nansen Programme, an endorsed Ocean
Decade Action. This study supported previous findings
that abandoned, lost, or otherwise discarded fishing gear
(ALDFG) can constitute a significant proportion of seafloor
litter in areas of higher fishing effort, such as seamounts
(Pham et al., 2014). Elsewhere, seafloor macro-litter
appears to be dominated by single-use plastic items,
including at abyssal depths (Chiba et al., 2018).
The current annual production of plastics (approximately
450 million tonnes) is predicted to double by 2045, under
current trends. The inadequacy of waste management to
meet this demand is a particular problem for developing
countries, and especially Small Island Developing States
(SIDS), with poorly developed waste infrastructure. Export
of plastic waste can exacerbate the problem for the
receiving countries, increasing the risk to marginalized
and vulnerable communities. Efforts to reduce waste
generation and improve waste management continue
to make some progress. The GloLitter Partnerships
Project aims to reduce sea-based sources of plastic
waste, principally from the shipping and fishing sectors.
GloLitter is being implemented by IMO and FAO and
provides support for developing countries, including SIDS
and Least Developed Countries.
In addition to waste reduction and litter prevention,
environmental clean-ups may be justified, provided these
are carefully targeted and designed to minimize further
harm (Bergmann et al., 2023; Falk-Andersson et al.,
2023). Developments in risk assessment methods for both
macro- (Roman et al., 2022) and micro- (Mehinto et al.,
A CLEAN OCEAN, FREE OF PLASTIC POLLUTION / 19
Figure 3. The distribution of sampling stations, 1979–2019, used to estimate the total quantity of floating plastic particles in
the ocean. Source: Eriksen et al. (2023).
2022) plastics will help to target appropriate responses.
The Digital Platform of the Global Partnership on Plastic
Pollution and Marine Litter provides a repository of
technical and other resources.
Conclusions and next steps
Working Group 1 (Clean Ocean) of the Vision 2030 process
of the UN Decade of Ocean Science for Sustainable
Development comprises experts from a wide range of
disciplines and geographic regions, and is supported by
Back to Blue, a joint initiative of Economist Impact and the
Nippon Foundation. A draft White Paper was completed
in early 2024, outlining ‘a set of strategic ambitions to
address the most pressing gaps in science, knowledge
and solutions needed to achieve a clean ocean by 2030’,
with plastic pollution a key component. The final version
was presented in a Science Solution Forum at the Ocean
Decade Conference in Barcelona, in April 2024.
Sustained, comprehensive and global actions are
needed to reduce the generation of plastic waste and
prevent unavoidable plastic waste from leaking into the
environment. Critical examination of effective policy
options (Economist Impact, 2023; Ferraro and Failler,
2020) provides essential input to current negotiations
towards an international binding instrument on plastic
pollution (UNEP/INC Secretariat, 2023).
References
Allen, D., Allen, S., Abbasi, S., Baker, A., Bergmann,
M., Brahney, J., Butler, T., Duce, R.A., Eckhardt,
S., Evangeliou, N. et al. 2022. Microplastics and
nanoplastics in the marine-atmosphere environment.
Nature Reviews Earth & Environment, Vol. 3, No. 6, pp.
393–405. https://doi.org/10.1038/s43017-022-00292-x
Bergmann, M., Arp, H.P.H., Carney Almroth, B., Cowger,
W., Eriksen, M., Dey, T., Gündoğdu, S., Helm, R.R.,
Krieger, A., Syberg, K. et al. 2023. Moving from
symptom management to upstream plastics prevention:
The fallacy of plastic cleanup technology. One
Earth, Vol. 6, pp. 1439–42. https://doi.org/10.1016/j.
oneear.2023.10.022
Buhl-Mortensen, L., Houssa, R., Weerakoon, W.R.W.M.A.P.,
Kainge, P., Olsen, M.N., Faye, S., Wagne, M.M., Thwe,
S.M., Voado, G.C. and Grøsvik, B.E., 2022. Litter on
the seafloor along the African coast and in the Bay of
Bengal based on trawl bycatches from 2011 to 2020.
Marine Pollution Bulletin, Vol. 184, p. 114094. https://doi.
org/10.1016/j.marpolbul.2022.114094
Chiba, S., Saito, H., Fletcher, R., Yogi, T., Kayo, M., Miyagi, S.,
Ogido, M. and Fujikura, K., 2018. Human footprint in the
abyss: 30 year records of deep-sea plastic debris.Marine
Policy,Vol. 96, pp. 204–12. https://doi.org/10.1016/j.
marpol.2018.03.022
Economist Impact. 2023. Peak plastics: Bending the
Consumption Curve. Evaluating the Effectiveness of
Policy Mechanisms to Reduce Plastic Use. https://
backtoblueinitiative.com/plastics-consumption/
Eriksen, M., Cowger, W., Erdle, L.M., Coffin, S., Villarrubia-
Gómez, P., Moore, C.J., Carpenter, E. J., Day, R.H.,
Thiel, M. and Wilcox, C. 2023. A growing plastic smog,
now estimated to be over 170 trillion plastic particles
afloat in the world’s oceans—Urgent solutions required.
PLOS ONE, Vol. 18, p. e0281596. https://doi.org/10.1371/
journal.pone.0281596
Sample year
1979−1995
1995−2001
2001−2006
2006−2011
2011−2019
20 / STATE OF THE OCEAN REPORT 2024
Falk-Andersson, J., Rognerud, I., De Frond, H., Leone, G.,
Karasik, R., Diana, Z., Dijkstra, H., Ammendolia, J.,
Eriksen, M., Utz, R. et al. 2023. Cleaning up without
messing up: Maximizing the benefits of plastic clean-
up technologies through new regulatory approaches.
Environmental Science & Technology,Vol. 57, No. 36, pp.
13304–12. https://doi.org/10.1021/acs.est.3c01885
Ferraro, G. and Failler, P. 2020. Governing plastic pollution
in the oceans: Institutional challenges and areas for
action. Environmental Science & Technology, 112, pp.
453–60. https://doi.org/10.1016/j.envsci.2020.06.015
MacLeod, M., Arp, H.P.H., Tekman, M.B. and Jahnke, A.
2021. The global threat from plastic pollution. Science,
Vol. 373, pp. 61–65. doi:10.1126/science.abg5433
Mehinto, A.C, Coffin S., Koelmans, A.A., Brander, S.B.,
Wagner, M., Thornton Hampton, L.M., Burton, A.G.,
Miller, E., Gouin, T., Weisberg, S.B. et al. 2022. Risk-
based management framework for microplastics in
aquatic ecosystems. Microplastics and Nanoplastics, Vol.
2, p. 17. https://doi.org/10.1186/s43591-022-00033-3
Persson, L., Carney Almroth, B.M., Collins, C.D., Cornell,
S., de Wit, C.A., Diamond, M.L., Fantke, P., Hassellöv,
M., MacLeod, M., Ryberg, M.W. et al. 2022. Outside the
safe operating space of the planetary boundary for novel
entities. Environmental Science & Technology, Vol. 56, pp.
1510–21. https://doi.org/10.1021/acs.est.1c04158
Pham, C.K., Ramirez-Llodra, E., Alt, C.H., Amaro, T.,
Bergmann, M., Canals, M., Company, J.B., Davies,
J., Duineveld, G., Galgani, F. et al. 2014. Marine litter
distribution and density in European seas, from the
shelves to deep basins. PLoS ONE, Vol. 9, No. 4, p.
e95839. https://doi.org/10.1371/journal.pone.0095839
Roman, L., Hardesty, B.D. and Schuyler, Q. 2022. A
systematic review and risk matrix of plastic litter
impacts on aquatic wildlife: A case study of the
Mekong and Ganges River basins. Science of the
Total Environment, Vol. 843, p. 156858. https://doi.
org/10.1016/j.scitotenv.2022.156858
UNEP/INC Secretariat. 2023. Zero Draft text of the
international legally binding instrument on plastic
pollution, including in the marine environment. Agenda
item, third session of the Intergovernmental Negotiating
Committee, Nairobi, 13–19 November. https://wedocs.
unep.org/bitstream/handle/20.500.11822/43239/
ZERODRAFT.pdf
Additional resources
Back to Blue. Caring for the Ocean, an initiative of
Economist Impact and The Nippon Foundation. https://
backtoblueinitiative.com/
Global Partnership on Plastic Pollution and Marine Litter
(GPML) Digital Platform https://digital.gpmarinelitter.
org/knowledge/library/map
GloLitter Partnerships Project https://glolitter.imo.org/
UN Decade of Ocean Science Working Group 1 – Clean
Ocean https://oceandecade.org/news/vision-2030-wg1-
takes-collaborative-effort-to-assess-and-mitigate-
marine-pollution/
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 21
Status and trends of ocean acidification
Introduction
The ocean absorbs around one-quarter of the annual
emissions of anthropogenic carbon dioxide (CO2) to the
atmosphere (WMO, 2023), thereby helping to alleviate the
impacts of climate change on the planet (Friedlingstein
et al., 2023). The cost of this process to the ocean is high,
as the absorbed CO2 gas reacts with seawater to change
the carbonate chemistry of the ocean; this process is
referred to as ‘ocean acidification’ due to the observed
Figure 4. Map illustrating surface ocean carbonate chemistry measurement locations received by the IOC for SDG 14.3.1 ocean
acidification reporting. Blue: countries whose data was reported in accordance with the SDG 14.3.1 Indicator Methodology.
