Our Work

Lead agency: World Meteorological Organization

Formation and Support of WG 38

Working Group 38 was formed in 2008 because of growing concern about the impact of atmospheric deposition of both natural and anthropogenic substances on ocean chemistry, biogeochemistry, and climate. Since its formation, it has held in-person meetings or workshops at the University of Arizona, Tucson, AZ, in 2008, at IMO in London in 2010, in Malta in 2011, and at the University of East Anglia, Norwich, UK in 2013 and 2017. It has held a virtual workshop in 2020 and a combined virtual/in-person workshop in 2022 in Gqeberha South Africa. Sponsors of those WG 38 efforts have included the World Meteorological Organization (WMO), the International Maritime Organization (IMO), the ICS Scientific Committee on Oceanic Research (SCOR), The Swedish International Development Agency (SIDA), the European Commission Joint Research Centre, the University of Arizona, the International Environment Institute at the University of Malta, the University of East Anglia, the US National Science Foundation, Nelson Mandela University and its Coastal and Marine Research Center, the British High Commission Pretoria, and the UK Science and Innovation Network in South Africa.

Activities of WG 38, 2008-2017

Initial workshops, 2008-2012

After addressing the initial terms of reference during workshops in London and Malta, the results were synthesized in GESAMP Reports and Studies 84, “The Atmospheric Input of Chemicals to the Ocean”, and four scientific papers were published in the peer-reviewed scientific literature. These papers are listed at the end of this report (numbers 1 through 4).

The Nitrogen Study and its Terms of Reference, 2013-2017

Although the early work of Working Group 38 above did consider some aspects of the deposition and impacts of atmospheric nitrogen species on the ocean, it was recognized that this was a significant and complex scientific issue that required a more in-depth study. Thus, at GESAMP’s 39^th session in 2012, Members approved additional terms of reference for continued work of GESAMP WG 38 to address issues related to the impact of the atmospheric deposition of anthropogenic nitrogen to the ocean. An abbreviated form of the new Terms of Reference was as follows:

• Update the geographical estimates of atmospheric anthropogenic nitrogen deposition to the global ocean;
• Re-evaluate the magnitude and impact of atmospheric nitrogen deposition on marine biogeochemistry;
• Provide a more reliable estimate of the impact of atmospheric anthropogenic nitrogen deposition on the production of additional nitrous oxide in the ocean and its subsequent emission to the atmosphere;
• Evaluate the extent to which anthropogenic nitrogen, delivered to the coastal zone via rivers, is transported to the open ocean; and
• Make a detailed estimate of the input and impact of anthropogenic nitrogen in the area of the Northern Indian Ocean and the South China Sea.

To address these new terms of reference, a highly successful and productive workshop on “The Atmospheric Deposition of Nitrogen and Its Impact on Marine Biogeochemistry” was held at the University of East Anglia (UEA) in Norwich, United Kingdom, from 11 to 14 February 2013. Twenty-three scientists participated in the workshop.

Results of the Nitrogen Study

The results of the nitrogen workshop were synthesized in GESAMP Reports and Studies 97, “The Magnitude and Impacts of Anthropogenic Atmospheric Nitrogen Inputs to the Ocean” and in seven papers listed at the end of this report (numbers 5 through 12). This synthesis by GESAMP WG 38 provides new current best estimates of nitrogen inputs to the ocean from the atmosphere (39 TgN y^-1), and for context it made comparable estimates of inputs from rivers (34 TgN y^-1) and natural biological nitrogen fixation (164 TgN y^-1). Most of the atmospheric nitrogen input reaches the open ocean beyond the shelf break, while a substantial part of the riverine input is trapped on the shelf. Both the riverine and atmospheric nitrogen inputs have been substantially increased by human activity, with the atmosphere now the main vehicle by which anthropogenic nitrogen reaches the open ocean. The atmospheric input of nitrogen is estimated to now be almost 4 times that in 1850, and even in 1850 conditions were not pristine.

Atmospheric deposition of nitrogen to the oceans involves several distinct chemical components, each of approximately the same magnitude; oxidized nitrogen, primarily nitrate aerosol and nitric acid; reduced nitrogen, primarily ammonium aerosol and ammonia; and a poorly characterized organic nitrogen component. The main anthropogenic source of oxidized nitrogen is fossil fuel combustion on land plus an increasingly important source from fuel combustion on ships, while for reduced nitrogen the primary anthropogenic emission source is from intensive agriculture. There is also an important but poorly understood natural recycling of ammonia and organic nitrogen between the atmosphere and the oceans.

