Multi-proxy data on sediment cores MD-1 (26° 24' 43.6598 N, 81° 52' 21.2388 W, 70 cm) and MD-3 (26° 22' 08.9963 N, 81° 51' 13.5940 W, 60 cm depth) acquired via an aluminum push corer from southwest Florida coast with tidal flats were obtained to determine the cause(s) of mangrove death. These data involves planialtimetric and stratigraphic analyzes, implemented in two phases: 1) Selection of degraded mangrove areas for a topographic survey based on laser/GNSS data and aerophotogrammetry of drone images, and determination of the stature and species of mangrove trees (Dieback location.jpg, Table 1); 2) Selection of the core sampling sites for a paleoenvironmental reconstruction on a decadal and century time scale (Table 2 and 3; Pollen MD-3-1, Isotope, CHD 1-3 Loi&XRF (MD-1), CHD 2-2 LOI&XR;; Grain size MD-3-1). A Drone DJI Phantom 4 Advanced recorded ~1421 high spatial resolution photos (2.6 cm) by a digital 4K/20MP (RGB) camera to cover ~158 ha in Nov/2019, following predetermined missions (90º camera angle, 90% frontal, and 75% lateral overlay, at 100 m altitude). Planialtimetric data (coordenates of Ground Control Points) were obtained by drone aerophotogrammetry using the Agisoft Metashape Professional version 1.8.4 (Table 1). Radiocarbon dates (Table 2) were obtained by accelerator mass spectrometry (AMS) at the Center for Applied Isotope Studies (UGAMS) of the University of Georgia and International Chemical Analysis, Inc. Radiocarbon ages were normalized to a δ13C of −25‰ VPDB and reported as calibrated years (calibrated years before the present; 2σ) using CALIB 8.2 (Stuiver et al., 2017). To obtain pollen data, sediment samples were treated following standard pollen analytical techniques (Faegri & Iversen, 1989)(Pollen M3-3-1). Pollen and spore classification, with at least 300 pollen grains identified for each sample, was based on reference collections of the LSU Global Paleoecology Laboratory, Laboratory of Coastal Dynamics – UFPA, 14C Laboratory of the Center for Nuclear Energy in Agriculture (CENA/USP), and various pollen keys (Markgraf & D'Antoni, 1978; Roubik & Moreno, 1991). Sediments were sampled at 2 cm intervals (0.5 g) to quantify sediment particle size in a laser diffraction particle size analyzer (SHIMADZU SALD 2101) at the Laboratory of Coastal Dynamics - Federal University of Pará (UFPA) (Grain size MD-3-1). Sedimentary organic matter was treated with 4% HCl to eliminate carbonate, washed with distilled water (pH 6), and dried at 50°C. Total organic carbon was determined at the Stable Isotope Laboratory of the Center for Nuclear Energy in Agriculture/University of São Paulo (CENA/USP). Results are presented in percentages of dry weight, with precision of 0.09% (Total Organic Carbon - TOC). The organic matter δ13C values are presented as δ13Corg (VPDB standard) with precision of ±0.2‰ (Pessenda, 2004). Loss-on-ignition (LOI) analysis was performed at 1 cm intervals, involving heating sediment samples at 105°, 550°, and 1000°C to determine the contents of water, organic matter, and carbonates, respectively. XRF analysis was carried out at 2 cm intervals using an Innov-X Delta XRF (Yao et al., 2015) (CHD 1-3 Loi&XRF (MD-1), CHD 2-2 LOI&XRF).