Black dots: location of sampling stations from which data was collected (539 stations in 2023). Source: IOC-UNESCO.
A healthy and resilient
ocean where marine
ecosystems are
understood, protected,
restored and managed
Katherina L. Schoo,1 Janet A. Newton,2 Steve Widdicombe3 and Kirsten Isensee1
1 Intergovernmental Oceanographic Commission of UNESCO
2 University of Washington, USA
3 Plymouth Marine Laboratory, UK
decrease in seawater pH. Ocean acidification threatens
marine organisms and ecosystem services, including
food security, by reducing biodiversity, degrading habitats
and endangering fisheries and aquaculture. Ocean
acidification will continue to increase with high confidence
(IPCC, 2021) as open-ocean surface pH is projected to
decrease by around 0.3 pH units by 2081–2100, relative
to 2006–2015, under RCP8.5 (virtually certain), with
consequences for the global climate. As the acidity of
22 / STATE OF THE OCEAN REPORT 2024
Figure 5. Variations in the annual average pH values from a suite of representative sampling stations in open and coastal
waters. Data from IOC/UNESCO, SDG14.3.1 ocean acidification reporting. Notes: Open water stations: Chá bă – USA, Pacific
Ocean (data from 2010–2022); Chatham Island – New Zealand, South Pacific Ocean (data from 2015–2023); K2 – Japan, North
Pacific Ocean (data from 2010–2019); LN6 – Iceland, Iceland Sea, North Atlantic Ocean (data from 2010–2023); SURLATLANT
– France, Atlantic Ocean (data from 2010–2019). Coastal water stations: Boya de recalada – Mexico, Pacific Ocean (data from
2016-2023); Dunedin Pylon – New Zealand (data from 2015–2023); NRSPHB – Australia, National Reference Station Port
Hacking station (data from 2010–2021); W03 – Belgium, Scheldt Estuary (data from 2013–2020); # BrOA1 – Brazil, Reference
Station (data from 2017–2022); REF M1V1 – Sweden, Reference Station (data from 2010–2020); SOMLIT-BREST – France,
Celtic Sea (data from 2010–2019); Bahía Santa Marta – Colombia, Caribbean Sea (data from 2019–2023); Kuwait – Kuwait Bay
(data from 2010–2020). Source: IOC-UNESCO.
7.5
7.6
7.7
7.8
7.9
8.0
8.1
8.2
8.3
8.4
2010 2012 2014 2016 2018 202 0 2022 2024
Average pH
Year
Open water stations
Chá bă (USA)
Chatham Islands (New Zealand)
K2 (Japan)
LN6 (Iceland)
SURATLANT (Fra nce)
7.5
7.6
7.7
7.8
7.9
8.0
8.1
8.2
8.3
8.4
2010 2012 2014 2016 2018 2020 2022 2024
Average pH
Year
Coastal stations
Boya de recalada (Mexico)
Dunedin Pylon (New Zealand)
NRSPHB (Austra lia)
W03 (Belgium)
# BrOA 1 (Brazil)
REF M1V1 (Sw eden)
SOMLIT-BREST (France)
Bahía Santa Marta (Colombia)
Kuwait
the ocean increases, its capacity to absorb CO2 from the
atmosphere decreases, impeding the ocean’s role in
moderating climate change (IPCC, 2019).
Findings: Status and trends
Global efforts are under way to provide society with the
evidence needed to sustainably identify, monitor, mitigate
and adapt to ocean acidification, led by the Global Ocean
Acidification Observing Network (GOA-ON) and the UN
Ocean Decade programme Ocean Acidification Research
for Sustainability (OARS). As part of the 2030 Agenda
and Sustainable Development Goal (SDG) 14, dedicated
to the ocean, the Intergovernmental Oceanographic
Commission of UNESCO (IOC-UNESCO) has been
identified as the custodian agency for SDG indicator
14.3.1: Average marine acidity (pH) measured at agreed
suite of representative sampling stations.
The data collected annually by IOC-UNESCO shows a
mean global increase in ocean acidification in all ocean
basins and seas. While there is an increasing number
of ocean acidification observations (308 stations in 35
countries reported in 2022, 539 stations in 2023; 638 in
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 23
2024: Data collected by IOC-UNESCO, Figure 4), the
current coverage is inadequate, with time series not long
enough to determine trends and data gaps due to lack of
observations found in all areas.
The rate of change in ocean acidification, its pattern
and scale, shows great regional variability. A limited
set of long-term observations in the open ocean have
shown a continuous decline in pH (open-ocean data:
Figure 4), with an average global surface ocean pH
decline of 0.017–0.027 pH units per decade since the late
1980s. In contrast, observations of ocean acidification
from coastal areas present a more varied picture (coastal
data: Figure 5). In addition to absorbing atmospheric
CO2, these coastal areas are subject to a wide range of
additional processes affecting the carbonate chemistry of
the water. Coastal ocean acidification can be caused by
natural processes, such as freshwater influx, biological
activity, temperature change and large ocean oscillations
(such as the El Niño/Southern Oscillation (ENSO) and
the North Atlantic Oscillation (NAO)), or human activities
including nutrient input from agricultural and industrial
activities. Due to this natural variability, longer term data
sets are needed for coastal areas than for the open ocean
in order to determine the time of emergence of ocean
acidification trends; observations should include those
other parameters that can affect carbonate chemistry
in coastal areas. The latest OSPAR Quality Status Report
(McGovern et al., 2023) on ocean acidification has observed
that overall pH is declining at faster rates in the shallow
coastal regions than in the open ocean due to these
additional stressors and processes. This is of particular
relevance as most of the ocean’s biodiversity is found in
the coastal zones.
Conclusions and next steps
More and better distributed long-term observations of
coupled chemical and biological parameters are required
to discern and map ocean acidification and its impacts,
and to develop strategies for mitigation and adaptation at
relevant scales.
While there is clear evidence of the impacts of ocean
acidification on marine organisms and ecosystems, the
identification of the precise impacts at relevant temporal
and geographical scales to the affected organisms, and the
attribution of impacts to acidification, remain a challenge.
The GOA-ON biological working group, co-led by IOC, is
spearheading efforts to establish agreed methodologies
for the observation of ocean acidification impacts on
organisms and ecosystems (Widdicombe et al., 2023).
Integrating these observations with forecasting models
will improve the understanding of the trends, patterns,
drivers and biological impacts of ocean acidification now
and in the future.
References
Friedlingstein, P., O'Sullivan, M., Jones, M.W., Andrew, R.M.,
Hauck, J., Olsen, A., Peters, G.P., Peters, W., Pongratz,
J., Sitch, S. et al. 2023. Global Carbon Budget 2023.
Earth System Science Data, Vol. 15, pp. 5301–69. https://
doi.org/10.5194/essd-15-5301-2023
IPCC. 2019. IPCC Special Report on the Ocean and Cryosphere
in a Changing Climate (eds H.-O. Pörtner, D.C. Roberts, V.
Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K.
Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold,
B. Rama and N.M. Weyer). https://www.ipcc.ch/srocc/
______. 2021. Climate Change 2021: The Physical Science
Basis. Contribution of Working Group I to the Sixth
Assessment Report of the Intergovernmental Panel
on Climate Change [eds V. Masson-Delmotte, et al.].
Cambridge University Press. https://www.ipcc.ch/report/
ar6/wg1/
McGovern, E., Schilder, J., Artioli, Y., Birchenough, S.,
Dupont, S., Findlay, H., Skjelvan, I., Skogen, M.D.,
Álvarez, M., Büsher, J.V. et al. 2023. Ocean Acidification.
OSPAR, The 2023 Quality Status Report for the North-
East Atlantic. London, OSPAR Commission. Available at:
https://oap.ospar.org/en/ospar-assessments/quality-
status-reports/qsr-2023/other-assessments/ocean-
acidification
Widdicombe, S., Isensee, K., Artioli, Y., Gaitán-Espitia,
J.D., Hauri, C., Newton, J.A., Wells, M. and Dupont, S.
2023. Unifying biological field observations to detect
and compare ocean acidification impacts across
marine species and ecosystems: What to monitor and
why. Ocean Science, Vol. 19, pp. 101–19. https://doi.
org/10.5194/os-19-101-2023
WMO. 2023. WMO Greenhouse Gas Bulletin (GHG Bulletin) –
No.19:The State of Greenhouse Gases in the Atmosphere
Based on Global Observations through 2022. https://
library.wmo.int/idurl/4/68532
Additional resources
Global Ocean Acidification Observing Network
http://goa-on.org
IOC SDG 14.3.1 portal http://oa.iode.org
Ocean Acidification Research for Sustainability Ocean
Decade Programme http://goa-on.org/oars/overview.
php
OSPAR. 2023. Quality Status Report 2023.
