Seasonal predictions of holopelagic sargassum across the Tropical Atlantic accounting for uncertainty in drivers and processes: The SARTRAC ensemble forecast system
Seasonal predictions of holopelagic sargassum across the Tropical Atlantic accounting for uncertainty in drivers and processes: The SARTRAC ensemble forecast system
The holopelagic macroalgae sargassum has proliferated across the tropical Atlantic since 2011, of consequence for coastal populations from West Africa to the Caribbean with limited early warning of major beaching events. As part of an interdisciplinary project, ‘Teleconnected SARgassum risks across the Atlantic: building capacity for TRansformational Adaptation in the Caribbean and West Africa’ (SARTRAC), an ensemble forecast system, SARTRAC-EFS, is providing seasonal predictions of sargassum drift. An eddy-resolving ocean model hindcast provides the winds and currents necessary to generate ensemble members. Ensemble forecasts are then obtained for different combinations of ‘windage’, the fractional influence of winds on sargassum mats, and in situ rates of growth, mortality, and sinking. Forecasts for north and south of Jamaica are evaluated with satellite-observed distributions, associated with beaching events in specific years of heavy inundation, 2015 and 2018-20. These seasonal forecasts are evaluated, on lead times of up to 180 days. Forecasts are subject to leading modes of tropical climate variability, in particular the Atlantic Meridional Mode (AMM). More accurate forecasts for a given year are obtained with ensemble members from hindcast years with a similar spring AMM-index. This is most clearly evident during negative AMM phases in spring of 2015 and 2018, when positive sea surface temperature anomalies and anomalously weak trade winds were established across the northern tropics. On this evidence, SARTRAC-EFS is potentially useful in providing early warning of high sargassum prevalence. Extended to sargassum drift off West Africa, extensive cloud cover limits availability of the satellite data needed for full application and evaluation of SARTRAC-EFS in this region, although experimental forecasts off the coast of Ghana are found highly sensitive to the windage that is associated with strong onshore winds during boreal summer. Alongside other forecast systems, SARTRAC-EFS is providing useful early warnings of sargassum inundation at seasonal timescale.
Ghana, Jamaica, currents, prediction, sargassum, seasonal, windage
Marsh, Robert
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Appeaning Addo, Kwasi
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Jayson-Quashigah, Philip-Neri
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Oxenford, Hazel A.
29104ad8-b2b9-4678-bba0-ab64032764be
Maxam, Ava
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Anderson, Romario
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Skliris, Nikolaos
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Dash, Jadunandan
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Tompkins, Emma
a6116704-7140-4e37-bea1-2cbf39b138c3
4 October 2021
Marsh, Robert
702c2e7e-ac19-4019-abd9-a8614ab27717
Appeaning Addo, Kwasi
8dffebf4-a2fa-4f21-a9c5-05ec6ee7f227
Jayson-Quashigah, Philip-Neri
ab7f7489-46ba-4bbd-885c-8a64a13bb2a7
Oxenford, Hazel A.
29104ad8-b2b9-4678-bba0-ab64032764be
Maxam, Ava
6af4015a-af16-4412-9bf3-8b611dc03731
Anderson, Romario
d02ad20d-089d-41dc-99ba-35b304f0d48b
Skliris, Nikolaos
07af7484-2e14-49aa-9cd3-1979ea9b064e
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8
Tompkins, Emma
a6116704-7140-4e37-bea1-2cbf39b138c3
Marsh, Robert, Appeaning Addo, Kwasi, Jayson-Quashigah, Philip-Neri, Oxenford, Hazel A., Maxam, Ava, Anderson, Romario, Skliris, Nikolaos, Dash, Jadunandan and Tompkins, Emma
(2021)
Seasonal predictions of holopelagic sargassum across the Tropical Atlantic accounting for uncertainty in drivers and processes: The SARTRAC ensemble forecast system.
Frontiers in Marine Science, 8, [722524].
(doi:10.3389/fmars.2021.722524).
Abstract
The holopelagic macroalgae sargassum has proliferated across the tropical Atlantic since 2011, of consequence for coastal populations from West Africa to the Caribbean with limited early warning of major beaching events. As part of an interdisciplinary project, ‘Teleconnected SARgassum risks across the Atlantic: building capacity for TRansformational Adaptation in the Caribbean and West Africa’ (SARTRAC), an ensemble forecast system, SARTRAC-EFS, is providing seasonal predictions of sargassum drift. An eddy-resolving ocean model hindcast provides the winds and currents necessary to generate ensemble members. Ensemble forecasts are then obtained for different combinations of ‘windage’, the fractional influence of winds on sargassum mats, and in situ rates of growth, mortality, and sinking. Forecasts for north and south of Jamaica are evaluated with satellite-observed distributions, associated with beaching events in specific years of heavy inundation, 2015 and 2018-20. These seasonal forecasts are evaluated, on lead times of up to 180 days. Forecasts are subject to leading modes of tropical climate variability, in particular the Atlantic Meridional Mode (AMM). More accurate forecasts for a given year are obtained with ensemble members from hindcast years with a similar spring AMM-index. This is most clearly evident during negative AMM phases in spring of 2015 and 2018, when positive sea surface temperature anomalies and anomalously weak trade winds were established across the northern tropics. On this evidence, SARTRAC-EFS is potentially useful in providing early warning of high sargassum prevalence. Extended to sargassum drift off West Africa, extensive cloud cover limits availability of the satellite data needed for full application and evaluation of SARTRAC-EFS in this region, although experimental forecasts off the coast of Ghana are found highly sensitive to the windage that is associated with strong onshore winds during boreal summer. Alongside other forecast systems, SARTRAC-EFS is providing useful early warnings of sargassum inundation at seasonal timescale.
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Published date: 4 October 2021
Additional Information:
Funding Information:
We acknowledge the Optical Oceanography Laboratory at the University of South Florida, for freely providing FA_density images via https://optics.marine.usf.edu. The NEMO-ORCA12 hindcast simulation was carried out by the Marine Systems Modelling group at the National Oceanography Centre (NOC). The version of ARIANE used here was developed by George Nurser of NOC and implemented by Jeff Blundell of the University of Southampton. RM acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No 759677. We are grateful to two anonymous reviewers for a wide range of insightful comments that helped us to substantially improve the manuscript.
Funding Information:
This publication is supported by the United Kingdom Economic and Social Research Council through the Global Challenges Research Fund (GCRF) project, Teleconnected SARgassum risks
Publisher Copyright:
© Copyright © 2021 Marsh, Addo, Jayson-Quashigah, Oxenford, Maxam, Anderson, Skliris, Dash and Tompkins.
Keywords:
Ghana, Jamaica, currents, prediction, sargassum, seasonal, windage
Identifiers
Local EPrints ID: 451684
URI: http://eprints.soton.ac.uk/id/eprint/451684
ISSN: 2296-7745
PURE UUID: b8f0f408-842a-4df1-bbab-f508510ce093
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Date deposited: 19 Oct 2021 17:42
Last modified: 17 Mar 2024 03:25
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Contributors
Author:
Kwasi Appeaning Addo
Author:
Philip-Neri Jayson-Quashigah
Author:
Hazel A. Oxenford
Author:
Ava Maxam
Author:
Romario Anderson
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