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Tropical and South Atlantic climate-based marine ecosystem predictions for sustainable management

Periodic Reporting for period 1 - TRIATLAS (Tropical and South Atlantic climate-based marine ecosystem predictions for sustainable management)

Reporting period: 2019-06-01 to 2020-11-30

Our knowledge of the status of the South and tropical Atlantic marine ecosystems and their future evolution is poor, especially in comparison to the North Atlantic, and this impedes the understanding of the whole Atlantic. At the same time, many of the countries bordering the South and tropical Atlantic depend heavily on marine ecosystems for providing relevant services such as food, genetic resources, recreation and climate regulation. TRIATLAS’ overarching objective is to enable sustainable management of human activities in the Atlantic Ocean as a whole, by closing knowledge gaps on the status of the South and tropical Atlantic marine ecosystem and developing a framework for predicting its future changes, from months to decades. We are achieving this through a basin-wide cooperation that combines ecosystem observations, climate-based ecosystem prediction and information on future socio-economic and ecosystem service changes, as well as close networking with relevant stakeholders and related projects and programs.
Based on the interdisciplinary cruises realized before the covid-19 caused shutdown, significant new information has been obtained. As an example, the 2019 Transatlantic Equatorial Cruise 1 from Walvis Bay, Namibia to Recife, Brazil, is improving knowledge about upwelling in the tropical Atlantic, its physical forcing; its importance for biological production, plankton communities, and associated chemical cycles; as well as on the ocean currents setting the background conditions for the downward carbon export. It was the first cruise to provide an entire equatorial section from the eastern to western boundaries including physical, chemical, biogeochemical and biological measurements from the sea surface to the ocean bottom. Work has started to synthesize the information into comparative data products for the six key areas considered, in order to obtain methodologically consistent deliverables for an unprecedented coverage of ecosystem components from phytoplankton to fish.

Analysis of observations and numerical model simulations is giving novel integrated findings on interannual to decadal fluctuations in physical and biogeochemical environments, and in marine ecosystems in the tropical and South Atlantic. We have studied marine heat waves, and changes in ocean circulation, stratification, and upwelling; and their effects on dissolved oxygen, primary productivity, and higher tropic levels of the marine ecosystem, including the abundance and distribution of tuna and sardinella. We identified climatic and anthropogenic drivers of Atlantic ecosystem variability. These include the Pacific El Niño and Atlantic Niño climate phenomena. We have also studied future climate change, and how it in combination with fisheries pressures will affect marine ecosystems.

Building on these results, we are developing climate-based predictions of marine ecosystem focusing on seasonal to decadal timescales, which are of interest to society and stakeholders. This involves combining state-of-the-art of Earth system and marine ecosystem models, and in assessing, understanding and improving predictive capability for the tropical and South Atlantic. We are developing novel approaches to reduce model systematic error and to optimally use observational data to improve models and predictions. Several groups have already performed retrospective decadal predictions, as well as scenario simulations for future climate and its impacts on marine ecosystems globally.

To deliver societal and policy relevant information, we are analyzing the complex interrelationships with human social drivers, considering large-scale and artisanal fisheries and the vulnerability of fishing communities. The most intense human activities influencing the marine ecosystems in the northeast Brazil shelf and southern Benguela regions were identified. Furthermore, we are developing scenario narratives to represent alternative futures of coastal fisheries, based on stakeholder workshops and surveys. Lastly, the Cross-Atlantic Network of Excellence in Marine Science (CANEMS) was established to enhance capacity in marine ecosystem, oceanographic, and climate research in countries bordering the South and tropical Atlantic Ocean, so as to increase the region’s ability for managing human activities and sustainable development in the Atlantic Ocean.
Novel research cruises are giving unprecedented insights into physical ocean processes and their impact on marine ecosystems. For example, observed tracer distributions allow quantification of ventilation and water mass exchange between western and eastern boundary as well as shelf-ocean and island-ocean effects. Analyses of isotope patterns and of biomass size spectra over multiple trophic levels is giving insight into basin-scale ecosystem properties and processes. Baseline isotope data will be in particular useful for investigating the ecology of marine mammals in the southwestern Atlantic Ocean. The wealth of observations in the TRITATLAS study regions will allow to disentangle effects of nutrient supply along gradients from oligotrophic to upwelling areas, effects of low oxygen levels found in the Benguela and Canary Current Systems, and changes along temperature gradients indicative of climate change effects. The Ocean’s vertical dimension will be better understood, through using depth resolved fish larval abundance data in hydroacoustical models of diel vertical migration. While enhanced plankton particle flux measurements will improve understanding of the carbon flux to mesopelagic and bathypelagic depths in the tropical/subtropical Atlantic.

New approaches are giving new findings on marine ecosystem variability. Isotope patterns from archived otolith material of sardine and horse mackerel will lead to new knowledge of the effects of long-term environmental changes on these stocks. In addition, machine learning techniques were used to derive information of the environment (water masses and prey fish distribution) from seabird at-sea behavior. Ecosystem responses are being identified by contrasting deep mixed-layer versus shallow mixed-layer scenarios; this approach is useful where marine ecosystem data are limited. The occurrence, frequency and impact of marine heatwaves in the Atlantic is a completely novel contribution to understanding of ecosystem dynamics. Statistical approaches show the potential to predict marine ecosystem changes in the Atlantic based on short- and long-term changes in climate.

The development of climate-based marine ecosystem prediction for seasonal to decadal timescale will provide a unique and timely tool to sustainably manage human activities (e.g. fisheries) in the Atlantic. We will deliver the first time near-term predictions made by combining Earth system and ecosystem models with advanced data assimilation approaches. This will give new knowledge on the ability to predict ecosystems changes in the tropical and South Atlantic.

Research into the analysis of the human social dimensions of fishing is its infancy for most regions of the Atlantic. Understanding the human dimension is increasingly recognised as important, for regional fisheries advisory organisations such as the International Council for the Exploration of the Sea, and for Intergovernmental Panel on Climate Change and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services assessment reports.
TRIATLAS consortium map showing the 33 institutes from 13 countries around the Atlantic Ocean.