Ocean Acidification
World Ocean. 2024. World Ocean Review 8. The Ocean –
A Climate Champion? How the ocean absorbs carbon
dioxide: https://worldoceanreview.com/en/wor-8/
the-role-of-the-ocean-in-the-global-carbon-cyclee/
how-the-ocean-absorbs-carbon-dioxide/
24 / STATE OF THE OCEAN REPORT 2024
Gulev et al., 2021; Abraham et al., 2013). Before Argo, the
major instrumentation relied on shipboard techniques,
which are known to be affected by instrumental biases,
for which the international community has developed
different solutions (Boyer et al., 2016; Cheng et al., 2016;
Good et al., 2011; Cowley et al., 2013; Wjiffels et al., 2009;
Ishii and Kimoto, 2008). The international community has
developed various methods and approaches to provide
global-scale estimates from these measurements, and
uncertainty could be largely reduced over the past decade
through fundamental advancements in science (e.g.
Cheng et al., 2022; Hosoda et al., 2008; Good et al., 2013;
Lyman and Johnson, 2014). However, given the limitation
of the observing system, particularly during the historical
era before 2005, inconsistencies remain, and reconciling
the different estimates remains an essential approach
(Johnson et al., 2022; Gulev et al., 2021; von Schuckmann
et al., 2023; Cheng et al., 2022). In addition, satellite-based
indirect estimates of full-depth ocean warming have been
developed from the year 1993 onwards (Hakuba et al.,
2021; Marti et al., 2022).
The upper 2,000 m of the ocean continued to warm in 2023
at a rate of 0.32± 0.03 W/m² since 1960 (Figure 6) and
it is expected that it will continue to warm in the future,
causing changes that are irreversible on centennial to
millennial time scales (IPCC, 2021). Over the past two
decades, the rate of ocean warming has increased to 0.66
± 0.10W/m2 – a doubling which is extensively discussed
in the scientific community (Loeb et al., 2021; Minière
et al., 2023; Cheng et al., 2024a; von Schuckmann et al.,
2023). At the regional scale, 2023 had been marked by
unusually high values of ocean heat content as compared
to the long-term state (Figure 7). The Tropical Atlantic
Ocean, the Mediterranean Sea and the Southern oceans
recorded their highest OHC observed since the 1950s
(Figure 7; Cheng et al., 2024b). Global ocean warming has
been enhancing the regional marine heatwave (a period
of abnormally high ocean temperatures relative to the
average seasonal temperature in a particular marine
region), with extremely high temperature values occurring
frequently in many regions (e.g. Frölicher et al., 2018).
Ocean warming
Karina von Schuckmann,1 Audrey Minière1 and Lijing Cheng2
1 Mercator Ocean International, France
2 Chinese Academy of Sciences, Beijing, China
Introduction
As assessed in the recent IPCC report, the global ocean
is warming from the surface down to the abyss at an
unprecedented pace, which is a direct consequence of
anthropogenic global warming (IPCC, 2021; Cheng et al.,
2022). Globally, ocean warming provides the fundamental
measure of Earth system heating in the climate system
from anthropogenic forcing (von Schuckmann et al., 2023).
At the regional scale, ocean warming has wide-reaching
implications (Cheng et al., 2022). For example, ocean
warming contributes to about 40% of the observed global
mean sea-level rise and alters ocean currents (Gulev
et al., 2021). It also indirectly alters storm tracks (IPCC,
2018), increases ocean stratification (Li et al., 2020) and
can lead to changes in marine ecosystems (Bindoff et al.,
2019). Particularly, and together with ocean acidification
and deoxygenation, ocean warming can lead to dramatic
changes in ecosystem assemblages, biodiversity loss,
population extinction, coral bleaching, infectious diseases
and changes in animal behaviour (including reproduction),
as well as the redistribution of habitats (García Molinos et
al., 2016; Gattuso et al., 2015; Ramírez et al., 2017). It is
hence essential to provide regular data and information
on the evolution and regional distribution of ocean
warming and its impacts on seascapes to support the
decade challenge for a healthy and resilient ocean where
marine ecosystems are understood, protected, restored
and managed (Ryabinin et al., 2019).
Findings: Status and trends
Ocean warming can be derived from direct
measurements of subsurface ocean temperature relying
on different measurement platforms like direct shipboard
observations, or autonomous instruments (Cheng et
al., 2022). Since 2005, technical evolutions under the
international Argo programme achieved near-global
ocean subsurface temperature sampling coverage from
the surface down to 2,000 m depth (Riser et al., 2016) –
a period which is often referred to as the golden period
for global climate studies (von Schuckmann et al.,
2016). Ocean warming estimates during the historical
dimension before the Argo era (i.e. from 2005 when
Argo reached targeted near-global sampling coverage),
reaching back to about the 1960s, is characterized by
spatially and seasonally inhomogeneous sampling,
including a strong interhemispheric bias favouring the
northern areas in some estimates (Cheng et al., 2022;
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 25
Figure 7. The annual OHC anomaly in 2023 relative to a 1981–2010 baseline for IAP/CAS data; units: 109 J m−2. Source: Cheng
et al. (2024b).
2023 OHC (0–2,000 m) anomaly relative to 1981–2010 baseline (IAP/CAS)
Figure 6. Global mean ocean heat content from 1960–2023 (in ZJ) for the upper 2,000 depth as derived as an ensemble mean
approach considering several subsurface temperature products and its uncertainty (shaded). Source: Minière et al. (2023).
26 / STATE OF THE OCEAN REPORT 2024
References
Abraham, J.P., Baringer, M., Bindoff, N.L., Boyer, T., Cheng,
L.J., Church, J.A., Conroy, J.L., Domingues, C.M.,
Fasullo, J.T., Gilson, J. and Goni, G., 2013. A review of
global ocean temperature observations: Implications
for ocean heat content estimates and climate change.
Reviews of Geophysics, Vol. 51, No. 3, pp. 450–83.
https://doi.org/10.1002/rog.20022
Bindoff, N.L., Cheung, W.W., Kairo, J.G., Arístegui, J.,
Guinder, V.A., Hallberg, R., Hilmi, N.J.M., Jiao, N.,
Karim, M.S., Levin, L. et al. 2019. Changing ocean,
marine ecosystems, and dependent communities. IPCC
Special Report on the Ocean and Cryosphere in a Changing
Climate, pp. 477–587. https://www.ipcc.ch/srocc/
Boyer, T., Domingues, C.M., Good, S.A., Johnson, G.C.,
Lyman, J.M., Ishii, M., Gouretski, V., Willis, J.K., Antonov,
J., Wijffels, S. et al. 2016. Sensitivity of global upper-
ocean heat content estimates to mapping methods, XBT
bias corrections, and baseline climatologies. Journal of
Climate, Vol. 29, No. 13, pp. 4817–42.
https://doi.org/10.1175/JCLI-D-15-0801.1
Cheng, L., Abraham, J., Goni, G., Boyer, T., Wijffels, S.,
Cowley, R., Gouretski, V., Reseghetti, F., Kizu, S., Dong,
S et al. 2016. XBT Science: Assessment of instrumental
biases and errors. Bulletin of the American Meteorological
Society, Vol. 97, No. 6, pp. 924–33.
https://doi.org/10.1175/BAMS-D-15-00031.1
Cheng, L., Abraham, J., Trenberth, K.E., Boyer, T., Mann,
M.E., Zhu, J., Wang, F., Yu, F., Locarnini, R., Fasullo, J. et
al. 2024a. New record ocean temperatures and related
climate indicators in 2023. Advances in Atmospheric
Sciences, pp. 1–15. https://doi.org/10.1007/s00376-024-
3378-5
Cheng, L., von Schuckmann, K., Abraham, J.P., Trenberth,
K.E., Mann, M.E., Zanna, L., England, M.H., Zika, J.D.,
Fasullo, J.T., Yu, Y. et al. 2022. Past and future ocean
warming. Nature Reviews Earth & Environment, Vol. 3, pp.
776–94. https://doi.org/10.1038/s43017-022-00345-1
Cheng, L., von Schuckmann, K., Minière, A., Hakuba, M.Z.,
Purkey, S., Schmidt, G.A. and Pan, Y. 2024b. Ocean heat
content in 2023. Nature Reviews Earth & Environment,
Vol. 3, pp. 776–94. https://doi.org/10.1038/s43017-024-
00539-9
Cowley, R., Wijffels, S., Cheng, L., Boyer, T. and Kizu, S.,
2013. Biases in expendable bathythermograph data: A
new view based on historical side-by-side comparisons.
