Diatom and pollen atlas dataset from the Northern Gulf of Mexico, USA

Diatom and pollen references such as atlases and identification keys are remarkably rare from the Gulf Coast region of the United States. This dataset describes modern and fossil diatom and pollen from Galveston Bay, Texas to Cedar Keys Florida, USA. An illustrated and descriptive atlas of diatom and pollen was compiled from original data to facilitate the identification of microfossil in sediments. For diatom atlas, we include light micrographs and detailed descriptions of a total of 32 diatom species, including 9 marine diatom species, 18 estuarine diatom species, and 5 freshwater diatom species. For pollen atlas, we include light micrographs and descriptions of a total of 28 pollen and non-pollen palynomorphs, including 3 mangrove taxa, 12 upland (tree and shrub) taxa, and 10 herbaceous taxa. The diatom atlas is referenced from LSU Global Change and Coastal Paleoecology Laboratory's light micrographs collection. The pollen and diatom datasets are associated with research articles by Yao et al. [1,2].

Earth and Planetary Sciences -Paleontology Specific subject area Diatom and pollen atlas Type of data Image and table How the data were acquired The images were acquired via an Olympus Light Microscope with a LC35 camera (3.5-megapixel CMOS sensor) in conjunction with ZEN Blue 2012 imaging software to photograph pollen grains under 10 0 0x magnification. Data format Raw Description of data collection Pollen identification was based on microstructural analysis of the aperture and ornamentation, such as the characteristics of pore, colpus, and texture. At least 300 pollen grains were counted for each pollen sample. Diatom identification was based on microstructural analysis of the silicified cell wall, such as pore size, external layer, volume of diatoms, and shapes. At least 500 valves were counted for each diatom sample. Data

Value of the Data
• The pollen atlas facilitates the identification of pollen taxa from subtropical coastal environments including mangroves, maritime forests, tidal wetlands, and beaches and dunes. • The diatom atlas facilitates the identification of diatom species live in marine, estuarine, and freshwater environments. • The relatively abundance of different diatom species permits the assessment of salinity, water level, and other environmental factors in the open bay water and on the coastal zone. • The relative abundance of different pollen taxa permits the assessment of vegetation, landform, salinity, and other environmental factors in paleo-ecological research.

Objective
Our objective is to provide an illustrated and descriptive diatom and pollen atlas from the Northern Gulf of Mexico coast in United States. These data can be used to reveal the dynamics of vegetation and phytoplankton communities in a millennial timescale and document the salinity, water level, and ecological variations associated with the rapid climate change during the Anthropocene.

Data Description
Diatoms are one of the most productive photosynthesizing algae living in offshore, inshore, and freshwater environments worldwide. Diatom analysis is widely used in paleoenvironmental studies to reveal the salinity, temperature, water depth, and other environmental factors in the past [3] . On the other hand, palynology is a time-tested technique in the reconstruction of paleoenvironmental changes and vegetation dynamics. Data from pollen analysis can reveal the vegetation community, climate, landform, and other environmental conditions during the past decades to millennia.
However, diatom and pollen atlases and identification keys are remarkably rare from the Northern Gulf of Mexico coast, which can hinder paleoecological reconstruction in the region. This dataset describes modern and microfossil diatom and pollen from Bolivar Flats near Galveston Bay, Texas, and from Cedar Keys National Wildlife Refuge, Florida, USA. An illustrated and descriptive atlas of diatom ( section 2.1 -2.3 ) and pollen ( section 2.4 -2.7 ) was compiled to facilitate the identification of these microfossils in sediments. We include light micrographs and detailed descriptions of a total of 32 diatom genera and species and 28 pollen and non-pollen palynomorphs. The original count and relative abundance of all the pollen [4] and diatom taxa [5] is listed in Mendeley Data. These data can be used as a reference for future studies to conduct pollen and diatom analyses from across the Gulf of Mexico.
Achnanthes inflata (#12 in Fig. 2   Cymbella lanceolata (#22 in Fig. 3 ): Valves are long and lanceolate with rounded apices. The dorsal margin is moderately arched. The ventral margin is concave with a gibbous center. The axial area is narrow and linear, slightly wider than the raphe. The central area is small and ovoid. The raphe is lateral, becoming filiform near the proximal and distal ends. Terminal raphe fissures are deflected dorsally at an angle of almost 90 degrees. Radiate striae.
Actinoptychus sp. (#23 in Fig. 3 ): Valves with little pronounced dorsiventrality; concave dorsal margin; ventral margin convex; attenuated-rounded ends; sternum of the raphe lanceolate on the side dorsal and linear narrow on the ventral side; rounded central area; circular valves; hyaline central area; hexagonal areolas; radial striations; Marginal rhinoportulas present at the base of each elevated sector. Valve diameter: 25 μm; 4 areolas in 10 μm.

Experimental Design, Materials and Methods
For pollen analysis, cores CK-2 (180 cm; from Atsena Otie Key, 29 °7'23.60" N, 83 °2 2.60" W) and SNK-2 (195 cm; from Seahorse Key, 29 °5'57.96" N, 83 °4'2.22" W) were retrieved in December 2018 by means of a vibra-corer from the fringing mangrove forests on these two islands in Cedar Keys, Florida, U.S.A. The cores were measured, photographed, and wrapped in the field and stored in a cold room (4 °C) at the LSU Global Change and Coastal Paleoecology Laboratory. A total of 58 samples consisting of ∼1 cm3 of sediment each were taken from core CK-2 and SNK-2 at a 5-cm interval for palynological analysis. All samples were processed following the standard procedure [15] . One Lycopodium tablet ( ∼20,848 grains) was added to each sample as an exotic marker to calculate the pollen concentration (grains/cm3). A minimum of 300 pollen grains were counted for each sample (except for samples from 130 to 190 cm in core SNK-2 where the pollen concentration is very low) to ensure the results were statistically robust. In addition, foraminifera linings, dinoflagellates, fungal spores, and charcoal fragments ( > 10 mm in size) were also counted.
For diatom analysis, Core BBS-1 (185 cm; 29 °22 10.60 N, 94 °44 0.20 W) was retrieved in December 2018 using a vibra-corer from the black mangrove stands on the flat. The core was pushed in until refusal to capture the most complete depositional history possible. Twenty-nine samples consisting of ∼1 cm 3 of sediment were collected at 2-5 cm intervals for diatom analysis, following the standard procedure and treatment described in Tomas et al. [16] and Wachnicka et al. [17] . Diatom identification was based on microstructural analysis of the silicified cell wall, such as pore size, external layer, volume of diatoms, and shapes. In order to yield a statistically meaningful relationship, at least 500 valves were counted for each sample. TILIA and TILIAGRAF software were used for calculation and plotting the pollen diagram [18] . CONISS was used for cluster analysis of the pollen data [19] .

Ethics Statements
This study does not involve any human subjects or animal experiments.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data Availability
Pollen dataset from Cedar Keys, Florida, USA (Original data) (Mendeley Data). Original diatom counts of core BBS-1 from Galveston Bay, Texas, USA (Original data) (Mendeley Data).