Atmospheric nitrogen emissions come predominantly from areas of high fossil fuel combustion and high rates of intensive agriculture. The largest emission sources are in North America, Europe, India and South-East Asia. Models based on future emission scenarios suggest that total nitrogen inputs to the oceans will change little between now and 2050, but that emissions are likely to increase over southern Asia and decline over North America and Europe. The largest inputs of nitrogen to the oceans occur downwind of these large emission sources over the North Atlantic, Northern Indian and north-west Pacific Oceans. Impacts of this atmospheric deposition on the marine environment have been previously suggested for the north-west Pacific, and impacts in this region and the Northern Indian Ocean are likely to increase in the future, based on the emission scenarios considered. Such impacts may include increases in phytoplankton production, and in the north-western Indian Ocean this may lead to increases in the emissions of the greenhouse gas N₂O from the low oxygen waters that occur naturally at depth in this region.

More generally the impact of nitrogen deposition to the ocean will be an increase in primary production in regions that are currently nitrogen limited, which include the surface waters of tropical ocean gyres. The increase in ocean production at the present day compared to 1850 levels is estimated to be about 0.4%, with an associated increase in the ocean uptake of CO2 of 0.15Pg C y^-1.

Several scientific gaps remain, and we recommended additional work on:

• The sources of atmospheric organic nitrogen,
• the magnitude and significance of recycling of ammonia and organic nitrogen from the oceans,
• the parameterization of deposition, particularly dry deposition
• an improved data base, particularly on wet deposition over the oceans
• the extent and thresholds for suppression of nitrogen fixation by ambient surface water dissolved nitrogen
• the retention of nitrogen within shelf systems, and particularly how the rates of bacterial processes that convert fixed nitrogen back to dinitrogen gas (denitrification and the related anammox both of which convert N_r into inert nitrogen gas) vary with temperature
• the impacts of possible changes in aerosol acidity over coming decades on the atmospheric delivery of nutrients to the oceans
• increasing atmospheric carbon dioxide concentrations are already driving ocean acidification and this is likely to increase in coming decades. The impacts of the changing ocean pH on ocean emissions of atmospherically important gases including nitrogen species, but also other gases, needs to be evaluated.

We also recommended further work in the following regions, which are particularly sensitive to likely changes in atmospheric deposition:

• the Northwest Pacific where deposition fluxes are expected to grow and where there may already be impacts from the current inputs,
• the northern Indian Ocean, an important source region for N₂O, which receives a large atmospheric input that is argued to already be increasing plankton productivity,
• areas of the Mediterranean and North Atlantic where primary production is phosphorus- or iron-limited and hence where additional nitrogen deposition may lead to different nutrient biogeochemical responses to those in other ocean areas where nitrogen is the primary limiting nutrient.

Activities of WG 38, 2017-2019

From 27 February to March 2, 2017, two linked WG 38 workshops took place at UEA. Recognizing that the acidity of atmospheric aerosols will change in the future as the balance of emissions of acid and alkali precursors to the atmosphere will change over coming decades and that ocean pH will also change due to anthropogenic CO₂ emissions, these two workshops focused on the impacts of these changes on air-sea exchange and the wider Earth system. The outputs from these workshops were synthesized in GESAMP Reports and Studies 109 “The changing acidity of the global atmosphere and ocean and its impact on air/sea chemical exchange” published in 2022, and in six papers listed at the end of this report (numbers 13 through 16 as well as numbers 19 and 20). This synthesis by GESAMP considered both the impact of ocean acidification on emissions of climate active gases from the ocean and the impact of changing atmospheric acidity of nutrient deposition to the ocean and the conclusions of the two workshops are briefly summarized below.

Workshop on the Impact of Ocean Acidification on Fluxes of Atmospheric non-CO2 Climate-Active Species

Surface ocean biogeochemistry and photochemistry regulate ocean-atmosphere fluxes of trace gases critical for Earth’s atmospheric chemistry and climate. The oceanic processes governing these fluxes are often sensitive to the changes in ocean pH (or pCO2) accompanying ocean acidification (OA), with potential for future climate feedbacks. Current understanding from observational, experimental, and model studies suggests impacts of OA on marine sources of key climate-active trace gases, including dimethyl sulfide (DMS), nitrous oxide (N2O), ammonia, and halocarbons. The available information for DMS is considerably greater than for other trace gases. OA-sensitive regions are particularly polar oceans and upwelling systems. OA will not operate alone in coming decades, and the combined effect of multiple climate stressors (ocean warming and deoxygenation) on trace gas fluxes need to be considered. Future ocean observations of trace gases should be routinely accompanied by measurements of two components of the carbonate system to improve our understanding of how in situ carbonate chemistry influences trace gas production. Together, this will lead to improvements in current process model capabilities and more reliable future predictions of future global marine trace gas fluxes.