Journal of Atmospheric and Oceanic Technology, Vol.
30, No. 6, pp. 1195-1225. https://doi.org/10.1175/
JTECH-D-12-00127.1
Frölicher, T.L., Fischer, E.M. and Gruber, N., 2018. Marine
heatwaves under global warming. Nature, Vol. 560, No.
7718, pp.360-364. https://doi.org/10.1038/s41586-018-
0383-9
García Molinos, J., Halpern, B.S., Schoeman, D.S.,
Brown, C.J., Kiessling, W., Moore, P.J., Pandolfi, J.M.,
Poloczanska, E.S., Richardson, A.J. and Burrows,
M.T. 2016. Climate velocity and the future global
redistribution of marine biodiversity. Nature Climate
Change, Vol. 6, pp. 83–88. https://doi.org/10.1038/
nclimate2769
Gattuso, J.P., Magnan, A., Billé, R., Cheung, W.W., Howes,
E.L., Joos, F., Allemand, D., Bopp, L., Cooley, S.R.,
Eakin, C.M. et al. 2015. Contrasting futures for ocean
and society from different anthropogenic CO2 emissions
scenarios. Science, Vol. 349, No. 6243.
https://doi.org/10.1126/science.aac4722.
Good, S.A., 2011. Depth biases in XBT data diagnosed using
bathymetry data. Journal of Atmospheric and Oceanic
Technology, Vol. 28, No. 2, pp. 287-300.
https://doi.org/10.1175/2010JTECHO773.1
Good, S.A., Martin, M.J. and Rayner, N.A., 2013. EN4: Quality
controlled ocean temperature and salinity profiles and
monthly objective analyses with uncertainty estimates.
Journal of Geophysical Research: Oceans, Vol. 118, No. 12,
pp. 6704–16. https://doi.org/10.1002/2013JC009067
Gulev, S.K., Thorne, P.W., Ahn, J., Dentener, F.J. Domingues,
C.M., Gerland, S., Gong, D., Kaufman, D.S., Nnamchi,
H.C., Quaas, J. et al. 2021. Changing state of the climate
system supplementary material. Climate Change 2021:
The Physical Science Basis. Contribution of Working Group
I to the Sixth Assessment Report of the Intergovernmental
Panel on Climate Change [Eds Masson-Delmotte, V., Zhai,
P., Pirani, A., Connors, S.L. Péan, C. Berger, S. Caud, N.
Chen, Y. Goldfarb, L. Gomis, M.I. et al.]. Available from
https://www.ipcc.ch/
Hakuba, M.Z., Frederikse, T. and Landerer, F.W., 2021.
Earth's energy imbalance from the ocean perspective
(2005–2019). Geophysical Research Letters, Vol. 48, No.
16, p. e2021GL093624.
https://doi.org/10.1029/2021GL093624
Hosoda, S., Ohira, T. and Nakamura, T., 2008. A monthly
mean dataset of global oceanic temperature and salinity
derived from Argo float observations. JAMSTEC Report of
Research and Development, Vol. 8, pp. 47–59.
https://doi.org/10.5918/jamstecr.8.47
Ishii, M. and Kimoto, M., 2009. Reevaluation of historical
ocean heat content variations with time-varying XBT and
MBT depth bias corrections. Journal of Oceanography,
Vol. 65, pp. 287–99. https://doi.org/10.1007/s10872-009-
0027-7
IPCC. 2018. Global Warming of 1.5° C. IPCC Special Report
[Eds Masson-Delmotte, V., Zhai, P., Pörtner, H.O.,
Roberts, D., Skea, J., Shukla, P.R., Pirani, A., Moufouma-
Okia, W., Péan, C., Pidcock, R. et al.].
https://www.ipcc.ch/sr15/.
______. 2021. Climate Change 2021: The Physical Science
Basis. Contribution of Working Group I to the Sixth
Assessment Report of the Intergovernmental Panel on
Climate Change [Eds Masson-Delmotte, V., Zhai, P.,
Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N.,
Chen, Y., Goldfarb, L., Gomis, M.I. et al.]. Cambridge, UK
and New York, Cambridge University Press.
https://doi.org/10.1017/9781009157896
Johnson, G.C., Landerer, F.W., Loeb, N.G., Lyman, J.M.,
Mayer, M., Swann, A.L. and Zhang, J., 2023. Closure
of Earth’s Global Seasonal Cycle of Energy Storage.
Surveys in Geophysics, pp. 1-13. https://doi.org/10.1007/
s10712-023-09797-6
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 27
Lyman, J.M. and Johnson, G.C., 2014. Estimating global
ocean heat content changes in the upper 1800 m since
1950 and the influence of climatology choice. Journal of
Climate, Vol. 27, No. 5, pp. 1945–57.
https://doi.org/10.1175/JCLI-D-12-00752.1
Li, G., Cheng, L., Zhu, J., Trenberth, K.E., Mann, M.E. and
Abraham, J.P. 2020. Increasing ocean stratification over
the past half-century. Nature Climate Change, Vol. 10, pp.
1116–23. https://www.nature.com/articles/s41558-020-
00918-2.
Loeb, N.G., Johnson, G.C., Thorsen, T.J., Lyman, J.M., Rose,
F.G. and Kato, S. 2021. Satellite and ocean data reveal
marked increase in Earth’s heating rate. Geophysical
Research Letters, Vol. 48, No. 13, p. e2021GL093047.
https://doi.org/10.1029/2021GL093047
Marti, F., Blazquez, A., Meyssignac, B., Ablain, M., Barnoud,
A., Fraudeau, R., Jugier, R., Chenal, J., Larnicol, G. and
Pfeffer, J., 2022. Monitoring the ocean heat content
change and the Earth energy imbalance from space
altimetry and space gravimetry. Earth System Science
Data, Vol. 14, No. 1, pp. 229–49. https://doi.org/10.5194/
essd-14-229-2022
Minière, A., von Schuckmann, K., Sallée, J.B. and Vogt,
L. 2023. Robust acceleration of Earth system heating
observed over the past six decades. Scientific Reports,
Vol. 13, No. 1, p. 22975. https://doi.org/10.1038/s41598-
023-49353-1
Ramírez, F., Afán, I., Davis, L.S. and Chiaradia, A. 2017.
Climate impacts on global hot spots of marine
biodiversity. Science Advances, Vol. 3, No. 2, p. e1601198.
https://doi.org/10.1126/sciadv.1601198.
Riser, S.C., Freeland, H.J., Roemmich, D., Wijffels, S.,
Troisi, A., Belbéoch, M., Gilbert, D., Xu, J., Pouliquen,
S., Thresher, A. et al. 2016. Fifteen years of ocean
observations with the global Argo array. Nature Climate
Change, Vol. 6, No. 2, pp.145–53. https://doi.org/10.1038/
nclimate2872
Ryabinin, V., Barbière, J., Haugan, P., Kullenberg, G.,
Smith, N., McLean, C., Troisi, A., Fischer, A., Aricò, S.,
Aarup, T. et al. 2019. The UN Decade of Ocean Science
for Sustainable Development. Frontiers in Marine
Science, Vol. 6, p. 470. https://www.frontiersin.org/
article/10.3389/fmars.2019.00470
von Schuckmann, K., Moreira, L. and Le Traon, P.Y., 2023.
Introduction to the 7th edition of the Copernicus Ocean
State Report (OSR7).State of the Planet, Vol. 1, pp. 1–7.
https://doi.org/10.5194/sp-1-osr7-1-2023
von Schuckmann, K., Palmer, M.D., Trenberth, K.E.,
Cazenave, A., Chambers, D., Champollion, N., Hansen,
J., Josey, S.A., Loeb, N., Mathieu, P.P. and Meyssignac,
B., 2016. An imperative to monitor Earth's energy
imbalance. Nature Climate Change, Vol. 6, No. 2, pp.
138–44. https://doi.org/10.1038/nclimate2876
Wijffels, S.E., Willis, J., Domingues, C.M., Barker, P., White,
N.J., Gronell, A., Ridgway, K. and Church, J.A., 2008.
Changing expendable bathythermograph fall rates and
their impact on estimates of thermosteric sea level rise.
Journal of Climate, Vol. 21, No. 21, pp. 5657–72.
https://doi.org/10.1175/2008JCLI2290.1
28 / STATE OF THE OCEAN REPORT 2024
Global ocean deoxygenation: Status and
challenges
Hernan Garcia,1 Takamitsu Ito,2 Zhankun Wang,1 James Reagan,1 Tim Boyer,1 Courtney Bouchard1 and Andreas Oschlies3
1 National Oceanic and Atmospheric Administration, USA
2 Georgia Institute of Technology, USA
3 GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
Observation-based global ocean deoxygenation estimates
require the aggregation and analysis of insitu O2 data that
have been collected worldwide over several decades using
different water samplers, methods and unit reporting
protocols. While O2 is a frequently sampled essential
ocean variable, its global 4-D (time, depth, latitude and
longitude) coverage and data quality (e.g. precision,
reproducibility, accuracy and uncertainty) are not well
quantified. All O2 measurements in the instrumental
record include some measurement error. Thus, the
analysis of compiled O2 observations require an internally
consistent, reproducible and quantifiable quality control
(QC) assessment of the time-variant quality of the
measurements.
