Name: Surface Chlorophyll a concentration and Secchi depth data from the SEAHAB project, March 2023
License: https://creativecommons.org/licenses/by-sa/4.0/

DOI: 10.15493/DEA.MIMS.14512023

Title	Surface Chlorophyll a concentration and Secchi depth data from the SEAHAB project, March 2023
Authors	Marie Smith Coastal Systems and Earth Observation Research Group, Council for Scientific and Industrial Research (CSIR); role: Senior Researcher; contact details: email: msmith2@csir.co.za
Publisher	Swiss Tropical and Public Health Institute, Leading House Africa (2025)
Contributors	Project Member: Lloyd Hughes École Polytechnique Fédérale de Lausanne (EPFL) / ECEO Lab; role: Postdoctoral Researcher; contact details: email: lloyd.hughes@epfl.ch Contact Person: Marie Smith Coastal Systems and Earth Observation Research Group, Council for Scientific and Industrial Research (CSIR); role: Senior Researcher; contact details: email: msmith2@csir.co.za
Abstract	This was the in situ data collection for the Sensor-agnostic Estimation of Harmful Algal Blooms (SEAHAB) project, March 2023. The data represents two days of surface water sampling between Table Bay and Kommetjie for the purpose of satellite chlorophyll a concentration and water clarity validation.
Methods	Secchi depth was measured using a weighted 30cm diameter white disk, which was lowered into the water until it can no longer be seen by the observer; the Secchi depth is the depth of the water at the point when the Secchi disk disappears/reappears. Surface seawater samples were collected in 2L plastic bottles, sealed and kept cool and in the dark until filtration on the same day. Filtration volumes ranged between 100 and 200 ml per sample. Samples were filtered onto GF/F filters (Whatman, diameter 25 mm, nominal pore size 0.7 um) and extracted in 90% acetone for 24h in the dark at -20 degrees Celcius, then measured with a Trilogy Laboratory Fluorometer following Welschmeyer (1994): Welschmeyer, N.A. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnol. Oceanog. 1994, 39, 1985–1992.
Data	Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) Cite 10.15493/DEA.MIMS.14512023 Style Terms of use These data are made available with the express understanding that any such use will properly acknowledge the originator(s) and publisher and cite the accession numbers and/or associated Digital Object Identifiers. Anyone wishing to use these data should properly cite and attribute the data providers listed as authors in the metadata provided with each dataset. It is expected that all the conditions of the data license will be strictly honoured. Use of any material herein should be properly cited using the dataset’s persistent identifiers such as accession numbers and DOIs. I agree to the terms of use
Temporal extent	27 Mar 2023 – 31 Mar 2023
Geographic extent	20 km Leaflet Tiles © Esri — Source: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2012 Table Bay; South African West Coast; Benguela Upwelling North: -33.82369 South: -34.18757 West: 18.27372 East: 18.45055
Vertical extent	Max: -0.5 m Min: 0 m
Keywords	Algal Blooms, Chlorophyll a, SDG 14.1.1 (a) Index of coastal eutrophication; and (b) plastic debris density, SDG Goal 14. Conserve and sustainably use the oceans, seas and marine resources for sustainable development, SEAHAB, Secchi depth, Sensor-agnostic Estimation of Harmful Algal Blooms (SEAHAB) project, SOUTH ATLANTIC OCEAN

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