Workshop on Changing Atmospheric Nutrient Solubility

Anthropogenic emissions of nitrogen and sulfur oxides and ammonia have altered the pH of aerosol, cloudwater and precipitation, with significant acidification over much of the marine atmosphere, although this trend is now reversing due to effective emission controls on combustion derived sources of sulphuric and nitric acid emissions. Some of these emissions have led to an increased atmospheric burden of reactive nitrogen and its deposition to ocean ecosystems. Changes in acidity in the atmosphere also have indirect effects on the supply of labile nutrients to the ocean. For nitrogen, these changes are caused by shifts in the chemical speciation of both oxidized (NO₃^- and HNO₃) and reduced (NH₃ and NH₄⁺) forms that result in altered partitioning between the gas and particulate phases that affect transport. Other important nutrients, notably iron and phosphorus, are impacted because their soluble fractions increase due to exposure to low pH environments during atmospheric transport. These changes affect the magnitude, distribution and deposition mode of individual nutrient supply to the ocean. The ratios of nitrogen, phosphorus, iron and other trace metals in atmospheric deposition are also affected. Since marine microbial populations are sensitive to nutrient supply ratio, the consequences of atmospheric acidity change include shifts in ecosystem composition, in addition to overall changes in marine productivity. Nitrogen and sulfur oxide emissions are decreasing in many regions, but ammonia emissions are much harder to control. The acidity of the atmosphere is therefore expected to decrease in the future, with further implications for nutrient supply to the ocean.With encouragement from WMO, several members of WG38 also contributed to a paper (number 17 in list below) looking at future strategies for making cost effective measurements of atmospheric parameters over the oceans using ships of opportunity.

Activities of WG 38, 2020-2022

Workshop on the Atmospheric Transport of Microplastics to and from the Ocean

WG 38, in partnership with GESAMP WG 40, carried out a virtual “Workshop on the atmospheric transport of microplastics to and from the ocean” on November 17-19, 2020. The Terms of Reference for this workshop were as follows:

• Identification of our current understanding and quantitative estimation of the major sources and types of atmospheric microplastics, their atmospheric transport paths, and their inputs to and emissions from the global ocean; and
• Development of guidelines on appropriate future atmospheric and marine sampling and measurement methods and strategies, to enable more accurate estimations of the above to be made.

Tim Jickells and Robert Duce (Co-chairs of WG 38) and Peter Kershaw (Chair, WG 40) were conveners of the workshop. Steve and Deonie Allen (UK), Daoji Li and Kai Liu (China), Peter Liss (UK), Maria Kanakidou (Greece), and Oksana Tarasova (WMO, Switzerland) were members of the Organizing Committee. Twenty-nine individuals from fourteen nations who have had experience with atmospheric and oceanic microplastics or with air/sea exchange of material participated in the three-day workshop. The workshop was organized around 8 different sessions related to microplastics in the atmosphere and ocean. These were:

• Brief presentations by individuals or groups that have made measurements of atmospheric microplastics or have made flux calculations to the ocean.
• A general discussion of what the major unknowns are in our understanding of atmospheric microplastics and their transport to/from the ocean.
• Discussion of sources of atmospheric microplastics, their relative strengths, and their emission and transport characteristics.
• Discussion of how to determine a good estimate of the transport of microplastics to and from the global ocean, considering sources, transport modelling, monitoring, recycling from the ocean surface, etc.
• Consideration of needs and required future advances relative to sampling and measurement techniques and sampling locations for microplastics.
• Discussion of possible modelling approaches for atmospheric transport of microplastics to the oceans and other information needs.
• Consideration of a synthesis report and publication writing tasks to be undertaken by individuals or groups, type of publications and/or reports, to be prepared, and timeframe for outputs to be completed.