Figure 8. Ocean OI (Pmol) as a function of depth (Garcia et
al., 2024) (Garcia et al., 2024). Source: World Ocean Database.
Introduction
Dissolved oxygen (O2) is required to sustain aerobic ocean
life and oxidation of organic matter. Its distribution in the
open ocean and coastal regions is sensitive to natural
biogeochemical and physical processes that are being
increasingly impacted by the ocean uptake of excess
Earth energy imbalance (EEI) from the addition of human-
induced greenhouse gasses (e.g. CO2, CH4 and N2O) and
excess nutrient inputs. About 90% of the EEI is being
absorbed by the ocean, resulting in a cumulative increase
in ocean heat content (OHC), mostly contained in the upper
2,000 m of the water column (von Schuckmann et al.,
2022). The OHC gained can impact ocean overturning
circulation, upper ocean stratification and lower the
preformed O2 content of near-surface high latitude waters,
reaching the interior deeper ocean through ventilation.
Near-surface thermal stratification intensification
weakens vertical mixing and the vertical flux of generally
nutrient-richer deeper waters into the euphotic zone that
fuels biologically mediated O2 production. The reduction
in ocean O2 loss (i.e. O2 inventory, OI) has been termed
‘deoxygenation’. While ocean deoxygenation would not
affect the much larger atmospheric O2 inventory, it can
have long-term negative impacts on the health of coastal
and large marine ecosystems, a sustainable blue economy
and coastal communities that depend on the ocean (e.g.
tourism, fisheries, aquaculture, ecosystem services and
marine protected areas). Nutrient over-enrichment of
coastal areas results in deoxygenation and the emergence
of hypoxia zones.
Findings: Status and trends
Deoxygenation results from a combination of climate
change impacts and feedback mechanisms that are
not well understood and quantified. More observations,
particularly in the Southern Hemisphere, data synthesis
and modelling efforts are needed to assess the
relative impact of factors causing ocean deoxygenation
superimposed on natural low-frequency variability. Here,
we describe some of the challenges associated with
resolving deoxygenation trends and uncertainties.
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 29
Since the 1900s, O2 measurements have been obtained
using modifications of the Winkler (1888) titration method.
Carpenter (1965) indicated that the accuracy of the
method using O2-saturated water is ~0.1%, or about ±0.22
µmol kg-1. The shipboard measuring precision of high-
quality data collected since the 1980s in relatively O2-rich
deep waters is in the range of about ±0.15 to 0.87 µmol
kg-1 (Saunders, 1986; Langdon, 2010). In the mid–1980s,
different types of O2 sensors have been mounted on CTD
frames, buoys, underway systems and, more recently,
on gliders and Argo and BGC Argo floats. The sensors
have a precision of ≥ ±2 µmol kg-1 range (Grégoire etal.
2021). It is not the scope of this brief note to quantify all
potential sources of error. One pressing problem is that
the accuracy of the data collected is difficult to quantify
directly because absolute or adopted reference standards
have not been in use over time.
The ocean OI varies as a function of depth and basin
(Figure 8). The 0–5,500 m depth global ocean OI is
~238.2 Pmol (Garcia etal., 2024). What is the net global
ocean OI loss in the past decades? Global deoxygenation
trend estimates vary significantly between observational
studies. Schmidtko et al. (2017) reported a negative
trend of about 0.96 ±0.43 Pmol decade-1 (1960–2014);
Ito (2022) indicated a negative trend of 0.33 ±0.05 Pmol
decade-1 (1965–2015); Roach and Bindoff (2023) indicated
a global ocean loss of 0.84 ±0.42% for the 1970–2010 time
period (about 0.35 ±0.18 Pmol decade-1 assuming an OI of
238.2 ±1.1 Pmol). The trends suggest approximate OI
losses after 60 years of 0.83 to 2.42% (equivalent to
about 1.43 to 4.15 µmol kg-1 . Resolving such OI changes
requires QC O2 data spanning several years and high 4-D
coverage. Different ocean regions and depths can have
different trends and OI losses.
Comparing, and independently reproducing, published
deoxygenation trends is difficult. Each study uses
different baseline time periods, data compilations, data
QC metrics and mapping algorithms (e.g. grid size and
data gap treatment). One initial step to help quantify
differences between the mappings could be conducting
an international intercomparison exercise using common
reference data.
The global ocean mean O2 solubility content loss
attributable to ocean warming alone is relatively small
when compared to the net OI loss. Figure 9 shows an
estimate of O2 solubility loss (0–1,500 m depth) after 60
years due to ocean warming alone (Garcia etal., 2024. The
global mean solubility estimated loss varies from about
0.5 to 3.1 µmol kg-1.
Figure 9. Global mean O2 solubility content decrease as a
function of depth after 60 years (Garcia et al., 2024). Source:
World Ocean Database.
O2 solubility change (μmol kg-1)
Depth (m)
Conclusions and next steps
The trends suggest a relatively rapid ocean response to
recent climate change with potentially long-term negative
impacts on the health and sustainability of coastal and
large marine ecosystems. What is unclear is whether
deoxygenation is accelerating in response to OHC
increases (Li etal., 2023). The use of machine learning
and artificial intelligence to potentially gain additional
insight seems promising (Sharp etal., 2022). Developing
international QC best practices and standards remains
an issue (Grégoire etal., 2021). Public engagement and
communication are needed for science-based informed
policy decision-making, societal adaption and sustainable
blue economy strategies.
30 / STATE OF THE OCEAN REPORT 2024
References
Carpenter, J.H. 1965. The accuracy of the Winkler
method for dissolved oxygen analysis 1. Limnology and
Oceanography, Vol. 10, No. 1, pp. 135–40. https://doi.
org/10.4319/lo.1965.10.1.0135
Garcia, H.E., Wang, Z., Bouchard, C., Cross, S. L., Paver,
C.R., Reagan, J.R., Boyer, T.P., Locarnini, R.A., Mishonov,
A.V., Baranova, O.K. and Seidov, D. 2024. World Ocean
Atlas 2023, Volume 3: Dissolved Oxygen, Apparent Oxygen
Utilization, Dissolved Oxygen Saturation and 30-year
Climate Normal. l. NOAA Atlas NESDIS 91.
Grégoire, M., Garçon, V., Garcia, H., Breitburg, D., Isensee,
K., Oschlies, A., Telszewski, M., Barth, A., Bittig, H.C.,
Carstensen, J. et al. 2021. A global ocean oxygen
database and atlas for assessing and predicting
deoxygenation and ocean health in the open and coastal
ocean.Frontiers in Marine Science,Vol. 8, p. 724913.
https://doi.org/10.3389/fmars.2021.724913
Ito, T., 2022. Optimal interpolation of global dissolved
oxygen: 1965–2015. Geoscience Data Journal, Vol. 9, No.
99, pp 167–76 https://doi.org/10.1002/gdj3.130
Langdon, C. 2010. Determination of dissolved oxygen in
seawater by Winkler titration using amperometric
technique. The GO-SHIP Repeat Hydrology Manual: A
Collection of Expert Reports and Guidelines. IOCCP Report
Number 14. E.M. Hood, C.L. Sabine and B.M. SLoyan
(eds).
Li, Z., England, M.H. and Groeskamp, S. 2023. Recent
acceleration in global ocean heat accumulation by mode
and intermediate waters.Nature Communications,Vol.
14, No. 1, p. 6888. https://doi.org/10.1038/s41467-023-
42468-z
Roach, C.J. and Bindoff, N.L. 2023. Developing a new oxygen
atlas of the world’s oceans using data interpolating
variational analysis.Journal of Atmospheric and Oceanic
Technology,Vol. 40, No. 11, pp. 1475–91. https://doi.
org/10.1175/JTECH-D-23-0007.1
Saunders, P.M. 1986. The accuracy of measurement
of salinity, oxygen and temperature in the deep
ocean.Journal of Physical Oceanography,Vol. 16,
No. 1, pp. 189–95. https://doi.org/10.1175/1520-
0485(1986)016<0189:TAOMOS>2.0.CO;2
Schmidtko, S., Stramma, L. and Visbeck, M. 2017. Decline
in global oceanic oxygen content during the past five
decades.Nature,Vol. 542, No. 7641, pp. 335–39. https://
doi.org/10.1038/nature21399.
von Schuckmann, K., Minère, A., Gues, F., Cuesta-
Valero, F.J., Kirchengast, G., Adusumilli, S., Straneo,
F., Allan, R., Barker, P.M., Beltrami, H. et al. 2022.
Heat stored in the Earth system 1960–2020: where
does the energy go?.Earth System Science Data
Discussions,2022, pp. 1–55. https://essd.copernicus.org/
articles/15/1675/2023/
Sharp, J.D., Fassbender, A.J., Carter, B.R., Johnson, G.C.,
Schultz, C. and Dunne, J.P. 2022. GOBAI-O2: Temporally
and spatially resolved fields of ocean interior dissolved
oxygen over nearly two decades.Earth System Science
Data Discussions,2022, pp. 1–46. https://doi.org/10.5194/
essd-15-4481-2023
Winkler, L.W. 1888. Die Bestimmung des im Wasser
gelösten Sauerstoffes. Berichte der Deutschen
Chemischen Gesellschaft, Vol. 21, No. 2, pp. 2843–54.
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 31
Biodiversity knowledge and threats on
marine life: Assessing no-take zones as
a refuge for marine species
Ward Appeltans,1 Pieter Provoost,1 Silas C. Principe,1 Alex Driedger,2 Tom Webb3 and Mark J. Costello4
1 Intergovernmental Oceanographic Commission of UNESCO
2 Anthropocene Institute, USA
3 University of Sheffield, UK
4 Nord University, Norway
Introduction
In our preceding StOR section entitled ‘New knowledge
on and threats to marine biodiversity’ (Costello et al.,
2022), our emphasis lay on elucidating the existing state
of biodiversity knowledge. In this chapter, our focus shifts
towards the conservation status of marine biodiversity. The
UN 2030 Agenda for Sustainable Development advocates
for heightened protection of marine biodiversity to ensure
sustainable food security. This aligns with the targets
outlined in the Kunming-Montreal Global Biodiversity
Framework under the Convention on Biological Diversity,
to protect 30% of the ocean by 2030, emphasizing both
conservation (Targets 1, 2, 3 and 4) and sustainable
resource utilization (Targets 5, 9, 10 and 11), as well as
ensuring knowledge is accessible (Target 12). To monitor
progress, we provide statistics on the total number of
marine species, and those most vulnerable to extinction,
within designated Marine Protected or Managed Areas
(MPA) as of now.
1 See. Ocean Biodiversity Information System. Intergovernmental Oceanographic Commission of UNESCO: https://www.obis.org.
2 See Global Biodiversity Information Facility:https://www.gbif.org.
We used a definition of MPA-based areas where
regulations impose significant restrictions on fishing
compared to adjacent regions (excluding areas that are
not protected from fishing), denoted by protection scores
of 3 (partly protected, n = 1,865 and 5.9 % of ocean area),
4 (very limited to fishing, n = 968 and 1.2 % of ocean area)
and 5 (no fishing, n = 4,201 and 2.4 % of ocean area) (total
n = 7,034) (Protected Seas, 2024). This classification
of areas is focused on the dominant threats to marine
species, habitats and food webs and is based on direct
assessment of national management regulations. This
avoids ambiguity where places may be called MPA but
may or may not allow different human activities. Due to
some overlap of MPA boundaries, when combined, they
constitute 9.0% of the entire ocean (comprising 2.8%
of the high seas and 18.7% of the country’s Exclusive
Economic Zones). To conduct our analysis, we downloaded
and indexed marine species distribution data sourced
from the Ocean Biodiversity Information System1 and the
Global Biodiversity Information Facility.2
Figure 10. Fraction of marine species in the MPA by higher-level taxonomic groups. We consider MPA those with a level of
fishing protection higher than 3. Thus, the fraction in level 2 or less includes species in areas with negligible or no protection
(i.e. not in MPAs). Source: OBIS/IOC-UNESCO.
32 / STATE OF THE OCEAN REPORT 2024
Figure 11. Level of protection for threatened marine species (IUCN red list categories CR, EN, VU). Each dot represents the
percentage of a species’ distribution in OBIS within a certain MPA level of protection from fishing. Source: OBIS/IOC-UNESCO.
VU
EN
CR
2 or lower
3
4
5
0%
1%
10%
100%
0%
1%
10%
100%
0%
1%
10%
100%
Fraction of known distribution in OBIS
Fraction
IQR
lfp
2 or lower
3
4
5
Findings: Status and trends
Number of marine species within MPA
As of now, a total of 93,106 marine species have been
documented within the MPA. These records encompass
nearly 50 million distribution data points, and half were
recorded in the past eight years. Looking at higher-level
taxonomic groups (Figure 10), most species of marine
turtles and seabirds and more than 50% of fish, sharks,
rays and mammals have reported occurrence records
that fall within at least one current MPA. Nevertheless, a
substantial portion of marine life lacks designated refuge
areas (level 2 or less).
Number of threatened marine species within MPA
Among the 1,473 marine species listed on the global
IUCN Red List as being at risk of extinction, specifically
categorized as Vulnerable (VU), Endangered (EN) and
Critically Endangered (CR), 1,061 (72%) are currently
reported within at least one MPA. These figures diminish to
912 (62%), 622 (42%) and 794 (54%) for each MPA category
3, 4 and 5, respectively. Based on known occurrences, we
calculated the fraction (%) of the species’ distribution
range (habitat) that falls within the MPA coverage. For the
majority of those threatened species, only a small fraction
(median 7%) of their distribution as reported in OBIS is
covered by MPA areas (Figure 11).
Conclusions and next steps
It is remarkable that about half of all catalogued
marine species have been reported in MPA, considering
that these occupy only 9% of the total ocean area
(Figure 10). Furthermore, a significant 72% of species
facing the threat of extinction find refuge within MPA
and 54% even occur in the highest level of protection
(also called no-take zones). However, it is important to
note that only a fraction of their reported distribution
falls under the highest level of protection (Figure 11),
raising questions about the effectiveness of safeguarding
threatened species in these areas.
That MPA have more published species distribution
records than non-MPA may reflect that areas of scientific
interest have been designated as MPA, and that once
designated there is increased interest in understanding
the biodiversity of these areas (50% of all data in MPA
were collected in the past eight years). It is important to
acknowledge a caveat in these statistics – the data do not
provide insight into the current presence of these species
in MPA, nor their abundance both inside and outside
these designated areas. Nevertheless, these findings
are promising, suggesting that existing MPA areas serve
as a commendable starting point in the endeavour to
safeguard marine biodiversity, crucial for supporting
both food security and the overall health of our oceans.
Establishing new MPAs and increasing their coverage have
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 33
the potential of maximizing fisheries and improving the
delivery of ecosystem services to the associated human
communities. In addition, they show how indicators of
progress in conservation can be quickly derived from data
that are accessible to everyone at no cost (i.e. open access)
and be reproducible. Incentivizing sharing more data to
global databases such as OBIS would increase the spatial
and temporal resolution of such indicators, providing
more refined information to guide the management and
conservation of marine ecosystems.
Acknowledgements
We are grateful to the thousands of data providers who
collectively have published several 100 million of marine
species distribution data in the public domain through
OBIS and GBIF. We also thank ProtectedSeas for providing
us with the data and shapefiles of the MPA. Both Silas
Principe and Mark J. Costello received support from
Horizon Europe project MPA Europe (GA 101059988).
References
Costello, M.J., Webb J.T., Provoost P. and Appeltans
W. 2022. New knowledge on and threats to marine
biodiversity. State of the Ocean Report: Pilot Edition. Paris,
IOC-UNESCO, IOC Technical Series, 173, pp 26–27.
Additional resources
Data processing source code and download links are
available at: https://github.com/iobis/protectedseas-
statistics
The ProtectedSeas Navigator Map of Conservation
Regulations. Available at:
https://map.navigatormap.org
34 / STATE OF THE OCEAN REPORT 2024
Marine spatial planning
A global update
Michele Quesada da Silva,1 Joanna Smith,2 Ingela Isaksson,3 Joseph O. Ansong4 and Zhiwei Zhang5
1 Intergovernmental Oceanographic Commission of UNESCO
2 The Nature Conservancy, Canada
3 Swedish Agency for Marine and Water Management, Sweden
4 University of Liverpool, UK
5 Intergovernmental Oceanographic Commission of UNESCO
Introduction
Marine (or Maritime) spatial planning (MSP) is a key area-
based policy to sustainably manage human activities
within maritime territories of countries on all continents. It
is a process to allocate human activities as well as priority
areas for coastal and marine protection and restoration to
achieve a productive, healthy and resilient ocean.
Through the joint MSP roadmap, IOC-UNESCO is
continuously working with the European Commission
to promote MSP (IOC-UNESCO/European Commission,
2022). With the support of countries, collaborators and
MSP practitioners, IOC-UNESCO is also tracking the
status of MSP processes through its survey on MSP
sent every two years to countries. In addition, status
and updates are researched through complementary
desk research of key sources, such as the European
MSP Platform, governmental and project websites and
publications, as well as discussions with the MSPglobal
network of MSP practitioners.