The workshop was quite a success. A GESAMP Reports and Studies document summarizing the results of this workshop is presently under preparation. Twp papers from this workshop were published in the peer-reviewed literature and are listed at the end of this report (numbers 18 and 21). One of these is a detailed review paper that was published by Nature Reviews – Earth Environment in May 2022, with lead authors Deonie and Steve Allen, who are among the leaders in the measurement of microplastics in the atmosphere/ocean system. The paper indicates that atmospheric transport may indeed be an important, and previously little considered, route by which microplastics reach the ocean. The sources of these atmospherically transported microplastics are both direct emissions and also the fragmentation, resuspension and redeposition (possibly many times) of plastics already released into the environment, meaning that emission control alone will not address this issue. Microplastics currently in the ocean may also be emitted into the atmosphere via air-sea exchange processes and transported back to land. The paper goes on to propose a cost-effective global strategy to better quantify the role of atmospheric cycling of microplastics by building on existing sampling networks of the Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization.

Workshop on “What is the potential role of atmospheric deposition in driving ocean productivity in the Madagascar Channel and Southwest Indian Ocean? - A case for an Adaptive-Dynamic Management approach within Large Marine Ecosystems”.

In the past WG 38 has focused on the scientific aspects of the deposition of chemicals to the ocean. In 2019 we began the development of a new type of workshop, which took place in October 4-7, 2022 at Nelson Mandela University in Gqeberha (Port Elizabeth), South Africa. This new workshop brought together scientists as well as ocean managers and policymakers to address issues related to the importance of atmospheric deposition to a specific area of the ocean and include an element of capacity building. This new workshop was titled: “What is the potential role of atmospheric deposition in driving ocean productivity in the Madagascar Channel and Southwest Indian Ocean? - A case for an Adaptive-Dynamic Management approach within Large Marine Ecosystems”.

The Agulhas Current Large Marine Ecosystem in the southwest Indian Ocean is an important region of periodic large-scale algal blooms which are readily identifiable by satellite observations. Paradoxically, these blooms are found during the austral summer months when much of the region is devoid of nutrients in the surface layer of the ocean and hence productivity would be expected to be low. Marine natural resources are of considerable societal importance in this region in the context of food security. Given the extent of these blooms, it is probable that they are having an impact on the regional trophic structures, which sustain the all-important local fisheries particularly for Mozambique and yet the drivers of these blooms are not understood, despite several scientific investigations, meaning that predicting their future persistence and the resulting societal impacts is challenging. One possibility that has not been evaluated yet is the role of atmospheric deposition of nutrients in creating and/or sustaining these blooms. The complexities and uncertainties of the environmental drivers of the blooms and their societal importance make this a challenging and important region in which to consider the most appropriate approach to the formulation of policy advice, providing a test case within which to evaluate new approaches to adaptive environmental management. The workshop was initiated by GESAMP at its meeting in New York in 2019 but was delayed for several years due to Covid.

The Workshop had a series of related objectives.

• To evaluate the current knowledge of the atmospheric inputs into the southwest Indian Ocean and scientific evidence for the factors that control algal blooms in this region, including the potential role of atmospheric deposition, and the confidence in our understanding of these factors.
• To debate the associated potential impacts and management implications with a broader group of stakeholders/experts (including social scientists and economists)
• To present this information to decision-makers at the senior management and policy level for their response and advice on adaptive management steps
• To identify the feasibility of institutionalizing such an adaptive/dynamic management process at the regional level and linking it into national management processes.
• In parallel with this process, to introduce young and emerging scientists to the debate and the science involved and to build capacity for this dialogue within the region.

The workshop took place in Gqeberha (formerly Port Elizabeth) South Africa 4-7 October 2022, and the results are now being synthesized for publication, both as part of the GESAMP Reports and Studies series as well as in the peer-reviewed scientific literature.

A photo of the in-person participants at this workshop is shown below:

European Geosciences Union Meetings

For the past seven years WG 38 has organized a session on the exchange of chemicals between the atmospheric and the ocean as part of the European Geosciences Union meeting held each year in Vienna, Austria. We expect this effort to continue in subsequent years.

Current Membership of Working Group 38

Robert Duce, Co-chair (USA) (M), Timothy Jickells, Co-chair (United Kingdom) (M)

Sajjad Abbasi, Iran (M) (early career), Deonie Allen, New Zealand (F), Katye Altieri, South Africa (F), Alex Baker, United Kingdom (M), Cecile Guieu, France (F), Frances Hopkins, United Kingdom (F), Akinori Ito, Japan (M), Maria Kanakidou, Greece (F), Daoji Li, China (M), Peter Liss, United Kingdom (M), Natalie Mahowald, USA (F), Morgane Perron, Australia/France (F) (early career), Mike Roberts, South Africa (M), Monmohan Sarin, India (M)

Peer-reviewed publications of GESAMP Working Group 38 can be found here.