Key findings, trends and status
By the end of 2023, a total of 126 countries/territories were
identified as engaged in MSP initiatives – an increase of
20% from the assessment completed for the 2022 Pilot
StOR (IOC-UNESCO, 2022), most notably in Africa and
Oceania (Figure 12). Engagement in MSP is defined here
as the existence of at least a pilot project in the country or
an MSP working group established by the government to
initiate discussions and scoping.
The increased number in Africa comes from projects
led by international organizations and cooperation
mechanisms supporting MSP in the Benguela Current,
Western Mediterranean, Western Indian Ocean and
part of the Gulf of Guinea (Mami Wata, 2023; MARISMA,
2023; MSPglobal, 2023a; SwAM, 2023a; TNC, 2023).
These projects are mainly focused on the development
of capacities and assessments relevant for the planning
process. Some areas in Africa are yet to fully engage in
MSP, such as Central Africa.
3 See https://oceanpanel.org/.
4 See https://www.cbd.int/doc/decisions/cop-15/cop-15-dec-04-en.pdf.
Initiatives in Oceania (MACBIO, 2023; Waitt Institute,
2023), the Caribbean (OECS, 2023) and Southeast Asia
(COBSEA, 2023; WESTPAC, 2023) reflect similar support
by international cooperation. In the continental part of the
Americas, most of the countries have engaged in MSP but
approved plans are mainly in North America. On the other
hand, the number of countries engaged in MSP in Europe
remains high and stable due to the European Union
Directive on MSP, which required all its coastal countries
to approve a marine spatial plan by 2021; although a few
plans are yet to be adopted (EU MSP Platform, 2023).
Notably, 45 countries/territories have now approved
national, subnational and/or local plans, a 10% increase
on last year. This number is still low, as the development
and approval of a marine spatial plan takes years due to the
nature of the necessary assessments and engagement of
stakeholders. It is critical to note that the transition from
MSP discussions to approved plans does not happen until
an authority is appointed. Besides, in countries that lack a
legal framework, which can take years to be established,
plans can be used as a guiding document, but this might
result in implementation gaps.
MSP is widely used as a platform for multisectoral
engagement and negotiation of diverse interests. A
current common trend is the link between MSP and the
development of sustainable ocean (or blue) economies.
This is clearly exemplified by a more than 25% increase
in the number of parties that have joined the High Level
Panel for a Sustainable Ocean Economy3 and their
commitment to develop sustainable ocean plans, an
umbrella for marine policies that includes MSP (Ocean
Panel, 2023). At the same time, the MSP approach is
continually promoting the achievement of significant
conservation goals, such as Target 1 (on participatory,
integrated and biodiversity inclusive spatial planning)
and Target 3 (on at least 30% of coastal and marine
areas effectively conserved and managed by 2030) of the
Kunming-Montreal Global Biodiversity Framework.4 MSP
has become the focus of calls for social inclusion and
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 35
Figure 12. IOC-UNESCO assessments about marine spatial planning status around the world: a. Number of countries/
territories engaged in MSP; and b. Number of countries/territories with approved marine spatial plans at national, subnational
and/or local level. Source: IOC-UNESCO.
a. Countries/territories engaged in marine spatial planning
b. Countries/territories with approved marine spatial plans
Africa Asia Europe Oceania Total
Total
Americas &
Caribbean
Africa Asia Europe OceaniaAmericas &
Caribbean
7
18 27
17
31 36
812 15
25 31 31
410 17
17
102
126
15
39
45
2 2 2
6
21
25
2
7 7
58 8
013
2017 2022 2023
social justice, especially concerning Indigenous peoples
and local communities (IPLCs) as well inclusion of gender
and poverty issues (MSPglobal, 2023b; SwAM, 2023b).
Finally, the development of climate-smart marine
spatial plans is seen as an opportunity to integrate
climate adaptation and mitigation measures towards
resilient marine ecosystems and less vulnerable
coastal communities and economies. However, the full
integration between MSP and climate change is still
limited (UNESCO-IOC, 2021) and more work is needed to
clarify approaches for climate-smart MSP.
MSP is a process that facilitates the adoption of a
transparent, inclusive and participatory approach to multi-
objective planning. In addition to planning national marine
areas, there are growing interests in transboundary MSP
(e.g. Baltic Sea, North Sea and Western Indian Ocean) and
its application in Areas Beyond National Jurisdiction.
Conclusion and next steps
The adoption of MSP continues to accelerate worldwide,
with the approval and implementation of marine spatial
plans still relatively low beyond Europe, perhaps due to
the lack of legal frameworks. Monitoring and evaluation
of MSP around the word is important to understand
how the plans are implemented and can be improved.
An in-depth monitoring and evaluation needs to cover
the following: (i) the process itself, including degree of
stakeholder engagement; (ii) the plan and its relevance;
(iii) the implementation of the plan; and (iv) the outcomes
of the plan (UNESCO-IOC/European Commission, 2021).
As a first step, to analyse the first two aspects, a typology
of ten criteria was proposed in the 2022 Pilot StOR and
presented during the 3rd International Conference on
MSP. IOC-UNESCO will implement this typology for the
first time in its next survey on MSP, which is scheduled
for mid-2024.
36 / STATE OF THE OCEAN REPORT 2024
References
COBSEA, 2023. Marine and Coastal Ecosystems Framework.
https://wedocs.unep.org/20.500.11822/42196
EU MSP Platform, 2023. MSP in the EU: Countries. https://
maritime-spatial-planning.ec.europa.eu/msp-practice/
countries
IOC-UNESCO. 2022. State of the Ocean Report: Pilot Edition.
Paris, IOC-UNESCO. (IOC Technical Series, 173) https://
unesdoc.unesco.org/ark:/48223/pf0000381921
IOC-UNESCO/European Commission. 2022. Updated Joint
Roadmap to Accelerate Marine/Maritime Spatial Planning
Processes Worldwide – MSProadmap (2022–2027). Paris,
UNESCO. (IOC Technical Series, 182) https://unesdoc.
unesco.org/ark:/48223/pf0000385718
MACBIO. 2023. MACBIO Project. https://macbio-pacific.
info/
Mami Wata. 2023. The Mami Wata Project. https://
mamiwataproject.org/
MARISMA. 2023. The MARISMA Project. https://marisma-
bclme.com/
MSPglobal. 2023a. Pilot Project: Western Mediterranean.
https://www.mspglobal2030.org/msp-global/pilot-
project-west-mediterranean/
MSPglobal. 2023b. MSPglobal 2.0 Dialogues: Engaging
Indigenous Peoples and Local Communities in MSP.
https://www.mspglobal2030.org/dialogues-iplcs-in-
msp/
Ocean Panel. 2023. What is the Ocean Panel? https://
oceanpanel.org/about-ocean-panel/
OECS. 2023. Caribbean Regional Oceanscape Project. https://
oecs.org/en/crop
SwAM. 2023a. Cooperation with the Western Indian Ocean.
https://www.havochvatten.se/en/eu-and-international/
international-cooperation/bilateral-environmental-and-
climate-cooperation/cooperation-with-the-western-
indian-ocean.html
SwAM. 2023b. Poverty and Gender Considerations in Marine
Spatial Planning. https://www.havochvatten.se/en/
our-organization/publications/swam-publications/2023-
02-12-poverty-and-gender-considerations-in-marine-
spatial-planning.html
TNC. 2023. Our Projects. https://marineplanning.org/
our-projects/
UNESCO-IOC. 2021. MSPglobal Policy Brief: Climate Change
and Marine Spatial Planning. Paris, UNESCO. (IOC Policy
Brief no 3) https://unesdoc.unesco.org/ark:/48223/
pf0000375721
UNESCO-IOC/European Commission. 2021. MSPglobal
International Guide on Marine/Maritime Spatial Planning.
Paris, UNESCO. (IOC Manuals and Guides no 89) https://
unesdoc.unesco.org/ark:/48223/pf0000379196
Waitt Institute. 2023. Our Projects. https://www.waittinstitute.
org/initiatives
WESTPAC. 2023. UN21: Accelerate Marine Spatial Planning
in the Western Pacific. https://ioc-westpac.org/decade-
actions/msp/
Additional resources
Country profiles about the status of MSP around the
world: https://www.mspglobal2030.org/msp-roadmap/
msp-around-the-world/
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 37
Protecting coastal blue carbon
ecosystems
Elisabetta Bonotto1
1 Intergovernmental Oceanographic Commission of UNESCO
Introduction
Healthy marine and coastal ecosystems provide a wide
array of benefits, including biodiversity and habitat
support, water filtration, coastal protection from storm
surges and erosion, carbon sequestration and storage,
and livelihoods of coastal communities, as well as
aesthetic and recreational values. According to the
Intergovernmental Panel on Climate Change (IPCC), all
biologically driven carbon fluxes and storage in marine
systems that are amenable to management can be
considered as blue carbon (IPCC, 2019). At present,
this definition encompasses mangroves, tidal marshes
and seagrasses, for which established methodologies
for carbon accounting are available and recognized
by the IPCC (IPCC, 2014). Other ecosystems, such as
macroalgae, benthic sediments and mudflats, are
emerging as blue carbon, but uncertainties remain as to
the rates of sequestration and permanence of carbon in
these habitats (Conservation International et al., 2023).
Key findings, trends and status
Coastal blue carbon ecosystems sequester carbon from
the atmosphere and store it in the biomass and in the
sediments below for hundreds to thousands of years, if
undisturbed, with the highest rates of nature-based carbon
sequestration per area: 168 g C m-2 yr-1 in mangroves, 242 g
C m-2 yr-1 in tidal marshes and 83 g C m-2 yr-1 in seagrasses
(Conservation International et al., 2023). However, when
these ecosystems are degraded or lost, for example when
mangroves are converted to shrimp ponds, up to 92% of
their original carbon stocks, as well as other greenhouse
gases such as methane and nitrous oxide, are released
into the atmosphere, thus exacerbating climate change
(Schindler Murray and Milligan, 2023). It is estimated that
Figure 13. Status of inclusion of coastal blue carbon ecosystems for climate change mitigation in IPBC country Partners’
new or updated Nationally Determined Contributions (NDC) to the Paris Agreement (as of 31 March 2024) and national
greenhouse gas inventories (GHGI). Four out of 18 countries include coastal blue carbon ecosystems in both the NDC and
GHGI (Indonesia, Republic of Korea, United Arab Emirates and United States of America); 6 out of 18 countries include coastal
blue carbon ecosystems in the NDC only (Costa Rica, Fiji, Papua New Guinea, Seychelles, Sierra Leone and the United
Kingdom of Great Britain and Northern Ireland); 3 out of 18 countries include coastal blue carbon ecosystems in the GHGI
only (Australia, Japan and Madagascar); and 4 out of 18 countries include coastal blue carbon ecosystems neither in the NDC
nor in the GHGI (France, Monaco, Norway and Somalia). Note: Australia, Republic of Korea and the United States of America
are the only countries that include coastal blue carbon ecosystems in the GHG under wetlands. The rest of the countries
include mangroves under the forest sector. Source: IPBC with data from Lecerf et al. (2023) and the IPBC Survey (2021, 2022
and 2024), validated by IPBC country Partners’ focal points.
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GHGI only
NDC only
Neither NDC nor GHGI
Both NDC and GHGI
38 / STATE OF THE OCEAN REPORT 2024
Figure 14. Status of inclusion of coastal blue carbon ecosystems for climate change mitigation in IPBC country Partners’
new or updated Nationally Determined Contributions (NDC) to the Paris Agreement and new or updated National Biodiversity
Strategies and Action Plans (NBSAP). Four out of 18 countries include coastal blue carbon ecosystems in both the NDC and
NBSAP (Fiji, Indonesia, Seychelles and the United Kingdom of Great Britain and Northern Ireland); 6 out of 18 countries
include coastal blue carbon ecosystems in the NDC only (Costa Rica, Papua New Guinea, Republic of Korea, Sierra Leone,
United Arab Emirates and the United States of America); 6 out of 18 countries include coastal blue carbon ecosystems in
the NBSAP only (Australia, France, Japan, Madagascar, Norway and Somalia); and 2 out of 18 countries include coastal blue
carbon ecosystems neither in the NDC nor in the NBSAP (Monaco and Portugal). Note: At the time of drafting this report, no
information is available about the inclusion of coastal blue carbon ecosystems in the NBSAP of the United Arab Emirates and
the United States of America. Source: IPBC with data from Lecerf et al. (2023), the Secretariat of the Convention on Biological
Diversity (CBD) (updated as of 31 March 2024) and the IPBC Survey (2021, 2022 and 2024), validated by IPBC country Partner’s
focal points.
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NBSAP only
NDC only
Both NDC and NBSAP
Neither NDC nor NBSAP
human activities such as destructive fishing practices,
pollution, coastal infrastructure development and land-
use change, combined with the impacts of climate change
on these ecosystems, have resulted in the loss of 20–35%
of their global cover since 1970 (Schindler Murray and
Milligan, 2023).
At the 21st Conference of the Parties to the United Nations
Framework Convention on Climate Change (UNFCCC COP
21) in 2015 in Paris, France, the International Partnership
for Blue Carbon (IPBC) was launched under the leadership
of Australia with the aim to increase global efforts to
conserve, restore and sustainably manage coastal blue
carbon ecosystems for climate change mitigation and
adaptation, biodiversity, ocean economies and livelihoods
of coastal communities. In 2023, the IPBC counts over
50 partners, including 18 countries that spearhead blue
carbon action at all levels, and is coordinated by Australia
with the support of the IOC/UNESCO.
Increased efforts towards the protection of coastal habitats
can take several forms. For example, 62 out of 148 countries
included the conservation or restoration of coastal blue
carbon ecosystems as a mitigation component of their
new or updated Nationally Determined Contribution (NDC)
to the Paris Agreement, as of October 2023 (Lecerf et al.,
2023). The inclusion of coastal blue carbon ecosystems
in national climate mitigation strategies goes hand in
hand with their inclusion in the national greenhouse gas
inventory (GHGI); however, to date only a few countries
have included coastal blue carbon ecosystems in both the
NDC and GHGI, while some countries may include them
in the NDC only, or in the GHGI but not in the NDC (Figure
13 provides an overview for the 18 IPBC country Partners).
Some countries – such as Somalia in the IPBC – may also
recognize coastal wetlands for their adaptation value in
their NDC, even when clear, quantifiable targets related
to their climate mitigation potential are not available yet.
Besides NDCs, some countries also recognize the role
of coastal wetlands for climate change mitigation and
adaptation in their National Biodiversity Strategies and
Action Plans (NBSAPs, Figure 14).
Other international frameworks, such as the Convention
on Wetlands of International Importance (Ramsar
Convention) and the UNESCO World Heritage Convention,
A HEALTHY AND RESILIENT OCEAN WHERE MARINE ECOSYSTEMS ARE UNDERSTOOD, PROTECTED, RESTORED AND MANAGED / 39
Table 1. Number and total area (ha) of Ramsar Sites and UNESCO World Heritage Sites in IPBC country Partners that
contain one or more coastal blue carbon ecosystems.
IPBC country Partner
Number of
Ramsar Sites
containing one
or more coastal
blue carbon
ecosystems
Total area of
Ramsar Sites
containing
one or more
coastal
blue carbon
ecosystems
(ha)
Number of
UNESCO
World
Heritage
Sites
containing
one or more
coastal
blue carbon
ecosystems
Total area of
UNESCO World
Heritage Sites
containing one or
more coastal blue
carbon ecosystems
(ha)
Australia 27 3623 828 6 39138 400
Costa Rica 7 240 190 2 346 700
Fiji 1 134 900 - -
France 17 650 401 3 70170 100
Indonesia 5 1292 976 2 297 847
Japan 10 27 727 1 71 100
Madagascar 6 623 569 - -
Monaco 1 23 - -
Norway 12 16 325 1 122 712
Papua New Guinea 1 590 000 - -
Portugal 6 59 538 - -
Republic of Korea 8 18 010 4 129 346
Seychelles 2 44 024 1 35 000
Sierra Leone 1 295 000 - -
Somalia - - - -
United Arab Emirates 5 18 816 - -
United Kingdom of Great Britain and
Northern Ireland 65 455 548 2 422 101
United States of America 8 1037 470 3 46613 637
Source: IPBC (2024) with data from the Secretariat of the Convention on Wetlands and the UNESCO World Heritage Centre
(2020) (updated as of 31 March 2024), validated by IPBC country Partners’ focal points.
also provide opportunities for countries to accelerate the
protection of coastal habitats, for example, through the
designation of Ramsar Sites and UNESCO World Heritage
Sites in coastal areas encompassing blue carbon
ecosystems, which may lay the groundwork for a better
protection of these habitats (Table 1).
Conclusions and next steps
Strengthening and aligning commitments across relevant
international policy frameworks is one of the possible
ways for countries to increase their efforts towards a
better protection of coastal blue carbon ecosystems (IUCN
and Conservation International, 2023). Progressively
integrating coastal wetlands into national climate and
biodiversity strategies, while at the same time reinforcing
existing protection mechanisms provided by multilateral
treaties such as the Ramsar Convention and the UNESCO
World Heritage Convention allows countries to streamline
national action on blue carbon. The global stocktake
process, the next round of NDCs due in 2025 and the new
Kunming-Montreal Global Biodiversity Framework (GBF)
all provide an opportunity for countries to enhance their
current ambition, and international networks such as the
IPBC and the Blue Carbon Initiative (BCI) offer a space
for governments, scientists and practitioners to exchange
knowledge and learn from each other’s experiences to
collectively drive global blue carbon action forward.
References
Conservation International, the Blue Carbon Initiative,
International Blue Carbon Institute. 2023. Actionable